Spatial Distribution Of Galaxies Research Articles

JWST’s First Glimpse of a z > 2 Forming Cluster Reveals a Top-heavy Stellar Mass Function

Clusters and their progenitors (protoclusters) at z ∼ 2 − 4, the peak epoch of star formation, are ideal laboratories to study the formation process of both the clusters themselves and their member galaxies. However, a complete census of their member galaxies has been challenging due to observational difficulties. Here we present new JWST/NIRCam observations targeting the distant cluster CLJ1001 at z = 2.51 from the COSMOS-Web program, which, in combination with previous narrowband imaging targeting Hα emitters and deep millimeter surveys of CO emitters, provide a complete view of massive galaxy assembly in CLJ1001. In particular, JWST reveals a population of massive, extremely red cluster members in the long-wavelength bands that were invisible in previous Hubble Space Telescope (HST)/F160W imaging (HST-dark members). Based on this highly complete spectroscopic sample of member galaxies, we show that the spatial distribution of galaxies in CLJ1001 exhibits a strong central concentration, with the central galaxy density already resembling that of low-z clusters. Moreover, we reveal a “top-heavy” stellar mass function for the star-forming galaxies (SFGs), with an overabundance of massive SFGs piled up in the cluster core. These features strongly suggest that CLJ1001 is caught in a rapid transition, with many of its massive SFGs likely soon becoming quiescent. In the context of cluster formation, these findings suggest that the earliest clusters form from the inside out and top to bottom, with the massive galaxies in the core assembling first, followed by the less massive ones in the outskirts.

Distribution of Merging and Post-merger Galaxies in Nearby Galaxy Clusters

We study the incidence and spatial distribution of galaxies that are currently undergoing gravitational merging (M) or that have signs of being post-merger (PM) in six galaxy clusters (A754, A2399, A2670, A3558, A3562, and A3716) within the redshift range of 0.05 ≲ z ≲0.08. To this aim, we obtained Dark Energy Camera mosaics in the u′ , g′ , and r′ bands covering up to 3 × R 200 of the clusters, reaching 28 mag arcsec−2 surface brightness limits. We visually inspect u′ g′ r′ color-composite images of volume-limited (M r < −20) cluster member galaxies to identify whether galaxies are of M or PM type. We find 4% M-type and 7% PM-type galaxies in the galaxy clusters studied. By adding spectroscopic data and studying the projected phase-space diagram (PPSD) of the projected clustocentric radius and the line-of-sight velocity, we find that PM-type galaxies are more virialized than M-type galaxies, having a 1%–5% higher fraction within the escape-velocity region, while the fraction of M-type was ∼10% higher than the PM type in the intermediate environment. Similarly, on a substructure analysis, M types were found in groups in the outskirts, while PM-type populated groups were found in ubiquitous regions of the PPSD. Adopting literature-derived dynamical state indicator values, we observed a higher abundance of M types in dynamically relaxed clusters. This finding suggests that galaxies displaying post-merger features within clusters likely merged in low-velocity environments, including clusters outskirts and dynamically relaxed clusters.

RXCJ1111.6+4050 galaxy cluster: Observational evidence of a transitional fossil group

We present a detailed kinematical and dynamical study of the galaxy cluster RXCJ1111.6+4050 (RXCJ1111), at z = 0.0756 using 104 new spectroscopic redshifts of galaxies observed at the Telescopio Nazionale Galileo and SDSS DR16 public archive. Our analysis is performed in a multiwavelength context in order to study and compare mainly optical and X-ray properties using XMM-Newton data. We find that RXCJ1111 is a galaxy cluster showing a velocity distribution with clear deviations from Gaussianity, that we are able to explain by the presence of a substructure within the cluster. The two cluster components show velocity dispersions of 644 ± 56 km s−1 and 410 ± 123 km s−1, which yield dynamical masses of M200 = 1.9 ± 0.4 × 1014 M⊙ and 0.6 ± 0.4 × 1014 M⊙ for the main system and substructure, respectively. The 2D spatial distribution of galaxies and X-ray surface brightness of RXCJ1111 presents an elongation in the North–South direction. These observational facts, together with a gradient of 250−350 km s−1 Mpc−1 in the velocity field, following the NNE–SSE direction, suggest that the merger axis between the main system and substructure is slightly tilted with respect to the line-of-sight. The substructure is characterized by a magnitude gap Δm12 ≥ 1.8, so it fits the “fossil-like” definition of a galaxy group. From the X-ray observations, we estimate a M500, X = 1.68 ± 0.25 × 1014 M⊙, which is in good agreement with the dynamical masses when two galaxy components are considered separately. This suggests that the mass estimates obtained from X-ray and velocity dispersion are compatible even for non-relaxed clusters, at least when we are able to identify and separate galaxy clumps and derive masses by considering the virialized regions. We propose a 3D merging model and find that the fossil group is in an early phase of collision with the RXCJ1111 main cluster and placed at ∼8° ( ± 3° ) from line-of-sight. This merging model would explain the slight increase found in the TX with respect to what we would expect for relaxed clusters. Due to the presence of several brightest galaxies, after this collision, the substructure would presumably lose its fossil condition. Therefore, RXCJ1111 represents the observational evidence that the fossil stage of a system can be temporary and transitional.

Magnification bias estimators for realistic surveys: an application to the BOSS survey

ABSTRACT In addition to the intrinsic clustering of galaxies themselves, the spatial distribution of galaxies observed in surveys is modulated by the presence of weak lensing due to matter in the foreground. This effect, known as magnification bias, is a significant contaminant to analyses of galaxy-lensing cross-correlations and must be carefully modelled. We present a method to estimate the magnification bias in spectroscopically confirmed galaxy samples based on finite differences of galaxy catalogues while marginalizing over errors due to finite step size. We use our estimator to measure the magnification biases of the CMASS and LOWZ samples in the SDSS BOSS galaxy survey, analytically taking into account the dependence on galaxy shape for fibre and PSF magnitudes, finding αCMASS = 2.71 ± 0.02 and αLOWZ = 2.45 ± 0.02 and quantify modelling uncertainties in these measurements. Finally, we quantify the redshift evolution of the magnification bias within the CMASS and LOWZ samples, finding a difference of up to a factor of three between the lower and upper redshift bounds for the former. We discuss how to account for this evolution in modelling and its interaction with commonly applied redshift-dependent weights. Our method should be readily applicable to upcoming surveys and we make our code publicly available as part of this work.

Search for a possible quasi-periodic structure based on data of the SDSS DR12 LOWZ

ABSTRACT We carry out a statistical analysis of the spatial distribution of galaxies at cosmological redshifts 0.16 ≤ z ≤ 0.47 based on the SDSS DR12 LOWZ catalogue. Our aim is to search and study possible large-scale quasi-regular structures embedded in the cosmic web. We calculate projections of the Cartesian galaxy coordinates on different axes (directions), densely covering certain regions in the sky to look for special directions along which 1D distributions of the projections contain significant quasi-periodic components. These components appear as peaks in the power spectra and lie in a narrow range of wave numbers 0.05 &amp;lt; k &amp;lt; 0.07. Particular attention is paid to the evaluation of the significance of the peaks. It is found that the significance of the dominant peaks for some selected directions exceeds (4–5)σ. In order to reduce possible selection effects, we create a mock homogeneous catalogue of spatial distribution of galaxies by adding a random set of artificial objects (points) to the real galaxies under study. The power spectrum of this cumulative model data also demonstrates significant peak corresponding to approximately the same scale. As a result we assume the existence of an anisotropic cosmological quasi-periodic structure with characteristic scale (116 ± 10) h−1 Mpc.

Correlation analysis of decaying sterile neutrino dark matter in the context of the SRG mission

We provide a correlation analysis of signatures associated with traces of the dark matter decay and the galaxy spatial distribution according to the 2MRS catalog of galaxies. Signature data analysis plays an important role in the context of current and future observations and cosmological constraints. Attention is paid to the constraints that can be obtained for decaying sterile neutrinos when analyzing observations in the context of the Spectr-Roentegn-Gamma (SRG) mission. We study the correlation spectra of dark matter and galaxies, which can be obtained both for the eROSITA telescope and for the first time for the ART-XC telescope. The analysis is carried out both within the framework of the Limber approximation and within the framework of the extended Limber approximation, which makes it possible to more accurately study the power spectra in the region of small multipoles. We calculate the power spectra in both approaches and examine the contribution of different ranges of multipoles to the resulting constraints on sterile neutrino parameters.

Consistent and simultaneous modelling of galaxy clustering and galaxy–galaxy lensing with subhalo abundance matching

ABSTRACT The spatial distribution of galaxies and their gravitational lensing signal offer complementary tests of galaxy formation physics and cosmology. However, their synergy can only be fully exploited if both probes are modelled accurately and consistently. In this paper, we demonstrate that this can be achieved using an extension of Sub-Halo Abundance Matching extended model (SHAMe), dubbed SHAMe. Specifically, we use mock catalogues built from the TNG300 hydrodynamical simulation to show that SHAMe can simultaneously model the multipoles of the redshift–space galaxy correlation function and galaxy–galaxy lensing, without noticeable bias within the statistical sampling uncertainties of a SDSS volume and on scales r ∈ [0.6 − 30]h−1 Mpc. Modelling the baryonic processes in galaxy–galaxy lensing with a baryonification scheme allows SHAMe’s range of validity to be extended to r ∈ [0.1 − 30] h−1 Mpc. Remarkably, our model achieves this level of precision with just five free parameters beyond those describing the baryonification model. At fixed cosmology, we find that galaxy–galaxy lensing provides a general consistency test but little additional information on galaxy modelling parameters beyond that encoded in the redshift-space multipoles. It does, however, improve constraints if only the projected correlation function is available, as in surveys with only photometric redshifts. We expect SHAMe to have a higher fidelity across a wider range of scales than more traditional methods such as Halo Occupation Distribution modelling. Thus it should provide a significantly more powerful and more robust tool for analysing next-generation large-scale surveys.

Evidence of galaxy assembly bias in SDSS DR7 galaxy samples from count statistics

ABSTRACT We present observational constraints on the galaxy–halo connection, focusing particularly on galaxy assembly bias from a novel combination of counts-in-cylinders statistics, P(NCIC), with the standard measurements of the projected two-point correlation function wp(rp), and number density ngal of galaxies. We measure ngal, wp(rp), and P(NCIC) for volume-limited, luminosity-threshold samples of galaxies selected from SDSS DR7, and use them to constrain halo occupation distribution (HOD) models, including a model in which galaxy occupation depends upon a secondary halo property, namely halo concentration. We detect significant positive central assembly bias for the Mr &amp;lt; −20.0 and Mr &amp;lt; −19.5 samples. Central galaxies preferentially reside within haloes of high concentration at fixed mass. Positive central assembly bias is also favoured in the Mr &amp;lt; −20.5 and Mr &amp;lt; −19.0 samples. We find no evidence of central assembly bias in the Mr &amp;lt; −21.0 sample. We observe only a marginal preference for negative satellite assembly bias in the Mr &amp;lt; −20.0 and Mr &amp;lt; −19.0 samples, and non-zero satellite assembly bias is not indicated in other samples. Our findings underscore the necessity of accounting for galaxy assembly bias when interpreting galaxy survey data, and demonstrate the potential of count statistics in extracting information from the spatial distribution of galaxies, which could be applied to both galaxy–halo connection studies and cosmological analyses.

Differentiating small-scale subhalo distributions in CDM and WDM models using persistent homology

The spatial distribution of galaxies at sufficiently small scales will encode information about the identity of the dark matter. We develop a novel description of the halo distribution using persistent homology summaries, in which collections of points are decomposed into clusters, loops, and voids. We apply these methods, together with a set of hypothesis tests, to dark matter haloes in Milky Way-analog environment regions of the cold dark matter (CDM) and warm dark matter (WDM) Copernicus Complexio $N$-body cosmological simulations. The results of the hypothesis tests find statistically significant differences (p-values $\ensuremath{\le}0.001$) between the CDM and WDM structures, and the functional summaries of persistence diagrams detect differences at scales that are distinct from the comparison spatial point process functional summaries considered (including the two-point correlation function). The differences between the models are driven most strongly at filtration scales $\ensuremath{\sim}100\text{ }\text{ }\mathrm{kpc}$, where CDM generates larger numbers of unconnected halo clusters while WDM instead generates loops. This study was conducted on dark matter haloes generally; future work will involve applying the same methods to realistic galaxy catalogues.

A Mesofractal Model of Interstellar Cloudiness

The interstellar medium (ISM), serving as a background for the propagation of cosmic rays (CRs) and other information carriers, has a complex ragged structure. Being chaotically scattered over interstellar space, together with the magnetic field perturbations frozen in them, CRs are connected with each other by a network of magnetic field lines creating long-range correlations of a power-law type, similar to those observed in the spatial distribution of galaxies. These lines solving interstellar transfer problems require the choice of an ISM model, adequately and concisely representing their statistical properties. This article discusses one such model, the Uchaikin–Zolotarev model: a four-parameter approximation of the power spectrum spatial correlations, derived from the generalized Ornstein–Zernike equation. The numerical analysis confirmed that this approximation satisfactorily agrees with the numerical data obtained in the quasi-linear model of plasma turbulence.

Galaxy populations in the Hydra I cluster from the VEGAS survey

Context. Due to their relatively low stellar mass content and diffuse nature, the evolution of dwarf galaxies can be strongly affected by their environment. Analyzing the properties of the dwarf galaxies over a wide range of luminosities, sizes, morphological types, and environments, we can obtain insights about their evolution. At ∼50 Mpc, the Hydra I cluster of galaxies is among the closest cluster in the z ≃ 0 Universe, and an ideal environment to study dwarf galaxy properties in a cluster environment. Aims. We exploit deep imaging data of the Hydra I cluster to construct a new photometric catalog of dwarf galaxies in the cluster core, which is then used to derive properties of the Hydra I cluster dwarf galaxy population as well as to compare it with other clusters. Moreover, we investigate the dependency of dwarf galaxy properties on their surrounding environment. Methods. The new wide-field g- and r-band images of the Hydra I cluster obtained with the OmegaCAM camera on the VLT Survey Telescope (VST) in the context of the VST Early-type GAlaxy Survey (VEGAS) were used to study the dwarf galaxy population in the Hydra I cluster core down to r-band magnitude Mr = −11.5 mag. We used an automatic detection tool to identify dwarf galaxies from a ∼1 deg2 field centered on the Hydra I core, covering almost half of the cluster virial radius. The photometric pipeline was used to estimate the principal photometric parameters for all targets. Scaling relations and visual inspection were used to assess the cluster membership and construct a new dwarf galaxy catalog. Finally, based on the new catalog, we studied the structural (Sérsic index n, effective radius Re, and axis ratio) and photometric (colors and surface brightness) properties of the dwarf galaxies, also investigating how they vary as a function of clustercentric distance. Results. The new Hydra I dwarf catalog contains 317 galaxies with a luminosity between −18.5 &lt; Mr &lt; −11.5 mag, a semi-major axis larger than ∼200 pc (a = 0.84″), of which 202 are new detections, and previously unknown dwarf galaxies in the Hydra I central region. We estimate that our detection efficiency reaches 50% at the limiting magnitude Mr = −11.5 mag, and at the mean effective surface brightness μ̄e,r = 26.5 mag arcsec−2. We present the standard scaling relations for dwarf galaxies, which are color-magnitude, size-luminosity, and Sérsic n-magnitude relations, and compare them with other nearby clusters. We find that there are no observational differences for dwarfs scaling relations in clusters of different sizes. We study the spatial distribution of galaxies, finding evidence for the presence of substructures within half the virial radius. We also find that mid- and high-luminosity dwarfs (Mr &lt; −14.5 mag) become, on average, redder toward the cluster center, and that they have a mild increase in Re with increasing clustercentric distance, similar to what is observed for the Fornax cluster. No clear clustercentric trends are reported for surface brightness and Sérsic index. Considering galaxies in the same magnitude bins, we find that for high and mid-luminosity dwarfs (Mr &lt; −13.5 mag), the g − r color is redder for the brighter surface brightness and higher Sérsic n index objects. This finding is consistent with the effects of harassment and/or partial gas stripping.

Spatial Structures in the Globular Cluster Distribution of Fornax Cluster Galaxies

Abstract We report the discovery of statistically significant spatial structures in the projected two-dimensional distributions of Globular Cluster (GC) systems of 10 galaxies that are among the brightest in the Fornax Cluster. We use a catalog of GCs extracted from the Hubble Space Telescope Advanced Camera for Surveys Fornax Cluster Survey imaging data. We characterize the size, shape, and location relative to the host galaxies of the GC structures and suggest a classification based on their morphology and location that is suggestive of different formation mechanisms. We also investigate the GC structures in the context of the positions of their host galaxies relative to the general spatial distributions of galaxies and intracluster GCs in the Fornax Cluster. We finally estimate the dynamical masses of the progenitors of some GC structures under the assumption that they are the relics of past accretion events of satellite galaxies by their hosts.

Об эффективной аппроксимации спектра мощности крупномасштабной структуры Вселенной

The article is focused on statistical properties of spatial distribution of galaxies in the universe at scales exceeding 5 Mpc. The investigation aims to find an appropriate algorithm for modeling random realizations of ensembles The object of research is the statistical properties of the spatial distribution of galaxies on scales exceeding 5 Mpc. The aim of the study is to find a suitable algorithm for modeling random realizations of a statistical ensemble of such distributions, which makes it possible to move to remote regions of large scales with depleted statistics, and on the constructed model to test signs of the transition from correlated to uncorrelated (if any) regions of the Universe. Information about such a boundary, called in the work the horizon of independence, is a necessary component of the modern model of the world in the era of extra-atmospheric astronomy. The need to determine it is dictated not only by the natural desire to "look beyond the horizon", but also by the reliance on mutually distant parts of the Universe, practiced in observational astronomy, as independent realizations of one statistical ensemble, ensuring the representativeness of the sample. The research method is based on the use of the Zolotarev-Uchaikin spectral density approximation and the Markov chain built on its basis. Comparison with observational data demonstrates the high flexibility of the approximation and its potential effectiveness in solving the problem of the horizon of independence.

Morphostatistical characterization of the spatial galaxy distribution through Gibbs point processes

ABSTRACT This paper proposes a morphostatistical characterization of the galaxy distribution through spatial statistical modelling based on inhomogeneous Gibbs point processes. The galaxy distribution is supposed to exhibit two components. The first one is related to the major geometrical features exhibited by the observed galaxy field, here, its corresponding filamentary pattern. The second one is related to the interactions exhibited by the galaxies. Gibbs point processes are statistical models able to integrate these two aspects in a probability density, controlled by some parameters. Several such models are fitted to real observational data via the ABC shadow algorithm. This algorithm provides simultaneous parameter estimation and posterior-based inference, hence allowing the derivation of the statistical significance of the obtained results.

Angular clustering and host halo properties of [O ii] emitters at z &amp;gt; 1 in the Subaru HSC survey

Abstract We study the angular correlation function of star-forming galaxies and properties of their host dark matter halos at z &amp;gt; 1 using the Hyper-Suprime Cam (HSC) Subaru Stragetic Program (SSP) survey. We use [O ii] emitters identified using two narrow-band (NB) filters, NB816 and NB921, in the Deep/UltraDeep layers, which respectively cover large angular areas of 16.3 deg2 and 16.9 deg2. Our sample contains 8302 and 9578 [O ii] emitters at z = 1.19 (NB816) and z = 1.47 (NB921), respectively. We detect a strong clustering signal over a wide angular range, $0{_{.}^{\circ}} 001$ &amp;lt; θ &amp;lt; 1 °, with bias $b=1.61^{+0.13}_{-0.11}$ (z = 1.19) and $b=2.09^{+0.17}_{-0.15}$ (z = 1.47). We also find a clear deviation of the correlation from a simple power-law form. To interpret the measured clustering signal, we adopt a halo occupation distribution (HOD) model that is constructed to explain the spatial distribution of galaxies selected by star formation rate. The observed correlation function and number density are simultaneously explained by the best-fitting HOD model. From the constrained HOD model, the average mass of halos hosting the [O ii] emitters is derived to be $\log {M_{\rm eff}/(h^{-1}\, {M}_{\odot })}=12.70^{+0.09}_{-0.07}$ and $12.61^{+0.09}_{-0.05}$ at z = 1.19 and 1.47, respectively, which will become halos with the present-day mass M ∼ 1.5 × 1013 h−1 M⊙. The satellite fraction of the [O ii] emitter sample is found to be fsat ∼ 0.15. All these values are consistent with previous studies of similar samples, but we obtain tighter constraints even in a larger parameter space due to the larger sample size from the HSC. The results obtained for host halos of [O ii] emitters in this paper enable the construction of mock galaxy catalogs and the systematic forecast study of cosmological constraints from upcoming emission line galaxy surveys such as the Subaru Prime Focus Spectrograph survey.

A new distant giant radio galaxy in the Boötes field serendipitously detected by Chandra

Context. Giant radio galaxies (GRGs) are the largest single structures in the Universe. Exhibiting extended radio morphology, their projected sizes range from 0.7 Mpc up to 4.9 Mpc. LOFAR has opened a new window on the discovery and investigation of GRGs and, despite the hundreds that are known today, their main growth catalyst is still under debate. Aims. One natural explanation for the exceptional size of GRGs is their old age. In this context, hard X-ray selected GRGs show evidence of restarting activity, with the giant radio lobes being mostly disconnected from the nuclear source, if any are present at all. In this paper, we present the serendipitous discovery of a distant (z = 0.629), medium X-ray-selected GRG in the Boötes field. Methods. High-quality, deep Chandra and LOFAR data allow for a robust study of the connection between the nucleus and the lobes, at a larger redshift, which has thus far been inaccessible to coded-mask hard X-ray instruments. Results. The radio morphology of the GRG presented in this work does not show evidence for restarted activity and the nuclear radio core spectrum does not appear to be gigahertz-peaked spectrum (GPS)-like. On the other hand, the X-ray properties of the new GRG are perfectly consistent with the ones previously studied with Swift/BAT and INTEGRAL at lower redshift. In particular, the bolometric luminosity measured from the X-ray spectrum is a factor of six larger than the one derived from the radio lobes, although the large uncertainties make them formally consistent at 1σ. Finally, the moderately dense environment around the GRG, traced by the spatial distribution of galaxies, supports recent findings that the growth of GRGs is not primarily driven by underdense environments.

Magnification bias in galaxy surveys with complex sample selection functions

ABSTRACT Gravitational lensing magnification modifies the observed spatial distribution of galaxies and can severely bias cosmological probes of large-scale structure if not accurately modelled. Standard approaches to modelling this magnification bias may not be applicable in practice as many galaxy samples have complex, often implicit, selection functions. We propose and test a procedure to quantify the magnification bias induced in clustering and galaxy–galaxy lensing (GGL) signals in galaxy samples subject to a selection function beyond a simple flux limit. The method employs realistic mock data to calibrate an effective luminosity function slope, αobs, from observed galaxy counts that can then be used with the standard formalism. We demonstrate this method for two galaxy samples derived from the Baryon Oscillation Spectroscopic Survey (BOSS) in the redshift ranges 0.2 &amp;lt; z ≤ 0.5 and 0.5 &amp;lt; z ≤ 0.75, complemented by mock data built from the MICE2 simulation. We obtain αobs = 1.93 ± 0.05 and αobs = 2.62 ± 0.28 for the two BOSS samples. For BOSS-like lenses, we forecast a contribution of the magnification bias to the GGL signal between the multipole moments, ℓ, of 100 and 4600 with a cumulative signal-to-noise ratio between 0.1 and 1.1 for sources from the Kilo-Degree Survey (KiDS), between 0.4 and 2.0 for sources from the Hyper Suprime-Cam survey (HSC), and between 0.3 and 2.8 for ESA Euclid-like source samples. These contributions are significant enough to require explicit modelling in future analyses of these and similar surveys. Our code is publicly available within the MagBEt module (https://github.com/mwiet/MAGBET).

Testing late-time cosmic acceleration with uncorrelated baryon acoustic oscillation dataset

Baryon acoustic oscillations (BAO) involve measuring the spatial distribution of galaxies to determine the growth rate of cosmic structures. We derive constraints on cosmological parameters from 17 uncorrelated BAO measurements that were collected from 333 published data points in the effective redshift range 0.106 ≤ z ≤ 2.36. We test the correlation of the subset using a random covariance matrix. The Λ cold dark matter (ΛCDM) model fit yields the cosmological parameters Ωm = 0.261 ± 0.028 and ΩΛ = 0.733 ± 0.021. Combining the BAO data with the Cosmic Chronometers data, the Pantheon type Ia supernova, and the Hubble diagram of gamma-ray bursts and quasars, the Hubble constant yields 69.85 ± 1.27 km s−1Mpc−1and the sound horizon distance gives 146.1 ± 2.15 Mpc. Beyond the ΛCDM model we test ΩkCDM andwCDM. The spatial curvature is Ωk = −0.076 ± 0.012 and the dark energy equation of states isw = −0.989 ± 0.049. We perform the Akaike information criteria test to compare the three models, and see that ΛCDM scores best.

Do galactic bars depend on environment?: an information theoretic analysis of Galaxy Zoo 2

ABSTRACT We use an information theoretic framework to analyse data from the Galaxy Zoo 2 project and study if there are any statistically significant correlations between the presence of bars in spiral galaxies and their environment. We measure the mutual information between the barredness of galaxies and their environments in a volume limited sample (Mr ≤ −21) and compare it with the same in data sets where (i) the bar/unbar classifications are randomized and (ii) the spatial distribution of galaxies are shuffled on different length scales. We assess the statistical significance of the differences in the mutual information using a t-test and find that both randomization of morphological classifications and shuffling of spatial distribution do not alter the mutual information in a statistically significant way. The non-zero mutual information between the barredness and environment arises due to the finite and discrete nature of the data set that can be entirely explained by mock Poisson distributions. We also separately compare the cumulative distribution functions of the barred and unbarred galaxies as a function of their local density. Using a Kolmogorov–Smirnov test, we find that the null hypothesis cannot be rejected even at $75{{\ \rm per\ cent}}$ confidence level. Our analysis indicates that environments do not play a significant role in the formation of a bar, which is largely determined by the internal processes of the host galaxy.

The results of analysis of Rich Galaxy Clusters from CfA2 Redshift Survey spatial distribution

Preliminary results of the investigation of the properties of 7 galaxy cluster from CfA2 redshift survey are discussed in the presented article. Clusters 933, 142, 1046, and 1652 have several peculiarities of the spatial distributions of galaxies. The distributions on absolute magnitude and luminosity represent two areas for clusters 933, 88, 142, 1046, 1101. The investigation of the spatial distribution and other characteristics of 88, 1101, 1046, 142, 933, 1242 and 1652 galaxy clusters allow concluding gravitational lensing effect. Galaxies from these areas are paired accordingly its spectral characteristics and position. Redshifts of these clusters are in the region 0.002 – 0.022. Preliminary results of analysis allow us concluding compact objects or dark matter blobs as lenses. Moreover, groups #933, #142, #1046 and #1652 reveals high-energy γ-associations on Fermi/LAT 10-Year Point Source Catalog 4FGL-DR2 (4FGL J1144.9 + 1937, 4FGL J0152.2 + 3714, 4FGL J1230.8 + 1223 and 4FGL J1653.8 + 3945); and sources 4FGL J0123.1+3421, 4FGL J1259.5+2332, 4FGL J1353.2+3740 are located inside sizes of clusters #88, #1101 and #1242. Also several anomalies of spatial dynamic of galaxies in these clusters were separated. Joint observations of such clusters by orbital gamma-ray observatories with high angular resolution and ground-based Cherenkov air-shower experiments could possibly clarify the type of gravitational lensing and processes of particle acceleration in these objects especially highest energy of emitted gammas. Thus we propose including these and similar clusters in the programs of observations of the planned experiment GAMMA-400 (Gamma Astronomical Multifunctional Modular Apparatus) with angular resolution ~0.01° at Eγ = 100 GeV. Also now it is discussed coordination of multiwavelength observations program of Cherenkov Telescope Array (CTA) and GAMMA-400 objects list for observations. Moreover, common observations of such clusters by orbital gamma-ray telescopes with high angular resolution and ground-based Cherenkov air-shower experiments could possibly clarify the type of gravitational lenses.