Galaxy Zoo papers and papers that build upon our results

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If the title is a link, it will take you to arXiv.org (or equivalent) where you can read the paper.  (Follow the pdf link top right on arXiv))

The authors listed here are the real names. not forum names.

Title:	Galaxy Zoo: the large-scale spin statistics of spiral galaxies in the Sloan Digital Sky Survey
Authors:	Kate Land, Anže Slosar, Chris Lintott, Dan Andreescu, Steven Bamford, Phil Murray, Robert Nichol, M. Jordan Raddick, Kevin Schawinski, Alex Szalay, Daniel Thomas, Jan Vandenberg
Status:	Published - MNRAS Volume 388, Issue 4, pp. 1686-1692
Blog:	introduction to the first four papers,  summary of the bias study, paper submitted, paper accepted
Abstract:	We re-examine the evidence for a violation of large-scale statistical isotropy in the distribution of projected spin vectors of spiral galaxies. We have a sample of ~37,000 spiral galaxies from the Sloan Digital Sky Survey, with their line of sight spin direction confidently classified by members of the public through the online project Galaxy Zoo. After establishing and correcting for a certain level of bias in our handedness results we find the winding sense of the galaxies to be consistent with statistical isotropy. In particular we find no significant dipole signal, and thus no evidence for overall preferred handedness of the Universe. We compare this result to those of other authors and conclude that these may also be affected and explained by a bias effect.

Title:	Galaxy Zoo : Morphologies derived from visual inspection of galaxies from the Sloan Digital Sky Survey
Authors:	Chris Lintott, Kevin Schawinski, Anže Slosar, Kate Land, Steven Bamford, Daniel Thomas, M. Jordan Raddick, Robert Nichol, Alex Szalay, Dan Andreescu, Phil Murray, Jan Vandenberg
Status:	Published - MNRAS Volume 389, Issue 3, pp. 1179-1189
Blog:	introduction to the first four papers,  preprint now online,  paper accepted
Abstract:	In order to understand the formation and subsequent evolution of galaxies one must first distinguish between the two main morphological classes of massive systems: spirals and early-type systems. This paper introduces a project, Galaxy Zoo, which provides visual morphological classifications for nearly one million galaxies, extracted from the Sloan Digital Sky Survey (SDSS). This achievement was made possible by inviting the general public to visually inspect and classify these galaxies via the internet. The project has obtained more than 40,000,000 individual classifications made by ~100,000 participants. We discuss the motivation and strategy for this project, and detail how the classifications were performed and processed. We find that Galaxy Zoo results are consistent with those for subsets of SDSS galaxies classified by professional astronomers, thus demonstrating that our data provides a robust morphological catalogue. Obtaining morphologies by direct visual inspection avoids introducing biases associated with proxies for morphology such as colour, concentration or structual parameters. In addition, this catalogue can be used to directly compare SDSS morphologies with older data sets. The colour--magnitude diagrams for each morphological class are shown, and we illustrate how these distributions differ from those inferred using colour alone as a proxy for morphology.

Title:	Galaxy Zoo: the dependence of morphology and colour on environment
Authors:	Steven P. Bamford, Robert C. Nichol, Ivan K. Baldry, Kate Land, Chris J. Lintott, Kevin Schawinski, Anže Slosar, Alexander S. Szalay, Daniel Thomas, Mehri Torki, Dan Andreescu, Edward M. Edmondson, Christopher J. Miller, Phil Murray, M. Jordan Raddick, Jan Vandenberg
Status:	Published - MNRAS Volume 393, Issue 4, pp. 1324-1352
Blog:
Abstract:	We analyse the relationships between galaxy morphology, colour, environment and stellar mass using data for over 100,000 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 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 relations can be attributed to 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. 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. We clearly show there is an environmental dependence for colour beyond that for morphology. 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 dataset, 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.

Title:	Galaxy Zoo: Chiral correlation function of galaxy spins
Authors:	Anže Slosar, Kate Land, Steven Bamford, Chris Lintott, Dan Andreescu, Phil Murray, Robert Nichol, M. Jordan Raddick, Kevin Schawinski, Alex Szalay, Daniel Thomas, Jan Vandenberg
Status:	Published - MNRAS, Volume 392, Issue 3, pp. 1225-1232
Blog:
Abstract:	Galaxy Zoo is the first study of nearby galaxies that contains reliable information about the spiral sense of rotation of galaxy arms for a sizeable number of galaxies. We measure the correlation function of spin chirality (the sense in which galaxies appear to be spinning) of face-on spiral galaxies in angular, real and projected spaces. Our results indicate a hint of positive correlation at separations less than ~0.5 Mpc at a statistical significance of 2-3 sigma. This is the first experimental evidence for chiral correlation of spins. Within tidal torque theory it indicates that the inertia tensors of nearby galaxies are correlated. This is complementary to the studies of nearby spin axis correlations that probe the correlations of the tidal field. Theoretical interpretation is made difficult by the small distances at which the correlations are detected, implying that substructure might play a significant role, and our necessary selection of face-on spiral galaxies, rather than a general volume-limited sample.

Title:	Galaxy Zoo: A sample of blue early-type galaxies at low redshift
Authors:	Kevin Schawinski, Chris Lintott, Daniel Thomas, Marc Sarzi, Dan Andreescu, Steven P. Bamford, Sugata Kaviraj, Sadegh Khochfar, Kate Land, Phil Murray, Robert C. Nichol, M. Jordan Raddick, Anže Slosar, Alex Szalay, Jan VandenBerg, Sukyoung K. Yi
Status:	Published MNRAS - Volume 396, Issue 2, pp. 818-829
Blog:	Fifth Galaxy Zoo paper accepted - Everything you’ve ever wanted to know about Blue Early-type galaxies!
Abstract:	We report the discovery of a population of nearby, blue early-type galaxies with high star formation rates (0.5 < SFR < 50 Msun/yr). They are identified by their visual morphology as provided by Galaxy Zoo for SDSS DR6 and their u-r colour. We select a volume-limited sample in the redshift range 0.02 < z < 0.05, corresponding to luminosities of approximately L* and above, and with u-r colours significantly bluer than the red sequence. We confirm the early-type morphology of the objects in this sample and investigate their environmental dependence and star formation properties. Blue early-type galaxies tend to live in lower-density environments than `normal' red sequence early-types and make up 5.7 +/-0.4% of the low-redshift early-type galaxy population. We find that such blue early-type galaxies are virtually absent at high velocity dispersions above 200 km/s. Our analysis uses emission line diganostic diagrams and we find that ~25% of them are actively starforming, while another ~25% host both star formation and an AGN. Another ~12% are AGN. The remaining 38% show no strong emission lines. When present and uncontaminated by an AGN contribution, the star formation is generally intense. We consider star formation rates derived from Halpha, u-band and infrared luminosities, and radial colour profiles, and conclude that the star formation is spatially extended. Of those objects that are not currently undergoing star formation must have ceased doing so recently in order to account for their blue optical colours. The gas phase metallicity of the actively starforming blue early-types galaxies is supersolar in all cases. We discuss the place of these objects in the context of galaxy formation. A catalogue of all 204 blue early-type galaxies in our sample, including star formation rates and emission line classification, is provided.

Title:	Galaxy Zoo: the fraction of merging galaxies in the SDSS and their morphologies
Authors:	Daniel. W. Darg, S. Kaviraj, Chris J. Lintott, Kevin Schawinski, M. Sarzi, Steven P. Bamford, J. Silk, R. Proctor, Dan Andreescu, Pill Murray, Robert C. Nichol, M. Jordan Raddick, Anže. Slosar, Alex S. Szalay, Daniel Thomas, Jan VandenBerg
Status:	Accepted by MNRAS
Blog:
Abstract:	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 visually-selected pairs of merging galaxies from the SDSS in the redshift range 0.005 < z <0.1. We use our merger sample and values of f_m applied to the SDSS Main Galaxy Spectral sample (MGS) to estimate that the fraction of volume-limited (M_r < -20.55) major mergers (1/3 < M_1/M_2 < 3) in the nearby universe is 1-3%. Having visually classified the morphologies of the constituent galaxies in our mergers, we find that the spiral-to-elliptical ratio of galaxies in mergers is higher by a factor ~2 relative to the global population. In a companion paper, we examine the internal properties of these merging galaxies and conclude that this high spiral-to-elliptical ratio in mergers is due to a longer time-scale over which mergers with spirals are detectable compared to mergers with ellipticals.

Title:	Galaxy Zoo: The properties of merging galaxies in the nearby Universe - local environments, colours, masses, star-formation rates and AGN activity
Authors:	Daniel W. Darg, S. Kaviraj, Chris J. Lintott, Kevin Schawinski, M. Sarzi, Steven P. Bamford, J. Silk, Dan Andreescu, Pill Murray, Robert C. Nichol, M. Jordan Raddick, Anže Slosar, Alex S. Szalay, Daniel Thomas, Jan VandenBerg
Status:	Accepted by MNRAS
Blog:
Abstract:	Following the study of Darg et al. (2009; hereafter D09a) we explore the environments, optical colours, stellar masses, star-formation and AGN activity in a sample of 3003 merging galaxies drawn from the SDSS using the Galaxy Zoo project. While D09a found that the spiral-to-elliptical ratio in (major) mergers appeared higher than that of the global galaxy population, no significant differences are found between the environmental distributions of mergers and a randomly selected control sample. This makes the high occurrence of spirals in mergers unlikely to be an environmental effect and must, therefore, arise from differing time-scales of detectability for spirals and ellipticals. We find that merging galaxies have a wider spread in colour than the global galaxy population, with a significant blue tail resulting from intense star-formation in spiral mergers. Galaxies classed as star-forming using their emission-line properties have average star-formation rates approximately doubled by the merger process though star formation is negligibly enhanced in merging elliptical galaxies. AGN activity appears largely unaffected by the merger process in this sample. We conclude that the internal properties of galaxies significantly affect the time-scales over which merging systems can be detected (as suggested by recent theoretical studies) which leads to spirals being 'over-observed' in mergers. We also suggest that the transition mass 3x10^10 M_solar, noted by Kauffmann et al. (2003) and below which ellipticals are rare, could be linked to disc survival/destruction in mergers.

Title:	Galaxy Zoo: A correlation between coherence of galaxy spin chirality and star formation efficiency
Authors:	Raul Jimenez, Anze Slosar, Licia Verde, Steven Bamford, Chris Lintott, Kevin Schawinski, Robert Nichol, Dan Andreescu, Kate Land, Phil Murray, M. Jordan Raddick, Alex Szalay, Daniel Thomas, Jan VandenBerg
Status:	Submitted to MNRAS
Blog:
Abstract:	We report on the finding of a correlation between galaxies' past star formation activity and the degree to which neighbouring galaxies rotation axes are aligned. This is obtained by cross-correlating star formation histories, derived with MOPED, and spin direction (chirality), as determined by the Galaxy Zoo project, for a sample of SDSS galaxies. Our findings suggest that spiral galaxies which formed the majority of their stars early (z > 2) tend to display coherent rotation over scales of ~10 Mpc/h. The correlation is weaker for galaxies with significant recent star formation. We find evidence for this alignment at more than the 5-sigma level, but no correlation with other galaxy stellar properties. This finding can be explained within the context of hierarchical tidal-torque theory if the SDSS galaxies harboring the majority of the old stellar population where formed in the past, in the same filament and at about the same time. Galaxies with significant recent star formation instead are in the field, thus influenced by the general tidal field that will align them in random directions or had a recent merger which would promote star formation, but deviate the spin direction.

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Title:	Galaxy Zoo: Disentangling the Environmental Dependence of Morphology and Colour
Authors:	Ramin A. Skibba, Steven P. Bamford, Robert C. Nichol, Chris J. Lintott, Dan Andreescu, Edward M. Edmondson, Phil Murray, M. Jordan Raddick, Kevin Schawinski, Anže Slosar, Alexander S. Szalay, Daniel Thomas, Jan VandenBerg
Status:	Accepted by MNRAS
Blog:	Another Zoo paper submitted!
Abstract:	We analyze 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 \textit{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 onto the red sequence of the colour-magnitude diagram without quickly becoming an early-type. We analyze 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.

Title:	Galaxy Zoo: Exploring the Motivations of Citizen Science Volunteers
Authors:	Jordan Riddick, Georgia Bracey, Pamela Gay, Chris J. Lintott, Kevin Scawinski, Alex Szalay, Jan VanderBerg
Status:	Accepted by Astronomy Education Review
Blog:	Eleventh Galaxy Zoo paper submitted!
Abstract:	The Galaxy Zoo citizen science website invites anyone with an Internet connection to participate in research by classifying galaxies from the Sloan Digital Sky Survey. As of April 2009, more than 200,000 volunteers had made more than 100 million galaxy classifications. In this paper, we present results of a pilot study into the motivations and demographics of Galaxy Zoo volunteers, and define a technique to determine motivations from free responses that can be used in larger multiple-choice surveys with similar populations. Our categories form the basis for a future survey, with the goal of determining the prevalence of each motivation.

Title:	Galaxy Zoo: 'Hanny's Voorwerp', a quasar light echo?
Authors:	Chris J Lintott, Kevin Scawinski, William Keel, Hanny van Arkel, Edward Edmondson, Daniel Thomas, Nicola Bennert, Danieal J.B. Smith, Peter D. Herbert, Matt J. Jarvis, Dan Andreescu, Steven P. Bamford, Kate Land, Phil Murray, Robert C. Nichol, M. Jordan Raddick, Anže Slosar, Alex Szalay, Jan Vandenberg
Status:	Published by MNRAS volume 399, pp. 129-140
Blog:	What’s the blue stuff below?, http://www.galaxyzooblog.org/2008/01/18/more-on-the-voorwerp/, Galaxy Zoo Paper update , Voorwerping Part 1
Discussion	Main discussion Topic, Hanny's Voorwerp as OOTD
Abstract:	We report the discovery of an unusual object near the spiral galaxy IC 2497, discovered by visual inspection of the Sloan Digital Sky Survey (SDSS) as part of the Galaxy Zoo project. The object, known as Hanny's Voorwerp, is bright in the SDSS g band due to unusually strong OIII 4959-5007 emission lines. We present the results of the first targeted observations of the object in the optical, UV and X-ray, which show that the object contains highly ionized gas. Although the line ratios are similar to extended emission-line regions near luminous AGN, the source of this ionization is not apparent. The emission-line properties, and lack of x-ray emission from IC 2497, suggest either a highly obscured AGN with a novel geometry arranged to allow photoionization of the object but not the galaxy's own circumnuclear gas, or, as we argue, the first detection of a quasar light echo. In this case, either the luminosity of the central source has decreased dramatically or else the obscuration in the system has increased within 10^5 years. This object may thus represent the first direct probe of quasar history on these timescales.

Title:	Galaxy Zoo Green Peas: Discovery of A Class of Compact Extremely Star Forming Galaxies
Authors:	Carolin Cardamone, Kevin Scawinski, Marc Sarzi, Steven P. Bamford, Nicola Bennert, C.M. Urry, Chris J. Lintott, William C. Keel, John Parejko, Robert C. Nichol, Daniel Thomas, Dan Andreescu, Phil Murray, M. Jordan Raddick, Anze Slosar, Jan Vandenberg
Status:	Published by the MNRAS volume 399, pp. 1191-1205
Blog:	Give Peas a Chance, The First Volunteer-inspired Galaxy Zoo Paper is Submitted!
Discussion	Peas Project
Abstract:	We investigate a class of rapidly growing emission line galaxies, known as "Green Peas", first noted by volunteers in the Galaxy Zoo project because of their peculiar bright green colour and small size, unresolved in SDSS imaging. Their appearance is due to very strong optical emission lines, namely [O III] 5007 A, with an unusually large equivalent width of up to ~1000 A. We discuss a well-defined sample of 251 colour-selected objects, most of which are strongly star forming, although there are some AGN interlopers including 8 newly discovered narrow Line Seyfert 1 galaxies. The star-forming Peas are low mass galaxies (M~10^8.5 - 10^10 M_sun) with high star formation rates (~10 M_sun/yr), low metallicities (log[O/H] + 12 ~ 8.7) and low reddening (E(B-V) < 0.25) and they reside in low density environments. They have some of the highest specific star formation rates (up to ~10^{-8} yr^{-1}) seen in the local Universe, yielding doubling times for their stellar mass of hundreds of Myrs. The few star-forming Peas with HST imaging appear to have several clumps of bright star-forming regions and low surface density features that may indicate recent or ongoing mergers. The Peas are similar in size, mass, luminosity and metallicity to Luminous Blue Compact Galaxies. They are also similar to high redshift UV-luminous galaxies, e.g., Lyman-break galaxies and Lyman-alpha emitters, and therefore provide a local laboratory with which to study the extreme star formation processes that occur in high-redshift galaxies. Studying starbursting galaxies as a function of redshift is essential to understanding the build up of stellar mass in the Universe.

Title:	Revealing Hanny's Voorwerp: radio observations of IC 2497
Authors:	G. I. G. Jozsa, M. A. Garrett, T. A. Oosterloo, H. Rampadarath, Z. Paragi, H. van Arkel, C. Lintott, W. C. Keel, K. Schawinski, E. Edmondson
Status:	Published by Astronomy & Astrophysics - A&A 500, L33–L36 (2009)
Blog:
Notes:	Not an official Galaxy Zoo Publication, but directly related
Discussion	News about publication and explanation
Abstract:	We present multi-wavelength radio observations in the direction of the spiral galaxy IC 2497 and the neighbouring emission nebula known as "Hanny's Voorwerp". Our WSRT continuum observations at 1.4 GHz and 4.9 GHz, reveal the presence of extended emission at the position of the nebulosity, although the bulk of the emission remains unresolved at the centre of the galaxy. e-VLBI 1.65 GHz observations show that on the milliarcsecond-scale a faint central compact source is present in IC 2497 with a brightness temperature in excess of 4E5 K. With the WSRT, we detect a large reservoir of neutral hydrogen in the proximity of IC 2497. One cloud complex with a total mass of 5.6E9 Msol to the South of IC 2497, encompasses Hanny's Voorwerp. Another cloud complex is located at the position of a small galaxy group ~100 kpc to the West of IC 2497 with a mass of 2.9E9 Msol. Our data hint at a physical connection between both complexes. We also detect HI in absorption against the central continuum source of IC 2497. Our observations strongly support the hypothesis that Hanny's Voorwerp is being ionised by an AGN in the centre of IC 2497. In this scenario, a plasma jet associated with the AGN, clears a path through the ISM/IGM in the direction towards the nebulosity. The large-scale radio continuum emission possibly originates from the interaction between this jet and the large cloud complex that Hanny's Voorwerp is embedded in. The HI kinematics do not fit regular rotation, thus the cloud complex around IC 2497 is probably of tidal origin. From the HI absorption against the central source, we derive a lower limit of 2.8E21 +- 0.4E21 atoms/sqcm to the HI column density. However, assuming non-standard conditions for the detected gas, we cannot exclude the possibility that the AGN in the centre of IC 2497 is Compton-thick.

Title:	Galaxy Zoo: an unusual new class of galaxy cluster
Authors:	Marven F. Pedbost, Trillean Pomalgu, the Galaxy Zoo team
Status:	Spoof paper produced on April 1st
Blog:	A startling discovery in the latest paper from the Zoo
Abstract:	We have identified a new class of galaxy cluster using data from the Galaxy Zoo project. These clusters are rare, and thus have apparently gone unnoticed before, despite their unusual properties. They appear especially anomalous when the morphological properties of their component galaxies are considered. Their identification therefore depends upon the visual inspection of large numbers of galaxies, a feat which has only recently been made possible by Galaxy Zoo, together with the Sloan Digital Sky Survey. We present the basic properties of our cluster sample, and discuss possible formation scenarios and implications for cosmology.

Title:	Galaxy Zoo: Reproducing Galaxy Morphologies via Machine Learning
Authors:	Manda Banerji, Ofer Lahav, Chris J. Lintott, Filipe B Abdalla, Kevin Schawinski, Dan Andreescu, Steven P. Bamford, Phil Murray, M. Jordan Raddick, Anze Slosar, Alex Szalay, Daniel Thomas, Jan Vandenberg
Status:	Accepted by MNRAS
Blog:	Latest Paper Submitted
Abstract:	We present morphological classifications obtained using machine learning for objects in SDSS DR7 that have been classified by Galaxy Zoo into three classes namely spirals, ellipticals and stars/unique objects. An artificial neural network is trained on a subset of objects classified by the human eye and we test whether the machine learning algorithm can reproduce the human classifications for the rest of the sample. We find that the success of the neural network in matching the human classifications depends crucially on the set of input parameters chosen for the machine-learning algorithm. The colours, concentrations and parameters associated with profile-fitting are reasonable in seperating the stars and galaxies into three classes. However, these results are considerably improved when adding adaptive shape parameters as well as texture. The adaptive moments and texture parameters alone cannot distinguish between stars and elliptical galaxies. Using a set of thirteen distance-independant parameters, the neural network is able to reproduce the human classifications to better than 90% for all three morphological classes. As the parameters have been specifically chosen to be distance independant, using a training set that is incomplete in magnitude does not degrade our results. We conclude that it is promising to use machine-learning algorithms to perform morphological classification for the next generation of wide-field imaging surveys and that the Galaxy Zoo catalogue provides an invaluable training set for such purposes.

Title:	Galaxy Zoo: The Fundamentally Different Co-Evolution of Supermassive Black Holes and their Early- and Late-type Host Galaxies
Authors:	Kevin Schawinski, C.Megan Urry, Shanil Virani, Paolo Coppi, Steven P. Bamford, Ezequiel Treister, Chris J. Lintott, Marc Sarzi, William C Keel, Sugata Kaviraj, Carolin N Cardamone, Karen L. Masters, Nicholas P. Ross, Dan Andreescu, Phil Murray, Robert C. Nichol, M. Jordan Raddick, Anze Slosar, Alex Szalay, Daniel Thomas, Jan Vandenberg
Status:	Accepted by Astrophysical Journal
Blog:	Galaxy Zoo paper on host galaxies of growing black holes submitted!
Abstract:	We use data from the Sloan Digital Sky Survey and visual classifications of morphology from the Galaxy Zoo project to study black hole growth in the nearby Universe (z < 0.05) and to break down the AGN host galaxy population by color, stellar mass and morphology. We find that black hole growth at luminosities L[Oiii] > 1040 ergs−1 in early- and late-type galaxies is fundamentally different. AGN host galaxies as a population have a broad range of stellar masses (1010 − 1011M⊙), reside in the green valley of the color-mass diagram and their central black holes have median masses around 106.5M⊙. However, by comparing early- and late-type AGN host galaxies to their non-active counterparts, we find several key differences: in early-type galaxies, it is preferentially the galaxies with the least massive black holes that are growing, while late-type galaxies, it is preferentially the most massive black holes that are growing. The duty cycle of AGN in early-type galaxies is strongly peaked in the green valley below the low-mass end (1010M⊙) of the red sequence at stellar masses where there is a steady supply of blue cloud progenitors. The duty cycle of AGN in late-type galaxies on the other hand peaks in massive (1011M⊙) green and red late-types which generally do not have a corresponding blue cloud population of similar mass. At high Eddington ratios (L/LEdd > 0.1), the only population with a substantial fraction of AGN are the low-mass green valley early-type galaxies. Finally, the Milky Way likely resides in the “sweet spot” on the color-mass diagram where the AGN duty cycle of late-type galaxies is highest. We discuss the implications of these results for our understanding of the role of AGN in the evolution of galaxies.

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Title:	Galaxy Zoo: Dust in Spiral Galaxies
Authors:	Karen L. Masters, Robert C. Nichol, Steven P. Bamford, Moein Mosleh, Chris J. Lintott, Dan Andreescu, Edward M. Edmondson, William C. Keel, Phil Murray, M. Jordan Raddick, Kevin Schawinski, Anže Slosar, Alexander S. Szalay, Daniel Thomas, Jan VandenBerg
Status:	Accepted by MNRAS
Blog:	Galaxy Zoo Paper on Dust in Spirals Submitted.
Abstract:	We investigate the effect of dust on spiral galaxies by measuring the inclination-dependence of optical colours for 24,276 well-resolved SDSS galaxies visually classified in Galaxy Zoo. 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 magnitudes for the ugri passbands. We split the sample into "bulgy" (early-type) and "disky" (late-type) spirals using the SDSS fracdeV (or f_DeV) parameter and show that the average face-on colour of "bulgy" spirals is redder than the average edge-on colour of "disky" spirals. This shows that the observed optical colour of a spiral galaxy is determined almost equally by the spiral type (via the bulge-disk ratio and stellar populations), and reddening due to dust. We find that both luminosity and spiral type affect the total amount of extinction, with "disky" spirals at M_r ~ -21.5 mags having the most reddening. This decrease of reddening for the most luminous spirals 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. (2004). We find that the model reproduces the observed trends reasonably well but overpredicts the amount of u-band attenuation in edge-on galaxies. 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.

Title:	Galaxy Zoo: Passive Red Spirals
Authors:	Karen L. Masters, Moein Mosleh, A. Kathy Romer, Robert C. Nichol, Steven P. Bamford, Kevin Schawinski, Chris J. Lintott, Dan Andreescu, Heather C Campbell, Ben Crowcroft, Isabelle Doyle, Edward M. Edmondson, Phil Murray, M. Jordan Raddick, Anže Slosar, Alexander S. Szalay, Jan VandenBerg
Status:	Submitted to MNRAS
Blog:	Galaxy Zoo Red Spiral Paper Submitted
Abstract:

Title:	Galaxy Zoo: Bars in Disk Galaxies
Authors:	Karen L. Masters (ICG, Portsmouth), Robert C. Nichol (ICG, Portsmouth), Ben Hoyle (ICG, Portsmouth/Barcelona), Chris Lintott (Oxford), Steven Bamford (Nottingham), Edward M. Edmondson (ICG, Portsmouth), Lucy Fortson (Adler Planetarium), William C. Keel (Alabama), Kevin Schawinski (Yale), Arfon Smith (Oxford), Daniel Thomas (ICG, Portsmouth)
Status:	Submitted to MNRAS
Blog:	Galaxy Zoo: Bars in Disk Galaxies
Abstract:	We present first results from Galaxy Zoo 2, the second phase of the highly successful Galaxy Zoo project (www.galaxyzoo.org). Using a volume-limited sample of 13665 disk galaxies (0.01< z < 0.06 and M_r<-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% 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 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, disk galaxies in our sample possess a bar. We see evidence for a colour bi-modality for our sample of disk 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 at higher redshift in the COSMOS survey, 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 classical bulges (which have a de Vaucouleurs profile) and pseudo-bulges (with exponential profiles) in disk galaxies.

Title:	On the oxygen and nitrogen chemical abundances and the evolution of the "green pea" galaxies
Authors:	Ricardo O. Amorín, E. Pérez-Montero, J.M. Vílchez  (IAA-CSIC)
Status:	Accepted for publication in ApJ Letters
Blog:	The latest on the peas – do they lack metals?
Abstract:	We have investigated the oxygen and nitrogen chemical abundances in extremely compact star-forming galaxies with redshifts between $\sim$0.11-0.35, popularly referred to as "green peas". Direct and strong-line methods sensitive to the N/O ratio applied to their SDSS spectra reveals that these systems are genuine metal-poor galaxies, with mean oxygen abundances 20% solar. At a given metallicity these galaxies display systematically large N/O ratios compared to normal galaxies, which can explain the strong difference between our metallicities measurements and previous ones. While their N/O ratios follow the relation with stellar mass of local star-forming galaxies in the SDSS, we find that the mass--metallicity relation of the "green peas" is offset $\ga$0.3 dex to lower metallicities. We argue that recent interaction-induced inflow of gas, possibly coupled with a selective metal-rich gas loss, driven by supernova winds, may explain our findings and the known galaxy properties, namely high specific star formation rates, extreme compactness, and disturbed optical morphologies. The "green pea" galaxy properties seem to be not common in the nearby Universe, suggesting a short and extreme stage of their evolution. Therefore, these galaxies may allow us to study in great detail many processes, such as starburst activity and chemical enrichment, under physical conditions approaching those in galaxies at higher redshifts.

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"The Galaxy Zoo survey for giant AGN-ionized clouds: past and present black-hole accretion events"
Authors: William C. Keel, S. Drew Chojnowski, Vardha N. Bennert, Kevin Schawinski, Chris J. Lintott, Stuart Lynn, Anna Pancoast, Chelsea Harris, A. M. Nierenberg, Alessandro Sonnenfeld, Richard Proctor
(Submitted on 31 Oct 2011 (v1), last revised 20 Dec 2011 (this version, v2))
http://arxiv.org/abs/1110.6921

[zutopian]

"Citizen Science: Contributions to Astronomy Research"
Authors: Carol Christian, Chris Lintott, Arfon Smith, Lucy Fortson, Steven Bamford
(Submitted on 12 Feb 2012)

The contributions of everyday individuals to significant research has grown dramatically beyond the early days of classical birdwatching and endeavors of amateurs of the 19th century. Now people who are casually interested in science can participate directly in research covering diverse scientific fields. Regarding astronomy, volunteers, either as individuals or as networks of people, are involved in a variety of types of studies. Citizen Science is intuitive, engaging, yet necessarily robust in its adoption of sci-entific principles and methods. Herein, we discuss Citizen Science, focusing on fully participatory projects such as Zooniverse (by several of the au-thors CL, AS, LF, SB), with mention of other programs. In particular, we make the case that citizen science (CS) can be an important aspect of the scientific data analysis pipelines provided to scientists by observatories.

http://arxiv.org/abs/1202.2577

[zutopian]

"Polar Ring Galaxies in the Galaxy Zoo"

We report observations of 16 candidate polar ring galaxies (PRGs) identified by the Galaxy Zoo project in the Sloan Digital Sky Survey (SDSS) database. Deep images of five galaxies are available in the SDSS Stripe82 database, while to reach similar depth we observed the remaining galaxies with the 1.8-m Vatican Advanced Technology Telescope. We derive integrated magnitudes and u-r colours for the host and ring components and show continuum-subtracted H\alpha+[NII] images for seven objects. We present a basic morphological and environmental analysis of the galaxies and discuss their properties in comparison with other types of early-type galaxies. Follow-up photometric and spectroscopic observations will allow a kinematic confirmation of the nature of these systems and a more detailed analysis of their stellar populations.

Ido Finkelman, Jose G. Funes S.J., Noah Brosch
(Submitted on 22 Feb 2012)
http://arxiv.org/abs/1202.5033

[zutopian]

"Galaxy Zoo: Morphological Classification and Citizen Science"
Authors: Lucy Fortson, Karen Masters, Robert Nichol, Kirk Borne, Edd Edmondson, Chris Lintott, Jordan Raddick, Kevin Schawinski, John Wallin
(Submitted on 28 Apr 2011)
to be published in Advances in Machine Learning and Data Mining for Astronomy
http://arxiv.org/abs/1104.5513

[zutopian]

"Chandra Observations of Galaxy Zoo Mergers: Frequency of Binary Active Nuclei in Massive Mergers"

We present the results from a Chandra pilot study of 12 massive galaxy mergers selected from Galaxy Zoo. The sample includes major mergers down to a host galaxy mass of 10$^{11}$ $M_\odot$ that already have optical AGN signatures in at least one of the progenitors. We find that the coincidences of optically selected active nuclei with mildly obscured ($N_H \lesssim 1.1 \times 10^{22}$ cm$^{-2}$) X-ray nuclei are relatively common (8/12), but the detections are too faint ($< 40$ counts per nucleus; $f_{2-10 keV} \lesssim 1.2 \times 10^{-13}$ erg s$^{-1}$ cm$^{-2}$) to reliably separate starburst and nuclear activity as the origin of the X-ray emission. Only one merger is found to have confirmed binary X-ray nuclei, though the X-ray emission from its southern nucleus could be due solely to star formation. Thus, the occurrences of binary AGN in these mergers are rare (0-8%), unless most merger-induced active nuclei are very heavily obscured or Compton thick.

Stacy H. Teng (UMD/GSFC), Kevin Schawinski (Yale), C. Megan Urry (Yale), Dan W. Darg (Oxford), Sugata Kaviraj (Oxford), Kyuseok Oh (Yonsei), Erin W. Bonning (Yale), Carolin N. Cardamone (Brown), William C. Keel (UAB), Chris J. Lintott (Oxford), Brooke D. Simmons (Yale), Ezequiel Treister (Concepcion)
(Submitted on 6 Jun 2012)
http://arxiv.org/abs/1206.1266

[zutopian]

"Galaxy Zoo: Bulgeless Galaxies With Growing Black Holes"
B. D. Simmons, C. Lintott, K. Schawinski, E. C. Moran, A. Han, S. Kaviraj, K. L. Masters, C. M. Urry, K. W. Willett, S. P. Bamford, R. C. Nichol
(Submitted on 17 Jul 2012)
http://arxiv.org/abs/1207.4190

[zutopian]

"Galaxy Zoo: Quantifying Morphological Indicators of Galaxy Interaction"
Kevin R. V. Casteels, Steven P. Bamford, Ramin A. Skibba, Karen L. Masters, Chris J. Lintott, William C. Keel, Kevin Schawinski, Robert C. Nichol, Arfon M. Smith
(Submitted on 21 Jun 2012 (v1), last revised 16 Nov 2012 (this version, v2))
http://arxiv.org/abs/1206.5020

[zutopian]

"Galaxy Zoo: A Catalog of Overlapping Galaxy Pairs for Dust Studies"
William C. Keel, Anna Manning, Benne W. Holwerda, Massimo Mezzoprete, Chris J. Lintott, Kevin Schawinski, Pamela Gay, Karen L. Masters
(Submitted on 28 Nov 2012)
http://arxiv.org/abs/1211.6723

[zutopian]

New "Publications Page":

All GZ papers are now listed here.: https://www.zooniverse.org/publications
There also the papers of the other Zooniverse Projects.

[zutopian]

New paper based on Galaxy Zoo classifications was announced in the GZ blog today.:

The different star-formation histories of blue and red spiral and elliptical galaxies
Authors: Rita Tojeiro (ICG, Portsmouth), Karen L. Masters (ICG, Portsmouth), Joshua Richards (Imperial College London), Will J. Percival (ICG, Portsmouth), Steven P. Bamford (Nottingham), Claudia Maraston (ICG, Portsmouth), Robert C. Nichol (ICG, Portsmouth), Ramin Skibba (University of California), Daniel Thomas (ICG, Portsmouth)
(Submitted on 14 Mar 2013)
http://arxiv.org/abs/1303.3551

[zutopian]

"Dynamic Bayesian Combination of Multiple Imperfect Classifiers"
Authors: Edwin Simpson, Stephen Roberts, Ioannis Psorakis, Arfon Smith
(Submitted on 8 Jun 2012)
http://arxiv.org/abs/1206.1831

[c_cld]

Title:	Galaxy Zoo: Motivations of Citizen Scientists
Authors:	M. Jordan Raddick, Georgia Bracey, Pamela L. Gay, Chris J. Lintott, Carie Cardamone, Phil Murray, Kevin Schawinski, Alexander S. Szalay, Jan Vandenberg
Status:	arxiv: Physics Education (physics.ed-ph);  Thu, 28 Mar 13
Blog:
Abstract:	Citizen science, in which volunteers work with professional scientists to conduct research, is expanding due to large online datasets. To plan projects, it is important to understand volunteers' motivations for participating. This paper analyzes results from an online survey of nearly 11,000 volunteers in Galaxy Zoo, an astronomy citizen science project. Results show that volunteers' primary motivation is a desire to contribute to scientific research. We encourage other citizen science projects to study the motivations of their volunteers, to see whether and how these results may be generalized to inform the field of citizen science.