%0 Generic %1 howk2017project %A Howk, J. Christopher %A Wotta, Christopher B. %A Berg, Michelle A. %A Lehner, Nicolas %A Lockman, Felix J. %A Hafen, Zachary %A Pisano, D. J. %A Faucher-Giguere, Claude-Andre %A Wakker, Bart P. %A Prochaska, J. Xavier %A Wolfe, Spencer A. %A Ribaudo, Joseph %A Barger, Kathleen A. %A Corlies, Lauren %A Fox, Andrew J. %A Jenkins, Edward B. %A Kalirai, Jason %A O'Meara, John M. %A Peeples, Molly S. %A Stewart, Kyle R. %A Strader, Jay %D 2017 %K Andromeda HI covering factor %T Project AMIGA: A Minimal Covering Factor for Optically Thick Circumgalactic Gas Around Andromeda %U http://arxiv.org/abs/1706.01893 %X We present a deep search for HI 21-cm emission from the gaseous halo of Messier 31 as part of Project AMIGA, a large program Hubble Space Telescope program to study the circumgalactic medium of Andromeda. Our observations with the Robert C. Byrd Green Bank Telesope target directions to 48 background AGNs within impact parameters $25 330$ kpc ($0.1 łesssim / R_vir 1.1$). We do not detect any 21-cm emission toward these AGNs, more than half of which have been observed in the ultraviolet with the Cosmic Origins Spectrograph, to limits of $N(HI) 4 \times10^17$ cm$^-2$ ($5\sigma$; per 2 kpc diameter beam). This column density corresponds to an optical depth of $\sim2.5$ at the Lyman limit; thus our observations overlap with absorption line studies of Lyman limit systems at higher redshift. We limit the covering factor of such optically-thick gas around Andromeda to $f_c < 0.051$ (at 90% confidence) for $R_\rm vir$. While individual clouds have previously been found in the region between M31 and M33, the covering factor of strongly optically-thick gas is quite small. Our limits to the covering factor are consistent with expectations from recent cosmological "zoom" simulations. Recent COS-Halos results for an ensemble of galaxies show significantly higher covering factors within $\rho 0.5 R_vir$ at the same $N(H I)$.

@misc{howk2017project, abstract = {We present a deep search for HI 21-cm emission from the gaseous halo of Messier 31 as part of Project AMIGA, a large program Hubble Space Telescope program to study the circumgalactic medium of Andromeda. Our observations with the Robert C. Byrd Green Bank Telesope target directions to 48 background AGNs within impact parameters $25 \lesssim \rho \lesssim 330$ kpc ($0.1 \lesssim \rho / R_{\rm vir} \lesssim 1.1$). We do not detect any 21-cm emission toward these AGNs, more than half of which have been observed in the ultraviolet with the Cosmic Origins Spectrograph, to limits of $N({\rm HI}) \approx 4 \times10^{17}$ cm$^{-2}$ ($5\sigma$; per 2 kpc diameter beam). This column density corresponds to an optical depth of $\sim2.5$ at the Lyman limit; thus our observations overlap with absorption line studies of Lyman limit systems at higher redshift. We limit the covering factor of such optically-thick gas around Andromeda to $f_c < 0.051$ (at 90% confidence) for $\rho \leq R_{\rm vir}$. While individual clouds have previously been found in the region between M31 and M33, the covering factor of strongly optically-thick gas is quite small. Our limits to the covering factor are consistent with expectations from recent cosmological "zoom" simulations. Recent COS-Halos results for an ensemble of galaxies show significantly higher covering factors within $\rho \lesssim 0.5 R_{\rm vir}$ at the same $N({\rm H I})$.}, added-at = {2017-06-08T09:55:34.000+0200}, author = {Howk, J. Christopher and Wotta, Christopher B. and Berg, Michelle A. and Lehner, Nicolas and Lockman, Felix J. and Hafen, Zachary and Pisano, D. J. and Faucher-Giguere, Claude-Andre and Wakker, Bart P. and Prochaska, J. Xavier and Wolfe, Spencer A. and Ribaudo, Joseph and Barger, Kathleen A. and Corlies, Lauren and Fox, Andrew J. and Jenkins, Edward B. and Kalirai, Jason and O'Meara, John M. and Peeples, Molly S. and Stewart, Kyle R. and Strader, Jay}, biburl = {https://www.bibsonomy.org/bibtex/2b05a415029759cadea18dee6289bf0d6/miki}, description = {[1706.01893] Project AMIGA: A Minimal Covering Factor for Optically Thick Circumgalactic Gas Around Andromeda}, interhash = {fa6f8237b08a306ce59e6598e358a903}, intrahash = {b05a415029759cadea18dee6289bf0d6}, keywords = {Andromeda HI covering factor}, note = {cite arxiv:1706.01893Comment: Submitted to AAS Journals; feedback welcome}, timestamp = {2017-06-08T09:55:34.000+0200}, title = {Project AMIGA: A Minimal Covering Factor for Optically Thick Circumgalactic Gas Around Andromeda}, url = {http://arxiv.org/abs/1706.01893}, year = 2017 }