Browsing by Subject "DARK-MATTER HALOES"
Now showing items 1-12 of 12
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(2016)We present the discovery of a giant >= 100 kpc Ly alpha nebula detected in the core of the X-ray emitting cluster CL J1449 +0856 at z = 1.99 through Keck/LRIS narrow-band imaging. This detection extends the known relation between Lya nebulae and overdense regions of the universe to the dense core of a 5-7 x 10(13) M-circle dot cluster. The most plausible candidates to power the nebula are two Chandra-detected AGN host cluster members, while cooling from the X-ray phase and cosmological cold flows are disfavored primarily because of the high Ly alpha to X-ray luminosity ratio (L-Ly alpha/L-X approximate to 0.3, greater than or similar to 10-1000 times. higher than in local cool-core clusters) and by current modeling. Given the physical conditions of the Ly alpha-emitting gas and the possible interplay with the X-ray phase, we argue that the Ly alpha nebula would be short-lived (less than or similar to 10 Myr) if not continuously replenished with cold gas at a rate of greater than or similar to 1000 M-circle dot yr(-1). We investigate the possibility that cluster galaxies supply the required gas through outflows and we show that their total mass outflow rate matches the replenishment necessary to sustain the nebula. This scenario directly implies the extraction of energy from galaxies and its deposition in the surrounding intracluster medium (ICM), as required to explain the thermodynamic properties of local clusters. We estimate an energy injection of the order of approximate to 2 keV per particle in the ICM over a 2 Gyr interval. In our baseline calculation, AGNs provide up to 85% of the injected energy and two-thirds. of the mass, while the rest is supplied by supernovae-driven winds.
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(2017)We present a stacked weak-lensing analysis of 27 richness selected galaxy clusters at 0.40
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(2017)We evaluate the effect of structure formation on the average expansion rate with a statistical treatment where density peaks and troughs are modelled as homogeneous ellipsoids. This extends earlier work that used spherical regions. We find that the shear and the presence of filamentary and planar structures have only a small impact on the results. The expansion rate times the age of the universe Ht increases from 2/3 to 0.83 at late times, in order of magnitude agreement with observations, although the change is slower and takes longer than in the real universe. We discuss shortcomings that have to be addressed for this and similar statistical models in the literature to develop into realistic quantitative treatment of backreaction.
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(2018)We report direct evidence of pre-processing of the galaxies residing in galaxy groups falling into galaxy clusters drawn from the Local Cluster Substructure Survey (LoCuSS). 34 groups have been identified via theirX-ray emission in the infall regions of 23 massive (<M-200 > = 10(15) M-circle dot) clusters at 0.15 <z <0.3. Highly complete spectroscopic coverage combined with 24 mu m imaging from Spitzer allows us to make a consistent and robust selection of cluster and group members including star-forming galaxies down to a stellar mass limit of M* = 2 x 10(10) M-circle dot. The fraction f(SF) of star-forming galaxies in infalling groups is lower and with a flatter trend with respect to clustercentric radius when compared to the rest of the cluster galaxy population. At R approximate to 1.3 r(200), the fraction of star-forming galaxies in infalling groups is half that in the cluster galaxy population. This is direct evidence that star-formation quenching is effective in galaxies already prior to them settling in the cluster potential, and that groups are favourable locations for this process.
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(2018)Galaxy clusters are expected to form hierarchically in a Lambda cold dark matter (Lambda CDM) universe, growing primarily through mergers with lower mass clusters and the continual accretion of group-mass haloes. Galaxy clusters assemble late, doubling their masses since z similar to 0.5, and so the outer regions of clusters should be replete with accreting group-mass systems. We present an XMM-Newton survey to search for X-ray groups in the infall regions of 23 massive galaxy clusters (<M-200 > similar to 10(15)M(circle dot)) at z similar to 0.2, identifying 39 X-ray groups that have been spectroscopically confirmed to lie at the cluster redshift. These groups have mass estimates in the range 2 x 10(13)-7 x 10(14)M(circle dot), and group-to-cluster mass ratios as low as 0.02. The comoving number density of X-ray groups in the infall regions is similar to 25x higher than that seen for isolated X-ray groups from the XXL survey. The average mass per cluster contained within these X-ray groups is 2.2 x 10(14)M(circle dot), or 19 +/- 5 per cent of the mass within the primary cluster itself. We estimate that similar to 10(15)M(circle dot) clusters increase their masses by 16 +/- 4 per cent between z = 0.223 and the present day due to the accretion of groups with M-200 >= 10(13.2)M(circle dot). This represents about half of the expected mass growth rate of clusters at these late epochs. The other half is likely to come from smooth accretion of matter not bound within haloes. The mass function of the infalling X-ray groups appears significantly top heavy with respect to that of 'field' X-ray systems, consistent with expectations from numerical simulations, and the basic consequences of collapsed massive dark matter haloes being biased tracers of the underlying large-scale density distribution.
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(2019)We use galaxy dynamical information to calibrate the richness-mass scaling relation of a sample of 428 galaxy clusters that are members of the CODEX sample with redshifts up to z similar to 0.7. These clusters were X-ray selected using the ROSAT All-Sky Survey (RASS) and then cross-matched to associated systems in the redMaPPer (the red sequence Matched-filter Probabilistic Percolation) catalogue from the Sloan Digital Sky Survey. The spectroscopic sample we analyse was obtained in the SPIDERS program and contains similar to 7800 red member galaxies. Adopting NFW mass and galaxy density profiles and a broad range of orbital anisotropy profiles, we use the Jeans equation to calculate halo masses. Modelling the scaling relation as lambda proportional to A(lambda) M-200c(B lambda) (1 + z)()lambda), we find the parameter constraints A(lambda) = 38.6(-4.1)(+3.1) +/- 3.9, B-lambda = 0.99(-0.07)(+0.06) +/- 0.04, and gamma(lambda) = -1.13(-0.34)(+0.32) +/- 0.49, where we present systematic uncertainties as a second component. We find good agreement with previously published mass trends with the exception of those from stacked weak lensing analyses. We note that although the lensing analyses failed to account for the Eddington bias, this is not enough to explain the differences. We suggest that differences in the levels of contamination between pure redMaPPer and RASS + redMaPPer samples could well contribute to these differences. The redshift trend we measure is more negative than but statistically consistent with previous results. We suggest that our measured redshift trend reflects a change in the cluster galaxy red sequence (RS) fraction with redshift, noting that the trend we measure is consistent with but somewhat stronger than an independently measured redshift trend in the RS fraction. We also examine the impact of a plausible model of correlated scatter in X-ray luminosity and optical richness, showing it has negligible impact on our results.
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(2016)A nearby source of Lyman-Werner (LW) photons is thought to be a central component in dissociating H-2 and allowing for the formation of a direct collapse black hole seed. Nearby sources are also expected to produce copious amounts of hydrogen ionizing photons and X-ray photons. We study here the feedback effects of the X-ray photons by including a spectrum due to high-mass X-ray binaries on top of a galaxy with a stellar spectrum. We explicitly trace photon packages emerging from the nearby source and track the radiative and chemical effects of the multifrequency source (E-photon = 0.76 eV -> 7500 eV). We find that X-rays have a strongly negative feedback effect, compared to a stellar only source, when the radiative source is placed at a separation greater than greater than or similar to 1 kpc. The X-rays heat the low and medium density gas in the envelope surrounding the collapsing halo suppressing the mass inflow. The result is a smaller enclosed mass compared to the stellar only case. However, for separations of less than or similar to 1 kpc, the feedback effects of the X-rays becomes somewhat neutral. The enhanced LW intensity at close separations dissociates more H-2 and this gas is heated due to stellar photons alone, the addition of X-rays is then not significant. This distance dependence of X-ray feedback suggests that a Goldilocks zone exists close to a forming galaxy where X-ray photons have a much smaller negative feedback effect and ideal conditions exist for creating massive black hole seeds.
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(2017)The appearance of supermassive black holes at very early times(1-3) in the Universe is a challenge to our understanding of star and black hole formation. The direct-collapse(4,5) black hole scenario provides a potential solution. A prerequisite for forming a direct-collapse black hole is that the formation of (much less massive) population III stars be avoided(6,7); this can be achieved by destroying H-2 by means of Lyman-Werner radiation (photons of energy around 12.6 eV). Here we show that two conditions must be met in the protogalaxy that will host the direct-collapse black hole. First, prior star formation must be delayed; this can be achieved with a background LymanWerner flux of J(BG) greater than or similar to 100J(21) (J(21) is the intensity of background radiation in units of 10(-21) erg cm(-2) s(-1) Hz(-1) sr(-1)). Second, an intense burst of Lyman-Werner radiation from a neighbouring star-bursting protogalaxy is required, just before the gas cloud undergoes gravitational collapse, to suppress star formation completely. Using high-resolution hydrodynamical simulations that include full radiative transfer, we find that these two conditions inevitably move the host protogalaxy onto the isothermal atomic cooling track, without the deleterious effects of either photo-evaporating the gas or polluting it with heavy elements. These atomically cooled, massive protogalaxies are expected ultimately to form a direct-collapse black hole of mass 10(4)-10(5)M circle dot.
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(2016)We present the measurement of the projected and redshift-space two-point correlation function (2pcf) of the new catalog of Chandra COSMOS-Legacy active galactic nucleus (AGN) at 2.9 similar to 10(46) erg s(-1)) using the generalized clustering estimator based on phot-z probability distribution functions in addition to any available spec-z. We model the projected 2pcf, estimated using pi(max) = 200 h(-1) Mpc with the two-halo term and we derive a bias at z similar to 3.4 equal to b. =. 6.6(+0.60) -(0.55), which corresponds to a typical mass of the hosting halos of log M-h. =. 12.83(+0.12) -(0.11) h(-1)M circle dot. A similar bias is derived using the redshift-space 2pcf, modeled including the typical phot-z error sigma(z). =. 0.052 of our sample at z >= 2.9. Once we integrate the projected 2pcf up to pi(max). =. 200 h(-1) Mpc, the bias of XMM and Chandra COSMOS at z =. 2.8 used in Allevato et al. is consistent with our results at higher redshifts. The results suggest only a slight increase of the bias factor of COSMOS AGNs at z greater than or similar to 3 with the typical hosting halo mass of moderate-luminosity AGNs almost constant with redshift and equal to log M-h = 12.92(+0.-13) (0.18) at z - 2.8 and log M-h - 12.83(+0.11) (-0.12) at z similar to 3.4, respectively. The observed redshift evolution of the bias of COSMOS AGNs implies that moderate-luminosity AGNs. still inhabit group-sized halos at z greater than or similar to 3, but slightly less massive than observed in different independent studies using X-ray AGNs. at z less than or similar to 2.
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(2019)Context. In the framework of the hierarchical model the intra-cluster medium properties of galaxy clusters are tightly linked to structure formation, which makes X-ray surveys well suited for cosmological studies. To constrain cosmological parameters accurately by use of galaxy clusters in current and future X-ray surveys, a better understanding of selection effects related to the detection method of clusters is needed. Aims. We aim at a better understanding of the morphology of galaxy clusters to include corrections between the different core types and covariances with X-ray luminosities in selection functions. In particular, we stress the morphological deviations between a newly described surface brightness profile characterization and a commonly used single beta-model. Methods. We investigated a novel approach to describe surface brightness profiles, where the excess cool-core emission in the centers of the galaxy clusters is modeled using wavelet decomposition. Morphological parameters and the residuals were compared to classical single beta-models, fitted to the overall surface brightness profiles. Results. Using single beta-models to describe the ensemble of overall surface brightness profiles leads on average to a non-zero bias (0.032 +/- 0.003) in the outer part of the clusters, that is an approximate 3% systematic difference in the surface brightness at large radii. Furthermore, beta-models show a general trend toward underestimating the flux in the outskirts for smaller core radii. Fixing the beta parameter to 2/3 doubles the bias and increases the residuals from a single beta-model up to more than 40%. Modeling the core region in the fitting procedure reduces the impact of these two effects significantly. In addition, we find a positive scaling between shape parameters and temperature, as well as a negative correlation of approximately -0.4 between extent and luminosity. Conclusion. We demonstrate the caveats in modeling galaxy clusters with single beta-models and recommend using them with caution, especially when the systematics are not taken into account. Our non-parametric analysis of the self-similar scaled emission measure profiles indicates no systematic core-type differences of median profiles in the galaxy cluster outskirts.
