New insights to the photometric structure of Blue Compact Dwarf Galaxies from deep Near-Infrared studies: II. The sample of northern BCDs

This paper is part of a series of publications which present a systematic study of Blue Compact Dwarf (BCD) Galaxies in the Near Infrared (NIR). Compared to the visible light, NIR data allow a better separation of the starburst emission from the light distribution of the old stellar low-surface brightness (LSB) host galaxy. We analyze deep NIR broad band images of a sample of 11 BCDs, observed with the Calar Alto 3.6m telescope. This work enlarges the samples presented in preceding papers of this study (Noeske et al. 2003, Cairos et al. 2003) by BCDs of the most common morphological type, displaying a regular elliptical LSB host galaxy. The data presented here allow the detection and quantitative study of the extended stellar LSB host galaxy in all sample BCDs. The NIR surface brightness profiles (SBPs) of the LSB host galaxies agree at large galactocentric radii with those from optical studies, showing also an exponential intensity decrease and compatible scale lengths. Similar to Noeske et al. (2003), we find centrally flattening exponential (type V) SBPs of the host galaxy for several BCDs. Such SBPs remain mostly undetected in optical bands, due to the comparatively stronger starburst emission at these wavelengths. We apply a modified exponential distribution to decompose and quantitatively analyze SBPs of LSB hosts with a type V intensity distribution. We present the results of the surface photometry and the decomposition of SBPs, and discuss individual objects with respect to morphological details of their star-forming regions.Comment: 18 pages, 11 figures; accepted for publication in Astronomy & Astrophysics; postscript file with full resolution images available at http://www.ucolick.org/~kai/PUB/noeske_nirbcds_2.ps.g

The stellar host in blue compact dwarf galaxies: the need for a two-dimensional fit

The structural properties of the low surface brightness stellar host in blue compact dwarf galaxies are often studied by fitting r^{1/n} models to the outer regions of their radial profiles. The limitations imposed by the presence of a large starburst emission overlapping the underlying component makes this kind of analysis a difficult task. We propose a two-dimensional fitting methodology in order to improve the extraction of the structural parameters of the LSB host. We discuss its advantages and weaknesses by using a set of simulated galaxies and compare the results for a sample of eight objects with those already obtained using a one-dimensional technique. We fit a PSF convolved Sersic model to synthetic galaxies, and to real galaxy images in the B, V, R filters. We restrict the fit to the stellar host by masking out the starburst region and take special care to minimize the sky-subtraction uncertainties. In order to test the robustness and flexibility of the method, we carry out a set of fits with synthetic galaxies. Furthermore consistency checks are performed to assess the reliability and accuracy of the derived structural parameters. The more accurate isolation of the starburst emission is the most important advantage and strength of the method. Thus, we fit the host galaxy in a range of surface brightness and in a portion of area larger than in previous published 1D fits with the same dataset. We obtain robust fits for all the sample galaxies, all of which, except one, show Sersic indices n very close to 1, with good agreement in the three bands. These findings suggest that the stellar hosts in BCDs have near-exponential profiles, a result that will help us to understand the mechanisms that form and shape BCD galaxies, and how they relate to the other dwarf galaxy classes.Comment: 22 pages, 15 figures (low resolution), accepted for publication in A&A. A higher resolution version of the figures can be provided upon reques

AEGIS: Extinction and Star Formation Tracers from Line Emission

Strong nebular emission lines are a sensitive probe of star formation and extinction in galaxies, and the [O II] line detects star forming populations out to z>1. However, star formation rates from emission lines depend on calibration of extinction and the [O II]/H-alpha line ratio, and separating star formation from AGN emission. We use calibrated line luminosities from the DEEP2 survey and Palomar K magnitudes to show that the behavior of emission line ratios depends on galaxy magnitude and color. For galaxies on the blue side of the color bimodality, the vast majority show emission signatures of star formation, and there are strong correlations of extinction and [O II]/H-alpha with restframe H magnitude. The conversion of [O II] to extinction-corrected H-alpha and thus to star formation rate has a significant slope with M_H, 0.23 dex/mag. Red galaxies with emission lines have a much higher scatter in their line ratios, and more than half show AGN signatures. We use 24 micron fluxes from Spitzer/MIPS to demonstrate the differing populations probed by nebular emission and by mid-IR luminosity. Although extinction is correlated with luminosity, 98% of IR-luminous galaxies at z~1 are still detected in the [O II] line. Mid-IR detected galaxies are mostly bright and intermediate color, while fainter, bluer galaxies with high [O II] luminosity are rarely detected at 24 microns.Comment: 4 pages, 3 figures. Accepted for publication in ApJ Letters AEGIS special editio

A HST study of the stellar populations in the cometary dwarf irregular galaxy NGC 2366

We present V and I photometry of the resolved stars in the cometary dwarf irregular galaxy NGC 2366, using Wide Field Planetary Camera 2 images obtained with the Hubble Space Telescope. The resulting color-magnitude diagram reaches down to I~26.0 mag. It reveals not only a young population of blue main-sequence stars (age <30 Myr) but also an intermediate-age population of blue and red supergiants (20 Myr<age<100 Myr), and an older evolved populations of asymptotic giant branch (AGB) stars (age >100 Myr) and red giant branch (RGB) stars (age >1 Gyr). The measured magnitude I=23.65+/-0.10 mag of the RGB tip results in a distance modulus m-M=27.67+/-0.10, which corresponds to a distance of 3.42+/-0.15 Mpc, in agreement with previous distance determinations. The youngest stars are associated with the bright complex of HII regions NGC 2363=Mrk 71 in the southwest extremity of the galaxy. As a consequence of the diffusion and relaxation processes of stellar ensembles, the older the stellar population is, the smoother and more extended is its spatial distribution. An underlying population of older stars is found throughout the body of NGC 2366. The most notable feature of this older population is the presence of numerous relatively bright AGB stars. The number ratio of AGB to RGB stars and the average absolute brightness of AGB stars in NGC 2366 are appreciably higher than in the BCD VII Zw 403, indicating a younger age of the AGB stars in NGC 2366. In addition to the present burst of age <100 Myr, there has been strong star formation activity in the past of NGC 2366, from ~100 Myr to <3 Gyr ago.Comment: 32 pages, 15 figures, accepted for publication in the Astrophysical Journa

New insights to the photometric structure of Blue Compact Dwarf Galaxies from deep Near-Infrared studies I. Observations, surface photometry and decomposition of surface brightness profiles

(shortened) We analyze deep Near Infrared (NIR) broad band images for a sample of Blue Compact Dwarf Galaxies (BCDs), allowing for the quantitative study of their extended stellar low-surface brightness (LSB) host galaxies. NIR surface brightness profiles (SBPs) of the LSB hosts agree at large galactocentric radii with those from optical studies. At small to intermediate radii, however, the NIR data reveal for more than half of our sample a significant flattening of the exponential SBP of the LSB host. Such SBPs ("type V" SBPs, Binggeli & Cameron 1991) have rarely been detected in LSB hosts of BCDs at optical wavelengths, where the relative flux contribution of the starburst is stronger than in the NIR and can hide such central intensity depressions of the LSB host. The structural properties, frequency and physical origin of type V LSB SBPs in BCDs and other dwarf galaxies have not yet been systematically studied. Nevertheless, their occurrence in a significant fraction of BCDs would impose important new constraints to the radial distribution of their stellar mass, and to the photometric fading of BCDs after the termination of star-forming activity. Both a modified exponential (Papaderos et al. 1996a) and the Sersic law give satisfactory empirical descriptions for type V SBPs. However, we argue that the practical applicability of Sersic fits to LSB SBPs of BCDs is limited by, e.g., the extreme sensitivity of the solutions to small SBP uncertainties. Most stellar LSB host galaxies in the sample show optical-NIR colors indicative of evolved stellar populations with subsolar metallicity. Unsharp-masked NIR images and optical-NIR maps reveal numerous morphological details, and cases of non-uniform dust absorption on spatial scales up to ~1 kpc.Comment: 29 pages, 17 figures; accepted for publication in Astronomy & Astrophysics; 1 typo in Table 2 corrected; higher resolution images are available at http://www.uni-sw.gwdg.de/~knoeske/PUB_LIST/noeske_BCDs_NIR.ps.g

AEGIS: The Nature of the Host Galaxies of Low-ionization Outflows at z < 0.6

We report on a S/N-limited search for low-ionization gas outflows in the spectra of the 0.11 < z < 0.54 objects in the EGS portion of the DEEP2 survey. Doppler shifts from the host galaxy redshifts are systematically searched for in the Na I 5890,96 doublet (Na D). Although the spectral resolution and S/N limit us to study the interstellar gas kinematics from fitting a single doublet component to each observed Na D profile, the typical outflow often seen in local luminous-infrared galaxies (LIRGs) should be detected at >~ 6 sigma in absorption equivalent width down to the survey limiting S/N (~ 5 per pixel) in the continuum around Na D. The detection rate of LIRG-like outflow clearly shows an increasing trend with star-forming activity and infrared luminosity. However, by virtue of not selecting our sample on star formation, we also find a majority of outflows in galaxies on the red sequence in the rest-frame (U-B, M_B) color-magnitude diagram. Most of these red-sequence outflows are of early-type morphology and show the sign of recent star formation in their UV-optical colors; some show enhanced Balmer H-beta absorption lines indicative of poststarburst as well as high dust extinction. These findings demonstrate that outflows outlive starbursts and suggest that galactic-scale outflows play a role in quenching star formation in the host galaxies on their way to the red sequence. The fate of relic winds, as well as the observational constraints on gaseous feedback models, may be studied in galaxies during their poststarburst phase. We also note the presence of inflow candidates in red, early-type galaxies, some with signs of AGNs/LINERs but little evidence for star formation.Comment: 19 pages & 19 figures (emulateapj); the revision to match the published version in Ap

Routine use of antimicrobial drugs during the 2004 cholera epidemic in Douala, Cameroon

Objectives: To evaluate routine use of antimicrobial drugs for treatment and prevention of cholera with special regards to the evolution of the antimicrobial drug resistance patterns of V. cholerae strains. Design: Retrospective population-based descriptive study. Subjects: Four thousand nine hundred and forty one notified cholera cases, their 15,381 patients' guards and their 159,263 household members and close neighbours. Results: A total of 4,941 patients received antibiotic therapy according to the treatment protocols. Prophylactic treatment was administered to 15,381 patients' guards in hospitals and to 159,263 household members and close neighbours during home visits. Over the entire outbreak, the antimicrobial susceptibility patterns of V. cholerae strains isolated remained stable. Conclusions: The routine use of antimicrobial therapy for cholera cases associated with simultaneous and large scale chemoprophylaxis of close contacts does not seem in our experience to compromise the stability of V. cholerae susceptibility profiles to drugs when applied within a comprehensive package of rigorously monitored community interventions. The role of therapy and chemoprophylaxis in limiting the extent of a cholera epidemic is however difficult to ascertain from our experience. Field trials need to be designed to elucidate this aspect. The East African Medical Journal Vol. 83 (11) 2006: pp. 596-60