哈勃太空望远镜捕捉到UGC~12591：一个非常巨大和快速旋转的混合星系中的膨胀/盘特性，恒星形成和"失踪重子"普查
Hubble Space Telescope Captures UGC~12591: Bulge/Disc Properties, Star Formation and `Missing Baryons' Census in a Very Massive and Fast Spinning Hybrid Galaxy
摘要：
我们介绍了哈勃太空望远镜（HST）对附近大质量、高度旋转的混合星系UGC~12591的观测，以及紫外到远红外波段的观测。在V，I和H带的HST数据被用来解开结构组件。表面光度测定表明，在H波段B/D比为$69\%$的光盘上的凸起占主导地位。光谱能量分布（SED）拟合揭示了一个极低的全球恒星形成率（SFR）的$\rm\sim0.1-0.2 M_\odot yr^{-1}$，特别是低的星系的巨大恒星质量的$\rm 1.6\times10^{11}M_\odot$，这意味着其强烈淬火的SFR与恒星形成效率的$3-5\%$。至少在过去的$\rm 10^{8}$年里，该星系一直处于静止状态，是一个贫瘠的、"红色和死亡"的星系。UGC~12591中存在一个$\rm 6.18\times 10^{8} M_\odot$的超大质量黑洞（SMBH），该黑洞目前可能处于静止状态，即既没有观测到大射电喷流（$\rm>1 kpc$），也没有对中红外SED有显著贡献，排除了活动星系核的强辐射反馈。我们对维里半径内总质量为$\rm 6.46\times10^{11} M_\odot$的所有可观测重子进行了详细的普查，相当于相对于宇宙学平均值而言，重子的质量不足$\sim$ $85\%$。这些重子中只有一小部分存在于温暖/热的环银河X射线晕中，而大多数仍然无法观测到。我们讨论了各种天体物理学场景来解释它的不寻常特性。我们的工作是理解这种极其巨大的孤立星系的组装历史的重要一步。
英文摘要：
We present Hubble Space Telescope (HST) observations of the nearby, massive, highly rotating hybrid galaxy UGC~12591, along with observations in UV to FIR bands. HST data in V, I, and H bands is used to disentangle the structural components. Surface photometry shows a dominance of the bulge over the disc with H-band B/D ratio of $69\%$. The spectral energy distribution (SED) fitting reveals an extremely low global star formation rate (SFR) of $\rm\sim0.1-0.2 M_\odot yr^{-1}$, exceptionally low for the galaxy's huge stellar mass of $\rm 1.6\times10^{11}M_\odot$, implying a strong quenching of its SFR with star formation efficiency of $3-5\%$. For at least the past $\rm 10^{8}$ years, the galaxy has remained in a quiescent state as a sterile, `red and dead' galaxy. UGC~12591 hosts a supermassive black hole (SMBH) of $\rm 6.18\times 10^{8} M_\odot$ which is possibly quiescent at present, i.e. neither we see large ($\rm>1 kpc$) radio jets nor is the SMBH contributing significantly to the mid-IR SED, ruling out strong radiative feedback of AGN. We obtained a detailed census of all observable baryons with a total mass of $\rm 6.46\times10^{11} M_\odot$ within the virial radius, amounting to a baryonic deficiency of $\sim$$85\%$ relative to the cosmological mean. Only a small fraction of these baryons resides in a warm/hot circum-galactic X-ray halo, while the majority are still unobservable. We discussed various astrophysical scenarios to explain its unusual properties. Our work is a major step forward in understanding the assembly history of such extremely massive, isolated galaxies.
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