ESO for GOODS' sake

Currently public ESO data sets pertinent to the CDFS/GOODS field are briefly illustrated along with an indication on how to get access to them. Future ESO plans for complementing the GOODS database with optical/IR imaging and optical spectroscopy are also described.Comment: 6 pages, 2 figures, to appear in the proceedings of the ESO/USM Workshop "The Mass of Galaxies at Low and High Redshift" (Venice, Italy, October 2001), eds. R. Bender and A. Renzin

The Sagittarius dwarf irregular galaxy: metallicity and stellar populations

We present deep $BVI$ observations of the dwarf irregular galaxy UKS1927-177 in Sagittarius. Statistically cleaned $V$, $(B-I)$ CMDs clearly display the key evolutionary features in this galaxy. Previously detected C stars are located in the CMDs and shown to be variable, thus confirming the presence of a significant upper-AGB intermediate age population. A group of likely red supergiants is also identified, whose magnitude and color is consistent with a 30 Myr old burst of star formation. The observed colors of both blue and red stars in SagDIG are best explained by introducing a differential reddening scenario in which internal dust extinction affects the star forming regions. Adopting a low reddening for the red giants, $E(B-V) = 0.07 \pm 0.02$, gives [Fe/H]=$-2.1 \pm 0.2$ for the mean stellar metallicity, a value consistent with the [O/H] abundance measured in the HII regions. This revised metallicity, which is in accord with the trend of metallicity against luminosity for dwarf irregular galaxies, is indicative of a ``normal'', although metal-poor, dIrr galaxy. A quantitative description is given of the spatial distribution of stars in different age intervals, in comparison with the distribution of the neutral hydrogen. We find that the youngest stars are located near the major peaks of emission on the HI shell, whereas the red giants and intermediate-age C stars define an extended halo or disk with scale length comparable to the size of the hydrogen cloud. The relationship between the distribution of ISM and star formation is briefly discussed.Comment: 10 pages, 7 figures, accepted A&

Deep U band and R imaging of GOODS-South: Observations,data reduction and first results

We present deep imaging in the {\em U} band covering an area of 630 arcmin$^{2}$ centered on the southern field of the Great Observatories Origins Deep Survey (GOODS). The data were obtained with the VIMOS instrument at the ESO Very Large Telescope. The final images reach a magnitude limit $U_{lim} \approx 29.8$ (AB, 1$\sigma$, in a 1\arcsec radius aperture), and have good image quality, with full width at half maximum \approx 0.8\arcsec. They are significantly deeper than previous U--band images available for the GOODS fields, and better match the sensitivity of other multi--wavelength GOODS photometry. The deeper U--band data yield significantly improved photometric redshifts, especially in key redshift ranges such as $2<z<4$, and deeper color--selected galaxy samples, e.g., Lyman--break galaxies at $z\approx 3$. We also present the coaddition of archival ESO VIMOS R band data, with $R_{lim} \approx 29$ (AB, 1$\sigma$, 1\arcsec radius aperture), and image quality \approx 0.75 \arcsec. We discuss the strategies for the observations and data reduction, and present the first results from the analysis of the coadded images.Comment: Accepted for publication ApJS, 54 pages, 27 figures. Released data and full-quality paper version available at http://archive.eso.org/cms/eso-data/data-packages/goods-vimos-imaging-data-release-version-1.

A simple model to interpret the ultraviolet, optical and infrared emission from galaxies

We present a simple, largely empirical but physically motivated model to interpret the mid- and far-infrared spectral energy distributions of galaxies consistently with the emission at ultraviolet, optical and near-infrared wavelengths. Our model relies on an existing angle-averaged prescription to compute the absorption of starlight by dust in stellar birth clouds and in the ambient ISM in galaxies. We compute the spectral energy distribution of the power reradiated by dust in stellar birth clouds as the sum of three components: a component of PAHs; a mid-IR continuum characterising the emission from hot grains; and a component of warm grains in thermal equilibrium with adjustable temperature. In the ambient ISM, we fix for simplicity the relative proportions of these three components to reproduce the spectral shape of diffuse cirrus emission in the Milky Way, and we include a component of cold grains in thermal equilibrium with adjustable temperature. Our model can be used to derive statistical constraints on the star formation histories and dust contents of large samples of galaxies using UV, optical and IR observations. We illustrate this by deriving median-likelihood estimates of the star formation rates, stellar masses, effective dust optical depths, dust masses, and relative strengths of different dust components of 66 well-studied nearby star- forming galaxies from the Spitzer Infrared Nearby Galaxy Survey (SINGS). From this analysis, we conclude that the mid- and far-IR colours of galaxies correlate strongly with the specific star formation rate, as well as with other galaxy-wide quantities connected to this parameter. Our model can be straightforwardly applied to interpret UV, optical and IR spectral energy distributions from any galaxy sample. [abridged]Comment: 27 pages, 15 figures, accepted for publication in MNRAS. Full-resolution figures available from ftp://ftp.iap.fr/pub/from_users/dacunha/fullres_figure

Dwarf Galaxies of the Local Group

The Local Group (LG) dwarf galaxies offer a unique window to the detailed properties of the most common type of galaxy in the Universe. In this review, I update the census of LG dwarfs based on the most recent distance and radial velocity determinations. I then discuss the detailed properties of this sample, including (a) the integrated photometric parameters and optical structures of these galaxies, (b) the content, nature and distribution of their ISM, (c) their heavy-element abundances derived from both stars and nebulae, (d) the complex and varied star-formation histories of these dwarfs, (e) their internal kinematics, stressing the relevance of these galaxies to the dark-matter problem and to alternative interpretations, and (f) evidence for past, ongoing and future interactions of these dwarfs with other galaxies in the Local Group and beyond. To complement the discussion and to serve as a foundation for future work, I present an extensive set of basic observational data in tables that summarize much of what we know, and what we still do not know, about these nearby dwarfs. Our understanding of these galaxies has grown impressively in the past decade, but fundamental puzzles remain that will keep the Local Group at the forefront of galaxy evolution studies for some time.Comment: 66 pages; 9 figures; 8 table