604 research outputs found
Beyond the current noise limit in imaging through turbulent medium
Shift-and-add is an approach employed to mitigate the phenomenon of
resolution degradation in images acquired through a turbulent medium. Using
this technique, a large number of consecutive short exposures is registered
below the coherence time of the atmosphere or other blurring medium. The
acquired images are shifted to the position of the brightest speckle and
stacked together to obtain high-resolution and high signal-to-noise frame. In
this paper we present a highly efficient method for determination of frames
shifts, even if in a single frame the object cannot be distinguished from the
background noise. The technique utilizes our custom genetic algorithm, which
iteratively evolves a set of image shifts. We used the maximal energy of
stacked images as an objective function for shifts estimation and validate the
efficiency of the method on simulated and real images of simple and complex
sources. Obtained results confirmed, that our proposed method allows for the
recovery of spatial distribution of objects even only 2% brighter than their
background. The presented approach extends significantly current limits of
image reconstruction with the use of shift-and-add method. The applications of
our algorithm include both the optical and the infrared imaging. Our method may
be also employed as a digital image stabilizer in extremely low light level
conditions in professional and consumer applications.Comment: 8 pages, 4 figure
The VIMOS Ultra Deep Survey. Luminosity and stellar mass dependence of galaxy clustering at z~3
We present the study of the dependence of galaxy clustering on luminosity and
stellar mass in the redshift range 2z3.5 using 3236 galaxies with robust
spectroscopic redshifts from the VIMOS Ultra Deep Survey (VUDS). We measure the
two-point real-space correlation function for four volume-limited
stellar mass and four luminosity, M absolute magnitude selected,
sub-samples. We find that the scale dependent clustering amplitude
significantly increases with increasing luminosity and stellar mass indicating
a strong galaxy clustering dependence on these properties. This corresponds to
a strong relative bias between these two sub-samples of b/b=0.43.
Fitting a 5-parameter HOD model we find that the most luminous and massive
galaxies occupy the most massive dark matter haloes with
M = 10 h M. Similar to the
trends observed at lower redshift, the minimum halo mass M depends on
the luminosity and stellar mass of galaxies and grows from M
=10 hM to M=10 hM
from the faintest to the brightest among our galaxy sample, respectively. We
find the difference between these halo masses to be much more pronounced than
is observed for local galaxies of similar properties. Moreover, at z~3, we
observe that the masses at which a halo hosts, on average, one satellite and
one central galaxy is M4M over all luminosity ranges,
significantly lower than observed at z~0 indicating that the halo satellite
occupation increases with redshift. The luminosity and stellar mass dependence
is also reflected in the measurements of the large scale galaxy bias, which we
model as b(L)=1.92+25.36(L/L). We conclude our study
with measurements of the stellar-to-halo mass ratio (SHMR).Comment: 20 pages, 11 figures, A&A in press, v2. revised discussion in sec.
5.5, changed Fig. 4 and Fig. 11, added reference
The VIMOS-VLT Deep Survey: Dependence of galaxy clustering on stellar mass
We have investigated the dependence of galaxy clustering on their stellar
mass at z~1, using the data from the VIMOS-VLT Deep Survey (VVDS). We have
measured the projected two-point correlation function of galaxies, wp(rp) for a
set of stellar mass selected samples at an effective redshift =0.85. We have
control and quantify all effects on galaxy clustering due to the incompleteness
of our low mass samples. We find that more massive galaxies are more clustered.
When compared to similar results at z~0.1 in the SDSS, we observed no evolution
of the projected correlation function for massive galaxies. These objects
present a stronger linear bias at z~1 with respect to low mass galaxies. As
expected, massive objects at high redshift are found in the highest pics of the
dark matter density field.Comment: 4 pages, 2 figures, 43rd Rencontres de Moriond - March 15-22, 2008 -
La Thuile (Val d'Aosta, Italy
Tracing dark energy with quasars
The nature of dark energy, driving the accelerated expansion of the Universe,
is one of the most important issues in modern astrophysics. In order to
understand this phenomenon, we need precise astrophysical probes of the
universal expansion spanning wide redshift ranges. Quasars have recently
emerged as such a probe, thanks to their high intrinsic luminosities and, most
importantly, our ability to measure their luminosity distances independently of
redshifts. Here we report our ongoing work on observational reverberation
mapping using the time delay of the Mg II line, performed with the South
African Large Telescope (SALT).Comment: 3 pages, 2 figures, submitted as PTA proceeding
Avaliação de giberela em genótipos de triticale.
Editores técnicos: Joseani Mesquita Antunes, Ana Lídia Variani Bonato, Márcia Barrocas Moreira Pimentel
The VIMOS-VLT Deep Survey: Dependence of Galaxy Clustering on Luminosity
We have investigated the dependence of galaxy clustering on their intrinsic luminosities at z ~ 1, using the data from the First Epoch VIMOS-VLT Deep Survey (VVDS). We have measured the projected two-point correlation function of galaxies, w_p(r_p), for a set of volume-limited samples at an effective redshift =0.9 and median absolute magnitude -19.6< M_B < -21.3. We find that the clustering strength is rising around M_B^*, apparently with a sharper turn than observed at low redshifts. The slope of the correlation function is observed to steepen significantly from \gamma=1.6^{+0.1}_{-0.1} to \gamma=2.4^{+0.4}_{-0.2}. This is due to a significant change in the shape of w_p(r_p), increasingly deviating from a power-law for the most luminous samples, with a strong upturn at small (< 1-2 h^{-1} Mpc) scales. This trend, not observed locally, also results in a strong scale dependence of the relative bias, b/b* and possibly imply a significant change in the way luminous galaxies trace dark-matter halos at z ~ 1 with respect to z ~ 0
Progresso da fusariose em espigas de triticale.
Editores técnicos: Joseani Mesquita Antunes, Ana Lídia Variani Bonato, Márcia Barrocas Moreira Pimentel
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&
Harmonising the definition of refinement
Russell and Burch's Three Rs (replacement, reduction and refinement) remain the cornerstone for principles guiding humane experimental research. However, the concept of refinement has evolved considerably since its first inception and there have been numerous interpretations, some of which are regressive from the original definition. In this paper we examine the interpretations of refinement, and propose a harmonised progressive definition that is in line with changes in animal ethics and animal welfare science. Our definition should be applied to all aspects of refinement: those related to housing, husbandry and care, techniques used in scientific procedures, periprocedural care, health and welfare monitoring, and experimental design. We argue not only that the concept should include the avoidance or minimisation of adverse effects experienced at any time during the life of an animal destined for use in a laboratory, but also that it should be applied to the founder animals. Furthermore, we take a proactive stance and argue that refinement should include enhancing well-being through environmental enrichment. The acceptance and application of this new definition by legislative authorities and in guidelines would represent a significant step forward for animal welfare
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
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