TY - JOUR
T1 - X-ray luminosities of galaxies in groups
AU - Helsdon, Stephen
AU - Ponman, Trevor
AU - O'Sullivan, Ewan
AU - Forbes, Duncan
PY - 2001/8/1
Y1 - 2001/8/1
N2 - We have derived the X-ray luminosities of a sample of galaxies in groups, making careful allowance for contaminating intragroup emission. The L-X : L-B and L-X : L-FIR relations of spiral galaxies in groups appear to be indistinguishable from those in other environments, however the elliptical galaxies fall into two distinct classes. The first class is central-dominant group galaxies, which are very X-ray luminous and may be the focus of group cooling flows. All other early-type galaxies in groups belong to the second class, which populates an almost constant band of L-X/L-B over the range 9.8 <log L-B <11.3. The X-ray emission from these galaxies can be explained by a superposition of discrete galactic X-ray sources together with a contribution from hot gas lost by stars, which varies a great deal from galaxy to galaxy. In the region where the optical luminosity of the non-central group galaxies overlaps with the dominant galaxies, the dominant galaxies are over an order of magnitude more luminous in X-rays. We also compared these group galaxies with a sample of isolated early-type galaxies, and used previously published work to derive L-X : L-B relations as a function of environment. The non-dominant group galaxies have mean L-X/L-B ratios very similar to those of isolated galaxies, and we see no significant correlation between L-X/L-B and environment. We suggest that previous findings of a steep L-X : L-B relation for early-type galaxies result largely from the inclusion of group-dominant galaxies in samples.
AB - We have derived the X-ray luminosities of a sample of galaxies in groups, making careful allowance for contaminating intragroup emission. The L-X : L-B and L-X : L-FIR relations of spiral galaxies in groups appear to be indistinguishable from those in other environments, however the elliptical galaxies fall into two distinct classes. The first class is central-dominant group galaxies, which are very X-ray luminous and may be the focus of group cooling flows. All other early-type galaxies in groups belong to the second class, which populates an almost constant band of L-X/L-B over the range 9.8 <log L-B <11.3. The X-ray emission from these galaxies can be explained by a superposition of discrete galactic X-ray sources together with a contribution from hot gas lost by stars, which varies a great deal from galaxy to galaxy. In the region where the optical luminosity of the non-central group galaxies overlaps with the dominant galaxies, the dominant galaxies are over an order of magnitude more luminous in X-rays. We also compared these group galaxies with a sample of isolated early-type galaxies, and used previously published work to derive L-X : L-B relations as a function of environment. The non-dominant group galaxies have mean L-X/L-B ratios very similar to those of isolated galaxies, and we see no significant correlation between L-X/L-B and environment. We suggest that previous findings of a steep L-X : L-B relation for early-type galaxies result largely from the inclusion of group-dominant galaxies in samples.
UR - http://www.scopus.com/inward/record.url?scp=0011371367&partnerID=8YFLogxK
U2 - 10.1046/j.1365-8711.2001.04490.x
DO - 10.1046/j.1365-8711.2001.04490.x
M3 - Article
SN - 1365-2966
VL - 325
SP - 693
EP - 706
JO - Royal Astronomical Society. Monthly Notices
JF - Royal Astronomical Society. Monthly Notices
IS - 2
ER -