Palomar/Las Campanas Imaging Atlas of Blue Compact Dwarf Galaxies: II. Surface Photometry and the Properties of the Underlying Stellar Population

We present the results from an analysis of surface photometry of B, R, and Halpha images of a total of 114 nearby galaxies drawn from the Palomar/Las Campanas Imaging Atlas of Blue Compact Dwarf galaxies. Surface brightness and color profiles for the complete sample have been obtained. We determine the exponential and Sersic profiles that best fit the surface brightness distribution of the underlying stellar population detected in these galaxies. We also compute the (B-R) color and total absolute magnitude of the underlying stellar population and compared them to the integrated properties of the galaxies in the sample. Our analysis shows that the (B-R) color of the underlying population is systematically redder than the integrated color, except in those galaxies where the integrated colors are strongly contaminated by line and nebular-continuum emission. We also find that galaxies with relatively red underlying stellar populations (typically (B-R)>~1mag) show structural properties compatible with those of dwarf elliptical galaxies (i.e. a smooth light distribution, fainter extrapolated central surface brightness and larger scale lengths than BCD galaxies with blue underlying stellar populations). At least ~15% of the galaxies in the sample are compatible with being dwarf elliptical (dE) galaxies experiencing a burst of star formation. For the remaining BCD galaxies in the sample we do not find any correlation between the recent star formation activity and their structural differences with respect to other types of dwarf galaxies.Comment: 35 pages, 6 figures, accepted for publication in ApJS. Postscript files of panels f1a-f1o of figure 1 are available online at http://www.ociw.edu/~agpaz/astro-ph/apjs2004

Global velocity field and bubbles in the BCD Mrk86

We have studied the velocity field of the Blue Compact Dwarf galaxy Mrk86 (NGC2537) using data provided by 14 long-slit optical spectra. This kinematical information is complemented with narrow-band ([OIII]5007A and Halpha) and broad-band (B, V, Gunn-r and K) imaging. The analysis of the galaxy global velocity field suggests that the ionized gas could be distributed in a rotating inclined disk, with projected central angular velocity of Omega=34 km/s/kpc. The comparison between the stellar, HI and modeled dark matter density profile, indicates that the total mass within its optical radius is dominated by the stellar component. Peculiarities observed in its velocity field can be explained by irregularities in the ionized gas distribution or local motions induced by star formation. Kinematical evidences for two expanding bubbles, Mrk86-B and Mrk86-C, are given. They show expanding velocities of 34 km/s and 17 km/s, Halpha luminosities of 3x10^38 erg/s and 1.7x10^39 erg/s, and physical radii of 374 and 120 pc, respectively. The change in the [SII]/Halpha, [NII]/Halpha, [OII]/[OIII] and [OIII]/Hbeta line ratios with the distance to the bubble precursor suggests a diminution in the ionization parameter and, in the case of Mrk86-B, an enhancement of the shock-excited gas emission. The optical-near-infrared colours of the bubble precursors are characteristic of low metallicity star forming regions (0.2 Zsun) with burst strengths of about 1 per cent in mass.Comment: 14 pages, 12 PostScript figures, accepted for publication in MNRAS, also available at ftp://cutrex.fis.ucm.es/pub/OUT/gil/PAPERS

A classical morphological analysis of galaxies in the Spitzer Survey of Stellar Structure in Galaxies (S ^(4) G)

The Spitzer Survey of Stellar Structure in Galaxies (S(4)G) is the largest available database of deep, homogeneous middle-infrared (mid-IR) images of galaxies of all types. The survey, which includes 2352 nearby galaxies, reveals galaxy morphology only minimally affected by interstellar extinction. This paper presents an atlas and classifications of S(4)G galaxies in the Comprehensive de Vaucouleurs revised Hubble-Sandage (CVRHS) system. The CVRHS system follows the precepts of classical de Vaucouleurs morphology, modified to include recognition of other features such as inner, outer, and nuclear lenses, nuclear rings, bars, and disks, spheroidal galaxies, X patterns and box/peanut structures, OLR subclass outer rings and pseudorings, bar ansae and barlenses, parallel sequence latetypes, thick disks, and embedded disks in 3D early-type systems. We show that our CVRHS classifications are internally consistent, and that nearly half of the S(4)G sample consists of extreme late-type systems (mostly bulgeless, pure disk galaxies) in the range Scd-Im. The most common family classification for mid-IR types S0/a to Sc is SA while that for types Scd to Sm is SB. The bars in these two type domains are very different in mid-IR structure and morphology. This paper examines the bar, ring, and type classification fractions in the sample, and also includes several montages of images highlighting the various kinds of "stellar structures" seen in mid-IR galaxy morphology

Systematic Variations of CO J=2-1/1-0 Ratio and Their Implications in The Nearby Barred Spiral Galaxy M83

We present spatial variations of the CO J = 2−1/1–0 line ratio (R_(21/10)) in the barred spiral galaxy M83 using Total Power Array (single-dish telescopes) data from the Atacama Large Millimeter/submillimeter Array. While the intensities of these two lines correlate tightly, R_(21/10) varies over the disk, with a disk average ratio of 0.69, and shows the galactic center and a two-arm spiral pattern. It is high (>̰0.7) in regions of high molecular gas surface density (Σ_(mol)), but ranges from low to high ratios in regions of low Σ_(mol). The ratio correlates well with the spatial distributions and intensities of far-ultraviolet (FUV) and infrared (IR) emissions, with FUV being the best correlated. It also correlates better with the ratio of specific intensities at 70 and 350 μm, a proxy for dust temperature, than with the IR intensities. Taken together, these results suggest either a direct or indirect link between the dust heating by the interstellar radiation field and the condition of giant molecular clouds (GMCs), even though no efficient mechanism is known for a thermal coupling of dust and bulk gas in GMCs. We speculate that the large spread of R_(21/10)in low Σ_(mol) regions, mostly at the downstream sides of spiral arms, may be due to the evolution of massive stars after spiral arm passage. Having in a late phase escaped from the spiral arms and their parental clouds, they may contribute to the dust heating by FUV and gas heating by cosmic rays produced by supernovae

MEGARA. High-precision alignment system for gluing fibers and microlenses

MEGARA is the multi-object medium-resolution spectrograph for the GTC 10m telescope. MEGARA offers two observing modes, the LCB mode, a large central IFU; and a MOS mode composed by 92 robotic positioners carrying 7 fibers minibundles. Microlens are required to fit the GTC f/17 to the f/3 at the fiber entrance, where pupil image is oversized to have a fiber-to-fiber flux variation better than 10%. This tight requirement imposed manufacturing tolerances for the different components and required the development of a gluing station to provide a centering precision better than 5μm. We present the overview of the optical bundles, the gluing station and the final performance obtained during the integration and tests

An Empirical Connection between the UV Color of Early Type Galaxies and the Stellar Initial Mass Function

Using new UV magnitudes for a sample of early-type galaxies, ETGs, with published stellar mass-to-light ratios, Upsilon_*, we find a correlation between UV color and Upsilon_* that is tighter than those previously identified between Upsilon_* and either the central stellar velocity dispersion, metallicity, or alpha enhancement. The sense of the correlation is that galaxies with larger Upsilon_* are bluer in the UV. We conjecture that differences in the lower mass end of the stellar initial mass function, IMF, are related to the nature of the extreme horizontal branch populations that are generally responsible for the UV flux in ETGs. If so, then UV color can be used to identify ETGs with particular IMF properties and to estimate Upsilon_*.Comment: Submitted for publication in ApJ Letter