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2971. Clustering the Orion B giant molecular cloud
ID:
ivo://CDS.VizieR/J/A+A/610/A12
Title:
Clustering the Orion B giant molecular cloud
Short Name:
J/A+A/610/A12
Date:
21 Oct 2021
Publisher:
CDS
Description:
Previous attempts at segmenting molecular line maps of molecular clouds have focused on using position-position-velocity data cubes of a single molecular line to separate the spatial components of the cloud. In contrast, wide field spectral imaging over a large spectral bandwidth in the (sub)mm domain now allows one to combine multiple molecular tracers to understand the different physical and chemical phases that constitute giant molecular clouds (GMCs). We aim at using multiple tracers (sensitive to different physical processes and conditions) to segment a molecular cloud into physically/ chemically similar regions (rather than spatially connected components), thus disentangling the different physical/chemical phases present in the cloud. We use a machine learning clustering method, namely the Meanshift algorithm, to cluster pixels with similar molecular emission, ignoring spatial information. Clusters are defined around each maximum of the multidimensional probability density function (PDF) of the line integrated intensities. Simple radiative transfer models were used to interpret the astrophysical information uncovered by the clustering analysis. A clustering analysis based only on the J=1-0 lines of three isotopologues of CO proves sufficient to reveal distinct density/column density regimes (n_H_~100cm^-3^, ~500cm^-3^, and >1000cm^-3^), closely related to the usual definitions of diffuse, translucent and high-column-density regions. Adding two UV-sensitive tracers, the J=1-0 line of HCO^+^ and the N=1-0 line of CN, allows us to distinguish two clearly distinct chemical regimes, characteristic of UV-illuminated and UV-shielded gas. The UV-illuminated regime shows overbright HCO^+^ and CN emission, which we relate to a photochemical enrichment effect. We also find a tail of high CN/HCO^+^ intensity ratio in UV-illuminated regions. Finer distinctions in density classes (n_H_~710^3^cm^-3^, ~410^4^cm^-3^) for the densest regions are also identified, likely related to the higher critical density of the CN and HCO^+^ (1-0) lines. These distinctions are only possible because the high-density regions are spatially resolved. Molecules are versatile tracers of GMCs because their line intensities bear the signature of the physics and chemistry at play in the gas. The association of simultaneous multi-line, wide-field mapping and powerful machine learning methods such as the Meanshift clustering algorithm reveals how to decode the complex information available in these molecular tracers.
2972. Cluster in superclusters of galaxies
ID:
ivo://CDS.VizieR/J/A+A/637/A31
Title:
Cluster in superclusters of galaxies
Short Name:
J/A+A/637/A31
Date:
21 Oct 2021
Publisher:
CDS
Description:
The characterization of the internal structure of the superclusters of galaxies (walls, filaments and knots where the clusters are located) is paramount for understanding the formation of the Large Scale Structure and for outlining the environment where galaxies evolved in the last Gyr. (i) To detect the compact regions of high relative density (clusters and rich groups of galaxies); (ii) to map the elongated structures of low relative density (filaments, bridges and tendrils of galaxies); (iii) to characterize the galaxy populations on filaments and study the environmental effects they are subject to. We employed optical galaxies with spectroscopic redshifts from the SDSS-DR13 inside rectangular boxes encompassing the volumes of a sample of 46 superclusters of galaxies, up to z=0.15. A virial approximation was applied to correct the positions of the galaxies in the redshift space for the "finger of God" projection effect. Our methodology implements different classical pattern recognition and machine learning techniques (Voronoi tessellation, hierarchical clustering, graph-network theory, minimum spanning trees, among others), pipelined in the Galaxy Systems-Finding algorithm and the Galaxy Filaments-Finding algorithm. We detected in total 2705 galaxy systems (clusters and groups, of which 159 are new) and 144 galaxy filaments in the 46 superclusters of galaxies. The filaments we detected have a density contrast above 3, with a mean value around 10, a radius of about 2.5h_70_^-1^Mpc and lengths between 9 and 130h_70_^-1^Mpc. Correlations between the galaxy properties (mass, morphology and activity) and the environment in which they reside (systems, filaments and the dispersed component) suggest that galaxies closer to the skeleton of the filaments are more massive by up to 25% compared to those in the dispersed component; 70% of the galaxies in the filament region present early type morphologies and the fractions of active galaxies (both AGN and SF) seem to decrease as galaxies approach the filament. Our results support thee idea that galaxies in filaments are subject to environmental effects leading them to be more massive (probably due to larger rates of both merging and gas accretion), less active both in star formation and nuclear activity, and prone to the density-morphology relation. These results suggest that preprocessing in large scale filaments could have significant effects on galaxy evolution.
2973. Clusterix 2.0
ID:
ivo://CDS.VizieR/J/MNRAS/492/5811
Title:
Clusterix 2.0
Short Name:
J/MNRAS/492/5811
Date:
21 Oct 2021
Publisher:
CDS
Description:
Clusterix 2.0 is a web-based, Virtual Observatory compliant, interactive tool for the determination of membership probabilities in stellar clusters based on proper-motion data using a fully non-parametric method. In an area occupied by a cluster, the frequency function is made up of two contributions: cluster and field stars. The tool performs an empirical determination of the frequency functions from the vector point diagram without relying on any previous assumption about their profiles. Clusterix 2.0 allows us to search the appropriate spatial areas in an interactive way until an optimal separation of the two populations is obtained. Several parameters can be adjusted to make the calculation computationally feasible without interfering with the quality of the results. The system offers the possibility to query different catalogues, such as Gaia, or upload a user's own data. The results of the membership determination can be sent via Simple Application Messaging Protocol (SAMP) to Virtual Observatory (VO) tools such as Tool for OPerations on Catalogues And Tables (TOPCAT). We apply Clusterix 2.0 to several open clusters with different properties and environments to show the capabilities of the tool: an area of five degrees radius around NGC 2682 (M67), an old, well-known cluster; a young cluster NGC 2516 with a striking elongated structure extended up to four degrees; NGC 1750 and NGC 1758, a pair of partly overlapping clusters; the area of NGC 1817, where we confirm a little-known cluster, Juchert 23; and an area with many clusters, where we disentangle two overlapping clusters situated where only one was previously known: Ruprecht 26 and the new Clusterix 1.
2974. Clusters and associations in SMC and LMC
ID:
ivo://CDS.VizieR/J/MNRAS/403/996
Title:
Clusters and associations in SMC and LMC
Short Name:
J/MNRAS/403/996
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate the degree of spatial correlation among extended structures in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC). To this purpose, we work with subsamples characterized by different properties such as age and size, taken from the updated catalogue of Bica et al. (2008, Cat. J/MNRAS/389/678), or gathered in the present work. The structures are classified as star clusters or non-clusters (basically, nebular complexes and their stellar associations).
2975. Clusters and groups of galaxies in 2dF
ID:
ivo://CDS.VizieR/J/AN/327/365
Title:
Clusters and groups of galaxies in 2dF
Short Name:
J/AN/327/365
Date:
21 Oct 2021
Publisher:
CDS
Description:
We create a new catalogue of groups and clusters, applying the friends-to-friends method to the 2dF GRS final release. We investigate various selection effects due to the use of a magnitude limited sample. For this purpose we follow the changes in group sizes and mean galaxy number densities within the groups when shifting nearby observed groups to larger distances. We study the distribution of sizes of dark matter haloes in N-body simulations and compare properties of these haloes and the 2dF groups.
2976. Cluster SC2008-57(A3667)
ID:
ivo://CDS.VizieR/J/MNRAS/259/233
Title:
Cluster SC2008-57(A3667)
Short Name:
J/MNRAS/259/233
Date:
21 Oct 2021
Publisher:
CDS
Description:
(Abstract of the paper) We present the results of photometric and spectroscopic observations of the cluster of galaxies SC2008-57 (A3667). The observations have resulted in a catalogue with positions and magnitudes for 203 galaxies, complete at b_25 = 18.0, and radial velocities for 128 galaxies, 91 per cent complete at b_25 = 17.5. The cluster can be classified as type L because its galaxy distribution is highly flattened. It shows two strong concentrations: a main concentration, centred on the cluster brightest galaxy (a D galaxy) and coincident with the peak of X-ray emission, and a substructure around the second brightest galaxy (also a D galaxy). Most of the galaxies in this substructure seem to be bound to the second-brightest galaxy, forming a dynamical subunit inside the cluster. The extreme flattening of the cluster may at least partially be due to the presence of the substructure. The cluster also shows evidence for luminosity segregation, with the brightest galaxies being preferentially found in high galaxy density regions. Most of the luminosity segregation, however, is produced by galaxies associated with the two clumps around the D galaxies, suggesting that dynamical friction is effective in subclusters with low velocity dispersions and may be associated with the formation of D galaxies. The velocity dispersion of SC2008-57 is high, about 1200 km/s, but consistent with the observed X-ray luminosity. The cluster mass, derived using several estimators, is about 2.6 x 10^15 M_solar. Both the cluster mass and velocity dispersion may be overestimates due to the presence of the substructure.
2977. Clusters candidates from PSZ1 catalogue
ID:
ivo://CDS.VizieR/J/A+A/616/A42
Title:
Clusters candidates from PSZ1 catalogue
Short Name:
J/A+A/616/A42
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have identified new clusters and characterized previously unknown Planck Sunyaev-Zeldovich (SZ) sources from the first Planck catalogue of SZ sources (PSZ1). The results presented here correspond to an optical follow-up observational programme developed during approximately one year (2014) at Roque de los Muchachos Observatory, using the 2.5m Isaac Newton telescope, the 3.5m Telescopio Nazionale Galileo, the 4.2m William Herschel telescope and the 10.4m Gran Telescopio Canarias. We have characterized 115 new PSZ1 sources using deep optical imaging and spectroscopy. We adopted robust criteria in order to consolidate the SZ counterparts by analysing the optical richness, the 2D galaxy distribution, and velocity dispersions of clusters. Confirmed counterparts are considered to be validated if they are rich structures, well aligned with the Planck PSZ1 coordinate and show relatively high velocity dispersion. Following this classification, we confirm 53 clusters, which means that 46% of this PSZ1 subsample has been validated and characterized with this technique. Sixty-two SZ sources (54% of this PSZ1 subset) remain unconfirmed. In addition, we find that the fraction of unconfirmed clusters close to the galactic plane (at |b|<25{deg}) is greater than that at higher galactic latitudes (|b|>25{deg}), which indicates contamination produced by radio emission of galactic dust and gas clouds on these SZ detections. In fact, in the majority of the cases, we detect important galactic cirrus in the optical images, mainly in the SZ target located at low galactic latitudes, which supports this hypothesis.
2978. Clusters of galaxies in SDSS-III
ID:
ivo://CDS.VizieR/J/ApJS/199/34
Title:
Clusters of galaxies in SDSS-III
Short Name:
J/ApJS/199/34
Date:
21 Oct 2021
Publisher:
CDS
Description:
Using the photometric redshifts of galaxies from the Sloan Digital Sky Survey III (SDSS-III), we identify 132684 clusters in the redshift range of 0.05<=z<0.8. Monte Carlo simulations show that the false detection rate is less than 6% for the whole sample. The completeness is more than 95% for clusters with a mass of M_200_>1.0x10^14^M_{sun}_ in the redshift range of 0.05<=z<0.42, while clusters of z>0.42 are less complete and have a biased smaller richness than the real one due to incompleteness of member galaxies. We compare our sample with other cluster samples, and find that more than 90% of previously known rich clusters of 0.05<=z<0.42 are matched with clusters in our sample. Richer clusters tend to have more luminous brightest cluster galaxies (BCGs). Correlating with X-ray and the Planck data, we show that the cluster richness is closely related to the X-ray luminosity, temperature, and Sunyaev-Zel'dovich measurements. Comparison of the BCGs with the SDSS luminous red galaxy (LRG) sample shows that 25% of LRGs are BCGs of our clusters and 36% of LRGs are cluster member galaxies. In our cluster sample, 63% of BCGs of r_petro_<19.5 satisfy the SDSS LRG selection criteria.
2979. Clusters of galaxies properties. II.
ID:
ivo://CDS.VizieR/J/A+AS/110/313
Title:
Clusters of galaxies properties. II.
Short Name:
J/A+AS/110/313
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present F band photometry, from digitized 48-inch Palomar plates, of 1167 galaxies brighter than m_3_ +3 in 10 Abell clusters. For each galaxy, absolute coordinates, magnitude, size, ellipticity and orientation are given. For each cluster we provide finding charts and contour maps of the galaxy surface density.
2980. Clusters of starburst galaxy NGC4214
ID:
ivo://CDS.VizieR/J/ApJ/767/51
Title:
Clusters of starburst galaxy NGC4214
Short Name:
J/ApJ/767/51
Date:
21 Oct 2021
Publisher:
CDS
Description:
The production rate of ionizing photons in young (<=8Myr), unresolved stellar clusters in the nearby irregular galaxy NGC 4214 is probed using multi-wavelength Hubble Space Telescope WFC3 data. We normalize the ionizing photon rate by the cluster mass to investigate the upper end of the stellar initial mass function (IMF). We have found that within the uncertainties the upper end of the stellar IMF appears to be universal in this galaxy, and that deviations from a universal IMF can be attributed to stochastic sampling of stars in clusters with masses {<~}10^3^M_{sun}_. Furthermore, we have found that there does not seem to be a dependence of the maximum stellar mass on the cluster mass. We have also found that for massive clusters, feedback may cause an underrepresentation in H{alpha} luminosities, which needs to be taken into account when conducting this type of analysis.

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