BARYON CONTENT TO THE OUTSKIRTS OF LOW-TEMPERATURE POOR GALAXY GROUPS

Abstract

Little is known concerning the overall properties of galaxy groups, especially at large radii. A better understanding of them will constrain numerical simulations regarding their formation and evolution, as well as reveal what role they play in the Missing Baryon Problem. I will present Suzaku off-center X-ray observations of two poor galaxy groups, NGC 3402 and NGC 5129, with temperatures below 1 keV. Through spectral decomposition, I measured their surface brightnesses and temperatures out to a large fraction of their outskirts. With the refined bolometric X-ray luminosities, both groups prefer L_x–T relations without a break in the group regime. Furthermore, I have determined the electron number densities and hydrostatic masses at these radii. I found that the surface brightness and electron number density profiles require two β model components, as well as an indication that a third β model may be needed for NGC 3402.

Adding the gas mass measured from the X-ray data and stellar mass from group galaxy members, I computed baryon fractions of f_b = 0.069 ± 0.007 and f_b = 0.095 ± 0.014 for NGC 3402 and NGC 5129, respectively. Combining other poor groups with well measured X-ray emission out to their outskirts, I found an average baryon fraction extrapolated to r_500 of f_b,500 = 0.091 ± 0.005 for X-ray bright groups with temperatures between 0.8–1.3 keV, extending existing constraints to lower mass systems and indicating that significant baryon losses exist below approximately r_500.