We present the analysis of the galaxy structural parameters from Halpha3, an Halpha narrow-band imaging follow-up survey of ~800 galaxies selected from the HI ALFALFA Survey in the Local and Coma Superclusters. Taking advantage of Halpha3 which provides the complete census of the recent star-forming, HI-rich galaxies in the local universe, we aim to investigate the structural parameters of both the young (<10 Myr) and the old (>1 Gyr) stellar populations. By comparing the sizes of these stellar components we investigated the spatial scale on which galaxies are growing at the present cosmological epoch and the role of the environment in quenching the star-formation activity. We computed the concentration, asymmetry, and clumpiness structural parameters. To quantify the sizes we computed half-light radii and a new parameter dubbed EW/r. The concentration index computed in the r band depends on the stellar mass and on the Hubble type, these variables being related since most massive galaxies are bulge dominated thus most concentrated. Going toward later spirals and irregulars both the concentration index and the stellar mass decrease. Blue Compact dwarfs represent an exception since they have similar stellar mass but they are more concentrated than dwarf irregulars. The asymmetry and the clumpiness increase along the spiral sequence then they decrease going into the dwarf regime, where the light distribution is smooth and more symmetric. When measured on Halpha images, the CAS parameters do not exhibit obvious correlations with Hubble type. We found that the concentration index is the main parameter that describes the current growth of isolated galaxies but, for a fixed concentration, the stellar mass plays a second order role. At the present epoch, massive galaxies are growing inside-out, conversely the dwarfs are growing on the scale of their already assembled mass.
The evolution of dwarf galaxies in the Coma supercluster
利用SDSS DR 7在500平方度区域的分光光度数据，研究后发座超星系团（z=0.023）中矮星系（~M*+2<M_z<M*+4）的演化。我们发现，在后发座超星系团中，红矮星主要集中在后发座和阿贝尔1367星系团的致密核心，以及嵌入连接它们的灯丝中的星系群中。然而，在后发座星系团和Abell 1367星系团的陷落区发现了后星爆（k+A）矮星，偶尔也在沿暗条嵌入的星系群中发现，这表明深势阱附近普遍存在的强速度场可能与导致矮星系后星爆阶段的机制密切相关。此外，后发座星系团中一些k+A矮星的蓝色，在其维里半径内发现，这表明这些星系中的恒星形成在过去的500 Myr中非常迅速地熄灭了。超星系团中60%以上的红矮星系的H_δ吸收角为0-3角，这表明在这些星系中有一个不可忽略的部分发生了一个主要的恒星形成事件，在最后一个Gyr内结束，使它们能够移动到红色序列。后发座超星系团中的蓝矮星系在EW（H_α）-EW（H_δ）平面上呈双峰分布，其中一个星系团在H_α中有很高的发射，在H_δ中也有一些发射。在EW（H_α）-EW（H_δ）平面上，蓝矮星和红矮星的一个子群重合，在H_δ上表现出吸收，在H_α上表现出相对较低的发射。我们认为，后者人口的很大一部分是被动矮星系的祖先，大量发现在低红移丰富的集群，如后发座的核心。
Halpha3: an Halpha imaging survey of HI selected galaxies from ALFALFA. II. The star formation properties of galaxies in the Virgo cluster and surroundings
Illuminating the Local Universe: Large-Scale Structure from ZTF Type Ia Supernovae
Stockholm University（斯德哥尔摩大学）；Yonsei University（延世大学）；Université Claude Bernard Lyon 1（里昂第一大学）；University of Cambridge（剑桥大学）；Trinity College Dublin（都柏林三一学院）；University of Washington（华盛顿大学）
