NAS's Astro2010 Decacal Survey recommendations

The National Academies of Sciences has released its Astro2010 decadal survey report and recommendations. A PDF of the release presentation is also available on that site. The panel's recommendations influence what programs NASA, NSF and DOE pursue and fund in astronomy and astrophysics for the next decade, so this is a big deal.

So far I've only read the presentation, and looked at Steinn Sigurdsson's comments on his blog [1, 2], so what follows is by no means a complete and final assessment.

My personal take is that its a mix of the good and the bad.

Whats good (from my perspective at least):

• A strong endorsement and emphasis on revitalizing the Explorer class mission program. This had suffered badly under O'Keefe and Griffin.
• A strong recognition of the importance of feedback, and flows of matter and energy into and out of galaxies (the 8th, 9th, and 10th points on slide 9 of the PDF copy of presensation).

Whats bad:

• IXO ranks 4th, behind some wide field IR telescope focussed on Dark Energy (yawn, a couple of billion bucks to get one not-very-interesting number) and LISA. IXO will only get $180m in the next decade, so basically that pushes it back to ~2030? And probably kills its chances in the ESA mission rankings too. Given that Constellation-X (IXO's forerunner prior to the merger with ESA) came 2nd (after JWST) in the previous decadal and IXO thought it had a good chance of coming 1st this time the current ranking is a real blow.
• LISA is somehow ranked as lower risk (and cheaper) than IXO! Seriously?
• Funding for astrophysics doesn't look like it going to get better.
• Unless you're an optical/IR astronomer, or the three gravitational wave astronomers, you're in for a bad decade and a half. X-ray astronomy, UV astronomy, and radio seem to be in trouble.
• From my perspective there is a disconnect between the science priorities for the next decade and the missions endorsed. Feedback and the galaxy/IGM interconnection isn't going to be answered by JWST, WFIRST, LISA or any Explorer mission

Interesting Astrophysics: May 03 to May 14

It looks like the Herschel folks have been busy, judged by the deluge of preprints that have appeared on arXiv over the last few weeks. I found Roussel et al's paper on dust in/around M82 and Fischer et al's paper on Markarian 231 (and its molecular outflow) of particular interest.

Nevertheless X-ray-related papers dominate this issue of Interesting Astrophysics, from hot gas in galaxy halos (Mulchaey & Jeltema; Henley et al; Crain et al) to the detection or modelling of the Warm/Hot Intergalactic Medium (Yao et al; Cen & Chisari).

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Galaxies and Starbursts

SPIRE imaging of M82: cool dust in the wind and tidal streams
H. Roussel, et al, arXiv:1005.1526 [pdf, ps, other]
Comments: accepted in A&A Herschel special issue

Their abstract in full: "M82 is a unique representative of a whole class of galaxies, starbursts with superwinds, in the Very Nearby Galaxy Survey with Herschel. In addition, its interaction with the M81 group has stripped a significant portion of its interstellar medium from its disk. SPIRE maps now afford better characterization of the far-infrared emission from cool dust outside the disk, and sketch a far more complete picture of its mass distribution and energetics than previously possible. They show emission coincident in projection with the starburst wind and in a large halo, much more extended than the PAH band emission seen with Spitzer. Some complex substructures coincide with the brightest PAH filaments, and others with tidal streams seen in atomic hydrogen. We subtract the far-infrared emission of the starburst and underlying disk from the maps, and derive spatially-resolved far-infrared colors for the wind and halo. We interpret the results in terms of dust mass, dust temperature, and global physical conditions. In particular, we examine variations in the dust physical properties as a function of distance from the center and the wind polar axis, and conclude that more than two thirds of the extraplanar dust has been removed by tidal interaction, and not entrained by the starburst wind."

The Stellar Kinematic Center and the True Galactic Nucleus of NGC253
F. Müller-Sánchez, O. González-Martín, J. A. Fernández-Ontiveros, J. A. Acosta-Pulido, M. A. Prieto, arXiv:1005.1645 [pdf, ps, other]

Comments: 33 pages, 7 figures, Accepted for publication in ApJ, Version with high resolution figures available at this http URL

Herschel PACS Spectroscopic Diagnostics of Local ULIRGs: Conditions and Kinematics in Mrk 231
Jacqueline Fischer, et al, arXiv:1005.2213 [pdf, other]
Comments: Accepted for publication in the Astronomy and Astrophysics Herschel Special Issue, 5 pages, 4 figures

Full abstract, emphasis mine: "In this first paper on the results of our Herschel PACS survey of local Ultraluminous Infrared Galaxies (ULIRGs), as part of our SHINING survey of local galaxies, we present far-infrared spectroscopy of Mrk 231, the most luminous of the local ULIRGs, and a type 1 broad absorption line AGN. For the first time in a ULIRG, all observed far-infrared fine-structure lines in the PACS range were detected and all were found to be deficient relative to the far infrared luminosity by 1 - 2 orders of magnitude compared with lower luminosity galaxies. The deficits are similar to those for the mid-infrared lines, with the most deficient lines showing high ionization potentials. Aged starbursts may account for part of the deficits, but partial covering of the highest excitation AGN powered regions may explain the remaining line deficits. A massive molecular outflow, discovered in OH and 18OH, showing outflow velocities out to at least 1400 km/sec, is a unique signature of the clearing out of the molecular disk that formed by dissipative collapse during the merger. The outflow is characterized by extremely high ratios of 18O / 16O suggestive of interstellar medium processing by advanced starbursts."

Hot Gas Halos in Early-Type Field Galaxies
John S. Mulchaey, Tesla E. Jeltema, arXiv:1004.5376 [pdf, ps, other]
Comments: Accepted for publication in ApJ Letters

Their abstract: "We use Chandra and XMM-Newton to study the hot gas content in a sample of field early-type galaxies. We find that the L_X-L_K relationship is steeper for field galaxies than for comparable galaxies in groups and clusters. The low hot gas content of field galaxies with L_K < L_star suggests that internal processes such as supernovae driven winds or AGN feedback expel hot gas from low mass galaxies. Such mechanisms may be less effective in groups and clusters where the presence of an intragroup or intracluster medium can confine outflowing material. In addition, galaxies in groups and clusters may be able to accrete gas from the ambient medium. While there is a population of L_K < L_star galaxies in groups and clusters that retain hot gas halos, some galaxies in these rich environments, including brighter galaxies, are largely devoid of hot gas. In these cases, the hot gas halos have likely been removed via ram pressure stripping. This suggests a very complex interplay between the intragroup/intracluster medium and hot gas halos of galaxies in rich environments with the ambient medium helping to confine or even enhance the halos in some cases and acting to remove gas in others. In contrast, the hot gas content of more isolated galaxies is largely a function of the mass of the galaxy, with more massive galaxies able to maintain their halos, while in lower mass systems the hot gas escapes in outflowing winds."

A fundamental relation between mass, SFR and metallicity in local and high redshift galaxies
F. Mannucci, G. Cresci, R. Maiolino, A. Marconi, A. Gnerucci, arXiv:1005.0006 [pdf, other]
Comments: 13 pages, submitted to MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Their abstract: "We show that the mass-metallicity relation observed in the local universe is due to a more general relation between stellar mass M*, gas-phase metallicity and SFR. Local galaxies define a tight surface in this 3D space, the Fundamental Metallicity Relation (FMR), with a small residual dispersion of ~0.05 dex in metallicity, i.e, ~12%. At low stellar mass, metallicity decreases sharply with increasing SFR, while at high stellar mass, metallicity does not depend on SFR. High redshift galaxies, up to z~2.5 are found to follow the same FMR defined by local SDSS galaxies, with no indication of evolution. The evolution of the mass-metallicity relation observed up to z=2.5 is due to the fact that galaxies with progressively higher SFRs, and therefore lower metallicities, are selected at increasing redshifts, sampling different parts of the same FMR. By introducing the new quantity mu_alpha=log(M*)-alpha log(SFR), with alpha=0.32, we define a projection of the FMR that minimizes the metallicity scatter of local galaxies. The same quantity also cancels out any redshift evolution up to z~2.5, i.e, all galaxies have the same range of values of mu_0.32. At z>2.5, evolution of about 0.6 dex off the FMR is observed, with high-redshift galaxies showing lower metallicities. The existence of the FMR can be explained by the interplay of infall of pristine gas and outflow of enriched material. The former effect is responsible for the dependence of metallicity with SFR and is the dominant effect at high-redshift, while the latter introduces the dependence on stellar mass and dominates at low redshift. The combination of these two effects, together with the Schmidt-Kennicutt law, explains the shape of the FMR and the role of mu_0.32. The small metallicity scatter around the FMR supports the smooth infall scenario of gas accretion in the local universe."

A fundamental plane for field star-forming galaxies
M.A. Lara-López, J. Cepa, A. Bongiovanni, A.M. Pérez García, A. Ederoclite, H. Castañeda, M. Fernández Lorenzo, M. Póvic, M. Sánchez-Portal, arXiv:1005.0509 [pdf, ps, other]
Comments: Submitted to A&amp;A as a letter to the Editor on April 15, 2010. 4 pages, 4 Figures

Their abstract: "Star formation rate (SFR), metallicity and stellar mass are within the important parameters of star--forming galaxies that characterize their formation and evolution. They are known to be related to each other at low and high redshift in the mass--metallicity, mass--SFR, and metallicity--SFR relations. In this work we demonstrate the existence of a plane in the 3D space defined by the axes SFR [log(SFR)(M_sun yr^-1)], gas metallicity [12+log(O/H)], and stellar mass [log(M_star/M_sun)] of star-forming galaxies. We used star--forming galaxies from the "main galaxy sample" of the Sloan Digital Sky Survey--Data Release 7 (SDSS-DR7) in the redshift range 0.04 < z < 0.1 and r-magnitudes between 14.5 and 17.77. Metallicities, SFRs, and stellar masses were taken from the Max-Planck-Institute for Astrophysics-John Hopkins University (MPA-JHU) emission line analysis database. From a final sample of 44214 galaxies, we find for the first time a fundamental plane for field galaxies relating the SFR, gas metallicity, and stellar mass for star--forming galaxies in the local universe. One of the applications of this plane would be estimating stellar masses from SFR and metallicity. High redshift data from the literature at redshift ~2.2 and 3.5, do not show evidence for evolution in this fundamental plane."

Our Milky Way as a Pure-Disk Galaxy -- A Challenge for Galaxy Formation
Juntai Shen, R. Michael Rich, John Kormendy, Christian D. Howard, Roberto De Propris, Andrea Kunder, arXiv:1005.0385 [pdf, ps, other]
Comments: 5 pages; emulateapj format; submitted to ApJL

Massive star formation in Wolf-Rayet galaxies. V: Star formation rates, masses and the importance of galaxy interactions
Angel R. Lopez-Sanchez
Comments: 33 pages, 21 figures, accepted for publication by A&A

From the abstract: "We have performed a comprehensive analysis of a sample of 20 starburst galaxies, most of them classified as Wolf-Rayet galaxies. In this paper, the last of the series, we analyze the global properties of our galaxy sample using multiwavelength data (X-ray, FUV, optical, NIR, FIR, and radio). The agreement between our Ha-based SFR and those provided by indicators at other wavelengths is remarkable, but we consider that the new Ha-based calibration provided by Calzetti et al. (2007) should be preferred over older calibrations. The FUV-based SFR provides a powerful tool to analyze the star-formation activity in both global and local scales independently to the Ha emission. We provide empirical relationships between the ionized gas mass, neutral gas mass, dust mass, stellar mass, and dynamical mass with the B-luminosity. ... Considering all data, we found that 17 up to 20 galaxies are clearly interacting or merging with low-luminosity dwarf objects or HI clouds. We conclude that interactions do play a fundamental role in the triggering mechanism of the strong star-formation activity observed in dwarf starburst galaxies."

The Dearth of Chemically Enriched Warm-Hot Circumgalactic Gas
Y. Yao, Q. D. Wang, S. V. Penton, T. M. Tripp, J. M. Shull, J. T. Stocke, arXiv:1005.0923 [pdf, ps, other]
Comments: 10 pages, 7 figures, and 5 tables. Accepted for publication in the ApJ, June 2010 - 20 v716 issue.

Argues against a local group origin for the z~0 X-ray absorbers, as have others. Also "These results indicate that the putative CGM [Circum Galactic Medium] in the temperature range of 10^{5.5}-10^{6.3} K may not be able to account for the missing baryons unless the metallicity is less than 10% solar." Of course its probably more accurate to say the mire astronomers believe the missing baryons to be in the warm-hot inter galactic medium, and not within galactic halos at all.

The Origin of the Hot Gas in the Galactic Halo: Confronting Models with XMM-Newton Observations
David B. Henley, Robin L. Shelton, Kyujin Kwak, M. Ryan Joung, Mordecai-Mark Mac Low, arXiv:1005.1085 [pdf, ps, other]
Comments: 18 pages, 13 figures. Submitted to the Astrophysical Journal
Subjects: Galaxy Astrophysics (astro-ph.GA)

Full abstract: "We compare the predictions of three physical models for the origin of the hot halo gas with the observed halo X-ray emission, derived from 26 high-latitude XMM-Newton observations of the soft X-ray background between $l=120\degr$ and $l=240\degr$. These observations were chosen from a much larger set of observations as they are expected to be the least contaminated by solar wind charge exchange emission. We characterize the halo emission in the XMM-Newton band with a single-temperature plasma model. We find that the observed halo temperature is fairly constant across the sky (~1.8e6-2.4e6 K), whereas the halo emission measure varies by an order of magnitude ($\sim$0.0005-0.006 cm^-6 pc), including significant sightline-to-sightline variation on scales as small as a few degrees. When we compare our observations with the model predictions, we find that most of the hot gas observed with XMM-Newton does not reside in an extended hot halo (predicted by disk galaxy formation models), nor is it contained within isolated extraplanar supernova remnants - both these models are at least an order of magnitude too faint in the XMM-Newton band. A model of a supernova-driven interstellar medium, one feature of which is a fountain of hot gas from the disk into the halo, gives the best agreement with the observed 0.4-2.0 keV surface brightness. This model overpredicts the halo X-ray temperature by a factor of ~2. However, there are a several plausible explanations for this discrepancy. Therefore, our general conclusion is that the hot halo gas observed with XMM-Newton originates in a fountain driven into the halo by disk supernovae."

Can galaxy outflows and re-accretion produce a downsizing in the specific star-formation rate of late-type galaxies?
C. Firmani, V. Avila-Reese and A. Rodríguez-Puebla, 2010, MNRAS, 404, 1100
Full Text: HTML, PDF (Size: 685K)

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Theoretical Cosmology

Star Formation Feedback and Metal Enrichment History Of The Intergalactic Medium
Renyue Cen, Nora Elisa Chisari, arXiv:1005.1451 [pdf, other]
Comments: 52 pages, 26 figures, submitted to ApJ, all comments welcome

From their abstract: "Using the state-of-the-art cosmological hydrodynamic simulations we compute the metal enrichment history of the intergalactic medium (IGM). Overall, we show that galactic superwind feedback from star formation is able to transport metals to the IGM that matches a broad range of observations. We find ... (6) While gravitational shocks from large-scale structure formation dominate the energy budget (80-90%) for turning about 50% of IGM to the warm-hot intergalactic medium (WHIM) by z=0, galactic superwind feedback shocks are energetically dominant over gravitational shocks at z>1-2. (7) Most of the so-called "missing metals" at z=2-3 are hidden in a warm-hot (T=10^{4.5-7}K) gaseous phase. (8) Approximately (37,46,10,7)% of the total metals at z=0 are in (stars, WHIM, X-ray gas, cold gas); the distribution stands at (23,57,2,18)% and (14,51,4,31)% at z=2 and z=4, respectively."

X-ray coronae in simulations of disc galaxy formation
Robert A. Crain, Ian G. McCarthy, Carlos S. Frenk, Tom Theuns, Joop Schaye, arXiv:1005.1642 [pdf, other]

Comments: 21 pages, 16 figures. Accepted for publication in MNRAS. Accompanying visualisations at this http URL

Their abstract: "The existence of X-ray luminous gaseous coronae around massive disc galaxies is a long-standing prediction of galaxy formation theory in the cold dark matter cosmogony. This prediction has garnered little observational support, with non-detections commonplace and detections for only a relatively small number of galaxies which are much less luminous than expected. We investigate the coronal properties of a large sample of bright, disc-dominated galaxies extracted from the GIMIC suite of cosmological hydrodynamic simulations recently presented by Crain et al. Remarkably, the simulations reproduce the observed scalings of X-ray luminosity with K-band luminosity and star formation rate and, when account is taken of the density structure of the halo, with disc rotation velocity as well. Most of the star formation in the simulated galaxies (which have realistic stellar mass fractions) is fuelled by gas cooling from a quasi-hydrostatic hot corona. However, these coronae are more diffuse, and of a lower luminosity, than predicted by the analytic models of White & Frenk because of a substantial increase in entropy at z ~ 1-3. Both the removal of low entropy gas by star formation and energy injection from supernovae contribute to this increase in entropy, but the latter is dominant for halo masses M_200 <~ 10^(12.5) Msun. Only a small fraction of the mass of the hot gas is outflowing as a wind but, because of its high density and metallicity, it contributes disproportionally to the X-ray emission. The bulk of the X-ray emission, however, comes from the diffuse quasi-hydrostatic corona which supplies the fuel for ongoing star formation in discs today. Future deep X-ray observations with high spectral resolution (e.g. with NeXT/ASTRO-H or IXO) should be able to map the velocity structure of the hot gas and test this fundamental prediction of current galaxy formation theory."

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Numerical Astrophysics

Multi-layered configurations in differentially-rotational equilibrium
Kenta Kiuchi, Hiroki Nagakura, Shoichi Yamada, arXiv:1005.2236 [pdf, ps, other]
Comments: To appear on APJ, high-resolution figures are available in the published version.

Full abstract: "We present a new formula to numerically construct configurations in rotational equilibrium, which consist of multiple layers. Each layer rotates uniformly or differentially according to cylindrical rotation-laws that are different from layer to layer. Assuming a different barotropic equation of state (EOS) for each layer, we solve the Bernoulli equation in each layer separately and combine the solutions by imposing continuity of the pressure at each boundary of the layers. It is confirmed that a single continuous barotropic EOS is incompatible with the junction condition. Identifying appropriate variables to be solved, we construct a convergent iteration scheme. For demonstration, we obtain two-layered configurations, each layer of which rotates rapidly with either an "$\Omega$-constant law" or a "$j$-constant law" or a "$v$-constant law". Other rotation laws and/or a larger number of layers can be treated similarly. We hope that this formula will be useful in studying the stellar evolution in multi-dimension with the non-spherical configuration induced by rotation being fully taken into account."

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Stars, Supernovae and Planets

On the evolution of a star cluster and its multiple stellar systems following gas dispersal
Nickolas Moeckel and Matthew R. Bate, 2010, MNRAS, 404, 712
Full Text: HTML, PDF (Size: 3726K)

Bursting SN 1996cr's Bubble: Hydrodynamic and X-ray Modeling of its Circumstellar Medium
Vikram V. Dwarkadas, Daniel Dewey, Franz Bauer, arXiv:1005.1090 [pdf, ps, other]
Comments: Accepted to MNRAS. 21 pages, 8 Figures, 6 in color. For a version with higher resolution colour figures see this http URL
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

From their abstract: "SN1996cr is one of the five closest SNe to explode in the past 30 years. Due to its fortuitous location in the Circinus Galaxy at ~ 3.7 Mpc, there is a wealth of recently acquired and serendipitous archival data available to piece together its evolution over the past decade, including a recent 485 ks Chandra HETG spectrum. In order to interpret this data, we have explored hydrodynamic simulations, followed by computations of simulated spectra and light curves under non-equilibrium ionization conditions, and directly compared them to the observations. Our simulated spectra manage to fit both the X-ray continuum and lines at 4 epochs satisfactorily, while our computed light curves are in good agreement with additional flux-monitoring data sets. These calculations allow us to infer the nature and structure of the circumstellar medium, the evolution of the SN shock wave, and the abundances of the ejecta and surrounding medium. The data imply that SN 1996cr exploded in a low-density medium before interacting with a dense shell of material about 0.03pc away from the progenitor star."

Radio and X-ray Observations of the Type Ic SN 2007gr Reveal an Ordinary, Non-relativistic Explosion
Alicia M. Soderberg, Andreas Brunthaler, Ehud Nakar, Roger A. Chevalier, arXiv:1005.1932 [pdf, ps, other]
Comments: 14 pages, 6 figures, submitted to ApJ

Again, evidence that the supernova blastwave is expanding into circum-stellar medium shaped by stellar winds.

Generation of radiative knots in a randomly pulsed protostellar jet II. X-ray emission
R. Bonito, S. Orlando, M. Miceli, J. Eislöffel, G. Peres, F. Favata, arXiv:1005.2125 [pdf, ps, other]
Comments: Accepted for publication in Astronomy and Astrophysics

Their abstract: "Protostellar jets are known to emit in a wide range of bands, from radio to IR to optical bands, and to date also about ten X-ray emitting jets have been detected, with a rate of discovery of about one per year. We aim at investigating the mechanism leading to the X-ray emission detected in protostellar jets and at constraining the physical parameters that describe the jet/ambient interaction by comparing our model predictions with observations. We perform 2D axisymmetric hydrodynamic simulations of the interaction between a supersonic jet and the ambient. The jet is described as a train of plasma blobs randomly ejected by the stellar source along the jet axis. We explore the parameter space by varying the ejection rate, the initial jet Mach number, and the initial density contrast between the ambient and the jet. We synthesized from the model the X-ray emission as it would be observed with the current X-ray telescopes. The mutual interactions among the ejected blobs and of the blobs with the ambient medium lead to complex X-ray emitting structures within the jet: irregular chains of knots; isolated knots with measurable proper motion; apparently stationary knots; reverse shocks. The predicted X-ray luminosity strongly depends on the ejection rate and on the initial density contrast between the ambient and the jet, with a weaker dependence on the jet Mach number. Our model represents the first attempt to describe the X-ray properties of all the X-ray emitting protostellar jets. The comparison between our model predictions and the observations can provide a useful diagnostic tool necessary for a proper interpretation of the observations. In particular, we suggest that the observable quantities derived from the spectral analysis of X-ray observations can be used to constrain the ejection rate, a parameter explored in our model that is not measurable by current observations."

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."

BBC discusses costs of ESA Cosmic Vision contenders

An article on the BBC by Jonathan Amos discusses the contenders for the two slots in ESA's Cosmic Visions program for 2017-2018 launches. Interestingly the article's focus is on the costs (see graph taken from article), but it also has a nice description of each mission (many of which I hadn't heard of).

The missions, and my shorter summary of their nature and aims, are:

• SPICA: Joint ESA/JAXA infrared space telescope (5 to 210 micron wavelength range) with a 3.5m primary mirror.
  
• Euclid: Map mass distributions using baryonic acoustic oscillations and weak lensing.
• PLATO: A planet hunter with a particular emphasis on finding Earth-like and super-earth terrestrial planets using milli-magnitude accuracy photometry.
• Solar Orbiter: Study the Sun and Solar wind from a relatively close-in orbit (as close as 48 Solar radii, it claims).
• Marco Polo: Joint ESA/JAXA sample return mission from a near-earth asteroid. Note the high cost!
• Cross-Scale: Study MHD plasma properties in the terrestrial magnetosphere and bow shock. 7 ESA spacecraft forming 2 nested tetrahedra with a shard corner. (International collaboration will produce the optimum fleet of 12 spacecraft in 3 nested tetrahedra.) High cost!
  

Interesting Astrophysics: 05 Oct to 09 Oct

A mixed bag of interesting preprints this week. Of note are local analogs of the Lyman Break Galaxies (Overzier et al), the radio-FIR correlation at high z (Lacki & Thompson), and a possible optical counterpart to an intermediate mass black hole candidate (Soria et al).

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Galaxies and Starbursts

Local Lyman Break Galaxy Analogs: The Impact of Massive Star-forming Clumps on the Interstellar Medium and the Global Structure of Young, Forming Galaxies
R.A. Overzier, T.M. Heckman, C. Tremonti, L. Armus, A. Basu-Zych, T. Goncalves, R.M. Rich, D.C. Martin, A. Ptak, D. Schiminovich, H.C. Ford, B. Madore, M. Seibert, arXiv:0910.1352 [ps, pdf, other]

Comments: The Astrophysical Journal, In Press (22 pages, 16 figures). For the full version with high-resolution colour figures, see: this http URL

Stationary models for the extra-planar gas in disc galaxies
F. Marinacci, F. Fraternali, L. Ciotti, C. Nipoti, arXiv:0910.0404 [ps, pdf, other]
Comments: 14 pages, 7 figures, accepted for pubblication in MNRAS

A cloudy halo model.

The Physics of the FIR-Radio Correlation: II. Synchrotron Emission as a Star-Formation Tracer in High-Redshift Galaxies
Brian C. Lacki, Todd A. Thompson, arXiv:0910.0478 [ps, pdf, other]
Comments: Submitted to ApJ

The fundamental gas depletion and stellar-mass buildup times of star forming galaxies
Jan Pflamm-Altenburg, Pavel Kroupa, arXiv:0910.1089 [ps, pdf, other]
Comments: accepted for publication in ApJ

The WMAP haze from the Galactic Center region due to massive star explosions and a reduced cosmic ray scale height
Peter L. Biermann, Julia K. Becker, Gabriel Caceres, Athina Meli, Eun-Suk Seo, Todor Stanev, arXiv:0910.1197 [ps, pdf, other]
Comments: 10 pages

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Black Holes and AGN

The Activity of the Neighbours of AGN and Starburst Galaxies: Towards an evolutionary sequence of AGN activity
E.Koulouridis, M.Plionis, V.Chavushyan, D.Dultzin, Y.Krongold, I.Georgantopoulos, C.Goudis, arXiv:0910.1355 [ps, pdf, other]
Comments: 50 pages, 5 figures, 41 spectra

Discovery of an optical counterpart to the hyperluminous X-ray source in ESO 243-49
Roberto Soria, George K. T. Hau, Alister W. Graham, Albert K. H. Kong, N. Paul M. Kuin, I-Hui Li, Ji-Feng Liu, Kinwah Wu, arXiv:0910.1356 [ps, pdf, other]
Comments: 5 pages, submitted to MNRAS Letters. Contact R Soria for higher-resolution figures

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Theoretical and Numerical Astrophysics, including Cosmology

Pressure Support vs. Thermal Broadening in the Lyman-alpha Forest II: Effects of the Equation of State on Transverse Structure
Molly S. Peeples, David H. Weinberg, Romeel Davé, Mark A. Fardal, Neal Katz, arXiv:0910.0250 [ps, pdf, other]
Comments: 11 figures, submitted to MNRAS

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Stars, Supernovae and Planets

Ionized Gas Towards Molecular Clumps: Physical Properties of Massive Star Forming Regions
Katharine G. Johnston, Debra S. Shepherd, James E. Aguirre, Miranda K. Dunham, Erik Rosolowsky, Kenneth Wood, arXiv:0910.0251 [ps, pdf, other]
Comments: 67 pages, 16 figures, 8 tables, accepted for publication in ApJ

From their abstract: "For clumps with associated ionized gas, the combined mass of the ionizing massive stars is compared to the clump masses to provide an estimate of the instantaneous star formation efficiency. These values range from a few percent to 25%, and have an average of 7 +/- 8%. We also find a correlation between the clump mass and the mass of the ionizing massive stars within it, which is consistent with a power law. This result is comparable to the prediction of star formation by competitive accretion that a power law relationship exists between the mass of the most massive star in a cluster and the total mass of the remaining stars."

New mega ring around Saturn discovered using Spitzer

Infrared observations using the Spitzer Space Telescope, published by Verbiscer et al (2009, Nature), have revealed the largest known ring around Saturn, an annulus of very tenuous material extending between 6 million and 18 million kilometers from Saturn, and tilted by 27 degree from the plane of the traditional rings (which only extend out to ~240,000 km).

The material in the new ring comes from the battered and cratered moon Phoebe. Of more interest, this new dust ring explains why the leading side of Iapetus is so much darker than the rest of it - the dark front surface of Iapetus is material from the ring swept up by Iapetus as it orbits at the inner edge of the new ring.

In truth a link between the dark front of Iapetus and Phoebe has been suspected before now, as the composition of the dark material is very similar to that of Phoebe based on near IR spectroscopy with Cassini. What the Spitzer observations reveal is the presence of the dust ring and hence the mechanism of material transfer from Phoebe to Iapetus.

Although the ring is physically huge, with a volume of ~5e21 km^3 (this is my BOTE calculation. As far as I can tell Verbiscer et al do not quote a volume), it is incredibly tenuous, and if all the material within it were collected back into one place it would possibly only occupy ~ 1 km^3 of rock, i.e. the volume of a crater on Phoebe.

The other interesting thing is that the material migrates inwards under the influence of radiation pressure. From Verbiscer et al:

On long timescales, collisions and inward transport become important. Collision with Phoebe, the dominant loss mechanism for particles larger than several centimetres in size, takes on the order of 10¹⁰ years. Re-radiation of absorbed sunlight exerts an asymmetric force on dust grains, causing them to spiral in towards Saturn with a characteristic timescale of 1.5 10⁵r_g years where r_g is the particle radius in micrometres. This force brings all centimetre-sized and smaller material to Iapetus and Titan unless mutual particle collisions occur first. The rate of mutual collisions depends on the size distribution of the ring particles and optical depth; if the ring were comprised entirely of 10 m grains, then the collisional timescale would be tens of millions of years, which is comparable to the inward drag timescale. Most material from 10 m to centimetres in size ultimately hits Iapetus, with smaller percentages striking Hyperion and Titan³.

References:

Verbiscer, A., Skrutskie, M., & Hamilton, D. (2009). Saturn's largest ring Nature DOI: 10.1038/nature08515

BBC article published by Jonathan Amos. 2009/10/08 (the source of the nice graphic shown above).

Spitzer press release, 2009/10/06.