1509.04275
Investigating the cores of fossil systems with Chandra
Bharadwaj, Reiprich, Sanders, Schellenberger
Investigate the cores of fossil galaxy groups and clusters ('fossil systems') using archival Chandra data for a sample of 17 fossil systems. Determined the cool-core fraction for fossils via three observable diagnostics, the central cooling time, cuspiness and concentration parameter. Quantified the dynamical state of the fossils by the X-ray peak/BCG, and the X-ray peak/emission weighted centre separations. Studied the X-ray emission coincident with the BCG to detect the presence of potential thermal coronae. A deprojection analysis was performed for z<0.05 fossils to obtain cooling time and entropy profiles, and to resolve subtle temperature structures. Investigated the Lx-T relation for fossils from the 400d catalogue to see if the scaling relation deviates form that of other groups. Most fossils are identified as cool-core objects via at least two cool-core diagnostics. All fossils have their dominant elliptical galaxy within 50 kpc of the X-ray peak, and most also have the emission weighted center within that distance. Do not see clear indications of a X-ray corona associated with the BCG unlike that has been observed for some other objects. Fossils do not have universal temperature profiles, with some low-temperature objects lacking features that are expected for ostensibly relaxed objects with a cool-core. The entropy profiles of the z<0.05 fossil systems can be well-described by a power law model, albeit with indices smaller than 1. The 400d fossils Lx-T relation shows indications of an elevated normalization with respect to other groups, which seems to persist even after factoring in selection effects.
1509.04290
Mitigating systematic errors in angular correlation function measurements from wide field surveys
Morrison, Hildebrandt
Present an investigation into the effects of survey systematics such as varying depth, PSF size, and extinction on the galaxy selection and correlation in photometric, multi-epoch, wide area surveys. Take the CFHTLenS as an example. Variations in galaxy selection due to systematics are found to cause density fluctuations of up to 10% for some small fraction of the area for most galaxy redshift slices and as much as 50% for some extreme cases of faint high-redshift samples. This results in correlations of galaxies against survey systematics of order ~1% when averaged over the survey area. Present an empirical method for mitigating these systematics correlations from measurements of angular correlation functions using weighted random points. These weighted random catalogs are estimated from the observed galaxy over-densities by mapping these to survey parameters. Able to model and mitigate the effect of systematic correlations allowing for non-linear dependences of density on systematics. Applied to CFHTLenS, find that the method reduces spurious correlations in the data by a factor of two for most galaxy samples and as much as an order of magnitude in others. Such a treatment is particularly important for an unbiased estimation of very small correlation signals, as e.g. from weak gravitational lensing magnification bias. Impose a criterion for using a galaxy sample in a magnification measurement of the majority of the systematic correlations show improvement and are less than 10% of the expected magnification signal when combined in the galaxy cross correlation. After correction the galaxy samples in CFHTLenS satisfy this criterion for z_phot<0.9 and will be used in a future analysis of magnification.
1509.04293
Gaussian covariance matrices for anisotropic galaxy clustering meausrements
Grieb, Sánchez, Salazar-Albornoz, dalla Veccia
Measurement of the redshift-space galaxy clustering have bee na prolific source of cosmological information in recent years. In the era of precision cosmology, accurate covariance estimates are an essential step for the validation of galaxy clustering models of the redshift-space two-point statistics. For cases where only a limited set of simulations is available, assessing the data covariance is not possible or only leads to a noisy estimate. Relying on simulated realizations of the survey data means that tests of the cosmo dependence of the covariance are expensive. With these two points in mind, this work aims at presenting a simple theoretical model for the linear covariance of anisotropic galaxy clustering observations with synthetic catalogues. Considering the Legendre moments ('multipoles') of the 2PT statistics and projections into wide bins of the line-of-sight parameter ('clustering wedges'), describe the modeling of the covariance for these anisotropic clustering measurements for galaxy samples with a trivial geometry in the case of a Gaussian approximation of the clustering likelihood. The explicit formulas are presented for Fourier space and for configuration space covariance matrices. To validate the model, create synthetic HOD galaxy catalogues by populating the haloes of an ensemble of large-volume N-body simulations. Using linear and non-linear input power spectra, find excellent agreement between the model predictions and the measurements on the synthetic catalogues.
1509.04345
Discovery of a strongly-lensed massive quiescent galaxy a z=2.636: spatially-resolved spectroscopy and indications of rotation
Newman, Belli, Ellis
As the title says. Velocity dispersion with the effective radius is sigma_e=271±41 km/s.
1509.04430
Spectral properties of galaxies in void regions
Liu, Pan, Hao, Hoyle, Constantin, Vogeley
Present a study of spectral properties of galaxies in underdense large-scale structures, voids. The void galaxy sample (75939 galaxies) is selected from SDSS DR7 with z<0.107. Find that there are no significant differences in the luminosities, stellar masses, stellar populations, and sSFRs between void galaxies of specific spectral types and their wall counterparts. However, the fraction of SF galaxies in voids is significantly higher (>9%) than that in walls. Void galaxies, when considering all spectral types, are slightly fainter, less massive, have younger stellar populations and of higher sSFRs than wall galaxies. These minor differences are totally caused by the higher fraction of SF galaxies in voids. Confirm that AGNs exist in voids, already found by CO08, with similar abundance as in walls. Type I AGNs contribute ~1-2% of void galaxies, similar to their fraction in walls. The intrinsic [OIII] luminosities, spanning over 1e6 Lsun~ 1e9 Lsun, and Eddington ratios are similar comparing the void AGNs versus wall AGNs. Small scale statistics show that all spectral types of void galaxies are less clustered than their counterparts in walls. major merger may not be the dominant trigger of BH accretion in the luminosity range probed. Study implies that the growth of BHs relies weakly on LSS.
No comments:
Post a Comment