- ID:
- ivo://CDS.VizieR/J/A+A/625/A114
- Title:
- Star-forming galaxies over 0.35<z<2.25
- Short Name:
- J/A+A/625/A114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To better constrain the physical mechanisms driving star formation, we present the first systematic study of the radio continuum size evolution of star-forming galaxies (SFGs) over the redshift range 0.35<z<2.25. We use the VLA COSMOS 3GHz map (noise rms=2.3Jy/beam, {theta}_beam_=0.75arcsec) to construct a mass-complete sample of 3184 radio-selected SFGs that reside on and above the main-sequence (MS) of SFGs. We constrain the overall extent of star formation activity in galaxies by applying a 2D-Gaussian model to their radio continuum emission. Extensive Monte Carlo simulations are used to validate the robustness of our measurements and characterize the selection function. We find no clear dependence between the radio size and stellar mass, M*, of SFGs with 10.5<log(M*/M_{sun}_)<11.5. Our analysis suggests that MS galaxies are preferentially extended, while SFGs above the MS are always compact. The median effective radius of SFGs on (above) the MS of Reff=1.5+/-0.2(1.0+/-0.2)kpc remains nearly constant with cosmic time; a parametrization of the form Reff{prop.to}(1+z)^alpha^ yields a shallow slope of only alpha=-0.26+/-0.08(0.12+/-0.14) for SFGs on (above) the MS. The size of the stellar component of galaxies is larger than that inferred from radio continuum emission by a factor ~2(1.3) at z=0.5(2), indicating star formation is enhanced at small radii. The galactic-averaged star formation rate surface density ({SIGMA}_SFR_) scales with the distance to the MS, except for a fraction of MS galaxies (~10%) that harbor starburst-like {SIGMA}_SFR_. These "hidden" starbursts might have experienced a compaction phase due to disk instability and/or merger-driven burst of star formation, which may or may not significantly offset a galaxy from the MS. We thus propose to use {SIGMA}_SFR_ and distance to the MS in conjunction to better identify the galaxy population undergoing a starbursting phase.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/692/556
- Title:
- Star forming galaxy templates
- Short Name:
- J/ApJ/692/556
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We show that measures of star formation rates (SFRs) for infrared galaxies using either single-band 24um or extinction-corrected Pa{alpha} luminosities are consistent in the total infrared luminosity =L(IR)~10^10^L_{{sun}}_ range. As a part of this work, we constructed spectral energy distribution templates for eleven luminous and ultraluminous purely star forming infrared galaxies and over the spectral range 0.4um to 30cm. We use these templates and the SINGS data to construct average templates from 5um to 30cm for infrared galaxies with L(IR)=5x10^9^ to 10^13^L_{{sun}}_.
- ID:
- ivo://CDS.VizieR/J/AJ/125/1696
- Title:
- Star-forming knots in NGC 3395/3396
- Short Name:
- J/AJ/125/1696
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained ultraviolet and visible wavelength images for the central regions of the interacting galaxies NGC 3395 and NGC 3396, using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. The images show many isolated sources of ultraviolet emission produced by young star-forming regions (knots). The FWHM of most of the knots in both galaxies is <=20pc. Far-UV flux distributions for the complete sample of knots can be fitted with a power law with exponent {alpha}=-1.20+/-0.35 for NGC 3395 and a power law with exponent {alpha}=-0.69+/-0.21 for NGC 3396. Comparison with models from Leitherer et al. indicates that the ages of most of the knots are <=80Myr. Reddening of the knots ranges from E(B-V)=0.0 to E(B-V)=0.3mag, indicating variable amounts of dust in these regions. Almost all the knots have masses less than 10^6^M_{sun}_. Many of the knots are probably bound and at least six knots are good proto-globular cluster candidates. There are no significant differences in the fluxes, sizes, and ages of the knots in the two galaxies. The average mass of the knots in NGC 3395 is an order of magnitude less than the average mass of the knots in NGC 3396. There is no obvious correlation between the age of a knot and its position the galaxy.
- ID:
- ivo://CDS.VizieR/J/AJ/127/1360
- Title:
- Star-forming knots in NGC 4194 center
- Short Name:
- J/AJ/127/1360
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report high-resolution ultraviolet and visible-wavelength imaging of the blue compact galaxy NGC 4194 (the Medusa) using the Hubble Space Telescope. A complete sample of 38 UV-bright knots is identified.
- 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/AZh/88/342
- Title:
- Star-forming regions in NGC 5585 and IC 1525
- Short Name:
- J/AZh/88/342
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use UBVRI CCD photometry to study star-forming regions (SFRs) in the galaxies NGC 5585 and IC 1525. The observations were acquired with the 1.5-m telescope of the Mt. Maidanak Observatory of the Astronomical Institute of the Uzbek Academy of Sciences (Uzbekistan), with seeing of 0.8"-1.8". We identified 47 SFRs in NGC 5585 and 16 SFRs in IC 1525.
- ID:
- ivo://CDS.VizieR/J/A+A/521/A8
- Title:
- Star-forming regions in NGC 2903 bar
- Short Name:
- J/A+A/521/A8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The nearby barred spiral NGC 2903 has an active starburst at its centre and HII regions distributed along its bar. We analyse the star-formation properties in the bar region of NGC 2903 and study its links to the typical bar morphological features. We combine space and ground-based data from the far-ultraviolet to the sub-millimeter spectral ranges to create a panchromatic view of the NGC 2903 bar. We produce two catalogues: one for the current star-formation regions, as traced by the H{alpha} compact emission, and a second for the ultraviolet (UV) emitting knots, containing positions and luminosities. From them, we obtain ultraviolet colours, star-formation rates, dust attenuation, and H{alpha} EWs, and analyse their spatial distribution. We estimate stellar cluster ages using stellar population synthesis models (Starburst99).
- ID:
- ivo://CDS.VizieR/J/ApJ/730/88
- Title:
- Star-forming regions in NGC 6822 from UV data
- Short Name:
- J/ApJ/730/88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We characterize the star formation in the low-metallicity galaxy NGC 6822 over the past few hundred million years, using GALEX far-UV (FUV, 1344-1786{AA}) and near-UV (NUV, 1771-2831{AA}) imaging, and ground-based H{alpha} imaging. From the GALEX FUV image, we define 77 star-forming (SF) regions with area >860pc^2^, and surface brightness <~26.8 mag (AB) arcsec^-2^, within 0.2{deg} (1.7kpc) of the center of the galaxy. We estimate the extinction by interstellar dust in each SF region from resolved photometry of the hot stars it contains: E(B-V) ranges from the minimum foreground value of 0.22mag up to 0.66+/-0.21mag. The integrated FUV and NUV photometry, compared with stellar population models, yields ages of the SF complexes up to a few hundred Myr, and masses from 2x10^2^M_{sun}_ to 1.5x10^6^M_{sun}_. The derived ages and masses strongly depend on the assumed type of interstellar selective extinction, which we find to vary across the galaxy. The total mass of the FUV-defined SF regions translates into an average star formation rate (SFR) of 1.4x10^-2^M_{sun}_/yr over the past 100Myr, and SFR=1.0x10^-2^M_{sun}_/yr in the most recent 10Myr. The latter is in agreement with the value that we derive from the H{alpha} luminosity, SFR=0.008M_{sun}_/yr. The SFR in the most recent epoch becomes higher if we add the SFR=0.02M_{sun}_/yr inferred from far-IR measurements, which trace star formation still embedded in dust (age <~ a few Myr).
- ID:
- ivo://CDS.VizieR/J/A+A/556/A98
- Title:
- Star-forming rings in NGC5248
- Short Name:
- J/A+A/556/A98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The distribution of gas in the central kiloparsec of a galaxy has a dynamically rapid evolution. Nonaxisymmetries in the gravitational potential of the galactic disk, such as a large scale stellar bar or spiral, can lead to significant radial motion of gaseous material from larger radii to the central region. The large influx of gas and the subsequent star formation keep the central region constantly changing. However, the ability of gas to reach the nucleus proper to fuel an AGN phase is not guaranteed. Gas inflow can be halted at a circumnuclear star forming ring several hundred parsec away. The nearby galaxy NGC5248 is especially interesting in this sense since it is said to host 2 circumnuclear star forming rings at 100pc and 370pc from its quiescent nucleus. Here we present new subarcsecond PdBI+30m CO(2-1) emission line observations of the central region. For the first time the molecular gas distribution at the smallest stellar ring is resolved into a gas ring, consistent with the presence of a quiescent nucleus. However, the molecular gas shows no ring structure at the larger ring. We combine analyses of the gaseous and stellar content in the central kiloparsec of this galaxy to understand the gas distribution and dynamics of this star forming central region. We discuss the probability of two scenarios leading to the current observations, given our full understanding of this system, and discuss whether there are really two circumnuclear star forming rings in this galaxy.
