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Date and Time of the Query: 2019-05-22 T02:52:49 PDT
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For refcode 2001MNRAS.325..693H:
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Copyright by Royal Astronomical Society. 2001MNRAS.325..693H X-ray luminosities of galaxies in groups Stephen F. Helsdon, Trevor J. Ponman, Ewan O'Sullivan and Duncan A. Forbes Accepted 2001 March 5. Received 2001 March 5; in original form 2000 September 6 ABSTRACT 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. Keywords: galaxies: elliptical and lenticular, cD - galaxies: ISM - galaxies: spiral - X-rays: galaxies.
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