30 research outputs found
Simulation view of galaxy clusters with low X-ray surface brightness
X-ray selected samples are known to miss galaxy clusters that are gas poor
and have a low surface brightness. This is different for the optically selected
samples such as the X-ray Unbiased Selected Sample (XUCS). We characterise the
origin of galaxy clusters that are gas poor and have a low surface-brightness
by studying covariances between various cluster properties at fixed mass using
hydrodynamic cosmological simulations. We extracted approx. 1800 galaxy
clusters from a high-resolution Magneticum hydrodynamic cosmological simulation
and computed covariances at fixed mass of the following properties:
core-excised X-ray luminosity, gas fraction, hot gas temperature, formation
redshift, concentration, galaxy richness, fossilness parameter, and stellar
mass of the bright central galaxy. We also compared the correlation between
concentration and gas fractions in non-radiative simulations, and we followed
the trajectories of particles inside galaxy clusters to assess the role of AGN
depletion on the gas fraction. In simulations and in observational data,
differences in surface brightness are related to differences in gas fraction.
Simulations show that the gas fraction strongly correlates with assembly time,
in the sense that older clusters are gas poor. Clusters that formed earlier
have lower gas fractions because the feedback of the active galactic nucleus
ejected a significant amount of gas from the halo. When the X-ray luminosity is
corrected for the gas fraction, it shows little or no covariance with other
quantities. Older galaxy clusters tend to be gas poor and possess a low X-ray
surface brightness because the feedback mechanism removes a significant
fraction of gas from these objects. Moreover, we found that most of the
covariance with the other quantities is explained by differences in the gas
fraction.Comment: 9 pages, 8 figures, accepte
Do gas-poor galaxy clusters have different galaxy populations? The positive covariance of hot and cold baryons
Galaxy clusters show a variety of intra-cluster medium properties at a fixed
mass, among which gas fractions, X-ray luminosity and X-ray surface brightness.
In this work we investigate whether the yet-undetermined cause producing
clusters of X-ray low surface brightness also affects galaxy properties, namely
richness, richness concentration, width and location of the red sequence,
colour, luminosity, and dominance of the brightest cluster galaxy. We use
SDSS-DR12 photometry and our analysis factors out the mass dependency to derive
trends at fixed cluster mass. Clusters of low surface brightness for their mass
have cluster richness in spite of their group-like luminosity. Gas-poor, low
X-ray surface brightness, X-ray faint clusters for their mass, display 25\%
lower richness for their mass at level. Therefore, richness and
quantities depending on gas, such as gas fraction, , and X-ray surface
brightness, are covariant at fixed halo mass. In particular, we do not confirm
the hint of an anti-correlation of hot and cold baryons at fixed mass put forth
in literature. All the remaining optical properties show no covariance at fixed
mass, within the sensitivities allowed by our data and sample size. We conclude
that X-ray and optical properties are disjoint, the optical properties not
showing signatures of those processes involving gas content, apart from the
richness-mass scaling relation. The covariance between X-ray surface brightness
and richness is useful for an effective X-ray follow-up of low surface
brightness clusters because it allows us to pre-select clusters using optical
data of survey quality and prevent expensive X-ray observations
Design and Development of a Learning Progression about Stellar Structure and Evolution
[This paper is part of the Focused Collection on Astronomy Education Research.] In this paper we discuss the design and development of a learning progression (LP) to describe and interpret students' understanding about stellar structure and evolution (SSE). The LP is built upon three content dimensions: hydrostatic equilibrium; composition and aggregation state; functioning and evolution. The data to build up the levels of the hypothetical LP (LP1) came from a 45-minute, seven-question interview, with 33 high school students previously taught about the topic. The questions were adapted from an existing multiple-choice instrument. Data were analyzed using Minstrell's "facets" approach. To assess the validity of LP1, we designed a twelve-hour teaching module featuring paper-and-pencil tasks and practical activities to estimate the stellar structure and evolution parameters. Twenty high school students were interviewed before and after the activities using the same interview protocol. Results informed a revision of LP1 (LP2) and, in parallel, of the module. The revised module included supplementary activities corresponding to changes made to LP1. We then assessed LP2 with 30 high school students through the same interview, submitted before and after the teaching intervention. A final version of the LP (LP3) was then developed drawing on students' emerging reasoning strategies. This paper contributes to research in science education by providing an example of the iterative development of the instruction required to support the student thinking that LPs' levels describe. Concerning astronomy education research, our findings can inform suitable instructional activities more responsive to students' reasoning strategies about stellar structure and evolution
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
Developing the use of visual representations to explain basic astronomy phenomena
Several decades of research have contributed to our understanding of students’ reasoning about astronomical phenomena. Some authors have pointed out the difficulty in reading and interpreting images used in school textbooks as factors that may justify the persistence of misconceptions. However, only a few studies have investigated to what extent usual textbook images influence students’ understanding of such phenomena. This study examines this issue exploring 13-14 years old students’ explanations, drawings and conceptions about three familiar phenomena: change of seasons, Moon phases and solar/lunar eclipses. The research questions that guided the study were: RQ1) How are students’ explanations and visual representations about familiar astronomical phenomena affected by different imagesupport conditions? RQ2) How are students’ conceptions about familiar astronomical phenomena affected by different image-support conditions? RQ3) Which features of the used images most affected the students’ visual representations and explanations of familiar astronomical phenomena? To answer our research questions, we designed three instructional contexts under increasing support conditions: textbook images and text; teaching booklets with specially designed images and text; only text. To analyze students’ drawings, we used exploratory factor analysis to deconstruct drawings into their most salient elements. To analyze students’ explanations, we adopted a constant comparison method identifying different levels of increasing knowledge. To investigate students’ conceptions, we used a mixed multiple choice/true false baseline questionnaire. For RQ1, results show that the specially designed images condition was effective in helping students producing informed drawings in comparison to text-only condition for all phenomena, and more effective than textbook images condition when one considers seasonal change drawings. Concerning RQ2, the specially designed images condition was the most effective for all phenomena. Concerning RQ3, prevalent elements of astronomy images that affected students’ explanations and visual representations were: elliptical Earth's orbit, position of the Sun with respect to the Moon orbit, Sun, Moon and Earth alignment. Our findings confirm concerns about textbook astronomy images, whose features may interfere with the identification of the relevant factors underlying the phenomena. Moreover, findings of this study suggest that affordances of the specially designed images may play an essential role in scaffolding meaningful understanding of the targeted phenomena. Implications for teaching through and learning from visual representations in astronomy education are briefly discussed
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
AMICO galaxy clusters in KiDS-DR3: galaxy population properties and their redshift dependence
A catalogue of galaxy clusters was obtained in an area of 414 sq deg up to a
redshift from the Data Release 3 of the Kilo-Degree Survey
(KiDS-DR3), using the Adaptive Matched Identifier of Clustered Objects (AMICO)
algorithm. The catalogue and the calibration of the richness-mass relation were
presented in two companion papers. Here we describe the selection of the
cluster central galaxy and the classification of blue and red cluster members,
and analyze the main cluster properties, such as the red/blue fraction, cluster
mass, brightness and stellar mass of the central galaxy, and their dependence
on redshift and cluster richness. We use the Illustris-TNG simulation, which
represents the state-of-the-art cosmological simulation of galaxy formation, as
a benchmark for the interpretation of the results. A good agreement with
simulations is found at low redshifts (), while at higher redshifts
the simulations indicate a lower fraction of blue galaxies than what found in
the KiDS-AMICO catalogue: we argue that this may be due to an underestimate of
star-forming galaxies in the simulations. The selection of clusters with a
larger magnitude difference between the two brightest central galaxies, which
may indicate a more relaxed cluster dynamical status, improves the agreement
between the observed and simulated cluster mass and stellar mass of the central
galaxy. We also find that at a given cluster mass the stellar mass of blue
central galaxies is lower than that of the red ones.Comment: 14 pages, 16 figures, accepted for publication on MNRA
Exploring the mass and redshift dependence of the cluster pressure profile with stacks on thermal SZ maps
We provide novel constraints on the parameters defining the universal
pressure profile (UPP) within clusters of galaxies, and explore their
dependence on the cluster mass and redshift, from measurements of
Sunyaev-Zel'dovich Compton- profiles. We employ both the
2015 MILCA and the ACT-DR4 maps over the common
footprint. We combine existing cluster catalogs based on KiDS, SDSS and DESI
observations, for a total of 23,820 clusters spanning the mass range
and the
redshift range . We split the clusters into three independent bins
in mass and redshift; for each combination we detect the stacked SZ cluster
signal and extract the mean angular profile. The latter is predicted
theoretically adopting a halo model framework, and MCMCs are employed to
estimate the UPP parameters, the hydrostatic mass bias and possible
cluster miscentering effects. We constrain to
with and to with ACT
using the full cluster sample, in agreement with previous findings. We do not
find any compelling evidence for a residual mass or redshift dependence, thus
expanding the validity of the cluster pressure profile over much larger
and ranges; this is the first time the model has been tested on
such a large (complete and representative) cluster sample. Finally, we obtain
loose constraints on the hydrostatic mass bias in the range 0.2-0.3, again in
broad agreement with previous works.Comment: 39 pages, 22 figures. Accepted for publication in Apj
Quantitative experiments to explain the change of seasons
The science education literature shows that students have difficulty understanding what causes the seasons. Incorrect explanations are often due to a lack of knowledge about the physical mechanisms underlying this phenomenon. To address this, we present a module in which the students engage in quantitative measurements with a photovoltaic panel to explain changes to the sunray flow on Earth’s surface over the year. The activities also provide examples of energy transfers between the incoming radiation and the environment to introduce basic features of Earth’s climate. The module was evaluated with 45 secondary school students (aged 17–18) and a pre-/posttest research design. Analysis of students’ learning outcomes supports the effectiveness of the proposed activities