An Empirical Framework Characterizing the Metallicity and Star-formation History Dependence of X-Ray Binary Population Formation and Emission in Galaxies

Authors

Bret D. Lehmer, University of Arkansas, FayettevilleFollow
Erik B. Monson, University of Arkansas, FayettevilleFollow
Rafael T. Eufrasio, University of Arkansas, Fayetteville
Amirnezam Amiri, University of Arkansas, Fayetteville
Keith Doore, University of Arkansas, FayettevilleFollow
Antara Basu-Zych, NASA Goddard Space Flight Center
Kristen Garofali, NASA Goddard Space Flight Center
Lidia Oskinova, Universitat Potsdam
Jeff J. Andrews, University of Florida
Vallia Antoniou, Texas Tech University
Robel Geda, Princeton University
Jenny E. Greene, Princeton University
Konstantinos Kovlakas, Universite de Geneve
Margaret Lazzarini, California State University, Los Angeles
Chris T. Richardson, Elon University

Document Type

Article

Publication Date

12-2024

Keywords

FUNCTION SCALING RELATIONS; ACTIVE GALACTIC NUCLEI; H II REGIONS; LUMINOSITY FUNCTIONS; STELLAR POPULATIONS; GLOBULAR-CLUSTERS; OXYGEN ABUNDANCES; MULTIWAVELENGTH CHARACTERIZATION; CHANDRA OBSERVATIONS; INFRARED-EMISSION

Abstract

We present a new empirical framework modeling the metallicity and star formation history (SFH) dependence of X-ray luminous (L ≳ 10³⁶ erg s⁻¹) point-source population X-ray luminosity functions (XLFs) in normal galaxies. We expect that the X-ray point-source populations are dominated by X-ray binaries (XRBs), with contributions from supernova remnants near the low luminosity end of our observations. Our framework is calibrated using the collective statistical power of 3731 X-ray detected point sources within 88 Chandra-observed galaxies at D ≲ 40 Mpc that span broad ranges of metallicity (Z ≈ 0.03–2 Z_⊙), SFH, and morphology (dwarf irregulars, late types, and early types). Our best-fitting models indicate that the XLF normalization per unit stellar mass declines by ≈2–3 dex from 10 Myr to 10 Gyr, with a slower age decline for low-metallicity populations. The shape of the XLF for luminous X-ray sources (L ≳ 10³⁸ erg s⁻¹) significantly steepens with increasing age and metallicity, while the lower-luminosity XLF appears to flatten with increasing age. Integration of our models provides predictions for X-ray scaling relations that agree very well with past results presented in the literature, including, e.g., the L_X–SFR–Z relation for high-mass XRBs in young stellar populations as well as the L_X/M_⋆ ratio observed in early-type galaxies that harbor old populations of low-mass XRBs. The model framework and data sets presented in this paper further provide unique benchmarks that can be used for calibrating binary population synthesis models.

Citation

Lehmer, B. D., Monson, E. B., Eufrasio, R. T., Amiri, A., Doore, K., Basu-Zych, A., Garofali, K., Oskinova, L., Andrews, J. J., Antoniou, V., Geda, R., Greene, J. E., Kovlakas, K., Lazzarini, M., & Richardson, C. T. (2024). An Empirical Framework Characterizing the Metallicity and Star-formation History Dependence of X-Ray Binary Population Formation and Emission in Galaxies. Astrophysical Journal, 977 (2), 189. https://doi.org/10.3847/1538-4357/ad8de7

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This work is licensed under a Creative Commons Attribution 4.0 International License.