Cluster X-ray Luminosity Function Research Articles

The Chandra Deep Field North Survey. IX. Extended X-Ray Sources

The ≈1 Ms Chandra Deep Field North observation is used to study the extended X-ray sources in the region surrounding the Hubble Deep Field North (HDF-N), yielding the most sensitive probe of extended X-ray emission at cosmological distances to date. A total of six such sources are detected, the majority of which align with small numbers of optically bright galaxies. Their angular sizes, band ratios, and X-ray luminosities—assuming they lie at the same distances as the galaxies coincident with the X-ray emission—are generally consistent with the properties found for nearby groups of galaxies. One source is notably different and is likely to be a poor-to-moderate X-ray cluster at high redshift (i.e., z 0.7). This source has a large angular extent, a double-peaked X-ray morphology, and an overdensity of unusual objects [very red objects, optically faint (I ≥ 24) radio and X-ray sources]. Another of the six sources is coincident with several z ≈ 1.01 galaxies located within the HDF-N itself, including the FR I radio galaxy VLA J123644+621133, and is likely to be a group or poor cluster of galaxies at that redshift. We are also able to place strong constraints on the optically detected cluster of galaxies ClG 1236+6215 at z = 0.85 and the wide-angle–tailed radio galaxy VLA J123725+621128 at z ~ 1–2; both sources are expected to have considerable associated diffuse X-ray emission, and yet they have rest-frame 0.5–2.0 keV X-ray luminosities of 3 × 1042 and (3–15) × 1042 ergs s-1, respectively. The environments of both sources are either likely to have a significant deficit of hot intracluster gas compared with local clusters of galaxies, or they are X-ray groups. We find the surface density of extended X-ray sources in this observation to be 167 deg-2 at a limiting soft-band flux of ≈3 × 10-16 ergs cm-2 s-1. No evolution in the X-ray luminosity function of clusters is needed to explain this value.

TheROSAT‐ESO Flux‐limited X‐Ray (REFLEX) Galaxy Cluster Survey. IV. The X‐Ray Luminosity Function

The X-ray galaxy cluster sample from the REFLEX Cluster Survey, which covers the X-ray brightest galaxy clusters detected in the ROSAT All-Sky Survey in the southern sky, is used to construct the X-ray luminosity function of clusters in the local universe. With 452 clusters detected above an X-ray flux limit of 3 × 10-12 ergs s-1 cm-2 in 4.24 sr of the sky, this sample is the most comprehensive X-ray cluster sample with a well-documented selection function, providing the best current census of the local X-ray galaxy cluster population. In this paper we discuss the construction of the luminosity function and the effects of flux measurement errors and of variations with sample region, and we compare the results with those from previous surveys.

Effects of Formation Epoch Distribution on X‐Ray Luminosity and Temperature Functions of Galaxy Clusters

We investigate statistical properties of galaxy clusters in the context of a hierarchical clustering scenario, taking into account their formation epoch distribution; this study is motivated by the recent finding by Fujita and Takahara that X-ray clusters form a fundamental plane in which the mass and the formation epoch are regarded as two independent parameters. Using the formalism that discriminates between major mergers and accretion, the epoch of a cluster formation is identified with that of the last major merger. Since tiny mass accretion following formation does not much affect the core structure of clusters, the properties of X-ray emission from clusters are determined by the total mass and density at their formation time. Under these assumptions, we calculate X-ray luminosity and temperature functions of galaxy clusters. We find that the behavior of the luminosity function differs from the model that does not take into account formation epoch distribution; the behavior of the temperature function, however, is not much different. In our model, the luminosity function is shifted to a higher luminosity and shows no significant evolution up to z ~ 1, independent of cosmological models. The clusters are populated on the temperature-luminosity plane, with a finite dispersion. Since the simple scaling model in which the gas temperature is equal to the virial temperature fails to reproduce the observed luminosity-temperature relation, we also consider a model that takes into account the effects of preheating. The preheating model reproduces the observations much more accurately.

The impact of galaxy formation on the X-ray evolution of clusters

We present a new model for the X-ray properties of the intracluster medium that explicitly includes heating of the gas by the energy released during the evolution of cluster galaxies. We calculate the evolution of clusters by combining the semi-analytic model of galaxy formation of Cole et al. with a simple model for the radial profile of the intracluster gas. We focus on the cluster X-ray luminosity function and on the relation between X-ray temperature and luminosity (the T–L relation). Observations of these properties are known to disagree with predictions based on scaling relations that neglect gas cooling and heating processes. We show that cooling alone is not enough to account for the flatness of the observed T–L relation or for the lack of strong redshift evolution in the observed X-ray luminosity function. Gas heating, on the other hand, can solve these two problems: in the Λ cold dark matter cosmology, our model reproduces fairly well the T–L relation and the X-ray luminosity function. Furthermore, it predicts only weak evolution in these two properties out to z=0.5, in agreement with recent observational data. A successful model requires an energy input of 1–2×1049 erg per solar mass of stars formed. This is comparable to the total energy released by the supernovae associated with the formation of the cluster galaxies. Thus, unless the transfer of supernovae energy to the intracluster gas is very (perhaps unrealistically) efficient, additional sources of energy, such as mechanical energy from active galactic nuclei winds are required. However, the amplification of an initial energy input by the response of the intracluster medium to protocluster mergers might ease the energy requirements. Our model makes definite predictions for the X-ray properties of groups and clusters at high redshift. Some of these, such as the T–L relation at z1, may soon be tested with data from the Chandra and Newton satellites.

Expectations for Sunyaev‐Zeldovich Cluster Counts: Mass Function versus X‐Ray Luminosity Function

We present a comparison of the Sunyaev-Zeldovich (SZ) cluster counts predicted by the Press-Schechter (PS) mass function (MF) and the X-ray luminosity function (XLF) of clusters. The employment of the cluster XLF, together with the observationally determined X-ray luminosity-temperature (LX-T) relation, may allow us to estimate the SZ cluster counts in a more realistic manner, although such an empirical approach depends sensitively on our current knowledge of the dynamical properties of intracluster gas and its cosmic evolution. Using both the nonevolving and evolving XLFs of clusters suggested by X-ray observations, we calculate the expectations for SZ surveys of clusters with X-ray luminosity LX ≥ 3 × 1044 ergs s-1 and LX ≥ 1 × 1043 ergs s-1 in the 0.5-2.0 band, respectively. The nonevolving XLF results in a significant excess of SZ cluster counts at high redshifts as compared with the evolving XLF, while a slightly steeper LX-T relation than the observed one is needed to reproduce the distributions of SZ clusters predicted by the standard PS formalism. It is pointed out that uncertainties in the cosmological application of future SZ cluster surveys via the standard PS formalism should be carefully studied.

The Bright SHARC Survey: The X-Ray Cluster Luminosity Function

We present here initial results on the X-ray cluster luminosity function (XCLF) from the Bright Serendipitous High-Redshift Archival Cluster (SHARC) sample of distant X-ray clusters of galaxies. This sample is 97% complete in its optical identifications and contains 12 X-ray-luminous clusters in the redshift range 0.3 ≤ z ≤ 0.83 (median z = 0.42) and 1.1 × 1044 ≤ LX ≤ 8.3 × 1044 ergs s-1 (0.5-2.0 keV). We present a preliminary selection function for the Bright SHARC Survey based on Monte Carlo simulations. Using this selection function, we have computed the Bright SHARC Survey XCLF and find it to be fully consistent with a nonevolving XCLF to LX 5 × 1044 ergs s-1 and z 0.7. At LX > 5 × 1044 ergs s-1, we find evidence for a deficit of clusters compared to that expected from a nonevolving XCLF. We detect only one such cluster in the redshift range 0.3 ≤ z ≤ 0.7 when we would expect 4.9 clusters based on the local XCLF of De Grandi et al. The statistical significance of this deficit is 96%. To increase the statistical significance of this possible deficit, we have combined the Bright SHARC Survey and the 160 deg2 survey of Vikhlinin et al. This joint survey covers 260 deg2 and contains only one confirmed 0.3 ≤ z ≤ 0.7, LX > 5 × 1044 ergs s-1 cluster, while we would expect 7.6 such clusters based on the local XCLF (De Grandi et al.). The statistical significance of the deficit in this joint survey increases to 99.5%. These results remain preliminary because of incompletenesses in the optical follow-up and uncertainties in the local XCLF.

An SZ temperature decrement-X-ray luminosity relation for galaxy clusters

We present the observed relation between the cosmic microwave background (CMB) temperature decrement due to the Sunyaev-Zeldovich (SZ) effect and the X-ray luminosity of galaxy clusters. We discuss this relation in terms of the cluster properties, and show that the slope of the observed relation is in agreement with both the L-T relation based on numerical simulations and X-ray emission observations, and the M_gas-L relation based on observations. The slope of the Delta T_SZ-L relation is also consistent with the M_tot-L relation, where M_tot is the cluster total mass based on gravitational lensing observations. This agreement may be taken to imply a constant gas mass fraction within galaxy clusters, however, there are large uncertainties, dominated by observational errors, associated with these relations. Using the Delta T_SZ-L relation and the cluster X-ray luminosity function, we evaluate the local cluster contribution to arcminute scale cosmic microwave background anisotropies. The Compton distortion y-parameter produced by massive galaxy clusters through SZ effect is roughly two orders of magnitude lower than the current upper limit based on FIRAS observations.

X-ray galaxy clusters as cosmological probes

The X-ray properties of the galaxy cluster population are reviewed with evidence that clusters form a nearly self-similar class of objects. The use of the cluster X-ray luminosity function to constrain cosmological models and the assessment of the large-scale structure by means of the X-ray cluster distribution is discussed.

X-ray galaxy clusters as cosmological probes

The X-ray properties of the galaxy cluster population are reviewed with evidence that clusters form a nearly self-similar class of objects. The use of the cluster X-ray luminosity function to constrain cosmological models and the assessment of the large-scale structure by means of the X-ray cluster distribution is discussed.

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.

A Deficit of High‐Redshift, High‐Luminosity X‐Ray Clusters: Evidence for a High Value of Ωm?

From the Press-Schechter mass function and the empirical X-ray cluster luminosity-temperature (L-T) relation, we construct an X-ray cluster luminosity function that can be applied to the growing number of high-redshift, X-ray cluster luminosity catalogs to constrain cosmological parameters. In this paper, we apply this luminosity function to the Einstein Medium Sensitivity Survey (EMSS) and the ROSAT Brightest Cluster Sample (BCS) luminosity function to constrain the value of ?m. In the case of the EMSS, we find a factor of 4-5 fewer X-ray clusters at redshifts above z = 0.4 than below this redshift at luminosities above LX = 7 ? 1044 ergs s-1 (0.3-3.5 keV), which suggests that the X-ray cluster luminosity function has evolved above L*. At lower luminosities, this luminosity function evolves only minimally, if at all. Using Bayesian inference, we find that the degree of evolution at high luminosities suggests that ?m=0.96+0.36-0.32, given the best-fit L-T relation of Reichart, Castander, & Nichol. When we account for the uncertainty in how the empirical L-T relation evolves with redshift, we find that ?m ? 1.0 ? 0.4. However, it is unclear to what degree systematic effects may affect this and similarly obtained results.

The Warps X-Ray Survey of Galaxies, Groups, and Clusters

We have embarked on a survey of ROSAT PSPC archival data searching for all detected surface brightness enhancements due to sources in the innermost R ≤ 15′ of the PSPC field of view in the energy band 0.5–2.0 keV. This project is part of the Wide Angle ROSAT Pointed Survey (WARPS) and is designed primarily to measure the low luminosity, high redshift, X-ray luminosity function of galaxy clusters and groups. Accurate measurements of the high redshift XLF would allow the form of the XLF evolution to be determined via the position of the Schechter function break. This would help discriminate between luminosity and density evolution, and discriminate between different hierarchical models, e.g., those including a different mix of fundamental particles, a flat power spectrum of the initial fluctuations, and reheating of the intracluster gas at high redshifts.

The Role of Cooling Flows in the Star Formation History of Central Cluster Galaxies

Using a recent determination of the X-ray luminosity function of galaxy clusters, accurate mass deposition rates and LX in cooling flow clusters from the literature, and reliable constraints on the star fomation episodes in cooling flows obtained by our group, we quantify the relevance of such star formation in comparison with the SFR in the local universe. We conclude that the SFR density in CF is ≲ 0.1% the total local reference.

The Southern SHARC Survey: the [CLC][ITAL]z[/ITAL][/CLC] = 0.3–0.7 Cluster X-Ray Luminosity Function

We present the z = 0.3-0.7 cluster X-ray luminosity function (XLF) determined from the Southern Serendipitous High-Redshift Archival ROSAT Cluster (SHARC) survey. Over the luminosity range L ~ (0.3-3) × 1044 ergs s-1 (0.5-2.0 keV), the XLF is in close agreement with that of the low-redshift X-ray cluster population. This result greatly strengthens our previous claim of no evolution of the cluster population, at these luminosities, at a median redshift of z=0.44.

Evolution in the X‐Ray Cluster Luminosity Function Revisited

We present new X-ray data taken from the ROSAT Position Sensitive Proportional Counter pointing archive for 21 clusters in the Einstein Extended Medium-Sensitivity Survey (EMSS). We have supplemented these data with new optical follow-up observations found in the literature, and, overall, 32 of the original 67 z > 0.14 EMSS clusters now have new information. Using this revised sample, we find no systematic difference, as a function of X-ray flux, between our measured X-ray cluster fluxes and those in the original EMSS (30% scatter). However, we do detect a marginal correlation between this observed difference in the flux and the redshift of the clusters, with the lower redshift systems having a greater scatter by nearly a factor of 2. We have also determined the X-ray extent of these reobserved EMSS clusters and find that 14 of them have significant extents compared with the ROSAT point-spread function. Combining these data with extended clusters seen in the original EMSS sample, at least 40% of z > 0.14 clusters now have an observed X-ray extent, thus justifying their classification as X-ray clusters. Using our improved EMSS sample, we have redetermined the EMSS X-ray cluster luminosity function as a function of redshift. We have removed potential misclassifications and included our new measurements of the clusters' X-ray luminosities and redshifts. We find similar luminosity functions to those originally presented by Henry et al., albeit with two important differences. First, we show that the original low-redshift EMSS luminosity function is insufficiently constrained. Second, the power-law shape of our new determination of the high-redshift EMSS luminosity function (z = 0.3-0.6) has a shallower slope than that seen by Henry et al. We have compared our new EMSS luminosity functions with those recently derived from a nearby sample of X-ray clusters and find that the overall degree of observed luminosity function evolution is mild at best. This is a result of the shallower slope seen in our EMSS high-redshift luminosity function and a more robust low-redshift determination of the X-ray cluster luminosity function from the literature. We have quantified the degree of evolution seen in the X-ray cluster luminosity by using several statistical tests. The most restrictive analysis indicates that our low- and high-redshift EMSS luminosity functions are statistically different at the 95% level. However, other tests indicate that these low- and high-redshift luminosity functions only differ by as little as 1 σ. These data are, therefore, consistent with no evolution in the X-ray cluster luminosity function out to z 0.5.

The [ITAL]ROSAT[/ITAL] Brightest Cluster Sample (BCS): The Cluster X-Ray Luminosity Function within [CLC][ITAL]z[/ITAL][/CLC] = 0.3

We present and discuss the X-ray luminosity function (XLF) of the ROSAT Brightest Cluster sample (BCS), an X-ray flux limited sample of clusters of galaxies in the northern hemisphere compiled from ROSAT All-Sky Survey data. The BCS allows the local cluster XLF to be determined with unprecedented accuracy over almost three decades in X-ray luminosity and provides an important reference for searches for cluster evolution at higher redshifts. We find the significance of evolution in both the XLF amplitude and in the characteristic cluster luminosity L -->X to be less than 1.8 ? within the redshift range covered by our sample thereby disproving previous claims of strong evolution within z 0.2.

The Wide‐AngleROSATPointed X‐Ray Survey of Galaxies, Groups, and Clusters. I. Method and First Results

We have embarked on a survey of ROSAT PSPC archival data with the aim of detecting all significant surface brightness enhancements resulting from sources in the innermost R ≤ 15' of the PSPC field of view in the energy band 0.5-2.0 keV. This project is part of the Wide-Angle ROSAT Pointed Survey (WARPS), and it is designed primarily to measure the low-luminosity, high-redshift, X-ray luminosity function of galaxy clusters and groups. The approach we have chosen for source detection (Voronoi Tessellation and Percolation [VTP]) represents a significant advance over conventional methods, and it is particularly suited for the detection and accurate quantification of extended and/or low surface brightness emission that could otherwise be missed or wrongly interpreted. We also use energy-dependent exposure maps to estimate the fluxes of sources that can amount to corrections of as much as 15%. In an extensive optical follow-up program, we are identifying galaxies, groups, and clusters at redshifts ranging from z ~ 0.1 to z ~ 0.7. In this paper, we present our method and its calibration using simulated and real data. We present first results for an initial 91 fields (17.2 deg2) at detected fluxes greater than 3.5 × 10-14 ergs s-1 cm-2 (the WARPS-I survey). We find the sky density of extended objects to be in the range 2.8-4.0 ( ± 0.4) deg-2. A comparison with a point-source detection algorithm demonstrates that our VTP approach typically finds 1-2 more objects deg-2 to this detected flux limit, suggesting that the conventional method fails to detect a significant fraction of extended objects. The surface brightness limit of the WARPS cluster survey is ~1 × 10-15 ergs s-1 cm-2 arcmin-2, approximately 6 times lower than the Extended Medium Sensitivity Survey (EMSS). The WARPS Log N-Log S (which currently represents a lower limit) shows a significant excess over previous measurements for S 8 × 10-14 ergs s-1 cm-2. We attribute this mainly to a larger measured flux from extended sources as well as new detections of low surface brightness systems in the WARPS.

On the Evolution of X-Ray Clusters at High Redshift

We report on the first results from a redshift survey of a flux-limited sample of X-ray clusters selected serendipitously from the ROSAT PSPC data archive. We spectroscopically confirm 15 clusters in the range 0.3 < z < 0.7, to a flux limit of 3.9 × 10-14 ergs s-1 cm-2, over a survey area of 17.2 deg2. The surface density of clusters in our survey is 2.0+ 0.4−0.3 deg-2, in good agreement with the number density of cluster candidates detected using algorithms designed to search for very extended sources. The number of clusters detected between 0.3 < z < 0.7 is consistent with a prediction based on a simple extrapolation of the local X-ray cluster luminosity function, which indicates that over this redshift range no significant evolution in the cluster population has taken place. These results are in conflict with recent claims that the number density of X-ray clusters found in deep ROSAT PSPC pointings evolves rapidly beyond z = 0.3.

The entropy-driven X-ray evolution of galaxy clusters

Observations of the evolution of the galaxy cluster X-ray luminosity function suggest that the entropy of the intracluster medium plays a significant role in determining the development of cluster X-ray properties. I present a theoretical framework in which the evolution of the entropy of the central intracluster gas is explicitly taken into account. The aim of this work is to develop a theoretical context within which steadily improving measurements of the X-ray luminosities and temperatures of distant galaxy clusters can be interpreted. I discuss the possible range of entropy evolution parameters and relate these to the physical processes heating and cooling the intracluster medium. The practical application of this work is demonstrated by combining currently available evolutionary constraints on the X-ray luminosity function and the luminosity-temperature correlation to determine the best-fitting model parameters.