18 research outputs found
Testing Evolutionary Models of Dwarf Irregular Galaxies through Gas and Stellar Metallicity Determinations in HII Galaxies
Dwarf irregular galaxies are usually low-metallicity objects, and show ongoing or very recent star formation, giving rise to their irregular appearance. Especially HII galaxies, a sub-category of dwarf irregulars showing unusually high star formation activity, are believed to be among the least evolved galaxies in existence today. Therefore, they are very interesting objects for studies of early galaxy evolution and of metallicity enrichment mechanisms. Several groups have developed theoretical evolutionary models of galaxies of this type, describing different possible formation and evolutionary scenarii, and varying factors such as gas infall and outflow, as well as the star formation history, and making predictions about their chemical evolution. One way to evaluate these models is by determining the metallicities of the different components of these galaxies, their gas and stars. We examine a sample of HII galaxies from the Sloan Digital Sky Survey, which possibly contains the largest homogeneous sample of HII galaxy spectra to date. Using very restrictive selection criteria, which guarantee a sample of high quality spectra and avoid "contamination” by spectra of objects of other nature, we defined a sample of ∼ 700 HII galaxies spectra. Through emission line strength calibrations and a detailed stellar population synthesis, we determined the metallicities of both the gas and the stellar content of these galaxies. For HII galaxies up to stellar masses of 5 × 109 M ⊙, we find enrichment mechanisms not to vary with galactic mass, being the same for low- and high-mass galaxies on average. They do seem to present a greater variety at the high-mass end, though, indicating a more complex assembly history. Our results favour galaxy evolutionary models featuring constantly infalling low-metallicity clouds that retain part of the galactic winds. Above 5 × 109 M ⊙ stellar mass, the retention of high metallicity gas by the galaxies' gravitational potential dominates. I would like to thank the Fundação de Amparo à Pesquisa do Estado do São Paulo (FAPESP) for financial suppor
Sub-Galactic Clumps at High Redshift: A Fragmentation Origin?
We investigate the origin of the clumpy structures observed at high redshift,
like the chain galaxies. We use a three dimensional chemodynamical simulation
describing the dynamics of stars and a two-phase interstellar medium, as well
as feedback processes from the stars. For high efficiency of energy dissipation
in the cold cloud medium, the initially gaseous disk fragments and develops
several massive clumps of gas and stars. We follow the evolution of the
individual clumps and determine their masses, metallicities and velocities. A
few dynamical times after fragmentation of the disk, the clumps merge to build
a massive bulge. Calculating HST- and UBVRIJHKLM-colors, including absorption
by interstellar dust, we determine the morphologies and colors of this model in
HST images. Several peculiar morphological structures seen in the HDF can be
well-explained by a fragmented galactic disk model, including chain galaxies
and objects consisting of several nearby knots.Comment: 20 pages, Latex, 9 figures, to appear in the Astrophysical Journal.
Version with high quality images available at
http://www.astro.unibas.ch/leute/ai.shtm
An Updated Small Magellanic Cloud and Magellanic Bridge Catalog of Star Clusters, Associations, and Related Objects
We present a catalog of star clusters, associations, and related extended objects in the Small Magellanic Cloud (SMC) and the Magellanic Bridge with 2741 entries, a factor 2 more than a previous version from a decade ago. Literature data up until 2018 December are included. The identification of star clusters was carried out with digital atlases in various bands currently available in the Digitized Sky Survey and the Machine Automatique à Mésurer pour l'Astronomie. imaging surveys. In particular, we cross-identified recent cluster samples from the Visible and Infrared Survey Telescope for Astronomy near-infrared YJK s survey of the Magellanic System, Optical Gravitational Lensing Experiment IV, and Survey of the MAgellanic Stellar History surveys, confirming new clusters and pointing out equivalencies. A major contribution of the present catalog consists of the accurate central positions for clusters and small associations, including a new sample of 45 clusters or candidates in the SMC and 19 in the Magellanic Bridge, as well as a compilation of the most reliable age and metallicity values from the literature. A general catalog must also deal with the recent discoveries of 27 faint and ultra-faint star clusters and galaxies projected on the far surroundings of the Clouds, most of them from the Dark Energy Survey. The information on these objects has been complemented with photometric, spectroscopic, and kinematical follow-up data from the literature. The underluminous galaxies around the Magellanic System, still very few as compared to the predictions from Λ Cold Dark Matter simulations, can bring constraints to galaxy formation and hierarchical evolution. Furthermore, we provide diagnostics, when possible, of the nature of the ultra-faint clusters, searching for borders of the Magellanic System extensions into the Milky Way gravitational potential. © 2020. The American Astronomical Society. All rights reserved..Indexación: Scopu
Virgo cluster early-type dwarf galaxies with the Sloan Digital Sky Survey. II. Early-type dwarfs with central star formation
Despite the common picture of an early-type dwarf (dE) as a quiescent galaxy
with no star formation and little gas, we identify 23 dEs that have blue
central colors caused by recent or ongoing star formation in our sample of 476
Virgo cluster dEs. In addition, 14 objects that were mostly classified as
(candidate) BCDs have similar properties. Among the certain cluster members,
the dEs with blue centers reach a fraction of more than 15% of the dE
population at brighter (B<=16) magnitudes. A spectral analysis of the centers
of 16 galaxies reveals in all cases an underlying old population that dominates
the mass, with M(old)>=90% for all but one object. Therefore the majority of
these galaxies will appear like ordinary dEs within ~one Gigayear or less after
the last episode of star formation. Their overall gas content is less than that
of dwarf irregular galaxies, but higher than that of ordinary dEs. Their
flattening distribution suggests the shape of a thick disk, similar to what has
been found for dEs with disk features in Paper I of this series. Their
projected spatial distribution shows no central clustering, and their
distribution with projected local density follows that of irregular galaxies,
indicative of an unrelaxed population. This is corroborated by their velocity
distribution, which displays two side peaks characteristic of recent infall. We
discuss possible formation mechanisms (ram-pressure stripping, tidally induced
star formation, harassment) that might be able to explain both the disk shape
and the central star formation of the dEs with blue centers.Comment: 16 pages + 15 figures. Accepted for publication in AJ. We recommend
downloading the full resolution version from
http://www.virgo-cluster.com/lisker2006b.ps.g
The Viscacha survey - II: Structure of star clusters in the Magellanic Clouds periphery
We provide a homogeneous set of structural parameters of 83 star clusters located at the periphery of the Small Magellanic Cloud (SMC) and the Large Magellanic Cloud (LMC). The clusters’ stellar density and surface brightness profiles were built from deep, AO assisted optical images, and uniform analysis techniques. The structural parameters were obtained from King and Elson et al. model fittings. Integrated magnitudes and masses (for a subsample) are also provided. The sample contains mostly low surface brightness clusters with distances between 4.5 and 6.5 kpc and between 1 and 6.5 kpc from the LMC and SMC centres, respectively. We analysed their spatial distribution and structural properties, comparing them with those of inner clusters. Half-light and Jacobi radii were estimated, allowing an evaluation of the Roche volume tidal filling. We found that: (i) for both MCs, the tidal radii are on average larger than those of inner clusters; (ii) the core radii dispersion tends to be greater for LMC clusters located towards the southwest, with position angles of ∼200 degrees and about ∼5 degrees from the LMC centre, i.e., those LMC clusters nearer to the SMC; (iii) the analysis of clusters with ages available revealed that the core radius evolution is similar to the one of inner clusters; (iv) Roche volumes are overfilled for SMC clusters with galactocentric distances closer than 3 kpc.Fil: Santos, Joao F. C.. Universidad de La Serena; Chile. Universidade Federal de Minas Gerais; BrasilFil: Maia, Francisco. Universidade Federal do Rio de Janeiro; BrasilFil: Dias, Bruno. Millennium Institute of Astrophysics; Chile. Universidad Andrés Bello; ChileFil: de O. Kerber, Leandro. Universidade Estadual de Santa Cruz; BrasilFil: Piatti, Andres Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Bica, Eduardo. Universidade Federal do Rio Grande do Sul; BrasilFil: Angelo, Mateus S.. Centro Federal de Educacao Tecnológica de Minas Gerais; BrasilFil: Minniti, Dante. Universidad Andrés Bello; Chile. Millennium Institute of Astrophysics; Chile. Vatican Observatory; ItaliaFil: Pérez Villegas, Angeles. Universidade de Sao Paulo; BrasilFil: Roman Lopes, Alexandre. Universidad de La Serena; ChileFil: Westera, Pieter. Universidad Federal Do Abc; BrasilFil: Fraga, Luciano. Laboratorio Nacional de Astrofísica; BrasilFil: Quint, Bruno. Gemini Observatory; ChileFil: Sanmartim, David. Carnegie Institution of Washington; Chil
Ages and metallicities of stellar clusters using S-PLUS narrow-band integrated photometry: the Small Magellanic Cloud
The Magellanic Clouds are the most massive and closest satellite galaxies of
the Milky Way, with stars covering ages from a few Myr up to 13 Gyr. This makes
them important for validating integrated light methods to study stellar
populations and star-formation processes, which can be applied to more distant
galaxies. We characterized a set of stellar clusters in the Small Magellanic
Cloud (SMC), using the .
This is the first age (metallicity) determination for 11 (65) clusters of this
sample. Through its 7 narrow bands, centered on important spectral features,
and 5 broad bands, we can retrieve detailed information about stellar
populations. We obtained ages and metallicities for all stellar clusters using
the Bayesian spectral energy distribution fitting code .
With a sample of clusters in the color range , for which
our determined parameters are most reliable, we modeled the age-metallicity
relation of SMC. At any given age, the metallicities of SMC clusters are lower
than those of both the Gaia Sausage-Enceladus disrupted dwarf galaxy and the
Milky Way. In comparison with literature values, differences are
log(age) and [Fe/H], which is
comparable to low-resolution spectroscopy of individual stars. Finally, we
confirm a previously known gradient, with younger clusters in the center and
older ones preferentially located in the outermost regions. On the other hand,
we found no evidence of a significant metallicity gradient.Comment: 12 pages, 11 figure
The VISCACHA survey - I. Overview and first results
TheVISCACHA (VIsible Soar photometry of star Clusters in tApii and Coxi HuguA) Survey is an ongoing project based on deep photometric observations of Magellanic Cloud star clusters, collected using the SOuthern Astrophysical Research (SOAR) telescope together with the SOAR Adaptive Module Imager. Since 2015 more than 200 h of telescope time were used to observe about 130 stellar clusters, most of them with low mass (M < 104MΘ) and/or located in the outermost regions of the Large Magellanic Cloud and the Small Magellanic Cloud.With this high-quality data set, we homogeneously determine physical properties from statistical analysis of colour-magnitude diagrams, radial density profiles, luminosity functions, and mass functions. Ages, metallicities, reddening, distances, present-day masses, mass function slopes, and structural parameters for these clusters are derived and used as a proxy to investigate the interplay between the environment in theMagellanic Clouds and the evolution of such systems. In this first paper we present the VISCACHA Survey and its initial results, concerning the SMC clusters AM3, K37, HW20, and NGC 796 and the LMC ones KMHK228, OHSC3, SL576, SL61, and SL897, chosen to compose a representative subset of our cluster sample. The project's long-term goals and legacy to the community are also addressed.Fil: Maia, Francisco F. S.. Universidade de Sao Paulo; BrasilFil: Dias, Bruno. Universidad Andrés Bello; Chile. European Southern Observatory Santiago; ChileFil: Santos, Joao F. C.. Universidade Federal de Minas Gerais; BrasilFil: De Kerber, Leandro. Universidade de Sao Paulo; BrasilFil: Bica, Eduardo. Universidade Federal do Rio Grande do Sul; BrasilFil: Piatti, Andres Eduardo. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Barbuy, Beatriz. Universidade de Sao Paulo; BrasilFil: Quint, Bruno. Gemini Observatory; ChileFil: Fraga, Luciano. Laboratório Nacional de Astrofísica; Brasil. Gemini Observatory; ChileFil: Sanmartim, David. Gemini Observatory; ChileFil: Angelo, Mateus S.. Centro Federal de Educação Tecnológica de Minas Gerais; BrasilFil: Hernandez-Jimenez, Jose A.. Universidade de Sao Paulo; BrasilFil: Santrich, Orlando J. Katime. Universidade Estadual de Santa Cruz; BrasilFil: Oliveira, Raphael A. P.. Universidade de Sao Paulo; BrasilFil: Pérez-Villegas, Angeles. Universidade de Sao Paulo; BrasilFil: Souza, Stefano O.. Universidade de Sao Paulo; BrasilFil: Vieira, Rodrigo G.. Universidade de Sao Paulo; BrasilFil: Westera, Pieter. Universidade Federal do ABC; Brasi