Revisiting the Lx-SFR Relationship in Nearby Galaxies: The Effectof HMXBVariability
Abstract
High mass X-ray binaries (HMXBs) are a natural by-product of recent massive star formation in normal galaxies. Not surprisingly, the number of HMXBs and their typical X-ray luminosities (Lx) tend to increase in galaxies with higher star formation rates (SFRs). However, to take the qualitatively observed Lx-SFR relationship and extract meaningful constraints on the evolutionary processes by which massive binaries survive compact object formation and establish mass transfer, the Lx-SFR relationship must be properly calibrated. HMXBs are inherently X-ray variable (Lx can change by factors of a few, up to orders of magnitude) and different techniques for measuring the SFR can yield results that are discrepant by up to an order of magnitude. Determining the X-ray flux variability of HMXBs in NGC 300 will allow for a more precise refinement of the Lx-SFR relationship. We investigate multiple epochs of the Lx-SFR relationship in the nearby galaxies NGC 300 and NGC 2403. We calculated the SFRs in each galaxy using two different approaches: (1) by combining images from Galaxy Evolution Explorer (GALEX, far ultraviolet) and the Spitzer Space Telescope (infrared), and (2) by using Hubble Space Telescope images of resolved stellar populations. We then measured the X-ray luminosities of each HMXB using imaging from the Chandra X-ray Observatory. X-ray variability is more frequently observed in lower-luminosity HMXBs; thus the overall shape of the Lx-SFR relationship depends sensitively on the assumed cut-off (or completeness) limit of each galaxy.
- Publication:
-
American Astronomical Society Meeting Abstracts #235
- Pub Date:
- January 2020
- Bibcode:
- 2020AAS...23517016A