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&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."

Prompt Global Strike

The NYT has an interesting article about a new weapon system.

WASHINGTON — In coming years, President Obama will decide whether to deploy a new class of weapons capable of reaching any corner of the earth from the United States in under an hour and with such accuracy and force that they would greatly diminish America’s reliance on its nuclear arsenal.

Yet even now, concerns about the technology are so strong that the Obama administration has acceded to a demand by Russia that the United States decommission one nuclear missile for every one of these conventional weapons fielded by the Pentagon. That provision, the White House said, is buried deep inside the New Start treaty that Mr. Obama and President Dmitri A. Medvedev signed in Prague two weeks ago.

Initially I thought this was a pure kinetic energy weapon, but on closer reading its a very large "conventional warhead." The hypersonic glider is very cool though.

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&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

The NSF censors itself with an astrophysicist's help

Wow, this story (reported in ScienceInsider by Yudhijit Bhattacharjee, "Evolution, Big Bang Polls Omitted From NSF Report") is a scandal.

In an unusual last-minute edit that has drawn flak from the White House and science educators, a federal advisory committee omitted data on Americans' knowledge of evolution and the big bang from a key report. The data shows that Americans are far less likely than the rest of the world to accept that humans evolved from earlier species and that the universe began with a big bang.

They're not surprising findings, but the National Science Board, which oversees the National Science Foundation (NSF), says it chose to leave the section out of the 2010 edition of the biennial Science and Engineering Indicators because the survey questions used to measure knowledge of the two topics force respondents to choose between factual knowledge and religious beliefs.

So the claim is that it is unfair to say people who reject evolution or the Big Bang are scientifically illiterate, as if to do so would somehow infringe their religious liberty. What utter nonsense. I'd almost be happier to believe the data was omitted because the terrible response rates are an embarrassment for this country.

The deleted text, obtained by ScienceInsider, does not differ radically from what has appeared in previous Indicators. The section, which was part of the unedited chapter on public attitudes toward science and technology, notes that 45% of Americans in 2008 answered true to the statement, "Human beings, as we know them today, developed from earlier species of animals." The figure is similar to previous years and much lower than in Japan (78%), Europe (70%), China (69%), and South Korea (64%). The same gap exists for the response to a second statement, "The universe began with a big explosion," with which only 33% of Americans agreed.

The sad thing is that one of the religious accommodationists responsible for arguing that knowledge of evolution and the big bang are "flawed indicators of scientific knowledge because responses conflated knowledge and beliefs," is an astrophysicist: Louis Lanzerotti, at the New Jersey Institute of Technology.

Lanzerotti isn't the only one to blame, as it seems a philosopher called John Bruer was the primary instigator of this pro-fundamentalist pandering.

When Science asked Bruer if individuals who did not accept evolution or the big bang to be true could be described as scientifically literate, he said: "There are many biologists and philosophers of science who are highly scientifically literate who question certain aspects of the theory of evolution," adding that such questioning has led to improved understanding of evolutionary theory. When asked if he expected those academics to answer "false" to the statement about humans having evolved from earlier species, Bruer said: "On that particular point, no."

If your arguments are trivially demolished within seconds of casual questioning by the Science reporter what business do you have being on the National Science Board?

[Bruer] calls the survey questions "very blunt instruments not designed to capture public understanding" of the two topics.

"I think that is a nonsensical response" that reflects "the religious right's point of view," says Jon Miller, a science literacy researcher at Michigan State University in East Lansing who authored the survey 3 decades ago and conducted it for NSF until 2001. "Evolution and the big bang are not a matter of opinion. If a person says that the earth really is at the center of the universe, even if scientists think it is not, how in the world would you call that person scientifically literate? Part of being literate is to both understand and accept scientific constructs."

Miller has it right. Lanzerotti and Bruer should be ashamed of themselves.

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."