اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدNew spectroscopic confirmations of high-redshift galaxy clusters
144
0
0.0
(
0
)
تأليف
L.F. Olsen
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We present new spectroscopic data in the field of five high-redshift (z>=0.6) candidate galaxy clusters, drawn from the EIS Cluster Candidate Catalog. A total of 327 spectra were obtained using FORS1 at the VLT, out of which 266 are galaxies with secure redshifts. In this paper, we use these data for confirming the existence of overdensities in redshift space at the approximate same location as the matched-filter detections in the projected distribution of galaxies from the EIS I-band imaging survey. The spectroscopic redshifts, associated to these overdensities, are consistent but, in general, somewhat lower than those predicted by the matched-filter technique. Combining the systems presented here with those analyzed earlier, we have spectroscopically confirmed a total of nine overdensities in the redshift range 0.6<z<1.3, providing an important first step in building an optically-selected, high-redshift sample for more detailed studies, complementing those based on the few available X-ray selected systems.
قيم البحث
اقرأ أيضاً
Francis & Hewett (1993) identified two 10-Mpc scale regions of the high redshift universe that were seemingly very overdense in neutral hydrogen. Subsequent observations showed that at least one of these gas-rich regions enveloped a cluster of galaxi
es at redshift 2.38. We present improved observations of the three background QSOs with sightlines passing within a few Mpc of this cluster of galaxies. All three QSOs show strong neutral hydrogen absorption at the cluster redshift, suggesting that this cluster (and perhaps all high redshift clusters) may be surrounded by a ~5 Mpc scale region containing ~ 10^12 solar masses of neutral gas. If most high redshift clusters are surrounded by such regions, we show that the gas must be in the form of many small (< 1 kpc), dense (> 0.03 cm^-3) clouds, each of mass < 10^6 solar masses. These clouds are themselves probably gathered into > 20 kpc sized clumps, which may be galaxy halos or protogalaxies. If this gas exists, it will be partially photoionised by the UV background. We predict the diffuse Ly-alpha flux from this photoionisation, and place observational limits on its intensity.
We discuss the possibility of performing blind surveys to detect large-scale features of the universe using 21cm emission. Using instruments with approx. 5-10 resolution currently in the planning stage, it should be possible to detect virialized gala
xy clusters at intermediate redshifts using the combined emission from their constituent galaxies, as well as less overdense structures, such as proto-clusters and the `cosmic web, at higher redshifts. Using semi-analytic methods we compute the number of virialized objects and those at turnaround which might be detected by such surveys. We find a surprisingly large number of objects might be detected even using small (approx. 5%) bandwidths and elaborate on some issues pertinent to optimising the design of the instrument and the survey strategy. The main uncertainty is the fraction of neutral gas relative to the total dark matter within the object. We discuss this issue in the context of the observations which are currently available.
We present a submillimetre survey of seven high-z galaxy clusters (0.64<z<1.0) using the Submillimetre Common-User Bolometer Array (SCUBA) at 850 and 450 um. The targets, of similar richness and redshift, are selected from the Red-sequence Cluster Su
rvey (RCS). We use this sample to investigate the apparent excess of submillimetre source counts in the direction of cluster fields compared to blank fields. The sample consists of three galaxy clusters that exhibit multiple optical arcs due to strong gravitational lensing, and a control group of four clusters with no apparent strong lensing. A tentative excess of 2.7-sigma is seen in the number density of submillimetre luminous galaxies (SMGs) within the lensing cluster fields compared to that in the control group. Ancillary observations at radio, mid-infrared, optical, and X-ray wavelengths allow for the identification of counterparts to many of the SMGs. Utilizing photometric redshifts, we conclude that at least three of the galaxies within the lensing fields have redshifts consistent with the clusters and implied infrared luminosities of ~10^12 Lsol. The existence of SMG cluster members may therefore be boosting source counts in the lensing cluster fields, which might be an effect of the dynamical state of those clusters. However, we find that the removal of potential cluster members from the counts analysis does not entirely eliminate the difference between the cluster samples. We also investigate possible occurrences of lensing between background SMGs and lower-z optical galaxies, though further observations are required to make any conclusive claims. Although the excess counts between the two cluster samples have not been unambiguously accounted for, these results warrant caution for interpreting submillimetre source counts in cluster fields and point source contamination for Sunyaev-Zeldovich surveys. [Abridged]
We present the results of optical identifications and spectroscopic redshifts measurements for galaxy clusters from 2-nd Planck catalogue of Sunyaev-Zeldovich sources (PSZ2), located at high redshifts, $zapprox0.7-0.9$. We used the data of optical ob
servations obtained with Russian-Turkish 1.5-m telescope (RTT150), Sayan observatory 1.6-m telescope, Calar Alto 3.5-m telescope and 6-m SAO RAS telescope (Bolshoi Teleskop Alt-azimutalnyi, BTA). Spectroscopic redshift measurements were obtained for seven galaxy clusters, including one cluster, PSZ2 G126.57+51.61, from the cosmological sample of PSZ2 catalogue. In central regions of two clusters, PSZ2 G069.39+68.05 and PSZ2 G087.39-34.58, the strong gravitationally lensed background galaxies are found, one of them at redshift $z=4.262$. The data presented below roughly double the number of known galaxy clusters in the second Planck catalogue of Sunyaev-Zeldovich sources at high redshifts, $zapprox0.8$.
Using photometric redshifts we determine the galaxy population of the clusters of galaxies Cl0016+16 at z=0.55, Cl1600+41 at z=0.54, Cl1601+42 at z=0.54 and MS1008-1224 at z=0.31. Comparing the clusters, we find no evidence for a universal shape of t
he total luminosity function (LF) at these redshifts. When dividing the LFs into spectral types, we find that the LF of the early-type galaxies alone can be described by a Gaussian, while the LF of the late-type galaxies is well fitted by a Schechter function, suggesting that the separate LFs for different populations may be universal. The difference in the total LFs can mainly be attributed to the varying relative normalisation of these populations, implying that clusters with an abundant population of late-type galaxies also have steeper faint-end slopes. In MS1008-1224 we detect a faint blue population that dominates over a population with colours consistent with dwarf ellipticals, opposite to clusters at lower redshift. Compared to low redshift clusters, we find that a general fading of the late-type population by ~2 mag and the early-type population by ~1 mag describes the evolution from z=0.55 to z=0 well. As a consequence of the different early-type and late-type LFs and their dependence on cluster radius, the fraction of blue cluster galaxies, as measured by the Butcher-Oemler effect, differs between the clusters and depends on limiting magnitude and radius. We find a correlation between the dwarf-to-giant ratio and the surface density, indicating that the high density environment in the cluster cores is hostile to dwarf galaxies.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
