4,912 research outputs found
METHODOLOGY FOR TREND ANALYSIS AND PROJECTION OF PRODUCTION, MARKET SHARES, AND CONSUMPTION
Food Consumption/Nutrition/Food Safety,
The VIRMOS deep imaging survey: I. overview and survey strategy
This paper presents the CFH12K-VIRMOS survey: a deep B, V, R and I imaging
survey in four fields totalling more than 17 deg^2, conducted with the 30x40
arcmin^2 field CFH-12K camera. The survey is intended to be a multi-purpose
survey used for a variety of science goals, including surveys of very high
redshift galaxies and weak lensing studies.
Four high galactic latitude fields, each 2x2 deg^2, have been selected along
the celestial equator: 0226-04, 1003+01, 1400+05, and 2217+00. The 16 deg^2 of
the "wide" survey are covered with exposure times of 2h, 1.5h, 1h, 1h, while
the 1.3x1 deg^2 area of the "deep" survey at the center of the 0226-04 field is
covered with exposure times of 7h, 4.5h, 3h, 3h, in B,V,R and I respectively.
The data is pipeline processed at the Terapix facility at the Institut
d'Astrophysique de Paris to produce large mosaic images. The catalogs produced
contain the positions, shape, total and aperture magnitudes for the 2.175
million objects. The depth measured (3sigma in a 3 arc-second aperture) is
I_{AB}=24.8 in the ``Wide'' areas, and I_{AB}=25.3 in the deep area. Careful
quality control has been applied on the data as described in joint papers.
These catalogs are used to select targets for the VIRMOS-VLT Deep Survey, a
large spectroscopic survey of the distant universe (Le F\`evre et al., 2003).
First results from the CFH12K-VIRMOS survey have been published on weak lensing
(e.g. van Waerbeke & Mellier 2003).
Catalogs and images are available through the VIRMOS database environment
under Oracle ({\tt http://www.oamp.fr/virmos}). They will be open for general
use on July 1st, 2003.Comment: 17 pages including 9 figures, submitted to A&
Relativistic Proton Production During the 14 July 2000 Solar Event: The Case for Multiple Source Mechanisms
Protons accelerated to relativistic energies by transient solar and
interplanetary phenomena caused a ground-level cosmic ray enhancement on 14
July 2000, Bastille Day. Near-Earth spacecraft measured the proton flux
directly and ground-based observatories measured the secondary responses to
higher energy protons. We have modelled the arrival of these relativistic
protons at Earth using a technique which deduces the spectrum, arrival
direction and anisotropy of the high-energy protons that produce increased
responses in neutron monitors. To investigate the acceleration processes
involved we have employed theoretical shock and stochastic acceleration
spectral forms in our fits to spacecraft and neutron monitor data. During the
rising phase of the event (10:45 UT and 10:50 UT) we find that the spectrum
between 140 MeV and 4 GeV is best fitted by a shock acceleration spectrum. In
contrast, the spectrum at the peak (10:55 UT and 11:00 UT) and in the declining
phase (11:40 UT) is best fitted with a stochastic acceleration spectrum. We
propose that at least two acceleration processes were responsible for the
production of relativistic protons during the Bastille Day solar event: (1)
protons were accelerated to relativistic energies by a shock, presumably a
coronal mass ejection (CME). (2) protons were also accelerated to relativistic
energies by stochastic processes initiated by magnetohydrodynamic (MHD)
turbulence.Comment: 38 pages, 9 figures, accepted for publication in the Astrophysical
Journal, January, 200
The VIRMOS deep imaging survey: III. ESO/WFI deep U-band imaging of the 0226-04 deep field
In this paper we describe the U-band imaging of the F02 deep field, one of
the fields in the VIRMOS Deep Imaging Survey. The observations were done at the
ESO/MPG 2.2m telescope at La Silla (Chile) using the 8k x 8k Wide-Field Imager
(WFI). The field is centered at alpha(J2000)=02h 26m 00s and
delta(J2000)=-04deg 30' 00", the total covered area is 0.9 deg**2 and the
limiting magnitude (50% completeness) is U(AB) ~ 25.4 mag. Reduction steps,
including astrometry, photometry and catalogue extraction, are first discussed.
The achieved astrometric accuracy (RMS) is ~ 0.2" with reference to the I-band
catalog and ~ 0.07" internally (estimated from overlapping sources in different
exposures). The photometric accuracy including uncertainties from photometric
calibration, is < 0.1 mag. Various tests are then performed as a quality
assessment of the data. They include: (i) the color distribution of stars and
galaxies in the field, done together with the BVRI data available from the
VIMOS survey; (ii) the comparison with previous published results of U-band
magnitude-number counts of galaxies.Comment: 10 pages, 13 figures, accepted for publication on Astronomy and
Astrophysic
Sub-millimeter galaxies as progenitors of compact quiescent galaxies
Three billion years after the big bang (at redshift z=2), half of the most
massive galaxies were already old, quiescent systems with little to no residual
star formation and extremely compact with stellar mass densities at least an
order of magnitude larger than in low redshift ellipticals, their descendants.
Little is known about how they formed, but their evolved, dense stellar
populations suggest formation within intense, compact starbursts 1-2 Gyr
earlier (at 3<z<6). Simulations show that gas-rich major mergers can give rise
to such starbursts which produce dense remnants. Sub-millimeter selected
galaxies (SMGs) are prime examples of intense, gas-rich, starbursts. With a
new, representative spectroscopic sample of compact quiescent galaxies at z=2
and a statistically well-understood sample of SMGs, we show that z=3-6 SMGs are
consistent with being the progenitors of z=2 quiescent galaxies, matching their
formation redshifts and their distributions of sizes, stellar masses and
internal velocities. Assuming an evolutionary connection, their space densities
also match if the mean duty cycle of SMG starbursts is 42 (+40/-29) Myr
(consistent with independent estimates), which indicates that the bulk of stars
in these massive galaxies were formed in a major, early surge of
star-formation. These results suggests a coherent picture of the formation
history of the most massive galaxies in the universe, from their initial burst
of violent star-formation through their appearance as high stellar-density
galaxy cores and to their ultimate fate as giant ellipticals.Comment: ApJ (in press
XMM-Newton Surveys of the Canada-France Redshift Survey Fields - III: The Environments of X-ray Selected AGN at 0.4<z<0.6
The environmental properties of a sample of 31 hard X-ray selected AGN are
investigated, from scales of 500 kpc down to 30 kpc, and are compared to a
control sample of inactive galaxies. The AGN all lie in the redshift range
0.4<z<0.6. The accretion luminosity-density of the Universe peaks close to this
redshift range, and the AGN in the sample have X-ray luminosities close to the
knee in the hard X-ray luminosity function, making them representative of the
population which dominated this important phase of energy conversion.
Using both the spatial clustering amplitude and near neighbour counts it is
found that the AGN have environments that are indistinguishable from normal,
inactive galaxies over the same redshift range and with similar optical
properties. Typically, the environments are of sub-cluster richness, in
contrast to similar studies of high-z quasars, which are often found in
clusters with comparable richness to the Abell R>=0 clusters.
It is suggested that minor mergers with low mass companions is a likely
candidate for the mechanism by which these modest luminosity AGN are fuelled.Comment: 12 pages, 6 figures, accepted by MNRA
The Evolution of the Number Density of Large Disk Galaxies in COSMOS
We study a sample of approximately 16,500 galaxies with I_(ACS,AB) ≤ 22.5 in the central 38% of the COSMOS field, which are extracted from a catalog constructed from the Cycle 12 ACS F814W COSMOS data set. Structural information on the galaxies is derived by fitting single Sérsic models to their two-dimensional surface brightness distributions. In this paper we focus on the disk galaxy population (as classified by the Zurich Estimator of Structural Types), and investigate the evolution of the number density of disk galaxies larger than approximately 5 kpc between redshift z ~ 1 and the present epoch. Specifically, we use the measurements of the half-light radii derived from the Sérsic fits to construct, as a function of redshift, the size function Φ(r_(1/2), z) of both the total disk galaxy population and of disk galaxies split in four bins of bulge-to-disk ratio. In each redshift bin, the size function specifies the number of galaxies per unit comoving volume and per unit half-light radius r_(1/2). Furthermore, we use a selected sample of roughly 1800 SDSS galaxies to calibrate our results with respect to the local universe. We find the following: (1) The number density of disk galaxies with intermediate sizes (r_(1/2) ~ 5-7 kpc) remains nearly constant from z ~ 1 to today. Unless the growth and destruction of such systems exactly balanced in the last eight billion years, they must have neither grown nor been destroyed over this period. (2) The number density of the largest disks (r_(1/2) > 7 kpc) decreases by a factor of about 2 out to z ~ 1. (3) There is a constancy—or even slight increase—in the number density of large bulgeless disks out to z ~ 1; the deficit of large disks at early epochs seems to arise from a smaller number of bulged disks. Our results indicate that the bulk of the large disk galaxy population has completed its growth by z ~ 1 and support the theory that secular evolution processes produce—or at least add stellar mass to—the bulge components of disk galaxies
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