# Suzaku Measurements of Hot Halo Emission at Outskirts for Two Poor Galaxy Groups: NGC 3402 and NGC 5129

## TL;DR

This study uses Suzaku X-ray observations to measure the properties of hot gas in the outskirts of two poor galaxy groups, revealing baryon fractions and gas profiles that extend understanding of low-mass systems.

## Contribution

First detailed X-ray measurements of hot gas at large radii in two poor galaxy groups, extending baryon fraction estimates to lower-mass systems.

## Key findings

- Surface brightness and density profiles fit with multiple β models.
- Baryon fractions are below cosmic mean, indicating baryon loss.
- No break found in the $L_X$-$T$ relation for these groups.

## Abstract

We present Suzaku off-center observations of two poor galaxy groups, NGC 3402 and NGC 5129, with temperatures below 1 keV. Through spectral decomposition, we measured their surface brightnesses and temperatures out to 530 and 1430 times the critical density of the universe for NGC 3402 and NGC 5129, respectively. These quantities are consistent with extrapolations from existing inner measurements of the two groups. With the refined bolometric X-ray luminosities, both groups prefer $L_X$-$T$ relations without a break in the group regime. Furthermore, we have determined the electron number densities and hydrostatic masses at these radii. We found that the surface brightness and electron number density profiles require two $\beta$ model components, as well as the indication that a third $\beta$ model may be needed for NGC 3402. Adding the gas mass measured from the X-ray data and stellar mass from group galaxy members, we computed baryon fractions of $f_b$ = 0.0693 $\pm$ 0.0068 and $f_b$ = 0.095 $\pm$ 0.014 for NGC 3402 and NGC 5129, respectively. Combining other poor groups with well-measured X-ray emission to the outskirts, we found an average baryon fraction extrapolated to $r_{500}$ of $\overline{f_{b,500}}$ = 0.0912 $\pm$ 0.0050 for X-ray-bright groups with temperatures between 0.8 and 1.3 keV, extending existing constraints to lower-mass systems and indicating that significant baryon losses exist below approximately $r_{500}$.