4,844 research outputs found
Carbon and oxygen abundances from recombination lines in low-metallicity star-forming galaxies. Implications for chemical evolution
We present deep echelle spectrophotometry of the brightest emission-line
knots of the star-forming galaxies He 2-10, Mkn 1271, NGC 3125, NGC 5408, POX
4, SDSS J1253-0312, Tol 1457-262, Tol 1924-416 and the HII region Hubble V in
the Local Group dwarf irregular galaxy NGC 6822. The data have been taken with
the Very Large Telescope Ultraviolet-Visual Echelle Spectrograph in the
3100-10420 {\AA} range. We determine electron densities and temperatures of the
ionized gas from several emission-line intensity ratios for all the objects. We
derive the ionic abundances of C and/or O from faint pure
recombination lines (RLs) in several of the objects, permitting to derive their
C/H and C/O ratios. We have explored the chemical evolution at low
metallicities analysing the C/O vs. O/H, C/O vs. N/O and C/N vs. O/H relations
for Galactic and extragalactic HII regions and comparing with results for halo
stars and DLAs. We find that HII regions in star-forming dwarf galaxies occupy
a different locus in the C/O vs. O/H diagram than those belonging to the inner
discs of spiral galaxies, indicating their different chemical evolution
histories, and that the bulk of C in the most metal-poor extragalactic HII
regions should have the same origin than in halo stars. The comparison between
the C/O ratios in HII regions and in stars of the Galactic thick and thin discs
seems to give arguments to support the merging scenario for the origin of the
Galactic thick disc. Finally, we find an apparent coupling between C and N
enrichment at the usual metallicities determined for HII regions and that this
coupling breaks in very low-metallicity objects.Comment: 27 pages, 12 figures, Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Quantum tomography via equidistant states
We study the possibility of performing quantum state tomography via
equidistant states. This class of states allows us to propose a non-symmetric
informationally complete POVM based tomographic scheme. The scheme is defined
for odd dimensions and involves an inversion which can be analytically carried
out by Fourier transform
On quadratic Hom-Lie algebras with equivariant twist maps and their relationship with quadratic Lie algebras
Hom-Lie algebras having non-invertible and equivariant twist maps are
studied. Central extensions of Hom-Lie algebras having these properties are
obtained and shown how the same properties are preserved. Conditions are given
so that the produced central extension has an invariant metric with respect to
its Hom-Lie product making its twist map self-adjoint when the original Hom-Lie
algebra has such a metric. This work is focused on algebras with these
properties and we call them quadratic Hom-Lie algebras. It is shown how a
quadratic Hom-Lie algebra gives rise to a quadratic Lie algebra and that the
Lie algebra associated to the given Hom-Lie central extension is a Lie algebra
central extension of it. It is also shown that if the 2-cocycle associated to
the central extension is not a coboundary, there exists a non-abelian and
non-associative algebra, the commutator of whose product is precisely the
Hom-Lie product of the Hom-Lie central extension. Moreover, the algebra whose
commutator realizes this Hom-Lie product is shown to be simple if the
associated Lie algebra is nilpotent. Non-trivial examples are provided
The cosmic evolution of the spatially-resolved star formation rate and stellar mass of the CALIFA survey
We investigate the cosmic evolution of the absolute and specific star
formation rate (SFR, sSFR) of galaxies as derived from a spatially-resolved
study of the stellar populations in a set of 366 nearby galaxies from the
CALIFA survey. The analysis combines GALEX and SDSS images with the 4000 break,
H_beta, and [MgFe] indices measured from the datacubes, to constrain parametric
models for the SFH, which are then used to study the cosmic evolution of the
star formation rate density (SFRD), the sSFR, the main sequence of star
formation (MSSF), and the stellar mass density (SMD). A delayed-tau model,
provides the best results, in good agreement with those obtained from
cosmological surveys. Our main results from this model are: a) The time since
the onset of the star formation is larger in the inner regions than in the
outer ones, while tau is similar or smaller in the inner than in the outer
regions. b) The sSFR declines rapidly as the Universe evolves, and faster for
early than for late type galaxies, and for the inner than for the outer regions
of galaxies. c) SFRD and SMD agree well with results from cosmological surveys.
At z< 0.5, most star formation takes place in the outer regions of late spiral
galaxies, while at z>2 the inner regions of the progenitors of the current E
and S0 are the major contributors to SFRD. d) The inner regions of galaxies are
the major contributor to SMD at z> 0.5, growing their mass faster than the
outer regions, with a lookback time at 50% SMD of 9 and 6 Gyr for the inner and
outer regions. e) The MSSF follows a power-law at high redshift, with the slope
evolving with time, but always being sub-linear. f) In agreement with galaxy
surveys at different redshifts, the average SFH of CALIFA galaxies indicates
that galaxies grow their mass mainly in a mode that is well represented by a
delayed-tau model, with the peak at z~2 and an e-folding time of 3.9 Gyr.Comment: 23 pages, 16 figures, 6 tables, accepted for publication in Astronomy
& Astrophysics. *Abridged abstract
Analysis of Silage Fermentation Characteristics Using Transflectance Measurements by Near Infrared Spectroscopy
The fermentation end products as lactic acid, volatile fatty acids and ammonia-nitrogen, are important indicators of the efficiency of silage fermentation and are closely related to nutritive value of them (Jaster, 1995). Drying is problematic in the case of silage as many fermentation products are volatile and may get lost during the drying process. This may be a reason why NIR technology is being little used for the evaluation of silage fermentation characteristics. The feasibility of using near infrared transflectance spectroscopy to evaluate the content in fermentation end products of grass and maize fresh silage was investigated in this study
The spatially resolved star formation history of CALIFA galaxies: Cosmic time scales
This paper presents the mass assembly time scales of nearby galaxies observed
by CALIFA at the 3.5m telescope in Calar Alto. We apply the fossil record
method of the stellar populations to the complete sample of the 3rd CALIFA data
release, with a total of 661 galaxies, covering stellar masses from 10
to 10 M and a wide range of Hubble types. We apply spectral
synthesis techniques to the datacubes and process the results to produce the
mass growth time scales and mass weighted ages, from which we obtain temporal
and spatially resolved information in seven bins of galaxy morphology and six
bins of stellar mass (M) and stellar mass surface density
(). We use three different tracers of the spatially resolved
star formation history (mass assembly curves, ratio of half mass to half light
radii, and mass-weighted age gradients) to test if galaxies grow inside-out,
and its dependence with galaxy stellar mass, , and morphology.
Our main results are as follows: (a) The innermost regions of galaxies assemble
their mass at an earlier time than regions located in the outer parts; this
happens at any given M, , or Hubble type, including
the lowest mass systems. (b) Galaxies present a significant diversity in their
characteristic formation epochs for lower-mass systems. This diversity shows a
strong dependence of the mass assembly time scales on and
Hubble type in the lower-mass range (10 to 10), but a very
mild dependence in higher-mass bins. (c) All galaxies show negative
log age gradients in the inner 1 HLR. The profile
flattens with increasing values of . There is no significant
dependence on M within a particular bin, except for
the lowest bin, where the gradients becomes steeper.Comment: 15 pages, 13 figures, 3 tables, accepted for publication in Astronomy
& Astrophysics. *Abridged abstract
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