اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدThe X-ray Properties of Moderate-redshift Galaxy Groups Selected by Association with Gravitational Lenses
54
0
0.0
(
0
)
تأليف
C. D. Fassnacht
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We present results from a systematic investigation of the X-ray properties of a sample of moderate redshift (0.3<z<0.6) galaxy groups. These groups were selected not by traditional X-ray or optical search methods, but rather by an association, either physical or along the line of sight, with a strong gravitational lens. We calculate the properties of seven galaxy groups in the fields of six lens systems. Diffuse X-ray emission from the intragroup medium is detected in four of the groups. All of the detected groups have X-ray luminosities greater than 10^{42} h^{-2} erg/s, and lie on the L_X-sigma_v relations defined by local groups and clusters. The upper limits for the non-detections are also consistent with the local L_X-sigma_v relationships. Although the sample size is small and deeper optical and X-ray data are needed, these results suggest that lens-selected groups are similar to X-ray selected samples and, thus, are more massive than the typical poor-group environments of local galaxies.
قيم البحث
اقرأ أيضاً
We present the first direct measurement of the mean Halo Occupation Distribution (HOD) of X-ray selected AGN in the COSMOS field at z < 1, based on the association of 41 XMM and 17 C-COSMOS AGN with member galaxies of 189 X-ray detected galaxy groups
from XMM and Chandra data. We model the mean AGN occupation in the halo mass range logM_200[Msun] = 13-14.5 with a rolling-off power-law with the best fit index alpha = 0.06(-0.22;0.36) and normalization parameter f_a = 0.05(0.04;0.06). We find the mean HOD of AGN among central galaxies to be modelled by a softened step function at logMh > logMmin = 12.75 (12.10,12.95) Msun while for the satellite AGN HOD we find a preference for an increasing AGN fraction with Mh suggesting that the average number of AGN in satellite galaxies grows slower (alpha_s < 0.6) than the linear proportion (alpha_s = 1) observed for the satellite HOD of samples of galaxies. We present an estimate of the projected auto correlation function (ACF) of galaxy groups over the range of r_p = 0.1-40 Mpc/h at <z> = 0.5. We use the large-scale clustering signal to verify the agreement between the group bias estimated by using the observed galaxy groups ACF and the value derived from the group mass estimates. We perform a measurement of the projected AGN-galaxy group cross-correlation function, excluding from the analysis AGN that are within galaxy groups and we model the 2-halo term of the clustering signal with the mean AGN HOD based on our results.
We report on the X-ray and optical observations of galaxy groups selected from the 2dfGRS group catalog, to explore the possibility that galaxy groups hosting a giant elliptical galaxy and a large optical luminosity gap present between the two bright
est group galaxies, can be associated with an extended X-ray emission, similar to that observed in fossil galaxy groups. The X-ray observations of 4 galaxy groups were carried out with Chandra telescope with 10-20 ksec exposure time. Combining the X-ray and the optical observations we find evidences for the presence of a diffuse extended X-ray emission beyond the optical size of the brightest group galaxy. Taking both the X-ray and the optical criteria, one of the groups is identified as a fossil group and one is ruled out because of the contamination in the earlier optical selection. For the two remaining systems, the X-ay luminosity threshold is close to the convention know for fossil groups. In all cases the X-ray luminosity is below the expected value from the X-ray selected fossils for a given optical luminosity of the group. A rough estimation for the comoving number density of fossil groups is obtained and found to be in broad agreement with the estimations from observations of X-ray selected fossils and predictions of cosmological simulations.
We present the X-ray and optical properties of the galaxy groups selected in the Chandra X-Bootes survey. Our final sample comprises 32 systems at textbf{$z<1.75$}, with 14 below $z = 0.35$. For these 14 systems we estimate velocity dispersions ($sig
ma_{gr}$) and perform a virial analysis to obtain the radii ($R_{200}$ and $R_{500}$) and total masses ($M_{200}$ and $M_{500}$) for groups with at least five galaxy members. We use the Chandra X-ray observations to derive the X-ray luminosity ($L_X$). We examine the performance of the group properties $sigma_{gr}$, $L_{opt}$ and $L_X$, as proxies for the group mass. Understanding how well these observables measure the total mass is important to estimate how precisely the cluster/group mass function is determined. Exploring the scaling relations built with the X-Bootes sample and comparing these with samples from the literature, we find a break in the $L_X$-$M_{500}$ relation at approximately $M_{500} = 5times10^{13}$ M$_odot$ (for $M_{500} > 5times10^{13}$ M$_odot$, $M_{500} propto L_X^{0.61pm0.02}$, while for $M_{500} leq 5times10^{13}$ M$_odot$, $M_{500} propto L_X^{0.44pm0.05}$). Thus, the mass-luminosity relation for galaxy groups cannot be described by the same power law as galaxy clusters. A possible explanation for this break is the dynamical friction, tidal interactions and projection effects which reduce the velocity dispersion values of the galaxy groups. By extending the cluster luminosity function to the group regime, we predict the number of groups that new X-ray surveys, particularly eROSITA, will detect. Based on our cluster/group luminosity function estimates, eROSITA will identify $sim$1800 groups ($L_X = 10^{41}-10^{43}$ ergs s$^{-1}$) within a distance of 200 Mpc. Since groups lie in large scale filaments, this group sample will map the large scale structure of the local universe.
Compared with numerous X-ray dominant active galactic nuclei (AGNs) without emission-line signatures in their optical spectra, the X-ray selected AGNs with optical emission lines are probably still in the high-accretion phase of black hole growth. Th
is paper presents an investigation on the fraction of these X-ray detected AGNs with optical emission-line spectra in 198 galaxy groups at $z<1$ in a rest frame 0.1-2.4 keV luminosity range 41.3 <log(L_X/erg s-1) < 44.1 within the COSMOS field, as well as its variations with redshift and group richness. For various selection criteria of member galaxies, the numbers of galaxies and the AGNs with optical emission lines in each galaxy group are obtained. It is found that, in total 198 X-ray groups, there are 27 AGNs detected in 26 groups. AGN fraction is on everage less than $4.6 (pm 1.2)%$ for individual groups hosting at least one AGN. The corrected overall AGN fraction for whole group sample is less than $0.98 (pm 0.11) %$. The normalized locations of group AGNs show that 15 AGNs are found to be located in group centers, including all 6 low-luminosity group AGNs. A week rising tendency with $z$ are found: overall AGN fraction is 0.30-0.43% for the groups at $z<0.5$, and 0.55-0.64% at 0.5 < z < 1.0. For the X-ray groups at $z>0.5$, most member AGNs are X-ray bright, optically dull, which results in a lower AGN fractions at higher redshifts. The AGN fraction in isolated fields also exhibits a rising trend with redshift, and the slope is consistent with that in groups. The environment of galaxy groups seems to make no difference in detection probability of the AGNs with emission lines. Additionally, a larger AGN fractions are found in poorer groups, which implies that the AGNs in poorer groups might still be in the high-accretion phase, whereas the AGN population in rich clusters is mostly in the low-accretion, X-ray dominant phase.
Compact groups of galaxies recently have been discovered in association with several strong gravitational lens systems. These groups provide additional convergence to the lensing potential and thus affect the value of H_0 derived from the systems. Le
ns system time delays are now being measured with uncertainties of only a few percent or better. Additionally, vast improvements are being made in incorporating observational constraints such as Einstein ring structures and stellar velocity dispersions into the lens models. These advances are reducing the uncertainties on H_0 to levels at which the the effects of associated galaxy groups may contribute significantly to the overall error budget. We describe a dedicated multiwavelength program, using Keck, HST, and Chandra, to find such groups and measure their properties. We present, as a case study, results obtained from observations of the CLASS lens system B1608+656 and discuss the implications for the value of H_0 derived from this system.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
