36 research outputs found
Clustering of red Galaxies near the Radio-loud Quasar 1335.8+2834 at z=1.1
We have obtained new deep optical and near-infrared images of the field of
the radio-loud quasar 1335.8+2834 at where an excess in the surface
number density of galaxies was reported by Hutchings et al. [AJ, 106, 1324]
from optical data. We found a significant clustering of objects with very red
optical-near infrared colors, and near the quasar. The colors and magnitudes of the reddest objects
are consistent with those of old (12 Gyr old at z=0) passively-evolving
elliptical galaxies seen at , clearly defining a `red envelope' like
that found in galaxy clusters at similar or lower redshifts. This evidence
strongly suggests that the quasar resides in a moderately-rich cluster of
galaxies (richness-class ). There is also a relatively large fraction
of objects with moderately red colors () which have a
distribution on the sky similar to that of the reddest objects. They may be
interpreted as cluster galaxies with some recent or on-going star formation.Comment: 14 pages text, 5 PostScript figures, 1 GIF figure, and 1 combined PS
file. Accepted for ApJ, Letter
Near-Infrared Integral Field Spectroscopy of Damped Lyman-alpha Systems
We assess the feasibility of detecting star formation in damped Lyman-alpha
systems (DLAs) at z>1 through near-infrared spectroscopy using the forthcoming
integral field units on 8m-class telescopes. Although their relation to
galaxies is not well established, high-z DLAs contain most of the neutral gas
in the Universe, and this reservoir is depleted with time - presumably through
star formation. Line emission should be an indicator of star formation
activity, but searches based on Lyman-alpha are unreliable because of the
selective extinction of this resonant UV line. Using more robust lines such as
H-alpha forces a move to the near-infrared at z>1. For line emission searches,
spectroscopy is more sensitive than imaging, but previous long-slit
spectroscopic searches have been hampered by the likelihood that any star
forming region in the DLA galaxy disk would fall outside the narrow slit. The
new integral field units such as CIRPASS on Gemini will cover sufficient solid
angles to intercept these, even in the extreme case of large galactic disks at
high redshift. On an 8m-class telescope, star formation rates of <1M_sun/yr
will be reached at z~1.4 with H-alpha in the H-band. Such star formation rates
are well below L* for the high-z Lyman-break population, and are comparable
locally to the luminous giant HII complexes in M101. It appears that
instruments such as CIRPASS on Gemini will have both the sensitivity and the
survey area to measure star formation rates in z>1 DLAs. These observations
will probe the nature of damped Lyman-alpha systems and address their relation
to galaxies.Comment: To appear in the proceedings of the ESO/ECF workshop on "Deep
Fields", 9-12 October 2000, Garching. 4 page
A Rich Cluster of Galaxies Near the Quasar B2 1335+28 at z=1.1: Color Distribution and Star-Formation Properties
We previously reported a significant clustering of red galaxies (R-K=3.5--6)
around the radio-loud quasar B2 1335+28 at z=1.086. In this paper, we establish
the existence of a rich cluster at the quasar redshift, and study the
properties of the cluster galaxies through further detailed analysis of the
photometric data. The color distribution of the galaxies in the cluster is
quite broad and the fraction of blue galaxies (\sim 70%) is much larger than in
intermediate-redshift clusters. Using evolutionary synthesis models, we show
that this color distribution can be explained by galaxies with various amounts
of star-formation activity mixed with the old stellar populations. Notably,
there are about a dozen galaxies which show very red optical-NIR colors but
also show significant UV excess with respect to passive-evolution models. They
can be interpreted as old early-type galaxies with a small amount of star
formation. The fact that the UV-excess red galaxies are more abundant than the
quiescent red ones suggests that a large fraction of old galaxies in this
cluster are still forming stars to some extent. However, a sequence of
quiescent red galaxies is clearly identified on the R-K versus K
color-magnitude (C-M) diagram. The slope and zero point of their C-M relation
appear to be consistent with those expected for the precursors of the C-M
relation of present-day cluster ellipticals when observed at z=1.1. We estimate
the Abell richness class of the cluster to be R \sim 1. New X-ray data
presented here place an upper limit of L_x < 2 10^{44} erg s^{-1} for the
cluster luminosity. Inspections of the wider optical images reveal some lumpy
structure, suggesting that the whole system is still dynamically young.Comment: 54 pages including 13 Postscript figures, 1 jpg figure, and 1 table,
uses aasms4.sty and epsf.sty. Accepted for publication in ApJ: Replaced as
the older verison was missed to include the figure 2c, 2d, and figure
The build-up of the colour-magnitude relation in galaxy clusters since z~0.8
Using galaxy clusters from the ESO Distant Cluster Survey, we study how the
distribution of galaxies along the colour-magnitude relation has evolved since
z~0.8. While red-sequence galaxies in all these clusters are well described by
an old, passively evolving population, we confirm our previous finding of a
significant evolution in their luminosity distribution as a function of
redshift. When compared to galaxy clusters in the local Universe, the high
redshift EDisCS clusters exhibit a significant "deficit" of faint red galaxies.
Combining clusters in three different redshift bins, and defining as `faint'
all galaxies in the range 0.4 > L/L* > 0.1, we find a clear decrease in the
luminous-to-faint ratio of red galaxies from z~0.8 to z~0.4. The amount of such
a decrease appears to be in qualitative agreement with predictions of a model
where the blue bright galaxies that populate the colour-magnitude diagram of
high redshift clusters, have their star formation suppressed by the hostile
cluster environment. Although model results need to be interpreted with
caution, our findings clearly indicate that the red-sequence population of
high-redshift clusters does not contain all progenitors of nearby red-sequence
cluster galaxies. A significant fraction of these must have moved onto the
red-sequence below z~0.8.Comment: 15 pages, 10 figures, accepted for publication in MNRA