A deficit of ultraluminous X-ray sources in luminous infrared galaxies
Abstract
Luminous infrared galaxies (LIRGs) are amongst the most energetic star-forming galaxies, producing total infrared luminosities > 10^{11} L_{⊙} that imply star formation rates (SFR) in excess of 10 M_{⊙} yr^{-1}. Given the close relationship between the number of ultraluminous X-ray sources (ULXs) and SFR, we might therefore expect to find larger populations of ULXs in LIRGs than in field galaxies. Here, we present the results of a study of the ULX population in 17 nearby (D < 60 Mpc) LIRGs, using Chandra data. Only 53 ULXs have been detected, compared to an expectation of ∼500 ULXs from studies of field galaxies (Swartz et al. 2011). We investigate the origin of this large deficit in the number of ULXs by several means. For instance, X-ray luminosity functions confirm the deficit and also reveal a possible break at a luminosity of ∼2×10^{39} erg s^{-1}. The physical interpretation for the deficit will be discussed. In addition, a study of the evolution of the ULX spectra with luminosity based on stacked X-ray spectra shows a possible transition from ∼Eddington to super-Eddington states, consistent with the ULXs being a population of ∼10 solar mass black holes.
- Publication:
-
The X-ray Universe 2014
- Pub Date:
- July 2014
- Bibcode:
- 2014xru..confE.120L