Preprint typeset using LATEX style emulateapj v. 11/10/09 A COMPLETE SPECTROSCOPIC SURVEY OF THE MILKY WAY SATELLITE SEGUE 1: THE DARKEST GALAXY* (original) (raw)
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2011
We investigate the kinematic and photometric properties of the Segue 3 Milky Way companion using Keck/DEIMOS spectroscopy and Magellan/IMACS g and r-band imaging. Using maximum likelihood methods to analyze the photometry, we study the structure and stellar population of Segue 3. We find the half–light radius of Segue 3 is 26′ ′ ± 5′ ′ (2.1 ± 0.4 pc, for a distance of 17 kpc) and the absolute magnitude is a mere MV = 0.0 ± 0.8 mag, making Segue 3 the least luminous old stellar system known. We find Segue 3 to be consistent with a single stellar population, with an age of 12.0+1.5−0.4 Gyr and an [Fe/H] of −1.7+0.07−0.27. Line–of–sight velocities from the spectra are combined with the photometry to determine a sample of 32 stars which are likely associated with Segue 3. The member stars within three half–light radii have a velocity dispersion of 1.2±2.6 km s−1. Photometry of the members indicates the stellar population has a spread in [Fe/H] of ∼< 0.3 dex. These facts, together wit...
Publications of the Astronomical Society of Australia, 2004
Although the Sloan Digital Sky Survey (SDSS) was primarily envisioned as a tool for understanding the nature of the ‘high redshift’ universe, significant discoveries have already been made at lower redshift,z∼ 0, through studies of stars in the Milky Way galaxy. We have begun to explore the nature of the Milky Way by detailed investigation of the publicly accessible SDSS archive, using spectroscopically targeted stars of special interest (e.g. field horizontal-branch stars, carbon-enhanced stars, and F- and G-type turnoff stars), as well as the stars originally selected as photometric and reddening standards. The first step is to use the SDSS data (which includes independently calibrated five-band photometry and spectrophotometry of individual stars) to derive reliable estimates of the stellar physical parameters, such as Teff, logg, and [Fe/H], for stars that have been observed to date. Of particular interest, at present, are the stars that are apparently associated with the Monoce...
2006
We present reliable measurements of the metallicity distribution function (MDF) at different points along the tidal stream of the Sagittarius (Sgr) dwarf spheroidal (dSph) galaxy, based on high resolution, echelle spectroscopy of candidate M giant members of the Sgr system. The Sgr MDF is found to evolve significantly from a median [Fe/H] ~-0.4 in the core to ~-1.1 dex over a Sgr leading arm length representing ~2.5-3.0 Gyr of dynamical (i.e. tidal stripping) age. This is direct evidence that there can be significant chemical differences between current dSph satellites and the bulk of the stars they have contributed to the halo. Our results suggest that Sgr experienced a significant change in binding energy over the past several Gyr, which has substantially decreased its tidal boundary across a radial range over which there must have been a significant metallicity gradient in the progenitor galaxy. By accounting for MDF variation along the debris arms, we approximate the MDF Sgr would have had several Gyr ago. We also analyze the MDF of a moving group of M giants we previously discovered towards the North Galactic Cap having opposite radial velocities to the infalling Sgr leading arm stars there and propose that most of these represent Sgr trailing arm stars overlapping the Sgr leading arm in this part of the sky. If so, these trailing arm stars further demonstrate the strong MDF evolution within the Sgr stream.