Spectral properties of XRBs in dusty early-type galaxies
Abstract
We present spectral properties of a total of 996 discrete X-ray sources resolved in a sample of 23 dusty early-type galaxies selected from different environments. The combined X-ray luminosity function of all the 996 sources within the optical D25 of the sample galaxies is well described by a broken power law with a break at 2.71 × 1038 erg s-1 and is close to the Eddington limit for a 1.4M⊙ neutron star. Out of the 996, about 63% of the sources have their X-ray luminosities in the range between few ×1037 to 2.0 × 1039 erg s-1 and are like normal LMXBs; about 15-20% with luminosities <few × 1037 erg s-1 are either super-soft or very-soft sources; while the remainder represents ULXs, HMXBs or unrelated heavily absorbed harder sources. More XRBs have been detected in the galaxies from isolated regions while those from rich groups and clusters host very few sources. The X-ray color-color plot for these sources has enabled us to classify them as SNRs, LMXBs, HMXBs and heavily absorbed AGNs. The composite X-ray spectra of the resolved sources within D25 region of each of the galaxies are best represented by a power law with the average photon spectral index close to 1.65. The contribution of the resolved sources to the total X-ray luminosity of their host is found to vary greatly, in the sense that, in galaxies like NGC 3379 the XRB contribution is about 81% while for NGC 5846 it is only 2%. A correlation has been evidenced between the cumulative X-ray luminosity of the resolved sources against the star formation rate and the Ks band luminosity of the target galaxies indicating their primordial origin.
- Publication:
-
New Astronomy
- Pub Date:
- July 2013
- DOI:
- 10.1016/j.newast.2012.10.005
- arXiv:
- arXiv:1205.6057
- Bibcode:
- 2013NewA...21....1V
- Keywords:
-
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 15 Pages, 6 Figures &