In the standard structure formation paradigm of LambdaCDM, galaxies form at the centers of dark matter halos. Smaller galaxies and their host halos can merge with larger halos, becoming the so-called satellite galaxies and subhalos. Orbiting around the central dominant galaxy of the host halo and undergoing tidal stripping, these satellites and subhalos lose mass, which form stellar streams and the diffuse stellar halos around the central galaxies.
Low-mass satellites are one of the most effective tools to distinguish different dark matter models, but previous studies on them are often focused within our Milky Way and the Local Group. Studies on distant low-mass satellites is more difficult because they often lack in spectroscopic distance measurements. We developed a statistical method of counting faint photometric satellites around spectroscopically identified isolated central galaxies, and the method has been applied to three different surveys (HSC, DECaLS and SDSS). I will introduce the properties of these faint satellites and the connection to their central galaxy properties and the host dark matter halo mass. A comparison is made against Milky Way satellites, indicating the Milky Way system is statistically atypical.
In the second part of the talk, I will introduce our efforts of investigating the faint diffuse stellar halos for isolated central galaxies, by stacking galaxy images from HSC. After PSF deconvolution, we found their surface brightness profiles are close to universal after scaled by the halo virial radius. High-concentration galaxies (mostly red) have more extended stellar halos, redder and shallower color profiles and also more satellites than blue counterparts. Satellites of red centrals are also redder. These results can be understood in the standard cosmological context that red galaxies formed early but stop forming stars at late times, while their host halos, population of satellites and outer stellar halos keep growing through accretion.
In the end, I will very briefly introduce a recent work on proper motion measurements for main sequence stars by cross matching sources in HSC and SDSS Stripe82, achieved by a student Tian Qiu from Kavli-IPMU.
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