scholarly journals An environmental dependence of the physical and structural properties in the Hydra cluster galaxies

2020 ◽  
Vol 500 (1) ◽  
pp. 1323-1339
Author(s):  
Ciria Lima-Dias ◽  
Antonela Monachesi ◽  
Sergio Torres-Flores ◽  
Arianna Cortesi ◽  
Daniel Hernández-Lang ◽  
...  
Keyword(s):  
Structural Properties ◽  
Clustering Algorithm ◽  
Spatial Clustering ◽  
Broad Band ◽  
Visible Region ◽  
Early Type ◽  
Cluster Galaxies ◽  
Using Data ◽  
Stellar Masses ◽  
Environmental Dependence

ABSTRACT The nearby Hydra cluster (∼50 Mpc) is an ideal laboratory to understand, in detail, the influence of the environment on the morphology and quenching of galaxies in dense environments. We study the Hydra cluster galaxies in the inner regions (1R200) of the cluster using data from the Southern Photometric Local Universe Survey, which uses 12 narrow and broad-band filters in the visible region of the spectrum. We analyse structural (Sérsic index, effective radius) and physical (colours, stellar masses, and star formation rates) properties. Based on this analysis, we find that ∼88 per cent of the Hydra cluster galaxies are quenched. Using the Dressler–Schectman test approach, we also find that the cluster shows possible substructures. Our analysis of the phase-space diagram together with density-based spatial clustering algorithm indicates that Hydra shows an additional substructure that appears to be in front of the cluster centre, which is still falling into it. Our results, thus, suggest that the Hydra cluster might not be relaxed. We analyse the median Sérsic index as a function of wavelength and find that for red [(u − r) ≥2.3] and early-type galaxies it displays a slight increase towards redder filters (13 and 18 per cent, for red and early type, respectively), whereas for blue + green [(u − r)<2.3] galaxies it remains constant. Late-type galaxies show a small decrease of the median Sérsic index towards redder filters. Also, the Sérsic index of galaxies, and thus their structural properties, do not significantly vary as a function of clustercentric distance and density within the cluster; and this is the case regardless of the filter.

scholarly journals The GALEX Ultraviolet Virgo Cluster Survey (GUViCS)

2018 ◽  
Vol 611 ◽  
pp. A42 ◽  
Author(s):  
S. Boissier ◽  
O. Cucciati ◽  
A. Boselli ◽  
S. Mei ◽  
L. Ferrarese
Keyword(s):  
Virgo Cluster ◽  
Small Error ◽  
Early Type ◽  
Redshift Range ◽  
Cluster Galaxies ◽  
The Past ◽  
Brightest Cluster Galaxies ◽  
Binary Channel ◽  
Using Data ◽  
Uv Upturn

Context. At low redshift, early-type galaxies often exhibit a rising flux with decreasing wavelength in the 1000–2500 Å range, called “UV upturn”. The origin of this phenomenon is debated, and its evolution with redshift is poorly constrained. The observed GALEX FUV-NUV color can be used to probe the UV upturn approximately to redshift 0.5.Aim. We provide constraints on the existence of the UV upturn up to redshift ~0.4 in the brightest cluster galaxies (BCG) located behind the Virgo cluster, using data from the GUViCS survey.Methods. We estimate the GALEX far-UV (FUV) and near-UV (NUV) observed magnitudes for BCGs from the maxBCG catalog in the GUViCS fields. We increase the number of nonlocal galaxies identified as BCGs with GALEX photometry from a few tens of galaxies to 166 (64 when restricting this sample to relatively small error bars). We also estimate a central color within a 20 arcsec aperture. By using the r-band luminosity from the maxBCG catalog, we can separate blue FUV-NUV due to recent star formation and candidate upturn cases. We use Lick indices to verify their similarity to redshift 0 upturn cases.Results. We clearly detect a population of blue FUV-NUV BCGs in the redshift range 0.10–0.35, vastly improving the existing constraints at these epochs by increasing the number of galaxies studied, and by exploring a redshift range with no previous data (beyond 0.2), spanning one more Gyr in the past. These galaxies bring new constraints that can help distinguish between assumptions concerning the stellar populations causing the UV upturn phenomenon. The existence of a large number of UV upturns around redshift 0.25 favors the existence of a binary channel among the sources proposed in the literature.

scholarly journals Galaxy properties from voids to clusters in the SDSS-DR4

2006 ◽  
Vol 2 (S235) ◽  
pp. 243-243
Author(s):  
G. Sorrentino ◽  
A. Rifatto ◽  
V. Antonuccio-Delogu
Keyword(s):  
Early Type ◽  
Late Type ◽  
Cluster Galaxies ◽  
Galaxy Populations ◽  
Galaxy Population ◽  
Environmental Dependence

AbstractWe investigate the environmental dependence of galaxy populations properties in the SDSS-DR4. Our aim is to search for systematic variations in the properties of galaxies with the local galaxy density in order to find hints that can be related to the presence of a void galaxy population. We find that galaxies in underdense regions (voids) are fainte and bluer than cluster galaxies. Moreover, the transition from underdense to overdense regions is smooth, as well as the percentage of late-type galaxies decreases while the percentage of early-type galaxies increases smoothly from underdense to dense environments.

scholarly journals The most massive, passive, and oldest galaxies at 0.5 < z < 2.1: Downsizing signature from galaxies selected from MgUV index

2019 ◽  
Vol 630 ◽  
pp. A145 ◽  
Author(s):  
R. Thomas ◽  
O. Le Fèvre ◽  
G. Zamorani ◽  
B. C. Lemaux ◽  
P. Hibon ◽  
...  
Keyword(s):  
Photometric Data ◽  
Early Type ◽  
Massive Galaxies ◽  
Spectral Fitting ◽  
Redshift Surveys ◽  
Deep Survey ◽  
Galaxy Redshift ◽  
Using Data ◽  
Stellar Masses ◽  
Best Fit

Aims. We seek is to identify old and massive galaxies at 0.5 < z < 2.1 on the basis of the magnesium index MgUV and then study their physical properties. Methods. We computed the MgUV index based on the best spectral fitting template of ∼3700 galaxies using data from the VLT VIMOS Deep Survey (VVDS) and VIMOS Ultra Deep Survey (VUDS) galaxy redshift surveys. Based on galaxies with the largest signal to noise and the best fit spectra we selected 103 objects with the highest spectral MgUV signature. We performed an independent fit of the photometric data of these galaxies and computed their stellar masses, star formation rates, extinction by dust and age, and we related these quantities to the MgUV index. Results. We find that the MgUV index is a suitable tracer of early-type galaxies at an advanced stage of evolution. Selecting galaxies with the highest MgUV index allows us to choose the most massive, passive, and oldest galaxies at any epoch. The formation epoch tf computed from the fitted age as a function of the total mass in stars supports the downsizing formation paradigm in which galaxies with the highest mass formed most of their stars at an earlier epoch.

scholarly journals Characterization of peculiar early-type galaxies in the local universe

2012 ◽  
Vol 10 (H16) ◽  
pp. 333-333
Author(s):  
Beatriz H. F. Ramos ◽  
Karín Menéndez-Delmestre ◽  
Taehyun Kim ◽  
Kartik Sheth ◽  
Keyword(s):  
Star Formation ◽  
Broad Band ◽  
Stellar Populations ◽  
Stellar Mass ◽  
Stellar Structure ◽  
Host Galaxy ◽  
Early Type ◽  
Local Universe ◽  
The Galaxy ◽  
Stellar Masses

AbstractEarly-type galaxies (ETGs) have been characterized as objects dominated by old stellar populations, containing little or no cold gas and dust, and thus, non-existent star formation. However, there are indications in the literature that some ETGs deviate from this: some have significant amounts of gas and dust, are forming stars, and/or display stellar substructures (tidal features, disks or shells, e.g., Kormendy et al. 1997, Rix, Carollo & Freeman 1999). A better understanding of the evolution of ETGs and the details of their “peculiarities” is critical to properly constrain models of galaxy formation. We present preliminary results on a photometric analysis of substructures in local ETGs, based on 3.6μm IRAC images from the Spitzer Survey of Stellar Structure in Galaxies (S4G; Sheth et al. 2010), which comprises one of the largest mid-IR photometric surveys of the local Universe. Relatively unhindered by extinction and dominated by the low-mass stellar populations that dominate a galaxy's stellar mass budget, the IR is the ideal waveband to trace the details of stellar structures in galaxies. Based on 2D GALFIT (Peng et al. 2002) decomposition, we find tidal features in 17% of 146 ETGs from S4G. For both the GALFIT model and the galaxy residual images, we calculate the total counts inside an annular region centered on the galaxy, where the inner radius is the effective radius of the galaxy. Assuming that a tidal feature and its host galaxy have the same mass-to-luminosity ratio (M/L), the ratio of the residual counts over model counts translates into the ratio of their stellar masses. We find that the tidal features in the majority of peculiar ETGs in our sample account for no more than 11% of the galaxy's total stellar mass. Considering that simulations (Canalizo et al. 2007) suggest an upper limit in relative stellar mass of 25% for shells resulting from a past major merger, the values we find support a merger origin. We are in the process of applying the decomposition method to GALEX UV images and optical SDSS images of these peculiar ETGs in order to characterize the underlying substructure and provide constraints on astrophysical properties such as star formation rates and stellar masses associated to these tidal features, based on broad-band SED template fitting techniques.

K-MEANS CLUSTERING ALGORITHM FOR SERVICE DATA ANALYSIS BASED ON CUSTOMERS COMBINATION

2018 ◽  
Vol 3 (1) ◽  
pp. 001
Author(s):  
Zulhendra Zulhendra ◽  
Gunadi Widi Nurcahyo ◽  
Julius Santony
Keyword(s):  
Data Mining ◽  
Data Analysis ◽  
Clustering Algorithm ◽  
Customer Complaints ◽  
Using Data ◽  
Clustering Data ◽  
Service Data ◽  
Selection Of

In this study using Data Mining, namely K-Means Clustering. Data Mining can be used in searching for a large enough data analysis that aims to enable Indocomputer to know and classify service data based on customer complaints using Weka Software. In this study using the algorithm K-Means Clustering to predict or classify complaints about hardware damage on Payakumbuh Indocomputer. And can find out the data of Laptop brands most do service on Indocomputer Payakumbuh as one of the recommendations to consumers for the selection of Laptops.

scholarly journals An Enhanced Spectral Clustering Algorithm with S-Distance

Symmetry ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 596
Author(s):  
Krishna Kumar Sharma ◽  
Ayan Seal ◽  
Enrique Herrera-Viedma ◽  
Ondrej Krejcar
Keyword(s):  
Spectral Clustering ◽  
Clustering Algorithm ◽  
Spatial Clustering ◽  
Clustering Algorithms ◽  
Rank Test ◽  
Customer Churn ◽  
Signed Rank ◽  
Signed Rank Test ◽  
Spectral Clustering Algorithm ◽  
Industrial Databases

Calculating and monitoring customer churn metrics is important for companies to retain customers and earn more profit in business. In this study, a churn prediction framework is developed by modified spectral clustering (SC). However, the similarity measure plays an imperative role in clustering for predicting churn with better accuracy by analyzing industrial data. The linear Euclidean distance in the traditional SC is replaced by the non-linear S-distance (Sd). The Sd is deduced from the concept of S-divergence (SD). Several characteristics of Sd are discussed in this work. Assays are conducted to endorse the proposed clustering algorithm on four synthetics, eight UCI, two industrial databases and one telecommunications database related to customer churn. Three existing clustering algorithms—k-means, density-based spatial clustering of applications with noise and conventional SC—are also implemented on the above-mentioned 15 databases. The empirical outcomes show that the proposed clustering algorithm beats three existing clustering algorithms in terms of its Jaccard index, f-score, recall, precision and accuracy. Finally, we also test the significance of the clustering results by the Wilcoxon’s signed-rank test, Wilcoxon’s rank-sum test, and sign tests. The relative study shows that the outcomes of the proposed algorithm are interesting, especially in the case of clusters of arbitrary shape.

scholarly journals Ultradiffuse galaxies in the IC 1459 group from the VEGAS survey

2020 ◽  
Vol 494 (4) ◽  
pp. 5293-5297
Author(s):  
Duncan A Forbes ◽  
Bililign T Dullo ◽  
Jonah Gannon ◽  
Warrick J Couch ◽  
Enrichetta Iodice ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Compact Objects ◽  
Early Type ◽  
Group Members ◽  
Measurement Uncertainties ◽  
Stellar Masses ◽  
Double Nucleus ◽  
Early Type Galaxy

ABSTRACT Using deep g, r, i imaging from the VST Early-type GAlaxy Survey (VEGAS), we have searched for ultradiffuse galaxies (UDGs) in the IC 1459 group. Assuming they are group members, we identify nine galaxies with physical sizes and surface brightnesses that match the UDG criteria within our measurement uncertainties. They have mean colours of g − i = 0.6 and stellar masses of ∼108 M⊙. Several galaxies appear to have associated systems of compact objects, e.g. globular clusters. Two UDGs contain a central bright nucleus, with a third UDG revealing a remarkable double nucleus. This appears to be the first reported detection of a double nucleus in a UDG – its origin is currently unclear.

scholarly journals A Precise Benchmark for Cluster Scaling Relations: Fundamental Plane, Mass Plane and IMF in the Coma Cluster from Dynamical Models

2020 ◽  
Author(s):  
Shravan Shetty ◽  
Michele Cappellari ◽  
Richard M McDermid ◽  
Davor Krajnović ◽  
P T de Zeeuw ◽  
...  
Keyword(s):  
Galaxy Formation ◽  
Scaling Relations ◽  
Coma Cluster ◽  
Dynamical Models ◽  
Fundamental Plane ◽  
Cluster Galaxies ◽  
Dynamical Scaling ◽  
Small Uncertainty ◽  
Cluster Distance ◽  
Using Data

Abstract We study a sample of 148 early-type galaxies in the Coma cluster using SDSS photometry and spectra, and calibrate our results using detailed dynamical models for a subset of these galaxies, to create a precise benchmark for dynamical scaling relations in high-density environments. For these galaxies, we successfully measured global galaxy properties, modeled stellar populations, and created dynamical models, and support the results using detailed dynamical models of 16 galaxies, including the two most massive cluster galaxies, using data taken with the SAURON IFU. By design, the study provides minimal scatter in derived scaling relations due to the small uncertainty in the relative distances of galaxies compared to the cluster distance. Our results demonstrate low (≤55% for 90th percentile) dark matter fractions in the inner 1Re of galaxies. Owing to the study design, we produce the tightest, to our knowledge, IMF-σe relation of galaxies, with a slope consistent with that seen in local galaxies. Leveraging our dynamical models, we transform the classical Fundamental Plane of the galaxies to the Mass Plane. We find that the coefficients of the mass plane are close to predictions from the virial theorem, and have significantly lower scatter compared to the Fundamental plane. We show that Coma galaxies occupy similar locations in the (M* - Re) and (M* - σe) relations as local field galaxies but are older. This, and the fact we find only three slow rotators in the cluster, is consistent with the scenario of hierarchical galaxy formation and expectations of the kinematic morphology-density relation.

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