Alexei Kniazev

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Galactic Structure

Galactic Structure:

During of last time I also was involved in an MPIA project to study Galactic Structure based on Sloan Digital Sky Survey (SDSS) stellar photometry. Our research concentrates on the following topics: (a) A study of structural parameters of globular clusters and a search for tidal disruption. (b) A study of structural parameters of Milky Way satellite galaxies and search for extratidal features. (c) A search for tidal streams of disrupted satellites in the Galactic halo and for new low surface brightness members of the Local Group. During this period of time I have created my own software to produce a matched-filter analysis of stellar density data, the derivation of surface photometry parameters and the analysis of surface brightness profiles using stellar counts. We have currently some exciting results from studying M31 SDSS data:

(1) we found a faint, extended stellar feature in the outer halo of M31, using a special scan from SDSS. Though the scan is relatively shallow, it covers a very large area along the major axis of M31, and reaches depths sufficient to detect bright red giant stars at the distance of M31. We used these data to estimate the feature's physical properties, such as its size and total luminosity, and to try to determine its true nature (see SDSS press-release:

M31 Stellar Substructure in the SDSS data
M31 Stellar Substructure in the SDSS Data: Top: The spatial distribution of all stars with 21 < i < 22, with an inset optical image of M31 to scale. The arrows indicate major halo substructures: the northern spur (NS), the giant stream (GS) and the G1 clump (G1C). Anromeda NE's center is located at about (3,0.5). Bottom: Same as (top), but with the grayscale adjusted to emphasize faint details. The arrow shows the position of Andromeda NE. The data in both pa
nels have been binned 2' x 2'. X and Y are in arcdegrees from the center of M31 (00:42:44.3 +41:16:08.5 J2000), along the major and minor axes, respectively.
(From Zucker, D.B., Kniazev, A.Y. et al., New Giant Stellar Structure Near the Outer Halo of M31: Satellite or Stream?, 2004, submitted to ApJL (astro-ph/0401098).).

(2) w
e reported the discovery of a new dwarf spheroidal satellite of M31, Andromeda IX. Using both SDSS and public archival data we have estimated its distance and other physical properties, and compared these to the properties of a previously known dwarf spheroidal companion, Andromeda V, also observed by SDSS. Based on our measurements, Andromeda IX is the lowest surface brightness galaxy found to date (mu_{V,0} ~ 27.0 mag/arcsec^2), and at the distance we estimate from the position of the tip of Andromeda IX's red giant branch, (m - M)_0 ~ 24.5 (805 kpc), Andromeda IX is the faintest galaxy as well (M(V) ~ -8.3).

Andromeda V and Andromeda IX as seen by SDSS
Andromeda V and Andromeda IX as seen by SDSS: Top: The spatial distribution of all SDSS stars with i > 20.5 in the fields of Andromeda V (left) and Andromeda IX. The data in both panels were binned
30" x 30"
and smoothed with a Gaussian (FWHM = 1').
Bottom: Combined g, r and i SDSS images of Andromeda V (left) and Andromeda IX. Each panel spans 14' x 14' and is oriented with north up and east to the left.

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