Alexei Kniazev

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Galactic Structure
Low-Surface-Brightness Galaxies:

Low-Surface-Brightness Galaxies started to be my scientific interest mainly during last 2.5 years of my work at MPIA (Heidelberg). The understanding of the important role of LSB galaxies for many issues of extragalactic research has come during the last 10-15 years. The detection of LSBGs is difficult owing to their intrinsically low global luminosities and their characteristic low surface brightness. Despite more than 25 years of LSBGs studies, their census remains highly incomplete. However, a thorough understanding of the properties of the LSB population is crucial for a number of fundamental questions in astrophysics, for instance: (a) the baryon mass fraction in the Universe; (b) the galaxy luminosity function, especially at its faint end; (c) the spatial distribution of lower-mass galaxies; (d) the physics of star formation at low gas surface densities; (e) the role of environment in galaxy evolution.

SDSS is uniquely suited to searches for and studies of LSBGs due to its homogeneity, area coverage, and depth. For this reason we proposed a project to search for LSBGs using the SDSS. The first goal of the project is to create a well-defined, large, uniform, and complete sample of LSBGs based on SDSS imaging data down to a surface brightness limit of 26.5 mag arcsec$^2$ in $g$. To deal with the SDSS data most effectively I developed my own programs to search for galaxies with defined angular sizes from SDSS images and to perform their integrated and surface photometry. The reliability of these programs was carefully tested using a training subsample of galaxies. This allowed me to choose my selection criteria such that I achieved very high efficiency in recovering galaxies from the test sample, limited only by cases when a candidate galaxy falls too close to a very bright star or galaxy.

I used Sloan Digital Sky Survey (SDSS) imaging data to establish a sample of all galaxies with radii $\ge$ 12$''$ and $\mu_{\rm lim}(g) \ge 26.5$ mag arcsec$^{-2}$ within an area of 228 deg$^2$ using my own detection and analysis software. The redshifts for these galaxies were collected from the SDSS, NED and 2dF databases. The total and surface photometry was produced for ALL selected galaxies in 5 bands. For all these galaxies their ugriz surface brightness profiles were determined and their $\mu_0$ using bulge/disk fitting routines in addition to $\mu_{\rm eff}$ were done. From the resulting sample of $\sim$5500 galaxies, I extracted a subsample with cz $\le$ 10000 kms$^{-1}$, which will be one of the most complete to probe galaxy content and properties of the Local Universe. A subset of 150 LSBGs had no redshifts because they are either below the SDSS spectroscopical limit or remained undetected by regular SDSS software. We spectroscopically observed all these LSBGs with the 2.2m and 3.6m telescopes at Calar Alto, the 6m of SAO RAS, NTT at La Silla (Chile) and VLT (Paranal,Chile) to determine their redshifts and to complete the sample of nearby galaxies in this region for more detailed analysis. All spectral data have been reduced now.

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South African Astronomical Observatory Last Updated: 10.December.2005