We present the data release for Galaxy Zoo 2 (GZ2), a citizen science project with more than 16 million morphological classifications of 304 122 galaxies drawn from the Sloan Digital Sky Survey ...(SDSS). Morphology is a powerful probe for quantifying a galaxy's dynamical history; however, automatic classifications of morphology (either by computer analysis of images or by using other physical parameters as proxies) still have drawbacks when compared to visual inspection. The large number of images available in current surveys makes visual inspection of each galaxy impractical for individual astronomers. GZ2 uses classifications from volunteer citizen scientists to measure morphologies for all galaxies in the DR7 Legacy survey with m
r
> 17, in addition to deeper images from SDSS Stripe 82. While the original GZ2 project identified galaxies as early-types, late-types or mergers, GZ2 measures finer morphological features. These include bars, bulges and the shapes of edge-on disks, as well as quantifying the relative strengths of galactic bulges and spiral arms. This paper presents the full public data release for the project, including measures of accuracy and bias. The majority ( 90 per cent) of GZ2 classifications agree with those made by professional astronomers, especially for morphological T-types, strong bars and arm curvature. Both the raw and reduced data products can be obtained in electronic format at http://data.galaxyzoo.org.
Galaxy Zoo: bars in disc galaxies Masters, Karen L.; Nichol, Robert C.; Hoyle, Ben ...
Monthly notices of the Royal Astronomical Society,
March 2011, Letnik:
411, Številka:
3
Journal Article
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We present first results from Galaxy Zoo 2, the second phase of the highly successful Galaxy Zoo project (http://www.galaxyzoo.org). Using a volume-limited sample of 13 665 disc galaxies (0.01 < z < ...0.06 and Mr
< −19.38), we study the fraction of galaxies with bars as a function of global galaxy properties like colour, luminosity and bulge prominence. Overall, 29.4 ± 0.5 per cent of galaxies in our sample have a bar, in excellent agreement with previous visually classified samples of galaxies (although this overall fraction is lower than that measured by automated bar-finding methods). We see a clear increase in the bar fraction with redder (g−r) colours, decreased luminosity and in galaxies with more prominent bulges, to the extent that over half of the red, bulge-dominated disc galaxies in our sample possess a bar. We see evidence for a colour bimodality for our sample of disc galaxies, with a 'red sequence' that is both bulge and bar dominated, and a 'blue cloud' which has little, or no, evidence for a (classical) bulge or bar. These results are consistent with similar trends for barred galaxies seen recently both locally and at higher redshift, and with early studies using the RC3. We discuss these results in the context of internal (secular) galaxy evolution scenarios and the possible links to the formation of bars and bulges in disc galaxies.
We analyse the relationships between galaxy morphology, colour, environment and stellar mass using data for over 105 objects from Galaxy Zoo, the largest sample of visually classified morphologies ...yet compiled. We conclusively show that colour and morphology fractions are very different functions of environment. Both colour and morphology are sensitive to stellar mass. However, at fixed stellar mass, while colour is also highly sensitive to environment, morphology displays much weaker environmental trends. Only a small part of both the morphology–density and colour–density relations can be attributed to the variation in the stellar-mass function with environment. Galaxies with high stellar masses are mostly red in all environments and irrespective of their morphology. Low stellar-mass galaxies are mostly blue in low-density environments, but mostly red in high-density environments, again irrespective of their morphology. While galaxies with early-type morphology do always have higher red fractions, this is subdominant compared to the dependence of red fraction on stellar mass and environment. The colour–density relation is primarily driven by variations in colour fractions at fixed morphology, in particular the fraction of spiral galaxies that have red colours, and especially at low stellar masses. We demonstrate that our red spirals primarily include galaxies with true spiral morphology, and that they constitute an additional population to the S0 galaxies considered by previous studies. We clearly show there is an environmental dependence for colour beyond that for morphology. The environmental transformation of galaxies from blue to red must occur on significantly shorter time-scales than the transformation from spiral to early-type. We also present many of our results as functions of the distance to the nearest galaxy group. This confirms that the environmental trends we present are not specific to the manner in which environment is quantified, but nevertheless provides plain evidence for an environmental process at work in groups. However, the properties of group members show little dependence on the total mass of the group they inhabit, at least for group masses . Before using the Galaxy Zoo morphologies to produce the above results, we first quantify a luminosity-, size- and redshift-dependent classification bias that affects this data set, and probably most other studies of galaxy population morphology. A correction for this bias is derived and applied to produce a sample of galaxies with reliable morphological-type likelihoods, on which we base our analysis.
We measure the redshift evolution of the bar fraction in a sample of 2380 visually selected disc galaxies found in Cosmic Evolution Survey (COSMOS) Hubble Space Telescope (HST) images. The visual ...classifications used both to identify the disc sample and to indicate the presence of stellar bars were provided by citizen scientists via the Galaxy Zoo: Hubble (GZH) project. We find that the overall bar fraction decreases by a factor of 2, from 22 ± 5 per cent at z = 0.4 (t
lb = 4.2 Gyr) to 11 ± 2 per cent at z = 1.0 (t
lb = 7.8 Gyr), consistent with previous analysis. We show that this decrease, of the strong bar fraction in a volume limited sample of massive disc galaxies stellar mass limit of log (M
/M) ≥ 10.0, cannot be due to redshift-dependent biases hiding either bars or disc galaxies at higher redshifts. Splitting our sample into three bins of mass we find that the decrease in bar fraction is most prominent in the highest mass bin, while the lower mass discs in our sample show a more modest evolution. We also include a sample of 98 red disc galaxies. These galaxies have a high bar fraction (45 ± 5 per cent), and are missing from other COSMOS samples which used SED fitting or colours to identify high-redshift discs. Our results are consistent with a picture in which the evolution of massive disc galaxies begins to be affected by slow (secular) internal process at z ∼ 1. We discuss possible connections of the decrease in bar fraction to the redshift, including the growth of stable disc galaxies, mass evolution of the gas content in disc galaxies, as well as the mass-dependent effects of tidal interactions.
Galaxy Zoo: passive red spirals Masters, Karen L.; Mosleh, Moein; Romer, A. Kathy ...
Monthly notices of the Royal Astronomical Society,
06/2010, Letnik:
405, Številka:
2
Journal Article
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We study the spectroscopic properties and environments of red (or passive) spiral galaxies found by the Galaxy Zoo project. By carefully selecting face-on disc-dominated spirals, we construct a ...sample of truly passive discs (i.e. they are not dust reddened spirals, nor are they dominated by old stellar populations in a bulge). As such, our red spirals represent an interesting set of possible transition objects between normal blue spiral galaxies and red early types, making up ∼6 per cent of late-type spirals. We use optical images and spectra from Sloan Digital Sky Survey to investigate the physical processes which could have turned these objects red without disturbing their morphology. We find red spirals preferentially in intermediate density regimes. However, there are no obvious correlations between red spiral properties and environment suggesting that environment alone is not sufficient to determine whether a galaxy will become a red spiral. Red spirals are a very small fraction of all spirals at low masses (M★ < 1010 M⊙), but are a significant fraction of the spiral population at large stellar masses showing that massive galaxies are red independent of morphology. We confirm that as expected, red spirals have older stellar populations and less recent star formation than the main spiral population. While the presence of spiral arms suggests that a major star formation could not have ceased a long ago (not more than a few Gyr), we show that these are also not recent post-starburst objects (having had no significant star formation in the last Gyr), so star formation must have ceased gradually. Intriguingly, red spirals are roughly four times as likely than the normal spiral population to host optically identified Seyfert/low-ionization nuclear emission region (LINER; at a given stellar mass and even accounting for low-luminosity lines hidden by star formation), with most of the difference coming from the objects with LINER-like emission. We also find a curiously large optical bar fraction in the red spirals (70 ± 5 verses 27 ± 5 per cent in blue spirals) suggesting that the cessation of star formation and bar instabilities in spirals are strongly correlated. We conclude by discussing the possible origins of these red spirals. We suggest that they may represent the very oldest spiral galaxies which have already used up their reserves of gas – probably aided by strangulation or starvation, and perhaps also by the effect of bar instabilities moving material around in the disc. We provide an online table listing our full sample of red spirals along with the normal/blue spirals used for comparison.
We present the data release paper for the Galaxy Zoo: Hubble (GZH) project. This is the third phase in a large effort to measure reliable, detailed morphologies of galaxies by using crowdsourced ...visual classifications of colour-composite images. Images in GZH were selected from various publicly released Hubble Space Telescope legacy programmes conducted with the Advanced Camera for Surveys, with filters that probe the rest-frame optical emission from galaxies out to z ~ 1. The bulk of the sample is selected to have mI814W < 23.5, but goes as faint as mI814W < 26.8 for deep images combined over five epochs. The median redshift of the combined samples is = 0.9 plus or minus 0.6, with a tail extending out to z ... 4. The GZH morphological data include measurements of both bulge- and disc-dominated galaxies, details on spiral disc structure that relate to the Hubble type, bar identification, and numerous measurements of clump identification and geometry. This paper also describes a new method for calibrating morphologies for galaxies of different luminosities and at different redshifts by using artificially redshifted galaxy images as a baseline. The GZH catalogue contains both raw and calibrated morphological vote fractions for 119 849 galaxies, providing the largest data set to date suitable for large-scale studies of galaxy evolution out to z ~ 1. (ProQuest: ... denotes formulae/symbols omitted.)
The GoCheck Kids smartphone photoscreening app (Gobiquity Mobile Health, Scottsdale, Arizona, USA), introduced in 2014, is marketed to pediatricians with little published validation. We wished to ...evaluate the GoCheck Kids Screener for accuracy in detecting amblyopia risk factors (ARF) using 2013 American Association for Pediatric Ophthalmology and Strabismus guidelines.
Validity assessment.
Children 6 months to 6 years of age presenting from October 2016 to August 2017 were included. Children were screened with the GoCheck preloaded Nokia Lumia 1020, software version 4.6 with image processing version R4d, prior to undergoing a comprehensive eye examination by a pediatric ophthalmologist masked to the screener results. Determination of the presence of age-specific ARF was made based upon the examination and compared with the GoCheck recommendation.
A total of 206 children were included (average age 43 months). When compared to examination, GoCheck had a sensitivity of 76.0% and specificity of 67.2% in detecting ARF. Positive predictive value was 57.0% and negative predictive value 83.0%. The screener results of 13 children were changed from “no risk factors” to “risk factors identified” based on the GoCheck remote review process. Four images remained “not gradable” and screening was unsuccessful in 3 children.
In our high-risk population, this version of the Gocheck Kids smartphone app was useful in identifying ARF in children who are often not able to cooperate with visual acuity testing. This study informs pediatricians about the efficacy of this new screener as they make decisions about how to best detect vision problems in young children.
We analyse the environmental dependence of galaxy morphology and colour with two-point clustering statistics, using data from the Galaxy Zoo, the largest sample of visually classified morphologies ...yet compiled, extracted from the Sloan Digital Sky Survey. We present two-point correlation functions of spiral and early-type galaxies, and we quantify the correlation between morphology and environment with marked correlation functions. These yield clear and precise environmental trends across a wide range of scales, analogous to similar measurements with galaxy colours, indicating that the Galaxy Zoo classifications themselves are very precise. We measure morphology marked correlation functions at fixed colour and find that they are relatively weak, with the only residual correlation being that of red galaxies at small scales, indicating a morphology gradient within haloes for red galaxies. At fixed morphology, we find that the environmental dependence of colour remains strong, and these correlations remain for fixed morphology and luminosity. An implication of this is that much of the morphology–density relation is due to the relation between colour and density. Our results also have implications for galaxy evolution: the morphological transformation of galaxies is usually accompanied by a colour transformation, but not necessarily vice versa. A spiral galaxy may move on to the red sequence of the colour–magnitude diagram without quickly becoming an early type. We analyse the significant population of red spiral galaxies, and present evidence that they tend to be located in moderately dense environments and are often satellite galaxies in the outskirts of haloes. Finally, we combine our results to argue that central and satellite galaxies tend to follow different evolutionary paths.
We present an analysis of the environmental dependence of bars and bulges in disc galaxies, using a volume-limited catalogue of 15 810 galaxies at z < 0.06 from the Sloan Digital Sky Survey with ...visual morphologies from the Galaxy Zoo 2 project. We find that the likelihood of having a bar, or bulge, in disc galaxies increases when the galaxies have redder (optical) colours and larger stellar masses, and observe a transition in the bar and bulge likelihoods at M
*= 2 × 1010 M⊙, such that massive disc galaxies are more likely to host bars and bulges. In addition, while some barred and most bulge-dominated galaxies are on the 'red sequence' of the colour-magnitude diagram, we see a wider variety of colours for galaxies that host bars. We use galaxy clustering methods to demonstrate statistically significant environmental correlations of barred, and bulge-dominated, galaxies, from projected separations of 150 kpc h
−1 to 3 Mpc h
−1. These environmental correlations appear to be independent of each other: i.e. bulge-dominated disc galaxies exhibit a significant bar-environment correlation, and barred disc galaxies show a bulge-environment correlation. As a result of sparse sampling tests - our sample is nearly 20 times larger than those used previously - we argue that previous studies that did not detect a bar-environment correlation were likely inhibited by small number statistics. We demonstrate that approximately half of the bar-environment correlation can be explained by the fact that more massive dark matter haloes host redder disc galaxies, which are then more likely to have bars; this fraction is estimated to be 50 ± 10 per cent from a mock catalogue analysis and 60 ± 5 per cent from the data. Likewise, we show that the environmental dependence of stellar mass can only explain a smaller fraction (25 ± 10 per cent) of the bar-environment correlation. Therefore, a significant fraction of our observed environmental dependence of barred galaxies is not due to colour or stellar mass dependences, and hence must be due to another galaxy property, such as gas content, or to environmental influences. Finally, by analysing the projected clustering of barred and unbarred disc galaxies with halo occupation models, we argue that barred galaxies are in slightly higher mass haloes than unbarred ones, and some of them (approximately 25 per cent) are satellite galaxies in groups. We discuss the implications of our results on the effects of minor mergers and interactions on bar formation in disc galaxies.
Galaxy Zoo: dust in spiral galaxies Masters, Karen L.; Nichol, Robert; Bamford, Steven ...
Monthly notices of the Royal Astronomical Society,
05/2010, Letnik:
404, Številka:
2
Journal Article
Recenzirano
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We investigate the effect of dust on spiral galaxies by measuring the inclination dependence of optical colours for 24 276 well-resolved Sloan Digital Sky Survey (SDSS) galaxies visually classified ...via the Galaxy Zoo project. We find clear trends of reddening with inclination which imply a total extinction from face-on to edge-on of 0.7, 0.6, 0.5 and 0.4 mag for the ugri passbands (estimating 0.3 mag of extinction in z band). We split the sample into ‘bulgy’ (early-type) and ‘discy’ (late-type) spirals using the SDSS fracdeV (or fDeV) parameter and show that the average face-on colour of ‘bulgy’ spirals is redder than the average edge-on colour of ‘discy’ spirals. This shows that the observed optical colour of a spiral galaxy is determined almost equally by the spiral type (via the bulge–disc ratio and stellar populations), and reddening due to dust. We find that both luminosity and spiral type affect the total amount of extinction, with discy spirals at Mr∼−21.5 mag having the most reddening – more than twice as much as both the lowest luminosity and most massive, bulge-dominated spirals. An increase in dust content is well known for more luminous galaxies, but the decrease of the trend for the most luminous has not been observed before and may be related to their lower levels of recent star formation. We compare our results with the latest dust attenuation models of Tuffs et al. We find that the model reproduces the observed trends reasonably well but overpredicts the amount of u-band attenuation in edge-on galaxies. This could be an inadequacy in the Milky Way extinction law (when applied to external galaxies), but more likely indicates the need for a wider range of dust–star geometries. We end by discussing the effects of dust on large galaxy surveys and emphasize that these effects will become important as we push to higher precision measurements of galaxy properties and their clustering.
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