277 research outputs found
Specific SFR profiles in nearby spiral galaxies: quantifying the inside-out formation of disks
We present specific Star Formation Rate (sSFR) radial profiles for a sample
of 161 relatively face-on spiral galaxies from the GALEX Atlas of Nearby
Galaxies. The sSFR profiles are derived from GALEX & 2MASS (FUV-K) color
profiles after a proper SFR calibration of the UV luminosity and K-band
mass-to-light ratio are adopted. The (FUV-K) profiles were first corrected for
foreground Galactic extinction and later for internal extinction using the
ratio of the total-infrared (TIR) to FUV emission. For those objects where
TIR-to-FUV-ratio radial profiles were not available, the (FUV-NUV) color
profiles as a measure of the UV slope. The sSFR radial gradients derived from
these profiles allow us to quantify the inside-out scenario for the growth of
spiral disks for the first time in the local Universe.
We find a large dispersion in the slope of the sSFR profiles with a slightly
positive mean value, which implies a moderate inside-out disk formation. There
is also a strong dependency of the value of this slope on the luminosity and
size of the disks, with large systems showing a uniform, slightly positive
slope in almost all cases and low-luminosity small disks showing a large
dispersion with both positive and negative large values. While a majority of
the galaxies can be interpreted as forming stars gradually either from inside
out or from outside in, a few disks require episodes of enhanced recent growth
with scale lengths of the SFR (or gas infall) being significantly larger at
present than in the past. We do not find any clear dependence of the sSFR
gradient on the environment (local galaxy density or presence of close
neighbors).Comment: 48 pages, 7 figures, accepted for publication in ApJ. For a version
with complete table 2 and all panels included in figures 1 and 3 see
http://t-rex.fis.ucm.es/repositorio/preprints/sSFRprofiles.ps.g
Recommended from our members
Cool dust heating and temperature mixing in nearby star-forming galaxies
Physical conditions of the interstellar medium in galaxies are closely linked
to the ambient radiation field and the heating of dust grains. In order to
characterize dust properties in galaxies over a wide range of physical
conditions, we present here the radial surface brightness profiles of the
entire sample of 61 galaxies from Key Insights into Nearby Galaxies:
Far-Infrared Survey with Herschel (KINGFISH). The main goal of our work is the
characterization of the grain emissivities, dust temperatures, and interstellar
radiation fields responsible for heating the dust. After fitting the dust and
stellar radial profiles with exponential functions, we fit the far-infrared
spectral energy distribution (SED) in each annular region with
single-temperature modified black bodies using both variable (MBBV) and fixed
(MBBF) emissivity indices beta, as well as with physically motivated dust
models. Results show that while most SED parameters decrease with radius, the
emissivity index beta also decreases with radius in some galaxies, but in
others is increasing, or rising in the inner regions and falling in the outer
ones. Despite the fixed grain emissivity (average beta~ 2.1) of the
physically-motivated models, they are well able to accommodate flat spectral
slopes with beta<= 1. We find that flatter slopes (beta<= 1.5) are associated
with cooler temperatures, contrary to what would be expected from the usual
Tdust-beta degeneracy. This trend is related to variations in Umin since beta
and Umin are very closely linked over the entire range in Umin sampled by the
KINGFISH galaxies: low Umin is associated with flat beta<=1. Both these results
strongly suggest that the low apparent \beta values (flat slopes) in MBBV fits
are caused by temperature mixing along the line-of-sight, rather than by
intrinsic variations in grain properties. Abstract truncated for arXiv.Comment: 28 pages, 20 figures, accepted for publication in A&
Supporting Spartina: Interdisciplinary Perspective Shows Spartina As A Distinct Solid Genus
In 2014, a DNA-based phylogenetic study confirming the paraphyly of the grass subtribe Sporobolinae proposed the creation of a large monophyletic genus Sporobolus, including (among others) species previously included in the genera Spartina, Calamovilfa, and Sporobolus. Spartina species have contributed substantially (and continue contributing) to our knowledge in multiple disciplines, including ecology, evolutionary biology, molecular biology, biogeography, experimental ecology, biological invasions, environmental management, restoration ecology, history, economics, and sociology. There is no rationale so compelling to subsume the name Spartina as a subgenus that could rival the striking, global iconic history and use of the name Spartina for over 200 yr. We do not agree with the subjective arguments underlying the proposal to change Spartina to Sporobolus. We understand the importance of both the objective phylogenetic insights and of the subjective formalized nomenclature and hope that by opening this debate we will encourage positive feedback that will strengthen taxonomic decisions with an interdisciplinary perspective. We consider that the strongly distinct, monophyletic clade Spartina should simply and efficiently be treated as the genus Spartina
The ASAS-SN Bright Supernova Catalog - II. 2015
This manuscript presents information for all supernovae discovered by the All-Sky Automated Survey for SuperNovae (ASAS-SN) during 2015, its second full year of operations. The same information is presented for bright (), spectroscopically confirmed supernovae discovered by other sources in 2015. As with the first ASAS-SN bright supernova catalog, we also present redshifts and near-UV through IR magnitudes for all supernova host galaxies in both samples. Combined with our previous catalog, this work comprises a complete catalog of 455 supernovae from multiple professional and amateur sources, allowing for population studies that were previously impossible. This is the second of a series of yearly papers on bright supernovae and their hosts from the ASAS-SN team
GLOBULAR CLUSTER POPULATIONS: RESULTS INCLUDING S(4)G LATE-TYPE GALAXIES
Using 3.6 and 4.5 mu m images of 73 late-type, edge-on galaxies from the S(4)G survey, we compare the richness of the globular cluster populations of these galaxies to those of early-type galaxies that we measured previously. In general, the galaxies presented here fill in the distribution for galaxies with lower stellar mass, M-*, specifically log(M-*/M-circle dot) < 10, overlap the results for early-type galaxies of similar masses, and, by doing so, strengthen the case for a dependence of the number of globular clusters per 10(9)M(circle dot) of galaxy stellar mass, T-N, on M-*. For 8.5 < log(M-*/M-circle dot) < 10.5 we find the relationship can be satisfactorily described as T-N = (M-*/10(6.7))(-0.56) M-* is expressed in solar masses. The functional form of the relationship is only weakly constrained, and extrapolation outside this range is not advised. Our late-type galaxies, in contrast to our early types, do not show the tendency for low-mass galaxies to split into two T-N families. Using these results and a galaxy stellar mass function from the literature, we calculate that, in a volume-limited, local universe sample, clusters are most likely to be found around fairly massive galaxies (M-* similar to 10(10.8)M(circle dot)) and present a fitting function for the volume number density of clusters as a function of parent-galaxy stellar mass. We find no correlation between T-N and large-scale environment, but we do find a tendency for galaxies of fixed M-* to have larger T-N if they have converted a larger proportion of their baryons into stars.</p
Interactions between selected bile salts and Triton X-100 or sodium lauryl ether sulfate
<p>Abstract</p> <p>Background</p> <p>In order to develop colloidal drug carriers with desired properties, it is important to determine physico-chemical characteristics of these systems. Bile salt mixed micelles are extensively studied as novel drug delivery systems. The objective of the present investigation is to develop and characterize mixed micelles of nonionic (Triton X-100) or anionic (sodium lauryl ether sulfate) surfactant having oxyethylene groups in the polar head and following bile salts: cholate, deoxycholate and 7-oxodeoxycholate.</p> <p>Results</p> <p>The micellization behaviour of binary anionic-nonionic and anionic-anionic surfactant mixtures was investigated by conductivity and surface tension measurements. The results of the study have been analyzed using Clint's, Rubingh's, and Motomura's theories for mixed binary systems. The negative values of the interaction parameter indicate synergism between micelle building units. It was noticed that Triton X-100 and sodium lauryl ether sulfate generate the weakest synergistic interactions with sodium deoxycholate, while 7-oxodeoxycholate creates the strongest attractive interaction with investigated co-surfactants.</p> <p>Conclusion</p> <p>It was concluded that increased synergistic interactions can be attributed to the larger number of hydrophilic groups at α side of the bile salts. Additionally, 7-oxo group of 7-oxodeoxycholate enhance attractive interactions with selected co-surfactants more than 7-hydroxyl group of sodium cholate.</p
Radial variation of attenuation and star formation in the largest late-type disks observed with GALEX
For a sample of 43 nearby, late-type galaxies, we have investigated the
radial variation of both the current star formation rate and the dust-induced
UV light attenuation. To do this we have cross-correlated IRAS images and GALEX
observations for each of these galaxies, and compiled observations of the gas
(CO and HI) and metal-abundance gradients found in the literature. We find that
attenuation correlates with metallicity. We then use the UV profiles, corrected
for attenuation, to study several variants of the Schmidt law and conclude that
our results are compatible with a simple law similar to the one of Kennicutt
but extending smoothly to lower surface densities, but with considerable
scatter. We do not detect an abrupt break in the UV light at the threshold
radius derived from H-alpha data (at which the H-alpha profile shows a break
and beyond which only a few HII regions are usually found). We interpret the
H-alpha sudden break not as a change in the star formation regime (as often
suggested) but as the vanishingly small number of ionizing stars corresponding
to low levels of star formation.Comment: 28 pages, 9 figures, accepted for the GALEX special issue of ApJS.
For a version with high-resolution figures, see
http://www.oamp.fr/boissier/preprint/preprint.htm
Reconstructing the Stellar Mass Distributions of Galaxies using S4G TRAC 3.6 and 4.5 (gamma)m Images I. Correcting for Contamination by Polycyclic Aromatic Hydrocarbons, Hot Dust and Intermediate-age Stars
The Large Early Galaxy Astrophysics Census (LEGA-C) Data Release 2:Dynamical and Stellar Population Properties of z lesssim 1 Galaxies in the COSMOS Field
We present the second data release of the Large Early Galaxy Astrophysics Census (LEGA-C), an ESO 130-night public spectroscopic survey conducted with VIMOS on the Very Large Telescope. We release 1988 spectra with typical continuum S / N ~= 20 /Angstrom of galaxies at 0.6 ~< z ~< 1.0, each observed for ~20 hours and fully reduced with a custom-built pipeline. We also release a catalog with spectroscopic redshifts, emission line fluxes, Lick/IDS indices, and observed stellar and gas velocity dispersions that are spatially integrated quantities including both rotational motions and genuine dispersion. To illustrate the new parameter space in the intermediate redshift regime probed by LEGA-C we explore relationships between dynamical and stellar population properties. The star-forming galaxies typically have observed stellar velocity dispersions of ~150 km/s and strong Hdelta absorption (Hd_A ~ 5 Angstrom), while passive galaxies have higher observed stellar velocity dispersions ~200 km/s and weak Hdelta absortion (Hd_A ~ 0 Angstrom). Strong [O III]5007 / Hbeta ratios tend to occur mostly for galaxies with weak Hd_A or galaxies with higher observed velocity dispersion. Beyond these broad trends, we find a large diversity of possible combinations of rest-frame colors, absorption line strengths and emission line detections, illustrating the utility of spectroscopic measurements to more accurately understand galaxy evolution. By making the spectra and value-added catalogs publicly available we encourage the community to take advantage of this very substantial investment in telescope time provided by ESO
- …