Observation has not yet determined whether the distribution of spin vectors of galaxies is truly random. It is unclear whether is there any large-scale symmetry-breaking in the distribution of the vorticity field in the universe. Here, we present a formulation to evaluate the dipole component D_{max} of the observed spin distribution, whose statistical significance sigma_{D} can be calibrated by the expected amplitude for 3D random walk (random flight) simulations.
We apply this formulation to evaluate the dipole component in the distribution of Sloan Digital Sky Survey (SDSS) spirals. Shamir(2017a) published a catalog of spiral galaxies from the SDSS DR8, classifying them with his pattern recognition tool into clockwise and counterclockwise (Z-spiral and S-spirals, respectively). He found significant photometric asymmetry in their distribution. We have confirmed that this sample provides dipole asymmetry up to a level of sigma_{D}=4.00.
However, we also found that the catalog contains a significant number of multiple entries of the same galaxies. After removing the duplicated entries, the number of samples shrunk considerably to 45%. The actual dipole asymmetry observed for the 'cleaned' catalog is quite modest, sigma_{D}=0.29. We conclude that SDSS data alone does not support the presence of a large-scale symmetry-breaking in the spin vector distribution of galaxies in the local universe. The data are compatible with a random distribution.
Using a sample of spiral galaxies selected from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) and Galaxy Zoo 2 (GZ2), we investigate the alignment of spin axes of spiral galaxies with their surrounding large scale structure, which is characterized by the large-scale tidal field reconstructed from the data using galaxy groups above a certain mass threshold. We find that the spin axes of only have weak tendency to be aligned with (or perpendicular to) the intermediate (or minor) axis of the local tidal tensor. The signal is the strongest in a \cluster environment where all the three eig…
The distribution of the spin directions of spiral galaxies in the Sloan Digital Sky Survey has been a topic of debate in the past two decades, with conflicting conclusions reported even in cases where the same data was used. Here we follow one of the previous experiments by applying the SpArcFiRe algorithm to annotate the spin directions in original dataset of Galaxy Zoo 1. The annotation of the galaxy spin directions is done after a first step of selecting the spiral galaxies in three different manners: manual analysis by Galaxy Zoo classifications, by a model-driven computer analysis, and wi…
Previous observations of a large number of galaxies show differences between the photometry of spiral galaxies with clockwise spin patterns and spiral galaxies with counterclockwise spin patterns. In this study the mean magnitude of a large number of clockwise galaxies is compared to the mean magnitude of a large number of counterclockwise galaxies. The observed difference between clockwise and counterclockwise spiral galaxies imaged by the space-based COSMOS survey is compared to the differences between clockwise and counterclockwise galaxies imaged by the Earth-based SDSS and Pan-STARRS arou…
Spiral galaxies can be classified into the {\it Grand-designs} and {\it Flocculents} based on the nature of their spiral arms. The {\it Grand-designs} exhibit almost continuous and high contrast spiral arms and are believed to be driven by density waves, while the {\it Flocculents} have patchy and low-contrast spiral features and are primarily stochastic in origin. We train a convolutional neural network (CNN) model to classify spirals into {\it Grand-designs} and {\it Flocculents}, with a testing accuracy of $\mathrm{97.2\%}$. We then use the above model for classifying $\mathrm{1,354}$ new s…
While galaxies with clockwise and counterclockwise handedness are visually different, they are expected to be symmetric in all of their other characteristics. Previous experiments using both manual analysis and machine vision have shown that the handedness of Sloan Digital Sky Survey (SDSS) galaxies can be predicted with accuracy significantly higher than mere chance using its photometric data alone, showing that SDSS photometry pipeline is sensitive to the handedness of the galaxy. However, some of these previous experiments were based on manually classified galaxies, and the results may ther…
Spin patterns of spiral galaxies can be broadly separated into galaxies with clockwise (Z-wise) patterns and galaxies with counterclockwise (S-wise) spin patterns. While the differences between these patterns are visually noticeable, they are a matter of the perspective of the observer, and therefore in a sufficiently large universe no other differences are expected between galaxies with Z-wise and S-wise patterns. Here large datasets of spiral galaxies separated by their spin patterns are used to show that spiral galaxies with Z-wise spin patterns are photometrically different from spiral gal…
The distribution of spin directions of $\sim6.4\cdot10^4$ SDSS spiral galaxies with spectra was examined, and compared to the distribution of $\sim3.3\cdot10^4$ Pan-STARRS galaxies. The analysis shows a statistically significant asymmetry between the number of SDSS galaxies with opposite spin directions, and the magnitude and direction of the asymmetry changes with the direction of observation and with the redshift. The redshift dependence shows that the distribution of the spin direction of SDSS galaxies becomes more asymmetric as the redshift gets higher. Fitting the distribution of the gala…
We investigate the 3D spin alignment of galaxies with respect to the large-scale filaments using the MaNGA survey. The cosmic web is reconstructed from the Sloan Digital Sky Survey using Disperse and the 3D spins of MaNGA galaxies are estimated using the thin disk approximation with integral field spectroscopy kinematics. Late-type spiral galaxies are found to have their spins parallel to the closest filament's axis. The alignment signal is found to be dominated by low-mass spirals. Spins of S0-type galaxies tend to be oriented preferentially in perpendicular direction with respect to the fila…
We perform a "fossil record" analysis for ~800 low-redshift spiral galaxies, using STARLIGHT applied to integral field spectroscopic observations from the SDSS-IV MaNGA survey to obtain fully spatially-resolved high-resolution star formation histories (SFHs). From the SFHs, we are able to build maps indicating the present-day distribution of stellar populations of different ages in each galaxy. We find small negative mean age gradients in most spiral galaxies, especially at high stellar mass, which reflects the formation times of stellar populations at different galactocentric radii. We show t…
We perform Jeans anisotropic modeling (JAM) on elliptical and spiral galaxies from the MaNGA DR13 sample. By comparing the stellar mass-to-light ratios estimated from stellar population synthesis (SPS) and from JAM, we find a similar systematic variation of the initial mass function (IMF) as in the earlier $\rm ATLAS^{3D}$ results. Early type galaxies (elliptical and lenticular) with lower velocity dispersions within one effective radius are consistent with a Chabrier-like IMF while galaxies with higher velocity dispersions are consistent with a more bottom heavy IMF such as the Salpeter IMF. …
We examine whether galaxy environments directly affect triggering nuclear activity in Sloan Digital Sky Survey (SDSS) local spiral galaxies using a volume-limited sample with the $r$-band absolute magnitude $M_{r} < -19.0$ and $0.02 < z < 0.055$ selected from the SDSS Data Release 7. To avoid incompleteness of the central velocity dispersion $σ$ of the volume-limited sample and to fix the black hole mass affecting AGN activity, we limit the sample to a narrow $σ$ range of $130$ km s$^{-1}<σ<200$ km s$^{-1}$. We define a variety of environments as a combination of neighbour interactions and loc…
Spectra of galaxies contain a wealth of information about the stellar populations from which they are made. With integral-field unit (IFU) surveys, such data can be used to map out stellar population properties across the face of a galaxy, allowing one to go beyond simple radial profiles and study details of non-axisymmetric structure. To-date, however, such studies have been limited by the quality of available data and the power of spectral analysis tools. We now take the next step and study the barred spiral galaxy MCG+07-28-064 from observations obtained as part of the SDSS-IV MaNGA project…
We investigate the origin of rare star-formation in an otherwise red-and-dead population of S0 galaxies using spatially resolved spectroscopy. Our sample consists of $120$ low redshift ($z<0.1$) star-forming S0 (SF-S0) galaxies from the SDSS-IV MaNGA DR15. We have selected this sample after a visual inspection of deep images from the DESI Legacy Imaging Surveys DR9 and the Subaru/HSC-SSP survey PDR3, to remove contamination from spiral galaxies. We also construct two control samples of star-forming spirals (SF-Sps) and quenched S0s (Q-S0s) to explore their evolutionary link with the star-formi…
The degeneracy among the disk, bulge and halo contributions to galaxy rotation curves prevents an understanding of the distribution of baryons and dark matter in disk galaxies. In an attempt to break this degeneracy, we present an analysis of the spiral galaxy strong gravitational lens SDSS J2141-0001, discovered as part of the SLACS survey. We present new Hubble Space Telescope multicolor imaging, gas and stellar kinematics data derived from long-slit spectroscopy, and K-band LGS adaptive optics imaging, both from the Keck telescopes. We model the galaxy as a sum of concentric axisymmetric bu…
Dust attenuation in star-forming spiral galaxies affects stars and gas in different ways due to local variations in dust geometry. We present spatially resolved measurements of dust attenuation for a sample of 232 such star-forming spiral galaxies, derived from spectra acquired by the SDSS-IV MaNGA survey. The dust attenuation affecting the stellar populations of these galaxies (obtained using full spectrum stellar population fitting methods) is compared with the dust attenuation in the gas (derived from the Balmer decrement). Both of these attenuation measures increase for local regions of ga…
We explore the significance of bars in triggering central star formation (SF) and AGN activity for spiral galaxy evolution using a volume-limited sample with $0.020<z<0.055$, $M_{\rm r}<-19.5$, and $σ>70\rm km s^{-1}$ selected from SDSS DR7. On a central SF rate-$σ$ plane, we measure the fraction of galaxies with strong bars in our sample and also the AGN fractions for barred and non-barred galaxies, respectively. The comparison between the bar and AGN fractions reveals a causal connection between the two phenomena of SF quenching and AGN activity. A massive BH and abundant gas fuels are suffi…
Several recent observations using large datasets 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 dataset of $\sim8.7\cdot10^3$ spiral galaxies imaged by Hubble Space Telescope 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 datasets contain different galaxies at different redshift ranges, …
Whether the spiral structure of galaxies is trailing or leading has been a subject of debate. We present a new spin parity catalog of 146 spiral galaxies that lists the following three pieces of information: whether the spiral structure observed on the sky is S-wise or Z-wise; which side of the minor axis of the galaxy is darker and redder, based on examination of Pan-STARRS and/or ESO/DSS2 red image archives, and which side of the major axis of the galaxy is approaching to us based on the published literature. This paper confirms that all of the spiral galaxies in the catalog show a consisten…
We investigate archaeologically how the metallicity in both stellar and gaseous components of spiral galaxies of differing masses evolve with time, using data from the SDSS-IV MaNGA survey. For the stellar component, we can measure this evolution directly by decomposing the galaxy absorption-line spectra into populations of different ages and determining their metallicities. For the gaseous component, we can only measure the present-day metallicity directly from emission lines. However, there is a well-established relationship between gas metallicity, stellar mass and star formation rate which…
Previous observations have suggested non-random distribution of spin directions of galaxies at scales far larger than the size of a supercluster. Here I use $\sim1.7\cdot10^5$ spiral galaxies from SDSS and $3.3\cdot10^4$ spiral galaxies from Pan-STARRS to analyze the distribution of galaxy spin patterns of spiral galaxies as observed from Earth. The analysis shows in both SDSS and Pan-STARRS that the distribution of galaxy spin directions forms a non-random pattern, and can be fitted to a dipole axis in probability much higher than mere chance. These observations agree with previous findings, …
We study the effects of bulge elongation on the star formation activity in the centers of spiral galaxies using the data from the Sloan Digital Sky Survey Data Release 7. We construct a volume-limited sample of face-on spiral galaxies with $M_r < -$19.5 mag at 0.02 $\leq z <$ 0.055 by excluding barred galaxies, where the aperture of the SDSS spectroscopic fibre covers the bulges of the galaxies. We adopt the ellipticity of bulges measured by Simard et al. (2011) who performed two-dimensional bulge+disc decompositions using the SDSS images of galaxies, and identify nuclear starbursts using the …
We report an automated morphological classification of galaxies into S-wise spirals, Z-wise spirals, and non-spirals using big image data taken from Subaru/Hyper Suprime-Cam (HSC) Survey and a convolutional neural network(CNN)-based deep learning technique. The HSC i-band images are about 25 times deeper than those from the Sloan Digital Sky Survey (SDSS) and have a two times higher spatial resolution, allowing us to identify substructures such as spiral arms and bars in galaxies at z>0.1. We train CNN classifiers by using HSC images of 1447 S-spirals, 1382 Z-spirals, and 51,650 non-spirals. A…
Recent studies have shown that SDSS galaxies with clockwise patterns are photometrically different from galaxies with anti-clockwise patterns. The purpose of this study is to identify possible differences between the colour of galaxies with clockwise handedness and the colour of galaxies with anti-clockwise handedness. A dataset of 162,514 SDSS galaxies was separated into clockwise and counterclockwise galaxies, and the colours of spiral galaxies with clockwise handedness were compared to the colour of spiral galaxies with anti-clockwise handedness. The results show that the i-r colour in cloc…
We report the discovery of spiral galaxies that are as optically luminous as elliptical brightest cluster galaxies, with r-band monochromatic luminosity L_r=8-14L* (4.3-7.5E44 erg/s). These super spiral galaxies are also giant and massive, with diameter D=57-134 kpc and stellar mass M_stars=0.3-3.4E11 M_sun. We find 53 super spirals out of a complete sample of 1616 SDSS galaxies with redshift z<0.3 and L_r>8L*. The closest example is found at z=0.089. We use existing photometry to estimate their stellar masses and star formation rates (SFRs). The SDSS and WISE colors are consistent with normal…
We perform full spectrum fitting stellar population analysis and Jeans Anisotropic modelling (JAM) of the stellar kinematics for about 2000 early-type galaxies (ETGs) and spiral galaxies from the MaNGA DR14 sample. Galaxies with different morphologies are found to be located on a remarkably tight mass plane which is close to the prediction of the virial theorem, extending previous results for ETGs. By examining an inclined projection (`the mass-size' plane), we find that spiral and early-type galaxies occupy different regions on the plane, and their stellar population properties (i.e. age, met…
In this article I extend an earlier study of spiral galaxies in the Sloan Digital Sky Survey (SDSS) to investigate whether the universe has an overall handedness. A preference for spiral galaxies in one sector of the sky to be left-handed or right-handed spirals would indicate a parity-violating asymmetry in the overall universe and a preferred axis. The previous study used 2616 spiral galaxies with redshifts <0.04 and identified handedness. The new study uses 15158 with redshifts <0.085 and obtains very similar results to the first with a signal exceeding 5 sigma, corresponding to a probabili…
We applied computer analysis to classify the broad morphological type of ~3,000,000 SDSS galaxies. The catalog provides for each galaxy the DR8 object ID, right ascension, declination, and the certainty of the automatic classification to spiral or elliptical. The certainty of the classification allows controlling the accuracy of a subset of galaxies by sacrificing some of the least certain classifications. The accuracy of the catalog was tested using galaxies that were classified by the manually annotated Galaxy Zoo catalog. The results show that the catalog contains ~900,000 spiral galaxies a…
Spiral-driven instabilities may drive gas inflow to enhance central star formation in disk galaxies. We investigate this hypothesis using the Sloan Digital Sky Survey (SDSS) in a sample of 2779 nearby unbarred star-forming main-sequence spiral galaxies. The strength of spiral arms is quantified by their average Fourier amplitude relative to the axisymmetric disk. The star formation properties in the central 1--3\,kpc region were derived from the SDSS spectra. We show that galaxies with stronger spiral arms not only tend to have more intense central specific star formation rate (sSFR), larger B…
Bars are common in low-redshift disk galaxies, and hence quantifying their influence on their host is of importance to the field of galaxy evolution. We determine the stellar populations and star formation histories of 245 barred galaxies from the MaNGA galaxy survey, and compare them to a mass- and morphology-matched comparison sample of unbarred galaxies. At fixed stellar mass and morphology, barred galaxies are optically redder than their unbarred counterparts. From stellar population analysis using the full spectral fitting code Starlight, we attribute this difference to both older and mor…
We present the largest, most homogeneous catalogue of merging galaxies in the nearby universe obtained through the Galaxy Zoo project - an interface on the world-wide web enabling large-scale morphological classification of galaxies through visual inspection of images from the Sloan Digital Sky Survey (SDSS). The method converts a set of visually-inspected classifications for each galaxy into a single parameter (the `weighted-merger-vote fraction,' $f_m$) which describes our confidence that the system is part of an ongoing merger. We describe how $f_m$ is used to create a catalogue of 3003 vis…
Properties of cluster red-sequence spiral galaxies
University of North Dakota（北达科他大学）；Colorado State University（科罗拉多州立大学）；New Mexico State University - Alamogordo（新墨西哥州立大学阿拉莫戈多分校）；INAOE（国家天体物理学、光学和电子学研究所）
We applied the image-based approach with a convolutional neural network model to the sample of low-redshifts galaxies with $-24^{m}<M_{r}<-19.4^{m}$ from the SDSS DR9. We divided it into two subsamples, SDSS DR9 galaxy dataset and Galaxy Zoo 2 (GZ2) dataset, considering them as the inference and training datasets, respectively. As a result, we created the morphological catalog of 315782 galaxies at 0.02<z<0.1, where morphological five classes and 34 detailed features (bar, rings, number of spiral arms, mergers, etc.) were first defined for 216148 galaxies (inference dataset) by the image-based…
We report two-dimensional spectroscopic analysis of massive red spiral galaxies ($M_{*}$ $>$ 10$^{10.5}$ $M_{\odot}$) and compare them to blue spiral and red elliptical galaxies above the same mass limit based on the public SDSS DR15 MaNGA observations. We find that the stellar population properties of red spiral galaxies are more similar to those of elliptical galaxies than to blue spiral galaxies. Red spiral galaxies show a shallow mass-weighted age profile, and they have higher stellar metallicity and Mgb/${\rm \langle Fe \rangle}$ across the whole 1.5$R_{\rm e}$ as compared to blue spirals…
The formation of the red spirals is a puzzling issue in the standard picture of galaxy formation and evolution. Most studies attribute the colour of the red spirals to different environmental effects. We analyze a volume limited sample from the SDSS to study the roles of small-scale and large-scale environments on the colour of spiral galaxies. We compare the star formation rate, stellar age and stellar mass distributions of the red and blue spirals and find statistically significant differences between them at $99.9\%$ confidence level. The red spirals inhabit significantly denser regions tha…
We created a catalog of photometric redshift of ~3,000,000 SDSS galaxies annotated by their broad morphology. The photometric redshift was optimized by testing and comparing several pattern recognition algorithms and variable selection strategies, trained and tested on a subset of the galaxies in the catalog that had spectra. The galaxies in the catalog have i magnitude brighter than 18 and Petrosian radius greater than 5.5''. The majority of these objects are not included in previous SDSS photometric redshift catalogs such as the photoz table of SDSS DR12. Analysis of the catalog shows that t…
Subjective classification of spiral galaxies is not sufficient for studying the effect of bars on their physical characteristics. In reality the problem is to comprehend the complex correlations in a multivariate parametric space. Multivariate tools are the best ones for understanding this complex correlation. In this work an objective classification of a large set (26,089) of spiral galaxies was compiled as a value added galaxy catalogue from sdss DR 15 virtual data archive. Initially for dimensionality reduction, Independent Component Analysis is performed to determine a set of Independent C…
We study the effects of applying observational techniques to derive the properties of simulated galaxies, with the aim of making an unbiased comparison between observations and simulations. For our study, we used fifteen galaxies simulated in a cosmological context using three different feedback and chemical enrichment models, and compared their z=0 properties with data from the Sloan Digital Sky Survey (SDSS). We show that the physical properties obtained directly from the simulations without post-processing can be very different to those obtained mimicking observational techniques. In order …
We investigate the impact of filament and void environments on galaxies, looking for residual effects beyond the known relations with environment density. We quantified the host environment of galaxies as the distance to the spine of the nearest filament, and compared various galaxy properties within 12 bins of this distance. We considered galaxies up to 10 $h^{-1}$Mpc from filaments, i.e. deep inside voids. The filaments were defined by a point process (the Bisous model) from the Sloan Digital Sky Survey data release 10. In order to remove the dependence of galaxy properties on the environmen…
We investigate the radial color gradients of galactic disks using a sample of about 20,000 face-on spiral galaxies selected from the fourth data release of the Sloan Digital Sky Survey (SDSS-DR4). We combine galaxies with similar concentration, size and luminosity to construct composite galaxies, and then measure their color profiles by stacking the azimuthally averaged radial color profiles of all the member galaxies. Except for the smallest galaxies (R_{50}<3 kpc), almost all galaxies show negative disk color gradients with mean g-r gradient G_{gr}=-0.006 mag kpc^{-1} and r-z gradient G_{rz}…
While it is clear that spiral galaxies can have different handedness, galaxies with clockwise patterns are assumed to be symmetric in all of their other characteristics to galaxies with counterclockwise patterns. Here we use data from SDSS DR7 to show that photometric data can distinguish between clockwise and counterclockwise galaxies. Pattern recognition algorithms trained and tested using the photometric data of a clean manually crafted dataset of 13,440 spiral galaxies with z<0.25 can predict the handedness of a spiral galaxy in ~64% of the cases, significantly higher than mere chance accu…
We present our recent results on the properties of the outskirts of disk galaxies. In particular, we focus on spiral galaxies with stellar disk truncations in their radial surface brightness profiles. Using SDSS, UDF and GOODS data we show how the position of the break (i.e., a direct estimator of the size of the stellar disk) evolves with time since z~1. Our findings agree with an evolution on the radial position of the break by a factor of 1.3+/-0.1 in the last 8 Gyr for galaxies with similar stellar masses. We also present radial color gradients and how they evolve with time. At all redshif…
We use the SDSS Stripe 82 to empirically quantify the stellar-mass and black-hole growth triggered by minor mergers in local spiral (disk) galaxies. Since major mergers destroy disks and create spheroids, morphologically disturbed spirals are likely remnants of minor mergers. Disturbed spirals exhibit enhanced specific star formation rates (SSFRs), the enhancement increasing in galaxies of 'later' morphological type (which have more gas and smaller bulges). By combining the SSFR enhancements with the fraction of time spirals spend in this 'enhanced' mode, we estimate that ~40% of the star form…
Using a sample of galaxies selected from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) and a catalog of bulge-disk decompositions, we study how the size distribution of galaxies depends on the intrinsic properties of galaxies, such as concentration, morphology, specific star formation rate (sSFR), and bulge fraction, and on the large-scale environments in the context of central/satellite decomposition, halo environment, the cosmic web: \cluster, \filament, \sheet ~and \void, as well as galaxy number density. We find that there is a strong dependence of the luminosity- or mass-size rel…
We explore properties of barred active spiral galaxies in groups selected from the SDSS-DR7, with the aim of assessing the effects of bars on AGN and the role of the high density environment. We identified barred active galaxies that reside in groups from SDSS-DR7 group catalog. To provide a suitable quantification of the effects of bars, a reliable control sample of unbarred active galaxies in high density environments with similar redshift, magnitude, morphology, and bulge size distributions was constructed. We found that the fraction of barred AGN galaxies in groups (~ 38 %) is higher than …
We discuss a novel approach to "weighing" the Milky Way dark matter halo, one that combines the latest samples of halo stars selected from the Sloan Digital Sky Survey (SDSS) with state-of-the-art numerical simulations of Milky Way analogs. The fully cosmological runs employed in the present study include "Eris", one of the highest-resolution hydrodynamical simulations of the formation of a M_vir=8e11 M_sun late-type spiral, and the dark-matter only M_vir=1.7e12 M_sun "Via Lactea II" simulation. Eris provides an excellent laboratory for creating mock SDSS samples of tracer halo stars, and we s…
We present an extended morphometric system to automatically classify galaxies from astronomical images. The new system includes the original and modified versions of the CASGM coefficients (Concentration $C_1$, Asymmetry $A_3$, and Smoothness $S_3$), and the new parameters entropy, $H$, and spirality $σ_ψ$. The new parameters $A_3$, $S_3$ and $H$ are better to discriminate galaxy classes than $A_1$, $S_1$ and $G$, respectively. The new parameter $σ_ψ$ captures the amount of non-radial pattern on the image and is almost linearly dependent on T-type. Using a sample of spiral and elliptical galax…
The aim of this study is to determine the fractions of different spiral galaxy types, especially bulgeless disks, from a complete and homogeneous sample of 15127 edge-on disk galaxies extracted from the sixth data release from the Sloan Digital Sky Survey. The sample is divided in broad morphological classes and sub types consisting of galaxies with bulges, intermediate types and galaxies which appear bulgeless. A small fraction of disky irregulars is also detected. The morphological separation is based on automated classification criteria which resemble the bulge sizes and the flatness of the…
The ability to collect unprecedented amounts of astronomical data has enabled the studying scientific questions that were impractical to study in the pre-information era. This study uses large datasets collected by four different robotic telescopes to profile the large-scale distribution of the spin directions of spiral galaxies. These datasets cover the Northern and Southern hemispheres, in addition to data acquired from space by the Hubble Space Telescope. The data were annotated automatically by a fully symmetric algorithm, as well as manually through a long labor-intensive process, leading…
The ability of digital sky surveys to collect and store very large amounts of data provides completely new ways to study the local universe. Perhaps one of the most provocative observations reported with such tools is the asymmetry between galaxies with clockwise and counterclockwise spin patterns. Here I use $\sim1.7\cdot10^5$ spiral galaxies from SDSS and sort them by their spin patterns (clockwise or counterclockwise) to identify and profile a possible large-scale pattern of the distribution of galaxy spin patterns as observed from Earth. The analysis shows asymmetry between the number of c…
Spiral arms are common features in low-redshift disc galaxies, and are prominent sites of star-formation and dust obscuration. However, spiral structure can take many forms: from galaxies displaying two strong `grand design' arms, to those with many `flocculent' arms. We investigate how these different arm types are related to a galaxy's star-formation and gas properties by making use of visual spiral arm number measurements from Galaxy Zoo 2. We combine UV and mid-IR photometry from GALEX and WISE to measure the rates and relative fractions of obscured and unobscured star formation in a sampl…
Gas stripping of spiral galaxies or mergers are thought to be the formation mechanisms of lenticular galaxies. In order to determine the conditions in which each scenario dominates, we derive stellar populations of both the bulge and disk regions of 279 lenticular galaxies in the MaNGA survey. We find a clear bimodality in stellar age and metallicity within the population of S0s and this is strongly correlated with stellar mass. Old and metal-rich bulges and disks belong to massive galaxies, and young and metal-poor bulges and disks are hosted by low-mass galaxies. From this we conclude that t…
In this paper we study the morphological properties of spiral galaxies, including measurements of spiral arm number and pitch angle. Using Galaxy Zoo 2, a stellar mass-complete sample of 6,222 SDSS spiral galaxies is selected. We use the machine vision algorithm SpArcFiRe to identify spiral arm features and measure their associated geometries. A support vector machine classifier is employed to identify reliable spiral features, with which we are able to estimate pitch angles for half of our sample. We use these machine measurements to calibrate visual estimates of arm tightness, and hence esti…
For spiral galaxies, the active galactic nucleus (AGN) and some physical parameters that concern the host galaxy such as spiral arm radius and density can play an important role in the morphological evolution of these galaxies. Considering the gravitational effect of the central black hole as a feeding mechanism, the gas flows from spiral arms to the accretion disk. Accordingly, we constructed our approach and derived an equation for the AGN luminosity that depends on parameters such as the black hole mass and the spiral arm density. The galaxy samples were taken from a catalog of type 1 AGN f…
To understand the formation and quenching processes of local massive red spiral galaxies with $M_{\ast} > 10^{10.5}M_{\odot}$, we perform a statistical analysis of their spectroscopic and structural properties, and compare them with elliptical and blue spiral galaxies of similar mass. The sample was selected from the stellar mass catalog of galaxies in SDSS DR7, according to their locations on the u-r color-stellar mass diagram. We find that red spirals harbor compact cores with high stellar mass surface densities measured by $Σ_1$ and they are bulge-dominated. Particularly, the red spirals, e…
Since the discovery that the majority of low-redshift galaxies exhibit some level of spiral structure, a number of theories have been proposed as to why these patterns exist. A popular explanation is a process known as swing amplification, yet there is no observational evidence to prove that such a mechanism is at play. By using a number of measured properties of galaxies, and scaling relations where there are no direct measurements, we model samples of SDSS and S$^4$G spiral galaxies in terms of their relative halo, bulge and disc mass and size. Using these models, we test predictions of swin…
