- ID:
- ivo://CDS.VizieR/J/MNRAS/412/2498
- Title:
- Galaxy groups and clouds in the local universe
- Short Name:
- J/MNRAS/412/2498
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an all-sky catalogue of 395 nearby galaxy groups revealed in the Local Supercluster and its surroundings. The groups and their associations are identified among 10914 galaxies at |b|>15{deg} with radial velocities V_LG_<3500km/s. Our group-finding algorithm requires the group members to be located inside their zero-velocity surface. Hereby, we assume that individual galaxy masses are proportional to their total K-band luminosities, M/L_K_=6M_{sun}_/L_{sun}_. The sample of our groups, where each group has n>=4 members, is characterized by the following medians: mean projected radius <R>=268kpc, radial velocity dispersion {sigma}_V_=74km/s, K-band luminosity L_K_=1.2x10^11^L_{sun}_, virial and projected masses M_vir_=2.4x10^12^ and M_p_=3.3x10^12^M_{sun}_, respectively. Accounting for measurement error reduces the median masses by 30 per cent. For 97 per cent of identified groups the crossing time does not exceed the cosmic time, 13.7Gyr, with the median at 3.8Gyr. We examine different properties of the groups, in particular of the known nearby groups and clusters in Virgo and Fornax. About a quarter of our groups can be classified as fossil groups where the dominant galaxy is at least 10 times brighter than the other group members.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/167/1
- Title:
- Galaxy groups and clusters from SDSS
- Short Name:
- J/ApJS/167/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We identify galaxy groups and clusters in volume-limited samples of the Sloan Digital Sky Survey (SDSS) redshift survey, using a redshift-space friends-of-friends algorithm. We optimize the friends-of-friends linking lengths to recover galaxy systems that occupy the same dark matter halos, using a set of mock catalogs created by populating halos of N-body simulations with galaxies. Extensive tests with these mock catalogs show that no combination of perpendicular and line-of-sight linking lengths is able to yield groups and clusters that simultaneously recover the true halo multiplicity function, projected size distribution, and velocity dispersion. We adopt a linking length combination that yields, for galaxy groups with 10 or more members: a group multiplicity function that is unbiased with respect to the true halo multiplicity function; an unbiased median relation between the multiplicities of groups and their associated halos; a spurious group fraction of less than ~1%; a halo completeness of more than 97%; the correct projected size distribution as a function of multiplicity; and a velocity dispersion distribution that is ~20% too low at all multiplicities. These results hold over a range of mock catalogs that use different input recipes of populating halos with galaxies. We apply our group-finding algorithm to the SDSS data and obtain three group and cluster catalogs for three volume-limited samples that cover 3495.1deg^2^ on the sky, go out to redshifts of 0.1, 0.068, and 0.045, and contain 57138, 37820, and 18895 galaxies, respectively. We correct for incompleteness caused by fiber collisions and survey edges and obtain measurements of the group multiplicity function, with errors calculated from realistic mock catalogs. These multiplicity function measurements provide a key constraint on the relation between galaxy populations and dark matter halos.
- ID:
- ivo://CDS.VizieR/J/ApJ/625/6
- Title:
- Galaxy groups in the DEEP2 Galaxy Redshift Survey
- Short Name:
- J/ApJ/625/6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the first 25% of the DEEP2 Galaxy Redshift Survey spectroscopic data to identify groups and clusters of galaxies in redshift space. The data set contains 8370 galaxies with confirmed redshifts in the range 0.7<=z<=1.4, over 1{deg}^2^ on the sky. Groups are identified using an algorithm (the Voronoi-Delaunay method) that has been shown to accurately reproduce the statistics of groups in simulated DEEP2-like samples. We optimize this algorithm for the DEEP2 survey by applying it to realistic mock galaxy catalogs and assessing the results using a stringent set of criteria for measuring group-finding success, which we develop and describe in detail here. We present the first DEEP2 group catalog, which assigns 32% of the galaxies to 899 distinct groups with two or more members, 153 of which have velocity dispersions above 350km/s. We provide locations, redshifts and properties for this high-dispersion subsample. This catalog represents the largest sample to date of spectroscopically detected groups at z~1.
- ID:
- ivo://CDS.VizieR/J/A+A/578/A61
- Title:
- Galaxy groups in the 2M++
- Short Name:
- J/A+A/578/A61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We provide the galaxy group sample used as tracers of the large scale structure in the work to study the compact group environment.
- ID:
- ivo://CDS.VizieR/J/A+A/520/A42
- Title:
- Galaxy groups in the VIMOS-VLT Deep Survey
- Short Name:
- J/A+A/520/A42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a homogeneous and complete catalogue of optical galaxy groups identified in the VIMOS-VLT Deep Survey (VVDS). We use mock catalogues extracted from the Millennium Simulation to study the potential systematics that might affect the overall distribution of the identified systems, and also to asses how well galaxy redshifts trace the line-of-sight velocity dispersion of the underlying mass overdensity. We train on these mock catalogues the adopted group-finding technique (the Voronoi-Delaunay Method, VDM), to recover in a robust and unbiased way the redshift and velocity dispersion distributions of groups and maximize the level of completeness (C) and purity (P) of the group catalogue. We identify 318(/144) VVDS groups with at least 2(/3) members within 0.2<=z<=1.0, globally with C=60% and P=50%. We use the group sample to study the redshift evolution of the fraction f_b_ of blue galaxies (U-B<=1) within 0.2<=z<=1 in both groups and in the whole ensemble of galaxies irrespectively of their environment.
- ID:
- ivo://CDS.VizieR/J/ApJ/843/16
- Title:
- Galaxy groups within 3500km/s
- Short Name:
- J/ApJ/843/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A study of the group properties of galaxies in our immediate neighborhood provides a singular opportunity to observationally constrain the halo mass function, a fundamental characterization of galaxy formation. Detailed studies of individual groups have provided the coefficients of scaling relations between a proxy for the virial radius, velocity dispersion, and mass that usefully allow groups to be defined over the range 10^10^-10^15^M_{sun}_. At a second hierarchical level, associations are defined as regions around collapsed halos extending to the zero-velocity surface at the decoupling from cosmic expansion. The most remarkable result of the study emerges from the construction of the halo mass function from the sample. At ~10^12^M_{sun}_, there is a jog from the expectation Sheth-Tormen function, such that halo counts drop by a factor ~3 in all lower mass bins.
- ID:
- ivo://CDS.VizieR/J/MNRAS/337/256
- Title:
- Galaxy in low X-ray luminosity clusters
- Short Name:
- J/MNRAS/337/256
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first spectroscopic survey of intrinsically low X-ray luminosity clusters at z>>0, with Hubble Space Telescope (HST) WFPC2 imaging and spectroscopy from Calar Alto and WHT-LDSS2. We study 172 confirmed cluster members in a sample of ten clusters at 0.23<z<0.3, with LX<~4x10^43^h^-2^erg/s[0.1-2.4keV]. The core of each cluster is imaged with WFPC2 in the F702W filter, and the spectroscopic sample is statistically complete to Mr~-19.0+5logh, within an 11' (~1.8h^-1^Mpc) field. The clusters are dynamically well-separated from the surrounding field and most have velocity distributions consistent with Gaussians. The velocity dispersions range from 350-850km/s, consistent with the local L_X_-{sigma} correlation. All 10 clusters host a bright, giant elliptical galaxy without emission lines, near the centre of the X-ray emission. We measure the equivalent width of two nebular emission lines, [O II] and H{alpha}, and the H{delta} absorption line to classify the cluster members spectrally. Galaxy morphologies are measured from the HST images, using the two-dimensional surface-brightness fitting software GIM2D.
- ID:
- ivo://CDS.VizieR/J/MNRAS/440/2810
- Title:
- Galaxy luminosity function at z =~ 7
- Short Name:
- J/MNRAS/440/2810
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a new search for bright star-forming galaxies at redshift z=~7 within the UltraVISTA second data release (DR2) and UKIDSS (UKIRT Infrared Deep Sky Survey) UDS (Ultra Deep Survey) DR10 data, which together provide 1.65deg^2^ of near-infrared imaging with overlapping optical and Spitzer data. Using a full photometric redshift analysis, to identify high-redshift galaxies and reject contaminants, we have selected a sample of 34 luminous (-22.7<M_UV_<-21.2) galaxies with 6.5<z<7.5. Crucially, the deeper imaging provided by UltraVISTA DR2 confirms all of the robust objects previously uncovered by Bowler et al., validating our selection technique. Our new expanded galaxy sample includes the most massive galaxies known at z=~7, with M*=~10^10^M_{sun}_, and the majority are resolved, consistent with larger sizes (r_1/2_=~1-1.5kpc) than displayed by less massive galaxies. From our final robust sample, we determine the form of the bright end of the rest-frame UV galaxy luminosity function (LF) at z=~7, providing strong evidence that it does not decline as steeply as predicted by the Schechter-function fit to fainter data. We exclude the possibility that this is due to either gravitational lensing, or significant contamination of our galaxy sample by active galactic nuclei (AGN). Rather, our results favour a double power-law form for the galaxy LF at high redshift, or, more interestingly, an LF which simply follows the form of the dark matter halo mass function at bright magnitudes. This suggests that the physical mechanism which inhibits star formation activity in massive galaxies (i.e. AGN feedback or some other form of 'mass quenching') has yet to impact on the observable galaxy LF at z=~7, a conclusion supported by the estimated masses of our brightest galaxies which have only just reached a mass comparable to the critical 'quenching mass' of M*=~10^10.2^M_{sun}_ derived from studies of the mass function of star-forming galaxies at lower redshift.
- ID:
- ivo://CDS.VizieR/J/MNRAS/432/2696
- Title:
- Galaxy luminosity function at z = 7-9
- Short Name:
- J/MNRAS/432/2696
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new determination of the ultraviolet (UV) galaxy luminosity function (LF) at redshift z=~7 and 8, and a first estimate at z=~9. An accurate determination of the form and evolution of the galaxy LF during this era is of key importance for improving our knowledge of the earliest phases of galaxy evolution and the process of cosmic reionization. Our analysis exploits to the full the new, deepest Wide Field Camera 3/infrared imaging from our Hubble Space Telescope (HST) Ultra-Deep Field 2012 (UDF12) campaign, with dynamic range provided by including a new and consistent analysis of all appropriate, shallower/wider area HST survey data. Our new measurement of the evolving LF at z=~7 to 8 is based on a final catalogue of =~600 galaxies, and involves a step-wise maximum-likelihood determination based on the photometric redshift probability distribution for each object; this approach makes full use of the 11-band imaging now available in the Hubble Ultra-Deep Field (HUDF), including the new UDF12 F140W data, and the latest Spitzer IRAC imaging. The final result is a determination of the z=~7 LF extending down to UV absolute magnitudes M_1500_=-16.75 (AB mag) and the z=~8 LF down to M_1500_=-17.00. Fitting a Schechter function, we find M_1500_^*^=-19.90^+0.23^_-0.28^, log{phi}^*^=-2.96^+0.18^_-0.23_ and a faint-end slope {alpha}=-1.90^+0.14^_-0.15_ at z=~7, and M_1500_^*^=-20.12^+0.37^_-0.48_, log{phi}^*^=-3.35^+0.28^_-0.47_ and {alpha}=-2.02^+0.22^_-0.23_ at z=~8. These results strengthen previous suggestions that the evolution at z>7 appears more akin to 'density evolution' than the apparent 'luminosity evolution' seen at z=~5-7. We also provide the first meaningful information on the LF at z=~9, explore alternative extrapolations to higher redshifts, and consider the implications for the early evolution of UV luminosity density. Finally, we provide catalogues (including derived z_phot_, M_1500_ and photometry) for the most robust z~6.5-11.9 galaxies used in this analysis. We briefly discuss our results in the context of earlier work and the results derived from an independent analysis of the UDF12 data based on colour-colour selection.
- ID:
- ivo://CDS.VizieR/J/MNRAS/470/755
- Title:
- Galaxy mergers and AGN activity
- Short Name:
- J/MNRAS/470/755
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Active galactic nuclei (AGNs), particularly the most luminous AGNs, are commonly assumed to be triggered through major mergers; however, observational evidence for this scenario is mixed. To investigate any influence of galaxy mergers on AGN triggering and luminosities through cosmic time, we present a sample of 106 luminous X-ray-selected type 1 AGNs from the COSMOS survey. These AGNs occupy a large redshift range (0.5<z<2.2) and two orders of magnitude in X-ray luminosity (~10^43^-10^45^erg/s). AGN hosts are carefully mass and redshift matched to 486 control galaxies. A novel technique for identifying and quantifying merger features in galaxies is developed, subtracting GALFIT galaxy models and quantifying the residuals. Comparison to visual classification confirms this measure reliably picks out disturbance features in galaxies. No enhancement of merger features with increasing AGN luminosity is found with this metric, or by visual inspection. We analyse the redshift evolution of AGNs associated with galaxy mergers and find no merger enhancement in lower redshift bins. Contrarily, in the highest redshift bin (z~2) AGNs are ~4 times more likely to be in galaxies exhibiting evidence of morphological disturbance compared to control galaxies, at 99 per cent confidence level (~2.4{sigma}) from visual inspection. Since only ~15 per cent of these AGNs are found to be in morphologically disturbed galaxies, it is implied that major mergers at high redshift make a noticeable but subdominant contribution to AGN fuelling. At low redshifts, other processes dominate and mergers become a less significant triggering mechanism.