Open AccessX‐ray luminosities for a magnitude‐limited sample of early‐type galaxies from the ROSAT All‐Sky Survey
Author(s) -
Beuing J.,
Döbereiner S.,
Böhringer H.,
Bender R.
Publication year - 1999
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1999.02108.x
Subject(s) - physics , astrophysics , rosat , galaxy , supernova , luminosity , sky , magnitude (astronomy) , flux (metallurgy) , astronomy , materials science , metallurgy
For a magnitude‐limited optical sample ( B T ≤ 13.5 mag) of early‐type galaxies, we have derived X‐ray luminosities from the ROSAT All‐Sky Survey. The results are 101 detections and 192 useful upper limits in the range from 10 36 to 10 44 erg s ‐1 . For most of the galaxies no X‐ray data have been available until now. On the basis of this sample with its full sky coverage, we find no galaxy with an unusually low flux from discrete emitters. Below log (L B ) ≈ 9.2 L ⊗ the X‐ray emission is compatible with being entirely due to discrete sources. Above log (L B ) ≈ 11.2 L o˙ no galaxy with only discrete emission is found. We further confirm earlier findings that L x is strongly correlated with L B . Over the entire data range the slope is found to be 2.23 (± 0.12). We also find a luminosity dependence of this correlation. Below log L x = 40.5 erg s ‐1 it is consistent with a slope of 1, as expected from discrete emission. Above this value the slope is close to 2, as expected from gaseous emission. Comparing the distribution of X‐ray luminosities with the models of Ciotti et al. leads to the conclusion that the vast majority of early‐type galaxies are in the wind or outflow phase. Some of the galaxies may have already experienced the transition to the inflow phase. They show X‐ray luminosities in excess of the value predicted by cooling flow models with the largest plausible standard supernova rates. A possible explanation for these super X‐ray‐luminous galaxies is suggested by the smooth transition in the L x ‐‐ L B plane from galaxies to clusters of galaxies. Gas connected to the group environment might cause the X‐ray overluminosity.