Casiana Munoz-Tunon

Multiband Analysis of a Sample of Blue Compact Dwarf Galaxies. II. Spatially Resolved and Integrated Photometry

This is the second in a series of papers devoted to the study of a sample of 28 blue compact dwarf galaxies (BCDs). In the first paper, we presented the broadband observations in B, V, R, and I. Deep contour maps, surface-brightness profiles, and color profiles were used to analyze and discuss their morphology and structure. Here, we present new U-band and Hα observations. We compute isophotal and asymptotic magnitudes of the sample galaxies and total Hα fluxes. Comparison with previous works is done to assess the quality of the data available for BCDs. Finally, we produce an atlas of detailed color and Hα maps, the first systematic atlas of this kind published so far. The high quality of the data allows us to identify the different star-forming knots in the maps and to discriminate between them and the regions where star formation activity has already ceased. We supplement the atlas with a morphological description of each galaxy and group the galaxies in four classes according to the distribution of their star-forming regions.

Star formation sustained by gas accretion

Numerical simulations predict that metal-poor gas accretion from the cosmic web fuels the formation of disk galaxies. This paper discusses how cosmic gas accretion controls star formation, and summarizes the physical properties expected for the cosmic gas accreted by galaxies. The paper also collects observational evidence for gas accretion sustaining star formation. It reviews evidence inferred from neutral and ionized hydrogen, as well as from stars. A number of properties characterizing large samples of star-forming galaxies can be explained by metal-poor gas accretion, in particular, the relationship among stellar mass, metallicity, and star-formation rate (the so-called fundamental metallicity relationship). They are put forward and analyzed. Theory predicts gas accretion to be particularly important at high redshift, so indications based on distant objects are reviewed, including the global star-formation history of the universe, and the gas around galaxies as inferred from absorption features in the spectra of background sources.

Young super star clusters in the starburst of M82: The catalog

Recent results from the Hubble Space Telescope (HST) have resolved starbursts as collections of compact young stellar clusters. Here we present a photometric catalog of the young stellar clusters in the nuclear starburst of M82, observed with the HST WFPC2 in Hα (F656N) and in four optical broadband filters. We identify 197 young super stellar clusters. The compactness and high density of the sources led us to develop specific techniques to measure their sizes. Strong extinction lanes divide the starburst into five different zones, and we provide a catalog of young super star clusters for each of these. In the catalog we include relative coordinates, radii, fluxes, luminosities, masses, equivalent widths, extinctions, and other parameters. Extinction values have been derived from the broadband images. The radii range between 3 and 9 pc, with a mean value of 5.7 ± 1.4 pc, and a stellar mass between 104 and 106 M☉. The inferred masses and mean separation, comparable to the size of the super star clusters, together with their high volume density, provide strong evidence for the key ingredients postulated by Tenorio-Tagle and coworkers as required for the development of a supergalactic wind.

Optical surface photometry of a sample of disk galaxies. II structural components

This work presents the structural decomposition of a sample of 11 disk galaxies, which span a range of different morphological types. The U, B, V, R, and I photometric information given in Paper I (color and color-index images and luminosity, ellipticity, and position-angle profiles) has been used to decide what types of components form the galaxies before carrying out the decomposition. We find and model such components as bulges, disks, bars, lenses and rings.

SYSTEMATIC SEARCH FOR EXTREMELY METAL-POOR GALAXIES IN THE SLOAN DIGITAL SKY SURVEY

We carry out a systematic search for extremely metal-poor (XMP) galaxies in the spectroscopic sample of Sloan Digital Sky Survey (SDSS) data release 7 (DR7). The XMP candidates are found by classifying all the galaxies according to the form of their spectra in a region 80 ? wide around H?. Due to the data size, the method requires an automatic classification algorithm. We use k-means. Our systematic search renders 32 galaxies having negligible [N II] lines, as expected in XMP galaxy spectra. Twenty-one of them have been previously identified as XMP galaxies in the literature?the remaining 11 are new. This was established after a thorough bibliographic search that yielded only some 130 galaxies known to have an oxygen metallicity 10 times smaller than the Sun (explicitly, with 12 + log (O/H) ? 7.65). XMP galaxies are rare; they represent 0.01% of the galaxies with emission lines in SDSS/DR7. Although the final metallicity estimate of all candidates remains pending, strong-line empirical calibrations indicate a metallicity about one-tenth solar, with the oxygen metallicity of the 21 known targets being 12 + log (O/H) 7.61 ? 0.19. Since the SDSS catalog is limited in apparent magnitude, we have been able to estimate the volume number density of XMP galaxies in the local universe, which turns out to be (1.32 ? 0.23) ? 10?4 Mpc?3. The XMP galaxies constitute 0.1% of the galaxies in the local volume, or ~0.2% considering only emission-line galaxies. All but four of our candidates are blue compact dwarf galaxies, and 24 of them have either cometary shape or are formed by chained knots.

A study of the interplay between ionized gas and star clusters in the central region of NGC 5253 with 2D spectroscopy

Context. Starbursts are one of the main contributors to the chemical enrichment of the interstellar medium. However, mechanisms governing the interaction between the recent star formation and the surrounding gas are not fully understood. Because of their a priori simplicity, the subgroup of H ii galaxies constitute an ideal sample to study these mechanisms. Aims. A detailed 2D study of the central region of NGC 5253 has been performed to characterize the stellar and ionized gas structure as well as the extinction distribution, physical properties and kinematics of the ionized gas in the central ∼210 pc × 130 pc. Methods. We utilized optical integral field spectroscopy (IFS) data obtained with FLAMES. Results. A detailed extinction map for the ionized gas in NGC 5253 shows that the largest extinction is associated with the prominent Giant H ii region. There is an offset of ∼0. �� 5 between the peak of the optical continuum and the extinction peak in agreement with findings in the infrared. We found that stars suffer less extinction than gas by a factor of ∼0.33. The [S ii]λ6717/[S ii]λ6731 map shows an electron density (Ne) gradient declining from the peak of emission in Hα (790 cm −3 ) outwards, while the argon line ratio traces areas with Ne ∼ 4200−6200 cm −3 . The area polluted with extra nitrogen, as deduced from the excess [N ii]λ6584/Hα, extends up to distances of 3. �� 3( ∼60 pc) from the maximum pollution, which is offset by ∼1. �� 5 from the peak of continuum emission. Wolf-Rayet features are distributed in an irregular pattern over a larger area (∼100 pc × 100 pc) and associated with young stellar clusters. We measured He + abundances over most of the field of view and values of He ++ /H + < 0.0005 in localized areas which do not coincide, in general, with the areas presenting W-R emission or extra nitrogen. The line profiles are complex. Up to three emission components were needed to reproduce them. One of them, associated with the giant H ii region, presents supersonic widths and [N ii]λ6584 and [S ii]λλ6717,6731 emission lines shifted up to 40 km s −1 with respect to Hα. Similarly, one of the narrow components presents offsets in the [N ii]λ6584 line of <20 km s −1 . This is the first time that maps with such velocity offsets for a starburst galaxy have been presented. The observables in the giant H ii region fit with a scenario where the two super stellar clusters (SSCs) produce an outflow that encounters the previously quiescent gas. The south-west part of the FLAMES IFU field is consistent with a more evolved stage where the star clusters have already cleared out their local environment.

Deep Near-Infrared Mapping of Young and Old Stars in Blue Compact Dwarf Galaxies

We analyze J, H, and Ks near-infrared data for nine blue compact dwarf (BCD) galaxies, selected from a larger sample that we have already studied in the optical. We present contour maps, surface brightness and color profiles, and color maps of the sample galaxies. The morphology of the BCDs in the near-infrared (NIR) has been found to be basically the same as in the optical. The inner regions of these systems are dominated by the starburst component. At low surface brightness levels the emission is due to the underlying host galaxy; the latter is characterized by red, radially constant colors and isophotes well fitted by ellipses. We derive accurate optical-NIR host galaxy colors for eight of the sample galaxies; these colors are typical of an evolved stellar population. Interestingly, optical-NIR color maps reveal the presence of a complex, large-scale absorption pattern in three of the sample galaxies. We study the applicability of the Sersic law to describe the surface brightness profiles of the underlying host galaxy and find that, because of the limited surface brightness interval over which the fit can be made, the derived Sersic parameters are very sensitive to the selected radial interval and to errors in the sky subtraction. Fitting an exponential model gives generally more stable results and can provide a useful tool to quantify the structural properties of the host galaxy and compare them with those of other dwarf classes, as well as with those of star-forming dwarfs at higher redshifts.

Structural Parameters of Dwarf Galaxies in the Coma Cluster: On the Origin of dS0 Galaxies

In this paper we analyze the structural parameters of the dwarf galaxies in the Coma Cluster with -18 ≤ MB ≤ -16 and classify them into two types; those with surface brightness profiles well fitted by a single Sersic law are called dwarf ellipticals (dEs), and those fitted with Sersic+exponential profiles are classified as dwarf lenticulars (dS0s). The comparison of the structural parameters of the dwarf galaxies in the Coma and Virgo Clusters shows that they are analogous. Photometrically, the dE and dS0 galaxies in Coma are equivalent, having similar colors and global scales. However, the scale of the innermost parts (bulges) of dS0 galaxies is similar to that of the bulges of late-type spiral galaxies. In contrast, dEs have larger scales than the bulges of bright galaxies. This may indicate that dS0 and dE galaxies have different origins. While dE galaxies can come from dwarf irregulars (dIs) or from processes similar to those that form bright E galaxies, the origin of dS0 galaxies could be harassed bright late-type spiral galaxies.

ENVIRONMENTAL EFFECTS IN THE STRUCTURAL PARAMETERS OF GALAXIES IN THE COMA CLUSTER

We have studied 116 bright galaxies from the Coma Cluster brighter than mr = 17 mag. From a quantitative morphological analysis we find that the scales of the disks are smaller than those of field spiral galaxies. There is a correlation between the scale of the disks and the position of the galaxy in the cluster; no large disks are present near the center of the cluster or in high-density environments. The structural parameters of the bulges are not affected by the environment. We have analyzed the distribution of blue and red objects in the cluster. For spirals there is a trend between color and position in the cluster. The bluest spiral galaxies are located at larger projected radii; they also show larger velocity dispersions than the red ones. The differences in the scale of the disks between cluster galaxies and local samples of isolated galaxies and the color distribution of the objects can be understood in terms of the harassment scenario.

ON THE FEEDBACK FROM SUPER STELLAR CLUSTERS. I. THE STRUCTURE OF GIANT H ii REGIONS AND H ii GALAXIES

We review the structural properties of giant extragalactic H II regions and H II galaxies based on two-dimensional hydrodynamic calculations and propose an evolutionary sequence that accounts for their observed detailed structure. The model assumes a massive and young stellar cluster surrounded by a large collection of clouds. These are thus exposed to the most important star formation feedback mechanisms: photoionization and the cluster wind. The models show how the two feedback mechanisms compete with each other in the disruption of clouds and lead to two different hydrodynamic solutions: the storage of clouds into a long-lasting ragged shell that inhibits the expansion of the thermalized wind and the steady filtering of the shocked wind gas through channels carved within the cloud stratum. Both solutions are here claimed to be concurrently at work in giant H II regions and H II galaxies, causing their detailed inner structure. This includes multiple large-scale shells, filled with an X-ray-emitting gas, that evolve to finally merge with each other, giving the appearance of shells within shells. The models also show how the inner filamentary structure of the giant superbubbles is largely enhanced with matter ablated from clouds and how cloud ablation proceeds within the original cloud stratum. The calculations point at the initial contrast density between the cloud and the intercloud media as the factor that defines which of the two feedback mechanisms becomes dominant throughout the evolution. Animated versions of the models presented can be found at http://www.iaa.csic.es/~eperez/ssc/ssc.html.