103 research outputs found
AMICO galaxy clusters in KiDS-DR3: sample properties and selection function
We present the first catalogue of galaxy cluster candidates derived from the
third data release of the Kilo Degree Survey (KiDS-DR3). The sample of clusters
has been produced using the Adaptive Matched Identifier of Clustered Objects
(AMICO) algorithm. In this analysis AMICO takes advantage of the luminosity and
spatial distribution of galaxies only, not considering colours. In this way, we
prevent any selection effect related to the presence or absence of the
red-sequence in the clusters. The catalogue contains 7988 candidate galaxy
clusters in the redshift range 0.13.5 with a purity
approaching 95% over the entire redshift range. In addition to the catalogue of
galaxy clusters we also provide a catalogue of galaxies with their
probabilistic association to galaxy clusters. We quantify the sample purity,
completeness and the uncertainties of the detection properties, such as
richness, redshift, and position, by means of mock galaxy catalogues derived
directly from the data. This preserves their statistical properties including
photo-z uncertainties, unknown absorption across the survey, missing data,
spatial correlation of galaxies and galaxy clusters. Being based on the real
data, such mock catalogues do not have to rely on the assumptions on which
numerical simulations and semi-analytic models are based on. This paper is the
first of a series of papers in which we discuss the details and physical
properties of the sample presented in this work.Comment: 16 pages, 14 figures, 3 tables, submitted to MNRA
GASP XIX: AGN and their outflows at the center of jellyfish galaxies
The GASP survey, based on MUSE data, is unveiling the properties of the gas
in the so-called "jellyfish" galaxies: these are cluster galaxies with
spectacular evidence of gas stripping by ram pressure. In a previous paper, we
selected the seven GASP galaxies with the most extended tentacles of ionized
gas, and based on individual diagnostic diagrams concluded that at least five
of them present clear evidence for an Active Galactic Nucleus. Here we present
a more detailed analysis of the emission lines properties in these galaxies.
Our comparison of several emission line ratios with both AGN and shock models
show that photoionization by the AGN is the dominant ionization mechanism. This
conclusion is strengthened by the analysis of luminosities, the
presence of nuclear iron coronal lines and extended ( kpc) emission line
regions ionized by the AGN in some of these galaxies. From emission line
profiles, we find the presence of outflows in four galaxies, and derive mass
outflow rates, timescales and kinetic energy of the outflows.Comment: 20 pages, 10 Figure
AMICO galaxy clusters in KiDS-DR3: weak-lensing mass calibration
We present the mass calibration for galaxy clusters detected with the AMICO
code in KiDS DR3 data. The cluster sample comprises 7000 objects and
covers the redshift range 0.1 < < 0.6. We perform a weak lensing stacked
analysis by binning the clusters according to redshift and two different mass
proxies provided by AMICO, namely the amplitude (measure of galaxy
abundance through an optimal filter) and the richness (sum of
membership probabilities in a consistent radial and magnitude range across
redshift). For each bin, we model the data as a truncated NFW profile plus a
2-halo term, taking into account uncertainties related to concentration and
miscentring. From the retrieved estimates of the mean halo masses, we construct
the - and the - relations. The relations extend
over more than one order of magnitude in mass, down to at = 0.2 (0.5), with small evolution in redshift.
The logarithmic slope is for the -mass relation, and
for the -mass relation, consistent with previous estimations on mock
catalogues and coherent with the different nature of the two observables.Comment: 19 pages, 16 figures, accepted by MNRA
Statistical analysis of probability density functions for photometric redshifts through the KiDS-ESO-DR3 galaxies
Despite the high accuracy of photometric redshifts (zphot) derived using
Machine Learning (ML) methods, the quantification of errors through reliable
and accurate Probability Density Functions (PDFs) is still an open problem.
First, because it is difficult to accurately assess the contribution from
different sources of errors, namely internal to the method itself and from the
photometric features defining the available parameter space. Second, because
the problem of defining a robust statistical method, always able to quantify
and qualify the PDF estimation validity, is still an open issue. We present a
comparison among PDFs obtained using three different methods on the same data
set: two ML techniques, METAPHOR (Machine-learning Estimation Tool for Accurate
PHOtometric Redshifts) and ANNz2, plus the spectral energy distribution
template fitting method, BPZ. The photometric data were extracted from the KiDS
(Kilo Degree Survey) ESO Data Release 3, while the spectroscopy was obtained
from the GAMA (Galaxy and Mass Assembly) Data Release 2. The statistical
evaluation of both individual and stacked PDFs was done through quantitative
and qualitative estimators, including a dummy PDF, useful to verify whether
different statistical estimators can correctly assess PDF quality. We conclude
that, in order to quantify the reliability and accuracy of any zphot PDF
method, a combined set of statistical estimators is required.Comment: Accepted for publication by MNRAS, 20 pages, 14 figure
GASP XIII. Star formation in gas outside galaxies
Based on MUSE data from the GASP survey, we study the Halpha-emitting
extraplanar tails of 16 cluster galaxies at z~0.05 undergoing ram pressure
stripping. We demonstrate that the dominating ionization mechanism of this gas
(between 64% and 94% of the Halpha emission in the tails depending on the
diagnostic diagram used) is photoionization by young massive stars due to
ongoing star formation (SF) taking place in the stripped tails. This SF occurs
in dynamically quite cold HII clumps with a median Halpha velocity dispersion
sigma = 27 km s^-1. We study the characteristics of over 500 star-forming
clumps in the tails and find median values of Halpha luminosity L_{Halpha} = 4
X 10^38 erg s^-1, dust extinction A_V=0.5 mag, star formation rate SFR=0.003
M_sun yr^-1, ionized gas density n_e =52 cm^-3, ionized gas mass M_gas = 4 X
10^4 Msun, and stellar mass M_{*} = 3 X 10^6 Msun. The tail clumps follow
scaling relations (M_gas-M_{*}, L_{Halpha} -sigma, SFR-M_gas) similar to disk
clumps, and their stellar masses are comparable to Ultra Compact Dwarfs and
Globular Clusters.The diffuse gas component in the tails is ionized by a
combination of SF and composite/LINER-like emission likely due to thermal
conduction or turbulence. The stellar photoionization component of the diffuse
gas can be due either to leakage of ionizing photons from the HII clumps with
an average escape fraction of 18%, or lower luminosity HII regions that we
cannot individually identify.Comment: accepted for publication in MNRA
Galaxy-galaxy weak-lensing measurement from SDSS: II. host halo properties of galaxy groups
As the second paper of a series on studying galaxy-galaxy lensing signals
using the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), we present our
measurement and modelling of the lensing signals around groups of galaxies. We
divide the groups into four halo mass bins, and measure the signals around four
different halo-center tracers: brightest central galaxy (BCG),
luminosity-weighted center, number-weighted center and X-ray peak position. For
X-ray and SDSS DR7 cross identified groups, we further split the groups into
low and high X-ray emission subsamples, both of which are assigned with two
halo-center tracers, BCGs and X-ray peak positions. The galaxy-galaxy lensing
signals show that BCGs, among the four candidates, are the best halo-center
tracers. We model the lensing signals using a combination of four
contributions: off-centered NFW host halo profile, sub-halo contribution,
stellar contribution, and projected 2-halo term. We sample the posterior of 5
parameters i.e., halo mass, concentration, off-centering distance, sub halo
mass, and fraction of subhalos via a MCMC package using the galaxy-galaxy
lensing signals. After taking into account the sampling effects (e.g. Eddington
bias), we found the best fit halo masses obtained from lensing signals are
quite consistent with those obtained in the group catalog based on an abundance
matching method, except in the lowest mass bin. Subject headings: (cosmology:)
gravitational lensing, galaxies: clusters: generalComment: 12 pages, 7 figures, submitted to Ap
Gas-phase metallicity of local AGN in the GASP and MaNGA surveys: the role of ram-pressure stripping
Growing evidence in support of a connection between Active Galactic Nuclei
(AGN) activity and the Ram-Pressure Stripping (RPS) phenomenon has been found
both observationally and theoretically in the past decades. In this work, we
further explore the impact of RPS on the AGN activity by estimating the
gas-phase metallicity of nuclear regions and the mass-metallicity relation of
galaxies at 0.07 and with stellar masses , either experiencing RPS or not. To measure oxygen
abundances, we exploit Integral Field Spectroscopy data from the GASP and MaNGA
surveys, photoionization models generated with the code CLOUDY and the code
Nebulabayes to compare models and observations. In particular, we build CLOUDY
models to reproduce line ratios induced by photoionization from stars, AGN, or
a contribution of both. We find that the distributions of metallicity and [O
III]5007 luminosity of galaxies undergoing RPS are similar to the ones
of undisturbed galaxies. Independently of the RPS, we do not find a correlation
between stellar mass and AGN metallicity in the mass range , while for the star-forming galaxies we observe the
well-known mass-metallicity relation (MZR) between with a scatter mainly driven by the star-formation
rate (SFR) and a plateau around . The
gas-phase metallicity in the nuclei of AGN hosts is enhanced with respect to
those of SF galaxies by a factor of 0.05 dex regardless of the RPS
CoMaLit -- VI. Intrinsic scatter in stacked relations. The weak lensing AMICO galaxy clusters in KiDS-DR3
Unbiased and precise mass calibration of galaxy clusters is crucial to fully
exploit galaxy clusters as cosmological probes. Stacking of weak lensing signal
allows us to measure observable-mass relations down to less massive halos halos
without extrapolation. We propose a Bayesian inference method to constrain the
intrinsic scatter of the mass proxy in stacked analyses. The scatter of the
stacked data is rescaled with respect to the individual scatter based on the
number of binned clusters. We apply this method to the galaxy clusters detected
with the AMICO (Adaptive Matched Identifier of Clustered Objects) algorithm in
the third data release of the Kilo-Degree Survey. The results confirm the
optical richness as a low scatter mass proxy. Based on the optical richness and
the calibrated weak lensing mass-richness relation, mass of individual objects
down to ~10^13 solar masses can be estimated with a precision of ~20 per cent.Comment: 12 pages, 6 figures; in press on MNRA
Evidence for enhanced star formation rates in z~0.35 cluster galaxies undergoing ram pressure stripping
Ram pressure stripping (RPS) is one of the most invoked mechanisms to explain
the observed differences between cluster and field galaxies. In the local
Universe, its effect on the galaxy star forming properties has been largely
tackled and the general consensus is that this process first compresses the gas
available in the galaxy disks, boosting the star formation for a limited amount
of time, and then removes the remaining gas leading to quenching. Much less is
known on the effect and preponderance of RPS at higher redshift, due to the
lack of statistical samples. Exploiting VLT/MUSE observations of galaxies at
0.2<z<0.55 and the catalog of ram pressure stripped galaxies by Moretti et al.,
we compare the global star formation rate-mass (SFR-M*) relation of 29 cluster
galaxies undergoing RPS to that of 26 field and cluster undisturbed galaxies
that constitute our control sample. Stripping galaxies occupy the upper
envelope of the control sample SFR-M* relation, showing a systematic
enhancement of the SFR at any given mass. The boost is >3sigma when considering
the SFR occurring in both the tail and disk of galaxies. The enhancement is
retrieved also on local scales: considering spatially resolved data, ram
pressure stripped galaxies overall have large {\Sigma}SFR values, especially
for Sigma_*>10^7.5M_sun kpc~2. RPS seems to leave the same imprint on the
SFR-M* and Sigma_SFR-Sigma_* relations both in the Local Universe and at
z~0.35.Comment: A&A in pres
Rejection Criteria Based on Outliers in the KiDS Photometric Redshifts and PDF Distributions Derived by Machine Learning
The Probability Density Function (PDF) provides an estimate of the photometric redshift (zphot) prediction error. It is crucial for current and future sky surveys, characterized by strict requirements on the zphot precision, reliability and completeness. The present work stands on the assumption that properly defined rejection criteria, capable of identifying and rejecting potential outliers, can increase the precision of zphot estimates and of their cumulative PDF, without sacrificing much in terms of completeness of the sample. We provide a way to assess rejection through proper cuts on the shape descriptors of a PDF, such as the width and the height of the maximum PDF's peak. In this work we tested these rejection criteria to galaxies with photometry extracted from the Kilo Degree Survey (KiDS) ESO Data Release 4, proving that such approach could lead to significant improvements to the zphot quality: e.g., for the clipped sample showing the best trade-off between precision and completeness, we achieve a reduction in outliers fraction of {\$}{\$}{\backslash}simeq 75{\backslash}{\%}{\$}{\$}≃75{\%}and an improvement of {\$}{\$}{\backslash}simeq 6{\backslash}{\%}{\$}{\$}≃6{\%}for NMAD, with respect to the original data set, preserving the {\$}{\$}{\backslash}simeq 93{\backslash}{\%}{\$}{\$}≃93{\%}of its content
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