9. CONCLUSIONS

Summarizing,

• B, R, and H images for a total of 114 galaxies have been obtained. According to the new set of criteria proposed to define the Blue Compact Dwarf class of galaxies all except 9 objects (II Zw 33, Mrk 7, Tol 1924-416, Mrk 314, II Zw 33B, UGC 4483, UCM 0049-0045, UCM 1446+2312, & VCC 0001) are classified as BCDs. This represents an increase of a factor of ~ 4 with respect to similar previous studies (Doublier et al. 1997, 1999; Cairós et al. 2001a, b). Indeed, previous studies were mostly based on only broad-band imaging data.
• The new set of criteria proposed for defining a galaxy as a BCD includes a limit in K-band luminosity (M_K > -21 mag), the peak surface brigthness (µ_{B, peak} < 22 mag/arcsec²), and the color at the peak surface brightness (µ_{B, peak} - µ_{R, peak} 1).
• The flux-calibrated and WCS-compliant images of the Atlas are publicly available through the NASA/IPAC Extragalactic Database (NED) image service on a object-by-objects basis and through a dedicated web page within LEVEL5: A Knowledgebase for Extragalactic Astronomy & Cosmology (/level5/).
• In all but three galaxies we detect H-line emission. About 73% of the galaxies show H emission distributed in more than one region (39% in 4 or more regions). Morphologically, 24% of the galaxies are classified as nE BCDs, 33% as iE, 35% as iI (10% cometary BCDs -iI,C- and 9% mergers -iI,M-), and 7% as i0 BCDs (see Loose & Thuan 1986). Four of the galaxies (Mrk 86, Mrk 400, Mrk 409, VCC 0655) show a nuclear ring of star-forming regions with radius 0.5-1kpc.
• Average colors, absolute magnitudes and H luminosities of the sample are (B - R) = 0.7 ± 0.3 mag, M_B = -16.1 ± 1.4mag, and log(L_H) = 40.0 ± 0.6 (erg s^-1). Galaxies classified as nE and iE BCDs show, on average, redder colors and lower H equivalent widths than those classified as iI and i0 BCDs. This is also true if only the iI-type BCDs are considered.
• For most of the galaxies ( ~ 80%) the integrated (B - R) colors and H equivalent widths require the presence of an evolved, underlying stellar population in addition to a young population with burst strength lower than 10% in mass. The most metal-poor BCDs (I Zw 18, Tol 65, UCM 1612+1308) are found in that 20% of the sample whose properties are compatible with the evolution of a pure, young burst. They also show the bluest colors and highest equivalent widths within the sample. However, due to the degraded sensitivity of the (B - R) color to the presence of an underlying stellar population for burst strengths 10%, the use of deep near-infrared imaging data will be required to further investigate, in a statistical way, their nature as young galaxies.

We are grateful to the Palomar and Las Campanas observatories staff for their support and hospitality, and to the Caltech/Palomar and OCIW/Las Campanas Time Allocation Committees for the generous allocation of time to this project. AGdP acknowledges financial support from NASA through a Long Term Space Astrophysics grant to BFM. AGdP is also partially supported by the CONACYT (Mexico) grant 36132-E and the Spanish Programa Nacional de Astronomía y Astrofísica under grant AYA2000-1790. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We would like also to thank K. G. Noeske , P. G. Pérez-González, and C. Sánchez Contreras for valuable discussions and the NED/LEVEL5 staff for helping us making this Atlas publicly available. For technical support on using the images from this atlas, please write to ned@ipac.caltech.edu or to one of the authors (agpaz, barry, olga@ipac.caltech.edu). We are grateful to the anonymous referee for her/his helpful comments and suggestions.