On Mass Concentrations & Magnitude Gaps of Galaxy Systems in the CS82 Survey

TL;DR

This study uses weak lensing measurements to analyze the mass concentration of galaxy systems with large magnitude gaps, finding that larger gaps correlate with higher concentrations at low redshift, supporting the idea of earlier formation.

Contribution

It provides observational evidence linking magnitude gaps to higher mass concentrations, indicating earlier formation of galaxy systems.

Findings

Systems with larger magnitude gaps are more concentrated at low redshift.

The correlation is statistically significant with high probability.

Supports the hypothesis that magnitude gaps indicate earlier formation histories.

Abstract

Galaxy systems with large magnitude gaps - defined as the difference in magnitude between the central galaxy and the brightest satellite in the central region - have been claimed to have earlier formation histories. In this study we measure the mass concentration, as an indicator of early formation, of ensembles of galaxy systems divided by redshift and magnitude gaps in the $r$ band. We use cross-correlation weak lensing measurements with NFW parametric mass profiles to measure masses and concentrations of these ensembles from a catalogue of systems built from the SDSS Coadd by the redMaPPer algorithm. The lensing shear data come from the CFHT Stripe 82 (CS82) survey, and consists of $i$-band images of the SDSS Stripe 82 region. We find that the stack made up of systems with larger magnitude gaps has a high probability of being more concentrated on average, in the lowest redshift slice ($0.2<z<0.4$), both when dividing in quartiles ($P=0.98$) and terciles ($P=0.85$). These results lend credibility to the claim that the magnitude gap is an indicator of earlier formed systems.