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Register a new userFinding and characterising WHIM structures using the luminosity density method
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We have developed a new method to approach the missing baryons problem. We assume that the missing baryons reside in a form of Warm Hot Intergalactic Medium, i.e. the WHIM. Our method consists of (a) detecting the coherent large scale structure in the spatial distribution of galaxies that traces the Cosmic Web and that in hydrodynamical simulations is associated to the WHIM, (b) map its luminosity into a galaxy luminosity density field, (c) use numerical simulations to relate the luminosity density to the density of the WHIM, (d) apply this relation to real data to trace the WHIM using the observed galaxy luminosities in the Sloan Digital Sky Survey and 2dF redshift surveys. In our application we find evidence for the WHIM along the line of sight to the Sculptor Wall, at redshifts consistent with the recently reported X-ray absorption line detections. Our indirect WHIM detection technique complements the standard method based on the detection of characteristic X-ray absorption lines, showing that the galaxy luminosity density is a reliable signpost for the WHIM. For this reason, our method could be applied to current galaxy surveys to optimise the observational strategies for detecting and studying the WHIM and its properties. Our estimates of the WHIM hydrogen column density in Sculptor agree with those obtained via the X-ray analysis. Due to the additional column density estimate, our method has potential for improving the constrains of the physical parameters of the WHIM as derived with X-ray absorption, and thus for improving the understanding of the missing baryons problem.
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We propose a new approach to the missing baryons problem. Building on the common assumption that the missing baryons are in the form of the Warm Hot Intergalactic Medium (WHIM), we further assumed here that the galaxy luminosity density can be used as a tracer of the WHIM. The latter assumption is supported by our finding of a significant correlation between the WHIM density and the galaxy luminosity density in the hydrodynamical simulations of Cui et al. (2012). We further found that the fraction of the gas mass in the WHIM phase is substantially (by a factor of $sim$1.6) higher within the large scale galactic filaments, i.e. $sim$70%, compared to the average in the full simulation volume of $sim$0.1,Gpc$^3$. The relation between the WHIM overdensity and the galaxy luminosity overdensity within the galactic filaments is consistent with linear: $delta_{rm whim},=,0.7,pm,0.1,times,delta_mathrm{LD}^{0.9 pm 0.2}$. We applied our procedure to the line of sight to the blazar H2356-309 and found evidence for the WHIM in correspondence of the Sculptor Wall (z $sim$0.03 and $log{N_H}$ = $19.9^{+0.1}_{-0.3}$) and Pisces-Cetus superclusters (z $sim$0.06 and $log{N_H}$ = $19.7^{+0.2}_{-0.3}$), in agreement with the redshifts and column densities of the X-ray absorbers identified and studied by Fang et al. (2010) and Zappacosta et al. (2010). This agreement indicates that the galaxy luminosity density and galactic filaments are reliable signposts for the WHIM and that our method is robust in estimating the WHIM density. The signal that we detected cannot originate from the halos of the nearby galaxies since they cannot account for the large WHIM column densities that our method and X-ray analysis consistently find in the Sculptor Wall and Pisces-Cetus superclusters.
We present the results of a new study of the K-band galaxy luminosity function (KLF) at redshifts z<3.75, based on a nested combination of the UltraVISTA, CANDELS and HUDF surveys. The large dynamic range in luminosity spanned by this new dataset (3-4 dex over the full redshift range) is sufficient to clearly demonstrate for the first time that the faint-end slope of the KLF at z>0.25 is relatively steep (-1.3<alpha<-1.5 for a single Schechter function), in good agreement with recent theoretical and phenomenological models. Moreover, based on our new dataset we find that a double Schechter function provides a significantly improved description of the KLF at z<2. At redshifts z>0.25 the evolution of the KLF is remarkably smooth, with little or no evolution evident at faint (M_K>-20.5) or bright magnitudes (M_K<-24.5). Instead, the KLF is seen to evolve rapidly at intermediate magnitudes, with the number density of galaxies at M_K~-23 dropping by a factor of ~5 over the redshift interval 0.25<z<3.75. Motivated by this, we explore a simple description of the evolving KLF based on a double Schechter function with fixed faint-end slopes (alpha_1=-0.5, alpha_2=-1.5) and a shared characteristic magnitude (M_K*). According to this parameterisation, the normalisation of the component which dominates the faint-end of the KLF remains approximately constant, with phi*_2 decreasing by only a factor of ~2 between z~0 and z~3.25. In contrast, the component which dominates the bright end of the KLF at low redshifts evolves dramatically, becoming essentially negligible by z~3. Finally, we note that within this parameterisation, the observed evolution of M_K* between z~0 and z~3.25 is entirely consistent with M_K* corresponding to a constant stellar mass of M*~5x10^10 Msun at all redshifts.
The classical cosmological V/Vm-test is introduced and elaborated. Use of the differential distribution p(V/Vm) of the V/Vm-variable rather than just the mean <V/Vm> leads directly to the cosmological number density without any need for assumptions about the cosmological evolution of the underlying (quasar) population. Calculation of this number density n(z) from p(V/Vm) is illustrated using the best sample that was available in 1981, when this method was developed. This sample of 76 quasars is clearly too small for any meaningful results. The method will be later applied to a much larger cosmological sample to infer the cosmological number density n(z) as a function of the depth z. Keywords: V/Vm . luminosity volume . cosmological number density . V/Vm distribution
In this paper we investigate the strong lensing statistics in galaxy clusters. We extract dark matter haloes from the Millennium-XXL simulation, compute their Einstein radius distribution, and find a very good agreement with Monte Carlo predictions produced with the MOKA code. The distribution of the Einstein radii is well described by a log-normal distribution, with a considerable fraction of the largest systems boosted by different projection effects. We discuss the importance of substructures and triaxiality in shaping the size of the critical lines for cluster size haloes. We then model and interpret the different deviations, accounting for the presence of a Bright Central Galaxy (BCG) and two different stellar mass density profiles. We present scaling relations between weak lensing quantities and the size of the Einstein radii. Finally we discuss how sensible is the distribution of the Einstein radii on the cosmological parameters {Omega}_M-{sigma}_8 finding that cosmologies with higher {Omega}_M and {sigma}_8 possess a large sample of strong lensing clusters. The Einstein radius distribution may help distinguish Planck13 and WMAP7 cosmology at 3{sigma}.
We use numerical simulations to predict the soft X-ray ([0.4-0.6] keV) and Sunyaev-Zeldovich signal (at 150 GHz) from the large scale structure in the Universe and then compute 2-point statistics to study the spatial distribution and time evolution of the signals. The average X-ray signal predicted for the WHIM is in good agreement with observational constraints that set it at about 10% of the total Diffuse X-ray Background. The characteristic angle computed with the Autocorrelation Function is of the order of some arcminutes and becomes smaller at higher redshift. The power spectrum peak of the SZ due to the WHIM is at l~10000 and has amplitude of ~0.2 muK^2, about one order of magnitude below the signal measured with telescopes like Planck, ACT, and SPT. Even if the high-redshift WHIM signal is too weak to be detected using X-rays only, the small-scale correlation between X-ray and SZ maps is dominated by the high-redshift WHIM. This makes the analysis of the SZ signal in support of X-rays a promising tool to study the early time WHIM.
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