459 research outputs found
A Coherent Study of Emission Lines from Broad-Band Photometry: Specific Star-Formation Rates and [OIII]/H{\beta} Ratio at 3 < z < 6
We measure the H{\alpha} and [OIII] emission line properties as well as
specific star-formation rates (sSFR) of spectroscopically confirmed 3<z<6
galaxies in COSMOS from their observed colors vs. redshift evolution. Our model
describes consistently the ensemble of galaxies including intrinsic properties
(age, metallicity, star-formation history), dust-attenuation, and optical
emission lines. We forward-model the measured H{\alpha} equivalent-widths (EW)
to obtain the sSFR out to z~6 without stellar mass fitting. We find a strongly
increasing rest-frame H{\alpha} EW that is flattening off above z~2.5 with
average EWs of 300-600A at z~6. The sSFR is increasing proportional to
(1+z)^2.4 at z<2.2 and (1+z)^1.5 at higher redshifts, indicative of a fast mass
build-up in high-z galaxies within e-folding times of 100-200Myr at z~6. The
redshift evolution at z>3 cannot be fully explained in a picture of cold
accretion driven growth. We find a progressively increasing
[OIII]{\lambda}5007/H{\beta} ratio out to z~6, consistent with the ratios in
local galaxies selected by increasing H{\alpha} EW (i.e., sSFR). This
demonstrates the potential of using "local high-z analogs" to investigate the
spectroscopic properties and relations of galaxies in the re-ionization epoch.Comment: 18 pages, 11 figures, 3 table
The extended epoch of galaxy formation: age dating of ~3600 galaxies with 2<z<6.5 in the VIMOS Ultra-Deep Survey
We aim at improving constraints on the epoch of galaxy formation by measuring
the ages of 3597 galaxies with spectroscopic redshifts 2<z<6.5 in the VIMOS
Ultra Deep Survey (VUDS). We derive ages and other physical parameters from the
simultaneous fitting with the GOSSIP+ software of observed UV rest-frame
spectra and photometric data from the u-band up to 4.5 microns using composite
stellar population models. We conclude from extensive simulations that at z>2
the joint analysis of spectroscopy and photometry combined with restricted age
possibilities when taking into account the age of the Universe substantially
reduces systematic uncertainties and degeneracies in the age derivation. We
find galaxy ages ranging from very young with a few tens of million years to
substantially evolved with ages up to ~1.5-2 Gyr. The formation redshifts z_f
derived from the measured ages indicate that galaxies may have started forming
stars as early as z_f~15. We produce the formation redshift function (FzF), the
number of galaxies per unit volume formed at a redshift z_f, and compare the
FzF in increasing redshift bins finding a remarkably constant 'universal' FzF.
The FzF is parametrized with (1+z)^\zeta, with \zeta~0.58+/-0.06, indicating a
smooth 2 dex increase from z~15 to z~2. Remarkably this observed increase is of
the same order as the observed rise in the star formation rate density (SFRD).
The ratio of the SFRD with the FzF gives an average SFR per galaxy of
~7-17Msun/yr at z~4-6, in agreement with the measured SFR for galaxies at these
redshifts. From the smooth rise in the FzF we infer that the period of galaxy
formation extends from the highest possible redshifts that we can probe at z~15
down to redshifts z~2. This indicates that galaxy formation is a continuous
process over cosmic time, with a higher number of galaxies forming at the peak
in SFRD at z~2 than at earlier epochs. (Abridged)Comment: Submitted to A&A, 24 page
Trapping microparticles in a structured dark focus
We experimentally demonstrate stable trapping and controlled manipulation of
silica microspheres in a structured optical beam consisting of a dark focus
surrounded by light in all directions - the so-called Dark Focus Tweezer.
Results from power spectrum and potential analysis demonstrate the
non-harmonicity of the trapping potential landspace, which is reconstructed
from experimental data in agreement to Lorentz-Mie numerical simulations.
Applications of the dark tweezer in levitated optomechanics and biophysics are
discussed.Comment: Final versio
The Subaru COSMOS 20: Subaru Optical Imaging of the HST COSMOS Field with 20 Filters
We present both the observations and the data reduction procedures of the
Subaru COSMOS 20 project that is an optical imaging survey of the HST COSMOS
field, carried out by using Suprime-Cam on the Subaru Telescope with the
following 20 optical filters: 6 broad-band (B, g', V, r', i', and z'), 2
narrow-band (NB711 and NB816), and 12 intermediate-band filters (IA427, IA464,
IA484, IA505, IA527, IA574, IA624, IA679, IA709, IA738, IA767, and IA827). A
part of this project is described in Taniguchi et al. (2007) and Capak et al.
(2007) for the six broad-band and one narrow-band (NB816) filter data. In this
paper, we present details of the observations and data reduction for remaining
13 filters (the 12 IA filters and NB711). In particular, we describe the
accuracy of both photometry and astrometry in all the filter bands. We also
present optical properties of the Suprime-Cam IA filter system in Appendix.Comment: 15 pages, 8 figures, 7 tables; accepted for publication in PASJ on
October 2, 201
Discovery of a rich proto-cluster at z=2.9 and associated diffuse cold gas in the VIMOS Ultra-Deep Survey (VUDS)
[Abridged] We characterise a massive proto-cluster at z=2.895 that we found
in the COSMOS field using the spectroscopic sample of the VIMOS Ultra-Deep
Survey (VUDS). This is one of the rare structures at z~3 not identified around
AGNs or radio galaxies, so it is an ideal laboratory to study galaxy formation
in dense environments. The structure comprises 12 galaxies with secure
spectroscopic redshift in an area of 7'x8', in a z bin of Dz=0.016. The
measured galaxy number overdensity is delta_g=12+/-2. This overdensity has
total mass of M~8.1x10^(14)M_sun in a volume of 13x15x17 Mpc^3. Simulations
indicate that such an overdensity at z~2.9 is a proto-cluster that will
collapse in a cluster of total mass M~2.5x10^(15)M_sun at z=0. We compare the
properties of the galaxies within the overdensity with a control sample at the
same z but outside the overdensity. We did not find any statistically
significant difference between the properties (stellar mass, SFR, sSFR, NUV-r,
r-K) of the galaxies inside and outside the overdensity. The stacked spectrum
of galaxies in the overdensity background shows a significant absorption
feature at the wavelength of Lya redshifted at z=2.895 (lambda=4736 A), with a
rest frame EW = 4+/- 1.4 A. Stacking only background galaxies without
intervening sources at z~2.9 along their line of sight, we find that this
absorption feature has a rest frame EW of 10.8+/-3.7 A, with a detection S/N of
~4. These EW values imply a high column density (N(HI)~3-20x10^(19)cm^(-2)),
consistent with a scenario where such absorption is due to intervening cold gas
streams, falling into the halo potential wells of the proto-cluster galaxies.
However, we cannot exclude the hypothesis that this absorption is due to the
diffuse gas within the overdensity.Comment: 15 pages, 9 figures, accepted for publication in A&A (revised version
after referee's comments and language editing
The VIMOS VLT Deep Survey final data release: a spectroscopic sample of 35016 galaxies and AGN out to z~6.7 selected with 17.5<=i_{AB}<=24.7
We describe the completed VIMOS VLT Deep Survey, and the final data release
of 35016 galaxies and type-I AGN with measured spectroscopic redshifts up to
redshift z~6.7, in areas 0.142 to 8.7 square degrees, and volumes from 0.5x10^6
to 2x10^7h^-3Mpc^3. We have selected samples of galaxies based solely on their
i-band magnitude reaching i_{AB}=24.75. Spectra have been obtained with VIMOS
on the ESO-VLT, integrating 0.75h, 4.5h and 18h for the Wide, Deep, and
Ultra-Deep nested surveys. A total of 1263 galaxies have been re-observed
independently within the VVDS, and from the VIPERS and MASSIV surveys. They are
used to establish the redshift measurements reliability, to assess
completeness, and to provide a weighting scheme taking into account the survey
selection function. We describe the main properties of the VVDS samples, and
the VVDS is compared to other spectroscopic surveys. In total we have obtained
spectroscopic redshifts for 34594 galaxies, 422 type-I AGN, and 12430 Galactic
stars. The survey has enabled to identify galaxies up to very high redshifts
with 4669 redshifts in 1<=z_{spec}<=2, 561 in 2<=z_{spec}<=3 and 468 with
z_{spec}>3, and specific populations like LAE have been identified out to
z=6.62. We show that the VVDS occupies a unique place in the parameter space
defined by area, depth, redshift coverage, and number of spectra. The VVDS
provides a comprehensive survey of the distant universe, covering all epochs
since z, or more than 12 Gyr of cosmic time, with a uniform selection, the
largest such sample to date. A wealth of science results derived from the VVDS
have shed new light on the evolution of galaxies and AGN, and their
distribution in space, over this large cosmic time. A final public release of
the complete VVDS spectroscopic redshift sample is available at
http://cesam.lam.fr/vvds.Comment: Submitted 30 June 2013, Accepted 22 August 2013. Updated with
published versio
The VIMOS Ultra-Deep Survey (VUDS): fast increase of the fraction of strong Lyman alpha emitters from z=2 to z=6
Aims. The aim of this work is to constrain the evolution of the fraction of
Lya emitters among UV selected star forming galaxies at 2<z<6, and to measure
the stellar escape fraction of Lya photons over the same redshift range.
Methods. We exploit the ultradeep spectroscopic observations collected by the
VIMOS Ultra Deep Survey (VUDS) to build an unique, complete and unbiased sample
of 4000 spectroscopically confirmed star forming galaxies at 2<z<6. Our galaxy
sample UV luminosities brighter than M* at 2<z<6, and luminosities down to one
magnitude fainter than M* at 2<z<3.5. Results. We find that 80% of the star
forming galaxies in our sample have EW0(Lya)<10A, and correspondingly
fesc(Lya)<1%. By comparing these results with literature, we conclude that the
bulk of the Lya luminosity at 2<z<6 comes from galaxies that are fainter in the
UV than those we sample in this work. The strong Lya emitters constitute, at
each redshift, the tail of the distribution of the galaxies with extreme
EW0(Lya) and fesc(Lya) . This tail of large EW0 and fesc(Lya) becomes more
important as the redshift increases, and causes the fraction of Lya with EW0>
25A to increase from 5% at z=2 to 30% at z=6, with the increase being
relatively stronger beyond z=4. We observe no difference, for the narrow range
of UV luminosities explored in this work, between the fraction of strong Lya
emitters among galaxies fainter or brighter than M*, although the fraction for
the FUV faint galaxies evolves faster, at 2<z<3.5, than for the bright ones. We
do observe an anticorrelation between E(B-V) and fesc(Lya): generally galaxies
with high fesc(Lya) have also small amounts of dust (and viceversa). However,
when the dust content is low (E(B-V)<0.05) we observe a very broad range of
fesc(Lya), ranging from 10^-3 to 1. This implies that the dust alone is not the
only regulator of the amount of escaping Lya photons.Comment: 12 pages, 6 figures, A&A in pres
Discovering extremely compact and metal-poor, star-forming dwarf galaxies out to z ~ 0.9 in the VIMOS Ultra-Deep Survey
We report the discovery of 31 low-luminosity (-14.5 > M_{AB}(B) > -18.8),
extreme emission line galaxies (EELGs) at 0.2 < z < 0.9 identified by their
unusually high rest-frame equivalent widths (100 < EW[OIII] < 1700 A) as part
of the VIMOS Ultra Deep Survey (VUDS). VIMOS optical spectra of unprecedented
sensitivity ( ~ 25 mag) along with multiwavelength photometry and HST
imaging are used to investigate spectrophotometric properties of this unique
sample and explore, for the first time, the very low stellar mass end (M* <
10^8 M) of the luminosity-metallicity (LZR) and mass-metallicity
(MZR) relations at z < 1. Characterized by their extreme compactness (R50 < 1
kpc), low stellar mass and enhanced specific star formation rates (SFR/M* ~
10^{-9} - 10^{-7} yr^{-1}), the VUDS EELGs are blue dwarf galaxies likely
experiencing the first stages of a vigorous galaxy-wide starburst. Using
T_e-sensitive direct and strong-line methods, we find that VUDS EELGs are
low-metallicity (7.5 < 12+log(O/H) < 8.3) galaxies with high ionization
conditions, including at least three EELGs showing HeII 4686A emission and four
EELGs of extremely metal-poor (<10% solar) galaxies. The LZR and MZR followed
by EELGs show relatively large scatter, being broadly consistent with the
extrapolation toward low luminosity and mass from previous studies at similar
redshift. However, we find evidences that galaxies with younger and more
vigorous star formation -- as characterized by their larger EWs, ionization and
sSFR -- tend to be more metal-poor at a given stellar mass.Comment: Letter in A&A 568, L8 (2014). This replacement matches the published
versio
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