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 measure their surface brightnesses and temperatures out to
330 and 680 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 X-ray
luminosities, both groups prefer $L_X-T$ relations without a break in the group
regime. Furthermore, we measure the electron number densities and hydrostatic
masses at these radii. We find that the electron number density profiles
require three $\beta$ model components, with nearly flat slopes in the 3$^rd$
$\beta$ component for both groups. However, we find the effective slope in the
outskirts to be $\beta_out$ = 0.59 and 0.49 for NGC 3402 and NGC 5129,
respectively. Adding the gas mass measured from the X-ray data and stellar mass
from group galaxy members, we measure baryon fractions of $f_b$ = 0.113 $\pm$
0.013 and 0.091 $\pm$ 0.006 for NGC 3402 and NGC 5129, respectively. Combining
other poor groups with well measured X-ray emission to the outskirts, we find
an average baryon fraction of $f_b,ave$ = 0.100 $\pm$ 0.004 for X-ray bright
groups with temperatures between 0.8$-$1.3 keV, extending existing constraints
to lower mass systems.
Description
[1704.08266] $Suzaku$ Measurements of Hot Halo Emission at Outskirts for Two Poor Galaxy Groups: NGC 3402 and NGC 5129
Links and resources
Tags