Molecular and atomic gas in dust lane early-type galaxies - I. Low star formation efficiencies in minor merger remnants
Molecular and atomic gas in dust lane early-type galaxies - I. Low star formation efficiencies in minor merger remnants
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DOI：
10.1093/mnras/stv597
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发表时间：
2015-03
影响因子：
4.8
通讯作者：
T. Davis;K. Rowlands;J. Allison;S. Shabala;Y. Ting;C. Lagos;S. Kaviraj;N. Bourne;L. Dunne
中科院分区：
文献类型：
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作者：
T. Davis;K. Rowlands;J. Allison;S. Shabala;Y. Ting;C. Lagos;S. Kaviraj;N. Bourne;L. Dunne
在这项工作中，我们提出了IRAM 30米望远镜观测的一个样本的膨胀为主的星系与大尘埃带，最近有一个小合并。我们发现这些星系非常富含气体，H2质量在4 × 108到2 × 1010 M <$。我们使用这些分子气体质量，结合随附论文中的原子气体质量，来计算气体与尘埃和气体与恒星质量的比值。我们的样本天体的气尘比变化很大（在1050和750之间），这表明许多天体具有低气相金属丰度，因此气体是通过最近与较低质量的伴星合并而吸积的。我们计算了隐含的次要伴星质量和气体分数，发现预测的恒星质量比中位数为1.40：1。小伴星的质量可能在107 - 1010 M <$m之间。隐含的合并质量比是一致的低红移气体丰富的合并模拟的预期。然后，我们继续提出证据表明（无论使用哪种星星形成率指标），我们的样本对象具有非常低的星星形成效率（每单位气体质量的星星形成率），甚至低于ATLAS 3D中已经显示出抑制的早期类型星系。这表明小的合并实际上可以抑制星星的形成活动。我们讨论了可能导致这种抑制的机制，包括未成年人合并引起的动力学效应。
In this work we present IRAM 30-m telescope observations of a sample of bulge-dominated galaxies with large dust lanes, which have had a recent minor merger. We find these galaxies are very gas rich, with H2 masses between 4 × 108 and 2 × 1010 M⊙. We use these molecular gas masses, combined with atomic gas masses from an accompanying paper, to calculate gas-to-dust and gas-to-stellar-mass ratios. The gas-to-dust ratios of our sample objects vary widely (between ≈50 and 750), suggesting many objects have low gas-phase metallicities, and thus that the gas has been accreted through a recent merger with a lower mass companion. We calculate the implied minor companion masses and gas fractions, finding a median predicted stellar mass ratio of ≈40:1. The minor companion likely had masses between ≈107 and 1010 M⊙. The implied merger mass ratios are consistent with the expectation for low-redshift gas-rich mergers from simulations. We then go on to present evidence that (no matter which star formation rate indicator is used) our sample objects have very low star formation efficiencies (star formation rate per unit gas mass), lower even than the early-type galaxies from ATLAS3D which already show a suppression. This suggests that minor mergers can actually suppress star formation activity. We discuss mechanisms that could cause such a suppression, include dynamical effects induced by the minor merger.