并合矮星系VCC322的性质研究

YNAO OpenIR > 星系类星体研究组

	并合矮星系VCC322的性质研究
其他题名	Properties of the merging dwarf galaxy VCC322
	张兰月
学位类型	硕士
导师	赵应和
	2024-07-01
学位授予单位	中国科学院大学
学位授予地点	北京
学位专业	天体物理
关键词	矮星系并合潮汐尾恒星形成
摘要	星系-星系相互作用包括星系并合和潮汐相互作用。当星系间的视向速度差值较小的时候，相邻的星系容易发生并合或是相互作用。星系之间的相互作用和并合可以增强或抑制恒星的形成，但我们对其中涉及的物理机制仍然缺乏完整的了解。由于观测限制，相比起大质量星系，我们对矮星系的了解有限。矮星系的引力阱相对较浅，与大质量系统相比，矮星系受到更强的环境效应和恒星负反馈，这可能会显著影响并合驱动的恒星形成的强度和分布。因此并合矮星系是研究并合和环境效应对矮星系演化影响的重要工具。在本文中，我们对Virgo星系团中的并合矮星系VCC322的性质进行研究，并探寻并合和环境效应与矮星系演化之间的联系。本文中我们首先分析了VCC322在Virgo星系团中的周围环境，根据视向速度差以及投影距离，我们发现它与VCC334正处于并合阶段，同时由于它在光学图像上，和VCC319有部分重合，我们分析VCC334/VCC322/VCC319可能构成一个矮星系组。在对VCC322的光学g波段数据进行处理后，在星系的东南方向可以看到有一个明显的长而直的潮汐尾结构，其大小与VCC322星系主体相当。通过比较颜色-颜色($g-r$ vs. $r-H$)分布与简单的星族模型，我们推断该潮汐尾的金属丰度和恒星年龄分别为$Z_\star \sim 0.02~Z_\odot$和$t_\star \sim 10$ Gyr。该潮汐尾的金属丰度低于我们用相同的方法得到的星系主体的金属丰度$Z_\star \sim 0.2-0.4~Z_\odot$，根据质量-金属丰度关系，我们推断是VCC322星系主体存在恒星形成，从而其金属丰度值比长潮汐尾的金属丰度值高。除了这个比较明显的潮汐尾结构，在减去了前背景源以及VCC319星系的模型值的图像上，我们看到了一个短且延伸方向垂直于星系主轴的短潮汐尾，以及在星系北部存在的一条相对比较微弱的潮汐尾。通过分析VCC319的表面亮度轮廓图，我们发现VCC319星系内部存在等光扭曲，这表明VCC319可能受到了潮汐相互作用的影响。我们利用Starlight对VCC322的SDSS光谱进行了分析，得到了其中心区域的星族和恒星形成历史。VCC322中心区域的恒星质量加权的年龄和光度加权的年龄分别约为10 $^{9.8}$ yr和10 $^{7.5}$ yr，这表明其中心存在恒星形成活动。然而，当我们将其恒星形成率与Virgo星系团中的恒星形成矮星系和一组并合矮星系对样本进行比较后，发现VCC322的恒星形成率与其他相似恒星质量的恒星形成矮星系相比偏低，VCC322的恒星形成似乎受到了抑制。之后我们分析了VCC322与对比样本的恒星形成率-中性氢质量，恒星形成率-星系质量以及恒星形成速率-中性氢质量占比等关系，发现VCC322的恒星形成率明显低于星系团中相似中性氢质量的矮星系的恒星形成率，而其伴星系VCC334则与星系团中其它恒星形成矮星系的数值比较接近，这说明VCC322的恒星形成因为什么原因受到了一定程度的抑制作用。然后我们将VCC322中观察到的发射线流量比与激波模型进行比较。当激波速度为$v_s=200-250$ km s $^{-1}$，磁场为$B=0.5-1\,\mu$G时，该激波可以很好地模拟各谱线比，表明并合/相互作用引起的激波很可能加热气体，从而抑制VCC322中的恒星形成。
其他摘要	Galaxy-galaxy interactions include galaxy mergers and tidal interactions. When the line of sight velocity separation between galaxies is small, neighboring galaxies tend to merge or interact. Observational challenges of dwarf mergers have resulted in a comparatively limited understanding of them, in contrast to their massive counterparts. The evolution of galaxy mergers may be different in low-mass end due to the shallow gravitational potential wells of dwarf galaxies. As a result, they are more susceptible to environmental influences and negative stellar feedback, which can significantly impact both the intensity and distribution of star formation (SF). Therefore, merging dwarf galaxies are important tools to study the influence of merger and environmental effects on the evolution of dwarf galaxies. In this paper, we study the properties of the merging dwarf galaxy VCC322 in the Virgo cluster, and explore the relationship between the evolution of the dwarf galaxy and the effects of the merger and environment.In this paper, we analyze its environmental characteristics in the Virgo cluster, firstly. According to the velocity separation and projection separation, we find that it is merging with VCC334. And because VCC322 and VCC319 partially overlap in optical images, it is likely that VCC334/322/319 constitute a triple system. After processing the optical g-band data of VCC322, a straight tidal tail structure can be seen on the southeast side of the stellar main body, with a size comparable with that of the main galaxy. By comparing the color-color ($g-r$ vs. $r-H$) distribution with simple stellar population models, we infer metal abundances and stellar ages of $Z_\star \sim 0.02 Z_\odot$ and $t_\star \sim 10$ Gyr for this tidal tail, respectively. Indicating there would be no star-forming activity occurred after its formation. For the stellar main body of VCC322, it agrees with the model tracks with metallicities of 0.2-0.4 $Z_\odot$, and has a younger luminosity-weighted stellar age. In addition to this apparent tidal tail structure, we see a short tidal tail perpendicular to the main axis of the galaxy, as well as a relatively faint tidal tail in the northern part of the galaxy, after subtracting the background and front sources and the model for VCC319. From the g-band stellar surface brightness profiles of VCC319, we found the existence of isophotal twisting inside VCC319 galaxy. This suggests that VCC319 may have been affected by tidal interactions.We use Starlight to analyze the SDSS spectrum of VCC322 and obtain the stellar population and star formation history of its central region. The mass- and light-weighted ages of about 10$^{9.8}$ yr and 10$^{7.5}$ yr, respectively, indicating an ongoing star formation activity. However, when we compare its star formation rate (SFR) with a sample of star-forming dwarf galaxies in the Virgo cluster and a sample of merging dwarf galaxy pairs, we find that the SFR of VCC322 is low compared to other star-forming dwarf galaxies of similar stellar mass.Thus the star formation of VCC322 seems to be suppressed. We further investigate the star formation properties of VCC322 by utilizing the SFR-$M_{HI}$ (i.e. atomic hydrogen gas mass), SFR-$M_$ and SFR-to-$M_{HI}$ ratio (i.e., the star formation efficiency; SFE), gas-to-stellar mass ratio ($M_{HI}$/${M_}$) relations. At a given $M_*$, merging dwarfs have a higher mean SFR. Virgo SFDs also show a lower SFE at a given gas-to-stellar mass ratio. These differences might be due to the suppressed SF activity under dense environment and/or enhanced SF activity in merging/interacting systems. Regarding VCC322, it has a lower-than-average SFR and SFE among the Virgo SFDs. However, its companion VCC334 has a much higher SFR and SFE, only slightly lower than the merging/interacting systems. Therefore, it seems that the SF activity in VCC322 is not enhanced but suppressed. Then we compared the observed emission line ratios in VCC322 to the radiative shock models. A model with shock speed of $v_s=200-250$ km~s$^{-1}$ and magnetic field $B=0.5-1\,\mu$G can well reproduce each observed line ratio, indicating that a merger/interaction-induced shock is highly likely to heat the gas and thus suppress the SF activity in VCC322.
学科领域	天文学
学科门类	理学 ; 理学::天文学
页数	0
语种	中文
文献类型	学位论文
条目标识符	http://ir.ynao.ac.cn/handle/114a53/28033
专题	星系类星体研究组
作者单位	中国科学院云南天文台
第一作者单位	中国科学院云南天文台
推荐引用方式 GB/T 7714	张兰月. 并合矮星系VCC322的性质研究[D]. 北京. 中国科学院大学,2024.

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