Abstract
This paper is the first of a series of papers constraining cosmological parameters with weak lensing peak statistics using ∼ 450 deg2 of imaging data from the Kilo Degree Survey (KiDS-450). ...We measure high signal-to-noise ratio (SNR: ν) weak lensing convergence peaks in the range of 3 < ν < 5, and employ theoretical models to derive expected values. These models are validated using a suite of simulations. We take into account two major systematic effects, the boost factor and the effect of baryons on the mass–concentration relation of dark matter haloes. In addition, we investigate the impacts of other potential astrophysical systematics including the projection effects of large-scale structures, intrinsic galaxy alignments, as well as residual measurement uncertainties in the shear and redshift calibration. Assuming a flat Λ cold dark matter model, we find constraints for $S_{\rm 8}=\sigma _{\rm 8}(\Omega _{\rm m}/0.3)^{0.5}=0.746^{+0.046}_{-0.107}$ according to the degeneracy direction of the cosmic shear analysis and $\Sigma _{\rm 8}=\sigma _{\rm 8}(\Omega _{\rm m}/0.3)^{0.38}=0.696^{+0.048}_{-0.050}$ based on the derived degeneracy direction of our high-SNR peak statistics. The difference between the power index of S8 and in Σ8 indicates that combining cosmic shear with peak statistics has the potential to break the degeneracy in σ8 and Ωm. Our results are consistent with the cosmic shear tomographic correlation analysis of the same data set and ∼2σ lower than the Planck 2016 results.
Abstract
We provide novel constraints on the parameters defining the universal pressure profile (UPP) within clusters of galaxies, and explore their dependencies on cluster mass and redshift, from ...measurements of Sunyaev–Zel’dovich (SZ) Compton
y-
profiles. We employ both Planck 2015 MILCA and Atacama Cosmology Telescope (ACT) Data Release 4
y
-maps over a common ∼2100 deg
2
footprint. We combine existing cluster catalogs, based on Kilo Degree Survey, Sloan Digital Sky Survey, and Dark Energy Spectroscopic Instrument Legacy Imaging Surveys observations, for a total of 23,820 clusters, spanning the mass range 10
14.0
M
⊙
<
M
500
< 10
15.1
M
⊙
and the redshift range 0.02 <
z
< 0.98. 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
y
angular profile. The latter is predicted theoretically by adopting a halo model framework, and a Markov Chain Monte Carlo approach is employed to estimate the UPP parameters, the hydrostatic mass bias
b
h
, and possible cluster miscentering effects. We constrain
P
0
,
c
500
,
α
,
β
to 5.9, 2.0, 1.8, 4.9 with Planck and to 3.8, 1.3, 1.0, 4.4 with ACT, using the full cluster sample, in agreement with previous findings. We do not find any compelling evidence for residual mass or redshift dependencies, thus expanding the validity of the cluster pressure profile over much larger
M
500
and
z
ranges; this is the first time that 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.
ABSTRACT
Galaxy clusters show a variety of intracluster medium properties at a fixed mass in gas fractions, X-ray luminosity and X-ray surface brightness. In this work, we investigate whether the ...yet-undetermined cause that produces clusters of X-ray low surface brightness also affects galaxy properties, such as richness, richness concentration, width and location of the red sequence, colour, luminosity, and dominance of the brightest cluster galaxy. We use Sloan Digital Sky Survey Data Release 12 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 per cent lower richness for their mass at the 4.4σ level. Therefore, richness and quantities depending on gas, such as gas fraction, Mgas and X-ray surface brightness, are covariant at fixed halo mass. In particular, we do not confirm the suggestion of anticorrelation of hot and cold baryons at fixed mass put forth in the 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 disjointed; the optical properties do not show 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 avoids expensive X-ray observations.
In this paper, we report about the development and validation of a learning progression about the Celestial Motion big idea. Existing curricula, research studies on alternative conceptions about ...these phenomena, and students' answers to an open questionnaire were the starting point to develop initial learning progressions about change of seasons, solar and lunar eclipses, and Moon phases; then, a two-tier multiple choice questionnaire was designed to validate and improve them. The questionnaire was submitted to about 300 secondary students of different school levels (14 to 18 years old). Item response analysis and curve integral method were used to revise the hypothesized learning progressions. Findings support that spatial reasoning is a key cognitive factor for building an explanatory framework for the Celestial Motion big idea, but also suggest that causal reasoning based on physics mechanisms underlying the phenomena, as light flux laws or energy transfers, may significantly impact a students' understanding. As an implication of the study, we propose that the teaching of the three discussed astronomy phenomena should follow a single teaching-learning path along the following sequence: (i) emphasize from the beginning the geometrical aspects of the Sun-Moon-Earth system motion; (ii) clarify consequences of the motion of the Sun-Moon-Earth system, as the changing solar radiation flow on the surface of Earth during the revolution around the Sun; (iii) help students moving between different reference systems (Earth and space observer's perspective) to understand how Earth's rotation and revolution can change the appearance of the Sun and Moon. Instructional and methodological implications are also briefly discussed.
This paper is part of the Focused Collection on Astronomy Education Research. 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 year old students' explanations, drawings, and conceptions about three familiar phenomena: change of seasons, Moon phases, and solar or 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 image-support 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 and 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 Earth's elliptical orbit; the position of the Sun with respect to the Moon orbit; and 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.
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.
We describe how young students situate themselves with respect to astronomy through an identity framework that features four dimensions: interest, utility value, confidence, and conceptual knowledge. ...Overall, about 900 Italian students, from 5th to 9th grade (9-14 years old), were involved in the study. We tested our model using confirmatory factor analysis and structural equation modeling. Differences between girls and boys and across school levels were also investigated. Results show that interest has both a direct and an indirect effect on astronomy identity. The indirect effect of interest on identity is mediated by utility value. Moreover, confidence mediates the effect of interest on conceptual knowledge. Concerning differences between girls and boys, we found that the effect of interest on identity is greater for girls than for boys and that the utility value mediates the effect of interest on identity for boys but not for girls. Finally, our findings show also that the students' interest in astronomy and confidence in their performance decrease with age, with a potential negative impact on conceptual knowledge and future career choice in astronomy. The astronomy identity framework can be employed to examine the role of affective variables on performance and persistence in astronomy and to improve the design of teaching-learning activities that can potentially stimulate a lasting interest in astronomy.
We present a teaching module focused on stellar structure, functioning and evolution. Drawing from literature in astronomy education, we identified three key ideas which are fundamental in ...understanding stars’ functioning: spectral analysis, mechanical and thermal equilibrium, energy and nuclear reactions. The module is divided into four phases, in which the above key ideas and the physical mechanisms involved in stars’ functioning are gradually introduced. The activities combine previously learned laws in mechanics, thermodynamics, and electromagnetism, in order to get a complete picture of processes occurring in stars. The module was piloted with two intact classes of secondary school students (N = 59 students, 17–18 years old) and its efficacy in addressing students’ misconceptions and wrong ideas was tested using a ten-question multiple choice questionnaire. Results support the effectiveness of the proposed activities. Implications for the teaching of advanced physics topics using stars as a fruitful context are briefly discussed.
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