Comparing Ultraviolet and Infrared-Selected Starburst Galaxies in Dust Obscuration and Luminosity

We present samples of starburst galaxies that represent the extremes discovered with infrared and ultraviolet observations, including 25 Markarian galaxies, 23 ultraviolet luminous galaxies discovered with GALEX, and the 50 starburst galaxies having the largest infrared/ultraviolet ratios. These sources have z < 0.5 and cover a luminosity range of ~ 10^4. Comparisons between infrared luminosities determined with the 7.7 um PAH feature and ultraviolet luminosities from the stellar continuum at 153 nm are used to determine obscuration in starbursts and dependence of this obscuration on infrared or ultraviolet luminosity. A strong selection effect arises for the ultraviolet-selected samples: the brightest sources appear bright because they have the least obscuration. Obscuration correction for the ultraviolet-selected Markarian+GALEX sample has the form log[UV(intrinsic)/UV(observed)] = 0.07(+-0.04)M(UV)+2.09+-0.69 but for the full infrared-selected Spitzer sample is log[UV(intrinsic)/UV(observed)] = 0.17(+-0.02)M(UV)+4.55+-0.4. The relation of total bolometric luminosity L_{ir} to M(UV) is also determined for infrared-selected and ultraviolet-selected samples. For ultraviolet-selected galaxies, log L_{ir} = -(0.33+-0.04)M(UV)+4.52+-0.69. For the full infrared-selected sample, log L_{ir} = -(0.23+-0.02)M(UV)+6.99+-0.41, all for L_{ir} in solar luminosities and M(UV) the AB magnitude at rest frame 153 nm. These results imply that obscuration corrections by factors of two to three determined from reddening of the ultraviolet continuum for Lyman Break Galaxies with z > 2 are insufficient, and should be at least a factor of 10 for M(UV) about -17, with decreasing correction for more luminous sources.Comment: accepted for publication in The Astrophysical Journa

The DFBS Spectroscopic Database and the Armenian Virtual Observatory

The Digitized First Byurakan Survey (DFBS) is the digitized version of the famous Markarian Survey. It is the largest low-dispersion spectroscopic survey of the sky, covering 17,000 square degrees at galactic latitudes |b|>15. DFBS provides images and extracted spectra for all objects present in the FBS plates. Programs were developed to compute astrometric solution, extract spectra, and apply wavelength and photometric calibration for objects. A DFBS database and catalog has been assembled containing data for nearly 20,000,000 objects. A classification scheme for the DFBS spectra is being developed. The Armenian Virtual Observatory is based on the DFBS database and other large-area surveys and catalogue data

Search and Study of UV-Excess Objects in the DFBS Database Authors:

DFBS is a digitized version of the famous Markarian survey (or the First Byurakan Survey, FBS). The project has been carried out by teams from Byurakan, Rome and Cornell, using an EPSON Expression 1680 Pro scanner. The DFBS will serve as a unique spectroscopic database for studies in large areas (total surface is 17,000 sq. degrees) at high galactic latitudes, approximate classification for objects (20,000,000 objects are present), selection of samples of objects for definite studies (UV-excess objects, extremely red objects, variables, etc.). A joint usage of the direct images and spectra give larger possibilities for various studies and more efficient use of the survey. Using the dedicated BSpec software written by one of the authors (GC), we have obtained a list of DFBS stars, their positions, B and R magnitudes, and preliminarily classification for DFBS zones with central DEC=+39° and DEC=+43°. The spectral length l>90pix (compared to the total length 10^7pix) was used as a criterion to search for UV-excess objects, as this corresponds to the criteria used during the 2nd part of the FBS. However, the spectra of objects with B80pix), as their spectra are shorter. An additional point for the UV excess object classification is the following: the spectra of the UV-excess objects are divided into two parts by a sensitivity gap in green; the red-yellow part of the spectra must be weaker and the blue-ultraviolet part must be brighter and more extended. We started the project in the DFBS zone +39° and +43° to compare the results with those obtained before during the 2nd part of the FBS. Later on, cross-correlations with available catalogs and a multi-wavelength analysis was made for the found objects. The preliminary results of the search and studies will be reported