Local X-ray Luminosity Function Research Articles

Variable Magellanic HMXB Sources versus Variable ULX Sources: Nothing to Brag about the ULX Sources

We carry out a meta-analysis of ultraluminous X-ray (ULX) sources that show large variabilities (by factors of >10) between their highest and lowest emission states in the X-ray energy range of 0.3–10 keV. We are guided by a recent stringent compilation of 25 such X-ray sources by Song et al. We examine the relation of logN versus logSmax, where N is the number of sources radiating above the maximum-flux level Smax. We find a strong deviation from all previously determined slopes in various high-mass X-ray binary (HMXB) samples. In fact, the ULX data clearly show a slope of −0.91. Thus, ULX sources do not appear to be uniform and isotropic in our Universe. We compare the ULX results against the local X-ray luminosity function of HMXBs in the Small Magellanic Cloud (SMC) constructed from our latest library that includes 41 Chandra 0.3–8 keV sources and 56 XMM-Newton 0.2–12 keV sources. The ULX data are not drawn from the same continuous distribution as the SMC data (the ULX data peak at the low tails of the SMC distributions), and none of our data sets is drawn from a normal distribution or from a log-normal distribution (they all show marked excesses at both tails). At a significance level of α=0.05 (2σ), the two-sample p-value of the Kolmogorov–Smirnov (KS) test gives p=4.7×10−3<α for the ULX versus the small Chandra sample and p=1.1×10−5<<α for the ULX versus the larger XMM-Newton sample, respectively. This adds to the evidence that ULX sources are not simply the higher end of the known local Be/X-ray pulsar distribution, but they represent a class of X-ray sources different from the young sources found in the SMC and in individual starburst galaxies. On the other hand, our two main SMC data sets are found to be statistically consistent, as they are drawn from the same continuous parent distribution (null hypothesis H0): at the α=0.05 significance level, the two-sample KS test shows an asymptotic p-value of 0.308>α, which tells us to accept H0.

THENuSTAREXTRAGALACTIC SURVEY: FIRST DIRECT MEASUREMENTS OF THE ≳10 keV X-RAY LUMINOSITY FUNCTION FOR ACTIVE GALACTIC NUCLEI ATz> 0.1

We present the first direct measurements of the rest-frame 10-40 keV X-ray luminosity function (XLF) of Active Galactic Nuclei (AGNs) based on a sample of 94 sources at 0.1 < z <3, selected at 8-24 keV energies from sources in the NuSTAR extragalactic survey program. Our results are consistent with the strong evolution of the AGN population seen in prior, lower-energy studies of the XLF. However, different models of the intrinsic distribution of absorption, which are used to correct for selection biases, give significantly different predictions for the total number of sources in our sample, leading to small, systematic differences in our binned estimates of the XLF. Adopting a model with a lower intrinsic fraction of Compton-thick sources and a larger population of sources with column densities N_H ~ 10^{23-24} /cm2 or a model with stronger Compton reflection component (with a relative normalization of R ~ 2 at all luminosities) can bring extrapolations of the XLF from 2-10 keV into agreement with our NuSTAR sample. Ultimately, X-ray spectral analysis of the NuSTAR sources is required to break this degeneracy between the distribution of absorbing column densities and the strength of the Compton reflection component and thus refine our measurements of the XLF. Furthermore, the models that successfully describe the high-redshift population seen by NuSTAR tend to over-predict previous, high-energy measurements of the local XLF, indicating that there is evolution of the AGN population that is not fully captured by the current models.

The WARPS Survey – VIII. Evolution of the galaxy cluster X-ray Luminosity Function

We present measurements of the galaxy cluster X-ray Luminosity Function (XLF) from the Wide Angle ROSAT Pointed Survey (WARPS) and quantify its evolution. WARPS is a serendipitous survey of the central region of ROSAT pointed observations and was carried out in two phases (WARPS-I and WARPS-II). The results here are based on a final sample of 124 clusters, complete above a flux limit of 6.5 10E-15 erg/s/cm2, with members out to redshift z ~ 1.05, and a sky coverage of 70.9 deg2. We find significant evidence for negative evolution of the XLF, which complements the majority of X-ray cluster surveys. To quantify the suggested evolution, we perform a maximum likelihood analysis and conclude that the evolution is driven by a decreasing number density of high luminosity clusters with redshift, while the bulk of the cluster population remains nearly unchanged out to redshift z ~ 1.1, as expected in a low density Universe. The results are found to be insensitive to a variety of sources of systematic uncertainty that affect the measurement of the XLF and determination of the survey selection function. We perform a Bayesian analysis of the XLF to fully account for uncertainties in the local XLF on the measured evolution, and find that the detected evolution remains significant at the 95% level. We observe a significant excess of clusters in the WARPS at 0.1 < z < 0.3 and LX ~ 2 10E42 erg/s compared with the reference low-redshift XLF, or our Bayesian fit to the WARPS data. We find that the excess cannot be explained by sample variance, or Eddington bias, and is unlikely to be due to problems with the survey selection function.

Revisit of Local X-Ray Luminosity Function of Active Galactic Nuclei with the MAXI Extragalactic Survey

Abstract We constructed a new X-ray (2–10 keV) luminosity function of Compton-thin active galactic nuclei (AGNs) in the local universe, using the first MAXI/GSC source catalog surveyed in the 4–10 keV band. The sample consists of 37 non-blazar AGNs at $z$$=$ 0.002–0.2, whose identification is highly ( $&amp;gt;\ $ 97%) complete. We confirmed the trend that the fraction of absorbed AGNs with $N_{\rm H}$$&amp;gt;\ $ 10 $^{22}$ cm $^{-2}$ rapidly decreases against the luminosity ( $L_{\rm X}$ ), from 0.73 $\ \pm\ $ 0.10 at $L_{\rm X}$$=$ 10 $^{42-43.5}$ erg s $^{-1}$ to 0.12 $\ \pm\ $ 0.08 at $L_{\rm X}$$=$ 10 $^{43.5-45.5}$ erg s $^{-1}$ . The obtained luminosity function was well-fitted with a smoothly connected double power-law model whose indices are $\gamma_1$$=$ 0.84 (fixed) and $\gamma_2$$=$ 2.0 $\ \pm\ $ 0.2 below and above the break luminosity, $L_{*}$$=$ 10 $^{43.3\pm0.4}$ erg s $^{-1}$ , respectively. While the result of the MAXI/GSC agrees well with that of HEAO-1 at $L_{\rm X}$$\gtrsim$ 10 $^{43.5}$ erg s $^{-1}$ , it gives a larger number density at the lower luminosity range. A comparison between our luminosity function in the 2–10 keV band and that in the 14–195 keV band obtained from the Swift/BAT survey indicates that the averaged broad-band spectra in the 2–200 keV band should depend on the luminosity, approximated by $\Gamma$$\sim$ 1.7 for $L_{\rm X}$$\lesssim$ 10 $^{44}$ erg s $^{-1}$ , while $\Gamma$$\sim$ 2.0 for $L_{\rm X}$$\gtrsim$ 10 $^{44}$ erg s $^{-1}$ . This trend was confirmed by the correlation between the luminosities in the 2–10 keV and 14–195 keV bands in our sample. We argue that there is no contradiction in the luminosity functions between above and below 10 keV once this effect is taken into account.

ERRATUM: “THE MASS FUNCTION OF ACTIVE BLACK HOLES IN THE LOCAL UNIVERSE” (2007, ApJ, 667, 131)

We present the first measurement of the black hole (BH) mass function for broad-line active galaxies in the local Universe. Using the ~9000 broad-line active galaxies from the Fourth Data Release of the Sloan Digital Sky Survey, we construct a broad-line luminosity function that agrees very well with the local soft X-ray luminosity function. Using standard virial relations, we then convert observed broad-line luminosities and widths into BH masses. A mass function constructed in this way has the unique capability to probe the mass region <10^6 M_sun, which, while insignificant in terms of total BH mass density, nevertheless may place important constraints on the mass distribution of seed BHs in the early Universe. The characteristic local active BH has a mass of ~10^7 M_sun radiating at 10% of the Eddington rate. The active fraction is a strong function of BH mass; at both higher and lower masses the active mass function falls more steeply than one would infer from the distribution of bulge luminosity. The deficit of local massive radiating BHs is a well-known phenomenon, while we present the first robust measurement of a decline in the space density of active BHs at low mass.

The Mass Function of Active Black Holes in the Local Universe

We present the first measurement of the BH mass function for broad-line active galaxies in the local universe. Using the ~8500 broad-line active galaxies from SDSS DR4, we construct a broad-line luminosity function that agrees very well with the local soft X-ray luminosity function. Using standard virial relations, we then convert observed broad-line luminosities and widths into BH masses. A mass function constructed in this way has the unique capability to probe the mass region <106 M☉, which, while insignificant in terms of total BH mass density, nevertheless may place important constraints on the mass distribution of seed BHs in the early universe. The characteristic local active BH has a mass of ~107 M☉ radiating at 10% of the Eddington rate. The active fraction is a strong function of BH mass; at both higher and lower masses the active mass function falls more steeply than one would infer from the distribution of bulge luminosity. The deficit of local massive radiating BHs is a well-known phenomenon, while we present the first robust measurement of a decline in the space density of active BHs at low mass.

The 400 Square Degree ROSAT PSPC Galaxy Cluster Survey: Catalog and Statistical Calibration

We present a catalog of galaxy clusters detected in a new ROSAT PSPC survey. The survey is optimized to sample, at high redshifts, the mass range corresponding to T > 5 keV clusters at z = 0. Technically, our survey is the extension of the 160 square degree survey (160d). We use the same detection algorithm, thus preserving high quality of the resulting sample; the main difference is a significant increase in sky coverage. The new survey covers 397 deg2 and is based on 1610 high Galactic latitude ROSAT PSPC pointings, virtually all pointed ROSAT data suitable for the detection of distant clusters. The search volume for X-ray luminous clusters within z < 1 exceeds that of the entire local universe (z < 0.1). We detected 287 extended X-ray sources with fluxes f > 1.4 × 10-13 ergs s-1 cm-2 in the 0.5-2 keV energy band, of which 266 (93%) are optically confirmed as galaxy clusters, groups or individual elliptical galaxies. This paper provides a description of the input data, the statistical calibration of the survey via Monte Carlo simulations, and the catalog of detected clusters. We also compare the basic results to those from previous, smaller area surveys and find good agreement for the log N- log S distribution and the local X-ray luminosity function. Our sample clearly shows a decrease in the number density for the most luminous clusters at z > 0.3. The comparison of our ROSAT-derived fluxes with the accurate Chandra measurements for a subset of high-redshift clusters demonstrates the validity of the 400 square degree survey's statistical calibration.

X-Ray Number Counts of Normal Galaxies

We use the number counts of X-ray selected normal galaxies to explore their evolution by combining the most recent wide-angle shallow and pencil-beam deep samples available. The differential X-ray number counts, dN/dS, for early and late-type normal galaxies are constructed separately and then compared with the predictions of the local X-ray luminosity function under different evolution scenarios. The dN/dS of early type galaxies is consistent with no evolution out to z~0.5. For late-type galaxies our analysis suggests that it is the sources with X-ray--to--optical flux ratio logfx/fopt>-2 that are evolving the fastest. Including these systems in the late-type galaxy sample yields evolution of the form ~(1+z)^{2.7} out to z~0.4. On the contrary late-type sources with logfx/fopt -2 population comprises the most powerful and fast evolving starbursts at moderate and high-z. We argue that although residual low-luminosity AGN contamination may bias our results toward stronger evolution, this is unlikely to modify our main conclusions.

Mining for normal galaxies in the first XMM-Newton Serendipitous Source Catalog

This paper uses the 1st XMM Serendipitous Source Catalog compiled by the XMM Science Center to identify low-z X-ray selected normal galaxy candidates. Our sample covers a total area of ~6deg^2 to the 0.5-2keV limit 1e-15cgs. A total of 23 sources are selected on the basis of low X-ray-to-optical flux ratio logfx/fopt 1e-15cgs). We estimate a slope of -1.46\pm0.13 for the cumulative number counts consistent with the euclidean prediction. We further combine our sample with 23 local (z<0.2) galaxies from the CDF North and South to construct the local X-ray luminosity function of normal galaxies. A Schechter form provides a good fit to the data with a break at logL*~41.02cgs and a slope of -1.76\pm0.10. Finally, for the sample of 46 systems we explore the association between X-ray luminosity and host galaxy properties, such as SFR and stellar mass. We find that the L_X of the emission-line systems correlates with Ha luminosity and 1.4GHz radio power, both providing an estimate of the current star-formation rate. In the case of early type galaxies with absorption line optical spectra we use the K-band as proxy to stellar mass and find a correlation of the form L_X~L_K^1.5. This is flatter than the L_X-L_B relation for local ellipticals. This may be due to either L_K providing a better proxy to galaxy mass or selection effects biasing our sample against very luminous early-type galaxies.

The XMM-Newton Needles in the Haystack Survey: the local X-ray luminosity function of 'normal' galaxies

In this paper we estimate the local (z<0.22) X-ray luminosity function of `normal' galaxies derived from the XMM-Newton Needles in the Haystack Survey. This is an on-going project that aims to identify X-ray selected `normal' galaxies (i.e. non-AGN dominated) in the local Universe. We are using a total of 70 XMM-Newton fields covering an area of 11 sq. degrees which overlap with the Sloan Digital Sky Survey Data Release-2. `Normal' galaxies are selected on the basis of their resolved optical light profile, their low X-ray--to--optical flux ratio (log(f_x/f_o)<-2) and soft X-ray colours. We find a total of 28 candidate `normal' galaxies to the 0.5-8 keV band flux limit of ~2x10^{-15} cgs. Optical spectra are available for most sources in our sample (82 per cent). These provide additional evidence that our sources are bona-fide 'normal' galaxies with X-ray emission coming from diffuse hot gas emission and/or X-ray binaries rather than a supermassive black hole. Sixteen of our galaxies have narrow emission lines or a late-type Spectral Energy Distribution (SED) while the remaining 12 present only absorption lines or an early-type SED. Combining our XMM-Newton sample with 18 local (z<0.22) galaxies from the Chandra Deep Field North and South surveys, we construct the local X-ray luminosity function of `normal' galaxies. This can be represented with a Schechter form with a break at L* ~ 3x10^{41} cgs and a slope of ~1.78+/-0.12. Using this luminosity function and assuming pure luminosity evolution of the form (1+z)^{3.3} we estimate a contribution to the X-ray background from `normal' galaxies of 10-20 per cent (0.5-8 keV). Finally, we derive, for the first time, the luminosity functions for early and late type systems separately.

Cosmological constraints from the local X-ray luminosity function of the most X-ray-luminous galaxy clusters

We present precise constraints on the normalization of the power spectrum of mass fluctuations in the nearby universe, sigma_8, as a function of the mean local matter density, Omega_m. Using the observed local X-ray luminosity function of galaxy clusters from the extended BCS and REFLEX studies, a mass-luminosity relation determined from Chandra and ROSAT X-ray data and weak gravitational lensing observations, and the mass function predicted by the Hubble Volume simulations of Evrard et al., we obtain sigma_8 = (0.508\pm0.019) Omega_m^-(0.253\pm0.024), with Omega_m < 0.34 at 68 per cent confidence. The degeneracy between sigma_8 and Omega_m can be broken using Chandra measurements of the X-ray gas mass fractions in dynamically relaxed clusters. Using this information and including Gaussian priors on the mean baryon density of the universe and the Hubble constant, we obtain sigma_8=0.695\pm0.042 and Omega_m=0.287\pm0.036, for an assumed flat LambdaCDM cosmology (marginalized 68 per cent confidence limits). Our results are in good agreement with some recent studies based on the local X-ray temperature function of clusters, the redshift evolution of the X-ray luminosity and temperature functions of clusters, early results from the Sloan Digitized Sky Survey, the most recent results from studies of cosmic shear, and combined analyses of the 2dF galaxy redshift survey and cosmic microwave background anisotropies.

Cosmological constraints from Chandra X-ray observations of galaxy clusters

Chandra X-ray observations of rich, dynamically relaxed galaxy clusters allow the properties of the X-ray gas and the total gravitating mass to be determined precisely. Here, we discuss how Chandra observations may be used as a powerful tool for cosmological studies. By combining Chandra X-ray results on the X-ray gas mass fractions in clusters with independent measurements of the Hubble constant and the mean baryonic matter density of the universe, we obtain a tight constraint on the mean total matter density of the universe, Ωm, and an interesting constraint on the cosmological constant, ΩΛ. Using these results, together with the observed local X-ray luminosity function of the most X-ray luminous galaxy clusters, a mass-luminosity relation determined from Chandra and ROSAT X-ray data and weak gravitational lensing observations, and the mass function predicted by numerical simulations, we obtain a precise constraint on the normalization of the power spectrum of density fluctuations in the nearby universe, σ8. We compare our results with those obtained from other, independent methods.

A reanalysis of the X-ray luminosities of clusters of galaxies with 0.3&lt;z&lt;0.6 in the EMSS sample

The X-ray luminosities of the Einstein Extended Medium Sensitivity Survey (EMSS) clusters of galaxies with redshifts 0.3 250kpc (the constant value assumed in the EMSS), the new luminosities are 2.2 ′ 0.15 times the previous measurements. The X-ray luminosity function (XLF) at 0.3 < z < 0.6 is recalculated and is found to be consistent with the local XLF. The constraints on the updated properties of the 0.3 < z < 0.6 EMSS sample, including a comparison with the number of clusters predicted from local XLFs, indicate that the space density of luminous, massive clusters either has not evolved or has increased by a small factor 2 since z = 0.4. The implications of this result are discussed in terms of constraints on the cosmological parameter Ω 0 .

Cosmological Constraints from theROSATDeep Cluster Survey

The ROSAT Deep Cluster Survey (RDCS) has provided a new large deep sample of X-ray selected galaxy clusters. Observables such as the flux number counts n(S), the redshift distribution n(z), and the X-ray luminosity function (XLF) over a large redshift baseline (z≲0.8) are used here in order to constrain cosmological models. Our analysis is based on the Press-Schechter approach, whose reliability is tested against N-body simulations. Following a phenomenological approach, no assumption is made a priori on the relation between cluster masses and observed X-ray luminosities. As a first step, we use the local XLF from RDCS, along with the high-luminosity extension provided by the XLF from the Brightest Cluster Survey, in order to constrain the amplitude of the power spectrum, σ8, and the shape of the local luminosity-temperature, Lbol-T, relation. We obtain σ8=(0.58 ± 0.06) × Ω0-0.47+0.16Ω for flat models (ΩΛ=1-Ω0) and σ8=(0.58 ± 0.06) × Ω0-0.53+0.27Ω for open models (ΩΛ=0) at a 90% confidence level, almost independent of the Lbol-T shape. The density parameter Ω0 and the evolution of the Lbol-T relation are constrained by the RDCS XLF at z>0 and the EMSS XLF at =0.33, and by the RDCS n(S) and n(z) distributions. By modeling the evolution for the amplitude of the Lbol-T relation as (1+z)A, an Ω0=1 model can be accommodated for the evolution of the XLF with 1≲A≲3 at a 90% confidence level, while Ω0=0.4+0.3−0.2 and Ω0≲0.6 are implied by a nonevolving Lbol-T (A=0) for open and flat models, respectively.

The X-ray luminosity function of local galaxies

We present an estimate of the local X-ray luminosity function and emissivity for different subsamples of galaxies, namely Seyferts, LINERS, star-forming and passive (no-emission-line) galaxies. This is performed by convolving their optical luminosity function, as derived from the Ho et al. spectroscopic sample of nearby galaxies with the corresponding Lx/LB relation. The local galaxy emissivity is ≈ 1.6 × 1039 h erg s-1 Mpc-3 in agreement with the results from a number of cross-correlation analyses using large-area surveys. From our analysis, it becomes evident that the largest fraction of the galaxy emissivity comes from galaxies associated with active galactic nuclei (Seyferts but also LINERS) while the contribution of star-forming and passive galaxies is small. This independently supports the view that most of the yet unidentified X-ray sources in deep ROSAT fields which are associated with faint optical galaxies do harbour an active galactic nucleus.

The X-Ray Luminosity Function of Nearby Rich and Poor Clusters of Galaxies:A Cosmological Probe

In this Letter, we present a new determination of the local (z≤0.09) X-ray luminosity function (XLF) using a large, statistical sample of 294 Abell clusters and the ROSAT All-Sky Survey. Despite the optical selection of this catalog, we find excellent agreement with other recent determinations of the local XLF. Given our large sample size, we have reduced errors by nearly a factor of 2 for LX(0.5−2.0 keV) ≥ 1043 h−250 ergs s-1. We combine our data with previous work to produce the most tightly constrained local determination of the XLF (over 3 orders of magnitude in LX) in order to explore possible constraints imposed by the shape of the XLF on cosmological models. A set of currently viable cosmologies is used to construct theoretical XLFs assuming L∝Mp and a σ8-Ω0 constraint based on the local X-ray temperature function. We fit these models to our observed XLF and verify that the simplest adiabatic, analytic scaling relation disagrees strongly with observations. If we assume that clusters can be described by the preheated, constant core entropy models of Evrard & Henry, then the observed XLF is consistent only with 0.1<Ω0<0.4 if the energy per unit mass in galaxies is roughly equal to the gas energy (i.e., if β~1).

The X-Ray Luminosity Function of Bright Galaxy Clusters in the Local Universe

We present the X-ray luminosity function (XLF) for clusters of galaxies derived from the RASS1 Bright Sample. The sample, selected from the ROSAT All-Sky Survey in a region of 2.5 sr within the southern Galactic cap, contains 130 clusters with flux limits in the range ~3-4×10−12 ergs cm-2 s-1 in the 0.5-2.0 keV band. A maximum likelihood fit with a Schechter function of the XLF over the entire range of luminosities (0.045-28.0×1044 ergs s-1) gives α=1.52+0.11−0.11, L*=3.80+0.70−0.55×1044 ergs s-1, and A=5.07±0.45×10−7 Mpc-3 (1044 ergs s-1)α-1. We investigate possible evolutionary effects within the sample, out to our redshift limit (z~0.3), finding no evidence for evolution. Our results are in good agreement with other local estimates of the XLF, implying that this statistic for the local universe is now well determined. Comparison with XLFs for distant clusters (0.3 < z < 0.6) shows that no evolution is present for LX 1044 ergs s-1. However, we detect differences at the 3 σ level between our local XLF and the distant one estimated by Henry et al. for the Einstein Extended Medium-Sensitivity Survey (EMSS) sample. This difference is still present when considering the EMSS sample revised by Nichol et al.

The [ITAL]ROSAT[/ITAL] Deep Cluster Survey: The X-Ray Luminosity Function out to [CLC][ITAL]z[/ITAL][/CLC] = 0.8

We present the X-ray luminosity function (XLF) of the ROSAT Deep Cluster Survey sample over the redshift range 0.05-0.8. Our results are derived from a complete flux-limited subsample of 70 galaxy clusters, representing the brightest half of the total sample, which have been spectroscopically identified down to the flux limit of 4×10 -->−14 ergs m-2 s-1 (0.5-2.0 keV) and have been selected via a serendipitous search in ROSAT PSPC pointed observations. The redshift baseline is large enough that evolutionary effects can be studied within the sample. The local XLF (z≤0.25) is found to be in excellent agreement with previous determinations using ROSAT All-Sky Survey data. The XLF at higher redshifts, when combined with the deepest number counts constructed to date (f>2×10 -->−14 ergs cm -->−2 s -->−1), reveals no significant evolution at least out to z=0.8, over a luminosity range of 2 × 1042 to 3 × 1044 ergs s -->−1 in the 0.5-2 keV band. These findings extend the study of cluster evolution to the highest redshifts and the faintest fluxes probed so far in X-ray surveys. They complement and do not necessarily conflict with those of the Einstein Extended Medium-Sensitivity Survey, leaving open the possibility of negative evolution of the brightest end of the XLF at high redshifts.

Space Distribution of X-Ray Clusters of Galaxies

The Intra-Cluster Plasma constitutes an archive of the past history of all clusters and of many groups of galaxies: statistical observations of their X-ray emission will set significant constraints on the dynamical, thermal and chemical events in these cosmic structures. Data on the local X-ray luminosity function N(L, z ≃ 0) were provided by the 1st generation X-ray surveys. HEAO II provided an integral of N(L, z) out to z ≃ 0.4, the counts from a subsample of the MSS (Gioia et al. 1984, Ap.J. 283, 495): these counts result very flat, cf. Fig. 2.