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Dwarf galaxies in the coma cluster: Star formation properties and evolution.

机译：昏迷星团中的矮星系：恒星形成特性和演化。

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摘要

The infall regions of galaxy clusters are unique laboratories for studying the impact of environment on galaxy evolution. This intermediate region links the low-density field environment and the dense core of the cluster, and is thought to host recently accreted galaxies whose star formation is being quenched by external processes associated with the cluster. In this dissertation, we measure the star formation properties of galaxies at the infall region of the nearby rich cluster of galaxies, Coma. We rely primarily on Ultraviolet (UV) data owing to its sensitivity to recent star formation and we place more emphasis on the properties of dwarf galaxies. Dwarf galaxies are good tracers of external processes in clusters but their evolution is poorly constrained as they are intrinsically faint and hence more challenging to detect.;We make use of deep GALEX far-UV and near-UV observations at the infall region of the Coma cluster. This area of the cluster has supporting photometric coverage at optical and IR wavelengths in addition to optical spectroscopic data that includes deep redshift coverage of dwarf galaxies in Coma. Our GALEX observations were the deepest exposures taken for a local galaxy cluster. The depth of these images required alternative data analysis techniques to overcome systematic effects that limit the default GALEX pipeline analysis. Specifically, we used a deblending method that improved detection efficiency by a factor of ∼2 and allowed reliable photometry a few magnitudes deeper than the pipeline catalog. We performed deep measurements of the total UV galaxy counts in our field that were used to measure the source confusion limit for crowded GALEX fields.;The star formation properties of Coma members were studied for galaxies that span from starbursts to passive galaxies. Star-forming galaxies in Coma tend to have lower specific star formation rates, on average, as compared to field galaxies. We show that the majority of these galaxies are likely in the process of being quenched or were only recently quenched. We modeled the quenching timescales for transition galaxies, or “green valley” objects, and found that the majority are quenched in less than 1 Gyr. This timescale is consistent with rapid dynamical processes that are active in the cluster environment as opposed to the more gradual quenching mechanisms that exist in the group environment. For the passive galaxy population, we have measured an average stellar age of 6–8 Gyr for the red sequence which is consistent with previous studies based on spectroscopic observations. We note that the star formation properties of Coma member galaxies were established from photometry alone, as opposed to using spectroscopic data which are more challenging to obtain for dwarf galaxies.;We have measured the faintest UV luminosity functions (LFs) presented for a rich galaxy cluster thus far. The Coma UV LFs are 3.5 mag fainter than previous studies in Coma, and are sufficiently deep that we reach the dwarf passive galaxy population for the first time. We have introduced a new technique for measuring the LF which avoids color selection effects associated with previous methods. The UV LFs constructed separately for star-forming and passive galaxies follow a similar distribution at faint magnitudes, which suggests that the recent quenching of infalling dwarf star-forming galaxies is sufficient to build the dwarf passive population in Coma. The Coma UV LFs show a turnover at faint magnitudes as compared to the field, owing to a deficit of dwarf galaxies with stellar masses below M∗ = 108 M⊙ . We show that the UV LFs for the field behind the Coma cluster are nearly identical to the average field environment, and do not show evidence for a turnover at faint magnitudes. We suspect that the missing dwarf galaxies in Coma are severely disrupted by tidal processes as they are accreted onto the cluster, just prior to reaching the infall region studied here.
机译：银河星系团的降落区域是研究环境对银河系演化影响的独特实验室。这个中间区域将低密度的野外环境与星团的稠密核心联系在一起，并被认为拥有新近增生的星系，其恒星形成被与星团相关的外部过程所猝灭。在本文中，我们测量了附近富裕星系昏迷区彗星进入区域的星系恒星形成特性。由于其对最近恒星形成的敏感性，我们主要依靠紫外线（UV）数据，并且我们更加重视矮星系的性质。矮星系是集群中外部过程的良好示踪剂，但由于它们本来就很微弱，因此它们的演化受到的约束较弱，因此很难检测。我们在彗星坠落区利用深GALEX远紫外线和近紫外线观测资料簇。除了包括在昏迷中矮星系的深红移覆盖范围的光谱数据之外，群集的这一区域还具有在光学和IR波长处的光度覆盖范围的支持。我们对GALEX的观测是对当地星系团进行的最深照射。这些图像的深度需要替代的数据分析技术来克服限制默认GALEX管道分析的系统效果。具体来说，我们使用了一种去混合方法，将检测效率提高了约2倍，并允许可靠的测光比管道目录更深几个数量级。我们对场中的总紫外线星系计数进行了深度测量，用于测量拥挤的GALEX场的源混淆极限。研究了彗星成员的恒星形成特性，研究范围涵盖了从星爆到被动星系的星系。与野外星系相比，昏迷中的恒星系星体平均具有较低的特定恒星形成率。我们表明，这些星系中的大多数很可能正在被淬灭或仅在最近才被淬灭。我们对过渡星系或“绿谷”物体的淬灭时间尺度进行了建模，发现大多数淬灭时间在不到1 Gyr的时间内。该时间尺度与在集群环境中活跃的快速动态过程是一致的，这与群体环境中存在的更渐进的淬灭机制相反。对于被动星系人口，我们测得红色序列的平均星体年龄为6-8 Gyr，这与以前基于光谱观测的研究一致。我们注意到昏迷成员星系的恒星形成特性仅通过光度学来确定，而不是使用光谱数据来获得矮星系更具挑战性。;我们已经测量了丰富星系最微弱的紫外线光度函数（LFs）。到目前为止。比以前在昏迷中研究的昏迷UV LF弱3.5磁，并且深度足够深，我们首次到达矮被动星系。我们引入了一种新的测量LF的技术，该技术避免了与先前方法相关的颜色选择效果。分别为恒星形成星系和被动星系构建的紫外LF的大小相似，分布相似，这表明最近坠入的矮星形成星系的淬灭足以建立昏迷的矮星被动群体。由于缺乏星系质量小于M ∗ = 108 M＆odot的矮星系，昏迷UV LFs与实地相比显示出微弱的周转率。 。我们显示，昏迷星团后面的野外的UV LF与平均野外环境几乎相同，并且没有显示微弱幅度的周转证据。我们怀疑彗星中缺失的矮星系在到达此处研究的进入区域之前被吸积到星团上时，受到潮汐过程的严重破坏。

著录项

  • 作者

    Hammer, Derek M.;

  • 作者单位

    The Johns Hopkins University.;

  • 授予单位 The Johns Hopkins University.;
  • 学科 Physics Astrophysics.;Physics Astronomy and Astrophysics.
  • 学位 Ph.D.
  • 年度 2012
  • 页码 166 p.
  • 总页数 166
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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