PRIMUS: One- and Two-Halo Galactic Conformity at $0.2 < z < 1$

TL;DR

This study detects galactic conformity signals at intermediate redshifts using spectroscopic data, revealing that environment influences galaxy quenching and that large survey volumes are essential for accurate measurements.

Contribution

First detection of one- and two-halo galactic conformity signals at 0.2<z<1.0 using spectroscopic data across multiple fields, accounting for cosmic variance.

Findings

Significant one-halo conformity signal (>3σ) of ~5% on 0-1 Mpc scales.

Two-halo conformity signal of ~1% on 1-3 Mpc scales, weaker than SDSS.

Central galaxies are more quenched in overdense environments, independent of stellar mass.

Abstract

We test for galactic conformity at $0.2<z<1.0$ to a projected distance of 5 Mpc using spectroscopic redshifts from the PRism MUlti-object Survey (PRIMUS). Our sample consists of $\sim60,000$ galaxies in five separate fields covering a total of $\sim5.5$ square degrees, which allows us to account for cosmic variance. We identify star-forming and quiescent "isolated primary" (i.e., central) galaxies using isolation criteria and cuts in specific star formation rate. We match the redshift and stellar mass distributions of these samples, to control for correlations between quiescent fraction and redshift and stellar mass. We detect a significant $(>3\sigma)$ one-halo conformity signal, or an excess of star-forming neighbors around star-forming central galaxies, of $\sim5$% on scales of 0-1 Mpc and a $2.5\sigma$ two-halo signal of $\sim1$% on scales of 1-3 Mpc. These signals are weaker than those detected in SDSS and are consistent with galactic conformity being the result of large-scale tidal fields and reflecting assembly bias. We also measure the star-forming fraction of central galaxies at fixed stellar mass as a function of large-scale environment and find that central galaxies are more likely to be quenched in overdense environments, independent of stellar mass. However, we find that environment does not affect the star formation efficiency of central galaxies, as long as they are forming stars. We test for redshift and stellar mass dependence of the conformity signal within our sample and show that large volumes and multiple fields are required at intermediate redshift to adequately account for cosmic variance.