772 research outputs found
The Role of Stellar Feedback and Dark Matter in the Evolution of Dwarf Galaxies
Supernova and multiple supernova events regulate several structural
properties of dwarf galaxies. In particular, they govern the metal enrichment
and the energy budget of the ISM; they might induce partial (blowout) or total
(blowaway) gas removal from the galaxy; the morphology of the galactic gaseous
body. Significant amounts of dark matter may play an equally important role:
the dark matter gravitational potential tends to concentrate baryons towards
the center, thus enhancing both the star formation rate and metal production.
Also, the dynamical properties of the ISM, and the occurrence of a blowout or
blowaway are shown to be determined by the dark matter content. We present
detailed analytical/numerical models describing the evolution of dwarf
Irregular galaxies including the above and other effects. The main results are:
(i) dwarfs with total masses M\simlt 5\times 10^6 M_\odot are blown away;
those with gas masses up to lose mass in an outflow; (ii)
metallicities are found to correlate tightly with dark matter content and are
consistent with a range of dark-to-visible mass ratios with
about 65% of the dwarfs in the sample having ; (iii) we
predict a lower limit to the oxygen abundance in dIs of ; (iv) outflows are not particularly important for the metallicity
evolution of dwarf galaxies and certainly less than star formation for gas
consumption; however, dwarfs with gas masses few are
shown to be the major pollutants of the IGM; (v) the ISM HI velocity dispersion
correlates with metallicity and, indepentently of dark matter, scales as
. (Abridged)Comment: 56 pages, aasms4.sty, LaTeX, 12 figures. MNRAS, submitte
The Effects of Age on Red Giant Metallicities Derived from the Near-Infrared Ca II Triplet
We have obtained spectra with resolution 2.5 Angstroms in the region
7500-9500 Angstroms for 116 red giants in 5 Galactic globular clusters and 6
old open clusters (5 with published metallicities, and one previously
unmeasured). The signal-to-noise ranges from 20 to 85. We measure the
equivalent widths of the infrared Ca II triplet absorption lines in each stars
and compare to cluster metallicities taken from the literature. With globular
cluster abundances on the Carretta & Gratton scale, and open cluster abundances
taken from the compilation of Friel and collaborators, we find a linear
relation between [Fe/H] and Ca II line strength spanning the range -2 < [Fe/H]
< -0.2 and ages from 2.5 - 13 Gyr. No evidence for an age effect on the
metallicity calibration is observed. Using this calibration, we find the
metallicity of the old open cluster Trumpler 5 to be [Fe/H] = -0.56 +/-0.11.
Considering the 10 clusters of known metallicity shifted to a common distance
and reddening, we find that the additional metallicity error introduced by the
variation of horizontal branch/red clump magnitude with metallicity and age is
of order +/-0.05 dex, which can be neglected in comparison to the intrinsic
scatter in our method. The results are discussed in the context of abundance
determinations for red giants in Local Group galaxies.Comment: Accepted by MNRAS; 21 pages in LaTeX MNRAS style, 6 tables, 6 figure
The mass content of the Sculptor dwarf spheroidal galaxy
We present a new determination of the mass content of the Sculptor dwarf
spheroidal galaxy, based on a novel approach which takes into account the two
distinct stellar populations present in this galaxy. This method helps to
partially break the well-known mass-anisotropy degeneracy present in the
modelling of pressure-supported stellar systems.Comment: 6 pages, 3 figures. To appear in the proceedings of IAU Symposium 254
"The Galaxy disk in a cosmological context", Copenhagen, June 200
M13 multiple stellar populations seen with the eyes of Stromgren photometry
We present a photometric study of M13 multiple stellar populations over a wide field of view, covering approximately 6.5 half-light radii, using archival Isaac Newton Telescope observations to build an accurate multiband Strömgren catalogue. The use of the Strömgren index cy permits us to separate the multiple populations of M13 on the basis of their position on the red giant branch. The comparison with medium and high resolution spectroscopic analysis confirms the robustness of our selection criterion. To determine the radial distribution of stars in M13, we complemented our data set with Hubble Space Telescope observations of the cluster core, to compensate for the effect of incompleteness affecting the most crowded regions. From the analysis of the radial distributions, we do not find any significant evidence of spatial segregation. Some residuals may be present in the external regions where we observe only a small number of stars. This finding is compatible with the short dynamical time-scale of M13 and represents, to date, one of the few examples of fully spatially mixed multiple populations in a massive globular cluster
Stellar Populations in the Phoenix Dwarf (dIrr/dSph) Galaxy as Observed by HST/WFPC2
We present HST/WFPC2 photometry of the central regions of the Phoenix dwarf.
Accurate photometry allows us to: 1) confirm the existence of the horizontal
branch previously detected by ground-based observations, and use it to
determine a distance to Phoenix, 2) clearly detect the existence of multiple
ages in the stellar population of Phoenix, 3) determine a mean metallicity of
the old red giant branch stars in Phoenix, and suggest that Phoenix has evolved
chemically over its lifetime, 4) extract a rough star formation history for the
central regions which suggests that Phoenix has been forming stars roughly
continuously over its entire lifetime.Comment: Accepted by AJ, 22 pages including 6 figures + 1 figure in JPEG
forma
Astrometry with MCAO: HST-GeMS proper motions in the globular cluster NGC 6681
Aims: for the first time the astrometric capabilities of the Multi-Conjugate
Adaptive Optics (MCAO) facility GeMS with the GSAOI camera on Gemini-South are
tested to quantify the accuracy in determining stellar proper motions in the
Galactic globular cluster NGC 6681. Methods: proper motions from HST/ACS for a
sample of its stars are already available, and this allows us to construct a
distortion-free reference at the epoch of GeMS observations that is used to
measure and correct the temporally changing distortions for each GeMS exposure.
In this way, we are able to compare the corrected GeMS images with a
first-epoch of HST/ACS images to recover the relative proper motion of the
Sagittarius dwarf spheroidal galaxy with respect to NGC 6681. Results: we find
this to be (\mu_{\alpha}cos\delta, \mu_{\delta}) = (4.09,-3.41) mas/yr, which
matches previous HST/ACS measurements with a very good accuracy of 0.03 mas/yr
and with a comparable precision (r.m.s of 0.43 mas/yr). Conclusions: this study
successfully demonstrates that high-quality proper motions can be measured for
quite large fields of view (85 arcsec X 85 arcsec) with MCAO-assisted,
ground-based cameras and provides a first, successful test of the performances
of GeMS on multi-epoch data.Comment: 5 pages, 4 figures. Accepted for publication by A&A Letter
On Some Lie Bialgebra Structures on Polynomial Algebras and their Quantization
We study classical twists of Lie bialgebra structures on the polynomial
current algebra , where is a simple complex
finite-dimensional Lie algebra. We focus on the structures induced by the
so-called quasi-trigonometric solutions of the classical Yang-Baxter equation.
It turns out that quasi-trigonometric -matrices fall into classes labelled
by the vertices of the extended Dynkin diagram of . We give
complete classification of quasi-trigonometric -matrices belonging to
multiplicity free simple roots (which have coefficient 1 in the decomposition
of the maximal root). We quantize solutions corresponding to the first root of
.Comment: 41 pages, LATE
The chemical connection between Damped Lyman-alpha systems and Local Group dwarf galaxies
Abundances of the volatile elements S and Zn have now been measured in around 80 individual stars in the Sculptor dwarf spheroidal galaxy, covering the metallicity range 2.
The ACS LCID project VII: the blue stragglers population in the isolated dSph galaxies Cetus and Tucana
We present the first investigation of the Blue Straggler star (BSS)
population in two isolated dwarf spheroidal galaxies of the Local Group, Cetus
and Tucana. Deep HST/ACS photometry allowed us to identify samples of 940 and
1214 candidates, respectively. The analysis of the star formation histories of
the two galaxies suggests that both host a population of BSSs. Specifically, if
the BSS candidates are interpreted as young main sequence stars, they do not
conform to their galaxy's age-metallicity relationship. The analysis of the
luminosity function and the radial distributions support this conclusion, and
suggest a non-collisional mechanism for the BSS formation, from the evolution
of primordial binaries. This scenario is also supported by the results of new
dynamical simulations presented here. Both galaxies coincide with the
relationship between the BSS frequency and the absolute visual magnitude Mv
found by Momany et al (2007). If this relationship is confirmed by larger
sample, then it could be a valuable tool to discriminate between the presence
of BSSs and galaxies hosting truly young populations.Comment: Accepted for publication on ApJ. 15 pages, 3 tables, 13 figures. A
version with high resolution figure can be downloaded from
http://rialto.ll.iac.es/proyecto/LCID/?p=publication
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