- ID:
- ivo://CDS.VizieR/J/ApJ/814/95
- Title:
- Star formation rate of 4<~z<~8 galaxies
- Short Name:
- J/ApJ/814/95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent observations have shown that the characteristic luminosity of the rest-frame ultraviolet (UV) luminosity function does not significantly evolve at 4<z<7 and is approximately M_UV_^*^~21. We investigate this apparent non-evolution by examining a sample of 173 bright, M_UV_<-21 galaxies at z=4-7, analyzing their stellar populations and host halo masses. Including deep Spitzer/IRAC imaging to constrain the rest-frame optical light, we find that M_UV_^*^ galaxies at z=4-7 have similar stellar masses of log(M/M_{sun}_)=9.6-9.9 and are thus relatively massive for these high redshifts. However, bright galaxies at z=4-7 are less massive and have younger inferred ages than similarly bright galaxies at z=2-3, even though the two populations have similar star formation rates and levels of dust attenuation for a fixed dust-attenuation curve. Matching the abundances of these bright z=4-7 galaxies to halo mass functions from the Bolshoi {Lambda}CDM simulation implies that the typical halo masses in ~M_UV_^*^ galaxies decrease from log(M_h_/M_{sun}_)=11.9 at z=4 to log(M_h_/M_{sun}_)=11.4 at z=7. Thus, although we are studying galaxies at a similar stellar mass across multiple redshifts, these galaxies live in lower mass halos at higher redshift. The stellar baryon fraction in ~M_UV_^*^ galaxies in units of the cosmic mean {Omega}_b_/{Omega}_m_ rises from 5.1% at z=4 to 11.7% at z=7; this evolution is significant at the ~3{sigma} level. This rise does not agree with simple expectations of how galaxies grow, and implies that some effect, perhaps a diminishing efficiency of feedback, is allowing a higher fraction of available baryons to be converted into stars at high redshifts.
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- ID:
- ivo://CDS.VizieR/J/A+A/601/A95
- Title:
- Star-forming dwarfs at intermediate-z in VUDS
- Short Name:
- J/A+A/601/A95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present emission line measurements and the main physical properties of a sample of 164 star-forming dwarf galaxies (SFDGs) in the VIMOS Ultra Deep Survey (VUDS, Le Fevre et al., 2015A&A...576A..79L). VUDS is one of the largest programs on the ESO-VLT with 640 hours of observing time, and covers a total of one square degree in three separate fields: COSMOS, ECDFS, and VVDS-02h. The spectroscopic observations were carried out at the VLT with the VIMOS Multi-Object Spectrograph (MOS) with two grisms (LRBLUE and LRRED) covering a wavelength range of 365<lambda<935nm at uniform spectral resolution of R=180 and R=210, respectively. The integration time (on-source) is ~14-hours per target for each grism, which allows to detect the continuum at 850nm for i_AB_=25, and emission lines with an observed flux limit F=1.5*10^-18^erg/s/cm2 at S/N~5. Redshift measurements in VUDS were performed using the EZ code (Garilli et al., 2010PASP..122..827G), both in automatic and manual modes (by two persons independently) for each spectrum. The overall redshift accuracy is dz/(1+z)=0.0005-0.0007. The spectra had already been fully calibrated in wavelength and flux by the VUDS team, which also did the sky subtraction. Emission lines fluxes and equivalent widths are measured manually on a one-by- one basis using the task 'splot' of IRAF by direct integration of the line profile after linear subtraction of the continuum. These fluxes are given in units of 10^-18^erg/s/cm^2^. The uncertainties in the line measurements were computed from the dispersion of values provided by multiple measurements adopting different possible band-passes (free of lines and strong residuals from sky subtraction) for the local continuum determination, which is fitted using a second order polynomial. No extinction correction has been applied to these fluxes. The EW measurements of H{gamma}, H{beta} and H{alpha} lines have been already corrected for absorption by +0.1nm for all galaxies, following Ly et al. (2014ApJ...780..122L). For each galaxy the reddening constant, c(H{beta}), is presented. These values and their uncertainties have been derived from the H{alpha}/H{beta} or H{gamma}/H{beta} ratios, whenever possible. We adopted the reddening constant from the best-fit SED, using the relations of Calzetti et al. (2000ApJ...533..682C), for (a) galaxies where the computation of c(H{beta}) from emission lines is not possible because the lines are not present, or (b) the line ratios give a negative extinction correction (i.e., H{alpha}/H{beta}<2.82 or H{gamma}/H{beta}<0.47, assuming Case B recombination with Te=2*10^4^K, ne=100cm^-3^).
- ID:
- ivo://CDS.VizieR/J/MNRAS/435/2861
- Title:
- Star-forming galaxies in near-IR
- Short Name:
- J/MNRAS/435/2861
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The near-infrared spectral region is becoming a very useful wavelength range to detect and quantify the stellar population of galaxies. Models are developing to predict the contribution of the thermally pulsating stars on the asymptotic giant branch stars that should dominate the near-infrared region (NIR) spectra of populations 0.3 to 2Gyr old. When present in a given stellar population, these stars leave unique signatures that can be used to detect them unambiguously. However, these models have to be tested in a homogeneous data base of star-forming galaxies, to check if the results are consistent with what is found from different wavelength ranges. In this work, we performed stellar population synthesis on the nuclear and extended regions of 23 star-forming galaxies to understand how the star formation tracers in the NIR can be used in practice. The stellar population synthesis shows that for the galaxies with strong emission in the NIR, there is an important fraction of young/intermediate population contributing to the spectra, which is probably the ionization source in these galaxies. Galaxies that had no emission lines measured in the NIR were found to have older average ages and less contribution of young populations. Although the stellar population synthesis method proved to be very effective to find the young ionizing population in these galaxies, no clear correlation between these results and the NIR spectral indexes were found. Thus, we believe that, in practice, the use of these indexes is still very limited due to observational limitations.
- ID:
- ivo://CDS.VizieR/J/A+A/632/A15
- Title:
- Star-forming low-mass gal. stellar host
- Short Name:
- J/A+A/632/A15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The morphological evolution of star-forming galaxies provides important clues to understand their physical properties, as well as the triggering and quenching mechanisms of star formation. We analyze the morphology of galaxies hosting star-forming events at low redshift (z<0.36). We aim at connecting morphology and star-formation properties of low-mass galaxies (median stellar mass ~10^8.5^M_{sun}_) beyond the local Universe. We use a sample of medium-band selected star-forming galaxies from the GOODS-North field. H images for the sample are created combining both spectral energy distribution fits and HST data. Using them, we mask the star forming regions to obtain an unbiased two-dimensional model of the light distribution of the host galaxies. For this purpose we use PHI, a new Bayesian photometric decomposition code. We applied it independently to 7 HST bands, from the ultraviolet to the near-infrared, assuming a Sersic surface brightness model. Star-forming galaxy hosts show low Sersic index (with median n~0.9), as well as small sizes (median Re~1.6kpc), and negligible change of the parameters with wavelength (except for the axis ratio, which grows with wavelength in 46% of the sample). Using a clustering algorithm, we find two different classes of star-forming galaxies: A more compact, redder, and high-n (class A) and a more extended, bluer and lower-n one (class B). This separation holds across all seven bands analyzed. In addition, we find evidence that the first class is more spheroidal-like (according to the distribution of observed axis ratios). We compute the color gradients of the host galaxies finding that 48% of the objects where the analysis could be performed show negative gradients, and only in 5% they are positive. The host component of low-mass star-forming galaxies at z<0.36 separates into two different classes, similar to what has been found for their higher mass counterparts. The results are consistent with an evolution from class B to class A. Several mechanisms from the literature, like minor and major mergers, and violent disk instability, can explain the physical process behind the likely transition between the classes.
- ID:
- ivo://CDS.VizieR/J/A+A/553/A87
- Title:
- Star forming regions in HST galaxies sample
- Short Name:
- J/A+A/553/A87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The presence of small- and large-scale star formation structures in a sample of six spiral Hubble Space Telescope (HST) galaxies is investigated to identify small structures of young stars known as OB associations and to tell whether they are formed inside larger scale star forming stellar structures in a hierarchical form. This process was based on a friend-of-friend (FOF) algorithm applied to the bright, early type stars above a certain color cutoff limit in order to ensure that we include main sequence stars. A size criterion was introduced in order to apply the same algorithm to different types of stellar structures. Depending on their size, the structures were divided into the four categories of associations, aggregates, complexes, and supercomplexes. Star forming structures of the four types mentioned above are found in all six galaxies of our sample. The majority of the associations and aggregates (the smaller structures) found are lying inside larger structures like complexes and supercomplexes, indicating a hierarchical star formation mechanism.
- ID:
- ivo://CDS.VizieR/J/A+A/645/A87
- Title:
- Star-galaxy classification feature importance
- Short Name:
- J/A+A/645/A87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Future astrophysical surveys such as J-PAS will produce very large datasets, the so-called "big data", which will require the deployment of accurate and efficient machine-learning (ML) methods. In this work, we analyze the miniJPAS survey, which observed about ~1deg^2^ of the AEGIS field with 56 narrow-band filters and 4 ugri broad-band filters. The miniJPAS primary catalog contains approximately 64 000 objects in the r detection band (mag_AB_<~24), with forced-photometry in all other filters. We discuss the classification of miniJPAS sources into extended (galaxies) and point-like (e.g., stars) objects, which is a step required for the subsequent scientific analyses. We aim at developing an ML classifier that is complementary to traditional tools that are based on explicit modeling. In particular, our goal is to release a value-added catalog with our best classification. In order to train and test our classifiers, we cross-matched the miniJPAS dataset with SDSS and HSC-SSP data, whose classification is trustworthy within the intervals 15<=r<=20 and 18.5<=r<=23.5, respectively. We trained and tested six different ML algorithms on the two cross-matched catalogs: K-nearest neighbors, decision trees, random forest (RF), artificial neural networks, extremely randomized trees (ERT), and an ensemble classifier. This last is a hybrid algorithm that combines artificial neural networks and RF with the J-PAS stellar and galactic loci classifier. As input for the ML algorithms we used the magnitudes from the 60 filters together with their errors, with and without the morphological parameters. We also used the mean point spread function in the r detection band for each pointing. We find that the RF and ERT algorithms perform best in all scenarios. When the full magnitude range of 15<=r<=23.5 is analyzed, we find an area under the curve AUC=0.957 with RF when photometric information alone is used, and AUC=0.986 with ERT when photometric and morphological information is used together. When morphological parameters are used, the full width at half maximum is the most important feature. When photometric information is used alone, we observe that broad bands are not necessarily more important than narrow bands, and errors (the width of the distribution) are as important as the measurements (central value of the distribution). In other words, it is apparently important to fully characterize the measurement. ML algorithms can compete with traditional star and galaxy classifiers; they outperform the latter at fainter magnitudes (r>~21). We use our best classifiers, with and without morphology, in order to produce a value-added catalog.
- ID:
- ivo://CDS.VizieR/J/A+A/627/A31
- Title:
- Statistial HATLAS Lensed Objects Selec.
- Short Name:
- J/A+A/627/A31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The statistical analysis of large sample of strong lensing events can be a powerful tool to extract astrophysical or cosmological valuable information. Their selection using submillimetre galaxies has been demonstrated to be very effective with more than ~200 proposed candidates in the case of Herschel-ATLAS data and several tens in the case of the South Pole Telescope. However, the number of confirmed events is still relatively low, i.e. a few tens, mostly because of the lengthy observational validation process on individual events. In this work we propose a new methodology with a statistical selection approach to increase by a factor of ~5 the number of such events within the Herschel-ATLAS data set. Although the methodology can be applied to address several selection problems, it has particular benefits in the case of the identification of strongly lensed galaxies: objectivity, minimal initial constrains in the main parameter space, and preservation of statistical properties. The proposed methodology is based on the Bhattacharyya distance as a measure of the similarity between probability distributions of properties of two different cross-matched galaxies. The particular implementation for the aim of this work is called SHALOS and it combines the information of four different properties of the pair of galaxies: angular separation, luminosity percentile, redshift, and the ratio of the optical to the submillimetre flux densities. The SHALOS method provides a ranked list of strongly lensed galaxies. The number of candidates within ~340{deg}^2^ of the Herschel-ATLAS surveyed area for the final associated probability, P_tot_>0.7, is 447 and they have an estimated mean amplification factor of 3.12 for a halo with a typical cluster mass. Additional statistical properties of the SHALOS candidates, as the correlation function or the source number counts, are in agreement with previous results indicating the statistical lensing nature of the selected sample.
- ID:
- ivo://CDS.VizieR/J/A+A/392/741
- Title:
- Stellar Catalogue in the Chandra DFS
- Short Name:
- J/A+A/392/741
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stellar catalogues in five passbands (UBVRI) over an area of approximately 0.3{deg}^2^, comprising about 1200 objects, and in seven passbands (UBVRIJK) over approximately 0.1{deg}^2^, comprising about 400 objects, in the direction of the Chandra Deep Field South are presented. The 90% completeness level of the number counts is reached at approximately U=23.8, B=24.0, V=23.5, R=23.0, I=21.0, J=20.5, K=19.0. These multi-band catalogues have been produced from publicly available, single passband catalogues. A scheme is presented to select point sources from these catalogues, by combining the SExtractor parameter CLASS_STAR from all available passbands. Probable QSOs and unresolved galaxies are identified by using the previously developed {chi}^2^-technique (Hatziminaoglou et al., 2002, Cat. <J/A+A/384/81>), that fits the overall spectral energy distributions to template spectra and determines the best fitting template. Approximately 15% of true galaxies are misclassified as stars by the {chi}^2^ method. The number of unresolved galaxies and QSOs identified by the {chi}^2^-technique, allows us to estimate that the remaining level of contamination by such objects is at the level of 2.4% of the number of stars. The fraction of missing stars being incorrectly removed as QSOs or unresolved galaxies is estimated to be similar. The resulting stellar catalogues and the objects identified as likely QSOs and unresolved galaxies with coordinates, observed magnitudes with errors and assigned spectral types by the {chi}^2^-technique are presented and are publicly available.
- ID:
- ivo://CDS.VizieR/J/A+A/597/A48
- Title:
- Stellar kinematics in CALIFA survey
- Short Name:
- J/A+A/597/A48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the stellar kinematic maps of a large sample of galaxies from the integral-field spectroscopic survey CALIFA. The sample comprises 300 galaxies displaying a wide range of morphologies across the Hubble sequence, from ellipticals to late-type spirals. This dataset allows us to homogeneously extract stellar kinematics up to several effective radii. In this paper, we describe the level of completeness of this subset of galaxies with respect to the full CALIFA sample, as well as the virtues and limitations of the kinematic extraction compared to other well-known integral-field surveys. In addition, we provide averaged integrated velocity dispersion radial profiles for different galaxy types, which are particularly useful to apply aperture corrections for single aperture measurements or poorly resolved stellar kinematics of high-redshift sources. The work presented in this paper sets the basis for the study of more general properties of galaxies that will be explored in subsequent papers of the survey.
- ID:
- ivo://CDS.VizieR/J/MNRAS/401/1521
- Title:
- Stellar masses of Lyman break galaxies at z~3
- Short Name:
- J/MNRAS/401/1521
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of a large survey of the mid-infrared (mid-IR) properties of 248 Lyman Break Galaxies (LBGs) with confirmed spectroscopic redshift using deep Spitzer/Infrared Array Camera (IRAC) observations in six cosmological fields. By combining the new mid-IR photometry with optical and near-infrared observations, we model the spectral energy distributions (SEDs) employing a revised version of the Bruzual and Charlot synthesis population code that incorporates a new treatment of the thermal-pulsating asymptotic giant branch phase (CB07). Our primary aim is to investigate the impact of the AGB phase in the stellar masses of the LBGs, and compare our new results with previous stellar mass estimates. We investigate the stellar mass of the LBG population as a whole and assess the benefits of adding longer wavelengths to estimates of stellar masses for high-redshift galaxies.
