The Resolved Sunyaev--Zel'dovich Profiles of Nearby Galaxy Groups

TL;DR

This study measures the Sunyaev--Zel'dovich profiles of nearby galaxy groups, revealing baryon depletion within $R_{500}$ and evidence of baryons driven outwards by feedback, with a potential shock feature at larger radii.

Contribution

First to present resolved SZ profiles of galaxy groups using recent Planck data, confirming baryon depletion and detecting a shock feature at large radii.

Findings

Significant SZ detection out to 3 $R_{500}$

Baryon fraction within $R_{500}$ is about 5.6%, lower than cosmic value

Detected a $ extasciitilde 3σ$ 'bump' near 2 $R_{500}$ indicating possible accretion shocks

Abstract

Much of the baryons in galaxy groups are thought to have been driven out to large distances ($\gtrsim$$R_{500}$) by feedback, but there are few constraining observations of this extended gas. This work presents the resolved Sunyaev--Zel'dovich (SZ) profiles for a stacked sample of 10 nearby galaxy groups within the mass range log$_{10}(M_{500}[M_{\odot}]) = 13.6 -13.9$. We measured the SZ profiles using the publicly available $y$-map from the Planck Collaboration as well as our own $y$-maps constructed from more recent versions of $Planck$ data. The $y$-map extracted from the latest data release yielded a significant SZ detection out to 3 $R_{500}$. In addition, the stacked profile from these data were consistent with simulations that included AGN feedback. Our best-fit model using the latest $Planck$ data suggested a baryon fraction $\approx 5.6\%$ within $R_{500}$. This is significantly lower than the cosmic value of $\approx 16\%$, supporting the idea that baryons have been driven to large radii by AGN feedback. Lastly, we discovered a significant ($\sim 3\sigma$) "bump" feature near $\sim 2$ $R_{500}$ that is most likely the signature of internal accretion shocks.