Black Holes and Neutron Stars in Nearby Galaxies: Insights from NuSTAR
Abstract
With the launch of the first focusing hard X-ray (E >10 keV) telescope, NuSTAR, critical diagnostics can be applied outside the Milky Way in this crucial bandpass. Determining the ratio of X-ray binaries (XRBs) that are black holes or neutron stars reveals clues about the formation and evolution of binary systems in different galactic environments. However, identifying the compact object types of extragalactic XRBs is problematic due to the similarity and/or degeneracy of their spectra. We analyze a NuSTAR-selected sample of 12 nearby galaxies within 5 Mpc that represent a range of star formation rates (0.1 - 10 M⊙ yr-1) and stellar masses (109-11 M⊙). Using X-ray color-color and color-intensity diagnostics we classify sources by their accretion states and compact object types. We find that most sources are black holes accreting in the intermediate state. We study the 4-25 keV and 12-25 keV X-ray luminosity functions of our sample scaled by specific star formation rate and compare with the 0.5-8 keV analogues from Chandra and XMM-Newton. The combined 12-25 keV X-ray luminosity function shows a break above 1039 erg s-1 indicating the ultraluminous X-ray source regime. We also present the relationship between the 12-25 keV X-ray point source luminosities and specific star formation rates of our galaxy sample.
- Publication:
-
American Astronomical Society Meeting Abstracts #231
- Pub Date:
- January 2018
- Bibcode:
- 2018AAS...23122706V