Abstract:Based on a homogeneous set of X-ray, infrared and ultraviolet observations
from Chandra, Spitzer, GALEX and 2MASS archives, we study populations of
high-mass X-ray binaries (HMXBs) in a sample of 29 nearby star-forming galaxies
and their relation with the star formation rate (SFR). In agreement with
previous results, we find that HMXBs are a good tracer of the recent star
formation activity in the host galaxy and their collective luminosity and
number scale with the SFR, in particular, Lx~2.6 10^{39} SFR. Howe… Show more
“…4. Taking into account the luminosity detection limit for each galaxy, and the XRB XLFs of Mineo et al (2012) and Gilfanov (2004) for late-and early-type galaxies, the probability of obtaining stochastically L X values equal or higher to those observed is generally low, but increases for about half of the galaxies if there is strong XRB variability. 5.…”
Section: Discussionmentioning
confidence: 99%
“…Some of these stars will be HMXB secondaries: Indeed several studies of late-type galaxies have established strong correlations between galaxy-wide X-ray luminosity and total SFR (e.g., Bauer et al 2002;Grimm et al 2003;Ranalli et al 2003;Gilfanov et al 2004a;Persic et al 2004;Hornschemeier et al 2005;Persic & Rephaeli 2007;Lehmer et al 2008Lehmer et al , 2010Mineo et al 2012). On the other hand, in quiescent (morphologically elliptical/S0) galaxies, longer-lived (1 Gyr) low-mass stars trace the total stellar mass accumulated over a galaxy's lifetime.…”
We obtain total galaxy X-ray luminosities, L X , originating from individually detected point sources in a sample of 47 galaxies in 15 compact groups of galaxies (CGs). For the great majority of our galaxies, we find that the detected point sources most likely are local to their associated galaxy, and are thus extragalactic X-ray binaries (XRBs) or nuclear active galactic nuclei (AGNs). For spiral and irregular galaxies, we find that, after accounting for AGNs and nuclear sources, most CG galaxies are either within the ±1σ scatter of the Mineo et al. L X -star formation rate (SFR) correlation or have higher L X than predicted by this correlation for their SFR. We discuss how these "excesses" may be due to low metallicities and high interaction levels. For elliptical and S0 galaxies, after accounting for AGNs and nuclear sources, most CG galaxies are consistent with the Boroson et al. L X -stellar mass correlation for low-mass XRBs, with larger scatter, likely due to residual effects such as AGN activity or hot gas. Assuming non-nuclear sources are low-or high-mass XRBs, we use appropriate XRB luminosity functions to estimate the probability that stochastic effects can lead to such extreme L X values. We find that, although stochastic effects do not in general appear to be important, for some galaxies there is a significant probability that high L X values can be observed due to strong XRB variability.
“…4. Taking into account the luminosity detection limit for each galaxy, and the XRB XLFs of Mineo et al (2012) and Gilfanov (2004) for late-and early-type galaxies, the probability of obtaining stochastically L X values equal or higher to those observed is generally low, but increases for about half of the galaxies if there is strong XRB variability. 5.…”
Section: Discussionmentioning
confidence: 99%
“…Some of these stars will be HMXB secondaries: Indeed several studies of late-type galaxies have established strong correlations between galaxy-wide X-ray luminosity and total SFR (e.g., Bauer et al 2002;Grimm et al 2003;Ranalli et al 2003;Gilfanov et al 2004a;Persic et al 2004;Hornschemeier et al 2005;Persic & Rephaeli 2007;Lehmer et al 2008Lehmer et al , 2010Mineo et al 2012). On the other hand, in quiescent (morphologically elliptical/S0) galaxies, longer-lived (1 Gyr) low-mass stars trace the total stellar mass accumulated over a galaxy's lifetime.…”
We obtain total galaxy X-ray luminosities, L X , originating from individually detected point sources in a sample of 47 galaxies in 15 compact groups of galaxies (CGs). For the great majority of our galaxies, we find that the detected point sources most likely are local to their associated galaxy, and are thus extragalactic X-ray binaries (XRBs) or nuclear active galactic nuclei (AGNs). For spiral and irregular galaxies, we find that, after accounting for AGNs and nuclear sources, most CG galaxies are either within the ±1σ scatter of the Mineo et al. L X -star formation rate (SFR) correlation or have higher L X than predicted by this correlation for their SFR. We discuss how these "excesses" may be due to low metallicities and high interaction levels. For elliptical and S0 galaxies, after accounting for AGNs and nuclear sources, most CG galaxies are consistent with the Boroson et al. L X -stellar mass correlation for low-mass XRBs, with larger scatter, likely due to residual effects such as AGN activity or hot gas. Assuming non-nuclear sources are low-or high-mass XRBs, we use appropriate XRB luminosity functions to estimate the probability that stochastic effects can lead to such extreme L X values. We find that, although stochastic effects do not in general appear to be important, for some galaxies there is a significant probability that high L X values can be observed due to strong XRB variability.
We investigate the population of high-redshift (3 z < 6) AGN selected in the two deepest X-ray surveys, the 7 Ms Chandra Deep Field-South and 2 Ms Chandra Deep Field-North. Their outstanding sensitivity and spectral characterization of faint sources allow us to focus on the sub-L * regime (logL X 44), poorly sampled by previous works using shallower data, and the obscured population. Taking fully into account the individual photometric-redshift probability distribution functions, the final sample consists of ≈ 102 X-ray selected AGN at 3 z < 6. The fraction of AGN obscured by column densities logN H > 23 is ∼ 0.6 − 0.8, once incompleteness effects are taken into account, with no strong dependence on redshift or luminosity. We derived the high-redshift AGN number counts down to F 0.5−2 keV = 7 × 10 −18 erg cm −2 s −1 , extending previous results to fainter fluxes, especially at z > 4. We put the tightest constraints to date on the low-luminosity end of AGN luminosity function at high redshift. The space-density, in particular, declines at z > 3 at all luminosities, with only a marginally steeper slope for low-luminosity AGN. By comparing the evolution of the AGN and galaxy densities, we suggest that such a decline at high luminosities is mainly driven by the underlying galaxy population, while at low luminosities there are hints of an intrinsic evolution of the parameters driving nuclear activity. Also, the black-hole accretion rate density and star-formation rate density, which are usually found to evolve similarly at z 3, appear to diverge at higher redshifts.
“…This requires to establish the nature of all X-ray sources, which remains difficult as the spatial resolution of Chandra and of the Hubble Space Telescope are not sufficient to unambiguously identify the counterparts and the nature of most sources. Therefore indirect methods, such as the construction of X-ray luminosity functions (LF), are needed to study of properties of populations of sources located in different regions of a galaxy (see, e.g., Gilfanov, 2004;Mineo et al, 2012a). …”
High-mass X-ray binaries are fundamental in the study of stellar evolution, nucleosynthesis, structure and evolution of galaxies and accretion processes. Hard X-rays observations by INTEGRAL and Swift have broadened significantly our understanding in particular for the super-giant systems in the Milky Way, which number has increased by almost a factor of three. INTEGRAL played a crucial role in the discovery, study and understanding of heavily obscured systems and of fast X-ray transients. Most super-giant systems can now be classified in three categories: classical/obscured, eccentric and fast transient.The classical systems feature low eccentricity and variability factor of ∼ 10 3 , mostly driven by hydrodynamic phenomena occurring on scales larger than the accretion radius. Among them, systems with short orbital periods and close to Roche-Lobe overflow or with slow winds, appear highly obscured. In eccentric systems, the variability amplitude can reach even higher factors, because of the contrast of the wind density along the orbit. Four super-giant systems, featuring fast outbursts, very short orbital periods and anomalously low accretion rates, are not yet understood.Simulations of the accretion processes on relatively large scales have progressed and reproduce parts of the observations. The combined effects of wind
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