Search

Start Over Subject galaxies Content Level Research
641. Classification of Coma early galaxies
ID:
ivo://CDS.VizieR/J/A+AS/116/429
Title:
Classification of Coma early galaxies
Short Name:
J/A+AS/116/429
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of an isophotal shape analysis of three samples of galaxies in the Coma cluster. Quantitative morphology, together with structural and photometric parameters, is given for each galaxy. Special emphasis has been placed on the detailed classification of early-type galaxies. The three samples are: i) a sample of 97 early-type galaxies brighter than m_B_=17.00 falling within one degree from the center of the Coma cluster; these galaxies were observed with CCD cameras, mostly in good to excellent resolution conditions; ii) a magnitude complete sample of 107 galaxies of all morphological types down to m_B_=17.00 falling in a circular region of 50arcmin diameter, slightly offcentered to the North-West of the cluster center; the images for this and the next sample come from digitized photographic plates; iii) a complete comparison sample of 26 galaxies of all morphological types down to m_R_=16.05 (or m_B_=~17.5), also in a region of 50arcmin diameter, but centered 2.6degrees West of the cluster center. The reliability of our morphological classifications and structural parameters of galaxies, down to the adopted magnitude limits, is assessed by comparing the results on those galaxies for which we had images taken with different instrumentation and/or seeing conditions, and by comparing our results with similar data from other observers.
642. Classification of emission-line gal.
ID:
ivo://CDS.VizieR/J/A+A/355/89
Title:
Classification of emission-line gal.
Short Name:
J/A+A/355/89
Date:
21 Oct 2021
Publisher:
CDS
Description:
The main goal of this work was to further investigate the classification of emission-line galaxies from the "Spectrophotometric Catalogue of HII galaxies" by Terlevich et al. (1991, Cat. J/A+AS/91/285) in a homogeneous and objective way, using the three line-ratio diagrams of Veilleux & Osterbrock (1987ApJS...63..295V). The re-measurements of the most important nebular lines and a revised classification are presented for 314 narrow-emission-line galaxies (represented by 405 spectra) from Terlevich's et al. (1991, Cat. J/A+AS/91/285) catalogue. The revised catalogue contains 267 HII galaxies, 25 Seyfert2 galaxies, 3 LINERs, 4 "revised" galaxies, 13 "transition" galaxies and 2 "ambiguous" galaxies.
643. Classification of IR galaxies
ID:
ivo://CDS.VizieR/J/ApJ/646/161
Title:
Classification of IR galaxies
Short Name:
J/ApJ/646/161
Date:
21 Oct 2021
Publisher:
CDS
Description:
Mid-infrared diagnostics are presented for a large portion of the Spitzer Infrared Nearby Galaxies Survey (SINGS) sample plus archival data from ISO and Spitzer. The SINGS data set includes low- and high-resolution spectral maps and broadband imaging in the infrared for over 160 nuclear and extranuclear regions within 75 nearby galaxies spanning a wide range of morphologies, metallicities, luminosities, and star formation rates. Our main result is that these mid-infrared diagnostics effectively constrain a targets dominant power source. The combination of a high-ionization line index and PAH strength serves as an efficient discriminant between AGNs and star-forming nuclei, confirming progress made with ISO spectroscopy on starbursting and ultraluminous infrared galaxies. The sensitivity of Spitzer allows us to probe fainter nuclear and star-forming regions within galaxy disks.
644. Classification of LAMOST DR4 galaxies
ID:
ivo://CDS.VizieR/J/MNRAS/474/1873
Title:
Classification of LAMOST DR4 galaxies
Short Name:
J/MNRAS/474/1873
Date:
21 Oct 2021
Publisher:
CDS
Description:
We study the classification and composite spectra of galaxies in the fourth data release (DR4) of the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST). We select 40182 spectra of galaxies from LAMOST DR4, which have photometric information but no spectroscopic observations in the Sloan Digital Sky Survey (SDSS). These newly observed spectra are recalibrated and classified into six classes - passive, H{alpha}-weak, star-forming, composite, LINER and Seyfert - using the line intensity (H{beta}, [OIII] 5007, H{alpha} and [NII] 6585). We also study the correlation between spectral class and morphological type through three parameters: concentration index, (u-r) colour and D4000n index. We calculate composite spectra of high signal-to-noise ratio (S/N) for six spectral classes and, using these composites, we pick out some features that can differentiate the classes effectively, including H{beta}, Fe5015, H{gamma}A, HK and the Mg2 band. In addition, we compare our composite spectra with the SDSS ones and analyse their differences. A galaxy catalogue of 40182 newly observed spectra (36601 targets) and the composite spectra of the six classes are available online (http://sciwiki.lamost.org/downloads/wll).
645. Classification of nearby galaxies
ID:
ivo://CDS.VizieR/J/ApJS/147/1
Title:
Classification of nearby galaxies
Short Name:
J/ApJS/147/1
Date:
21 Oct 2021
Publisher:
CDS
Description:
A major problem in extragalactic astronomy is the inability to distinguish in a robust, physical, and model-independent way how galaxy populations are physically related to each other and to their formation histories. A similar, but distinct, and also long-standing question is whether the structural appearances of galaxies, as seen through their stellar light distributions, contain enough physical information to offer this classification. We argue through the use of 240 images of nearby galaxies that three model-independent parameters measured on a single galaxy image reveal its major ongoing and past formation modes and can be used as a robust classification system. These parameters quantitatively measure: the concentration (C), asymmetry (A), and clumpiness (S) of a galaxy's stellar light distribution. When combined into a three-dimensional "CAS" volume all major classes of galaxies in various phases of evolution are cleanly distinguished. We argue that these three parameters correlate with important modes of galaxy evolution: star formation and major merging activity. This is argued through the strong correlation of H{alpha} equivalent width and broadband colors with the clumpiness parameter S, the uniquely large asymmetries of 66 galaxies undergoing mergers, and the correlation of bulge to total light ratios, and stellar masses, with the concentration index. As an obvious goal is to use this system at high redshifts to trace evolution, we demonstrate that these parameters can be measured, within a reasonable and quantifiable uncertainty with available data out to z~3 using the Hubble Space Telescope GOODS ACS and Hubble Deep Field images.
646. Classification of 1.5<=z<=3 HUDF galaxies
ID:
ivo://CDS.VizieR/J/ApJ/805/181
Title:
Classification of 1.5<=z<=3 HUDF galaxies
Short Name:
J/ApJ/805/181
Date:
21 Oct 2021
Publisher:
CDS
Description:
At z>~1, the distinction between merging and "normal" star-forming galaxies based on single band morphology is often hampered by the presence of large clumps which result in a disturbed, merger-like appearance even in rotationally supported disks. In this paper we discuss how a classification based on canonical, non-parametric structural indices measured on resolved stellar mass maps, rather than on single-band images, reduces the misclassification of clumpy but not merging galaxies. We calibrate the mass-based selection of mergers using the MIRAGE hydrodynamical numerical simulations of isolated and merging galaxies which span a stellar mass range of 10^9.8^-10^10.6^M_{sun}_ and merger ratios between 1:1-1:6.3. These simulations are processed to reproduce the typical depth and spatial resolution of observed Hubble Ultra Deep Field (HUDF) data. We test our approach on a sample of real z~=2 galaxies with kinematic classification into disks or mergers and on ~100 galaxies in the HUDF field with photometric/spectroscopic redshift between 1.5<=z<=3 and M>10^9.4^M_{sun}_. We find that a combination of the asymmetry A_MASS_ and M_20,MASS_ indices measured on the stellar mass maps can efficiently identify real (major) mergers with <~20% contamination from clumpy disks in the merger sample. This mass-based classification cannot be reproduced in star-forming galaxies by H-band measurements alone, which instead result in a contamination from clumpy galaxies which can be as high as 50%. Moreover, we find that the mass-based classification always results in a lower contamination from clumpy galaxies than an H-band classification, regardless of the depth of the imaging used (e.g., CANDELS versus HUDF).
647. Classifications of 188 SNe Ia
ID:
ivo://CDS.VizieR/J/other/Sci/340.170
Title:
Classifications of 188 SNe Ia
Short Name:
J/other/Sci/340.
Date:
21 Oct 2021
Publisher:
CDS
Description:
Type Ia supernovae (SNe Ia) have been used as excellent standardizable candles for measuring cosmic expansion, but their progenitors are still elusive. Here, we report that the spectral diversity of SNe Ia is tied to their birthplace environments. We found that those with high-velocity ejecta are substantially more concentrated in the inner and brighter regions of their host galaxies than are normal-velocity SNe Ia. Furthermore, the former tend to inhabit larger and more luminous hosts. These results suggest that high-velocity SNe Ia likely originate from relatively younger and more metal-rich progenitors than do normal-velocity SNe Ia and are restricted to galaxies with substantial chemical evolution.
648. Classifying galaxy spectra at 0.5<z<1
ID:
ivo://CDS.VizieR/J/MNRAS/478/4416
Title:
Classifying galaxy spectra at 0.5<z<1
Short Name:
J/MNRAS/478/4416
Date:
10 Dec 2021 13:08:01
Publisher:
CDS
Description:
The spectrum of a galaxy contains information about its physical properties. Classifying spectra using templates helps to elucidate the nature of a galaxy's energy sources. In this paper, we investigate the use of self-organizing maps in classifying galaxy spectra against templates. We trained semi-supervised self-organizing map networks using a set of templates covering the wavelength range from far ultraviolet to near-infrared. The trained networks were used to classify the spectra of a sample of 142 galaxies with 0.5<z<1 and the results compared to classifications performed using K-means clustering, a supervised neural network, and chi-squared minimization. Spectra corresponding to quiescent galaxies were more likely to be classified similarly by all methods while starburst spectra showed more variability. Compared to classification using chi-squared minimization or the supervised neural network, the galaxies classed together by the self-organizing map had more similar spectra. The class ordering provided by the 1D self-organizing maps corresponds to an ordering in physical properties, a potentially important feature for the exploration of large data sets.
649. Cl 1103.7-1245 at z=0.96: spectroscopic catalog
ID:
ivo://CDS.VizieR/J/A+A/544/A104
Title:
Cl 1103.7-1245 at z=0.96: spectroscopic catalog
Short Name:
J/A+A/544/A104
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present new spectroscopic observations in a field containing the highest redshift cluster of the ESO Distant Cluster Survey (EDisCS). We measure galaxy redshifts and determine the velocity dispersions of the galaxy structures located in this field. Together with the main cluster Cl 1103.7-1245 (z=0.9580; {sigma}_clus_=522+/-111km/s) we find a secondary structure at z=0.9830, Cl 1103.7-1245c. We then characterize the galaxy properties in both systems. These new spectroscopic observations for Cl 1103.7-1245 complement the previous analysis of Milvang-Jensen et al. (2008, Cat. J/A+A/482/419), whose observations targetted z=0.70.
650. CLEAR. II. SFRs of quiescent galaxies
ID:
ivo://CDS.VizieR/J/ApJ/898/171
Title:
CLEAR. II. SFRs of quiescent galaxies
Short Name:
J/ApJ/898/171
Date:
16 Mar 2022 00:57:30
Publisher:
CDS
Description:
The origin of the correlations between mass, morphology, quenched fraction, and formation history in galaxies is difficult to define, primarily due to the uncertainties in galaxy star formation histories (SFHs). SFHs are better constrained for higher redshift galaxies, observed closer to their formation and quenching epochs. Here we use "nonparametric" SFHs and a nested sampling method to derive constraints on the formation and quenching timescales of quiescent galaxies at 0.7<z<2.5. We model deep HST grism spectroscopy and photometry from the CLEAR (CANDELS Ly{alpha} Emission at Reionization) survey. The galaxy formation redshifts, z50 (defined as the point where they had formed 50% of their stellar mass) range from z_50_~2 (shortly prior to the observed epoch) up to z_50_~5-8. We find that early formation redshifts are correlated with high stellar-mass surface densities, log{Sigma}_1_/(M_{sun}_kpc^-2^)>10.25, where {Sigma}_1_ is the stellar mass within 1pkpc (proper kpc). Quiescent galaxies with the highest stellar-mass surface density, log{Sigma}_1_/(M_{sun}_kpc^-2^)>10.25, show a minimum formation redshift: all such objects in our sample have z_50_>2.9. Quiescent galaxies with lower surface density, log{Sigma}_1_/(M_{sun}_kpc^-2^)=9.5-10.25, show a range of formation epochs (z_50_~1.5-8), implying these galaxies experienced a range of formation and assembly histories. We argue that the surface density threshold log{Sigma}_1_/(M_{sun}_kpc^-2^)>10.25 uniquely identifies galaxies that formed in the first few Gyr after the big bang, and we discuss the implications this has for galaxy formation models.