分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： M104 (NGC 4594, the Sombrero galaxy) is a mysterious massive early-type
galaxy that shows a dominant bulge and a prominent disk. However, the presence
of a halo in M104 has been elusive, and it is not yet known how M104 has
acquired such a peculiar structure. Using wide ($\sim2$ deg$^2$) and deep $ugi$
images of M104 obtained with the CFHT/MegaCam, we detect a large number of
globular clusters (GCs) found out to $R\approx35'$ ($\sim100$ kpc). The color
distribution of these GCs shows two subpopulations: a blue (metal-poor) system
and a red (metal-rich) system. The total number of GCs is estimated to be
$N_{GC}=1610\pm30$ and the specific frequency to be $S_{N}=1.8\pm0.1$. The
radial number density profile of the GCs is steep in the inner region at
$R<20'$, and becomes shallow in the outer region at $20'
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yiming Wu
Chengze Liu
Eric W. Peng
Youkyung Ko
Patrick Côté
Rashi Jain
Laura Ferrarese
Xiaohu Yang
Ariane Lançon
Thomas Puzia
Sungsoon Lim
摘要： Combining data from the ACS Virgo Cluster Survey (ACSVCS) and the Next Generation Virgo cluster Survey (NGVS), we extend previous studies of color gradients of the globular cluster (GC) systems of the two most massive galaxies in the Virgo cluster, M87 and M49, to radii of $\sim 15~R_e$ ($\sim 200$ kpc for M87 and $\sim 250$ kpc for M49). We find significant negative color gradients, i.e., becoming bluer with increasing distance, out to these large radii. The gradients are driven mainly by the outwards decrease of the ratio of red to blue GC numbers. The color gradients are also detected out to $\sim 15~R_e$ in the red and blue sub-populations of GCs taken separately. In addition, we find a negative color gradient when we consider the satellite low-mass elliptical galaxies as a system, i.e., the satellite galaxies closer to the center of the host galaxy usually have redder color indices, both for their stars and GCs. According to the "two phase" formation scenario of massive early-type galaxies, the host galaxy accretes stars and GCs from low-mass satellite galaxies in the second phase. So the accreted GC system naturally inherits the negative color gradient present in the satellite population. This can explain why the color gradient of the GC system can still be observed at large radii after multiple minor mergers.
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