scholarly journals A study on the statistical significance of mutual information between morphology of a galaxy and its large-scale environment

2020 ◽  
Vol 497 (4) ◽  
pp. 4077-4090 ◽  
Author(s):  
Suman Sarkar ◽  
Biswajit Pandey
Keyword(s):  
Mutual Information ◽  
Large Scale ◽  
Statistical Significance ◽  
Sloan Digital Sky Survey ◽  
Data Sets ◽  
Information Theoretic ◽  
Galaxy Distribution ◽  
Sky Survey ◽  
The Galaxy ◽  
Physical Correlations

ABSTRACT A non-zero mutual information between morphology of a galaxy and its large-scale environment is known to exist in Sloan Digital Sky Survey (SDSS) upto a few tens of Mpc. It is important to test the statistical significance of these mutual information if any. We propose three different methods to test the statistical significance of these non-zero mutual information and apply them to SDSS and Millennium run simulation. We randomize the morphological information of SDSS galaxies without affecting their spatial distribution and compare the mutual information in the original and randomized data sets. We also divide the galaxy distribution into smaller subcubes and randomly shuffle them many times keeping the morphological information of galaxies intact. We compare the mutual information in the original SDSS data and its shuffled realizations for different shuffling lengths. Using a t-test, we find that a small but statistically significant (at $99.9{{\ \rm per\ cent}}$ confidence level) mutual information between morphology and environment exists upto the entire length-scale probed. We also conduct another experiment using mock data sets from a semi-analytic galaxy catalogue where we assign morphology to galaxies in a controlled manner based on the density at their locations. The experiment clearly demonstrates that mutual information can effectively capture the physical correlations between morphology and environment. Our analysis suggests that physical association between morphology and environment may extend to much larger length-scales than currently believed, and the information theoretic framework presented here can serve as a sensitive and useful probe of the assembly bias and large-scale environmental dependence of galaxy properties.

scholarly journals Characterising filaments in the SDSS volume from the galaxy distribution

2020 ◽  
Vol 642 ◽  
pp. A19 ◽  
Author(s):  
Nicola Malavasi ◽  
Nabila Aghanim ◽  
Marian Douspis ◽  
Hideki Tanimura ◽  
Victor Bonjean
Keyword(s):  
Large Scale ◽  
Sloan Digital Sky Survey ◽  
Specific Method ◽  
Redshift Surveys ◽  
Galaxy Distribution ◽  
Systematic Uncertainties ◽  
Sky Survey ◽  
The Galaxy ◽  
Free Parameters ◽  
The Universe

Detecting the large-scale structure of the Universe based on the galaxy distribution and characterising its components is of fundamental importance in astrophysics but is also a difficult task to achieve. Wide-area spectroscopic redshift surveys are required to accurately measure galaxy positions in space that also need to cover large areas of the sky. It is also difficult to create algorithms that can extract cosmic web structures (e.g. filaments). Moreover, these detections will be affected by systematic uncertainties that stem from the characteristics of the survey used (e.g. its completeness and coverage) and from the unique properties of the specific method adopted to detect the cosmic web (i.e. the assumptions it relies on and the free parameters it may employ). For these reasons, the creation of new catalogues of cosmic web features on wide sky areas is important, as this allows users to have at their disposal a well-understood sample of structures whose systematic uncertainties have been thoroughly investigated. In this paper we present the filament catalogues created using the discrete persistent structure extractor tool in the Sloan Digital Sky Survey (SDSS), and we fully characterise them in terms of their dependence on the choice of parameters pertaining to the algorithm, and with respect to several systematic issues that may arise in the skeleton as a result of the properties of the galaxy distribution (such as Finger-of-God redshift distortions and defects of the density field that are due to the boundaries of the survey).

scholarly journals Detecting multi-scale filaments in galaxy distribution

2014 ◽  
Vol 10 (S306) ◽  
pp. 45-47
Author(s):  
Elmo Tempel
Keyword(s):  
Point Process ◽  
Large Scale ◽  
Three Dimensional ◽  
Sloan Digital Sky Survey ◽  
Point Distribution ◽  
Multi Scale ◽  
Galaxy Distribution ◽  
Sky Survey ◽  
The Galaxy ◽  
Redshift Survey

AbstractThe main feature of the spatial large-scale galaxy distribution is its intricate network of galaxy filaments. This network is spanned by the galaxy locations that can be interpreted as a three-dimensional point distribution. The global properties of the point process can be measured by different statistical methods, which, however, do not describe directly the structure elements. The morphology of the large-scale structure, on the other hand, is an important property of the galaxy distribution. Here, we apply an object point process with interactions (the Bisous model) to trace and extract the filamentary network in the presently largest galaxy redshift survey, the Sloan Digital Sky Survey (SDSS data release 10). We search for multi-scale filaments in the galaxy distribution that have a radius of about 0.5, 1.0, 2.0, and 4.0h−1Mpc. We extract the spines of the filamentary network and divide the detected network into single filaments.

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

2020 ◽  
Vol 501 (1) ◽  
pp. 994-1001
Author(s):  
Suman Sarkar ◽  
Biswajit Pandey ◽  
Snehasish Bhattacharjee
Keyword(s):  
Spatial Distribution ◽  
Mutual Information ◽  
Local Density ◽  
Statistical Significance ◽  
Distribution Functions ◽  
Cumulative Distribution ◽  
Host Galaxy ◽  
Data Sets ◽  
Data Set ◽  
Information Theoretic

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.

scholarly journals Finding and characterising WHIM structures using the luminosity density method

2014 ◽  
Vol 11 (S308) ◽  
pp. 368-371
Author(s):  
Jukka Nevalainen ◽  
L. J. Liivamägi ◽  
E. Tempel ◽  
E. Branchini ◽  
M. Roncarelli ◽  
...  
Keyword(s):  
Large Scale ◽  
Real Data ◽  
Sloan Digital Sky Survey ◽  
Physical Parameters ◽  
X Ray ◽  
Galaxy Surveys ◽  
Sky Survey ◽  
The Galaxy ◽  
Hydrodynamical Simulations ◽  
X Ray Absorption

AbstractWe have developed a new method to approach the missing baryons problem. We assume that the missing baryons reside in a form of Warm Hot Intergalactic Medium, i.e. the WHIM. Our method consists of (a) detecting the coherent large scale structure in the spatial distribution of galaxies that traces the Cosmic Web and that in hydrodynamical simulations is associated to the WHIM, (b) mapping its luminosity into a galaxy luminosity density field, (c) using numerical simulations to relate the luminosity density to the density of the WHIM, (d) applying this relation to real data to trace the WHIM using the observed galaxy luminosities in the Sloan Digital Sky Survey and 2dF redshift surveys. In our application we find evidence for the WHIM along the line of sight to the Sculptor Wall, at redshifts consistent with the recently reported X-ray absorption line detections. Our indirect WHIM detection technique complements the standard method based on the detection of characteristic X-ray absorption lines, showing that the galaxy luminosity density is a reliable signpost for the WHIM. For this reason, our method could be applied to current galaxy surveys to optimise the observational strategies for detecting and studying the WHIM and its properties. Our estimates of the WHIM hydrogen column density NH in Sculptor agree with those obtained via the X-ray analysis. Due to the additional NH estimate, our method has potential for improving the constrains of the physical parameters of the WHIM as derived with X-ray absorption, and thus for improving the understanding of the missing baryons problem.

scholarly journals The Apache Point Observatory Galactic Evolution Experiment (APOGEE)

2009 ◽  
Vol 5 (S262) ◽  
pp. 428-429
Author(s):  
Ricardo P. Schiavon ◽  
Steven R. Majewski
Keyword(s):  
Large Scale ◽  
Near Infrared ◽  
Milky Way ◽  
Galactic Evolution ◽  
Sloan Digital Sky Survey ◽  
Elemental Abundances ◽  
Sky Survey ◽  
The Galaxy ◽  
Evolution Experiment ◽  
Under Construction

AbstractThe Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a large scale, high-resolution, near-infrared spectroscopic survey of Milky Way stellar populations and one of the four experiments in the Sloan Digital Sky Survey III (SDSS-III). APOGEE will be based on a new multi-fiber cryogenic spectrograph, currently under construction, expected to begin survey observations on the 2.5 m Sloan telescope in the Spring of 2011. APOGEE will measure high-precision radial velocities and elemental abundances for ~15 elements for ~ 105 stars, and is expected to shed new light on the processes that led to the formation of the Galaxy.

scholarly journals SEGUE, and the future of large scale surveys of the Galaxy

2008 ◽  
Vol 4 (S254) ◽  
pp. 461-468
Author(s):  
Timothy C. Beers ◽  
Young Sun Lee ◽  
Daniela Carollo
Keyword(s):  
Large Scale ◽  
Milky Way ◽  
Sloan Digital Sky Survey ◽  
Atmospheric Parameters ◽  
Near Ir ◽  
Medium Resolution ◽  
Sky Survey ◽  
The Galaxy ◽  
Scientific Results

AbstractThe Sloan Extension for Galactic Exploration and Understanding (SEGUE) has now been completed. This is one of three surveys that were executed as part of the first extension of the Sloan Digital Sky Survey (SDSS-II), which consist of LEGACY, SUPERNOVA SURVEY, and SEGUE. The SEGUE program has obtained over 3600 square degrees of ugriz imaging of the sky outside the original SDSS-I footprint. The regions of sky targeted for SEGUE imaging were primarily at lower Galactic latitudes (|b| < 35°), in order to better sample the disk/halo interface of the Milky Way. SEGUE also obtained medium-resolution (R = 2000) spectroscopy, over the wavelength range 3800-9200 Å, for over 200,000 stars in 200 selected areas over the sky available from Apache Point, New Mexico. We discuss the determination of stellar atmospheric parameters (Teff, log g, and [Fe/H]) for these stars, and highlight several of the scientific results obtained to date. The proposed second extension of SDSS, known as SDSS-III, will include SEGUE-2, a program to roughly double the numbers of stars with available spectroscopy, as well as APOGEE, a program to obtain high-resolution (R = 20000) near-IR spectroscopy for over 100,000 stars in the disk, bulge and halo populations of the Galaxy. Other massive spectroscopic surveys of interest to Galactic science are also briefly discussed.

scholarly journals The orientation of galaxy pairs with filamentary structures: dependence on morphology

2018 ◽  
Vol 619 ◽  
pp. A24 ◽  
Author(s):  
Valeria Mesa ◽  
Fernanda Duplancic ◽  
Sol Alonso ◽  
Maria Rosa Muñoz Jofré ◽  
Georgina Coldwell ◽  
...  
Keyword(s):  
Large Scale ◽  
Elliptical Galaxies ◽  
Sloan Digital Sky Survey ◽  
Morphological Classification ◽  
Large Scale Structures ◽  
Significant Alignment ◽  
Sky Survey ◽  
The Galaxy ◽  
High Fraction ◽  
Scale Structures

Aims. With the aim of performing an analysis of the orientations of galaxy pair systems with respect to the underlying large-scale structure, we study the alignment between the axis connecting the pair galaxies and the host cosmic filament where the pair resides. In addition, we analyze the dependence of the amplitude of the alignment on the morphology of pair members as well as filament properties. Methods. We build a galaxy pair catalog requiring rp < 100 h−1 kpc and ΔV < 500 km s−1 within redshift z < 0.1 from the Sloan Digital Sky Survey (SDSS). We divided the galaxy pair catalog taking into account the morphological classification by defining three pair categories composed by elliptical–elliptical (E–E), elliptical–spiral (E–S) and spiral–spiral (S–S) galaxies. We use a previously defined catalog of filaments obtained from SDSS and we select pairs located closer than 1 h−1 Mpc to the filament spine, which are considered as members of filaments. For these pairs, we calculate the relative angle between the axis connecting each galaxy, and the direction defined by the spine of the parent filament. Results. We find a statistically significant alignment signal between the pair axes and the spine of the host filaments consistent with a relative excess of ∼15% aligned pairs. We obtain that pairs composed by elliptical galaxies exhibit a stronger alignment, showing a higher alignment signal for pairs closer than 200 h−1 kpc to the filament spine. In addition, we find that the aligned pairs are associated with luminous host filaments populated with a high fraction of elliptical galaxies. The findings of this work show that large-scale structures play a fundamental role in driving galactic anisotropic accretion as induced by galaxy pairs exhibiting a preferred alignment along the filament direction.

scholarly journals Galaxy spin direction distribution in HST and SDSS show similar large-scale asymmetry

2020 ◽  
Vol 37 ◽  
Author(s):  
Lior Shamir
Keyword(s):  
Large Scale ◽  
Spiral Galaxies ◽  
Hubble Space Telescope ◽  
Gravitational Interaction ◽  
Large Data ◽  
Sloan Digital Sky Survey ◽  
Data Sets ◽  
Dipole Axis ◽  
Data Set ◽  
The Asymmetry

Abstract Several recent observations using large data sets of galaxies showed non-random distribution of the spin directions of spiral galaxies, even when the galaxies are too far from each other to have gravitational interaction. Here, a data set of $\sim8.7\cdot10^3$ spiral galaxies imaged by Hubble Space Telescope (HST) is used to test and profile a possible asymmetry between galaxy spin directions. The asymmetry between galaxies with opposite spin directions is compared to the asymmetry of galaxies from the Sloan Digital Sky Survey. The two data sets contain different galaxies at different redshift ranges, and each data set was annotated using a different annotation method. The results show that both data sets show a similar asymmetry in the COSMOS field, which is covered by both telescopes. Fitting the asymmetry of the galaxies to cosine dependence shows a dipole axis with probabilities of $\sim2.8\sigma$ and $\sim7.38\sigma$ in HST and SDSS, respectively. The most likely dipole axis identified in the HST galaxies is at $(\alpha=78^{\rm o},\delta=47^{\rm o})$ and is well within the $1\sigma$ error range compared to the location of the most likely dipole axis in the SDSS galaxies with $z>0.15$ , identified at $(\alpha=71^{\rm o},\delta=61^{\rm o})$ .

scholarly journals Searching for Mg ii absorbers in and around galaxy clusters

2021 ◽  
Vol 503 (3) ◽  
pp. 4309-4319
Author(s):  
Jong Chul Lee ◽  
Ho Seong Hwang ◽  
Hyunmi Song
Keyword(s):  
Galaxy Clusters ◽  
Detection Rate ◽  
Massive Star ◽  
Sloan Digital Sky Survey ◽  
Number Density ◽  
Cluster Galaxies ◽  
Star Forming ◽  
Quasar Spectra ◽  
Sky Survey ◽  
The Galaxy

ABSTRACT To study environmental effects on the circumgalactic medium (CGM), we use the samples of redMaPPer galaxy clusters, background quasars, and cluster galaxies from the Sloan Digital Sky Survey (SDSS). With ∼82 000 quasar spectra, we detect 197 Mg ii absorbers in and around the clusters. The detection rate per quasar is 2.7 ± 0.7 times higher inside the clusters than outside the clusters, indicating that Mg ii absorbers are relatively abundant in clusters. However, when considering the galaxy number density, the absorber-to-galaxy ratio is rather low inside the clusters. If we assume that Mg ii absorbers are mainly contributed by the CGM of massive star-forming galaxies, a typical halo size of cluster galaxies is smaller than that of field galaxies by 30 ± 10 per cent. This finding supports that galaxy haloes can be truncated by interaction with the host cluster.

scholarly journals Surface Photometry of Spiral Galaxy NGC 5005 and Elliptical Galaxy NGC 4278

2018 ◽  
Vol 15 (3) ◽  
pp. 314-323
Author(s):  
Baghdad Science Journal
Keyword(s):  
Spiral Galaxy ◽  
Surface Brightness ◽  
Elliptical Galaxy ◽  
Position Angle ◽  
Sloan Digital Sky Survey ◽  
Surface Photometry ◽  
Contour Maps ◽  
Sky Survey ◽  
Flat Field ◽  
The Galaxy

Two galaxies have been chosen, spiral galaxy NGC 5005 and elliptical galaxy NGC 4278 to study their photometric properties by using surface photometric techniques with griz-Filters. Observations are obtained from the Sloan Digital Sky Survey (SDSS). The data reduction of all images have done, like bias and flat field, by SDSS pipeline. The overall structure of the two galaxies (a bulge, a disk), together with isophotal contour maps, surface brightness profiles and a bulge/disk decomposition of the galaxy images were performed, although the disk position angle, ellipticity and inclination of the galaxies have been estimated.

Sign in / Sign up

Export Citation Format

Share Document