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Title: EVIDENCE FOR ELEVATED X-RAY EMISSION IN LOCAL LYMAN BREAK GALAXY ANALOGS

Our knowledge of how X-ray emission scales with star formation at the earliest times in the universe relies on studies of very distant Lyman break galaxies (LBGs). In this paper, we study the relationship between the 2-10 keV X-ray luminosity (L{sub X}), assumed to originate from X-ray binaries (XRBs), and star formation rate (SFR) in ultraviolet (UV) selected z < 0.1 Lyman break analogs (LBAs). We present Chandra observations for four new Galaxy Evolution Explorer selected LBAs. Including previously studied LBAs, Haro 11 and VV 114, we find that LBAs demonstrate L{sub X}/SFR ratios that are elevated by {approx}1.5{sigma} compared to local galaxies, similar to the ratios found for stacked LBGs in the early universe (z > 2). Unlike some of the composite LBAs studied previously, we show that these LBAs are unlikely to harbor active galactic nuclei, based on their optical and X-ray spectra and the spatial distribution of the X-rays in three spatially extended cases. Instead, we expect that high-mass X-ray binaries (HMXBs) dominate the X-ray emission in these galaxies, based on their high specific SFRs (sSFRs {identical_to} SFR/M{sub *} {>=} 10{sup -9} yr{sup -1}), which suggest the prevalence of young stellar populations. Since both UV-selected populations (LBGsmore » and LBAs) have lower dust attenuations and metallicities compared to similar samples of more typical local galaxies, we investigate the effects of dust extinction and metallicity on the L{sub X}/SFR for the broader population of galaxies with high sSFRs (>10{sup -10} yr{sup -1}). The estimated dust extinctions (corresponding to column densities of N{sub H} < 10{sup 22} cm{sup -2}) are expected to have insignificant effects on observed L{sub X}/SFR ratio for the majority of galaxy samples. We find that the observed relationship between L{sub X}/SFR and metallicity appears consistent with theoretical expectations from XRB population synthesis models. Therefore, we conclude that lower metallicities, related to more luminous HMXBs such as ultraluminous X-ray sources, drive the elevated L{sub X}/SFR observed in our sample of z < 0.1 LBAs. The relatively metal-poor, active mode of star formation in LBAs and distant z > 2 LBGs may yield higher total HMXB luminosity than found in typical galaxies in the local universe.« less
Authors:
; ; ;  [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6]
  1. NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771 (United States)
  2. Observatorio do Valongo, Universidade Federal do Rio de Janeiro, Ladeira Pedro Antonio 43, Saude, Rio de Janeiro-RJ, CEP 22240-060 (Brazil)
  3. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  4. Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States)
  5. Department of Astronomy, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712 (United States)
  6. Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027 (United States)
Publication Date:
OSTI Identifier:
22133872
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 774; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BINARY STARS; COSMIC DUST; COSMIC X-RAY SOURCES; DENSITY; GALAXY NUCLEI; KEV RANGE; LUMINOSITY; MILKY WAY; PHOTON EMISSION; RED SHIFT; SPATIAL DISTRIBUTION; STARS; ULTRAVIOLET RADIATION; UNIVERSE; X RADIATION; X-RAY SOURCES; X-RAY SPECTRA