Galactic conformity and central / satellite quenching, from the satellite profiles of M$^{\ast}$ galaxies at $0.4<z<1.9$ in the UKIDSS UDS

TL;DR

This study investigates how the star-formation activity of central galaxies correlates with their satellites across redshifts 0.4 to 1.9, revealing that passive centrals tend to have passive satellites, suggesting environmental or formation bias influences.

Contribution

It provides new insights into the redshift evolution of galactic conformity and suggests that the correlation may be driven by formation bias or central galaxy outbursts, not solely halo mass.

Findings

Passive satellites are more common around passive centrals at all studied redshifts.

The satellite distribution slopes range from -1.1 to -1.6, indicating their radial density profiles.

No significant redshift evolution of the conformity trend was observed.

Abstract

We explore the redshift evolution of a curious correlation between the star-formation properties of central galaxies and their satellites (`galactic conformity') at intermediate to high redshift ($0.4<z<1.9$). Using an extremely deep near-infrared survey, we study the distribution and properties of satellite galaxies with stellar masses, ${\rm log} ({\rm M}_*/{\rm M}_{\odot})>9.7$, around central galaxies at the characteristic Schechter function mass, ${\rm M} \sim {\rm M}^{\ast}$. We fit the radial profiles of satellite number densities with simple power laws, finding slopes in the range -1.1 to -1.4 for mass-selected satellites, and -1.3 to -1.6 for passive satellites. We confirm the tendency for passive satellites to be preferentially located around passive central galaxies at $3\sigma$ significance and show that it exists to at least $z\sim2$. Meanwhile, the quenched fraction of satellites around star-forming galaxies is consistent with field galaxies of equal stellar masses. We find no convincing evidence for a redshift-dependent evolution of these trends. One simple interpretation of these results is that only passive central galaxies occupy an environment that is capable of independently shutting off star-formation in satellite galaxies. By examining the satellites of higher stellar mass star-forming galaxies (${\rm log} ({\rm M}_*/{\rm M}_{\odot}) > 11$), we conclude that the origin of galactic conformity is unlikely to be exclusively due to the host dark-matter halo mass. A halo-mass-independent correlation could be established by either formation bias or a more physical connection between central and satellite star-formation histories. For the latter, we argue that a star-formation (or AGN) related outburst event from the central galaxy could establish a hot halo environment which is then capable of quenching both central and satellite galaxies.