Monday Jan. 14, 2012

Molecular Gas and Star Formation in Nearby Disk Galaxies

Authors: Adam K. Leroy, Fabian Walter, Karin Sandstrom, Andreas Schruba, Juan-Carlos Munoz-Mateos, Frank Bigiel, Alberto Bolatto, Elias Brinks, W.J.G. de Blok, Sharon Meidt, Hans-Walter Rix, Erik Rosolowsky, Eva Schinnerer, Karl-Friedrich Schuster, Antonio Usero
(Submitted on 10 Jan 2013)

Abstract: We compare molecular gas traced by 12CO(2-1) maps from the HERACLES survey, with tracers of the recent star formation rate (SFR) across 30 nearby disk galaxies. We demonstrate a first-order linear correspondence between Sig_mol and Sig_SFR but also find important second-order systematic variations in the apparent molecular gas depletion time, t_dep^mol = Sig_mol / Sig_SFR. At our 1 kpc common resolution, CO correlates closely with many tracers of the recent SFR. Weighting each line of sight equally and using a fixed, Milky Way alpha_CO, our data yield a molecular gas depletion time, t_dep^mol=Sig_mol/Sig_SFR ~ 2.2 Gyr with 0.3 dex scatter, in good agreement with literature data. We apply a forward-modeling approach to constrain the power-law index, N, that relates the SFR surface density and the molecular gas surface density and find N=1+/-0.15 for our full data set with some variation from galaxy to galaxy. However, we caution that a power law treatment oversimplifies the topic given that we observe correlations between t_dep^mol and other local and global quantities. The strongest of these are a decreased t_dep^mol in low-mass, low-metallicity galaxies and a correlation of the kpc-scale t_dep^mol with dust-to-gas ratio, D/G. These correlations can be explained by a CO-to-H2 conversion factor that depends on D/G in the theoretically expected way. This is not a unique interpretation, but external evidence of conversion factor variations makes it a conservative one. After applying a D/G-dependent alpha_CO, some weak correlations between t_dep^mol and local conditions persist. In particular, we observe lower t_dep^mol and enhanced CO excitation associated with some nuclear gas concentrations. These appear to reflect real enhancements in the SFR/H2 and t_dep appears multivalued at fixed Sig_mol, supporting the the idea of "disk" and "starburst" modes driven by environmental factors.

Comments: 39 pages (incl. 10 page appendix), 19 figures, figures degraded for astro-ph. Until publication a higher resolution version available at this http URL – we suggest that one
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1301.2328 [astro-ph.CO]
(or arXiv:1301.2328v1 [astro-ph.CO] for this version)

The Atlas3D project – XIX. The hot-gas content of early-type galaxies: fast versus slow rotators

Authors: Marc Sarzi, Katherine Alatalo, Leo Blitz, Maxime Bois, Frederic Bournaud, M. Bureau, Michele Cappellari, Alison F. Crocker, Roger L. Davies, Timothy A. Davis, P. T. de Zeeuw, Pierre-Alain Duc, Sadegh Khochfar, Davor Krajnovic, Harald Kuntschner, Richard M. McDermid, Raffaella Morganti, Thorsten Naab, Tom Oosterloo, Nicholas Scott, Paolo Serra, Anne-Marie Weijmans, Lisa M. Young

Abstract: For early-type galaxies, the ability to sustain a corona of hot, X-ray emitting gas could have played a key role in quenching their star-formation history. Yet, it is still unclear what drives the precise amount of hot gas around these galaxies. By combining photometric and spectroscopic measurements for the early-type galaxies observed during the Atlas3D integral-field survey with measurements of their X-ray luminosity based on X-ray data of both low and high spatial resolution we conclude that the hot-gas content of early-type galaxies can depend on their dynamical structure. Specifically, whereas slow rotators generally have X-ray halos with luminosity L_X,gas and temperature T values that are in line with what is expected if the hot-gas emission is sustained by the thermalisaton of the kinetic energy carried by the stellar-mass loss material, fast rotators tend to display L_X,gas values that fall consistently below the prediction of this model, with similar T values that do not scale with the stellar kinetic energy as observed in the case of slow rotators. Considering that fast rotators are likely to be intrinsically flatter than slow rotators, and that the few L_X,gas-deficient slow rotators also happen to be relatively flat, the observed L_X,gas deficiency in these objects would support the hypothesis whereby flatter galaxies have a harder time in retaining their hot gas. We discuss the implications that a different hot-gas content could have on the fate of both acquired and internally-produced gaseous material, considering in particular how the L_X,gas deficiency of fast rotators would make them more capable to recycle the stellar-mass loss material into new stars than slow rotators. This is consistent with the finding that molecular gas and young stars are detected only in fast rotators in the Atlas3D sample, and that fast rotators tend to dustier than slow rotators. [Abridged]

Comments: 16 pages, 10 figures, accepted for publications on MNRAS. More information about our Atlas3D project see this http URL
Subjects: Galaxy Astrophysics (astro-ph.GA); Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1301.2589 [astro-ph.GA]
(or arXiv:1301.2589v1 [astro-ph.GA] for this version)
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