Search

Start Over Subject catalogs Validation Level 2
791. Star formation histories of LG dwarf galaxies
ID:
ivo://CDS.VizieR/J/ApJ/789/147
Title:
Star formation histories of LG dwarf galaxies
Short Name:
J/ApJ/789/147
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present uniformly measured star formation histories (SFHs) of 40 Local Group (LG) dwarf galaxies based on color-magnitude diagram (CMD) analysis from archival Hubble Space Telescope imaging. We demonstrate that accurate SFHs can be recovered from CMDs that do not reach the oldest main sequence turn-off (MSTO), but emphasize that the oldest MSTO is critical for precisely constraining the earliest epochs of star formation. We find that: (1) the average lifetime SFHs of dwarf spheroidals (dSphs) can be approximated by an exponentially declining SFH with {tau} ~ 5 Gyr; (2) lower luminosity dSphs are less likely to have extended SFHs than more luminous dSphs; (3) the average SFHs of dwarf irregulars (dIrrs), transition dwarfs, and dwarf ellipticals can be approximated by the combination of an exponentially declining SFH ({tau} ~ 3-4 Gyr) for lookback ages >10-12 Gyr ago and a constant SFH thereafter; (4) the observed fraction of stellar mass formed prior to z = 2 ranges considerably (80% for galaxies with M < 10^5^ M_{sun}_ to 30% for galaxies with M > 10^7^ M_{sun}_) and is largely explained by environment; (5) the distinction between "ultra-faint" and "classical" dSphs is arbitrary; (6) LG dIrrs formed a significantly higher fraction of stellar mass prior to z = 2 than the Sloan Digital Sky Survey galaxies from Leitner and the SFHs from the abundance matching models of Behroozi et al. This may indicate higher than expected star formation efficiencies at early times in low mass galaxies. Finally, we provide all the SFHs in tabulated electronic format for use by the community.
792. Star Formation in Early-type galaxies
ID:
ivo://CDS.VizieR/J/A+AS/130/251
Title:
Star Formation in Early-type galaxies
Short Name:
J/A+AS/130/251
Date:
21 Oct 2021
Publisher:
CDS
Description:
The paper is the first of a series (Longhetti et al., 1998A&AS..130..267L, 1998b (Paper III) in press) dedicated to the study of the star formation history in early-type galaxies which show fine structures and/or interaction signatures. It presents nuclear line-strength indices for a sample composed of 21 shell galaxies, from the Malin & Carter (1983ApJ...274..534M) southern survey, and 30 members of isolated interacting pairs, from the Reduzzi & Rampazzo (1995ApL....30....1R) catalogue, located in low density environments. The spectral range covers 3700{AA}<{lambda}<5700{AA} at 2.1{AA}FWHM resolution. We measure 16 red ({lambda}>4200{AA}) indices defined by the Lick Group. Measures have been transformed into the Lick-IDS ``standard'' system. The procedure has been tested on a set of 5 elliptical galaxies selected from the Gonzalez (1993, Ph.D. thesis) sample. We derive also three blue ({lambda}<4200) indices, namely {DELTA}(4000{AA}) defined by Hamilton (1985ApJ...297..371H), H+K(CaII) and Hdelta/FeI defined by Rose (1984AJ.....89.1238R, 1985AJ.....90.1927R). Blue indices are correlated to the age of the last starburst occurred in a galaxy (Leonardi & Rose, 1996AJ....111..182L). The indices determination, the estimate of the measurement errors and the correction for the galaxies velocity dispersions are discussed in detail. In the Appendix A we present the indices for a set of hot stars (T>10000K) which may be used for extending, toward high temperatures, Worthey (1992, Ph.D. Thesis) fitting functions.
793. Star formation in spectroscopic survey
ID:
ivo://CDS.VizieR/J/ApJ/559/606
Title:
Star formation in spectroscopic survey
Short Name:
J/ApJ/559/606
Date:
21 Oct 2021
Publisher:
CDS
Description:
The 15R-North galaxy redshift survey is a uniform spectroscopic survey (S/N~10) covering the range 3650-7400{AA} for 3149 galaxies with median redshift 0.05. The sample is 90% complete to R=15.4. The median slit covering fraction is 24% of the galaxy, apparently sufficient to minimize the effects of aperture bias on the EW(H{alpha}). Forty-nine percent of the galaxies in the survey have one or more emission lines detected at >=2{sigma}. In agreement with previous surveys, the fraction of absorption-line galaxies increases steeply with galaxy luminosity. We use H{beta}, [O III], H{alpha}, and [N II] to discriminate between star-forming galaxies and AGNs. At least 20% of the galaxies are star-forming, at least 17% have AGN-like emission, and 12% have unclassifiable emission. The data for the entire survey will appear in Geller et al. 2002, in preparation.
794. Star formation in the Vela Molecular Ridge
ID:
ivo://CDS.VizieR/J/A+A/617/A63
Title:
Star formation in the Vela Molecular Ridge
Short Name:
J/A+A/617/A63
Date:
21 Oct 2021
Publisher:
CDS
Description:
Most stars born in clusters and recent results suggest that star formation (SF) preferentially occurs in subclusters. Studying the morphology and SF history of young clusters is crucial to understanding early SF. We identify the embedded clusters of young stellar objects (YSOs) down to M stars, in the HII regions RCW33, RCW32 and RCW27 of the Vela Molecular Ridge. Our aim is to characterise their properties, such as morphology and extent of the clusters in the three HII regions, derive stellar ages and the connection of the SF history with the environment. Through public photometric surveys such as Gaia, VPHAS, 2MASS and Spitzer/GLIMPSE, we identify YSOs with IR, Halpha and UV excesses, as signature of circumstellar disks and accretion. In addition, we implement a method to distinguish M dwarfs and giants, by comparing the reddening derived in several optical/IR color-color diagrams assuming suitable theoretical models. Since this diagnostic is sensitive to stellar gravity, the procedure allows us to identify pre-main sequence stars. We find a large population of YSOs showing signatures of circumstellar disks with or without accretion. In addition, with the new technique of M-type star selection, we find a rich population of young M stars with a spatial distribution strongly correlated to the more massive population. We find evidence of three young clusters, with different morphology. In addition, we identify field stars falling in the same region, by securely classifying them as giants and foreground MS stars. We identify the embedded population of YSOs, down to about 0.1M_{sun}_, associated with the HII regions RCW33, RCW32 and RCW27 and the clusters Vela T2, Cr197 and Vela T1, respectively, showing very different morphologies. Our results suggest a decreasing SF rate in Vela T2 and triggered SF in Cr197 and Vela T1.
795. Star Formation Rate in nearby galaxies
ID:
ivo://CDS.VizieR/J/AJ/146/46
Title:
Star Formation Rate in nearby galaxies
Short Name:
J/AJ/146/46
Date:
21 Oct 2021
Publisher:
CDS
Description:
A distance-limited sample of 869 objects from the Updated Nearby Galaxy Catalog is used to characterize the star formation status of the Local Volume population. We present a compiled list of 1217 star formation rate (SFR) estimates for 802 galaxies within 11Mpc, derived from the H{alpha} imaging surveys and the GALEX far-ultraviolet survey. We briefly discuss some basic scaling relations between SFR and luminosity, morphology, HI mass, surface brightness, and the environment of the galaxies. About 3/4 of our sample consist of dwarf galaxies, for which we offer a more refined classification. We note that the specific SFR of nearly all luminous and dwarf galaxies does not exceed the maximum value: log(SFR/L_K_)=-9.4[yr^-1^]. Most spiral and blue dwarf galaxies have enough time to generate their stellar mass during the cosmological time, T_0_, with the observed SFRs. They dispose of a sufficient amount of gas to support their present SFRs over the next T_0_term. We note that only a small fraction of BCD, Im, and Ir galaxies (about 1/20) proceed in a mode of vigorous starburst activity. In general, the star formation history of spiral and blue dwarf galaxies is mainly driven by their internal processes. The present SFRs of E, S0, and dSph galaxies typically have 1/30-1/300 of their former activity.
796. Star formation rate of 4<~z<~8 galaxies
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.
797. Star-forming dwarfs at intermediate-z in VUDS
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^).
798. Star-forming galaxies in near-IR
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.
799. Star-forming low-mass gal. stellar host
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.
800. Star forming regions in HST galaxies sample
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.

Limit your search

more »

more »

more »

more »