اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدCross Correlations of X-ray and Optically Selected Clusters With Near Infrared and Optical Galaxies
55
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We compute the real-space cluster-galaxy cross-correlation xi_cg(r) using the ROSAT-ESO Flux Limited X-ray (REFLEX) cluster survey, a group catalogue constructed from the final version of the 2dFGRS, and galaxies extracted from 2MASS and APM surveys. This first detailed calculation of the cross-correlation for X-ray clusters and groups, is consistent with previous works and shows that xi_cg(r) can not be described by a single power law. We analyse the clustering dependence on the cluster X-ray luminosity L_X and virial mass M_vir thresholds as well as on the galaxy limiting magnitude. We also make a comparison of our results with those obtained for the halo-mass cross-correlation function in a LambdaCDM N-body simulation to infer the scale dependence of galaxy bias around clusters. Our results indicate that the distribution of galaxies shows a significant anti-bias at highly non-linear small cluster-centric distances (b_cg(r) ~ 0.7), irrespective of the group/cluster virial mass or X-ray luminosity and galaxy characteristics, which show that a generic process controls the efficiency of galaxy formation and evolution in high density regions. On larger scales b_cg(r) rises to a nearly constant value of order unity, the transition occuring at approximately 2 Mpch^(-1) for 2dF groups and 5 Mpch^(-1) for REFLEX clusters.
قيم البحث
اقرأ أيضاً
The relation between X-ray luminosity and near-infrared luminosity for early-type galaxies has been examined. Near-infrared (NIR) luminosities should provide a superior measure of stellar mass compared to optical luminosities used in previous studies
, especially if there is significant star-formation or dust present in the galaxies. However, we show that the X-ray-NIR relations are remarkably consistent with the X-ray-optical relations. This indicates that the large scatter of the relations is dominated by scatter in the X-ray properties of early-type galaxies, and is consistent with early-types consisting of old, quiescent stellar populations. We have investigated scatter in terms of environment, surface brightness profile, Mg2, H_beta, H_gamma line strength indices, spectroscopic age, and nuclear H_alpha emission. We found that galaxies with high Mg2 index, low H_beta and H_gamma indices or a `core profile have a large scatter in Lx, whereas galaxies with low Mg2, high H_beta and H_gamma indices or `power-law profiles, generally have Lx<10^41 erg/s. There is no clear trend in the scatter with environment or nuclear H_alpha emission.
We present the first X-ray Luminosity Function (XLF) for an optically-selected sample of 49 nearby poor clusters of galaxies and a sample of 67 Abell clusters with z < 0.15. We have extended the measured cluster XLF by more than a factor of 10 in X-r
ay luminosity. Our poor cluster sample was drawn from an optical catalog of groups with 0.01<z<0.03 composed of Zwicky galaxies. The X-ray emission was measured from the ROSAT all-sky survey. About 45% of the poor clusters were detected with 0.5-2.0 keV luminosities from (1.7-65)x 10^{41} h^{-2} ergs/sec. These are among the X-ray brightest, optically-selected poor clusters in the northern hemisphere. For this sample, the poor cluster XLF was found to be smooth extrapolation of the rich cluster XLF. A new Hydro/N-body simulation of a Hot +Cold dark matter model with Omega_{total}=1, Omega_{ u}=0.2, and a baryon fraction of 7.5% was used to model and understand our observational selection effects. We found that the observed cluster Gas Mass Function was consistent with our model.
A sample of 103 quasars from the Large Bright Quasar Survey (LBQS) has been observed with the VLA at 8.4 GHz to study the evolution of the radio luminosity distribution and its dependence on absolute magnitude. Radio data from pointed observations ar
e now available for 359 of the 1055 LBQS quasars. The radio-loud fraction is constant at ~10% over the absolute magnitude range -28 <= MB <= -23, and it rises to ~20% (log R > 1) or ~35% (log L > 25) at the brightest absolute magnitudes in the sample. This nearly flat distribution differs markedly from those of the optically selected Palomar-Green (PG) Bright Quasar Survey and the X-ray selected Extended Medium Sensitivity Survey (EMSS), both of which have lower radio-loud fractions for absolute magnitudes fainter than MB = -24 and higher fractions at brighter magnitudes. The reason for the high radio-loud fraction at bright absolute magnitudes in the PG, compared to the LBQS and other optically selected quasar surveys, is unknown. The trend of increasing radio-loud fraction with absolute magnitude in the EMSS is due at least in part to a correlation between X-ray and radio luminosity. Combining the LBQS data with radio studies of high-redshift quasars leads to the conclusion that the radio-loud fraction in optically selected quasars does not appear to evolve significantly, aside from a modest increase at z ~1, from z = 0.2 to redshifts approaching 5, a result that is contrary to previous studies which found a decrease in radio-loud fraction with increasing redshift by comparing the low-z fraction in the PG to higher redshift samples.
We develop a new diagnostic method to classify galaxies into AGN hosts, star-forming galaxies, and absorption-dominated galaxies by combining the [O III]/Hbeta ratio with rest-frame U-B color. This can be used to robustly select AGNs in galaxy sample
s at intermediate redshifts (z<1). We compare the result of this optical AGN selection with X-ray selection using a sample of 3150 galaxies with 0.3<z<0.8 and I_AB<22, selected from the DEEP2 Galaxy Redshift Survey and the All-wavelength Extended Groth Strip International Survey (AEGIS). Among the 146 X-ray sources in this sample, 58% are classified optically as emission-line AGNs, the rest as star-forming galaxies or absorption-dominated galaxies. The latter are also known as X-ray bright, optically normal galaxies (XBONGs). Analysis of the relationship between optical emission lines and X-ray properties shows that the completeness of optical AGN selection suffers from dependence on the star formation rate and the quality of observed spectra. It also shows that XBONGs do not appear to be a physically distinct population from other X-ray detected, emission-line AGNs. On the other hand, X-ray AGN selection also has strong bias. About 2/3 of all emission-line AGNs at L_bol>10^44 erg/s in our sample are not detected in our 200 ks Chandra images, most likely due to moderate or heavy absorption by gas near the AGN. The 2--7 keV detection rate of Seyfert 2s at z~0.6 suggests that their column density distribution and Compton-thick fraction are similar to that of local Seyferts. Multiple sample selection techniques are needed to obtain as complete a sample as possible.
We report the discovery of a compact supercluster structure at z=0.9. The structure comprises three optically-selected clusters, all of which are detected in X-rays and spectroscopically confirmed to lie at the same redshift. The Chandra X-ray temper
atures imply individual masses of ~5x10^14 Msun. The X-ray masses are consistent with those inferred from optical--X-ray scaling relations established at lower redshift. A strongly-lensed z~4 Lyman break galaxy behind one of the clusters allows a strong-lensing mass to be estimated for this cluster, which is in good agreement with the X-ray measurement. Optical spectroscopy of this cluster gives a dynamical mass in good agreement with the other independent mass estimates. The three components of the RCS2319+00 supercluster are separated from their nearest neighbor by a mere <3 Mpc in the plane of the sky and likely <10 Mpc along the line-of-sight, and we interpret this structure as the high-redshift antecedent of massive (~10^15 Msun) z~0.5 clusters such as MS0451.5-0305.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
