- ID:
- ivo://CDS.VizieR/J/A+A/327/952
- Title:
- Centaurus cluster velocities
- Short Name:
- J/A+A/327/952
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on the photometric survey of the inner region of the Centaurus cluster (Jerjen & Dressler, 1997, Cat. <J/A+AS/124/1>) we measured redshifts for a deep, surface brightness limited sample of galaxies using the MEFOS multifibre spectrograph at the ESO 3.6m telescope. With the new data set radial velocities for 120 centrally located cluster members become available which is equivalent to 78% of all known cluster galaxies in the region brighter than B_T_=18.5. The relevant aspect of this investigation is that new redshifts for 32 dwarf galaxies have been measured, rising the total number to 48. We investigate the prominent bimodal velocity distribution of Centaurus in more detail, discussing the very different characteristics of the velocity distributions for the main Hubble types E&S0, spirals, Im&BCD, and dE&dS0. The nucleated, bright dwarf ellipticals are the only galaxies with a Gaussian-like distribution centred at 3148+/-98km/s. The remarkable coincidence of this velocity with the mean velocity of Cen 30 and the redshift of NGC 4696 in particular strongly suggests a connection of the dE&dS0s to the gravitational centre of the Centaurus cluster and/or to the cluster dominant E galaxy. The application of statistical tests reveals the existence of a population dwarf galaxies bound to NGC 4696. The dynamical parameters for the two velocity components suggest that Cen 30 is the real Centaurus cluster whereas Cen 45 can only be a loosely bound group of galaxies. This conclusion is followed up with a type-mixture analysis. All results are fully consistent with the cluster-group scenario. Whether Cen 45 is merging with the cluster or is located in the close background remains unclear. We show that the poorness of Cen 45 represents an intrinsic problem which makes it difficult to approach this question.
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- ID:
- ivo://CDS.VizieR/J/A+A/472/111
- Title:
- Centaurus Compact Object Survey
- Short Name:
- J/A+A/472/111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our aim is to extend the investigations of ultra-compact dwarf galaxies (UCD) beyond the well studied Fornax and Virgo clusters. We measured spectroscopic redshifts of about 400 compact object candidates with 19.2<V<22.4mag in the central region of the Centaurus galaxy cluster (d=43Mpc), using 3 pointings with VIMOS@VLT. The luminosity range of the candidates covers the bright end of the globular cluster (GC) luminosity function and the luminosity regime of UCDs in Fornax and Virgo. Within the area surveyed, our completeness in terms of slit allocation is ~30%.
- ID:
- ivo://CDS.VizieR/J/A+AS/134/75
- Title:
- Central Fornax Cluster. II. Galaxy spectroscopy
- Short Name:
- J/A+AS/134/75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, radial velocities of 94 galaxies brighter than about V_tot=20mag in the direction of the central Fornax cluster have been measured. The galaxies have been selected from the photometric catalog of Paper I (Hilker et al., 1998, Cat. <J/A+AS/134/59>). Most of the velocity determinations of the fainter galaxies are based on strong emission lines of late type galaxies. Table 2 of this paper contains the position, magnitude and velocity of all galaxies. Except for 8 Fornax members, all galaxies lie in the background. Among the 8 members, there are 5 nucleated dwarf ellipticals that are already listed in the FCC (Ferguson, 1989, Cat. <VII/180>). Two of the 3 "new" members are very compact and have surface brightnesses comparable to globular clusters, however their luminosities are in the range of dwarf elliptical nuclei.
- ID:
- ivo://CDS.VizieR/J/MNRAS/398/1129
- Title:
- Central galaxies in groups and clusters
- Short Name:
- J/MNRAS/398/1129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using a statistically representative sample of 911 central galaxies (CENs) from the Sloan Digital Sky Survey (SDSS) Data Release 4 group catalogue, we study how the structure (shape and size) of the first rank (by stellar mass) group and cluster members depends on (1) galaxy stellar mass (M_star_), (2) the global environment defined by the dark matter halo mass (M_halo_) of the host group and (3) the local environment defined by their special halocentric position. We quantify the structure of SDSS galaxies with a galfit-based pipeline that fits two-dimensional Sersic models to the r-band image data. Through tests with simulated and real galaxy images, we demonstrate that our pipeline can recover Sersic parameters without significant bias. Moreover, to test the impact of local environment on CENs, we compare the structure of CENs with that satellite galaxies (SATs) of comparable M_star_.
- ID:
- ivo://CDS.VizieR/J/MNRAS/423/2436
- Title:
- CES ultra deep catalogue of galaxy structures
- Short Name:
- J/MNRAS/423/2436
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents a large sample of intermediate- to high-redshift galaxy groups and clusters detected using a fully automated search in the Cosmic Evolution Survey field. The detection algorithm is based on density peak extraction from a density distribution sampled using Voronoi tessellation within overlapping slices in the photometric redshift space. The cluster catalogue contains 1780 structures covering the redshift range 0.2<z<3.0, spanning three orders of magnitude in luminosity (10^8^<L_4_<5x10^11^L_{sun}_) and richness from eight to hundreds of galaxies. All clusters at z>0.4 and many even below this threshold show very prominent substructure indicating that z~0.4 marks the slow emergence of virialized clusters in this field in agreement with published findings for other regions of the sky. The redshift distribution of detected structures shows strong variations with prominent peaks suggesting the presence of large-scale structures across the whole range covered by this catalogue. Supercluster candidates have been identified at redshifts z=0.35, 0.72, 0.94, 1.12, 1.27, 1.45, 2.0 and 2.52. At z=2.9 we identified a compact agglomeration of galaxy groups and clusters suggesting the presence of another supercluster-like structure which has been the highest redshift candidate so far. Out of the nine supercluster candidates found in this study, six are new detections.
- ID:
- ivo://CDS.VizieR/J/A+A/587/A23
- Title:
- CFHT r- and z-band images 28 Planck sources
- Short Name:
- J/A+A/587/A23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Planck catalogue of SZ sources limits itself to a significance threshold of 4.5 to ensure a low contamination rate by false cluster candidates. This means that only the most massive clusters at redshift z>0.5, and in particular z>0.7, are expected to enter into the catalogue, with a large number of systems in that redshift regime being expected around and just below that threshold. In this paper, we follow-up a sample of SZ sources from the Planck SZ catalogues from 2013 and 2015. In the latter maps, we consider detections around and at lower significance than the threshold adopted by the Planck Collaboration. To keep the contamination rate low, our 28 candidates are chosen to have significant WISE detections, in combination with non-detections in SDSS/DSS, which effectively selects galaxy cluster candidates at redshifts z>~0.5. By taking r- and z-band imaging with MegaCam@CFHT, we bridge the 4000{AA} rest-frame break over a significant redshift range, thus allowing accurate redshift estimates of red-sequence cluster galaxies up to z~0.8. After discussing the possibility that an overdensity of galaxies coincides -by chance- with a Planck SZ detection, we confirm that 16 of the candidates have likely optical counterparts to their SZ signals, 13 (6) of which have an estimated redshift z>0.5 (z>0.7). The richnesses of these systems are generally lower than expected given the halo masses estimated from the Planck maps. However, when we follow a simplistic model to correct for Eddington bias in the SZ halo mass proxy, the richnesses are consistent with a reference mass-richness relation established for clusters detected at higher significance. This illustrates the benefit of an optical follow-up, not only to obtain redshift estimates, but also to provide an independent mass proxy that is not based on the same data the clusters are detected with, and thus not subject to Eddington bias
- ID:
- ivo://CDS.VizieR/J/ApJ/728/27
- Title:
- Chandra and AAOmega observations of Abell 2744
- Short Name:
- J/ApJ/728/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New Chandra X-ray data and extensive optical spectroscopy, obtained with AAOmega on the 3.9m Anglo-Australian Telescope, are used to study the complex merger taking place in the galaxy cluster Abell 2744. Combining our spectra with data from the literature provides a catalog of 1237 redshifts for extragalactic objects lying within 15' of the cluster center. From these, we confirm 343 cluster members projected within 3Mpc of the cluster center. Combining positions and velocities, we identify two major substructures, corresponding to the remnants of two major subclusters. The new data are consistent with a post-core-passage, major merger taking place along an axis that is tilted well out of the plane of the sky, together with an interloping minor merger. Supporting this interpretation, the new X-ray data reveal enriched, low entropy gas from the core of the approaching, major subcluster, lying ~2' north of the cluster center, and a shock front to the southeast of the previously known bright, compact core associated with the receding subcluster. The X-ray morphology of the compact core is consistent with a Bullet-like cluster viewed from within ~45{deg} of the merger axis. An X-ray peak ~3' northwest of the cluster center, with an associated cold front to the northeast and a trail of low entropy gas to the south, is interpreted as the remnant of an interloping minor merger taking place roughly in the plane of the sky. We infer approximate paths for the three merging components.
- ID:
- ivo://CDS.VizieR/J/ApJ/690/295
- Title:
- Chandra observations of J1604+4314 supercluster
- Short Name:
- J/ApJ/690/295
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of Chandra observations of the Cl1604 supercluster at z~0.9. The system is the largest structure mapped at redshifts approaching unity, containing at least eight spectroscopically confirmed galaxy clusters and groups. Using two 50ks ACIS-I pointings we examine both the X-ray point-source population and the diffuse emission from individual clusters in the system. Over an area encompassing the entire supercluster (~0.154deg^2^), we find a 2.5{sigma} excess of point sources detected in the hard band (2-10keV) relative to the number of sources found in blank fields observed by Chandra. No such excess is observed in the soft band (0.5-2keV). The hard-band source density is 1.47 times greater than that of a blank field, in agreement with the previously reported correlation between overdensity amplitude and cluster redshift. Using a maximum likelihood technique, we have matched 112 of the 161 detected X-ray point sources to optical counterparts and found 15 sources that are associated with the supercluster. All 15 sources have rest-frame luminosities consistent with emission from active galactic nuclei (AGNs).
- ID:
- ivo://CDS.VizieR/J/ApJ/681/1017
- Title:
- Chandra observations of lens groups
- Short Name:
- J/ApJ/681/1017
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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^ergs/s and lie on the L_X_^-{sigma}_v_^ relations defined by local groups and clusters. The upper limits for the nondetections 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.
- ID:
- ivo://CDS.VizieR/J/ApJ/774/23
- Title:
- Chandra observations of SPT-SZ clusters
- Short Name:
- J/ApJ/774/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present first results on the cooling properties derived from Chandra X-ray observations of 83 high-redshift (0.3<z<1.2) massive galaxy clusters selected by their Sunyaev-Zel'dovich signature in the South Pole Telescope data. We measure each cluster's central cooling time, central entropy, and mass deposition rate, and compare these properties to those for local cluster samples. We find no significant evolution from z~0 to z~1 in the distribution of these properties, suggesting that cooling in cluster cores is stable over long periods of time. We also find that the average cool core entropy profile in the inner ~100kpc has not changed dramatically since z~1, implying that feedback must be providing nearly constant energy injection to maintain the observed "entropy floor" at ~10keV cm^2^.
