136 research outputs found
Photometric redshifts with Quasi Newton Algorithm (MLPQNA). Results in the PHAT1 contest
Context. Since the advent of modern multiband digital sky surveys,
photometric redshifts (photo-z's) have become relevant if not crucial to many
fields of observational cosmology, from the characterization of cosmic
structures, to weak and strong lensing. Aims. We describe an application to an
astrophysical context, namely the evaluation of photometric redshifts, of
MLPQNA, a machine learning method based on Quasi Newton Algorithm. Methods.
Theoretical methods for photo-z's evaluation are based on the interpolation of
a priori knowledge (spectroscopic redshifts or SED templates) and represent an
ideal comparison ground for neural networks based methods. The MultiLayer
Perceptron with Quasi Newton learning rule (MLPQNA) described here is a
computing effective implementation of Neural Networks for the first time
exploited to solve regression problems in the astrophysical context and is
offered to the community through the DAMEWARE (DAta Mining & ExplorationWeb
Application REsource) infrastructure. Results. The PHAT contest (Hildebrandt et
al. 2010) provides a standard dataset to test old and new methods for
photometric redshift evaluation and with a set of statistical indicators which
allow a straightforward comparison among different methods. The MLPQNA model
has been applied on the whole PHAT1 dataset of 1984 objects after an
optimization of the model performed by using as training set the 515 available
spectroscopic redshifts. When applied to the PHAT1 dataset, MLPQNA obtains the
best bias accuracy (0.0006) and very competitive accuracies in terms of scatter
(0.056) and outlier percentage (16.3%), scoring as the second most effective
empirical method among those which have so far participated to the contest.
MLPQNA shows better generalization capabilities than most other empirical
methods especially in presence of underpopulated regions of the Knowledge Base.Comment: Accepted for publication in Astronomy & Astrophysics; 9 pages, 2
figure
: A Command-line Catalogue Cross-matching tool for modern astrophysical survey data
In the current data-driven science era, it is needed that data analysis
techniques has to quickly evolve to face with data whose dimensions has
increased up to the Petabyte scale. In particular, being modern astrophysics
based on multi-wavelength data organized into large catalogues, it is crucial
that the astronomical catalog cross-matching methods, strongly dependant from
the catalogues size, must ensure efficiency, reliability and scalability.
Furthermore, multi-band data are archived and reduced in different ways, so
that the resulting catalogues may differ each other in formats, resolution,
data structure, etc, thus requiring the highest generality of cross-matching
features. We present (Command-line Catalogue Cross-match), a
multi-platform application designed to efficiently cross-match massive
catalogues from modern surveys. Conceived as a stand-alone command-line process
or a module within generic data reduction/analysis pipeline, it provides the
maximum flexibility, in terms of portability, configuration, coordinates and
cross-matching types, ensuring high performance capabilities by using a
multi-core parallel processing paradigm and a sky partitioning algorithm.Comment: 6 pages, 4 figures, proceedings of the IAU-325 symposium on
Astroinformatics, Cambridge University pres
CLASH-VLT: Is there a dependence in metallicity evolution on galaxy structures?
We investigate the environmental dependence of the mass-metallicty (MZ)
relation and it's connection to galaxy stellar structures and morphologies. In
our studies, we analyze galaxies in massive clusters at z~0.4 from the CLASH
(HST) and CLASH-VLT surveys and measure their gas metallicities, star-formation
rates, stellar structures and morphologies. We establish the MZ relation for 90
cluster and 40 field galaxies finding a shift of ~-0.3 dex in comparison to the
local trends seen in SDSS for the majority of galaxies with logM<10.5. We do
not find significant differences of the distribution of 4 distinct
morphological types that we introduce by our classification scheme (smooth,
disc-like, peculiar, compact). Some variations between cluster and field
galaxies in the MZ relation are visible at the high mass end. However, obvious
trends for cluster specific interactions (enhancements or quenching of SFRs)
are missing. In particular, galaxies with peculiar stellar structures that hold
signs for galaxy interactions, are distributed in a similar way as disc-like
galaxies - in SFRs, masses and O/H abundances. We further show that our sample
falls around an extrapolation of the star-forming main sequence (the SFR-M*
relation) at this redshift, indicating that emission-line selected samples do
not have preferentially high star-formation rates (SFRs). However, we find that
half of the high mass cluster members (M*>10^10Msun) lie below the main
sequence which corresponds to the higher mass objects that reach solar
abundances in the MZ diagram.Comment: Proceedings of IAU Symposium 309, Vienna, ed. B.L. Ziegler, F.
Combes, H. Dannerbauer, M. Verdug
Command-line Cross-matching Tool for Modern Astrophysical Pipelines
The emerging need for efficient, reliable and scalable astronomical catalog cross-matching is becoming more pressing in the current data-driven science era, where the size of data has rapidly increased up to the Petabyte scale. C3 (Command-line Catalogue Cross-matching) is a multi-platform tool designed to efficiently cross-match massive catalogues from modern astronomical surveys, ensuring high-performance capabilities through the use of a multi-core parallel processing paradigm. The tool has been conceived to be executed as a stand-alone command-line process or integrated within any generic data reduction/analysis pipeline, providing the maximum flexibility to the end user, in terms of parameter configuration, coordinates and cross-matching types. In this work we present the architecture and the features of the tool. Moreover, since the modular design of the tool enables an easy customization to specific use cases and requirements, we present also an example of a customized C3 version designed and used in the FP7 project ViaLactea, dedicated to cross-correlate Hi-GAL clumps with multi-band compact sources...
Machine learning based data mining for Milky Way filamentary structures reconstruction
We present an innovative method called FilExSeC (Filaments Extraction,
Selection and Classification), a data mining tool developed to investigate the
possibility to refine and optimize the shape reconstruction of filamentary
structures detected with a consolidated method based on the flux derivative
analysis, through the column-density maps computed from Herschel infrared
Galactic Plane Survey (Hi-GAL) observations of the Galactic plane. The present
methodology is based on a feature extraction module followed by a machine
learning model (Random Forest) dedicated to select features and to classify the
pixels of the input images. From tests on both simulations and real
observations the method appears reliable and robust with respect to the
variability of shape and distribution of filaments. In the cases of highly
defined filament structures, the presented method is able to bridge the gaps
among the detected fragments, thus improving their shape reconstruction. From a
preliminary "a posteriori" analysis of derived filament physical parameters,
the method appears potentially able to add a sufficient contribution to
complete and refine the filament reconstruction.Comment: Proceeding of WIRN 2015 Conference, May 20-22, Vietri sul Mare,
Salerno, Italy. Published in Smart Innovation, Systems and Technology,
Springer, ISSN 2190-3018, 9 pages, 4 figure
A Command-line Cross-matching tool for modern astrophysical pipelines
The emerging need for efficient, reliable and scalable astronomical catalog cross-matching is becoming more pressing in the current data-driven science era, where the size of data has rapidly increased up to the Petabyte scale. C3 (Command-line Catalogue Cross-matching) is a multi-platform tool designed to efficiently cross-match massive catalogues from modern astronomical surveys, ensuring high-performance capabilities through the use of a multi-core parallel processing paradigm. The tool has been conceived to be executed as a stand-alone command-line process or integrated within any generic data reduction/analysis pipeline, providing the maximum flexibility to the end user, in terms of parameter configuration, coordinates and cross-matching types. In this work we present the architecture and the features of the tool. Moreover, since the modular design of the tool enables an easy customization to specific use cases and requirements, we present also an example of a customized C3 version designed and used in the FP7 project ViaLactea, dedicated to cross-correlate Hi-GAL clumps with multi-band compact sources...
Shapley Supercluster Survey: mapping the dark matter distribution
We present a 23deg weak gravitational lensing survey of the Shapley
supercluster core and its surroundings using VST images as part of the
Shapley Supercluster Survey (ShaSS). This study reveals the overall matter
distribution over a region containing 11 clusters at that are
all interconnected, as well as several ongoing cluster-cluster interactions.
Galaxy shapes have been measured by using the Kaiser-Squires-Broadhurst method
for the - and -band images and background galaxies were selected via the
colour-colour diagram. This technique has allowed us to detect all of the
clusters, either in the -band or -band images, although at different
levels, indicating that the underlying dark matter distribution is
tightly correlated with the number density of the member galaxies. The deeper
-band images have traced the five interacting clusters in the supercluster
core as a single coherent structure, confirmed the presence of a filament
extending North from the core, and have revealed a background cluster at
. We have measured the masses of the four richest clusters (A3556,
A3558, A3560 and A3562) in the two-dimensional shear pattern, assuming a
spherical Navarro-Frenk-White (NFW) profile and obtaining a total mass of
, which is consistent with dynamical and X-ray studies. Our
analysis provides further evidence of the ongoing dynamical evolution in the
ShaSS region.Comment: 16 pages, 11 figures, 4 tables. Accepted for publication in MNRA
Exploring the low-mass regime of galaxy-scale strong lensing: Insights into the mass structure of cluster galaxies
We aim at a direct measurement of the compactness of three galaxy-scale
lenses in massive clusters, testing the accuracy of the scaling laws that
describe the members in strong lensing (SL) models of galaxy clusters. We
selected the multiply imaged sources MACS J0416.12403 ID14 (), MACS
J0416.12403 ID16 (), and MACS J1206.20847 ID14 ().
Eight images were observed for the first SL system, and six for the latter two.
We focused on the main deflector of each galaxy-scale SL system (identified as
members 8971, 8785, and 3910, respectively), and modelled its total mass
distribution with a truncated isothermal sphere. We accounted for the lensing
effects of the remaining cluster components, and included the uncertainty on
the cluster-scale mass distribution through a bootstrapping procedure. We
measured a truncation radius value of ,
, and
for members 8971, 8785, and 3910, respectively. Alternative non-truncated
models with a higher number of free parameters do not lead to an improved
description of the SL system. We measured the stellar-to-total mass fraction
within the effective radius for the three members, finding ,
, and , respectively. We find that a parameterisation
of the properties of cluster galaxies in SL models based on power-law scaling
relations with respect to the total luminosity cannot accurately describe their
compactness over their full total mass range. Our results agree with modelling
of the cluster members based on the Fundamental Plane relation. Finally, we
report good agreement between our values of the stellar-to-total mass fraction
within and those of early-type galaxies from the SLACS Survey. Our work
significantly extends the regime of the current samples of lens galaxies.Comment: Astronomy & Astrophysics, 679, A124 (2023), 15 pages, 12 figures, 8
table
Systematic search for lensed X-ray sources in the CLASH fields
We search for unresolved X-ray emission from lensed sources in the FOV of 11
CLASH clusters with Chandra data. We consider the solid angle in the lens plane
corresponding to a magnification , that amounts to a total of ~100
arcmin. Our main goal is to assess the efficiency of massive clusters as
cosmic telescopes to explore the faint end of X-ray extragalactic source
population. We search for X-ray emission from strongly lensed sources
identified in the optical, and perform an untargeted detection of lensed X-ray
sources. We detect X-ray emission only in 9 out of 849 lensed/background
optical sources. The stacked emission of the sources without detection does not
reveal any signal in any band. Based on the untargeted detection, we find 66
additional X-ray sources that are consistent with being lensed sources. After
accounting for completeness and sky coverage, we measure for the first time the
soft- and hard-band number counts of lensed X-ray sources. The results are
consistent with current modelization of the AGN population distribution. The
distribution of de-lensed fluxes of the sources identified in moderately deep
CLASH fields reaches a flux limit of ~ and ~ erg/s/cm
in the soft and hard bands, respectively. We conclude that, in order to match
the depth of the CDFS exploiting massive clusters as cosmic telescopes, the
required number of cluster fields is about two orders of magnitude larger than
that offered by the 20 years Chandra archive. A significant step forward will
be made when future X-ray facilities, with ~1' angular resolution and large
effective area, will allow the serendipitous discovery of rare, strongly lensed
high- X-ray sources, enabling the study of faint AGN activity in early
Universe and the measurement of gravitational time delays in the X-ray
variability of multiply imaged AGN.Comment: Accepted for publication in A&
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