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Galaxy Zoo and ALFALFA: Atomic Gas and the Regulation of Star Formation in Barred Disc Galaxies

ArXiv 1205.5271 (2012)

Authors:

Karen L Masters, Robert C Nichol, Martha P Haynes, William C Keel, Chris Lintott, Brooke Simmons, Ramin Skibba, Steven Bamford, Riccardo Giovanelli, Kevin Schawinski

Abstract:

We study the observed correlation between atomic gas content and the likelihood of hosting a large scale bar in a sample of 2090 disc galaxies. Such a test has never been done before on this scale. We use data on morphologies from the Galaxy Zoo project and information on the galaxies' HI content from the ALFALFA blind HI survey. Our main result is that the bar fraction is significantly lower among gas rich disc galaxies than gas poor ones. This is not explained by known trends for more massive (stellar) and redder disc galaxies to host more bars and have lower gas fractions: we still see at fixed stellar mass a residual correlation between gas content and bar fraction. We discuss three possible causal explanations: (1) bars in disc galaxies cause atomic gas to be used up more quickly, (2) increasing the atomic gas content in a disc galaxy inhibits bar formation, and (3) bar fraction and gas content are both driven by correlation with environmental effects (e.g. tidal triggering of bars, combined with strangulation removing gas). All three explanations are consistent with the observed correlations. In addition our observations suggest bars may reduce or halt star formation in the outer parts of discs by holding back the infall of external gas beyond bar co-rotation, reddening the global colours of barred disc galaxies. This suggests that secular evolution driven by the exchange of angular momentum between stars in the bar, and gas in the disc, acts as a feedback mechanism to regulate star formation in intermediate mass disc galaxies.
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Constraining stellar assembly and AGN feedback at the peak epoch of star formation

ArXiv 1205.3801 (2012)

Authors:

Taysun Kimm, Sugata Kaviraj, Julien Devriendt, Seth Cohen, Rogier Windhorst, Yohan Dubois, Adrianne Slyz, Nimish Hathi, Russell Ryan Jr, Robert O'Connell, Michael Dopita, Joseph Silk

Abstract:

We study stellar assembly and feedback from active galactic nuclei (AGN) around the epoch of peak star formation (1
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Constraining stellar assembly and AGN feedback at the peak epoch of star formation

(2012)

Authors:

Taysun Kimm, Sugata Kaviraj, Julien Devriendt, Seth Cohen, Rogier Windhorst, Yohan Dubois, Adrianne Slyz, Nimish Hathi, Russell Ryan, Robert O'Connell, Michael Dopita, Joseph Silk
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Probing quasar shutdown timescales with Hanny's Voorwerp

AIP Conference Proceedings 1427 (2012) 193-200

Authors:

DA Evans, K Schawinski, S Virani, CM Urry, WC Keel, P Natarajan, CJ Lintott, A Manning, P Coppi, S Kaviraj, SP Bamford, GIG Józsa, M Garrett, H Van Arkel, P Gay, L Fortson

Abstract:

Galaxy formation is significantly modulated by energy output from supermassive black holes at the centers of galaxies which grow in highly efficient luminous quasar phases. The timescale on which black holes transition into and out of such phases is, however, unknown. We present the first measurement of the shutdown timescale for an individual quasar using Suzaku and XMM-Newton X-ray observations of the nearby galaxy IC 2497, which hosted a luminous quasar no more than ∼230,000 years ago that is still seen as a light echo in 'Hanny's Voorwerp', but whose presentday radiative output is lower by at least 2 and more likely by over 4 orders of magnitude. This extremely rapid shutdown provides new insights into the physics of accretion in supermassive black holes, and may signal a transition of the accretion disk to a radiatively inefficient state. These results were first presented by [1]. © 2012 American Institute of Physics.
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X-ray signatures of circumnuclear gas in AGN

AIP Conference Proceedings 1427 (2012) 165-172

Authors:

TJ Turner, L Miller, M Tatum

Abstract:

X-ray spectra of AGN are complex. X-ray absorption and emission features trace gas covering a wide range of column densities and ionization states. High resolution spectra show the absorbing gas to be outflowing, perhaps in the form of an accretion disk wind. The absorbing complex shapes the form of the X-ray spectrum while X-ray reverberation and absorption changes explain the spectral and timing behaviour of AGN. We discuss recent progress, highlighting some new results and reviewing the implications that can be drawn from the data. © 2012 American Institute of Physics.
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