611 research outputs found
The ESO-Sculptor Survey: Luminosity functions of galaxies per spectral type at redshifts 0.1-0.5
[ABRIDGED] We present the first statistical analysis of the complete
ESO-Sculptor redshift survey (ESS). The flux-calibrated sample of 617 galaxy
spectra with R_c<20.5 is separated into 3 spectral classes (early,
intermediate, and late). We report in detail on the spectral classification,
the polynomial K-corrections, and all sources of corresponding random and
systematic errors. The derived luminosity functions (LF) in the Johnson-Cousins
B and Rc bands are in agreement with the results from the comparable CNOC2
survey (Lin et al. 1999), whereas the ESS provides the first estimates of LFs
per spectral type in the Johnson V band. A renewed interpretation of the galaxy
LFs from a redshift survey are obtained by fitting the ESS LFs with composite
functions based on the local LFs per morphological type (Sandage, Binggeli &
Tammann 1985; Jerjen & Tammann 1997). As good or better fits than with pure
Schechter functions are obtained using: for the early-type LF, a two-wing
Gaussian; for the intermediate-type LF, the sum of a Gaussian modeling the
Spiral galaxies and a steep Schechter function (alpha=-1.5) representing the
dwarf elliptical galaxies; for the late-type LF, a similar composite function
with a flat or weaker slope (-0.8<alpha<-0.3) for the Schechter component which
represents the dwarf Irregular galaxies. This analysis illustrates how LFs per
spectral type may be affected by morphological type mixing, and emphasizes the
need for a quantitative morphological classification at z>0.1 which separates
the giant and dwarf galaxy populations.Comment: 33 Pages, 13 color figures, A&A Latex macro. Published in A&
Heated Intracluster Gas and Radio Connections: the Singular case of MKW3s
Similarly to other cluster of galaxies previously classified as cooling flow
systems, the Chandra observation of MKW3s reveals that this object has a
complex X-ray structure hosting both a X-ray cavity and a X-ray filament.
Unlike the other clusters, however, the temperature map of the core of MKW3s
shows the presence of extended regions of gas heated above the radially
averaged gas temperature at any radius.
As the cluster does not show evidences for ongoing major mergers Mazzotta et
al. suggest a connection between the heated gas and the activity of the central
AGN. Nevertheless, due to the lack of high quality radio maps, this
interpretation was controversial.
In this paper we present the results of two new radio observations of MKW3s
at 1.28GHz and 604MHz obtained at the GMRT. Together with the Chandra
observation and a separate VLA observation at 327MHz from Young, we show
unequivocal evidences for a close connection between the heated gas region and
the AGN activity and we briefly summarize possible implications.Comment: To appear in a special issue of the "Journal of the Korean
Astronomical Society" (JKAS). Proceedings of the International conference on
Cosmic Rays and Magnetic Fields in Large Scale Structure, Busan, Korea, 200
Reconstructing the galaxy density field with photometric redshifts: II. Environment-dependent galaxy evolution since
Although extensively investigated, the role of the environment in galaxy
formation is still not well understood. In this context, the Galaxy Stellar
Mass Function (GSMF) is a powerful tool to understand how environment relates
to galaxy mass assembly and the quenching of star-formation. In this work, we
make use of the high-precision photometric redshifts of the UltraVISTA Survey
to study the GSMF in different environments up to , on physical
scales from 0.3 to 2 Mpc, down to masses of . We
witness the appearance of environmental signatures for both quiescent and
star-forming galaxies. We find that the shape of the GSMF of quiescent galaxies
is different in high- and low-density environments up to with the
high-mass end () being enhanced in high-density
environments. On the contrary, for star-forming galaxies a difference between
the GSMF in high- and low density environments is present for masses . Star-forming galaxies in this mass range appear to
be more frequent in low-density environments up to . Differences in
the shape of the GSMF are not visible anymore at . Our results, in terms
of general trends in the shape of the GSMF, are in agreement with a scenario in
which galaxies are quenched when they enter hot gas-dominated massive haloes
which are preferentially in high-density environments.Comment: 18 pages, 10 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Brightest Cluster Galaxies in the Extended GMRT radio halo cluster sample. Radio properties and cluster dynamics
Brightest Cluster Galaxies (BCGs) show exceptional properties over the whole
electromagnetic spectrum. Their special location at the centres of galaxy
clusters raises the question of the role of the environment on their radio
properties. To decouple the effect of the galaxy mass and of the environment in
their statistical radio properties, we investigate the possible dependence of
the occurrence of radio loudness and of the fractional radio luminosity
function on the dynamical state of the hosting cluster. We studied the radio
properties of the BCGs in the Extended GMRT Radio Halo Survey (EGRHS). We
obtained a statistical sample of 59 BCGs, which was divided into two classes,
depending on the dynamical state of the host cluster, i.e. merging (M) and
relaxed (R). Among the 59 BCGs, 28 are radio-loud, and 31 are radio--quiet. The
radio-loud sources are located favourably located in relaxed clusters (71\%),
while the reverse is true for the radio-quiet BCGs, mostly located in merging
systems (81\%). The fractional radio luminosity function (RLF) for the BCGs is
considerably higher for BCGs in relaxed clusters, where the total fraction of
radio loudness reaches almost 90\%, to be compared to the 30\% in merging
clusters. For relaxed clusters, we found a positive correlation between the
radio power of the BCGs and the strength of the cool core, consistent with
previous studies on local samples. Our study suggests that the radio loudness
of the BCGs strongly depends on the cluster dynamics, their fraction being
considerably higher in relaxed clusters. We compared our results with similar
investigations, and briefly discussed them in the framework of AGN feedback.Comment: 12 pages, 6 figures, 3 tables, A&A accepte
Workshop: Insegnare e raccontare il cielo e le stelle - Fare il punto per ripartire
In this talk we resume the results of a workshop which we have recently organized in collaboration with
other colleagues (25-26 marzo 2014). Supported by various institutions, among them the Bologna
Childresn’s Book Fair, which has hosted us in one of its stands, the peculiarity of the meeting was that
it fi nally gave the possibility of a dialogue between astronomers, popularizers, teachers, pedagogues,
psychologists and other specialists, concerning the didactics and popularization of astronomy for children
between 2 and 12 years old. The meeting was a success and highlighted some very interesting aspects of
the subject which we wish to present to the UAI audience
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
Exploring the Astronomical Knowledge of Italian Students: Surveying Middle Schools and Informal Courses
Kids receive most of their astronomical knowledge through three fonts: formal educations (schools), informal education (laboratories,scientific festivals and other out-school activities) and from TV, cinema movies and documentaries. In the first case, students have to learn astronomy from certified fonts (school books and others teaching tools) and their knowledge is verified by teachers. However, for younger students, deep competence of teachers in a specific topics of science is not usually requested. In the second case the situation is less homogeneous. Informal education is located in scientific structures (Universities, Planetarium, Observatories), scientific festivals or dedicated structures for science outreach and it is lead by researchers (with little if any educational preparation) or by members of associations for scientific popularization.The skills of these members vary a lot since one can find teachers, university or high school students or experts, that in the case of Astronomy are in numerous cases amateur astronomers. Moreover, an important source of informal education is found on internet, where one can found numerous science outreach blogs, facebook and web site. In this latter case the quality of fonts is very hard to evaluate. The aim of this work is to explore the astronomy knowledge and misconceptions in students of age range of about 10-13 and to compare two types of students: one attending only regular school lessons and the others attending also informal education. We tested the hypothesis that latter students are more motivated to go deeply in their astronomical education and should have a more precise astronomical knowledge. Data have been collected form 2014 to 2017 and the final sample regarded 1017 students.We proposed questionnaires with questions about Black Holes, Star life, Seasons and Moon phases
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
A study of the core of the Shapley Concentration: VI. Spectral properties of galaxies
We present the results of a study of the spectral properties of galaxies in
the central part of the Shapley Concentration, covering an extremely wide range
of densities, from the rich cluster cores to the underlying supercluster
environment. Our sample is homogeneous, in a well defined magnitude range
(17=<b_J=<18.8) and contains ~1300 spectra of galaxies at the same distance,
covering an area of ~26 sq.deg. These characteristics allowed an accurate
spectral classification, that we performed using a Principal Components
Analysis technique.
This spectral classification, together with the [OII] equivalent widths and
the star formation rates, has been used to study the properties of galaxies at
different densities: cluster, intercluster (i.e. galaxies in the supercluster
but outside clusters) and field environment.
No significant differences are present between samples at low density regimes
(i.e. intercluster and field galaxies). Cluster galaxies, instead, not only
have values significantly different from the field ones, but also show a
dependence on the local density. Moreover, a well defined morphology-density
relation is present in the cluster complexes, although these structures are
known to be involved in major merging events. Also the mean equivalent width of
[OII] shows a trend with the local environment, decreasing at increasing
densities, even if it is probably induced by the morphology-density relation.
Finally we analyzed the mean star formation rate as a function of the
density, finding again a decreasing trend (at ~ 3sigma significance level). Our
analysis is consistent with the claim of Balogh et al. (1998) that the star
formation in clusters is depressed.Comment: 13 pages with encapsulated figures; MNRAS in pres
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