78 research outputs found
The gas metallicity gradient and the star formation activity of disc galaxies
We study oxygen abundance profiles of the gaseous disc components in
simulated galaxies in a hierarchical universe. We analyse the disc metallicity
gradients in relation to the stellar masses and star formation rates of the
simulated galaxies. We find a trend for galaxies with low stellar masses to
have steeper metallicity gradients than galaxies with high stellar masses at z
~0. We also detect that the gas-phase metallicity slopes and the specific star
formation rate (sSFR) of our simulated disc galaxies are consistent with
recently reported observations at z ~0. Simulated galaxies with high stellar
masses reproduce the observed relationship at all analysed redshifts and have
an increasing contribution of discs with positive metallicity slopes with
increasing redshift. Simulated galaxies with low stellar masses a have larger
fraction of negative metallicity gradients with increasing redshift. Simulated
galaxies with positive or very negative metallicity slopes exhibit disturbed
morphologies and/or have a close neighbour. We analyse the evolution of the
slope of the oxygen profile and sSFR for a gas-rich galaxy-galaxy encounter,
finding that this kind of events could generate either positive and negative
gas-phase oxygen profiles depending on their state of evolution. Our results
support claims that the determination of reliable metallicity gradients as a
function of redshift is a key piece of information to understand galaxy
formation and set constrains on the subgrid physics.Comment: 12 pages, 8 figures, accepted MNRA
Is There a Fundamental Line for Disk Galaxies?
We show that there are strong local correlations between metallicity, surface
brightness, and dynamical mass-to-light ratio within M33, analogous to the
fundamental line of dwarf galaxies identified by Prada & Burkert (2002). Using
near-infrared imaging from 2MASS, the published rotation curve of M33, and
literature measurements of the metallicities of HII regions and supergiant
stars, we demonstrate that these correlations hold for points at radial
distances between 140 pc and 6.2 kpc from the center of the galaxy. At a given
metallicity or surface brightness, M33 has a mass-to-light ratio approximately
four times as large as the Local Group dwarf galaxies; other than this constant
offset, we see broad agreement between the M33 and dwarf galaxy data. We use
analytical arguments to show that at least two of the three fundamental line
correlations are basic properties of disk galaxies that can be derived from
very general assumptions. We investigate the effect of supernova feedback on
the fundamental line with numerical models and conclude that while feedback
clearly controls the scatter in the fundamental line, it is not needed to
create the fundamental line itself, in agreement with our analytical
calculations. We also compare the M33 data with measurements of a simulated
disk galaxy, finding that the simulation reproduces the trends in the data
correctly and matches the fundamental line, although the metallicity of the
simulated galaxy is too high, and the surface brightness is lower than that of
M33.Comment: 14 pages, 14 figures (5 in color). Accepted for publication in Ap
J-PLUS : the Javalambre Photometric Local Universe Survey
The Javalambre Photometric Local Universe Survey (J-PLUS ) is an ongoing 12-band photometric optical survey, observing thousands of square degrees of the Northern Hemisphere from the dedicated JAST/T80 telescope at the Observatorio AstrofĂsico de Javalambre (OAJ). The T80Cam is a camera with a field of view of 2 deg2 mounted on a telescope with a diameter of 83 cm, and is equipped with a unique system of filters spanning the entire optical range (3500â10â000 Ă
). This filter system is a combination of broad-, medium-, and narrow-band filters, optimally designed to extract the rest-frame spectral features (the 3700â4000 Ă
Balmer break region, HÎŽ, Ca H+K, the G band, and the Mg b and Ca triplets) that are key to characterizing stellar types and delivering a low-resolution photospectrum for each pixel of the observed sky. With a typical depth of AB âŒ21.25 mag per band, this filter set thus allows for an unbiased and accurate characterization of the stellar population in our Galaxy, it provides an unprecedented 2D photospectral information for all resolved galaxies in the local Universe, as well as accurate photo-z estimates (at the ÎŽâz/(1â
+â
z)âŒ0.005â0.03 precision level) for moderately bright (up to rââŒâ20 mag) extragalactic sources. While some narrow-band filters are designed for the study of particular emission features ([OII]/λ3727, Hα/λ6563) up to zâ< â0.017, they also provide well-defined windows for the analysis of other emission lines at higher redshifts. As a result, J-PLUS has the potential to contribute to a wide range of fields in Astrophysics, both in the nearby Universe (Milky Way structure, globular clusters, 2D IFU-like studies, stellar populations of nearby and moderate-redshift galaxies, clusters of galaxies) and at high redshifts (emission-line galaxies at zâââ0.77,â2.2, and 4.4, quasi-stellar objects, etc.). With this paper, we release the first âŒ1000 deg2 of J-PLUS data, containing about 4.3 million stars and 3.0 million galaxies at râ< â21 mag. With a goal of 8500 deg2 for the total J-PLUS footprint, these numbers are expected to rise to about 35 million stars and 24 million galaxies by the end of the survey
An empirical calibration of sulphur abundance in ionised gaseous nebulae
We have derived an empirical calibration of the abundance of S/H as a
function of the S23 parameter, defined using the bright sulphur lines of [SII]
and SIII]. Contrary to what is the case for the widely used O parameter,
the calibration remains single valued up to the abundance values observed in
the disk HII regions. The calibration is based on a large sample of nebulae for
which direct determinations of electron temperatures exist and the sulphur
chemical abundances can be directly derived. ICFs, as derived from the [SIV]
10.52 emission line (ISO observations), are shown to be well reproduced
by Barker's formula for a value of alpha = 2.5. At any rate, only about 30% of
the objects in the sample require ICFs larger than 1.2. The use of the proposed
calibration opens the possibility of performing abundance analysis with red to
IR spectroscopic data using S/H as a metallicity tracer.Comment: 9 pages, 5 figures. Accepted for publication by Astronomy &
Astrophysic
Optical and mid-infrared neon abundance determinations in star-forming regions
We employed observational spectroscopic data of star-forming regions compiled
from the literature and photoionization models to analyse the neon ionic
abundances obtained using both optical and mid-infrared emission-lines.
Comparing Ne++/H+ ionic abundances from distinct methods, we found that, in
average, the abundances obtained via IR emission-lines are higher than those
obtained via optical lines by a factor of 4. Photoionization models with
abundance variations along the radius of the hypothetical nebula provide a
possible explanation for a large part of the difference between ionic
abundances via optical and infrared emission-lines. Ionization Correction
Factor (ICF) for the neon is obtained from direct determinations of ionic
fractions using infrared emission-lines. A constant Ne/O ratio (logNe/O \approx
-0.70) for a large range of metallicity, independently of the ICF used to
compute the neon total abundance is derived.Comment: 17 pages, 14 figures, accepted by MNRA
New Red-Emitting Chloride-Sensitive Fluorescent Protein with Biological Uses
This work was financially supported by CTQ2017-85685-R, CTQ2017-85454-C2-1-P, and CTQ2017-86125-P (MICIU/AEI/ERDF). J.M.P. and J.D.V. thank UEQ for funding. J.V.P. is supported by an FPU fellowship (FPU17/04749). D.A. was supported by the Italian Cystic Fibrosis Foundation (grant FFC#3/2019) and by Fondazione Cassa Rurale Trento Rovereto (ref 2018.256). The authors acknowledge the Universidad of Granada (Spain) cell culture and microscopy central facilities (CIC-UGR).A new chloride-sensitive red fluorescent protein
derived from Entacmaea quadricolor is described. We found that
mBeRFP exhibited moderate sensitivity to chloride and, via sitedirected
mutagenesis (S94V and R205Y), we increased the
chloride affinity by more than an order of magnitude (kd = 106
± 6 mM) at physiological pH. In addition, cisâtrans isomerization
of the chromophore produces a dual emission band with different
chloride sensitivities, which allowed us to develop a ratiometric
methodology to measure intracellular chloride concentrations.MICIU/AEI/ERDF CTQ2017-85685-R
CTQ2017-85454-C2-1-P
CTQ2017-86125-PUEQSpanish Government FPU17/04749Ministry of Health, ItalyItalian Cystic Fibrosis Research Foundation 3/2019Fondazione Cassa Rurale Trento Rovereto 2018.25
Spectrophotometric Observations of Blue Compact Dwarf Galaxies: Mrk 370
We present results from a detailed spectrophotometric analysis of the blue
compact dwarf galaxy (BCD) Mrk 370, based on deep UBVRI broad-band and Halpha
narrow-band observations, and long-slit and two-dimensional spectroscopy of its
brightest knots. The spectroscopic data are used to derive the internal
extinction, and to compute metallicities, electronic density and temperature in
the knots. By subtracting the contribution of the underlying older stellar
population, modeled by an exponential function, removing the contribution from
emission lines, and correcting for extinction, we can measure the true colors
of the young star-forming knots. We show that the colors obtained this way
differ significantly from those derived without the above corrections, and lead
to different estimates of the ages and star-forming history of the knots. Using
predictions of evolutionary synthesis models, we estimate the ages of both the
starburst regions and the underlying stellar component. We found that we can
reproduce the colors of all the knots with an instantaneous burst of star
formation and the Salpeter initial mass function with an upper mass limit of
100 solar masses. The resulting ages range between 3 and 6 Myrs. The colors of
the low surface brightness component are consistent with ages larger than 5
Gyr. The kinematic results suggest ordered motion around the major axis of the
galaxy.Comment: 26 pages with 14 figures; accepted for publication in Ap
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