- ID:
- ivo://CDS.VizieR/J/MNRAS/380/986
- Title:
- Lyman-break galaxies from GALEX
- Short Name:
- J/MNRAS/380/986
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ultraviolet (UV) galaxies have been selected from the Galaxy Evolution Explorer deep imaging survey. The presence of a far-UV (FUV) drop-out in their spectral energy distributions (SEDs) proved to be a very complete (83.3 per cent) but not very efficient (21.4 per cent) tool for identifying Lyman break galaxies (LBGs) at z~1. In this paper, we explore the physical properties of these galaxies and how they contribute to the total star formation rate (SFR).
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- ID:
- ivo://CDS.VizieR/J/MNRAS/431/2080
- Title:
- Lyman break galaxies (LBG) at z~1
- Short Name:
- J/MNRAS/431/2080
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- After carefully cross-identifying previously discovered - and selected by the Galaxy Evolution Explorer (GALEX) - Lyman break galaxy (LBG) candidates one-to-one with their optical counterparts in the field of the Chandra Deep Field South (CDF-S), we re-estimate their photometric redshifts using multiwavelength data from ultraviolet and optical to near-infrared. Considering their re-estimated photometric redshifts and spectral energy distributions, we refine a new updated sample of 383 LBGs at 0.7<~z<~1.4, with two confirmed active galactic nuclei being excluded. There are 260 and 111 LBGs classified as starburst and irregular types, respectively. The ages of the LBGs span from several Myr to 1.5Gyr with a median of ~50Myr. Their dust-corrected star formation rates (SFRs) and stellar masses (M*) are 4-220M_{sun}_/yr and from 2.3x10^8^ to 4x10^11^M_{sun}_, with median values of ~25M_{sun}_/yr and ~10^10^M_{sun}_. The rest-frame far-ultraviolet luminosity function of the LBGs is presented with the best-fitting Schechter parameters of {alpha}=-1.61+/-0.40, M*=-20.40+/-0.22 and {phi}*=(0.89+/-0.30)x10^-3^/Mpc^3^/dex. LBGs of irregular types are mainly distributed along the main sequence of star-forming galaxies, while most LBGs of starburst types are located in the starburst region. Together with previous studies, we suggest that the star formation mode for LBGs at z>3 is mainly starburst, and that it evolves to be more significant to the quenching mode after z~3. A downsizing effect is clearly found, and we discuss the physical implications and comparisons with previous studies in detail. LBGs with larger SFRs are, on average, more compact. In the rest-frame colour (U-B)-M* diagram, LBGs are distributed in the `blue' cloud. We suggest that LBGs might evolve along the blue cloud from later to earlier types. The Hubble Space Telescope images in F606W (V band) and F850LP (z band) are taken from the Galaxy Evolution from Morphology and SEDs (GEMS) survey and the Great Observatories Origins Deep Survey South (GOODS-S) for morphological studies of LBGs. sextractor and galfit are applied in order to obtain their morphological parameters. We establish an image gallery of 277 LBGs, commonly detected in both bands, by visually classifying individual LBGs into the following types: chain, spiral, tadpole, bulge and clump. We define a morphological sample of 142 LBGs with reliable results of Sersic indices and sizes in both bands. We find that LBGs at z~1 are dominated by disc-like galaxies, with median sizes of 2.34 and 2.68kpc in F606W and F850LP, respectively. The correlations between the photometric and morphological properties of LBGs are investigated. Strong correlations between their half-light radii and M* (i.e. size-stellar mass relations) are found in both bands. We discuss the physical connections between the correlations and the downsizing effect.
- ID:
- ivo://CDS.VizieR/J/ApJ/703/2033
- Title:
- Lyman-break galaxies (LBG) in the HUDF
- Short Name:
- J/ApJ/703/2033
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of 407 z~3 Lyman break galaxies (LBGs) to a limiting isophotal u-band magnitude of 27.6mag in the Hubble Ultra Deep Field. The LBGs are selected using a combination of photometric redshifts and the u-band drop-out technique enabled by the introduction of an extremely deep u-band image obtained with the Keck I telescope and the blue channel of the Low Resolution Imaging Spectrometer. The Keck u-band image, totaling 9hr of integration time, has a 1{sigma} depth of 30.7mag/arcsec^2^, making it one of the most sensitive u-band images ever obtained. The u-band image also substantially improves the accuracy of photometric redshift measurements of ~50% of the z~3 LBGs, significantly reducing the traditional degeneracy of colors between z~3 and z~0.2 galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/736/18
- Title:
- Lyman-continuum emission at z~3 in SSA22 field
- Short Name:
- J/ApJ/736/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of an ultradeep, narrowband imaging survey for Lyman-continuum (LyC) emission at z~3 in the SSA22a field. We employ a custom narrowband filter centered at {lambda}=3640{AA} (NB3640), which probes the LyC region for galaxies at z>=3.06. We also analyze new and archival NB4980 imaging tuned to the wavelength of the Ly{alpha} emission line at z=3.09, and archival broadband B, V, and R images of the non-ionizing UV continuum. Our NB3640 images contain 26 z>=3.06 Lyman break galaxies (LBGs) as well as a set of 130 Ly{alpha} emitters (LAEs), identified by their excess NB4980 flux relative to the BV continuum. Six LBGs and 28 LAEs are detected in the NB3640 image. LBGs appear to span a range of NB3640-R colors, while LAEs appear bimodal in their NB3640-R properties. We estimate average UV-to-LyC flux density ratios.
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/316
- Title:
- Lyman continuum LAEs and LBGs in SSA22 field
- Short Name:
- J/MNRAS/465/316
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the largest to date sample of hydrogen Lyman continuum (LyC) emitting galaxy candidates at any redshift, with 18 Lyman {alpha} emitters (LAEs) and seven Lyman break galaxies (LBGs), obtained from the SSA22 field with Subaru/Suprime-Cam. The sample is based on the 159 LAEs and 136 LBGs observed in the field, all with spectroscopically confirmed redshifts, and these LyC candidates are selected as galaxies with counterparts in a narrow-band filter image which traces LyC at z>=3.06. Many LyC candidates show a spatial offset between the rest-frame non-ionizing ultraviolet (UV) detection and the LyC-emitting substructure or between the Ly{alpha} emission and LyC. The possibility of foreground contamination complicates the analysis of the nature of LyC emitters, although statistically it is highly unlikely that all candidates in our sample are contaminated by foreground sources. Many viable LyC LAE candidates have flux density ratios inconsistent with standard models, while also having too blue UV slopes to be foreground contaminants. Stacking reveals no significant LyC detection, suggesting that there is a dearth of objects with marginal LyC signal strength, perhaps due to a bimodality in the LyC emission. The foreground contamination corrected 3{sigma} upper limits of the observed average flux density ratios are fLyC/fUV < 0.08 from stacking LAEs and f_LyC_/f_UV_<0.02 from stacking LBGs. There is a sign of a positive correlation between LyC and Ly{alpha}, suggesting that both types of photons escape via a similar mechanism. The LyC detection rate among protocluster LBGs is seemingly lower compared to the field.
- ID:
- ivo://CDS.VizieR/J/A+A/596/A86
- Title:
- Lynx-Cancer void sample galaxies HI data
- Short Name:
- J/A+A/596/A86
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Void population consists mainly of late-type and low surface brightness (LSB) dwarf galaxies, whose atomic hydrogen is the main component of their baryonic matter. Therefore observations of void galaxy HI are mandatory to understand both their evolution and dynamics. Our aim was to obtain integrated HI parameters for a fainter part of the nearby Lynx-Cancer void galaxy sample (total of 45 objects) with the Nancay Radio Telescope (NRT) and to conduct the comparative analysis of the whole 103 void galaxies with known HI data with a sample of similar galaxies residing in denser environments of the Local Volume. For HI observations we used the NRT with its sensitive antenna/receiver system FORT and standard processing. The comparison of the void and "control" samples on the parameter M(HI)/L_B_ is conducted with the non-parametric method "The 2x2 Contingency Table test". We obtained new HI data for about 40% of the Lynx-Cancer galaxy sample. Along with data from the literature, we use for further analysis data for 103 void objects. The proxy of the evolutional parameter M(HI)/L_B_ of the void sample is compared with that of 82 galaxies of morphological types 8-10 residing in the Local Volume groups and aggregates. At the confidence level of P=0.988, we conclude that for the same luminosity, these void galaxies are systematically gas-richer, in average by ~39%. This result is consistent with the authors' earlier conclusion on the smaller gas metallicities and evidences for the slower low-mass galaxy evolution in voids.
- ID:
- ivo://CDS.VizieR/J/ApJS/230/20
- Title:
- Machine learning technique to classify CoNFIG gal.
- Short Name:
- J/ApJS/230/20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the application of a deep machine learning technique to classify radio images of extended sources on a morphological basis using convolutional neural networks (CNN). In this study, we have taken the case of the Fanaroff-Riley (FR) class of radio galaxies as well as radio galaxies with bent-tailed morphology. We have used archival data from the Very Large Array (VLA)-Faint Images of the Radio Sky at Twenty Centimeters survey and existing visually classified samples available in the literature to train a neural network for morphological classification of these categories of radio sources. Our training sample size for each of these categories is ~200 sources, which has been augmented by rotated versions of the same. Our study shows that CNNs can classify images of the FRI and FRII and bent-tailed radio galaxies with high accuracy (maximum precision at 95%) using well-defined samples and a "fusion classifier," which combines the results of binary classifications, while allowing for a mechanism to find sources with unusual morphologies. The individual precision is highest for bent-tailed radio galaxies at 95% and is 91% and 75% for the FRI and FRII classes, respectively, whereas the recall is highest for FRI and FRIIs at 91% each, while the bent-tailed class has a recall of 79%. These results show that our results are comparable to that of manual classification, while being much faster. Finally, we discuss the computational and data-related challenges associated with the morphological classification of radio galaxies with CNNs.
- ID:
- ivo://CDS.VizieR/J/ApJS/226/5
- Title:
- MACT survey. I. Opt. spectroscopy in Subaru Deep Field
- Short Name:
- J/ApJS/226/5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Deep rest-frame optical spectroscopy is critical for characterizing and understanding the physical conditions and properties of the ionized gas in galaxies. Here, we present a new spectroscopic survey called "Metal Abundances across Cosmic Time" or MACT, which will obtain rest-frame optical spectra for ~3000 emission-line galaxies. This paper describes the optical spectroscopy that has been conducted with MMT/Hectospec and Keck/DEIMOS for ~1900 z=0.1-1 emission-line galaxies selected from our narrowband and intermediate-band imaging in the Subaru Deep Field. In addition, we present a sample of 164 galaxies for which we have measured the weak [OIII]{lambda}4363 line (66 with at least 3{sigma} detections and 98 with significant upper limits). This nebular emission line determines the gas-phase metallicity by measuring the electron temperature of the ionized gas. This paper presents the optical spectra, emission-line measurements, interstellar properties (e.g., metallicity, gas density), and stellar properties (e.g., star formation rates, stellar mass). Paper II of the MACT survey (Ly et al. 2016ApJ...828...67L) presents the first results on the stellar mass-gas metallicity relation at z<=1 using the sample with [OIII]{lambda}4363 measurements.
- ID:
- ivo://CDS.VizieR/J/ApJ/883/11
- Title:
- Magellan/IMACS spectra of Crater II & Hercules
- Short Name:
- J/ApJ/883/11
- Date:
- 21 Jan 2022 09:25:05
- Publisher:
- CDS
- Description:
- We investigate the possibility that the dwarf galaxies Crater II and Hercules have previously been tidally stripped by the Milky Way. We present Magellan/IMACS spectra of candidate member stars in both objects. We identify 37 members of Crater II, 25 of which have velocity measurements in the literature, and we classify three stars within that subset as possible binaries. We find that including or removing these binary candidates does not change the derived velocity dispersion of Crater II. Excluding the binary candidates, we measure a velocity dispersion of {sigma}_Vlos_=2.7_-0.4_^+0.5^km/s, corresponding to M/L=47_-13_^+17^M_{sun}_/L_{sun}_. We measure a mean metallicity of [Fe/H]=-1.95_-0.05_^+0.06^, with a dispersion of {sigma}_[Fe/H]_=0.18_-0.08_^+0.06^. Our velocity dispersion and metallicity measurements agree with previous measurements for Crater II, and confirm that the galaxy resides in a kinematically cold dark-matter halo. We also search for spectroscopic members stripped from Hercules in the possible extratidal stellar overdensities surrounding the dwarf. For both galaxies, we calculate proper motions using Gaia DR2 astrometry, and use their full 6D phase space information to evaluate the probability that their orbits approach sufficiently close to the Milky Way to experience tidal stripping. Given the available kinematic data, we find a probability of ~40% that Hercules has suffered tidal stripping. The proper motion of Crater II makes it almost certain to be stripped.
- ID:
- ivo://CDS.VizieR/J/AJ/154/113
- Title:
- Magellan/M2FS spectroscopy of Abell 267
- Short Name:
- J/AJ/154/113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of a pilot program to use the Magellan/M2FS spectrograph to survey the galactic populations and internal kinematics of galaxy clusters. For this initial study, we present spectroscopic measurements for 223 quiescent galaxies observed along the line of sight of the galaxy cluster Abell 267 (z~0.23). We develop a Bayesian method for modeling the integrated light from each galaxy as a simple stellar population, with free parameters that specify the redshift (v_los_/c) and characteristic age, metallicity ([Fe/H]), alpha-abundance ([{alpha}/Fe]), and internal velocity dispersion ({sigma}_int_) for individual galaxies. Parameter estimates derived from our 1.5hr observation of A267 have median random errors of {sigma}_Vlos_=20km/s, {sigma}_Age_=1.2Gyr, {sigma}_[Fe/H]_=0.11dex, {sigma}_[{alpha}/Fe]_=0.07dex, and {sigma}_{sigma}int_=20km/s. In a companion paper, we use these results to model the structure and internal kinematics of A267.
