分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The discovery of massive galaxies at high redshifts, especially the passive ones, poses a big challenge for the current standard galaxy formation models. Here we use the semi-analytic galaxy formation model developed by Henriques et al. to explore the formation and evolution of massive galaxies (MGs, stellar-mass $M_{*}> 10^{11}$ M$_{\odot}$). Different from previous works, we focus on the ones just formed (e.g. just reach $\simeq 10^{11}$ M$_{\odot}$). We find that most of the MGs are formed around $z=0.6$, with the earliest formation at $z>4$. Interestingly, although most of the MGs in the local Universe are passive, we find that only $13\%$ of the MGs are quenched at the formation time. Most of the quenched MGs at formation already hosts a very massive supermassive black hole (SMBH) which could power the very effective AGN feedback. For the star-forming MGs, the ones with more massive SMBH prefer to quench in shorter timescales; in particular, those with $M_{\textrm{SMBH}} > 10^{7.5}$ M$_{\odot}$ have a quenching timescale of $\sim 0.5$ Gyr and the characteristic $M_{\textrm{SMBH}}$ depends on the chosen stellar mass threshold in the definition of MGs as a result of their co-evolution. We also find that the "in-situ" star formation dominates the stellar mass growth of MGs until they are formed. Over the whole redshift range, we find the quiescent MGs prefer to stay in more massive dark matter halos, and have more massive SMBH and less cold gas masses. Our results provide a new angle on the whole life of the growth of MGs in the Universe.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Mengting Ju
Jun Yin
Rongrong Liu
Lei Hao
Zhengyi Shao
Shuai Feng
Rogério Riffel
Chenxu Liu
David V. Stark
Shiyin Shen
Eduardo Telles
José G. Fernández-Trincado
Junfeng Wang
Haiguang Xu
Dmitry Bizyaev
Yu Rong
摘要： Gas accretion is an important process in the evolution of galaxies, but it has limited direct observational evidences. In this paper, we report the detection of a possible ongoing gas accretion event in a Blue Compact Dwarf (BCD) galaxy, MaNGA 8313-1901, observed by the Mapping Nearby Galaxies and Apache Point Observatory (MaNGA) program. This galaxy has a distinct off-centered blue clump to the northeast (the NE clump) that shows low metallicity and enhanced star-formation. The kinematics of the gas in the NE clump also seems to be detached from the host BCD galaxy. Together with the metallicity drop of the NE clump, it suggests that the NE clump likely has an external origin, such as the gas accretion or galaxy interaction, rather than an internal origin, such as an \hii~complex in the disk. After removing the underlying host component, we find that the spectrum of the "pure" clump can match very well with a modeled spectrum containing a stellar population of the young stars ($\le 7$ Myr) only. This may imply that the galaxy is experiencing an accretion of cold gas, instead of a merger event involving galaxies with significant pre-existing old stars. We also find signs of another clump (the SW clump) at the south-west corner of the host galaxy, and the two clumps may share the same origin of gas accretion.
分类： 物理学 >> 核物理学 提交时间： 2016-09-14
摘要： The orientations of the red galaxies in a filament are aligned with the orientation of the filament. We thus develop a location-alignment-method (LAM) of detecting filaments around clusters of galaxies, which uses both the alignments of red galaxies and their distributions in two-dimensional images. For the first time, the orientations of red galaxies are used as probes of filaments. We apply LAM to the environment of Coma cluster, and find four filaments (two filaments are located in sheets) in two selected regions, which are compared with the filaments detected with the method of \cite{Falco14}. We find that LAM can effectively detect the filaments around a cluster, even with 3σ confidence level, and clearly reveal the number and overall orientations of the detected filaments. LAM is independent of the redshifts of galaxies, and thus can be applied at relatively high redshifts and to the samples of red galaxies without the information of redshifts. We also find that the images of background galaxies (interlopers) which are lensed by the gravity of foreground filaments are amplifiers to probe the filaments.
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