583 research outputs found
Lyman-break galaxies at z~5 -I. First significant stellar mass assembly in galaxies that are not simply z~3 LBGs at higher redshift
We determine the ensemble properties of z~5 Lyman break galaxies (LBGs)
selected as V-band dropouts to i(AB)<26.3 in the Chandra Deep Field South using
their rest-frame UV-to-visible SEDs. By matching the selection and performing
the same analysis that has been used for z~3 samples, we show clear differences
in the properties of two samples of LBGs which are separated by ~1Gyr in
lookback time. We find that z~5 LBGs are typically much younger (<100Myr) and
have lower stellar masses (10^9Msol) than their z~3 counterparts. The
difference in mass is significant even when considering the presence of an
older, underlying population in both samples. Such young and moderately massive
systems dominate the luminous z~5 LBG population (>70%), whereas they comprise
<30% of LBG samples at z~3. This result is robust under all reasonable
modelling assumptions. These intense starbursts appear to be experiencing their
first (few) generations of large-scale star formation and are accumulating
their first significant stellar mass. Their dominance in luminous LBG samples
suggests that z~5 witnesses a period of wide-spread, recent galaxy formation.
As such, z~5 LBGs are the likely progenitors of the spheroidal components of
present-day massive galaxies. This is supported by their high stellar mass
surface densities, their core phase-space densities, as well as the ages of
stars in the bulge of our Galaxy and other massive systems. Their high star
formation rates per unit area suggest that these systems host outflows or winds
that enrich the intra- and inter-galactic media with metals. Their estimated
young ages are consistent with inefficient metal-mixing on galaxy-wide scales.
Therefore these galaxies may contain a significant fraction of metal-free stars
as has been proposed for z~3 LBGs (Jimenez & Haiman 2006). [Abridged]Comment: Accepted for publication in MNRAS. 21 pages, 9 postscript figures.
For a PDF file with high resolution figures, see
http://www-astro.physics.ox.ac.uk/~averma
A method for space-variant deblurring with application to adaptive optics imaging in astronomy
Images from adaptive optics systems are generally affected by significant
distortions of the point spread function (PSF) across the field of view,
depending on the position of natural and artificial guide stars. Image
reduction techniques circumventing or mitigating these effects are important
tools to take full advantage of the scientific information encoded in AO
images. The aim of this paper is to propose a method for the deblurring of the
astronomical image, given a set of samples of the space-variant PSF. The method
is based on a partitioning of the image domain into regions of isoplanatism and
on applying suitable deconvolution methods with boundary effects correction to
each region. The effectiveness of the boundary effects correction is proved.
Moreover, the criterion for extending the disjoint sections to partially
overlapping sections is validated. The method is applied to simulated images of
a stellar system characterized by a spatially variable PSF. We obtain good
photometric quality, and therefore good science quality, by performing aperture
photometry on the deblurred images. The proposed method is implemented in IDL
in the Software Package "Patch", which is available on
http://www.airyproject.eu.Comment: 11 pages, 9 figures, 7 tables, accepted by A&
High Fidelity Simulation with Peer Debriefing: Influence of Student Observation and Participation Roles on Student Perception of Confidence with Learning and Feedback
High fidelity simulation (HFS) has been used successfully to prepare students in a range of health professions for the acute care setting. HFS consists of three phases, with debriefing identified as most important. Instructor-led debriefing has been the most documented form of providing feedback. This pilot study looked at the relationship between the use of peer debriefing in HFS on graduate occupational therapy studentsâ perceived level of confidence with giving and receiving performance related feedback. Students in an entry-level Master of Occupational Therapy program engaged in both an observational role and an active participation role in HFS followed by peer debriefing. Students completed a Likert scale pre- and post-survey to determine perceived confidence and competence with learning modalities (active participation vs. observation) and with giving and receiving feedback during HFS. Results indicate that students perceived benefit from both active participation and observation during HFS experiences. A separate analysis determined the relationship between the studentsâ perceived confidence with learning modalities and the order of the student roles (observer and doer). Initially, there appeared to be a benefit to the doer role. However, after experiencing both roles, student responses indicated all students perceived value in multimodal learning. The current study presents useful information regarding student perceptions related to learning and feedback within an HFS experience
End to end numerical simulations of the MAORY multiconjugate adaptive optics system
MAORY is the adaptive optics module of the E-ELT that will feed the MICADO
imaging camera through a gravity invariant exit port. MAORY has been foreseen
to implement MCAO correction through three high order deformable mirrors driven
by the reference signals of six Laser Guide Stars (LGSs) feeding as many
Shack-Hartmann Wavefront Sensors. A three Natural Guide Stars (NGSs) system
will provide the low order correction. We develop a code for the end-to-end
simulation of the MAORY adaptive optics (AO) system in order to obtain
high-delity modeling of the system performance. It is based on the IDL language
and makes extensively uses of the GPUs. Here we present the architecture of the
simulation tool and its achieved and expected performance.Comment: 8 pages, 4 figures, presented at SPIE Astronomical Telescopes +
Instrumentation 2014 in Montr\'eal, Quebec, Canada, with number 9148-25
Deblurring of post-adaptive optics images
The novel and freely available âPatchâ software package can be used to deconvolve images that have spatially variable point spread functions
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