X-Ray Binary Luminosity Function Scaling Relations in Elliptical Galaxies: Evidence for Globular Cluster Seeding of Low-mass X-Ray Binaries in Galactic Fields

Lehmer, Bret; Ferrell, A. P.; Doore, Keith; Eufrasio, Rafael T.; Monson, Erik B.; Alexander, D. M.; Basu-Zych, Antara; Brandt, W. N.; Sivakoff, Gregory R.; Tzanavaris, P.; Yukita, Mihoko; Fragos, Tassos; Ptak, Andrew

doi:10.3847/1538-4365/ab9175

Cited by 31 publications

(30 citation statements)

References 91 publications

(135 reference statements)

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“…Thus, LMXBs are generally correlated with the integrated stellar light (L k ) and, by extension, with the total stellar mass of the host galaxies because of the long evolutionary timescales of the low-mass (< 1 M ) donor star in the binary system (Gilfanov 2004;Boroson et al 2011;Zhang et al 2012;Lehmer et al 2019). This relation seems to be enhanced by the globular cluster (GC) specific frequency, S N = N GC 10 0.4(M T V +15) , where gravitationally dissolving GCs seed LMXBs into the galactic field, which join the LMXBs formed in situ (Irwin 2005;Zhang et al 2011;Boroson et al 2011;Zhang et al 2012;Lehmer et al 2020). In high-mass X-ray binaries (HMXBs) the donor star is a massive O/B star (> 8 M ) that fuels accretion onto the CO with intense stellar winds.…”

Section: Introductionmentioning

confidence: 99%

Decomposition of galactic X-ray emission with PHOX

Vladutescu-Zopp

Biffi

Dolag

2023

A&A

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Context. X-ray observations of galaxies with high spatial resolution instruments such as Chandra have revealed that major contributions to their diffuse emission originate from X-ray-bright point sources in the galactic stellar field. It has been established that these point sources, called X-ray binaries, are accreting compact objects with stellar donors in a binary configuration. They are classified according to the predominant accretion process: wind-fed in the case of high-mass donors and Roche-lobe mass transfer in the case of low-mass donors. Observationally, it is challenging to reliably disentangle these two populations from each other because of their similar spectra. Aims. We provide a numerical framework with which spatially and spectrally accurate representations of X-ray binary populations can be studied from hydrodynamical cosmological simulations. We construct average spectra, accounting for a hot gas component, and verify the emergence of observed scaling relations between galaxy-wide X-ray luminosity (L X ) and stellar mass (M * ) and between L X and the star-formation rate (SFR). Methods. Using simulated galaxy halos extracted from the (48 h −1 cMpc) 3 volume of the Magneticum Pathfinder cosmological simulations at z = 0.07, we generate mock spectra with the X-ray photon-simulator Phox. We extend the Phox code to account for the stellar component in the simulation and study the resulting contribution in composite galactic spectra. Results. Well-known X-ray binary scaling relations with galactic SFR and M * emerge self-consistently, verifying our numerical approach. Average X-ray luminosity functions are perfectly reproduced up to the one-photon luminosity limit. Comparing our resulting L X − SFR − M * relation for X-ray binaries with recent observations of field galaxies in the Virgo galaxy cluster, we find significant overlap. Invoking a metallicity-dependent model for high-mass X-ray binaries yields an anticorrelation between mass-weighted stellar metallicity and SFR-normalized luminosity. The spatial distribution of high-mass X-ray binaries coincides with star-formation regions of simulated galaxies, while low-mass X-ray binaries follow the stellar mass surface density. X-ray binary emission is the dominant contribution in the hard X-ray band (2-10 keV) in the absence of an actively accreting central super-massive black hole, and it provides a ∼ 50% contribution in the soft X-ray band (0.5-2 keV), rivaling the hot gas component. Conclusions. We conclude that our modeling remains consistent with observations despite the uncertainties connected to our approach. The predictive power and easily extendable framework hold great value for future investigations of galactic X-ray spectra.

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Section: Introductionmentioning

confidence: 99%

Decomposition of galactic X-ray emission with PHOX

Vladutescu-Zopp

Biffi

Dolag

2023

A&A

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“…Globular clusters are known to contain XRBs (e.g. Hut et al 1992;Becker et al 2003;Maccarone et al 2003), and it has been speculated that their capture may contribute to the LMXB population in galaxies (Lehmer et al 2020). With a stellar mass of ∼3×10 6 M , Nikhuli is more massive than most globular clusters.…”

Section: Discussionmentioning

confidence: 99%

“…However, this expectation is based upon field star statistics. The number of LMXBs in globular clusters is ∼10 3 times greater than in the field (Sivakoff et al 2007;Kim et al 2013;Lehmer et al 2020). As a former nuclear star cluster, Nikhuli may thus have a ∼7% chance of being an LMXB, if globular clusters and nuclear star clusters have a similar LMXB formation efficiency.…”

Section: X-ray Binariesmentioning

confidence: 96%

Potential Black Hole Seeding of the Spiral Galaxy NGC 4424 via an Infalling Star Cluster

Graham,

Soria,

Ciambur

et al. 2021

Preprint

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Galaxies can grow through their mutual gravitational attraction and subsequent union. While orbiting a regular high-surface-brightness galaxy, the body of a low-mass galaxy can be stripped away. However, the stellar heart of the infalling galaxy, if represented by a tightly bound nuclear star cluster, is more resilient. From archival Hubble Space Telescope images, we have discovered a red, tidallystretched star cluster positioned ∼5 (∼400 pc in projection) from, and pointing toward the center of, the post-merger spiral galaxy NGC 4424. The star cluster, which we refer to as 'Nikhuli', has a near-infrared luminosity of (6.88 ± 1.85) × 10 6 L ,F 160W and likely represents the nucleus of a captured/wedded galaxy. Moreover, from our Chandra X-ray Observatory image, Nikhuli is seen to contain a high-energy X-ray point source, with L 0.5−8 keV = 6.31 +7.50 −3.77 × 10 38 erg s −1 (90% confidence). We argue that this is more likely to be an active massive black hole than an X-ray binary. Lacking an outward-pointing comet-like appearance, the stellar structure of Nikhuli favors infall rather than the ejection from a gravitational-wave recoil event. A minor merger with a low-mass early-type galaxy may have sown a massive black hole, aided an X-shaped pseudobulge, and be sewing a small bulge. The stellar mass and the velocity dispersion of NGC 4424 predict a central black hole of (0.6-1.0)×10 5 M , similar to the expected intermediate-mass black hole in Nikhuli, and suggestive of a black hole supply mechanism for bulgeless late-type galaxies. We may potentially be witnessing black hole seeding by capture and sinking, with a nuclear star cluster the delivery vehicle.

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“…The LMXB population of a galaxy is itself composed of two subpopulations: one formed in globular clusters and the other in the field of the galaxy. Due to the higher stellar density and higher rate of stellar encounters in globular clusters, they are ∼1000 times more efficient than field stars at forming LMXBs, per unit stellar mass (Sivakoff et al 2007;Kim et al 2013;Lehmer et al 2020). The HMXBs, on the other hand, are not known to get such a boost (Garofali et al 2012;Johns Mulia et al 2019); they are generally not formed from close encounters and captures like LMXBs, but instead come from the initial fragmentation of molecular clouds.…”

Section: X-ray Contamination: X-ray Binariesmentioning

confidence: 99%

Central X-ray point-sources found to be abundant in low-mass, late-type galaxies predicted to contain an intermediate-mass black hole

Graham,

Soria,

Davis

et al. 2021

Preprint

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Building upon three late-type galaxies in the Virgo cluster with both a predicted black hole mass of less than ∼10 5 M and a centrally-located X-ray point-source, we reveal 11 more such galaxies, more than tripling the number of active intermediate-mass black hole candidates among this population. Moreover, this amounts to a ∼36±8% X-ray detection rate (despite the sometimes high, X-ray-absorbing, H I column densities), compared to just 10±5% for (the largely H I-free) dwarf earlytype galaxies in the Virgo cluster. The expected contribution of X-ray binaries from the galaxies' inner field stars is negligible. Moreover, given that both the spiral and dwarf galaxies contain nuclear star clusters, the above inequality appears to disfavor X-ray binaries in nuclear star clusters. The higher occupation, or rather detection, fraction among the spiral galaxies may instead reflect an enhanced cool gas/fuel supply and Eddington ratio. Indeed, four of the 11 new X-ray detections are associated with known LINERs or LINER/H II composites. For all (four) of the new detections for which the X-ray flux was strong enough to establish the spectral energy distribution in the Chandra band, it is consistent with power-law spectra. Furthermore, the X-ray emission from the source with the highest flux (NGC 4197: L X ≈ 10 40 erg s −1 ) suggests a non-stellar-mass black hole if the X-ray spectrum corresponds to the 'low/hard state'. Follow-up observations to further probe the black hole masses, and prospects for spatially resolving the gravitational spheres-of-influence around intermediate-mass black holes, are reviewed in some detail.

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X-Ray Binary Luminosity Function Scaling Relations in Elliptical Galaxies: Evidence for Globular Cluster Seeding of Low-mass X-Ray Binaries in Galactic Fields

Abstract: Andrew (2020) 'X-ray binary luminosity function scaling relations in elliptical galaxies : evidence for globular cluster seeding of low-mass x-ray binaries in galactic elds.', Astrophysical journal supplement series., 248 (2). p. 31.

Cited by 31 publications

References 91 publications

Decomposition of galactic X-ray emission with PHOX

Decomposition of galactic X-ray emission with PHOX

Potential Black Hole Seeding of the Spiral Galaxy NGC 4424 via an Infalling Star Cluster

Central X-ray point-sources found to be abundant in low-mass, late-type galaxies predicted to contain an intermediate-mass black hole

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