Luz Marina Cair'os

MULTIBAND ANALYSIS OF A SAMPLE OF BLUE COMPACT DWARF GALAXIES. I. SURFACE BRIGHTNESS DISTRIBUTION, MORPHOLOGY, AND STRUCTURAL PARAMETERS

Broadband observations in B, V, R, and I have been performed for a sample of 28 galaxies cataloged as blue compact dwarf galaxies (BCDs). Our deep imaging, reaching surface brightness levels of a few percent of the sky brightness, has allowed the detection of underlying emission or low surface brightness features for a substantial fraction of the sample. In this paper we present the first results of the program: deep contour maps in the B band, surface brightness profiles, and color profiles for all the galaxies. The information derived for this sample of galaxies has allowed us to analyze the morphology and the structural components of BCDs. Over 70% of the galaxies show complex profiles that preclude fitting by a single standard law, with extra structure at high to intermediate intensity levels. In 21 galaxies of the sample, an underlying low surface brightness component has been detected.

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

We have analyzed deep Near Infrared (NIR) broad band images for a sample of Blue Compact Dwarf Galaxies (BCDs), observed with the ESO NTTand Calar Alto �� 3.6 m telescopes. The data presented here allows for the detection and quantitative study of the extended stellar low-surface brightness (LSB) host galaxy in all sample BCDs. 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. At small to intermediate radii (within 1-3 exponential scale lengths), however, the NIR data reveals for more than one half of our sample BCDs evidence for a significant flattening of the exponential profile of the LSB component. Such profiles (type V SBPs, Binggeli & Cameron 1991) have rarely been detected in the LSB component of BCDs at optical wavelengths, where the relative flux contribution of the starburst, being stronger than in the NIR, can readily hide a possible central intensity depression in the underlying LSB host. The structural properties, frequency and physical origin of type V LSB profiles in BCDs and dwarf galaxies in general have not yet been subject to systematic studies. Nevertheless, the occurrence of such profiles in an appreciable fraction of BCDs would impose important new observational constraints to the radial mass distribution of the stellar LSB component, as well as to the photometric fading of these systems after the termination of star-forming activities. We test the suitability of two empirical fitting functions, a modified exponential distribution (Papaderos et al. 1996a) and the Sersic law, for the systematization of the structural properties of BCD host galaxies which show a type V intensity distribution. Either function has been found to satisfactorily fit a type V distribution. However, it is argued that the practical applicability of Sersic fits to the LSB emission of BCDs is limited by the extreme sensitivity of the achieved solutions to, e.g., small uncertainties in the sky subtraction and SBP derivation. We find that most of the sample BCDs show in their stellar LSB host galaxy optical-NIR colors indicative of an evolved stellar population with subsolar metallicity. Unsharp-masked NIR maps reveal numerous morphological details and indicate in some cases, in combination with optical data, appreciable non-uniform dust absorption on a spatial scale as large as ∼1 kpc.

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.

The host in blue compact galaxies. - Structural properties and scaling relations

Aims. We characterise the underlying stellar host in a sample of 20 blue compact galaxies (BCGs), by fitting their two-dimensional light distributions. Their derived host structural parameters and those of eight other BCGs already obtained in a previous paper are related to galaxy properties, such as colours and gas content. These properties are also compared with those of other galaxy types. Methods. The structural parameters of the host were derived by fitting a two-dimensional PSF-convolved Sersic model to deep optical images in several bandpasses (B, V, R, I). We followed a fitting technique that consists in the accurate masking-out of the star-forming regions in several steps. Results. All the BCG hosts but one show low Sersic indexes (0.5 ≤ n ≤ 2), with mean effective radius = 1.11 ± 0.74 kpc and mean surface brightness = 22.59 ± 0.68 mag arcsec ―2 . Host effective radii scale linearly with their luminosity, while n and μ e do not. In addition, host colours and structural parameters are not linearly correlated. Overall, the flux enhancement caused by the starburst is about 0.8 mag, while their B - R colours decrease by about 0.2 mag. Galaxies with more luminous and extended hosts show larger and luminous starburst components, whereas the relative strength of the burst (L burst/ L host ) does not show any significant dependence on the host luminosity (or mass). While hosts show B - R = 0.95 ± 0.26 in median, galaxies with redder hosts ((B - R) = 1.29 ± 0.10) and with bluer hosts ((B - R) = 0.66 ± 0.10) are distinguished among the more and less luminous systems, respectively. Overall, BCG hosts are more compact (by a factor ∼2) and have higher central surface brightnesses (by about ∼2 mag) than dIs and most dEs. BCG hosts and isolated dIs are indistinguishable in the B-band Tully-Fisher relation (TFR). We found that about 50-60% of the galaxies are more underluminous than those late-type discs with the same circular velocity. This feature is more important when luminosities are converted into stellar masses, while it tends to diminish when the HI gas mass is added. Deviations among host masses for a given circular velocity from the stellar TFR correlate with their HI mass-to-luminosity ratio (M HI /L B ), whereas deviations from the gas+stellar TFR do not. Overall, our findings suggest that the baryonic mass in BCGs tends to normal values, but BCGs tend to be inefficient by producing stars, especially toward the low-mass, gas-rich, and bluest hosts, in a similar way to dIs.

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

Context. 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. Aims. 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. Methods. 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. Results. 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.

Mapping the starburst in Blue Compact Dwarf Galaxies PMAS Integral Field Spectroscopy of Mrk 1418

Aims. By means of optical Integral Field Spectroscopy observations, we aim to disentangle and characterize the starburst component in the Blue Compact Dwarf Galaxy Mrk 1418. In particular we propose to study the stellar and ionized gas morphology, to investigate the ionization mechanism(s) acting in the interstellar medium, to derive the physical parameters and abundances of the ionized gas. Methods. Integral Field Spectroscopy observations of Mrk 1418 were carried out with the Potsdam Multi-Aperture Spectrophotometer (PMAS) at the 3.5 m telescope at Calar Alto Observatory. The central 16 ′′ × 16 ′′ (1.14× 1.14 kpc 2 at the distance of Mrk 1418) were mapped with a spatial sampling of 1 ′′ ; we took data in the 3590-6996 A spectral range, with a linear dispersion of 3.2 A per pixel. The seeing was about 1. ′′ 5. From these data we built maps of the most prominent emission lines, namely [Oii], Hβ, [Oiii], Hα, [Nii] and [Sii] as well as of several continuum bands, plus maps of the main line ratios: [Oiii]/Hβ, [Nii]/Hα, [Sii]/Hα, and Hα/Hβ, and derived the physical parameters and gaseous metal abundances of the different star-forming regions detected in the field of view. Results. Mrk 1418 shows a distorted morphology both in the continuum and in the ionized gas maps; the current star- formation episode is taking place in five knots, distributed around the nucleus of the galaxy. The interstellar medium surrounding these knots is photo-ionized by stars, with no clear evidence for other excitation mechanisms. The galaxy displays an inhomogeneous dust distribution, with the high Hα/Hβ ratio in the central areas indicating a large amount of dust. The oxygen abundances derived for the individual star-forming knots are very similar, sugges ting that the ionized interstellar medium is chemically homogeneous in O/H over spatial scales of hundreds of parsecs. This abundance (Z≈ 0.4Z⊙ from the empirical calibrations) places Mrk 1418 among the high metallicity BCD group. Conclusions. These findings show the advantages of IFS when investigating the properties of such complex objects as BCDs, with an asymmetric star forming component. Only a bidimensional mapping of their central regions allows to approach such questions as the star formation processes in BCDs, the star-forming history of the individual starburst knots, or the abundance gradients.

Mapping the properties of blue compact dwarf galaxies: integral field spectroscopy with PMAS

Context. Blue compact dwarf (BCD) galaxies are low-luminosity, low-metal content dwarf systems undergoing violent bursts of star formation. They present a unique opportunity to probe galaxy formation and evolution and to investigate the process of star formation in a relatively simple scenario. Spectrophotometric studies of BCDs are essential to disentangle and characterize their stellar populations. Aims. We perform integral field spectroscopy of a sample of BCDs with the aim of analyzing their morphology, the spatial distribution of some of their physical properties (excitation, extinction, and electron density) and their relationship with the distribution and evolutionary state of the stellar populations. Methods. Integral field spectroscopy observations of the sample galaxies were carried out with the Potsdam Multi-Aperture Spectrophotometer (PMAS) at the 3.5 m telescope at Calar Alto Observatory. An area 16 �� × 16 �� in size was mapped with a spatial sampling of 1 �� × 1 �� . We obtained data in the 3590−6996 A spectral range, with a linear dispersion of 3.2 A per pixel. From these data we built two-dimensional maps of the flux of the most prominent emission lines, of two continuum bands, of the most relevant line ratios, and of the gas velocity field. Integrated spectra of the most prominent star-forming regions and of whole objects within the FOV were used to derive their physical parameters and the gas metal abundances. Results. Six galaxies display the same morphology both in emission line and in continuum maps; only in two objects, Mrk 32 and Tololo 1434+032, the distributions of the ionized gas and of the stars differ considerably. In general the different excitation maps for a same object display the same pattern and trace the star-forming regions, as expected for objects ionized by hot stars; only the outer regions of Mrk 32, I Zw 123 and I Zw 159 display higher [S ii]/Hα values, suggestive of shocks. Six galaxies display an inhomogeneous dust distribution. Regarding the kinematics, Mrk 750, Mrk 206 and I Zw 159 display a clear rotation pattern, while in Mrk 32, Mrk 475 and I Zw 123 the velocity fields are flat.

Spectrophotometric investigations of blue compact dwarf galaxies : Markarian 35

We present results from a detailed spectrophotometric analysis of the blue compact dwarf galaxy Mrk 35 (Haro 3), based on deep optical (BVRI) and near-IR (JHK) imaging, Hα narrowband observations, and long-slit spectroscopy. The optical emission of the galaxy is dominated by a central young starburst, with a barlike shape, while an underlying component of stars, with elliptical isophotes and red colors, extends more than 4 kpc from the galaxy center. High-resolution Hα and color maps allow us to identify the star-forming regions, to spatially discriminate them from the older stars, and to recognize several dust patches. We derive colors and Hα parameters for all the identified star-forming knots. Observables derived for each knot are corrected for the contribution of the underlying older stellar population, the contribution by emission lines, and from interstellar extinction, and compared with evolutionary synthesis models. We find that the contributions of these three factors are by no means negligible and that they significantly vary across the galaxy. Therefore, careful quantification and subtraction of emission lines, galaxy host contribution, and interstellar reddening at every galaxy position are essential to derive the properties of the young stars in blue compact dwarfs. We find that we can reproduce the colors of all the knots with an instantaneous burst of star formation and the Salpeter initial mass function with an upper mass limit of 100 M☉. In all cases the knots are just a few Myr old. The underlying population of stars has colors consistent with being several Gyr old.

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 ��� 3.6 m telescope. This work enlarges the samples presented in preceding papers of this study (Noeske et al. 2003, AA Cairos et al. 2003, ApJ, 593, 312) 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.

Three-dimensional Spectroscopy of Blue Compact Galaxies: Diagnostic Diagrams

Here we present the analysis of three-dimensional spectroscopic data of three blue compact galaxies (Mrk 324, Mrk 370, and III Zw 102). Each of the more than 22,500 spectra obtained for each galaxy has been fitted by a single Gaussian from which we have inferred the velocity dispersion (σ), the peak intensity (Ipeak), and the central wavelength (λc). The analysis shows that the σ versus Ipeak diagrams look remarkably similar to those obtained for giant extragalactic H II regions. They all present a supersonic narrow horizontal band that extends across the entire range of intensities and that results from the massive nuclear star-forming regions of each galaxy. The σ versus Ipeak diagrams also present several inclined bands of lower intensity and an even larger σ arising from the large galactic volumes that surround the main central emitting knots. We also show that the σ versus λc and λc versus Ipeak diagrams are powerful tools that are able to unveil the presence of high- and low-mass stellar clusters, and thus allow for the possibility of inferring the star formation activity of distant galaxies even if they are not spatially resolved.