Abstract
ABSTRACT We present an analysis of the ultraluminous X-ray source (ULX) population in 75 Virgo cluster late-type galaxies, including all those with a star formation rate ≳1 M⊙ yr−1 and a representative sample of the less star forming ones. This study is based on 110 observations obtained over 20 yr with the Chandra X-ray Observatory Advanced Camera for Imaging Spectroscopy. As part of a Large Chandra Program, new observations were obtained for 52 of these 75 galaxies. The data are complete to a sensitivity of ≈1039 erg s−1, with a typical detection limit of ≈3 × 1038 erg s−1 for the majority of the sources. The catalogue contains about 80 ULXs (0.3–10 keV luminosity >1039 erg s−1), and provides their location, observed flux, de-absorbed luminosity, and (for the 25 most luminous ones) simple X-ray spectral properties. We discuss the ULX luminosity function in relation to the mass and star formation rate of the sample galaxies. We show that recent models of low-mass plus high-mass X-ray binary populations (scaling with stellar mass and star formation rate, respectively) are mostly consistent with our observational results. We tentatively identify the most luminous X-ray source in the sample (a source in IC 3322A with LX ≈ 6 × 1040 erg s−1) as a recent supernova or its young remnant. The properties of the sample galaxies (morphologies, stellar masses, star formation rates, total X-ray luminosities from their point-source population) are also summarized.
Highlights
The population properties of compact X-ray sources are a tracer of star formation rate (SFR) and stellar mass ( ∗) (Grimm et al 2003; Gilfanov 2004; Mineo et al 2012a; Fragos et al 2013a; Lehmer et al 2019)
2.1 Selection criteria The selection of targets for our study resulted from a necessary compromise between various ideal requirements: a large number of galaxies, with high SFR, and a good sampling of all morphological types from early-type to late-type spirals and with a sufficiently large range of specific SFR
The main reason for computing a total stellar mass is that we shall estimate the number of low mass X-ray binaries (LMXBs) ultraluminous X-ray source (ULX) per unit stellar mass in our sample of star-forming galaxies (Section 4.4, Section 5), and compare it both with the value found in the early-type galaxies of the AMUSE sample (Plotkin et al 2014) and with theoretical predictions of X-ray binary populations
Summary
The population properties of compact X-ray sources are a tracer of star formation rate (SFR) and stellar mass ( ∗) The AMUSE X-ray survey provided an exceptional view of nuclear BH activity and Eddington ratio in “normal” early-type galaxies (Gallo et al 2010; Miller et al 2012; Graham & Soria 2019), as well as a sample of bright off-nuclear sources. For centrally-located, i.e., nuclear, BHs, a Chandra study can reveal, for example, the difference in the Eddington ratio distribution between galaxies dominated by hot gas (early-type) or cold gas (late-type) It can reveal the presence of candidate X-ray-bright intermediate-mass BHs in the nuclei of spiral galaxies with a small bulge or no bulge (as predicted by galaxy/BH scaling relations), which can be the subject of subsequent multiband investigations (Chilingarian et al 2018; Mezcua et al 2018). A census of the nuclear sources, a study of the diffuse X-ray emission in the most star-forming galaxies, and an investigation of the multiband counterparts will be presented in further work
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