384 research outputs found
THE CANADA-FRANCE REDSHIFT SURVEY II: Spectroscopic Program; Data for the 0000-00 and 1000+25 Fields
This paper describes the methods used to obtain the spectroscopic data and
construct redshift catalogs for the Canada-France deep Redshift Survey (CFRS).
The full data set consists of more than one thousand spectra, of objects with
17.5 < I_{AB} < 22.5, obtained from deep multi-slit data with the MARLIN and
MOS-SIS spectrographs at the CFHT. The final spectroscopic catalog contains 200
stars, 591 galaxies with secure redshifts in the range 0 < z < 1.3, 6 QSOs, and
146 objects with very uncertain or unknown redshifts, leading to an overall
success rate of identification of 85%. Additionally, 67 objects affected by
observational problems have been placed in a supplemental list.
We describe here the instrumental set up, and the observing procedures used
to efficiently gather this large data set. New optimal ways of packing spectra
on the detector to significantly increase the multiplexing gain offered by
multi-slit spectroscopy are described. Dedicated data reduction procedures have
been developed under the IRAF environment to allow for fast and accurate
processing.
Very strict procedures have been followed to establish a reliable list of
final spectroscopic measurements. Fully independent processing of the data has
been carried out by three members of the team for each data set associated with
a multi-slit mask, and final redshifts were
assigned only after the careful comparison of the three independent
measurements. A confidence class scheme was established. We strongly emphasize
the benefits of such procedures.
Finally, we present the spectroscopic data obtained for 303 objects in the
0000-00 and 1000+25 fields. The success rate in spectroscopic identification isComment: 16 uuencoded postcript pages with figures 4,5,8,9 and 12. Other
(large) figures available from the authors. Large data table not yet
released. Also available at http://www.dao.nrc.ca/DAO/SCIENCE/science.html
and coming soon on a CFRS homepage. Accepted June 19, scheduled for the Dec
10 issue of Ap
The CANADA-FRANCE REDSHIFT SURVEY I: Introduction to the Survey, Photometric Catalogs and Surface Brightness Selection Effects
The Canada-France Redshift Survey has been undertaken to provide a large
well-defined sample of faint galaxies at high redshift in which the selection
criteria match as closely as possible those of samples of nearby galaxies. The
survey is designed to have a median redshift of z ~ 0.6 corresponding to a
look-back time of half the present age of the Universe for Omega ~ 1. Such a
survey can then be used for studying many different aspects of the evolution of
galaxies over the interval 0 < z < 1. In this paper we describe the selection
of the fields, the multicolor imaging observations and the construction and
validation of the photometric catalogs. Particular attention is paid to
quantifying the unavoidable selection effects in surface brightness and their
impact on the survey is assessed in the context of the properties of known
populations of galaxies. The photometric catalogs contain several thousand
objects brighter than I_{AB}< 22.5 and are essentially complete for central
surface brightnesses as faint as 24.5 mag arcsec.
This should be sufficient to include both normal surface brightness galaxies
and prototypes of extreme low surface brightness galaxies.Comment: 17 pages, 2 tables, 10 postscript figures (in 2 parts), uses
aaspp.sty Also available at http://www.dao.nrc.ca/DAO/SCIENCE/science.html
and coming soon on a CFRS homepag
THE CANADA-FRANCE REDSHIFT SURVEY IX: HST Imaging of High-Redshift Field Galaxies
HST B and I images are presented of 32 CFRS galaxies with secure redshifts in
the range 0.5 < z < 1.2. These galaxies exhibit the same range of morphological
types as seen locally, i.e., ellipticals, spirals and irregulars. The galaxies
look far less regular in the images (rest-frame ultraviolet) than at longer
wavelengths, underlining the fact that optical images of galaxies at still
higher redshift should be interpreted with caution. Quantitative analyses of
the galaxies yield disk sizes, bulge fractions, and colors for each component.
At these redshifts, galaxy disks show clear evidence for surface brightness
evolution. The mean rest-frame central surface brightness of the disks of
normal late-type galaxies is mu_{AB}(B)=20.2 \pm 0.25 mag arcsec^{-2}, about
1.2 mag brighter than the Freeman (1970) value. Some degree of peculiarity is
measurable in 10 (30%) of the galaxies and 4 (13%) show clear signs of
interaction/mergers. There are 9 galaxies (30%) dominated by blue compact
components. These components, which appear to be related to star formation,
occur most often in peculiar/asymmetric galaxies (some of which appear to be
interacting), but a few are in otherwise normal galaxies. Thus, of the galaxies
bluer than present-day Sb, one-third are "blue nucleated galaxies", and half
are late-type galaxies with disks which are significantly brighter than normal
galaxies at z=0. Taken together, these two effects must be responsible for much
of the observed evolution of the luminosity function of blue galaxies.Comment: uuencoded compressed postscript, 8 pages, 1 table + 5 figures in a
separate part. Also available at http://www.astro.utoronto.ca/~lilly/CFRS/ .
Accepted for publication in ApJ Letter
Compact Nuclei in Moderately Redshifted Galaxies
The Hubble Space Telescope WFPC2 is being used to obtain high-resolution
images in the V and I bands for several thousand distant galaxies as part of
the Medium Deep Survey (MDS). An important scientific aim of the MDS is to
identify possible AGN candidates from these images in order to measure the
faint end of the AGN luminosity function as well as to study the host galaxies
of AGNs and nuclear starburst systems. We are able to identify candidate
objects based on morphology. Candidates are selected by fitting bulge+disk
models and bulge+disk+point source nuclei models to HST imaged galaxies and
determining the best model fit to the galaxy light profile. We present results
from a sample of MDS galaxies with I less than 21.5 mag that have been searched
for AGN/starburst nuclei in this manner. We identify 84 candidates with
unresolved nuclei in a sample of 825 galaxies. For the expected range of galaxy
redshifts, all normal bulges are resolved. Most of the candidates are found in
galaxies displaying exponential disks with some containing an additional bulge
component. 5% of the hosts are dominated by an r^-1/4 bulge. The V-I color
distribution of the nuclei is consistent with a dominant population of
Seyfert-type nuclei combined with an additional population of starbursts. Our
results suggest that 10% +/- 1% of field galaxies at z less than 0.6 may
contain AGN/starburst nuclei that are 1 to 5 magnitudes fainter than the host
galaxies.Comment: 12 pages AASTeX manuscript, 3 separate Postscript figures, to be
published in ApJ Letter
The CANADA-FRANCE REDSHIFT SURVEY VI: Evolution of the galaxy luminosity function to z ~ 1
The cosmic evolution of the field galaxy population has been studied out to a
redshift of z ~ 1 using a sample of 730 I-band selected galaxies, of which 591
have secure redshifts with median ~ 0.56. The tri-variate luminosity
function phi(M,color,z) shows unambiguously that the population evolves and
that this evolution is strongly differential with color and, less strongly,
with luminosity. The luminosity function of red galaxies shows very little
change in either number density or luminosity over the entire redshift range 0
< z < 1. In contrast, the luminosity function of blue galaxies shows
substantial evolution at redshifts z > 0.5. By 0.5 < z < 0.75, the blue
luminosity function appears to have uniformly brightened by approximately 1
mag. At higher redshifts, the evolution appears to saturate at the brightest
magnitudes but continues at fainter levels leading to a steepening of the
luminosity function. A significant excess of galaxies relative to the Loveday
et al. (1992) local luminosity function is seen at low redshifts z < 0.2 around
M(B) ~ -18$ and these galaxies may possibly represent the descendants of the
evolving blue population seen at higher redshifts. The changes seen in the
luminosity function are also apparent in color-magnitude diagrams constructed
at different epochs and in the V/V_max statistic computed as a function of
spectral type. Finally, it is argued that the picture of galaxy evolution
presented here is consistent with the very much smaller samples of field
galaxies that have been selected in other wavebands, and with the results of
studies of galaxies selected on the basis of Mg II 2799 absorption.Comment: uuencoded compressed Tex (first part) with 9 uuencoded compressed
postscript figures and 2 tables (second part). Also available at
http://www.astro.utoronto.ca/~lilly/CFRS/papers.html . Accepted July 17 by
ApJ, scheduled for Dec 10 issu
Hubble Space Telescope imaging of the CFRS and LDSS redshift surveys - IV. Influence of mergers in the evolution of faint field galaxies from z~1
HST images of a sample of 285 galaxies with measured z from the CFRS and
Autofib-LDSS redshift surveys are analysed to derive the evolution of the
merger fraction out to z~1. We have performed visual and machine-based merger
identifications, as well as counts of bright pairs of galaxies with magnitude
differences less than 1.5 mag. We find that the pair fraction increases with z,
with up to ~20% of the galaxies being in physical pairs at z~0.75-1. We derive
a merger fraction varying with z as (1+z)^{3.2 +/- 0.6}, after correction for
line-of-sight contamination, in excellent agreement with the merger fraction
derived from the visual classification of mergers for which m = 3.4 +/- 0.6.
After correcting for seeing effects on the ground-based selection of survey
galaxies, we conclude that the pair fraction evolves as (1+z)^{2.7 +/- 0.6}.
This implies that an average L* galaxy will have undergone 0.8 to 1.8 merger
events from z=1 to 0, with 0.5 to 1.2 merger events occuring in a 2 Gyr time
span at z~0.9. This result is consistent with predictions from semi-analytical
models of galaxy formation. From the simple co-addition of the observed
luminosities of the galaxies in pairs, physical mergers are computed to lead to
a brightening of 0.5 mag for each pair on average, and a boost in star
formation rate of a factor of 2, as derived from the average [O II] equivalent
widths. Mergers of galaxies are therefore contributing significantly to the
evolution of both the luminosity function and luminosity density of the
Universe out to z~1.Comment: 14 pages, 6 PS figures included. Accepted for publication in MNRA
Misleading results from low-resolution spectroscopy: from galaxy interstellar medium chemistry to cosmic star formation density
Low resolution spectroscopy (R=150) from the Canada-France-Redshift Survey
(CFRS) had revealed intriguing properties for low redshift galaxies (z<=0.3):
nearly half of their spectra show prominent H\alpha emission line, but no
H\beta emission line and barely detected [O II]3727 and [O III]5007 lines. We
call these objects "CFRS H\alpha-single" galaxies and have re-observed a
subsample of them at higher spectral resolution, associated with a subsample of
more normal emission line galaxies. Good S/N spectroscopy at the VLT and the
CFHT, with moderate spectral resolution (R>600), reveals that the "CFRS
H\alpha-single" galaxies and most of the star forming spirals have high
extinctions (A_V>2), high stellar masses and over-solar oxygen abundances. The
present study shows that it is hard to derive the detailed properties of
galaxies (gas chemical abundances, interstellar extinction, stellar population,
star formation rates and history) using spectra with resolution below 600. One
major drawback is indeed that the underlying Balmer absorption cannot be
estimated properly, which could cause the SFRs be either underestimated or
overestimated by factors reaching 10 (average 3.1) for the sample galaxies.
These effects are prominent for a large fraction of evolved massive galaxies
especially those experiencing successive bursts (A and F stars dominating their
absorption spectra). Further estimates of the cosmic star formation density at
all redshifts mandatorily requires moderate resolution spectroscopy to avoid
severe biases.Comment: 14 pages, 12 PS figures, Accepted for publication in A&
The Canada France Redshift Survey VIII: Evolution of the clustering of galaxies from z~1
We have used the projected two-point correlation function, , to
investigate the spatial distribution of the 591 galaxies with secure redshifts
between in the five CFRS fields.
The slope of the two-point correlation function for the sample as a whole is
, very similar to the local slope, and is
therefore not strongly evolving with redshift. However, the amplitude of the
correlation function decreases strongly with increasing redshift, so that at
it is a factor of 10 lower (for ) than for a
similarly-selected local galaxy population, on scales Mpc
(). As a whole, the CFRS data is adequately represented by
Mpc for , and Mpc for .
Unless the galaxy population at high redshift is quite different from any
population seen locally, an unlikely possibility, then this implies growth of
clustering as described by the evolutionary parameter to be between
.
No difference in the clustering of red and blue galaxies is seen at , although at lower redshifts, , blue galaxies are
somewhat less strongly correlated than the redder galaxies, as seen in local
samples. This effect could be the equivalent for field galaxies to the
Butcher-Oemler effect seen in clusters of galaxies. The cross-correlation
functions between red and blue samples have comparable amplitudes to the
auto-correlation functions of each.
The distribution and power spectrum of pair separations does not indicateComment: 17 pages, 10 figure
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