Chandra observations of diffuse gas and luminous X-ray sources around the x-ray-bright elliptical galaxy NGC 1600.
SIVAKOFF G.R., SARAZIN C.L. and CARLIN J.L.
Abstract (from CDS):
We observed the X-ray-bright E3 galaxy NGC 1600 and nearby members of the NGC 1600 group with the Chandra X-Ray Observatory ACIS-S3 to study their X-ray properties. Unresolved emission dominates the observation; however, we resolved some of the emission into 71 sources, most of which are low-mass X-ray binaries associated with NGC 1600. Twenty-one of the sources have LX>2x1039 ergs/s (0.3-10.0 keV; assuming they are at the distance of NGC 1600), marking them as ultraluminous X-ray point source (ULX) candidates; we expect that only 11±2 are unrelated foreground/background sources. NGC 1600 may have the largest number of ULX candidates in an early-type galaxy to date; however, cosmic variance in the number of background active galactic nuclei cannot be ruled out. The spectrum and luminosity function (LF) of the resolved sources are more consistent with sources found in other early-type galaxies than with sources found in star-forming regions of galaxies. The source LF and the spectrum of the unresolved emission both indicate that there are a large number of unresolved point sources. We propose that these sources are associated with globular clusters (GCs) and that NGC 1600 has a large GC specific frequency. Observations of the GC population in NGC 1600 would be very useful for testing this prediction. Approximately 50%-75% of the unresolved flux comes from diffuse gaseous emission. The spectral fits, hardness ratios, and X-ray surface brightness profile all point to two gas components. We interpret the soft inner component (a≲25'', kT∼0.85 keV) as the interstellar medium of NGC 1600 and the hotter outer component (a≳25'', kT∼1.5 keV) as the intragroup medium of the NGC 1600 group. The X-ray image shows several interesting structures. First, there is a central region of excess emission that is roughly cospatial with Hα and dust filaments immediately west of the center of NGC 1600. There appear to be holes in the X-ray emission to the north and south of the galaxy center that are roughly coincident with the lobes of the NGC 1600 radio source. On larger scales, there is excess emission to the northeast, which we suggest may indicate the center of the group potential. The group galaxy NGC 1603 shows a tail of X-ray emission to its west that is probably due to ram pressure stripping.
Galaxies: Elliptical and Lenticular, cD - Galaxies: ISM - Galaxies: Intergalactic Medium - X-Rays: Binaries - X-Rays: Galaxies - X-Rays: ISM
VizieR on-line data:
<Available at CDS (J/ApJ/617/262): table1.dat>