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Register a new userThe Herschel Fornax Cluster Survey I: The Bright Galaxy Sample
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Jonathan Davies Dr.
Publication date
2012
fields
Physics
and research's language is
English
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We present Herschel observations of the Fornax cluster at 100, 160, 250, 350 and 500u with a spatial resolution of 7 - 36 arc sec (10 = 1 kpc at d_Fornax=17.9 Mpc). We define a sample of 11 bright galaxies, selected at 500u, directly comparable with our past work on Virgo. We find good agreement with previous observations made by IRAS and Planck. The FIR luminosity density is higher (factor of three) in Fornax compared to Virgo. The 100u (42.5-122.5u) luminosity is two orders of magnitude larger in Fornax than in the local field as measured by IRAS. Using stellar (L_{0.4-2.5}) and FIR (L_{100-500}) luminosities we estimate a mean optical depth of tau=0.4+/-0.1 - the same value as Virgo. For 10 of the 11 galaxies (NGC1399 excepted) we fit a modified blackbody curve (beta=2.0) to the SEDs to derive dust masses and temperatures of 10^{6.54-8.35} M_0 and T=14.6-24.2K respectively, comparable to Virgo. The derived stars-to-gas(atomic) and gas(atomic)-to-dust ratios vary from 1.1-67.6 and 9.8-436.5 respectively, again consistent with Virgo. Fornax is a mass overdensity in stars and dust of about 120 compared to the local field (30 for Virgo). Fornax and Virgo are both a factor of 6 lower over densities in gas(atomic) than in stars and dust indicating loss of gas, but not dust and stars, in the cluster environment. As the brightest FIR source in either Fornax and Virgo, NGC1365 is detected by Planck. The Planck data fit the PACS/SPIRE SED out to 1382u with no evidence of other sources of emission (spinning dust, free-free, synchrotron). At the opposite end of the scale NGC1399 is detected only at 500$mu$m with the emission probably arising from the nuclear radio source rather than inter-stellar dust.
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Traditionally, galaxy clusters have been expected to retain all the material accreted since their formation epoch. For this reason, their matter content should be representative of the Universe as a whole, and thus their baryon fraction should be close to the Universal baryon fraction. We make use of the sample of the 100 brightest galaxy clusters discovered in the XXL Survey to investigate the fraction of baryons in the form of hot gas and stars in the cluster population. We measure the gas masses of the detected halos and use a mass--temperature relation directly calibrated using weak-lensing measurements for a subset of XXL clusters to estimate the halo mass. We find that the weak-lensing calibrated gas fraction of XXL-100-GC clusters is substantially lower than was found in previous studies using hydrostatic masses. Our best-fit relation between gas fraction and mass reads $f_{rm gas,500}=0.055_{-0.006}^{+0.007}left(M_{rm 500}/10^{14}M_odotright)^{0.21_{-0.10}^{+0.11}}$. The baryon budget of galaxy clusters therefore falls short of the Universal baryon fraction by about a factor of two at $r_{rm 500}$. Our measurements require a hydrostatic bias $1-b=M_X/M_{rm WL}=0.72_{-0.07}^{+0.08}$ to match the gas fraction obtained using lensing and hydrostatic equilibrium. Comparing our gas fraction measurements with the expectations from numerical simulations, our results favour an extreme feedback scheme in which a significant fraction of the baryons are expelled from the cores of halos. This model is, however, in contrast with the thermodynamical properties of observed halos, which might suggest that weak-lensing masses are overestimated. We note that a mass bias $1-b=0.58$ as required to reconcile Planck CMB and cluster counts should translate into an even lower baryon fraction, which poses a major challenge to our current understanding of galaxy clusters. [Abridged]
We present a catalogue of X-ray selected galaxy clusters and groups as a first release of the 2XMMi/SDSS Galaxy Cluster Survey. The survey is a search for galaxy clusters detected serendipitously in observations with XMM-Newton in the footprint of the Sloan Digital Sky Survey (SDSS). The main aims of the survey are to identify new X-ray galaxy clusters, investigate their X-ray scaling relations, identify distant cluster candidates and study the correlation of the X-ray and optical properties. In this paper we describe the basic strategy to identify and characterize the X-ray cluster candidates that currently comprise 1180 objects selected from the second XMM-Newton serendipitous source catalogue (2XMMi-DR3). Cross-correlation of the initial catalogue with recently published optically selected SDSS galaxy cluster catalogues yields photometric redshifts for 275 objects. Of these, 182 clusters have at least one member with a spectroscopic redshift from existing public data (SDSS-DR8). Here we present the X-ray properties of the first cluster sample which comprises 175 clusters, among which 139 objects are new X-ray discoveries while the others were previously known as X-ray sources. The first cluster sample from the survey covers a wide range of redshifts from 0.09 to 0.61, bolometric luminosities L_500 = 1.9 x 10^42 - 1.2 x 10^45 erg/s, and masses M_500 = 2.3 x 10^13 - 4.9 x 10^14 Msun. We extend the relation between the X-ray bolometric luminosity L_500 and the X-ray temperature towards significantly lower T and L and still find that the slope of the linear L-T relation is consistent with values published for high luminosities.
The XXL survey is the largest survey carried out by XMM-Newton. Covering an area of 50deg$^2$, the survey contains $sim450$ galaxy clusters out to a redshift $sim$2 and to an X-ray flux limit of $sim5times10^{-15}erg,s^{-1}cm^{-2}$. This paper is part of the first release of XXL results focussed on the bright cluster sample. We investigate the scaling relation between weak-lensing mass and X-ray temperature for the brightest clusters in XXL. The scaling relation is used to estimate the mass of all 100 clusters in XXL-100-GC. Based on a subsample of 38 objects that lie within the intersection of the northern XXL field and the publicly available CFHTLenS catalog, we derive the $M_{WL}$ of each system with careful considerations of the systematics. The clusters lie at $0.1<z<0.6$ and span a range of $ Tsimeq1-5keV$. We combine our sample with 58 clusters from the literature, increasing the range out to 10keV. To date, this is the largest sample of clusters with $M_{WL}$ measurements that has been used to study the mass-temperature relation. The fit ($Mpropto T^b$) to the XXL clusters returns a slope $b=1.78^{+0.37}_{-0.32}$ and intrinsic scatter $sigma_{ln M|T}simeq0.53$; the scatter is dominated by disturbed clusters. The fit to the combined sample of 96 clusters is in tension with self-similarity, $b=1.67pm0.12$ and $sigma_{ln M|T}simeq0.41$. Overall our results demonstrate the feasibility of ground-based weak-lensing scaling relation studies down to cool systems of $sim1keV$ temperature and highlight that the current data and samples are a limit to our statistical precision. As such we are unable to determine whether the validity of hydrostatic equilibrium is a function of halo mass. An enlarged sample of cool systems, deeper weak-lensing data, and robust modelling of the selection function will help to explore these issues further.
Context. The XXL Survey is the largest survey carried out by the XMM-Newton satellite and covers a total area of 50 square degrees distributed over two fields. It primarily aims at investigating the large-scale structures of the Universe using the distribution of galaxy clusters and active galactic nuclei as tracers of the matter distribution. Aims. This article presents the XXL bright cluster sample, a subsample of 100 galaxy clusters selected from the full XXL catalogue by setting a lower limit of $3times 10^{-14},mathrm{erg ,s^{-1}cm^{-2}}$ on the source flux within a 1$^{prime}$ aperture. Methods. The selection function was estimated using a mixture of Monte Carlo simulations and analytical recipes that closely reproduce the source selection process. An extensive spectroscopic follow-up provided redshifts for 97 of the 100 clusters. We derived accurate X-ray parameters for all the sources. Scaling relations were self-consistently derived from the same sample in other publications of the series. On this basis, we study the number density, luminosity function, and spatial distribution of the sample. Results. The bright cluster sample consists of systems with masses between $M_{500}=7times 10^{13}$ and $3times 10^{14} M_odot$, mostly located between $z=0.1$ and 0.5. The observed sky density of clusters is slightly below the predictions from the WMAP9 model, and significantly below the predictions from the Planck 2015 cosmology. In general, within the current uncertainties of the cluster mass calibration, models with higher values of $sigma_8$ and/or $Omega_m$ appear more difficult to accommodate. We provide tight constraints on the cluster differential luminosity function and find no hint of evolution out to $zsim1$. We also find strong evidence for the presence of large-scale structures in the XXL bright cluster sample and identify five new superclusters.
We present the first results of a deep Chandra survey of the inner 1 degree of the Fornax cluster of galaxies. Ten 50 ksec pointings were obtained in a mosaic centered on the giant elliptical galaxy NGC 1399 at the nominal cluster center. Emission and temperature maps of Fornax are presented, and an initial study of 771 detected X-ray point sources is made. Regions as small as 100pc are resolved. The intra-cluster gas in Fornax exhibits a highly asymmetric morphology and temperature structure, dominated by a 180 kpc extended ``plume of low surface brightness, cool, ~1 keV) gas to the North-East of NGC 1399 with a sharper edge to the South West. The elliptical galaxy NGC 1404 also exhibits a cool halo of X-ray gas within the cluster, with a highly sharpened leading edge as it presumably falls into the cluster, and a cometary-like tail. We estimate that some ~200-400 point sources are physically associated with Fornax. Confirming earlier works, we find that the globular cluster population in NGC 1399 is highly X-ray active, extending to globulars which may in fact be intra-cluster systems. We have also found a remarkable correlation between the location of giant and dwarf cluster galaxies and the presence of X-ray counterparts, such that systems inhabiting regions of low gas density are more likely to show X-ray activity. Not only does this correlate with the asymmetry of the intra-cluster gas but also with the axis joining the center of Fornax to an infalling group 1 Mpc to the South-West. We suggest that Fornax may be experiencing an intergalactic ``headwind due to motion relative to the surrounding large-scale structure.
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