38 research outputs found
Wide-field CCD imaging at CFHT: the MOCAM example
We describe a new 4096x4096 pixel CCD mosaic camera (MOCAM) available at the
prime focus of the Canada-France-Hawaii Telescope (CFHT). The camera is a
mosaic of four 2048x2048\mu$m
pixels, providing a field of view of 14'x14' at a scale of 0.21''/pixel. MOCAM
is equipped with B, V, R and I filters and has demonstrated image quality of
0.5''-0.6'' FWHM over the entire field. MOCAM will also be used with the CFHT
adaptive optic bonnette and will provide a field of view of 90'' at a scale of
0.02 ''/pixel. MOCAM works within the CFHT Pegasus software environment and
observers familiar with this system require no additional training to use this
camera effectively. The technical details, the performance and the first images
obtained on the telescope with MOCAM are presented. In particular, we discuss
some important improvements with respect to the standard single-CCD FOCAM
camera, such as multi-output parallel readout and dynamic anti-blooming. We
also discuss critical technical issues concerning future wide-field imaging
facilities at the CFHT prime focus in light of our experience with MOCAM and
our recent experience with the even larger UH 8192x8192 pixel CCD mosaic
camera.Comment: Accepted for publication in Publication of the Astronomical Society
of the Pacific. Latex with aas2pp4.sty and epsf.sty. 12 pages, 10 figure
The Gemini Deep Deep Survey: II. Metals in Star-Forming Galaxies at Redshift 1.3<z<2
The goal of the Gemini Deep Deep Survey (GDDS) is to study an unbiased sample
of K<20.6 galaxies in the redshift range 0.8<z<2.0. Here we determine the
statistical properties of the heavy element enrichment in the interstellar
medium (ISM) of a subsample of 13 galaxies with 1.34<z<1.97 and UV absolute
magnitude M_2000 < -19.65. The sample contains 38% of the total number of
identified galaxies in the first two fields of the survey with z>1.3. The
selected objects have colors typical of irregular and Sbc galaxies. Strong
[OII] emission indicates high star formation activity in the HII regions
(SFR~13-106 M_sun/yr). The high S/N composite spectrum shows strong ISM MgII
and FeII absorption, together with weak MnII and MgI lines. The FeII column
density, derived using the curve of growth analysis, is logN_FeII =
15.54^{+0.23}_{-0.13}. This is considerably larger than typical values found in
damped Ly-alpha systems (DLAs) along QSO sight lines, where only 10 out of 87
(~11%) have logN_FeII > 15.2. High FeII column densities are observed in the
z=2.72 Lyman break galaxy cB58 (logN_FeII ~ 15.25) and in gamma-ray burst host
galaxies (logN_FeII ~ 14.8-15.9). Given our measured FeII column density and
assuming a moderate iron dust depletion (delta_Fe ~ 1 dex), we derive an
optical dust extinction A_V ~ 0.6. If the HI column density is log N(HI)<21.7
(as in 98% of DLAs), then the mean metallicity is Z/Z_sun > 0.2. The high
completeness of the GDDS sample implies that these results are typical of
star-forming galaxies in the 1<z<2 redshift range, an epoch which has
heretofore been particularly challenging for observational programs.Comment: ApJ in press, corrected HI column density estimat
The Gemini Deep Deep Survey: VIII. When Did Early-type Galaxies Form?
We have used the Hubble Space Telescope's Advanced Camera for Surveys (Ford et al. 2003) to measure the cumulative mass density in morphologically-selected early-type galaxies over the redshift range 0.8 < z < 1.7. Our imaging data set covers four well-separated sight-lines, and is roughly intermediate (in terms of both depth and area) between the GOODS/GEMS imaging data, and the images obtained in the Hubble Deep Field campaigns. Our images contain 144 galaxies with ultra-deep spectroscopy obtained as part of the Gemini Deep Deep Survey. These images have been analyzed using a new purpose-written morphological analysis code which improves the reliability of morphological classifications by adopting a 'quasi-Petrosian' image thresholding technique. We find that at z \~ 1 about 80% of the stars living in the most massive galaxies reside in early-type systems. This fraction is similar to that seen in the local Universe. However, we detect very rapid evolution in this fraction over the range 0.8 < z < 1.7, suggesting that over this redshift range the strong morphology-mass relationship seen in the nearby Universe is beginning to fall into place. By comparing our images to published spectroscopic classifications, we show that little ambiguity exists in connecting spectral classes to morphological classes for spectroscopically quiescent systems. However, the mass density function of early-type galaxies is evolving more rapidly than that of spectroscopically quiescent systems, which we take as further evidence that we are witnessing the formation of massive early-type galaxies over the 0.8 < z < 1.7 redshift range
A Compact Cluster of Massive Red Galaxies at a Redshift of 1.51
We describe a compact cluster of massive red galaxies at z=1.51 discovered in
one of the Gemini Deep Deep Survey (GDDS) fields. Deep imaging with the Near
Infrared Camera and Multi Object Spectrometer (NICMOS) on the Hubble Space
Telescope reveals a high density of galaxies with red optical to near-IR colors
surrounding a galaxy with a spectroscopic redshift of 1.51. Mid-IR imaging with
Infrared Array Camera (IRAC) on the Spitzer Space telescope shows that these
galaxies have spectral energy distributions that peak between 3.6 and 4.5
microns. Fits to 12-band photometry reveal 12 or more galaxies with spectral
shapes consistent with z = 1.51. Most are within ~170 co-moving kpc of the GDDS
galaxy. Deep F814W images with the Advanced Camera for Surveys (ACS) on HST
reveal that these galaxies are a mix of early-type galaxies, disk galaxies and
close pairs. The total stellar mass enclosed within a sphere of 170 kpc in
radius is > 8E+11 solar masses. The colors of the most massive galaxies are
close to those expected from passive evolution of simple stellar populations
(SSP) formed at much higher redshifts. We suggest that several of these
galaxies will merge to form a single, very massive galaxy by the present day.
This system may represent an example of a short-lived dense group or cluster
core typical of the progenitors of massive clusters in the present day and
suggests the red sequence was in place in over-dense regions at early times.Comment: 14 pages, 6 figures, submitted to ApJ Letter
A survey for low luminosity quasars at redshift z~5
We present the results of a multi-colour (VIZ) survey for low luminosity
(M_B<-23.5) quasars with z~5 using the 12K CCD mosaic camera on CFHT. The
survey covers 1.8deg^2 to a limiting magnitude of m_z=22.5(Vega), about two
magnitudes fainter than the SDSS quasar survey. 20 candidates were selected by
their VIZ colours and spectra for 15 of these were obtained with GMOS on the
Gemini North telescope. A single quasar with z=4.99 was recovered, the
remaining candidates are all M stars.
The detection of only a single quasar in the redshift range accessible to the
survey (4.8<5.2) is indicative of a possible turn over in the luminosity
function at faint quasar magnitudes, and a departure from the form observed at
higher luminosities (in agreement with quasar lensing observations by Richards
etal (2003)). However, the derived space densitys, of quasars more luminous
than M_B(Vega)<-23.5, of 2.96x10^-7 Mpc^-3 is consistent at the 65% confidence
level with extrapolation of the quasar luminosity function as derived by Fan
etal (2001a) at m_i<19.6(Vega).Comment: 8 Pages, 8 Figures, accepted for publication in MNRA
Overview of the Far Ultraviolet Spectroscopic Explorer Mission
The Far Ultraviolet Spectroscopic Explorer satellite observes light in the
far-ultraviolet spectral region, 905 - 1187 A with high spectral resolution.
The instrument consists of four coaligned prime-focus telescopes and Rowland
spectrographs with microchannel plate detectors. Two of the telescope channels
use Al:LiF coatings for optimum reflectivity from approximately 1000 to 1187 A
and the other two use SiC coatings for optimized throughput between 905 and
1105 A. The gratings are holographically ruled to largely correct for
astigmatism and to minimize scattered light. The microchannel plate detectors
have KBr photocathodes and use photon counting to achieve good quantum
efficiency with low background signal. The sensitivity is sufficient to examine
reddened lines of sight within the Milky Way as well as active galactic nuclei
and QSOs for absorption line studies of both Milky Way and extra-galactic gas
clouds. This spectral region contains a number of key scientific diagnostics,
including O VI, H I, D I and the strong electronic transitions of H2 and HD.Comment: To appear in FUSE special issue of the Astrophysical Journal Letters.
6 pages + 4 figure
Red Nuggets at z~1.5: Compact passive galaxies and the formation of the Kormendy Relation
We present the results of NICMOS imaging of a sample of 16 high mass
passively evolving galaxies with 1.3<z<2, taken primarily from the Gemini Deep
Deep Survey. Around 80% of galaxies in our sample have spectra dominated by
stars with ages >1 Gyr. Our rest-frame R-band images show that most of these
objects have compact regular morphologies which follow the classical R^1/4 law.
These galaxies scatter along a tight sequence in the Kormendy relation. Around
one-third of the massive red objects are extraordinarily compact, with
effective radii under one kiloparsec. Our NICMOS observations allow the
detection of such systems more robustly than is possible with optical
(rest-frame UV) data, and while similar systems have been seen at z>2, this is
the first time such systems have been detected in a rest-frame optical survey
at 1.3<z<2. We refer to these compact galaxies as "red nuggets". Similarly
compact massive galaxies are completely absent in the nearby Universe. We
introduce a new "stellar mass Kormendy relation" (stellar mass density vs size)
which isolates the effects of size evolution from those of luminosity and color
evolution. The 1.1 < z < 2 passive galaxies have mass densities that are an
order of magnitude larger then early type galaxies today and are comparable to
the compact distant red galaxies at 2 < z < 3. We briefly consider mechanisms
for size evolution in contemporary models focusing on equal-mass mergers and
adiabatic expansion driven by stellar mass loss. Neither of these mechanisms
appears able to transform the high-redshift Kormendy relation into its local
counterpart. Comment: Accepted version (to appear in ApJ
The Gemini Deep Deep Survey. VII. The Redshift Evolution of the Mass-Metallicity Relation
We have investigated the mass-metallicity (M-Z) relation using galaxies at
0.4<z<1.0 from the Gemini Deep Deep Survey and Canada-France Redshift Survey.
Deep K and z' band photometry allowed us to measure stellar masses for 69
galaxies. From a subsample of 56 galaxies, for which metallicity of the
interstellar medium is also measured, we identified a strong correlation
between mass and metallicity, for the first time in the distant Universe. This
was possible because of the larger base line spanned by the sample in terms of
metallicity (a factor of 7) and mass (a factor of 400) than in previous works.
This correlation is much stronger and tighter than the luminosity-metallicity,
confirming that stellar mass is a more meaningful physical parameter than
luminosity. We find clear evidence for temporal evolution in the M-Z relation
in the sense that at a given mass, a galaxy at z=0.7 tends to have lower
metallicity than a local galaxy of similar mass. We use the z=0.1 SDSS M-Z
relation, and a small sample of z=2.3 Lyman break galaxies with known mass and
metallicity, to propose an empirical redshift-dependent M-Z relation, according
to which the stellar mass and metallicity in small galaxies evolve for a longer
time than in massive galaxies. This relation predicts that the generally metal
poor damped Lyman-alpha galaxies have stellar masses of the order of 10^8.8
M_sun (with a dispersion of 0.7 dex) all the way from z=0.2 to z=4. The
observed redshift evolution of the M-Z relation can be reproduced remarkably
well by a simple closed-box model where the key assumption is an e-folding time
for star formation which is higher or, in other words, a period of star
formation that lasts longer in less massive galaxies than in more massive
galaxies. Such a picture supports the downsizing scenario for galaxy formation.Comment: ApJ in pres