NuSTAR doing OK

NuSTAR (an acronym for Nuclear Spectroscopic Telescope Array) is a new NASA hard X-ray observatory which was launched on June 13th, appears to be well in in-Orbit check-out.

There is a nice "first light" image of the classic Galactic black hole Cygnus X-1 comparing the blurry image of Cyg X-1 taken with Integral compared to NuSTAR's image. See the NuSTAR-related NASA News page for more information.

Interesting Astrophysics: June 01 to June 11

This is the final edition of Interesting Astrophysics with me working as a professional astrophysicist, as I start a new job outside astronomy next week. If I have the spare time at home I may try to continue this series, but perhaps at a reduced rate.

Nevertheless, there is some interesting stuff to look at. Molecular gas in starbursts is the subject of the Bothwell et al, Naylor et al, and Feruglio et al papers. In terms of winds, Muzic et al discuss possible/futher evidence of a wind within the central regions of our own galaxy (I still remain somewhat sceptical that the Milky Way hosts a true galactic wind), Kobulnicky & Martin present X-ray observations of the dwarf starburst Henize 2-10, Feruglio et al claim there is a hugely energetic molecular outflow in Markarian 231 that can only be power by an AGN, and Fischer discuss the geometry of the outflow in the central kiloparsec of the Seyfert 2 galaxy Mrk 573. Randall Smith and collaborators have posted two interesting X-ray line diagnostics papers, for all your X-ray spectroscopists out there.

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Galaxies and Starbursts

AKARI infrared observations of edge-on spiral galaxy NGC 3079
Mitsuyoshi Yamagishi, Hidehiro Kaneda, Daisuke Ishihara, Shinya Komugi, Takashi Onaka, Toyoaki Suzuki, arXiv:1005.5251 [pdf, ps, other]
Comments: 15 pages, 7 figures, accepted for publication in PASJ

High-resolution CO and radio imaging of ULIRGs: extended CO structures and implications for the universal star formation law
M. S. Bothwell, S. C. Chapman, L. Tacconi, Ian Smail, R. J. Ivison, C. M. Casey, F. Bertoldi, R. Beswick, A. Biggs, A. W. Blain, P. Cox, R. Genzel, T. R. Greve, R. Kennicutt, T. Muxlow, R. Neri, A. Omont, 2010, MNRAS, 405, 219
Full Text: HTML, PDF (Size: 1391K)

From their abstract: "We find a difference in size between the CO and radio emission regions, and as such we suggest that using the spatial extent of the CO emission region to estimate the surface density of star formation may lead to error. This size difference also causes the star formation efficiencies within systems to vary by up to a factor of 5. We also find, with our new accurate sizes, that SMGs lie significantly above the KS relation, indicating that stars are formed more efficiently in these extreme systems than in other high- z star-forming galaxies."

A Census of the High-Density Molecular Gas in M82
B. J. Naylor, C. M. Bradford, J. E. Aguirre, J. J. Bock, L. Earle, J. Glenn, H. Inami, J. Kamenetzky, P. R. Maloney, H. Matsuhara, H. T. Nguyen, J. Zmuidzinas, arXiv:1006.1964 [pdf, ps, other]
Comments: 15 pages (using emulateapj.cls), 6 figures, submitted to the Astrophysical Journal

From their abstract: "We present a three-pointing study of the molecular gas in the starburst nucleus of M82 based on 190 - 307 GHz spectra obtained with Z-Spec at the Caltech Submillimeter Observatory. We measure intensities or upper-limits for 20 transitions, including several new detections of CS, HNC, C2H, H2CO and CH3CCH lines. We combine our measurements with previously-published measurements at other frequencies for HCN, HNC, CS, C34S, and HCO+ in a multi-species likelihood analysis constraining gas mass, density and temperature, and the species' relative abundances. We find some 1.7 - 2.7 x 10^8 M_sun of gas with n_H2 between 1 - 6 x 10^4 cm^-3 and T > 50 K. While the mass and temperature are comparable to values inferred from mid-J CO transitions, the thermal pressure is a factor of 10 - 20 greater."

Their median thermal pressure estimate P/k ~ 10^6.4 K cm^-3 for the molecular gas, is a little lower than our (Strickland & Heckman 2009) estimates for the very hot gas in the starburst (P/k ~10⁷), but for astrophysical work that's actually pretty close - its certainly closer than some other estimates in the literature. Nor would I expect the molecular gas to be in exact thermal pressure equilibrium with the hot gas.

Cometary shaped sources at the Galactic Center - Evidence for a wind from the central 0.2 pc
K. Muzic, A. Eckart, R. Schoedel, R. Buchholz, M. Zamaninasab, arXiv:1006.0909 [pdf, other]
Comments: to appear in A&A

Abstract in full: "In 2007 we reported two cometary shaped sources in the vicinity of Sgr A* (0.8" and 3.4" projected distance), named X7 and X3. The symmetry axes of the two sources are aligned to within 5 degrees in the plane of the sky and the tips of their bow-shocks point towards Sgr A*. Our measurements show that the proper motion vectors of both features are pointing in directions more than 45 deg away from the line that connects them with Sgr A*. This misalignment of the bow-shock symmetry axes and their proper motion vectors, combined with the high proper motion velocities of several 100 km/s, suggest that the bow-shocks must be produced by an interaction with some external fast wind, possibly coming from Sgr A*, or stars in its vicinity. We have developed a bow-shock model to fit the observed morphology and constrain the source of the external wind. The result of our modeling allows us to estimate the velocity of the external wind, making sure that all likely stellar types of the bow-shock stars are considered. We show that neither of the two bow-shocks (one of which is clearly associated with a stellar source) can be produced by influence of a stellar wind of a single mass-losing star in the central parsec. Instead, an outflow carrying a momentum comparable to the one contributed by the ensemble of the massive young stars, can drive shock velocities capable of producing the observed cometary features. We argue that a collimated outflow arising perpendicular to the plane of the clockwise rotating stars (CWS), can easily account for the two features and the mini-cavity. However, the collective wind from the CWS has a scale of >10''. The presence of a strong, mass-loaded outbound wind at projected distances from Sgr A* of <1'' is in fact in agreement with models that predict a highly inefficient accretion onto the central black hole due to a strongly radius dependent accretion flow."

Exploring the Origin and Fate of the Magellanic Stream with Ultraviolet and Optical Absorption
Andrew J. Fox, Bart P. Wakker, Jonathan V. Smoker, Philipp Richter, Blair D. Savage, Kenneth R. Sembach, arXiv:1006.0974 [pdf, ps, other]
Comments: Accepted for publication in ApJ. 18 pages, 7 figures, all in color

From their abstract: "Summing over the low-ion and high-ion phases, we derive conservative lower limits on the ratio N(total H II)/N(H I) of >19 toward NGC 7469 and >330 toward Mrk 335, showing that along these two directions the vast majority of the Stream has been ionized. The presence of warm-hot plasma together with the small-scale structure observed at 21 cm provides evidence for an evaporative interaction with the hot Galactic corona. This scenario, predicted by hydrodynamical simulations, suggests that the fate of the MS will be to replenish the Galactic corona with new plasma, rather than to bring neutral fuel to the disk."

The Diffuse and Compact X-ray Components of the Starburst Galaxy Henize~2-10
Henry A. Kobulnicky, Crystal L. Martin, arXiv:1006.1189 [pdf, ps, other]
Comments: Accepted for publication in The Astrophysical Journal; a version with high-resolution figures can be found at this http URL

From their abstract: "Chandra X-ray imaging spectroscopy of the starburst galaxy Henize 2-10 reveals a strong nuclear point source and at least two fainter compact sources embedded within a more luminous diffuse thermal component. ...Two-temperature solar-composition plasmas (kT~0.2 keV and kT~0.7 keV) fit the diffuse X-ray component as well as single-temperature plasmas with enhanced alpha/Fe ratios. Since the observed radial gradient of the X-ray surface brightness closely follows that of the Halpha emission, the composition of the X-ray plasma likely reflects mixing of the ambient cool/warm ISM with an even hotter, low emission measure plasma, thereby explaining the ~solar ISM composition. Aperture synthesis 21-cm maps show an extended neutral medium to radii of 60" so that the warm and hot phases of the ISM, which extend to ~30", are enveloped within the 8x10^20 /cm^2 contour of the cool neutral medium. This extended neutral halo may serve to inhibit a starburst-driven outflow unless it is predominantly along the line of sight. The high areal density of star formation can also be reconciled with the lack of prominent outflow signatures if Henize 2-10 is in the very early stages of developing a galactic wind."

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Black Holes and AGN

Quasar feedback revealed by giant molecular outflows
Chiara Feruglio, Roberto Maiolino, Enrico Piconcelli, Nicola Menci, Herve' Aussel, Alessandra Lamastra, Fabrizio Fiore, arXiv:1006.1655 [pdf, ps, other]
Comments: Submitted for publication in A&A Letters. 4 pages, 3 figures

From their abstract: "We used the IRAM PdBI to observe the CO(1-0) transition in Mrk 231, the closest quasar known. We detect broad wings of the CO line, with velocities up to 750 km/s and spatially resolved on the kpc scale. Such broad CO wings trace a giant molecular outflow of about 2000 MSun/year, far larger than the ongoing star-formation rate (~200 MSun/year) observed in the host galaxy. This wind will totally expel the cold gas reservoir in Markarian 231 in less than 1e7 yrs, therefore halting the star-formation activity on the same timescale. The inferred kinetic energy in the molecular outflow is ~4e44 erg/s, corresponding to 7% of the AGN bolometric luminosity, which is very close to the fraction expected by models ascribing quasar feedback to highly supersonic shocks generated by radiatively accelerated nuclear winds. Instead, the contribution by the SNe fall short by orders of magnitude to account for the outflow kinetic energy."

There is going to be some skepticism about this paper in the superwind community, given the uncertainties in CO to hydrogen conversion factors. In terms of the larger scale (10+ kpc) superwind Mrk 231 is not that different from other ULIRGs with winds.

Modeling the Outflow in the Narrow-Line Region of Markarian 573: Biconical Illumination of a Gaseous Disk
T. C. Fischer, D. M. Crenshaw, S. B. Kraemer, H. R. Schmitt, M. L. Trippe, arXiv:1006.1875 [pdf]
Comments: 20 pages, 5 figures (1 color), to be published in The Astronomical Journal
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Abstract in full: "We present a study of the outflowing ionized gas in the resolved narrow-line region (NLR) of the Seyfert 2 galaxy Mrk 573, and its interaction with an in- ner dust/gas disk, based on Hubble Space Telescope (HST) WFPC2 and STIS observations. From the spectroscopic and imaging information, we determined the fundamental geometry of the outflow and inner disk, via two modeling pro- grams used to recreate the morphology of these regions imaged with HST. We also determined that the bicone of ionizing radiation from the Active Galactic Nucleus (AGN) intersects with the inner disk, illuminating a section of the disk including inner segments of spiral arms, fully seen through structure mapping, which appear to be outflowing and expanding. In addition, we see high velocities at projected distances of \geq 2'' (- 700 pc) from the nucleus, which could be due to rotation or to in situ acceleration of gas off the spiral arms. We find that the true half opening angle of the ionizing bicone (53 degrees) is much larger than the apparent half-opening angle (34 degrees) due to the above geometry, which may apply to a number of other Seyferts as well."

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X-ray Astronomy

Ionization Equilibrium Timescales in Collisional Plasmas
Randall K. Smith, John P. Hughes, arXiv:1006.0254 [pdf, ps, other]
Comments: 4 pages, 2 figures. Accepted for publication by the Astrophysical Journal

Full abstract: "Astrophysical shocks or bursts from a photoionizing source can disturb the typical collisional plasma found in galactic interstellar media or the intergalactic medium. The spectrum emitted by this plasma contains diagnostics that have been used to determine the time since the disturbing event, although this determination becomes uncertain as the elements in the plasma return to ionization equilibrium. A general solution for the equilibrium timescale for each element arises from the elegant eigenvector method of solution to the problem of a non-equilibrium plasma described by Masai (1984) and Hughes & Helfand (1985). In general the ionization evolution of an element Z in a constant electron temperature plasma is given by a coupled set of Z+1 first order differential equations. However, they can be recast as Z uncoupled first order differential equations using an eigenvector basis for the system. The solution is then Z separate exponential functions, with the time constants given by the eigenvalues of the rate matrix. The smallest of these eigenvalues gives the scale of slowest return to equilibrium independent of the initial conditions, while conversely the largest eigenvalue is the scale of the fastest change in the ion population. These results hold for an ionizing plasma, a recombining plasma, or even a plasma with random initial conditions, and will allow users of these diagnostics to determine directly if their best-fit result significantly limits the timescale since a disturbance or is so close to equilibrium as to include an arbitrarily-long time"

Hooray, it has finally appeared!

A New Calculation of Ne IX Line Diagnostics
Randall K. Smith, Guo-Xin Chen, Kate Kirby, Nancy S. Brickhouse, arXiv:1006.0667 [pdf, ps, other]
Journal-ref: 2009, ApJ, 700, 679

Their abstract: "We describe the effect that new atomic calculations, including fully-relativistic R-matrix calculations of collisional excitation rates and level-specific dielectronic and radiative recombination rates, have on line ratios from the astrophysically significant ion Ne IX. The new excitation rates systematically change some predicted Ne IX line ratios by 25% at temperatures at or below the temperature of maximum emissivity (4x10^6 K), while the new recombination rates lead to systematic changes at higher temperatures. The new line ratios are shown to agree with observations of Capella and sigma^2 CrB significantly better than older line ratios, showing that 25-30% accuracy in atomic rates is inadequate for high-resolution X-ray observations from existing spectrometers."

This paper is from last year, but worth keeping in mind.

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Numerical Astrophysics and Hydrodynamics

Inviscid SPH
Lee Cullen, Walter Dehnen, arXiv:1006.1524 [pdf, ps, other]
Comments: 14 pages (15 in arXiv), 15 figures, accepted for publication in MNRAS

Abstract in full: "In smooth-particle hydrodynamics (SPH), artificial viscosity is necessary for the correct treatment of shocks, but often generates unwanted dissipation away from shocks. We present a novel method of controlling the amount of artificial viscosity, which uses the total time derivative of the velocity divergence as shock indicator and aims at completely eliminating viscosity away from shocks. We subject the new scheme to numerous tests and find that the method works at least as well as any previous technique in the strong-shock regime, but becomes virtually inviscid away from shocks, while still maintaining particle order. In particular sound waves or oscillations of gas spheres are hardly damped over many periods."

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Stars, Supernovae and Planets

Atmospheric mass loss by stellar wind from planets around main sequence M stars
Jesus Zendejas, Antigona Segura, Alejandro Raga, arXiv:1006.0021 [pdf, ps, other]
Comments: Icarus, submitted. 18 pages, 6 figures

They conclude that for late type M dwarfs (later than M5),most planets within the habitable zone may have lost their atmospheres in 1 Gyr or less.

The Evolution of Cloud Cores and the Formation of Stars
Avery E. Broderick, Eric Keto, arXiv:1006.0733 [pdf, ps, other]
Comments: 12 pages, 7 figures, submitted to ApJ

Interesting Astrophysics: 17 May to 28 May

The final batch of interesting preprints (and a few accepted papers) for May 2010.

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Galaxies and Starbursts

Witnessing the Formation of a Brightest Cluster Galaxy in a Nearby X-ray Cluster
Jesper Rasmussen, John S. Mulchaey, Lei Bai, Trevor J. Ponman, Somak Raychaudhury, Ali Dariush, arXiv:1005.3538 [pdf, ps, other]
Comments: 16 pages, 12 figures. ApJ accepted

UV+IR Star Formation Rates: Hickson Compact Groups with Swift and Spitzer
P. Tzanavaris, A. E. Hornschemeier, S. C. Gallagher, K. E. Johnson, C. Gronwall, S. Immler, A. E. Reines, E. Hoversten, J. C. Charlton, arXiv:1005.4059 [pdf, ps, other]
Comments: Accepted by ApJ. [8 Tables, 16 Figures. Color figures have reduced size for ArXiv - emulateapj v. 2/16/10]
Journal-ref: Astrophysical Journal 716 (2010) 556-573

From their abstract: "We present Swift UVOT (1600-3000A) 3-band photometry for 41 galaxies in 11 nearby (<4500km/s) Hickson Compact Groups (HCGs) of galaxies. We use the uvw2-band (2000A) to estimate the dust-unobscured component, SFR_UV, of the total star-formation rate, SFR_T. We use Spitzer MIPS 24-micron photometry to estimate SFR_IR, the dust-obscured component of SFR_T. We obtain SFR_T=SFR_UV+SFR_IR. Using 2MASS K_s band based stellar mass, M*, estimates, we calculate specific SFRs, SSFR=SFR_T/M*. SSFR values show a clear and significant bimodality, with a gap between low (<~3.2x10^-11 / yr) and high SSFR (>~1.2x10^-10 / yr) systems. All galaxies with MIR activity index a_IRAC <= 0 (>0) are in the high- (low-) SSFR locus, as expected if high levels of star-formation power MIR emission from polycyclic aromatic hydrocarbon molecules and a hot dust continuum. All elliptical/S0 galaxies are in the low-SSFR locus, while 22 out of 24 spirals/irregulars are in the high-SSFR locus, with two borderline cases. ... Unlike HCG galaxies, galaxies in a comparison quiescent SINGS sub-sample are continuously distributed both in SSFR and a_IRAC. Any uncertainties can only further enhance the SSFR bimodality. These results suggest that an environment characterized by high galaxy number-densities and low galaxy velocity-dispersions, such as the one found in compact groups, plays a key role in accelerating galaxy evolution by enhancing star-formation processes in galaxies and favoring a fast transition to quiescence."

Radiation pressure from massive star clusters as a launching mechanism for super-galactic winds
Norman Murray, Brice Ménard, Todd A. Thompson, arXiv:1005.4419 [pdf, ps, other]
Comments: Submitted to ApJ, comments welcome
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)

Their abstact: "Galactic outflows of low ionization, cool gas are ubiquitous in local starburst galaxies, and in the majority of galaxies at high redshift. How these cool outflows arise is still in question. Hot gas from supernovae has long been suspected as the primary driver, but this mechanism suffers from its tendency to destroy the cool gas as the latter is accelerated. We propose a modification of the supernova scenario that overcomes this difficulty.
Star formation is observed to take place in clusters; in a given galaxy, the bulk of the star formation is found in the ~20 most massive clusters. We show that, for L* galaxies, the radiation pressure from clusters with M>10^6 M_sun is able to expel the surrounding gas at velocities in excess of the circular velocity of the disk galaxy. This cool gas can travel above the galactic disk in less than 2 Myr, well before any supernovae erupt in the driving cluster. Once above the disk, the cool outflowing gas is exposed to radiation, and supernovae induced hot gas outflows, from other clusters in the disk, which drive it to distances of several tens to hundreds of kpc. Because the radiatively driven clouds grow in size as they travel, and because the hot gas is more dilute at large distance, the clouds are less subject to destruction if they do eventually encounter hot gas. Therefore, unlike wind driven clouds, radiatively driven clouds can survive to distances ~50 kpc. We identify these cluster-driven winds with large-scale galactic outflows. Another implication of our model is that only starburst galaxies, where massive clusters reside, are able to drive winds cold outflows on galactic scales via this mechanism. We find that the critical star formation rates above which large scale cool outflows will be launched to be ~0.1 M_sun/yr/kpc^2, which is in good agreement with observations."

I can see a quite a few problems with this line of argumentation. Hopefully I'll get around to addressing them in the monster paper I'm still adding to. Why write three papers when you can just write one absurdly large one?

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Black Holes and AGN

"Comets" orbiting a black hole
R. Maiolino, G. Risaliti, M. Salvati, P. Pietrini, G. Torricelli-Ciamponi, M. Elvis, G. Fabbiano, V. Braito, J. Reeves, arXiv:1005.3365 [pdf, ps, other]
Comments: Accepted for publication in A&A. 11 pages, 9 figures

Their abstract: "We use a long (300 ksec), continuous Suzaku X-ray observation of the active nucleus in NGC1365 to investigate the structure of the circumnuclear BLR clouds through their occultation of the X-ray source. The variations of the absorbing column density and of the covering factor indicate that the clouds surrounding the black hole are far from having a spherical geometry (as sometimes assumed), instead they have a strongly elongated and cometary shape, with a dense head (n=10^11 cm^-3) and an expanding, dissolving tail. We infer that the cometary tails must be longer than a few times 10^13 cm and their opening angle must be smaller than a few degrees. We suggest that the cometary shape may be a common feature of BLR clouds in general, but which has been difficult to recognize observationally so far. The cometary shape may originate from shocks and hydrodynamical instabilities generated by the supersonic motion of the BLR clouds into the intracloud medium. As a consequence of the mass loss into their tail, we infer that the BLR clouds probably have a lifetime of only a few months, implying that they must be continuously replenished. We also find a large, puzzling discrepancy (two orders of magnitude) between the mass of the BLR inferred from the properties of the absorbing clouds and the mass of the BLR inferred from photoionization models; we discuss the possible solutions to this discrepancy."

Adaptive optics near infrared integral field spectroscopy of NGC 2992
S. Friedrich, R. I. Davies, E. K. S. Hicks, H. Engel, F. Müller-Sánchez, R. Genzel, L. J. Tacconi, arXiv:1005.4791 [pdf, ps, other]
Comments: 10 pages, 8 figures, accepted for publication in A&amp;A

From their abstract: "NGC 2992 is an intermediate Seyfert 1 galaxy showing outflows on kilo parsec scales which might be due either to AGN or starburst activity. We therefore aim at investigating its central region for a putative starburst in the past and its connection to the AGN and the outflows. Observations were performed with the adaptive optics near infrared integral field spectrograph SINFONI on the VLT, complemented by longslit observations with ISAAC on the VLT, as well as N- and Q-band data from the Spitzer archive. The spatial and spectral resolutions of the SINFONI data are 50 pc and 83 km/s, respectively. ... A simple geometric model of two mutually inclined disks and an additional cone to describe an outflow was developed to explain the observed complex velocity field in H_2 1-0S(1). ... We find a starburst age of 40 Myr - 50 Myr from Br_gamma line diagnostics and the radio continuum; ongoing star formation can be excluded. Both the energetics and the timescales indicate that the outflows are driven by the AGN rather than the starburst. The complex velocity field observed in H_2 1-0S(1) in the central 450 pc can be explained by the superposition of the galaxy rotation and an outflow."

So, the questions remains - is there really an outflow on larger scales too?. The lack of clear cases of purely AGN-driven large scale winds really makes me doubt radiation-driven wind models.

Fading hard X-ray emission from the Galactic Centre molecular cloud Sgr B2
R. Terrier, G. Ponti, G. Belanger, A. Decourchelle, V. Tatischeff, A. Goldwurm, G. Trap, M. R. Morris, R. Warwick, arXiv:1005.4807 [pdf, ps, other]
Comments: Accepted for publication in ApJ. 10 pages, 5 figures

From their abstract: "The centre of our Galaxy harbours a 4 million solar mass black hole that is unusually quiet: its present X-ray luminosity is more than 10 orders of magnitude less than its Eddington luminosity. The observation of iron fluorescence and hard X-ray emission from some of the massive molecular clouds surrounding the Galactic Centre has been interpreted as an echo of a past flare. ... Here we report the observation of a clear decay of the hard X-ray emission from the molecular cloud Sgr B2 during the past 7 years thanks to more than 20 Ms of INTEGRAL exposure. The measured decay time is compatible with the light crossing time of the molecular cloud core . Such a short timescale rules out inverse bremsstrahlung by cosmic-ray ions as the origin of the X ray emission. We also obtained 2-100 keV broadband X-ray spectra by combining INTEGRAL and XMM-Newton data and compared them with detailed models of X-ray emission due to irradiation of molecular gas by (i) low-energy cosmic-ray electrons and (ii) hard X-rays. Both models can reproduce the data equally well, but the time variability constraints and the huge cosmic ray electron luminosity required to explain the observed hard X-ray emission strongly favor the scenario in which the diffuse emission of Sgr B2 is scattered and reprocessed radiation emitted in the past by Sgr A*. Using recent parallax measurements that place Sgr B2 in front of Sgr A*, we find that the period of intense activity of Sgr A* ended between 75 and 155 years ago."

Black Hole Mass, Host galaxy classification and AGN activity
Barry McKernan, K.E.Saavik Ford, Chris Reynolds, arXiv:1005.4907 [pdf, ps, other]
Comments: MNRAS accepted. 14 pages, 11 figures, complete Table 1 in online journal

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Theoretical Cosmology

The intergalactic medium over the last 10 billion years I: Lyman alpha absorption and physical conditions
Romeel Davé, Benjamin D. Oppenheimer, Neal Katz, Juna A. Kollmeier, David H. Weinberg, arXiv:1005.2421 [pdf, ps, other]
Comments: 21 pages, submitted to MNRAS

Intergalactic Dust Extinction in Hydrodynamic Cosmological Simulations
Ying Zu, David H. Weinberg, Romeel Davé, Mark Fardal, Neal Katz, Dusan Keres, Benjamin D. Oppenheimer, arXiv:1005.4406 [pdf, ps, other]
Comments: 12 pages, 7 figures, to be submitted to MNRAS

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Astrophysical Processes

Secondary ionization and heating by fast electrons
Steven R. Furlanetto and Samuel Johnson Stoever, 2010, MNRAS, 404, 1869
Full Text: HTML, PDF (Size: 720K)

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Numerical Astrophysics and Computational Techniques

Searchable Sky Coverage of Astronomical Observations: Footprints and Exposures
Tamas Budavari, Alex Szalay, Gyorgy Fekete, arXiv:1005.2606 [pdf, other]
Comments: 11 pages, 7 figures, submitted to PASP

Their abstract: "Sky coverage is one of the most important pieces of information about astronomical observations. We discuss possible representations, and present algorithms to create and manipulate shapes consisting of generalized spherical polygons with arbitrary complexity and size on the celestial sphere. This shape specification integrates well with our Hierarchical Triangular Mesh indexing toolbox, whose performance and capabilities are enhanced by the advanced features presented here. Our portable implementation of the relevant spherical geometry routines comes with wrapper functions for database queries, which are currently being used within several scientific catalog archives including the Sloan Digital Sky Survey, the Galaxy Evolution Explorer and the Hubble Legacy Archive projects as well as the Footprint Service of the Virtual Observatory."

The Role of Provenance Management in Accelerating the Rate of Astronomical Research
G. Bruce Berriman, Ewa Deelman, arXiv:1005.3358 [pdf, other]
Comments: 8 pages, 1 figure; Proceedings of Science, 2010

Their abstract: "The availability of vast quantities of data through electronic archives has transformed astronomical research. It has also enabled the creation of new products, models and simulations, often from distributed input data and models, that are themselves made electronically available. These products will only provide maximal long-term value to astronomers when accompanied by records of their provenance; that is, records of the data and processes used in the creation of such products. We use the creation of image mosaics with the Montage grid-enabled mosaic engine to emphasize the necessity of provenance management and to understand the science requirements that higher-level products impose on provenance management technologies. We describe experiments with one technology, the "Provenance Aware Service Oriented Architecture" (PASOA), that stores provenance information at each step in the computation of a mosaic. The results inform the technical specifications of provenance management systems, including the need for extensible systems built on common standards. Finally, we describe examples of provenance management technology emerging from the fields of geophysics and oceanography that have applicability to astronomy applications."

Montage: a grid portal and software toolkit for science-grade astronomical image mosaicking
Joseph C. Jacob, et al, arXiv:1005.4454 [pdf, other]
Comments: 16 pages, 11 figures
Journal-ref: Int. J. Computational Science and Engineering. 2009

Their abstract: "Montage is a portable software toolkit for constructing custom, science-grade mosaics by composing multiple astronomical images. The mosaics constructed by Montage preserve the astrometry (position) and photometry (intensity) of the sources in the input images. The mosaic to be constructed is specified by the user in terms of a set of parameters, including dataset and wavelength to be used, location and size on the sky, coordinate system and projection, and spatial sampling rate. Many astronomical datasets are massive, and are stored in distributed archives that are, in most cases, remote with respect to the available computational resources. Montage can be run on both single- and multi-processor computers, including clusters and grids. Standard grid tools are used to run Montage in the case where the data or computers used to construct a mosaic are located remotely on the Internet. This paper describes the architecture, algorithms, and usage of Montage as both a software toolkit and as a grid portal. Timing results are provided to show how Montage performance scales with number of processors on a cluster computer. In addition, we compare the performance of two methods of running Montage in parallel on a grid."

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Stars, Supernovae and Planets

Who Pulled the Trigger: a Supernova or an AGB Star?
Alan P. Boss, Sandra A. Keiser, arXiv:1005.3981 [pdf, ps, other]
Comments: 14 pages, 4 figures, 1 table, Astrophysical Journal Letters, in press

Their abstract: "The short-lived radioisotope $^{60}$Fe requires production in a core collapse supernova or AGB star immediately before its incorporation into the earliest solar system solids. Shock waves from a somewhat distant supernova, or a relatively nearby AGB star, have the right speeds to simultaneously trigger the collapse of a dense molecular cloud core and to inject shock wave material into the resulting protostar. A new set of FLASH2.5 adaptive mesh refinement hydrodynamical models shows that the injection efficiency depends sensitively on the assumed shock thickness and density. Supernova shock waves appear to be thin enough to inject the amount of shock wave material necessary to match the short-lived radioisotope abundances measured for primitive meteorites. Planetary nebula shock waves from AGB stars, however, appear to be too thick to achieve the required injection efficiencies. These models imply that a supernova pulled the trigger that led to the formation of our solar system. "

Herschel Observations of the W43 "mini-starburst"
J. Bally, et al, arXiv:1005.4092 [pdf, ps, other]
Comments: 5 pages, 3 figures, accepted for A&amp;A Special Issue

From their abstract: "Aims: To explore the infrared and radio properties of one of the closest Galactic starburst regions. Methods: Images obtained with the Herschel Space Observatory at wavelengths of 70, 160, 250, 350, and 500 microns using the PACS and SPIRE arrays are analyzed and compared with radio continuum VLA data and 8 micron images from the Spitzer Space Telescope. ... Results: The W43 star-forming complex is resolved into a dense cluster of protostars, infrared dark clouds, and ridges of warm dust heated by massive stars. The 4 brightest compact sources with L > 1.5 x 10^4 Lsun embedded within the Z-shaped ridge of bright dust emission in W43 remain single at 4" (0.1 pc) resolution. These objects, likely to be massive protostars or compact clusters in early stages of evolution are embedded in clumps with masses of 10^3 to 10^4 Msun, but contribute only 2% to the 3.6 x 10^6 Lsun far-IR luminosity of W43 measured in a 16 by 16 pc box. The total mass of gas derived from the far-IR dust emission inside this region is ~10^6 Msun. Cometary dust clouds, compact 6 cm radio sources, and warm dust mark the locations of older populations of massive stars. Energy release has created a cavity blowing-out below the Galactic plane."

I wish people would stop calling individual star forming regions, even the biggest ones, starbursts. The term starburst has historically been used to denote significantly enhanced star formation at a galactic scale, and makes most sense when used thusly. See, e.g. Heckman, T., 2005, A&SS, 329, 3.

Evolution of massive stars with pulsation-driven superwinds during the RSG phase
Sung-Chul Yoon, Matteo Cantiello, arXiv:1005.4925 [pdf, ps, other]
Comments: Accepted for publications in ApJ Letters

Interesting to note the significance of pulsation in driving these winds. They're not just steady dust-driven winds. Are there any cases of steady dust-driven winds?

Interesting Astrophysics: Apr 19 to Apr 30

There really haven't been many papers or preprints that have caught my eye over the last two weeks or so, so this edition of Interesting Astrophysics is pretty short. The most interesting (to me) of the bunch are Nobukawa et al - on origin of K shell X-ray line emission in the Galactic Center - and Parkin & Pittard's work on the effects of numerical heat conduction on the dynamics of colliding winds.

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Galaxies and Starbursts

The Buried Starburst in the Interacting Galaxy II Zw 096 as Revealed by the Spitzer Space Telescope
Hanae Inami, et al, arXiv:1004.3543 [pdf, ps, other]
Comments: 46 pages, 10 figures, accepted for publication in AJ

Discovery of K-Shell Emission Lines of Neutral Atoms in the Galactic Center Region
Masayoshi Nobukawa, Katsuji Koyama, Takeshi Go Tsuru, Syukyo G Ryu, Vincent Tatischeff, arXiv:1004.3891 [pdf, ps, other]
Comments: 7 pages, 5 figures, accepted for publication in PASJ (Vol.62, No.2, pp.423--429)

This is potentially important. If the interpretation is correct then we don't have to worry so much about unusual (non-Maxwellian) electron energy distributions creating exotic X-ray spectra, and can also still trust and use more traditional models/processes in interpreting diffuse X-ray emission in galaxies other than the Milky Way. This comes at the price of invoking an explanation that posits substantially higher X-ray luminosities for the Milky Way's central black hole in the past than is observed now.

Their abstract: "The K-shell emission line of neutral irons from the Galactic center (GC) region is one of the key for the structure and activity of the GC. The origin is still open question, but possibly due either to X-ray radiation or to electron bombarding to neutral atoms. To address this issue, we analyzed the Suzaku X-ray spectrum from the GC region of intense neutral iron line emission, and report on the discovery of Kalpha lines of neutral argon, calcium, chrome, and manganese atoms. The equivalent widths of these Kalpha lines indicate that the metal abundances in the GC region should be ~1.6 and ~4 of solar value, depending on the X-ray and the electron origins, respectively. On the other hand, the metal abundances in the hot plasma in the GC region are found to be ~1-2 solar. These results favor that the origin of the neutral Kalpha lines are due to X-ray irradiation."

Note that what they observe is K-alpha emission from neutral Fe, Ar, Ca, Mg and Chrome(!). This is unlike M82 (Griffiths et al 2000, Strickland & Heckman 2007, 2009), where we see Helium-like emission from S, Ar, Ca and Fe, i.e. direct emission from highly ionized gas, not X-ray fluorescence from irradiated neutral atoms.

Relating dust, gas and the rate of star formation in M31
F. S. Tabatabaei, E. M. Berkhuijsen, arXiv:1004.4306 [pdf, ps, other]
Comments: 22 pages accepted for publication in A&amp;A

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Black Holes and AGN

X-ray and multiwavelength view of NGC 4278. A LINER-Seyfert connection?

G. Younes, D. Porquet, B. Sabra, N. Grosso, J.N. Reeves, M.G. Allen, arXiv:1004.5134 [pdf, other]

Comments: 14 pages, 15 figures, accepted for publication in Astronomy and Astrophysics

Mid-Infrared Properties of the Swift Burst Alert Telescope Active Galactic Nuclei Sample of the Local Universe. I. Emission-Line Diagnostics
K. A. Weaver, M. Meléndez, R. F. Mushotzky, S. Kraemer, K. Engle, E. Malumuth, J. Tueller, C. Markwardt, C.T. Berghea, R. P. Dudik, L. M. Winter, L. Armus, arXiv:1004.5321 [pdf, ps, other]
Comments: 54 pages, 9 Figures. Accepted for publication in The Astrophysical Journal.

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Numerical Astrophysics and Hydrodynamics

Numerical heat conduction in hydrodynamical models of colliding hypersonic flows
E. R. Parkin, J. M. Pittard, arXiv:1004.3753 [pdf, ps, other]
Comments: 14 pages, 10 figures, accepted for publication in MNRAS

Their abstract: "Hydrodynamical models of colliding hypersonic flows are presented which explore the dependence of the resulting dynamics and the characteristics of the derived X-ray emission on numerical conduction and viscosity. For the purpose of our investigation we present models of colliding flow with plane-parallel and cylindrical divergence. Numerical conduction causes erroneous heating of gas across the contact discontinuity which has implications for the rate at which the gas cools. We find that the dynamics of the shocked gas and the resulting X-ray emission are strongly dependent on the contrast in the density and temperature either side of the contact discontinuity, these effects being strongest where the postshock gas of one flow behaves quasi-adiabatically while the postshock gas of the other flow is strongly radiative. Introducing additional numerical viscosity into the simulations has the effect of damping the growth of instabilities, which in some cases act to increase the volume of shocked gas and can re-heat gas via sub-shocks as it flows downstream. The resulting reduction in the surface area between adjacent flows, and therefore of the amount of numerical conduction, leads to a commensurate reduction in spurious X-ray emission, though the dynamics of the collision are compromised. The simulation resolution also affects the degree of numerical conduction. A finer resolution better resolves the interfaces of high density and temperature contrast and although numerical conduction still exists the volume of affected gas is considerably reduced. However, since it is not always practical to increase the resolution, it is imperative that the degree of numerical conduction is understood so that inaccurate interpretations can be avoided. This work has implications for the dynamics and emission from astrophysical phenomena which involve high Mach number shocks."

Microquasar in M82?

I'm seeing this story all over the Internet. Sadly I don't have time to make much comment on it.

The hard working and often sadly under-appreciated folks at Jodrell Bank have made a splash with news of the sudden appearance of a mysterious radio source (woo!) in M82, which is possibly a microquasar (e.g. like SS 433 in our own Galaxy. *). The official Jodrell Bank press release is definitely the best place to get the background on this exciting discovery, as the press stories tend to be... superficial.

It is unfortunate that the images used in all the press stories I've seen so far, and even the lead image on the Jodrell Bank press release, are NOT actual radio images of M82, let alone images showing the new source, but either the Hubble ACS image (i.e. optical light) or a Spitzer image (near Infra-red light). This is the tyranny of Hubble - its a pretty picture machine, but very often the real science can't be done in the optical. Yet what mission does the public associate with astronomy and astrophysics... Hubble. If your mission or observatory doesn't make pretty pictures, or perish the thought, doesn't make images at all (e.g. FUSE) then you have a public relations problem, and potentially a funding problem.

(*) Sadly the wikipedia entry on SS 433 doesn't do a great job in conveying how interesting and awesome this object is.

Interesting Astrophysics: Apr 05 to Apr 16

The last two weeks have produced quite a number of interesting papers and preprints. Given the diversity I'll let them speak for themselves. Note to self: two papers on cloud statistics.

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Galaxies and Starbursts

An Empirical Characterization of Extended Cool Gas Around Galaxies Using MgII Absorption Features
Hsiao-Wen Chen, Jennifer E. Helsby, Jean-Rene Gauthier, Stephen A. Shectman, Ian B. Thompson, Jeremy L. Tinker, arXiv:1004.0705 [pdf, ps, other]

Comments: 20 pages, 13 figures; to appear in the Astrophysical Journal 2010 May 10 issue; a version with higher resolution figures can be found at this http URL

From their abstract: "... The lack of correlation between Wr(2796) and galaxy colors suggests a lack of physical connection between the origin of extended MgII halos and recent star formation history of the galaxies ..."

Seeing Through the Trough: Outflows and the Detectability of Lyman Alpha Emission from the First Galaxies
Mark Dijkstra, Stuart Wyithe, arXiv:1004.2490 [pdf, ps, other]
Comments: 11 pages, 7 figures, submitted to MNRAS

From their abstract: "In this paper we demonstrate that the radiative transfer effects in the interstellar medium (ISM), which cause Lya flux to emerge from galaxies at frequencies where the Gunn-Peterson optical depth is reduced, can substantially enhance the prospects for detection of the Lya line at high redshift. In particular, scattering off outflows of interstellar HI gas can modify the Lya spectral line shape such that >5% of the emitted Lya radiation is transmitted directly to the observer, even through a fully neutral IGM. It may therefore be possible to directly observe `strong' Lya emission lines (EW > 50 Angstrom rest frame) from the highest redshift galaxies that reside in the smallest HII `bubbles' early in the reionization era with JWST. In addition, we show that outflows can boost the fraction of Lya radiation that is transmitted through the IGM during the latter stages of reionization, and even post-reionization."

The Great Observatories All-Sky LIRG Survey: Comparison of Ultraviolet and Far-Infrared Properties
Justin H. Howell, et al, arXiv:1004.0985 [pdf, ps, other]
Comments: 37 pages, 10 figures, accepted for publication in ApJ

From their abstract: "The Great Observatories All-sky LIRG Survey (GOALS) consists of a complete sample of 202 Luminous Infrared Galaxies (LIRGs) selected from the IRAS Revised Bright Galaxy Sample (RBGS). The galaxies span the full range of interaction stages, from isolated galaxies to interacting pairs to late stage mergers. We present a comparison of the UV and infrared properties of 135 galaxies in GOALS observed by GALEX and Spitzer. For interacting galaxies with separations greater than the resolution of GALEX and Spitzer (2-6"), we assess the UV and IR properties of each galaxy individually. The contribution of the FUV to the measured SFR ranges from 0.2% to 17.9%, with a median of 2.8% and a mean of 4.0 +/- 0.4%. The specific star formation rate of the GOALS sample is extremely high, with a median value (3.9*10^{-10} yr^{-1}) that is comparable to the highest specific star formation rates seen in the Spitzer Infrared Nearby Galaxies Survey sample."

Dwarf-Galaxy Cosmology
Regina Schulte-Ladbeck, Ulrich Hopp, Elias Brinks, Andrey Kravtsov, arXiv:1004.1139 [pdf, other]
Comments: This is the editorial paper which introduces the Special Issue on Dwarf-Galaxy Cosmology published in Advances in Astronomy. The issue contains fourteen review papers, and one original research article. All papers were peer-reviewed by a minimum of two referees. To read the Special Issue, please follow this link: this http URL .

Their abstract: "Dwarf galaxies provide opportunities for drawing inferences about the processes in the early universe by observing our "cosmological backyard"-the Local Group and its vicinity. This special issue of the open-access journal Advances in Astronomy is a snapshot of the current state of the art of dwarf-galaxy cosmology."

Sadly no articles focussing on outflows or supernova feedback.

Comparing Ultraviolet and Infrared-Selected Starburst Galaxies in Dust Obscuration and Luminosity
Lusine A. Sargsyan, Daniel W. Weedman, James R. Houck, arXiv:1004.1551 [pdf, ps, other]
Comments: accepted for publication in The Astrophysical Journal

Concludes that the "obscuration corrections by factors of two to three determined from reddening of the ultraviolet continuum for Lyman Break Galaxies with z > 2 are insufficient, and should be at least a factor of 10 for M(UV) about -17, with decreasing correction for more luminous sources."

A Multi-wavelength analysis of M81: insight on the nature of Arp's loop
A. Sollima, A. Gil de Paz, D. Martinez-Delgado, R.J. Gabany, J. Gallego, T. Hallas, arXiv:1004.1610 [pdf, ps, other]
Comments: 7 pages, 7 figures, accepted for publication by A&amp;A

Their abstract: "The optical ring like structure detected by Arp (1965) around M81 (commonly referenced as "Arp's loop") represents one of the most spectacular feature observed in nearby galaxies. Arp's loop is commonly interpreted as a tail resulting from the tidal interaction between M81 and M82. However, since its discovery the nature of this feature has remained controversial. Aims: Our primary purpose was to identify the sources of optical and infrared emission observed in Arp's loop. Methods: The morphology of the Arp's loop has been investigated with deep wide-field optical images. We also measured its colors using IRAS and Spitzer-MIPS infrared images and compared them with those of the disk of M81 and Galactic dust cirrus that fills the area where M81 is located. Results: Optical images reveal that this peculiar object has a filamentary structure characterized by many dust features overlapping M81's field. The ratios of far-infrared fluxes and the estimated dust-to-gas ratios indicate the infrared emission of Arp's loop is dominated by the contribution of cold dust that is most likely from Galactic cirrus. Conclusions: The above results suggest that the light observed at optical wavelengths is a combination of emission from i) a few recent star forming regions located close to M81, where both bright UV complexes and peaks in the HI distribution are found, ii) the extended disk of M81 and iii) scattered light from the same Galactic cirrus that is responsible for the bulk of the far infrared emission."

I've mentioned the Galactic cirrus emission along the line of sight to the M81/M82 group previously in this blog, as the cirrus is visible even in scattered optical/UV light. Amateur astronomers have termed this cirrus-associated nebulosity Integrated Flux Nebulae.

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Black Holes and AGN

Momentum-driven winds and positive AGN feedback
Joe Silk, Adi Nusser, arXiv:1004.0857 [pdf, ps, other]
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Their abstract: "Force balance considerations put a limit on the rate of AGN radiation momentum output, $L/c$, capable of driving galactic superwinds. We show that this condition is insufficient: black holes obeying the observed $\mbh -\sigma $ relation cannot supply enough energy in radiation which can drive the gas out by pressure alone. The shortfall is by up to an order of magnitude in most, but not all, cases. We propose that outflow-triggering of star formation by enhancing the intercloud medium turbulent pressure and squeezing clouds can supply the necessary boost, and suggest possible tests of this hypothesis. We further point out that the time-scales for Bondi accretion and for orbital decay of merging clumps by dynamical friction in the nuclear disk around a central black hole both follow a similar scaling with mass, favoring the most massive black holes, but the latter process is up to two orders of magnitude more rapid at $z\gtsim 10.$ The combination of accretion and coalescence results in earlier formation of more massive black holes, and, in particular, can account for the masses of the black holes inferred to power AGN at $z\sim 6.$"

Molecular clouds: X-ray mirrors of the Galactic nuclear activity
Gabriele Ponti, Regis Terrier, Andrea Goldwurm, Guillaume Belanger, Guillaume Trap, arXiv:1004.1412 [pdf, ps, other]
Comments: 4 pages, "The Galactic Center: A Window on the Nuclear Environment of Disk Galaxies" ASP Conference Series, 2010 eds: M. Morris, D. Q. Wang and F. Yuan

Did the supermassive black hole that currently lurks quietly at the center of our Galaxy flare up about 100 years ago?

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Interstellar Medium

The Mass-Size Relation from Clouds to Cores. II. Solar Neighborhood Clouds
Jens Kauffmann, Thushara Pillai, Rahul Shetty, Philip C. Myers, Alyssa A. Goodman, arXiv:1004.1170 [pdf, ps, other]
Comments: accepted to the Astrophysical Journal

I must read this more carefully.

Abstract in full: "We measure the mass and size of cloud fragments in several molecular clouds continuously over a wide range of spatial scales (0.05 < r / pc < 3). Based on the recently developed "dendrogram-technique", this characterizes dense cores as well as the enveloping clouds. "Larson's 3rd Law" of constant column density, m(r) = C*r^2, is not well suited to describe the derived mass-size data. Solar neighborhood clouds not forming massive stars (< 10 M_sun; Pipe Nebula, Taurus, Perseus, and Ophiuchus) obey m(r) < 870 M_sun (r / pc)^1.33 . In contrast to this, clouds forming massive stars (Orion A, G10.15$-$0.34, G11.11$-$0.12) do exceed the aforementioned relation. Thus, this limiting mass-size relation may approximate a threshold for the formation of massive stars. Across all clouds, cluster-forming cloud fragments are found to be---at given radius---more massive than fragments devoid of clusters. The cluster-bearing fragments are found to roughly obey a mass-size law m = C*r^1.27 (where the exponent is highly uncertain in any given cloud, but is certainly smaller than 1.5).

Physical Properties of Giant Molecular Clouds in the Large Magellanic Cloud
A. Hughes, et al, arXiv:1004.2094 [pdf, ps, other]
Comments: 28 pages, 10 figures, accepted by MNRAS

Searching for Diffuse Nonthermal X-Rays from the Superbubbles N11 and N51D in the Large Magellanic Cloud
H. Yamaguchi, M. Sawada, A. Bamba, arXiv:1004.0753 [pdf, ps, other]
Comments: 9 pages, accepted for publication in ApJ.

Their abstract (emphasis mine): "We report on observations of the superbubbles (SBs) N11 and N51D in the Large Magellanic Cloud (LMC) with Suzaku and XMM-Newton. The interior of both SBs exhibits diffuse X-ray emission, which is well represented by thin thermal plasma models with a temperature of 0.2-0.3keV. The presence of nonthermal emission, claimed in previous works, is much less evident in our careful investigation. The 3-sigma upper limits of 2-10keV flux are 3.6*10^{-14}ergs/cm^2/s and 4.7*10^{-14}ergs/cm^2/s for N11 and N51D, respectively. The previous claims of the detection of nonthermal emission are probably due to the inaccurate estimation of the non X-ray background. We conclude that no credible nonthermal emission has been detected from the SBs in the LMC, with the exception of 30 Dor C. "

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Hydrodynamics and Numerical Astrophysics

A comparison between grid and particle methods on the statistics of driven, supersonic, isothermal turbulence
Daniel J. Price, Christoph Federrath, arXiv:1004.1446 [pdf, ps, other]

Comments: 16 pages, 15 figures, accepted to MNRAS. Associated movies, images and full res version at: this http URL

The Athena Astrophysical MHD Code in Cylindrical Geometry
Aaron Skinner, Eve Ostriker, arXiv:1004.2487 [pdf, ps, other]

Their abstract: "A method for implementing cylindrical coordinates in the Athena magnetohydrodynamics (MHD) code is described. The extension follows the approach of Athena's original developers and has been designed to alter the existing Cartesian-coordinates code as minimally and transparently as possible. The numerical equations in cylindrical coordinates are formulated to maintain consistency with constrained transport, a central feature of the Athena algorithm, while making use of previously implemented code modules such as the Riemann solvers. Angular-momentum transport, which is critical in astrophysical disk systems dominated by rotation, is treated carefully. We describe modifications for cylindrical coordinates of the higher-order spatial reconstruction and characteristic evolution steps as well as the finite-volume and constrained transport updates. Finally, we present a test suite of standard and novel problems in one-, two-, and three-dimensions designed to validate our algorithms and implementation and to be of use to other code developers. The code is suitable for use in a wide variety of astrophysical applications and is freely available for download on the web."

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Instrumentation

The New Hard X-ray Mission
G. Tagliaferri, et al, arXiv:1004.2691 [pdf]
Comments: 9 pages, 5 figures. Accepted for publication on PoS, proceedings of "The Extreme sky: Sampling the Universe above 10 keV", held in Otranto (Italy), 13-17 October 2009

Their abstract: "The Italian New Hard X-ray Mission (NHXM) has been designed to provide a real breakthrough on a number of hot astrophysical issues that includes: black holes census, the physics of accretion, the particle acceleration mechanisms, the effects of radiative transfer in highly magnetized plasmas and strong gravitational fields. NHXM is an evolution of the HEXIT-Sat concept and it combines fine imaging capability up to 80 keV, today available only at E<10 keV, with sensitive photoelectric imaging polarimetry. It consists of four identical mirrors, with a 10 m focal length, achieved after launch by means of a deployable structure. Three of the four telescopes will have at their focus identical spectral-imaging cameras, while X-ray imaging polarimetric cameras will be placed at the focus of the fourth. In order to ensure a low and stable background, NHXM will be placed in a low Earth equatorial orbit. In this paper we provide an overall description of this mission that is currently in phase B."

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Stars, Supernovae and Planets

One-sided Outflows/Jets from Rotating Stars with Complex Magnetic Fields
R.V.E. Lovelace, M.M. Romanova, G.V. Ustyugova, A.V. Koldoba, arXiv:1004.0385 [pdf, other]
Comments: 10 pages, 11 figures

Dusty Disks around White Dwarfs I: Origin of Debris Disks
Ruobing Dong, Yan Wang, D. N.C. Lin, X.-W. Liu, arXiv:1004.0696 [pdf, ps, other]
Comments: 38 pages, 7 figures, single column, accepted by ApJ

Interesting Astrophysics: Mar 23 to Mar 31

Dwarfs and giants compete in this edition of Interesting Astrophysics. The dwarfs (or dwarves, as Tolkien would have us write it) are dwarf starburst galaxies and the giants are very very luminous starbursting galaxies.

There are two very nice papers on the very popular (if somewhat atypical) dwarf starburst galaxy NGC 1569 (Kepley et al, and Westmoquette et al), both of interest with respect to its galactic wind. Monreal-Ibero et al present a paper on NGC 5253 (possibly the second most popular dwarf starburst galaxy judged by number of papers published). And yes, that region of nitrogen enrichment that is the one clear case of localized chemical enrichment by recently formed massive stars is still there.

Younger et al discuss the physical sizes of the star forming regions in submillimeter galaxies, and argue that the data supports an interpretation as merger-driven starbursts rather than simply over-active disks. This is not particularly surprising, as the SMGs have long been thought to be semi-equivalent to local Ultraluminous IR galaxies (ULIRGs are merger driven starbursts).

Not content with merely Ultraluminosity, Rowan-Robinson et al present a catalog of 179 Hyperluminous IR galaxies, and discuss their spectral energy distributions and star formation rates.

Last but not least I'll mention Chen et al's work on probing outflows from star forming galaxies with Na I absorption in SDSS spectra. Its a big paper, but for me the results that seem coolest are that their results appear to confirm the Lehnert & Heckman star formation per unit area threshold above which winds (or extra-planar gas) appear, and that outflows really do seem to have a prefer opening angle of ~60 degrees.

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Galaxies and Starbursts

The Role of the Magnetic Field in the Interstellar Medium of the Post-Starburst Dwarf Irregular Galaxy NGC 1569
Amanda A. Kepley, Stefanie Mühle, John Everett, Ellen G. Zweibel, Eric M. Wilcots and Uli Klein, 2010, ApJ, 712, 536

This is a really nice piece of work. Their are relatively few studies of magnetic field structures and strengths in starbursts with superwinds that answer the kind of questions that this paper addresses, so this paper is a very valuable addition to the literature.

Their abstract (emphasis mine): "NGC 1569 is a nearby dwarf irregular galaxy which underwent an intense burst of star formation 10-40 Myr ago. We present observations that reach surface brightnesses 2-80 times fainter than previous radio continuum observations and the first radio continuum polarization observations of this galaxy at 20 cm, 13 cm, 6 cm, and 3 cm. These observations allow us to probe the relationship of the magnetic field of NGC 1569 to the rest of its interstellar medium (ISM). We confirm the presence of an extended radio continuum halo at 20 cm and see for the first time the radio continuum feature associated with the western Hα arm at wavelengths shorter than 20 cm. Although, in general, the spectral indices derived for this galaxy steepen as one moves into the halo of the galaxy, there are filamentary regions of flat spectral indices extending to the edge of the galaxy. The spectral index trends in this galaxy support the theory that there is a convective wind at work in this galaxy. There is strong polarized emission at 3 cm and 6 cm and weak polarized emission at 20 cm and 13 cm. We estimate that the thermal fraction is 40%-50% in the center of the galaxy and falls off rapidly with height above the disk. Using this estimate, we derive a total magnetic field strength of 38 μG in the central regions and 10-15 μG in the halo. The magnetic field is largely random in the center of the galaxy; the uniform field is ~3-9 μG and is strongest in the halo. Using our total magnetic field strength estimates and the results of previous observations of NGC 1569, we find that the magnetic pressure is the same order of magnitude but, in general, a factor of a few less than the other components of the ISM in this galaxy. The uniform magnetic field in NGC 1569 is closely associated with the Hα bubbles and filaments. We suggest that a supernova-driven dynamo may be operating in this galaxy. Based on our pressure estimates and the morphology of the magnetic field, the outflow of hot gas from NGC 1569 is clearly shaping the magnetic field, but the magnetic field in turn may be aiding the outflow by channeling gas out of the disk of the galaxy. Dwarf galaxies with extended radio continuum halos like that of NGC 1569 may play an important role in magnetizing the intergalactic medium."

Mapping the roots of the galactic outflow in NGC1569
Mark S. Westmoquette, Linda J. Smith, Jay S. Gallagher and Katrina M. Exter, 2009, Ap&SS, 324, 187

The physical scale of the far-infrared emission in the most luminous submillimetre galaxies II: evidence for merger-driven star formation
J. D. Younger, G. G. Fazio, M. L. N. Ashby, F. Civano, M. Elvis, M. A. Gurwell, J.-S. Huang, D. Iono, A. B. Peck, G. R. Petitpas, K. S. Scott, D. J. Wilner, G. W. Wilson, M. S. Yun, arXiv:1003.4264 [pdf, ps, other]
Comments: 9 pages, 3 Figures, submitted to MNRAS

From their abstract: "These relatively compact sizes (<5-10 kpc) argue strongly for merger-driven starbursts, rather than extended gas-rich disks, as the preferred channel for forming SMGs. For the most luminous objects, the derived sizes may also have important physical consequences; under a series of simplifying assumptions, we find that these two objects in particular are forming stars close to or at the Eddington limit for a starburst."

Hyperluminous infrared galaxies from IIFSCz
Michael Rowan-Robinson, Lingyu Wang, arXiv:1003.4869 [pdf, ps, other]
Comments: 11 pages, 11 figures: accepted for publication in MNRAS.

From their abstract: "We present a catalogue of 179 hyperluminous infrared galaxies (HLIRGs) from the Imperial IRAS-FSS Redshift (IIFSCz) Catalogue. Of the 92 with detections in at least two far infrared bands, 62 are dominated by an M82-like starburst, 22 by an Arp220-like starburst and 8 by an AGN dust torus. On the basis of previous gravitational lensing studies and an examination of HST archive images for a further 5 objects, we estimate the fraction of HLIRGs that are significantly lensed to be 10-30%. ... The implied star-formation rates, even after correcting for lensing magnification, are in excess of 1000 Mo /yr."

A study of the interplay between ionized gas and star clusters in the central region of NGC 5253 with 2D spectroscopy
A. Monreal-Ibero, J. M. Vilchez, J. R. Walsh, C. Munoz-Tunon, arXiv:1003.5329 [pdf, ps, other]
Comments: accepted in Astronomy & Astrophysics. 21 pages, 22 figures

From their abstract: "A detailed 2D study of the central region of NGC5253 has been performed to characterize the stellar and ionized gas structure as well as the extinction distribution, physical properties and kinematics of the ionized gas in the central ~210pc x 130pc. ... The [SII]l6717/[SII]l6731 map shows an electron density (N_e) gradient declining from the peak of emission in Ha (790cm^-3) outwards, while the argon line ratio traces areas with $N_e~4200 - 6200cm^(-3). The area polluted with extra nitrogen, as deduced from the excess [NII]/Ha, extends up to distances of 3.3" (~60pc) from the maximum pollution, which is offset by ~1.5" from the peak of continuum emission. Wolf-Rayet features are distributed in an irregular pattern over a larger area (~100pc x 100pc) and associated with young stellar clusters. ... The line profiles are complex. Up to three emission components were needed to reproduce them. One of them, associated with the giant HII region, presents supersonic widths and [NII] and [SII] emission lines shifted up to 40km/s with respect to Ha. Similarly, one of the narrow components presents offsets in the [NII] line of <~20km/s. This is the first time that maps with such velocity offsets for a starburst galaxy have been presented."

Absorption-line probes of the prevalence and properties of outflows in present-day star-forming galaxies
Yan-Mei Chen, Christy A. Tremonti, Timothy M. Heckman, Guinevere Kauffmann, Benjamin J. Weiner, Jarle Brinchmann, Jing Wang, arXiv:1003.5425 [pdf, ps, other]
Comments: 18 pages, 18 figures, submitted to AJ

Their abstract: "We analyze star forming galaxies drawn from SDSS DR7 to show how the interstellar medium (ISM) Na I 5890, 5896 (Na D) absorption lines depend on galaxy physical properties, and to look for evidence of galactic winds. We combine the spectra of galaxies with similar geometry/physical parameters to create composite spectra with signal-to-noise ~300. The stellar continuum is modeled using stellar population synthesis models, and the continuum-normalized spectrum is fit with two Na I absorption components. We find that: (1) ISM Na D absorption lines with equivalent widths EW > 0.8A are only prevalent in disk galaxies with specific properties -- large extinction (Av), high star formation rates (SFR), high star formation rate per unit area ($\Sigma_{\rm SFR}$), or high stellar mass (M*). (2) the ISM Na D absorption lines can be separated into two components: a quiescent disk-like component at the galaxy systemic velocity and an outflow component; (3) the disk-like component is much stronger in the edge-on systems, and the outflow component covers a wide angle but is stronger within 60deg of the disk rotation axis; (4) the EW and covering factor of the disk component correlate strongly with dust attenuation, highlighting the importance that dust shielding may play the survival of Na I. (5) The EW of the outflow component depends primarily on $\Sigma_{\rm SFR}$ and secondarily on Av; (6) the outflow velocity varies from ~120 to 160km/s but shows little hint of a correlation with galaxy physical properties over the modest dynamic range that our sample probes (1.2 dex in log$\Sigma_{\rm SFR}$ and 1 dex in log M*)."

Massive star formation in Wolf-Rayet galaxies. III: Analysis of the O and WR populations
Angel R. Lopez-Sanchez, Cesar Esteban, arXiv:1004.0051 [pdf, ps, other]
Comments: Accepted in A&A, 19 pages, 13 figures

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Black Holes and AGN

Infrared Excess Sources: Compton Thick QSOs, low luminosity Seyferts or starbursts?
A. Georgakakis, M. Rowan-Robinson, K. Nandra, J. Digby-North, P. G. Perez-Gonzalez, G. Barro, arXiv:1003.5218 [pdf, other]
Comments: Accepted by MNRAS

Full abstract: "We explore the nature of Infrared Excess sources (IRX), which are proposed as candidates for luminous L_X(2-10keV)>1e43erg/s Compton Thick (N_H>2e24cm^{-2}$) QSOs at z~2. Lower redshift, z~1, analogues of the distant IRX population are identified by firstly redshifting to z=2 the SEDs of all sources with secure spectroscopic redshifts in the AEGIS (6488) and the GOODS-North (1784) surveys and then selecting those that qualify as IRX sources at that redshift. A total of 19 galaxies are selected. The mean redshift of the sample is $z\approx1$. We do not find strong evidence for Compton Thick QSOs in the sample. For 9 sources with X-ray counterparts, the X-ray spectra are consistent with Compton Thin AGN. Only 3 of them show tentative evidence for Compton Thick obscuration. The SEDs of the X-ray undetected population are consistent with starburst activity. There is no evidence for a hot dust component at the mid-infrared associated with AGN heated dust. If the X-ray undetected sources host AGN, an upper limit of L_X(2-10keV) =1e43erg/s is estimated for their intrinsic luminosity. We propose that a large fraction of the $z\approx2$ IRX population are not Compton Thick QSOs but low luminosity [L_X(2-10keV)<1e43erg/s], possibly Compton Thin, AGN or dusty starbursts. It is shown that the decomposition of the AGN and starburst contribution to the mid-IR is essential for interpreting the nature of this population, as star-formation may dominate this wavelength regime. "

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Numerical Methods and Hydrodynamics

A method for reconstructing the PDF of a 3D turbulent density field from 2D observations
Christopher M. Brunt, Christoph Federrath, Daniel J. Price, arXiv:1003.4151 [ps, pdf, other]
Comments: 5 pages, 2 figures, accepted for publication in MNRAS Letters

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Theoretical Cosmology

Toward the Formation of Realistic Galaxy Disks
Alyson Brooks, arXiv:1003.3882 [pdf]
Comments: Proceedings of the Frank N. Bash Symposium 2009: "New Horizons in Astronomy." Comments welcome.

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Stars, Supernovae and Planets

Direct Confirmation of the Asymmetry of the Cas A SN Explosion with Light Echoes
A. Rest, et al, arXiv:1003.5660 [pdf, ps, other]
Comments: 12 pages, 7 figures, submitted to ApJ

Spectral Classification; Old and Contemporary
Sunetra Giridhar, arXiv:1003.4002 [ps, pdf, other]
Comments: To be published in "Principles and Perspectives in Cosmochemistry" Lecture Notes on Kodai School on Synthesis of Elements in Stars: Ed Aruna Goswami &amp; Eswar Reddy, Springer Verlag, 2009, 17 pages, 10 figures

Updating the Historical Sunspot Record
Leif Svalgaard, arXiv:1003.4666 [pdf, other]
Comments: SOHO23 Conference Proceedings, Astronomical Society of the Pacific

Abstract: "We review the evidence for the argument that Rudolf Wolf's calibration of the Sunspot Number is likely to be correct and that Max Waldmeier introduced an upwards jump in the sunspot number in 1945. The combined effect of these adjustments suggests that there has been no secular change in the sunspot number since coming out of the Maunder Minimum ~1700."

Interesting Astrophysics: Mar 08 to Mar 22

I return from a much-needed holiday in the Caribbean to an energetic bunch of preprints and papers making its appearance in this edition of Interesting Astrophysics.

Galactic winds, including possible AGN-driven galactic winds, are of course my major interest, so Scannapieco & Brüggen's paper is of particular note, but note also Dadina et al, Shu et al (twice) and Jiménez-Vicente et al's papers.

X-ray emission from star forming galaxies also makes an appearance, with Wang's PNAS review, Owen & Warwick's XMM-Newton study of M33, and Anderson & Bregman's discussion of the baryon content of hot halos around galaxies. Martin Weisskopf's history of the project to build the Chandra X-ray Observatory is also well worth reading.

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Galaxies and Starbursts

X-raying Galaxies: A Chandra Legacy
Q. Daniel Wang, arXiv:1003.1282 [pdf, other]
Comments: Refereed review article to be published in Proceedings of the National Academy of Sciences

The submillimetre properties of ultraluminous infrared galaxies
D. L. Clements, L. Dunne, S. Eales, 2010, MNRAS, 403, 274
Full Text: HTML, PDF (Size: 859K)

A blue tilt in the globular cluster system of the Milky Way-like galaxy NGC 5170
Duncan A. Forbes, Lee R. Spitler, W. E. Harris, Jeremy Bailin, Jay Strader, Jean P. Brodie, S. S. Larsen, 2010, MNRAS, 403, 429
Full Text: HTML, PDF (Size: 3707K)

The likeness of a galaxy to the Milky-Way often depends greatly on whose opinion you ask. NGC 5170 has a circular rotation velocity of ~250 km/s and a star formation rate of ~0.5 Solar masses per year, making it somewhat more massive and less active than the Milky Way. Nevertheless an interesting galaxy (No X-ray halo was detected around NGC 5170 in Chandra observations, see Pedersen et al 2006 and Rasmussen et al 2009. Note that the detection of an X-ray halo around NGC 5746 claimed in Pedersen et all 2006 was effectively retracted by Rasmussen et al 2009).

Ongoing Star Formation In AGN Host Galaxy Disks: A View From Core-collapse Supernovae
J. Wang, J. S. Deng, J. Y. Wei, arXiv:1003.1358 [ps, pdf, other]
Comments: 5 pages, 4 figures, accepted by MNRAS

A Region of Violent Star Formation in the Irr Galaxy IC 10: Structure and Kinematics of Ionized and Neutral Gas
O. V. Egorov, T. A. Lozinskaya, A. V. Moiseev, arXiv:1003.1705 [ps, pdf, other]
Comments: 22 pages, 10 figures; accepted in Astronomy Reports

Do Hot Haloes Around Galaxies Contain the Missing Baryons?
Michael E. Anderson, Joel N. Bregman, arXiv:1003.3273 [ps, pdf, other]
Comments: accepted for publication in the Astrophysical Journal

As with most papers that pose a question in their title, the answer is no. A nice paper worth looking at.

On The GeV & TeV Detections of the Starburst Galaxies M82 & NGC 253
Brian C. Lacki, Todd A. Thompson, Eliot Quataert, Abraham Loeb, Eli Waxman, arXiv:1003.3257 [ps, pdf, other]
Comments: 14 pages, emulateapj format, submitted to ApJ.

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Black Holes and AGN

X-ray imaging of the ionisation cones in NGC 5252
M.Dadina, M.Guainazzi, M.Cappi, S.Bianchi, C. Vignali, G. Malaguti, A. Comastri, rXiv:1003.1665 [ps, pdf, other]
Comments: Accepted for publication in A&A

NGC 2992 in an X-ray high state observed by XMM: Response of the Relativistic Fe K$\alpha$ Line to the Continuum
X. W. Shu, T. Yaqoob, K. D. Murphy, V. Braito, J. X. Wang, W. Zheng, arXiv:1003.1789 [ps, pdf, other]
Comments: 30 pages, 6 figures, Accepted to ApJ

The Cores of the Fe Kα Lines in Active Galactic Nuclei: an Extended Chandra High Energy Grating Sample
X. W. Shu, T. Yaqoob, J. X. Wang, arXiv:1003.1790 [ps, pdf, other]
Comments: 54 pages, 7 figures, and 4 tables, to appear in ApJ Supplement Series

Blasts and shocks in the disc of NGC 4258
J. Jiménez-Vicente, E. Mediavilla, A. Castillo-Morales, E. Battaner, arXiv:1003.3635 [ps, pdf, other]
Comments: 7 pages, 10 colour figures. Accepted for publication in MNRAS.

Na I observations with an IFU.

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Numerical Methods

General two-dimensional least-squares image subtraction
J. L. Quinn, A. Clocchiatti and M. Hamuy, 2010, MNRAS, 403, L1
Full Text: HTML, PDF (Size: 514K)

Shape: A 3D Modeling Tool for Astrophysics
Wolfgang Steffen, Nicholas Koning, Stephan Wenger, Christophe Morisset, Marcus Magnor, arXiv:1003.2012 [pdf, other]
Comments: 13 pages, 11 figures, accepted for publication in the "IEEE Transactions on Visualization and Computer Graphics"

Simulating Supersonic Turbulence in Galaxy Outflows
Evan Scannapieco, Marcus Brüggen, arXiv:1003.3234 [pdf, other]
Comments: 22 pages, 13 figures, MNRAS, in press

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X-rays

Innovations in the Analysis of Chandra-ACIS Observations
Patrick S. Broos, Leisa K. Townsley, Eric D. Feigelson, Konstantin V. Getman, Franz E. Bauer, Gordon P. Garmire, arXiv:1003.2397 [pdf, other]
Comments: Accepted by the ApJ, 2010 Mar 10, 39 pages, 16 figures

The Making of the Chandra X-ray Observatory: the Project Scientist's Perspective
Martin C. Weisskopf, arXiv:1003.1990 [pdf]
Comments: 6 pages, 17 figures. To be published in the Proceedings of the national Academy of Sciences of the United States of America.

I found this to be a really interesting article. It discusses both technical and political development with a sprinkling of dry humor. Also note the time span between the conceptual birth of AXAF/Chandra (1963, and the updated 1976 proposal) and the actual launch in 1999.

Soft X-ray emission from the inner disc of M33
R. A. Owen and R. S. Warwick, 2010, MNRAS, 403, 558
Full Text: HTML, PDF (Size: 4702K)