Lopsided distribution of MATLAS and ELVES dwarf satellite systems around isolated host galaxies

TL;DR

This study investigates the uneven distribution of dwarf satellite galaxies around isolated hosts, revealing a higher-than-expected occurrence of lopsidedness, especially among recently accreted satellites, with implications for cosmological models.

Contribution

It introduces a comprehensive analysis of satellite lopsidedness using multiple metrics across two surveys, highlighting a significant excess of lopsided systems and differences based on galaxy type.

Findings

Approximately 16% of systems show significant lopsidedness with the wedge metric.

Combining metrics, about 21% of systems are significantly lopsided.

More lopsided systems are found around red early-type galaxies than blue late-type ones.

Abstract

The properties of satellite dwarf galaxies pose important empirical constraints to verify cosmological models on galaxy scales. Their phase-space correlations, in particular, offer interesting insights into various models. Next to the planes-of-satellites phenomenon, the lopsided distribution of satellites relative to their host galaxy has been studied observationally and in cosmological simulations. It is still unclear how observed lopsidedness aligns with expectations from simulations. We measure lopsidedness in observed isolated satellite systems using six different metrics. We study 47 systems from the MATLAS survey beyond the Local Volume (LV) as well as 21 LV satellite systems from the ELVES survey. We find that the so-called wedge metric, counting the number of dwarfs in wedges with varying opening angles, is best suited to capture a system's overall lopsidedness. Under this metric, our analysis reveals that ~16 percent of the tested satellite systems exhibit a statistically significant degree of lopsidedness when compared to systems with randomly generated satellite position angles. This presents a notable excess over the expected 5% (2 sigma level) of significantly lopsided systems in a sample with no overall inherent lopsidedness. However, using multiple metrics provides a more complete picture. Combining all tested metrics, the number of significantly lopsided systems increases to ~21 percent. Contrary to recent results from the literature, we find more lopsided systems among the red early-type galaxies in the MATLAS survey compared to the mostly blue late-type hosts in ELVES. We further find that satellite galaxies at larger distances from the host, potentially recently accreted, are likely the primary contributors to the reported excess of lopsidedness. Our results enable comparisons with similar systems in simulations to assess consistency with the standard model.