178 research outputs found
Synthesis Characterization and Antimicrobial Activity of Metal Chelates of 1, 7-Di (2-hydroxyphenyl) 1, 7 di (N-methyl) aza-1, 3, 5 heptarine-3-ol hydrochloride
Abstract: The Schiff base complexes derived from 2-furancarboxaldehyde and N-methyl-2-amino phenol have been prepared and characterized using several physical techniques, like elemental analysis, thermogravimetric analysis, magnetic moment measurements, infrared and resonance spectra. N-Methyl-2-amino phenol was condensed stoichiometrically with 2-furancarboxaldehyde in presence of methanol. The resulting 1,7-di(2-hydroxyphenyl) 1,7 di(N-methyl) aza-1,3,5 heptarine-3-ol hydrochloride was characterized by elemental analysis and spectral studies. The transition metal complexes of Cu 2+ , Zn 2+ , Ni 2+ , Co 2+ and Mn 2+ of the synthesized complexes were prepared. Metal ligand (M:L) ratio, IR, reflectance spectral studies, magnetic properties and antimicrobial activity of the synthesized complexes and its metal complexes were carried out
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
Clues to AGN Growth from Optically Variable Objects in the Hubble Ultra Deep Field
We present a photometric search for objects with point-source components that
are optically variable on timescales of weeks--months in the Hubble Ultra Deep
Field (HUDF) to i'(AB)=28.0 mag. The data are split into four sub-stacks of
approximately equal exposure times. Objects exhibiting the signature of optical
variability are selected by studying the photometric error distribution between
the four different epochs, and selecting 622 candidates as 3.0 sigma outliers
from the original catalog of 4644 objects. Of these, 45 are visually confirmed
as free of contamination from close neighbors or various types of image
defects. Four lie within the positional error boxes of Chandra X-ray sources,
and two of these are spectroscopically confirmed AGN. The photometric redshift
distribution of the selected variable sample is compared to that of field
galaxies, and we find that a constant fraction of ~1% of all field objects show
variability over the range of 0.1<z<4.5. Combined with other recent HUDF
results, as well as those of recent state-of-the-art numerical simulations, we
discuss a potential link between the hierarchical merging of galaxies and the
growth of AGN.Comment: 9 pages, 6 figures, accepted for publication in Astrophysical
Journal, minor changes to reference
Limits on the LyC signal from z~3 sources with secure redshift and HST coverage in the E-CDFS field
Aim: We aim to measure the LyC signal from a sample of sources in the Chandra
deep field south. We collect star-forming galaxies (SFGs) and active galactic
nuclei (AGN) with accurate spectroscopic redshifts, for which Hubble Space
Telescope (HST) coverage and multi-wavelength photometry are available. Method:
We selected a sample of about 200 sources at z~3. Taking advantage of HST
resolution, we applied a careful cleaning procedure and rejected sources
showing nearby clumps with different colours, which could be lower-z
interlopers. Our clean sample consisted of 86 SFGs (including 19 narrow-band
selected Lya emitters) and 8 AGN (including 6 detected in X-rays). We measured
the LyC flux from aperture photometry in four narrow-band filters covering
wavelengths below a 912 A rest frame (3.11<z<3.53). We estimated the ratio
between ionizing (LyC flux) and 1400 A non-ionizing emissions for AGN and
galaxies. Results: By running population synthesis models, we assume an average
intrinsic L(1400 A)/L(900 A) ratio of 5 as the representative value for our
sample. With this value and an average treatment of the lines of sight of the
inter-galactic medium, we estimate the LyC escape fraction relative to the
intrinsic value (fesc_rel(LyC)). We do not directly detect ionizing radiation
from any individual SFG, but we are able to set a 1(2)sigma upper limit of
fesc_rel(LyC)<12(24)%. This result is consistent with other non-detections
published in the literature. No meaningful limits can be calculated for the
sub-sample of Lya emitters. We obtain one significant direct detection for an
AGN at z=3.46, with fesc_rel(LyC) = (72+/-18)%. Conclusions: Our upper limit on
fescrel(LyC) implies that the SFGs studied here do not present either the
physical properties or the geometric conditions suitable for efficient
LyC-photon escape.Comment: Accepted for publication in A&A on Jan 5th, 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 Hawk-I UDS and GOODS Survey (HUGS): Survey design and deep K-band number counts
We present the results of a new, ultra-deep, near-infrared imaging survey
executed with the Hawk-I imager at the ESO VLT, of which we make all the data
public. This survey, named HUGS (Hawk-I UDS and GOODS Survey), provides deep,
high-quality imaging in the K and Y bands over the CANDELS UDS and GOODS-South
fields. We describe here the survey strategy, the data reduction process, and
the data quality. HUGS delivers the deepest and highest quality K-band images
ever collected over areas of cosmological interest, and ideally complements the
CANDELS data set in terms of image quality and depth. The seeing is exceptional
and homogeneous, confined to the range 0.38"-0.43". In the deepest region of
the GOODS-S field, (which includes most of the HUDF) the K-band exposure time
exceeds 80 hours of integration, yielding a 1-sigma magnitude limit of ~28.0
mag/sqarcsec. In the UDS field the survey matches the shallower depth of the
CANDELS images reaching a 1-sigma limit per sq.arcsec of ~27.3mag in the K band
and ~28.3mag in the Y-band, We show that the HUGS observations are well matched
to the depth of the CANDELS WFC3/IR data, since the majority of even the
faintest galaxies detected in the CANDELS H-band images are also detected in
HUGS. We present the K-band galaxy number counts produced by combining the HUGS
data from the two fields. We show that the slope of the number counts depends
sensitively on the assumed distribution of galaxy sizes, with potential impact
on the estimated extra-galactic background light (abridged).Comment: Accepted for publication on Astronomy and Astrophysic
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
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
The VIMOS Ultra Deep Survey: Ly Emission and Stellar Populations of Star-Forming Galaxies at 2<z<2.5
The aim of this paper is to investigate spectral and photometric properties
of 854 faint (<~25 mag) star-forming galaxies (SFGs) at 2<z<2.5 using
the VIMOS Ultra-Deep Survey (VUDS) spectroscopic data and deep multi-wavelength
photometric data in three extensively studied extragalactic fields (ECDFS,
VVDS, COSMOS). These SFGs were targeted for spectroscopy based on their
photometric redshifts. The VUDS spectra are used to measure the UV spectral
slopes () as well as Ly equivalent widths (EW). On average, the
spectroscopically measured (-1.360.02), is comparable to the
photometrically measured (-1.320.02), and has smaller measurement
uncertainties. The positive correlation of with the Spectral Energy
Distribution (SED)-based measurement of dust extinction, E(B-V),
emphasizes the importance of as an alternative dust indicator at high
redshifts. To make a proper comparison, we divide these SFGs into three
subgroups based on their rest-frame Ly EW: SFGs with no Ly
emission (SFG; EW0\AA), SFGs with Ly emission (SFG; EW0\AA), and Ly emitters (LAEs; EW20\AA). The fraction of
LAEs at these redshifts is 10%, which is consistent with previous
observations. We compared best-fit SED-estimated stellar parameters of the
SFG, SFG and LAE samples. For the luminosities probed here
(L), we find that galaxies with and without Ly in emission
have small but significant differences in their SED-based properties. We find
that LAEs have less dust, and lower star-formation rates (SFR) compared to
non-LAEs. We also find that LAEs are less massive compared to non-LAEs, though
the difference is smaller and less significant compared to the SFR and E(B-V). [abridged]Comment: Accepted for publication in A&A, 19 pages, 10 figures, 1 tabl
The evolution of clustering length, large-scale bias and host halo mass at 2<z<5 in the VIMOS Ultra Deep Survey (VUDS)
We investigate the evolution of galaxy clustering for galaxies in the
redshift range 2.0<<5.0 using the VIMOS Ultra Deep Survey (VUDS). We present
the projected (real-space) two-point correlation function measured
by using 3022 galaxies with robust spectroscopic redshifts in two independent
fields (COSMOS and VVDS-02h) covering in total 0.8 deg. We quantify how the
scale dependent clustering amplitude changes with redshift making use of
mock samples to evaluate and correct the survey selection function. Using a
power-law model we find that the correlation
function for the general population is best fit by a model with a clustering
length =3.95 hMpc and slope
=1.8 at ~2.5, =4.350.60 hMpc and
=1.6 at ~3.5. We use these clustering parameters
to derive the large-scale linear galaxy bias , between galaxies and
dark matter. We find = 2.680.22 at redshift ~3 (assuming
= 0.8), significantly higher than found at intermediate and low
redshifts. We fit an HOD model to the data and we obtain that the average halo
mass at redshift ~3 is =10 hM. From
this fit we confirm that the large-scale linear galaxy bias is relatively high
at = 2.820.27. Comparing these measurements with similar
measurements at lower redshifts we infer that the star-forming population of
galaxies at ~3 should evolve into the massive and bright (<-21.5)
galaxy population which typically occupy haloes of mass =
10 h at redshift =0.Comment: 19 pages, 10 figures, submitted to A&
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