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arXiv 1602.09077astro-ph.GA
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室女星系团中的成星矮星系:分子气体、原子气体和尘埃之间的联系

Star-forming dwarf galaxies in the Virgo cluster: the link between molecular gas, atomic gas, and dust

M. Grossi, E. Corbelli, L. Bizzocchi, C. Giovanardi, D. Bomans, B. Coelho, I. De Looze, T. S. Gonçalves, L. K. Hunt, E. Leonardo, S. Madden, K. Menéndez-Delmest… 展开作者

M. Grossi, E. Corbelli, L. Bizzocchi, C. Giovanardi, D. Bomans, B. Coelho, I. De Looze, T. S. Gonçalves, L. K. Hunt, E. Leonardo, S. Madden, K. Menéndez-Delmestre, C. Pappalardo, L. Riguccini

摘要:

本文介绍了从赫歇尔室女星系团巡天中选出的20个成星矮星的$^{12}$ CO(1-0)和$^{12}$ CO(2-1)观测结果,它们的氧丰度范围为12 + log(O/H)~ 8.1 ~ 8.8。在10个星系中观测到CO发射,在另一个星系中勉强检测到。CO通量与FIR 250 $μ$ m发射相关,矮星遵循相同的线性关系,适用于更大质量的螺旋星系扩展到更广泛的动力学范围。我们比较不同的方法来估计H2分子量,即金属依赖CO到H2的转换因子和依赖于H-带光度。分子与恒星的质量比在恒星质量<~ 10 $^9$ M $_{\odot}$时几乎保持不变,与原子氢比例M $_{HI}$ /M $_*$相反,后者与M $_*$成反比。在低恒星质量下,M $_{H_2}$ /M $_*$的扁平化似乎与星团环境的影响无关,因为它发生在HI缺乏和HI正常的矮星上。分子与原子的比率与恒星表面密度的关系比与金属丰度的关系更密切,这证实了星际气体压力在决定星际介质中两种气体成分之间的平衡方面起着关键作用。室女座矮星的分子气体质量和恒星形成率之间的线性趋势与更大质量的螺旋一样,但气体耗尽的时间尺度$τ_{dep}$并不是恒定的,范围在1亿年到6亿年之间。与室女星系团环境的相互作用正在去除矮星的原子气体和尘埃成分,但分子气体在星系团内目前的演化阶段似乎受到的影响较小。然而,HI缺乏和分子气体耗尽时间之间的相关性表明,缺乏来自盘外部区域的气体补充降低了恒星形成活动。

英文摘要:

We present $^{12}$CO(1-0) and $^{12}$CO(2-1) observations of a sample of 20 star-forming dwarfs selected from the Herschel Virgo Cluster Survey, with oxygen abundances ranging from 12 + log(O/H) ~ 8.1 to 8.8. CO emission is observed in ten galaxies and marginally detected in another one. CO fluxes correlate with the FIR 250 $μ$m emission, and the dwarfs follow the same linear relation that holds for more massive spiral galaxies extended to a wider dynamical range. We compare different methods to estimate H2 molecular masses, namely a metallicity-dependent CO-to-H2 conversion factor and one dependent on H-band luminosity. The molecular-to-stellar mass ratio remains nearly constant at stellar masses <~ 10$^9$ M$_{\odot}$, contrary to the atomic hydrogen fraction, M$_{HI}$/M$_*$, which increases inversely with M$_*$. The flattening of the M$_{H_2}$/M$_*$ ratio at low stellar masses does not seem to be related to the effects of the cluster environment because it occurs for both HI-deficient and HI-normal dwarfs. The molecular-to-atomic ratio is more tightly correlated with stellar surface density than metallicity, confirming that the interstellar gas pressure plays a key role in determining the balance between the two gaseous components of the interstellar medium. Virgo dwarfs follow the same linear trend between molecular gas mass and star formation rate as more massive spirals, but gas depletion timescales, $τ_{dep}$, are not constant and range between 100 Myr and 6 Gyr. The interaction with the Virgo cluster environment is removing the atomic gas and dust components of the dwarfs, but the molecular gas appears to be less affected at the current stage of evolution within the cluster. However, the correlation between HI deficiency and the molecular gas depletion time suggests that the lack of gas replenishment from the outer regions of the disc is lowering the star formation activity.

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