Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCross-correlating the gamma-ray sky with catalogs of galaxy clusters
67
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report the detection of a cross-correlation signal between {it Fermi} Large Area Telescope diffuse gamma-ray maps and catalogs of clusters. In our analysis, we considered three different catalogs: WHL12, redMaPPer and PlanckSZ. They all show a positive correlation with different amplitudes, related to the average mass of the objects in each catalog, which also sets the catalog bias. The signal detection is confirmed by the results of a stacking analysis. The cross-correlation signal extends to rather large angular scales, around 1 degree, that correspond, at the typical redshift of the clusters in these catalogs, to a few to tens of Mpc, i.e. the typical scale-length of the large scale structures in the Universe. Most likely this signal is contributed by the cumulative emission from AGNs associated to the filamentary structures that converge toward the high peaks of the matter density field in which galaxy clusters reside. In addition, our analysis reveals the presence of a second component, more compact in size and compatible with a point-like emission from within individual clusters. At present, we cannot distinguish between the two most likely interpretations for such a signal, i.e. whether it is produced by AGNs inside clusters or if it is a diffuse gamma-ray emission from the intra-cluster medium. We argue that this latter, intriguing, hypothesis might be tested by applying this technique to a low redshift large mass cluster sample.
rate research
Read More
Cross-correlating gamma-ray maps with locations of galaxies in the low-redshift Universe vastly increases sensitivity to signatures of annihilation of dark matter particles. Low-redshift galaxies are ideal targets, as the largest contribution to anisotropy in the gamma-ray sky from annihilation comes from $zlesssim 0.1$, where we expect minimal contributions from astrophysical sources such as blazars. Cross-correlating the five-year data of Fermi-LAT with the redshift catalog of the 2MASS survey can detect gamma rays from annihilation if dark matter has the canonical annihilation cross section and its mass is smaller than $sim$100 GeV.
Unveiling the origin of the coalescing binaries detected via gravitational waves (GW) is challenging, notably if no multi-wavelength counterpart is detected. One important diagnostic tool is the coalescing binary distribution with respect to the large scale structures (LSS) of the universe, which we quantify via the cross-correlation of galaxy catalogs with GW ones. By using both existing and forthcoming galaxy catalogs and using realistic Monte Carlo simulations of GW events, we find that the cross-correlation signal should be marginally detectable in a 10-year data taking of advanced LIGO-Virgo detectors at design sensitivity, at least for binary neutron star mergers. The expected addition of KAGRA and LIGO-India to the GW detector network would allow for a firmer detection of this signal and, in combination with future cosmological surveys, would also permit the detection of cross-correlation for coalescing black holes. Such a measurement may unveil, for instance, a primordial origin of coalescing black holes. To attain this goal, we find that it is crucial to adopt a tomographic approach and to reach a sufficiently accurate localization of GW events. The depth of forthcoming surveys will be fully exploited by third generation GW detectors such as the Einstein Telescope or the Cosmic Explorer, which will allow one to perform precision studies of the coalescing black hole LSS distribution and attain rather advanced model discrimination capabilities.
We report the measurement of the angular power spectrum of cross-correlation between the unresolved component of the Fermi-LAT gamma-ray sky-maps and the CMB lensing potential map reconstructed by the Planck satellite. The matter distribution in the Universe determines the bending of light coming from the last scattering surface. At the same time, the matter density drives the growth history of astrophysical objects, including their capability at generating non-thermal phenomena, which in turn give rise to gamma-ray emissions. The Planck lensing map provides information on the integrated distribution of matter, while the integrated history of gamma-ray emitters is imprinted in the Fermi-LAT sky maps. We report here the first evidence of their correlation. We find that the multipole dependence of the cross-correlation measurement is in agreement with current models of the gamma-ray luminosity function for AGN and star forming galaxies, with a statistical evidence of 3.0$sigma$. Moreover, its amplitude can in general be matched only assuming that these extra-galactic emitters are also the bulk contribution of the measured isotopic gamma-ray background (IGRB) intensity. This leaves little room for a big contribution from galactic sources to the IGRB measured by Fermi-LAT, pointing toward a direct evidence of the extragalactic origin of the IGRB.
Galaxy surveys probe both structure formation and the expansion rate, making them promising avenues for understanding the dark universe. Photometric surveys accurately map the 2D distribution of galaxy positions and shapes in a given redshift range, while spectroscopic surveys provide sparser 3D maps of the galaxy distribution. We present a way to analyse overlapping 2D and 3D maps jointly and without loss of information. We represent 3D maps using spherical Fourier-Bessel (sFB) modes, which preserve radial coverage while accounting for the spherical sky geometry, and we decompose 2D maps in a spherical harmonic basis. In these bases, a simple expression exists for the cross-correlation of the two fields. One very powerful application is the ability to simultaneously constrain the redshift distribution of the photometric sample, the sample biases, and cosmological parameters. We use our framework to show that combined analysis of DESI and LSST can improve cosmological constraints by factors of ${sim}1.2$ to ${sim}1.8$ on the region where they overlap relative to identically sized disjoint regions. We also show that in the overlap of DES and SDSS-III in Stripe 82, cross-correlating improves photo-$z$ parameter constraints by factors of ${sim}2$ to ${sim}12$ over internal photo-$z$ reconstructions.
In principle, the angular anisotropy in the extragalactic gamma-ray background (EGRB) places severe constraints upon putative populations of unresolved gamma-ray point sources. Existing estimates of the EGRB anisotropy have been constructed by excising known point sources, e.g., taken from the First or 2 Year Fermi-LAT Source Catalog (1FGL or 2FGL, respectively) and statistically analyzing the residual gamma-ray sky maps. We perform an independent check of the EGRB anisotropy limits by comparing the values obtained from the 1FGL-masked sky maps to the signal implied by sources that lie below the 1FGL detection threshold in the more sensitive 2FGL and 1FHL (First Fermi-LAT catalog of >10 GeV sources). As such, our analysis provides an internal consistency check of implications for source counts and spectral index distributions of gamma-ray bright active galactic nuclei obtained from Fermi-LAT data. Based on this, we find evidence for substantially larger anisotropies than those previously reported at energies above 5 GeV, where BL Lac objects are likely to provide the bulk of their contribution to the EGRB. This uncertainty in the EGRB anisotropy cautions against using it as an independent constraint for the high-redshift gamma-ray universe. Moreover, this would suggest that contrary to previous claims, smooth extensions of the resolved point-source population may be able to simultaneously explain both the isotropic and anisotropic components of the EGRB.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
