150 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
Galaxy destruction and diffuse light in clusters
Deep images of the Centaurus and Coma clusters reveal two spectacular arcs of
diffuse light that stretch for over 100 kpc, yet are just a few kpc wide. At a
surface brightness of m_b \sim 27-28th arcsec^-2, the Centaurus arc is the most
striking example known of structure in the diffuse light component of a rich
galaxy cluster. We use numerical simulations to show that the Centaurus feature
can be reproduced by the tidal debris of a spiral galaxy that has been tidally
disrupted by the gravitational potential of NGC 4709. The surface brightness
and narrow dimensions of the diffuse light suggest that the disk was
co-rotating with its orbital path past pericentre. Features this prominent in
clusters will be relatively rare, although at fainter surface brightness levels
the diffuse light will reveal a wealth of structure. Deeper imaging surveys may
be able to trace this feature for several times its presently observed extent
and somewhere along the tidal debris, a fraction of the original stellar
component of the disk will remain bound, but transformed into a faint
spheroidal galaxy. It should be possible to confirm the galactic origin of the
Centaurus arc by observing planetary nebulae along its length with redshifts
close to that of NGC 4709.Comment: Replaced with version accepted by MNRAS (Dec. 1999): Added missing
reference (to pg. 4 & reference list). Section 3 shortened; removed three
figures. Now 8 pages long, with 8 figures. Low resolution images included,
high resolution version available at
http://star-www.dur.ac.uk:80/~calcaneo/cenarc.htm
Angular clustering in the SUMSS radio survey
We measure the angular correlation function of radio galaxies selected by the
843 MHz Sydney University Molonglo Sky Survey (SUMSS). We find that the
characteristic imprint of large-scale structure is clearly detectable, and that
the survey is very uniform. Through comparison with similar analyses for other
wide-area radio surveys - the 1400 MHz NRAO VLA Sky Survey (NVSS) and the 325
MHz Westerbork Northern Sky Survey (WENSS) - we are able to derive consistent
angular clustering parameters, including a steep slope for the clustering
function, . We revise upwards previous
estimates of the NVSS clustering amplitude, and find no evidence for dependence
of clustering properties on radio frequency. It is important to incorporate the
full covariance matrix when fitting parameters to the measured correlation
function. Once the redshift distribution for mJy radio galaxies has been
determined, these projected clustering measurements will permit a robust
description of large-scale structure at , the median redshift of
the sources.Comment: 8 pages, 9 figures, accepted for publication by MNRA
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