The outer stellar populations and environments of unusually H i-rich galaxies

Abstract

We investigate the nature of HI-rich galaxies from the ALFALFA and GASS surveys, which are defined as galaxies in the top 10th percentile in atomic gas fraction at a given stellar mass. We analyze outer (R > 1.5R e ) stellar populations for a subset of face-on systems using optical g − r versus r − z colour/colour diagrams. The results are compared with those from control samples that are defined without regard to atomic gas content, but are matched in redshift, stellar mass and structural parameters. HIrich early-type (C > 2.6) and late-type (C < 2.6) galaxies are studied separately. When compared to the control sample, the outer stellar populations of the majority of HI-rich early-type galaxies are shifted in the colour/colour plane along a locus consistent with younger stellar ages, but similar metallicities. The outer colours of HI-rich late-type galaxies are much bluer in r − z than the HI-rich early types, and we infer that they have outer disks which are both younger and more metal-poor. We then proceed to analyze the galaxy environments of HI-rich galaxies on scales comparable to the expected virial radii of their dark matter halos (R < 500 kpc). Low mass (log M * < 10.5) HI-rich early-type galaxies have galaxy environments that differ significantly from the control sample. HI-rich early types are more likely to be central rather than satellite systems. Their satellites are also less massive and have younger stellar populations. Similar, but weaker effects are found for HI-rich late-type galaxies of the same mass. In addition, we find that the satellites of HI-rich late-types exhibit a greater tendency to align along the major axis of the primary. No environmental differences are found for massive (log M * > 10.5) HI-rich galaxies, regardless of type.We then undertook a follow-up program to map the HI in a small sample of 25 unusually HI-rich galaxies and 25 "control" galaxies with normal HI content using the Westerbork Synthesis Radio Telescope (WSRT; Wang et al 2013, c 0000 RAS

An H i view of galaxy conformity: H i-rich environment around H i-excess galaxies

“…The most prominent trend found in this paper is that the primary galaxies with lower stellar masses have higher H I mass in candidates around them, which may suggest a transition between coldand hot-mode accretion, as predicted by the simulations (Dekel & Birnboim 2006). Recently, Kauffmann (2015) found a tendency for the satellites to align along the major axis of late-type H I-rich central galaxies with M * < 10 10.5 M ; they found no such phenomenon for more massive central galaxies. Their result also suggests such a transition.…”

Resolution-independent modelling of environmental effects in semi-analytic models of galaxy formation that include ram-pressure stripping of both hot and cold gas

“…It would also lower the specific star formation rates of a significant fraction of galaxies being accreted as satellites, perhaps causing them to exhaust their existing gas reservoirs more slowly. Another issue that was pointed out in a paper by Kauffmann (2015) is that there is a correlation between low mass galaxies that are quenched and the quenched fraction of their neighbours that extends over very large scales and that is not currently reproduced by semi-analytic models or by the Illustris simulation.…”

Neutral atomic hydrogen observation of low redshift galaxies

“…这些观测结 果暗示着在研究 HI 气体吸积时, 我们需要将早晚型 星系分开. 毕竟相比晚型星系只有极少数早型星系 存在大量 HI 气体 [13] , 此外 HI 丰富的早、晚型星系 表现出很不相同的外盘金属丰度以及星系与外部环 境的联系 [69] , 这也暗示着它们不同的吸积模式. 然 而对于不同类型 (如快旋转体和慢旋转体) 的早型星 系, HI 气体分布的形态似乎并无区别 [70] .…”

“…一个突破口是星系的 "一致性" 现象: 卫星星系 的颜色和中心星系的颜色有相关性 [27,42,86] . Kauffmann 等人 [27,69] 的一系列工作发现这种现象对恒星 形成活跃的中心星系更明显, 并且延伸到星系的维里 半径以外, 于是指出这暗示着中心星系和卫星星系由 一个共同的大尺度气体库支持着恒星形成活动. 她进 一步指出, 这个可能的气体库可以是冷吸积.…”