222 research outputs found
Identification of a galaxy responsible for a high-redshift Lyman-α absorption system
Damped Lyman-α systems are high-column-density intergalactic clouds of hydrogen, the existence of which is inferred from absorption lines appearing in the emission spectra of distant quasars. The galaxies believed to be responsible for these absorption systems have been suggested as possible progenitors of the normal disk galaxies observed in the local Universe. Indeed, Lyman-α systems appear to contain a substantial fraction of the baryons known to exist in galaxies today. Here we report the optical detection of a galaxy (designated DLA2233 + 131) associated with a known damped Lyman-α absorption system at a redshift of z = 3.150. The properties of this galaxy correspond closely to those expected of a young disk galaxy in the early stages of formation, and show no evidence for an active nucleus. This finding gives strong support to the idea that damped Lyman-α systems represent a population of young galaxies at high red-shifts
A Tolman Surface Brightness Test for Universal Expansion, and the Evolution of Elliptical Galaxies in Distant Clusters
We use the intercept of the elliptical galaxy radius--surface brightness (SB)
relation at a fixed metric radius as the standard condition for the Tolman SB
test of the universal expansion. We use surface photometry in the optical and
near-IR of elliptical galaxies in Abell~2390 () and Abell~851
(), and compare them to the Coma cluster at . The
photometric data for each cluster are well-described by the Kormendy relation
, where in the optical and in the
near-IR. The scatter about this near-IR relation is only in
at the highest redshift, which is much smaller than at low redshifts,
suggesting a remarkable homogeneity of the cluster elliptical population at
. We use the intercept of these fixed-slope correlations at ~kpc (assuming ~km~s~Mpc, , and
, where the results are only weakly dependent on the cosmology) to
construct the Tolman SB test for these three clusters. The data are fully
consistent with universal expansion if we assume simple models of passive
evolution for elliptical galaxies, but are inconsistent with a non-expanding
geometry (the tired light cosmology) at the confidence level at
. These results suggest luminosity evolution in the restframe -band
of ~mag from to the present, and are consistent with
the ellipticals having formed at high redshift. The SB intercept in elliptical
galaxy correlations is thus a powerful tool for investigating models of their
evolution for significant lookback times.Comment: to appear in The Astrophysical Journal (Letters); 13 pages, including
3 Postscript figures and 1 table; uuencoded, compressed format; the paper is
also available in various formats from
http://astro.caltech.edu/~map/map.bibliography.refereed.htm
The scaling relations of early--type galaxies in clusters I. Surface photometry in seven nearby clusters
This is the first paper of a series investigating the scaling relations of
early-type galaxies in clusters. Here we illustrate the multi-band imagery and
the image reduction and calibration procedures relative to the whole sample of
22 clusters at 0.05 < z < 0.25. We also present the detailed surface photometry
of 312 early-type galaxies in 7 clusters in the first redshift bin,
z~0.025-0.075. We give for each galaxy the complete set of luminosity and
geometrical profiles, and and a number of global, photometric and morphological
parameters. They have been evaluated taking into account the effects of seeing.
Internal consistency checks and comparisons with data in the literature confirm
the quality of our analysis. These data, together with the spectroscopic ones
presented in the second paper of the series, will provide the local calibration
of the scaling relations.Comment: 36 pages, 13 figures, 7 tables, accepted for publication in A&
Faint M-dwarfs and the structure of the Galactic disk
We use broadband photometry and low-resolution spectra of a complete sample
of late-K and M dwarfs brighter than I=22 in three fields at high galactic
latitude to study issues relating to galactic structure and large scale
abundance gradients in the Galaxy. The observed starcounts in each field are a
good match to the predictions of models based on deep starcount data in other
intermediate-latitude fields, and these models identify the late-type stars as
members of the Galactic disk. Abundances for these late type stars are
estimated via narrowband indices that measure the strength of the TiO and CaH
bands in their spectra. Our results show that the average abundance in the
Galactic disk remains close to solar even at heights of more than 2 kpc above
the Plane.Comment: to appear in PASP; 17 pages, including 7 embedded, postscript figures
and 1 embedded table; uses AAS LaTeX style files (not included); also
available at http://astro.caltech.edu/~map/map.bibliography.htm
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