Photometric Objects Around Cosmic Webs (PAC). VI. High Satellite Fraction of Quasars

Abstract: The Photometric objects Around Cosmic webs (PAC) approach developed in Xu et al. (2022b) has the advantage of making full use of spectroscopic and deeper photometric surveys. With the merits of PAC, the excess surface density $\bar{n}2w{{\rm{p}}}$ of neighboring galaxies can be measured down to stellar mass $10^{10.80}\,M_{\odot}$ around quasars at redshift $0.8<z_{\rm{s}}<1.0$, with the data from the Sloan Digital Sky Survey IV (SDSS-IV) extended Baryon Oscillation Spectroscopic Survey (eBOSS) and the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys. We find that $\bar{n}2w{{\rm{p}}}$ generally increases quite steeply with the decrease of the separation. Using subhalo abundance matching method, we can accurately model the $\bar{n}2w{{\rm{p}}}$ both on small and large scales. We show that the steep increase of the $\bar{n}2w{{\rm{p}}}$ towards the quasars requires that a large fraction $f_{\mathrm{sate}}=0.29_{-0.06}^{+0.05}$ of quasars should be satellites in massive halos, and find that this fraction measurement is insensitive to the assumptions of our modeling. This high satellite fraction indicates that the subhalos have nearly the same probability to host quasars as the halos for the same (infall) halo mass, and the large scale environment has negligible effect on the quasar activity. We show that even with this high satellite fraction, each massive halo on average does not host more than one satellite quasar due to the sparsity of quasars.