176 research outputs found
K Giants in Baade's Window. II. The Abundance Distribution
This is the second in a series of papers in which we analyze spectra of over
400 K and M giants in Baade's Window, including most of the stars with proper
motions measured by Spaenhauer et al. [AJ, 103, 297 (1992)]. In our first
paper, we measured line--strength indices of Fe, Mg, CN and H and
calibrated them on the system of Faber et al. [ApJS, 57, 711 (1985)]. Here, we
use the index to derive an abundance distribution in
[Fe/H] for 322 stars with effective temperatures between 3900 K and 5160 K.
Our derived values of [Fe/H] agree well with those measured from
high--resolution echelle spectra (e.g., McWilliam \& Rich [ApJS, 91, 749
(1994)]) for the small number of stars in common. We find a mean abundance
for our sample of Baade's Window
K giants. More than half the sample lie in the range \feh\ .
We estimate line--of--sight distances for individual stars in our sample and
confirm that, in Baade's Window, most K giants with are foreground
disk stars, but the great majority (more than 80\%) with belong to the
bulge.
We also compare the metallicities derived from the CN and Mg indices to
those from iron. Most of the metal--rich stars in our sample appear to be
CN--weak, in contrast to the situation in metal--rich globular clusters and
elliptical galaxies. The metal--poor half of our sample ([Fe/H] ) shows
evidence for a mild Mg overenhancement ([Mg/Fe] ); but this is not
seen in the more metal--rich stars ([Fe/H] 0). The K giants in Baade's
Window therefore share some, but not all, of the characteristics of stars in
elliptical galaxies as inferred from their integrated light.Comment: Accepted for publication in the Astronomical Journal, tentatively
scheduled for July, 1996. LaTex source which generates 40 pages of text (no
figures or tables). Complete (text + 15 figs + 5 tables) preprint in gzip/tar
format is also available at
ftp://bessel.mps.ohio-state.edu/pub/terndrup/kg2.tar.gz (227 kbyte
The clustering of radio galaxies at z~0.55 from the 2SLAQ LRG survey
We examine the clustering properties of low-power radio galaxies at redshift
0.4<z<0.8, using data from the 2SLAQ Luminous Red Galaxy (LRG) survey. We find
that radio-detected LRGs (with optical luminosities of 3-5L* and 1.4GHz radio
powers between 1e24 and 1e26 W/Hz) are significantly more clustered than a
matched sample of radio-quiet LRGs with the same distribution in optical
luminosity and colour. The measured scale length of the 2pt auto-correlation
function, r0, is 12.3+/-1.2 1/h Mpc and 9.02+/-0.52 1/h Mpc for the
radio-detected and radio-quiet samples respectively. Using the halo model
framework we demonstrate that the radio-loud LRGs have typical halo masses of
10.1+/-1.4 x10^13 1/h M_sun compared to 6.44+/-0.32 x10^13 1/h M_sun for the
radio-quiet sample. A model in which the radio-detected LRGs are almost all
central galaxies within haloes provides the best fit, and we estimate that at
least 30% of LRGs with the same clustering amplitude as the radio-detected LRGs
are currently radio-loud. Our results imply that radio-loud LRGs typically
occupy more massive haloes than other LRGs of the same optical luminosity, so
the probability of finding a radio-loud AGN in a massive galaxy at z~0.55 is
influenced by the halo mass in addition to the dependence on optical
luminosity. If we model the radio-loud fraction of LRGs, F_rad, as a function
of halo mass M, then the data are well-fitted by a power law of the form F_rad
\propto M^(0.65+/-0.23). The relationship between radio emission and clustering
strength could arise either through a higher fuelling rate of gas onto the
central black holes of galaxies in the most massive haloes (producing more
powerful radio jets) or through the presence of a denser IGM (providing a more
efficient working surface for the jets, thus boosting their radio luminosity).Comment: Accepted for publication in MNRA
- …