Old and Young X-Ray Point Source Populations in Nearby Galaxies

By E. Colbert, T. Heckman, A. Ptak, D. Strickland, K. Weaver. 2003

181 citations recorded by the source corpus.

We have analyzed Chandra ACIS observations of 32 nearby spiral and elliptical galaxies and present the results of 1441 X-ray point sources that were detected in these galaxies. The total point-source X-ray (0.3-8.0 keV) luminosity LXP is well correlated with the B-band, K-band, and FIR+UV luminosities of spiral host galaxies and is well correlated with the B-band and K-band luminosities of elliptical galaxies. This suggests an intimate connection between LXP and both the old and young stellar populations, for which K and FIR+UV luminosities are reasonable proxies for the galaxy mass M and star formation rate SFR. We derive proportionality constants α = 1.3 × 1029 ergs s-1 M and β = 0.7 × 1039 ergs s-1 (M☉ yr-1)-1, which can be used to estimate the old and young components from M and SFR, respectively. The cumulative X-ray luminosity functions for the point sources have significantly different slopes. For the spiral and starburst galaxies, γ ≈ 0.6-0.8, and for the elliptical galaxies, γ ≈ 1.4. This implies that the most luminous point sources—those with LX ≳ 1038 ergs s-1—dominate LXP for the spiral and starburst galaxies. Most of the point sources have X-ray colors that are consistent with soft-spectrum (photon index Γ ~ 1-2) low-mass X-ray binaries, accretion-powered black hole high-mass X-ray binaries (BH HMXBs), or ultraluminous X-ray sources (ULXs, also known as IXOs). We rule out hard-spectrum neutron star HMXBs (e.g., accretion-powered X-ray pulsars) as contributing much to LXP. Thus, for spirals, LXP is dominated by ULXs and BH HMXBs. We find no discernible difference between the X-ray colors of ULXs (LX ≥ 1039 ergs s-1) in spiral galaxies and point sources with LX ≈ 1038-1039 ergs s-1. We estimate that ≳20% of all ULXs found in spirals originate from the older (Population II) stellar populations, indicating that many of the ULXs that have been found in spiral galaxies are in fact Population II ULXs, like those in elliptical galaxies. We find that LXP depends linearly (within uncertainties) on both M and SFR for our sample galaxies (M ≲ 1011 M☉ and SFR ≲ 10 M☉ yr-1).

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/0cc1de3814373962f5786caca892bac6319d2fde

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In Astronomy and Astrophysics

1. D. M. Alexander
2. W. N. Brandt
3. R. Ivison
4. L. Hernquist
5. P. Hopkins
6. I. Smail
7. S. Chapman
8. R. Hickox

In Nuclear and High Energy Physics

1. D. M. Alexander
2. W. N. Brandt
3. R. Ivison
4. I. Smail
5. S. Chapman
6. A. Blain
7. F. E. Bauer
8. G. Fabbiano

Citations in the corpus

• Star Formation in the Milky Way and Nearby Galaxies (2012, background): “Calibrations of the SFR in terms of X-ray luminosity and stellar mass have been published by Colbert et al. (2004) and Lehmer et al. (2010).”
• Spectral Energy Distributions of Hard X-Ray Selected Active Galactic Nuclei in the XMM-Newton Medium Deep Survey (2007, unknown): “Star-forming galaxies are typically characterized by luminosities below 1042 erg s 1 and show steep X-ray spectral slopes (Kim et al. 1992a, 1992b; Colbert et al. 2004; Persic et al. 2004).”
• The Ultraluminous X-Ray Source Population from the Chandra Archive of Galaxies (2004, methodology): “More recently, Colbert et al. (2004) show that X-ray point source populations can also be described as a superposition of contributions from these two stellar populations.”
• Ultraluminous X-ray sources in the Chandra and XMM-Newton era (2011, result): “…and ULXs in ellipticals are the high-luminosity tail of LMXBs. SeveralChandra and XMM-Newtonsurveys of discrete Xray sources in nearby galaxies have produced consistent results in agreement with this interpretation (Grimm et al. 2003; Colbert et al. 2004; Swartz et al. 2004; Walton et al. 2011).”
• Populations of X-Ray Sources in Galaxies (2006, methodology): “…by the good FIR-X-ray correlations and by the work on the XLFs of star-forming galactic populations discussed earlier in this review (Fabbiano & Shapley 2002; Grimm, Gilfanov & Sunyaev 2003; Ranalli, Comastri & Setti 2003; Colbert et al. 2004; Gilfanov, Grimm & Sunyaev 2004a; Persic et al. 2004).”
• The Fall of Active Galactic Nuclei and the Rise of Star-forming Galaxies: A Close Look at the Chandra Deep Field X-Ray Number Counts (2004, background): “From X-ray observations in the local universe, purely star-forming galaxies do not appear to have X-ray luminosities exceeding L0:5 8:0 keV 3 ; 1042 ergs s 1 and rarely, if ever, have intrinsic absorption column densities above NH 1022 cm 2 (e.g., Fabbiano 1989; Colbert et al. 2004).”
• A Significant Population of Very Luminous Dust-Obscured Galaxies at Redshift z ~ 2 (2008, background): “This luminosity is more typical of AGN than of star-forming systems (e.g., Colbert et al. 2004).”
• REVISITING WITH CHANDRA THE SCALING RELATIONS OF THE X-RAY EMISSION COMPONENTS (BINARIES, NUCLEI, AND HOT GAS) OF EARLY-TYPE GALAXIES (2010, background): “The linear relation between the integrated X-ray luminosity of the LMXB population and the stellar K-band luminosity of early-type galaxies is well established (e.g., White et al. 2002; Colbert et al. 2004; Kim & Fabbiano 2004; David et al. 2006).”
• THE 4 Ms CHANDRA DEEP FIELD-SOUTH NUMBER COUNTS APPORTIONED BY SOURCE CLASS: PERVASIVE ACTIVE GALACTIC NUCLEI AND THE ASCENT OF NORMAL GALAXIES (2012, background): “…are expected to provide dominant contributions (i.e., high-mass and low-mass X-ray binaries, supernovae and their remnants, hot gas from starburst flows, and young stars; Colbert et al. 2004; Iwasawa et al. 2009, 2011; Lehmer et al. 2010; Pereira-Santaella et al. 2011; Mineo et al. 2012).”
• The X-Ray Spectral Properties of SCUBA Galaxies (2005, background): “However, since SMGs are potentially massive galaxies undergoing intense star formation, they could have a large population of high-mass X-ray binaries (HMXBs), which may have comparatively flat X-ray spectral slopes (e.g., neutron star HMXBs can have 0:5 1:0; Colbert et al. 2004).”
• A CHANDRA PERSPECTIVE ON GALAXY-WIDE X-RAY BINARY EMISSION AND ITS CORRELATION WITH STAR FORMATION RATE AND STELLAR MASS: NEW RESULTS FROM LUMINOUS INFRARED GALAXIES (2010, background): “…shown that the X-ray point source emission from relatively young ( <∼ 100 Myr) high-mass X-ray binaries (HMXBs) and older ( >∼ 1 Gyr) low-mass X-ray binaries (LMXBs) correlate well with galaxy SFR and stellar mass (M⋆), respectively (e.g., Grimm et al. 2003; Colbert et al. 2004; Gilfanov 2004).”