## Friday, January 29, 2010

### Interesting Astrophysics: Jan 18 to Jan 29

Of particular note among the crop of preprint and papers released within the last two week are observational and theoretical papers on galactic winds (Sharp & Hawthorn; Choi & Nagamine), and the physics of dust-driven flows (Miniati; Ivezic & Elitzur). Other papers cover feedback ad galaxy scaling relations (Dutton & van den Bosch; Spitoni et al), universality versus variations in the IMF (Bastian et al) and a slew of planet related papers.

Galaxies and Starbursts

The Impact of Feedback on Disk Galaxy Scaling Relations
Aaron A. Dutton, Frank C. van den Bosch,
Comments: 7 pages, 2 figures. To appear in proceedings of "Galaxy Evolution: Emerging Insights and Future Challenges", November 11-14, 2008, The University of Texas at Austin
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Their abstract: "We use a disk formation model to study the effects of galactic outflows (a.k.a. feedback) on the rotation velocity - stellar mass - disk size, gas fraction - stellar mass, and gas phase metalicity - stellar mass scaling relations of disk galaxies. We show that models without outflows are unable to explain these scaling relations, having both the wrong slopes and normalization. The problem can be traced to the model galaxies having too many baryons. Models with outflows can solve this "over-cooling" problem by removing gas before it has time to turn into stars. Models with both momentum and energy driven winds can reproduce the observed scaling relations. However, these models predict different slopes which, with better observations, may be used to discriminate between these models."

Pet peeve. Galactic winds are not either exclusively momentum-driven or energy-driven. The standard model of starburst-driven winds is a multi-phase wind model, and some phases are best described as energy driven and some phases better as momentum driven.

Gas circulation and galaxy evolution
Filippo Fraternali,
Comments: 12 pages, 5 figures. Invited review at the conference "Hunting for the Dark: The Hidden Side of Galaxy Formation", Malta, 19-23 Oct. 2009. Eds. V.P. Debattista and C.C. Popescu, AIP Conf. Ser

3D Integral Field Observations of Ten Galactic Winds - I. Extended phase (>10 Myr) of mass/energy injection before the wind blows

R.G. Sharp, J. Bland-Hawthorn,
Comments: 43 pages, 30 figures, Accepted for publication in ApJ Jan-2010, Full resolution figures available from: this http URL

Haven't read, but abstract sounds provocative.

The issue of whether the apparent differences between outflows from different starburst galaxies is evolutionary (i.e. they change with time, and different galaxies are observed at different times) or environmental (winds in dwarf starbursts may have different intrinsic structure or visibility in comparison to a wind from a massive spiral or Ultraluminous IR galaxy, and that winds may not change much in *observable* properties as they age) is an old question, and I doubt it will go away soon.

The Origin of the Mass-Metallicity relation: an analytical approach
E. Spitoni, F. Calura, F. Matteucci, S. Recchi,

From their abstract: "The existence of a mass-metallicity (MZ) relation in star forming galaxies at all redshift has been recently established. We aim at studying some possible physical mechanisms contributing to the MZ relation by adopting analytical solutions of chemical evolution models including infall and outflow. ... It is difficult to disentangle among the outflow and IMF solutions only by considering the MZ relation, and other observational constraints should be taken into account to select a specific solution. For example, a variable efficiency of star formation increasing with galactic mass can also reproduce the MZ relation and explain the downsizing in star formation suggested for ellipticals. The best solution could be a variable efficiency of star formation coupled with galactic winds, which are indeed observed in low mass galaxies."

Black Holes and AGN

AGN population in Hickson's Compact Groups. I. Data and Nuclear Activity Classification

M.A. Martinez, A. del Olmo, R. Coziol, J. Perea,
Comments: 44 pages, 8 figures and 5 tables. Accepted for publication in AJ

Spectral Energy Distributions of Weak Active Galactic Nuclei Associated With Low-Ionization Nuclear Emission Regions
Michael Eracleous, Jason A. Hwang, Helene M. L. G. Flohic,
emulateapj format, 12 pages in total, to appear in ApJS, one large table and one large figure abridged (will be available in electronic journal)

Cosmology and the IGM

Confirmation of X-Ray Absorption by WHIM in the Sculptor Wall
Taotao Fang, David A. Buote, Philip J. Humphrey, Claude R. Canizares, Luca Zappacosta, Roberto Maiolino, Gianpiero Tagliaferri, Fabio Gastaldello,
Comments: 11 pages, 5 figures. Submitted to ApJ

Hydrodynamics and Numerical Astrophysics

High-Order Finite Difference GLM-MHD Schemes for Cell-Centered MHD
A. Mignone, P. Tzeferacos, G. Bodo,
Comments: 32 pages, 14 figure, submitted to Journal of Computational Physics (Aug 7 2009)

Multiphase and Variable Velocity Galactic Outflow in Cosmological SPH Simulations
Jun-Hwan Choi, Kentaro Nagamine,
Comments: 13 pages, 10 figures, and 1 table submitted to MNRAS. A full resolution version is available at this http URL

Their abstact: "We develop a new multiphase and variable velocity (MVV) galactic outflow model for cosmological smoothed particle hydrodynamic (SPH) simulations. The MVV wind model captures the multiphase nature of the outflow, and the mass-loading factor in the MVV model is a function of galaxy stellar mass. We find that the simulation with the MVV outflow has the following characteristics: (i) the intergalactic medium (IGM) is hardly heated up, and the mean IGM temperature is almost the same as in the no-wind run; (ii) it has lower cosmic star formation rates (SFRs) compared to the no-wind run, but higher SFRs than the constant velocity wind run; (iii) it roughly agrees with the observed IGM metallicity, and roughly follows the observed evolution of Omega(Civ); (iv) the lower mass galaxies have larger mass-loading factors, and the low-mass end of galaxy stellar mass function is flatter than in the previous simulations. Therefore the MVV outflow model mildly alleviates the problem of too steep galaxy stellar mass function seen in the previous SPH simulations. In summary, the new MVV outflow model shows reasonable agreement with observations, and gives better results than the constant velocity wind model."

Will need to read this to see what exactly they've implemented and how it differs from the Oppenheimer/Davé mass-loaded wind model.

A Hybrid Scheme for Gas-Dust Systems Stiffly Coupled via Viscous Drag
Francesco Miniati,
Comments: 41 pages, 3 figures, 14 tables, accepted to J. Comp. Phys.

Supernova-driven Turbulence and Magnetic Field Amplification in Disk Galaxies
Oliver Gressel, Comments: 99 pages, 46 figures (in part
strongly degraded), 8 tables, PhD thesis, University of Potsdam (2009).
Resolve URN "urn:nbn:de:kobv:517-opus-29094" (e.g. via this http URL) for a version with high-resolution figures

High Energy Astrophysics

The International X-ray Observatory
Nicholas E. White, Arvind Parmar, Hideyo Kunieda, Kirpal Nandra, Takaya Ohashi, Jay Bookbinder,
Comments: 6 pages, 3 figures, for conference "X-ray Astronomy 2009 Present status, multi-wavelength approach and future perspectives"

I'm still very pleased with the IXO versus Chandra figure I made for the IXO folks last year (LHS panel in Fig 2).

Stars, Supernovae, and Planets

The Interior Dynamics of Water Planets
Roger Fu, Richard J. OConnell, Dimitar D. Sasselov,
Journal-ref: ApJ 708:1326 1334, 2010 January 10

The Diversity of Extrasolar Terrestrial Planets
J. C. Bond, D. S. Lauretta, D. P. O'Brien,
Comments: 4 pages, 1 figure. Submitted to the proceedings of IAU symposium 265 Chemical Abundances in the Universe: Connecting First Stars to Planets

From their abstract: "A wide variety of resulting planetary compositions exist, ranging from those that are essentially "Earth-like", containing metallic Fe and Mg-silicates, to those that are dominated by graphite and SiC. This implies that a diverse range of terrestrial planets are likely to exist within extrasolar planetary systems."

Rocky Planetesimals as the Origin of Metals in DZ Stars
J. Farihi, M.A. Barstow, S. Redfield, P. Dufour, N.C. Hambly,

A Universal Stellar Initial Mass Function? A Critical Look at Variations
Nate Bastian, Kevin R. Covey, Michael R. Meyer,
Comments: 49 pages, 5 figures, to appear in Annual Reviews of Astronomy and Astrophysics (2010, volume 48)

Full abstract: "Few topics in astronomy initiate such vigorous discussion as whether or not the initial mass function (IMF) of stars is universal, or instead sensitive to the initial conditions of star formation. The distinction is of critical importance: the IMF influences most of the observable properties of stellar populations and galaxies, and detecting variations in the IMF could provide deep insights into the process by which stars form. In this review, we take a critical look at the case for IMF variations, with a view towards whether other explanations are sufficient given the evidence. Studies of the field, local young clusters and associations, and old globular clusters suggest that the vast majority were drawn from a "universal" IMF: a power-law of Salpeter index ($\Gamma=1.35$) above a few solar masses, and a log normal or shallower power-law ($\Gamma \sim 0-0.25$) between a few tenths and a few solar masses (ignoring the effects of unresolved binaries). The shape and universality of the IMF at the stellar-substellar boundary is still under investigation and uncertainties remain large, but most observations are consistent with a IMF that declines ($\Gamma < -0.5$) well below the hydrogen burning limit. Observations of resolved stellar populations and the integrated properties of most galaxies are also consistent with a "universal IMF", suggesting no gross variations in the IMF over much of cosmic time. There are indications of "non-standard" IMFs in specific local and extragalactic environments, which clearly warrant further study. Nonetheless, there is no clear evidence that the IMF varies strongly and systematically as a function of initial conditions after the first few generations of stars."

Dusty winds II. Observational Implications
Zeljko Ivezic, Moshe Elitzur,