501 research outputs found
HeII emitters in the VIMOS VLT Deep Survey: PopIII star formation or peculiar stellar populations in galaxies at 2<z<4.6?
The aim of this work is to identify HeII emitters at 2<z<4.6 and to constrain
the source of the hard ionizing continuum that powers the HeII emission. We
have assembled a sample of 277 galaxies with a high quality spectroscopic
redshift at 2<z<4.6 from the VVDS survey, and we have identified 39 HeII1640A
emitters. We study their spectral properties, measuring the fluxes, equivalent
widths (EW) and FWHM for most relevant lines. About 10% of galaxies at z~3 show
HeII in emission, with rest frame equivalent widths EW0~1-7A, equally
distributed between galaxies with Lya in emission or in absorption. We find 11
high-quality HeII emitters with unresolved HeII line (FWHM_0<1200km/s), 13
high-quality emitters with broad He II emission (FWHM_0>1200km/s), 3 AGN, and
an additional 12 possible HeII emitters. The properties of the individual broad
emitters are in agreement with expectations from a W-R model. On the contrary,
the properties of the narrow emitters are not compatible with such model,
neither with predictions of gravitational cooling radiation produced by gas
accretion. Rather, we find that the EW of the narrow HeII line emitters are in
agreement with expectations for a PopIII star formation, if the episode of star
formation is continuous, and we calculate that a PopIII SFR of 0.1-10 Mo yr-1
only is enough to sustain the observed HeII flux. We conclude that narrow HeII
emitters are either powered by the ionizing flux from a stellar population rare
at z~0 but much more common at z~3, or by PopIII star formation. As proposed by
Tornatore et al. (2007), incomplete ISM mixing may leave some small pockets of
pristine gas at the periphery of galaxies from which PopIII may form, even down
to z~2 or lower. If this interpretation is correct, we measure at z~3 a SFRD in
PopIII stars of 10^6Mo yr^-1 Mpc^-3 qualitatively comparable to the value
predicted by Tornatore et al. (2007).Comment: accepted for publication in A&
Studying the evolution of large-scale structure with the VIMOS-VLT Deep Survey
The VIMOS-VLT Deep Survey (VVDS) currently offers a unique combination of
depth, angular size and number of measured galaxies among surveys of the
distant Universe: ~ 11,000 spectra over 0.5 deg2 to I_{AB}=24 (VVDS-Deep),
35,000 spectra over ~ 7 deg2 to I_{AB}=22.5 (VVDS-Wide). The current ``First
Epoch'' data from VVDS-Deep already allow investigations of galaxy clustering
and its dependence on galaxy properties to be extended to redshifts ~1.2-1.5,
in addition to measuring accurately evolution in the properties of galaxies up
to z~4. This paper concentrates on the main results obtained so far on galaxy
clustering. Overall, L* galaxies at z~ 1.5 show a correlation length r_0=3.6\pm
0.7. As a consequence, the linear galaxy bias at fixed luminosity rises over
the same range from the value b~1 measured locally, to b=1.5 +/- 0.1. The
interplay of galaxy and structure evolution in producing this observation is
discussed in some detail. Galaxy clustering is found to depend on galaxy
luminosity also at z~ 1, but luminous galaxies at this redshift show a
significantly steeper small-scale correlation function than their z=0
counterparts. Finally, red galaxies remain more clustered than blue galaxies
out to similar redshifts, with a nearly constant relative bias among the two
classes, b_{rel}~1.4, despite the rather dramatic evolution of the
color-density relation over the same redshift range.Comment: 14 pages. Extended, combined version of two invited review papers
presented at: 1) XXVIth Astrophysics Moriond Meeting: "From Dark Halos to
Light", March 2006, proc. edited by L.Tresse, S. Maurogordato and J. Tran
Thanh Van (Editions Frontieres); 2) Vulcano Workshop 2006 "Frontier Objects
in Astrophysics and Particle Physics", May 2006, proc. edited by F.
Giovannelli & G. Mannocchi, Italian Physical Society (Editrice Compositori,
Bologna
Avaliação preliminar do nanismo amarelo em genótipos de triticale.
Editores tĂ©cnicos: Joseani Mesquita Antunes, Ana LĂdia Variani Bonato, MĂĄrcia Barrocas Moreira Pimentel
The VIMOS Public Extragalactic Redshift Survey (VIPERS). Never mind the gaps: comparing techniques to restore homogeneous sky coverage
[Abridged] Non-uniform sampling and gaps in sky coverage are common in galaxy
redshift surveys, but these effects can degrade galaxy counts-in-cells and
density estimates. We carry out a comparison of methods that aim to fill the
gaps to correct for the systematic effects. Our study is motivated by the
analysis of the VIMOS Extragalactic Redshift Survey (VIPERS), a flux-limited
survey (i<22.5) based on one-pass observations with VIMOS, with gaps covering
25% of the surveyed area and a mean sampling rate of 35%. Our findings are
applicable to other surveys with similar observing strategies. We compare 1)
two algorithms based on photometric redshift, that assign redshifts to galaxies
based on the spectroscopic redshifts of the nearest neighbours, 2) two Bayesian
methods, the Wiener filter and the Poisson-Lognormal filter. Using galaxy mock
catalogues we quantify the accuracy of the counts-in-cells measurements on
scales of R=5 and 8 Mpc/h after applying each of these methods. We also study
how they perform to account for spectroscopic redshift error and inhomogeneous
and sparse sampling rate. We find that in VIPERS the errors in counts-in-cells
measurements on R<10 Mpc/h scales are dominated by the sparseness of the
sample. All methods underpredict by 20-35% the counts at high densities. This
systematic bias is of the same order as random errors. No method outperforms
the others. Random and systematic errors decrease for larger cells. We show
that it is possible to separate the lowest and highest densities on scales of 5
Mpc/h at redshifts 0.5<z<1.1, over a large volume such as in VIPERS survey.
This is vital for the characterisation of cosmic variance and rare populations
(e.g, brightest galaxies) in environmental studies at these redshifts.Comment: 17 pages, 13 figures, accepted for publication in A&A (revised
version after minor revision and language editing
The VLA-VIRMOS Deep Field I. Radio observations probing the microJy source population
We have conducted a deep survey (r.m.s noise 17 microJy) with the Very Large
Array (VLA) at 1.4 GHz, with a resolution of 6 arcsec, of a 1 square degree
region included in the VIRMOS VLT Deep Survey. In the same field we already
have multiband photometry down to I(AB)=25, and spectroscopic observations will
be obtained during the VIRMOS VLT survey. The homogeneous sensitivity over the
whole field has allowed to derive a complete sample of 1054 radio sources (5
sigma limit). We give a detailed description of the data reduction and of the
analysis of the radio observations, with particular care to the effects of
clean bias and bandwidth smearing, and of the methods used to obtain the
catalogue of radio sources. To estimate the effect of the resolution bias on
our observations we have modelled the effective angular-size distribution of
the sources in our sample and we have used this distribution to simulate a
sample of radio sources. Finally we present the radio count distribution down
to 0.08 mJy derived from the catalogue. Our counts are in good agreement with
the best fit derived from earlier surveys, and are about 50 % higher than the
counts in the HDF. The radio count distribution clearly shows, with extremely
good statistics, the change in the slope for the sub-mJy radio sources.Comment: 13 pages, Accepted for publication in Astronomy & Astrophysic
The VIMOS-VLT Deep Survey: Evolution in the Halo Occupation Number since z 1
We model the evolution of the mean galaxy occupation of dark-matter halos
over the range , using the data from the VIMOS-VLT Deep Survey
(VVDS). The galaxy projected correlation function was computed for a
set of luminosity-limited subsamples and fits to its shape were obtained using
two variants of Halo Occupation Distribution models. These provide us with a
set of best-fitting parameters, from which we obtain the average mass of a halo
and average number of galaxies per halo. We find that after accounting for the
evolution in luminosity and assuming that we are largely following the same
population, the underlying dark matter halo shows a growth in mass with
decreasing redshift as expected in a hierarchical structure formation scenario.
Using two different HOD models, we see that the halo mass grows by 90% over the
redshift interval z=[0.5,1.0]. This is the first time the evolution in halo
mass at high redshifts has been obtained from a single data survey and it
follows the simple form seen in N-body simulations with , and . This provides evidence for a rapid accretion
phase of massive halos having a present-day mass , with a merger event occuring between redshifts of 0.5
and 1.0. Futhermore, we find that more luminous galaxies are found to occupy
more massive halos irrespectively of the redshift. Finally, the average number
of galaxies per halo shows little increase from redshift z 1.0 to z
0.5, with a sharp increase by a factor 3 from z 0.5 to z 0.1,
likely due to the dynamical friction of subhalos within their host halos.Comment: 14 pages, 6 figures, 5 tables. MNRAS accepted
The VIMOS Public Extragalactic Redshift Survey (VIPERS): PCA-based automatic cleaning and reconstruction of survey spectra
Identifying spurious reduction artefacts in galaxy spectra is a challenge for
large surveys. We present an algorithm for identifying and repairing residual
spurious features in sky-subtracted galaxy spectra with application to the
VIPERS survey. The algorithm uses principal component analysis (PCA) applied to
the galaxy spectra in the observed frame to identify sky line residuals
imprinted at characteristic wavelengths. We further model the galaxy spectra in
the rest-frame using PCA to estimate the most probable continuum in the
corrupted spectral regions, which are then repaired. We apply the method to
90,000 spectra from the VIPERS survey and compare the results with a subset
where careful editing was performed by hand. We find that the automatic
technique does an extremely good job in reproducing the time-consuming manual
cleaning and does it in a uniform and objective manner across a large data
sample. The mask data products produced in this work are released together with
the VIPERS second public data release (PDR-2).Comment: Find the VIPERS data release at http://vipers.inaf.i
The VIMOS Integral Field Unit: data reduction methods and quality assessment
With new generation spectrographs integral field spectroscopy is becoming a
widely used observational technique. The Integral Field Unit of the VIsible
Multi-Object Spectrograph on the ESO-VLT allows to sample a field as large as
54" x 54" covered by 6400 fibers coupled with micro-lenses. We are presenting
here the methods of the data processing software developed to extract the
astrophysical signal of faint sources from the VIMOS IFU observations. We focus
on the treatment of the fiber-to-fiber relative transmission and the sky
subtraction, and the dedicated tasks we have built to address the peculiarities
and unprecedented complexity of the dataset. We review the automated process we
have developed under the VIPGI data organization and reduction environment
(Scodeggio et al. 2005), along with the quality control performed to validate
the process. The VIPGI-IFU data processing environment is available to the
scientific community to process VIMOS-IFU data since November 2003.Comment: 19 pages, 10 figures and 1 table. Accepted for publication in PAS
The VIMOS VLT Deep Survey :Evolution of the major merger rate since z~1 from spectroscopicaly confirmed galaxy pairs
From the VIMOS VLT Deep Survey we use a sample of 6447 galaxies with I_{AB} <
24 to identify 251 pairs of galaxies, each member with a secure spectroscopic
redshift, which are close in both projected separation and in velocity. We find
that at z ~ 0.9, 10.9 +/- 3.2 % of galaxies with M_B(z) < -18-Qz are in pairs
with separations dr < 20 kpc/h, dv < 500 km/s, and with dM_B < 1.5,
significantly larger than 3.76 +/- 1.71 % at z ~ 0.5; we find that the pair
fraction evolves as (1+z)^m with m = 2.49 +/- 0.56. For brighter galaxies with
M_B(z=0) < -18.77, the pair fraction is higher and its evolution with redshift
is somewhat flatter with m=1.88 \pm 0.40, a property also observed for galaxies
with increasing stellar masses. Early type, dry mergers, pairs increase their
relative fraction from 3 % at z ~ 0.9 to 12 % at z ~ 0.5. We find that the
merger rate evolves as N_{mg}=(9.05 +/- 3.76) * 10^{-4}) * (1+z)^{2.43 +/-
0.76}. We find that the merger rate of galaxies with M_B(z) < -18-Qz has
significantly evolved since z ~ 1. The merger rate is increasing more rapidly
with redshift for galaxies with decreasing luminosities, indicating that the
flat evolution found for bright samples is not universal. The merger rate is
also strongly dependent on the spectral type of galaxies involved, late type
mergers being more frequent in the past, while early type mergers are more
frequent today, contributing to the rise in the local density of early type
galaxies. About 20 % of the stellar mass in present day galaxies with
log(M/M_{sun}) > 9.5 has been accreted through major merging events since z ~
1, indicating that major mergers have contributed significantly to the growth
in stellar mass density of bright galaxies over the last half of the life of
the Universe.Comment: 22 pages, 19 figures, accepted in A&
Comparison of the VIMOS-VLT Deep Survey with the Munich semi-analytical model - I. Magnitude counts, redshift distribution, colour bimodality, and galaxy clustering
This paper presents a detailed comparison between high-redshift observations
from the VIMOS-VLT Deep Survey (VVDS) and predictions from the Munich
semi-analytical model of galaxy formation. In particular, we focus this
analysis on the magnitude, redshift, and colour distributions of galaxies, as
well as their clustering properties. We constructed 100 quasi-independent mock
catalogues, using the output of the semi-analytical model presented in De Lucia
& Blaizot (2007).We then applied the same observational selection function of
the VVDS-Deep survey, so as to carry out a fair comparison between models and
observations. We find that the semi-analytical model reproduces well the
magnitude counts in the optical bands. It tends, however, to overpredict the
abundance of faint red galaxies, in particular in the i' and z' bands. Model
galaxies exhibit a colour bimodality that is only in qualitative agreement with
the data. In particular, we find that the model tends to overpredict the number
of red galaxies at low redshift and of blue galaxies at all redshifts probed by
VVDS-Deep observations, although a large fraction of the bluest observed
galaxies is absent from the model. In addition, the model overpredicts by about
14 per cent the number of galaxies observed at 0.2<z<1 with I_AB<24. When
comparing the galaxy clustering properties, we find that model galaxies are
more strongly clustered than observed ones at all redshift from z=0.2 to z=2,
with the difference being less significant above z~1. When splitting the
samples into red and blue galaxies, we find that the observed clustering of
blue galaxies is well reproduced by the model, while red model galaxies are
much more clustered than observed ones, being principally responsible for the
strong global clustering found in the model. [abridged]Comment: 15 pages, 14 figures, accepted for publication in A&
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