Browsing by Author "Lintott, Chris"
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Item Galaxy Zoo and ALFALFA: atomic gas and the regulation of star formation in barred disc galaxies(Oxford University Press, 2012) Masters, Karen L.; Nichol, Robert C.; Haynes, Martha P.; Keel, William C.; Lintott, Chris; Simmons, Brooke; Skibba, Ramin; Bamford, Steven; Giovanelli, Riccardo; Schawinski, Kevin; University of Portsmouth; Cornell University; University of Alabama Tuscaloosa; University of Oxford; Yale University; University of Arizona; University of NottinghamWe study the observed correlation between atomic gas content and the likelihood of hosting a large-scale bar in a sample of 2090 disc galaxies. Such a test has never been done before on this scale. We use data on morphologies from the Galaxy Zoo project and information on the galaxies H?I content from the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) blind H?I survey. Our main result is that the bar fraction is significantly lower among gas-rich disc galaxies than gas-poor ones. This is not explained by known trends for more massive (stellar) and redder disc galaxies to host more bars and have lower gas fractions: we still see at fixed stellar mass a residual correlation between gas content and bar fraction. We discuss three possible causal explanations: (1) bars in disc galaxies cause atomic gas to be used up more quickly, (2) increasing the atomic gas content in a disc galaxy inhibits bar formation and (3) bar fraction and gas content are both driven by correlation with environmental effects (e.g. tidal triggering of bars, combined with strangulation removing gas). All three explanations are consistent with the observed correlations. In addition our observations suggest bars may reduce or halt star formation in the outer parts of discs by holding back the infall of external gas beyond bar co-rotation, reddening the global colours of barred disc galaxies. This suggests that secular evolution driven by the exchange of angular momentum between stars in the bar, and gas in the disc, acts as a feedback mechanism to regulate star formation in intermediate-mass disc galaxies.Item Galaxy Zoo Green Peas: discovery of a class of compact extremely star-forming galaxies(Wiley-Blackwell, 2009) Cardamone, Carolin; Schawinski, Kevin; Sarzi, Marc; Bamford, Steven P.; Bennert, Nicola; Urry, C. M.; Lintott, Chris; Keel, William C.; Parejko, John; Nichol, Robert C.; Thomas, Daniel; Andreescu, Dan; Murray, Phil; Raddick, M. Jordan; Slosar, Anze; Szalay, Alex; VandenBerg, Jan; Yale University; University of Hertfordshire; University of Nottingham; University of California System; University of California Santa Barbara; University of Oxford; University of Alabama Tuscaloosa; Drexel University; University of Portsmouth; Johns Hopkins University; United States Department of Energy (DOE); Lawrence Berkeley National Laboratory; University of California BerkeleyWe 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 Sloan Digital Sky Survey imaging. Their appearance is due to very strong optical emission lines, namely [O iii] lambda 5007 A, with an unusually large equivalent width of up to similar 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 active galactic nuclei interlopers including eight newly discovered narrow-line Seyfert 1 galaxies. The star-forming Peas are low-mass galaxies (M similar to 108.5-1010 M(circle dot)) with high star formation rates (similar to 10 M(circle dot) yr-1), low metallicities (log[O/H] + 12 similar to 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 similar to 10-8 yr-1) seen in the local Universe, yielding doubling times for their stellar mass of hundreds of Myr. The few star-forming Peas with Hubble Space Telescope 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 ultraviolet-luminous galaxies, e.g. Lyman-break galaxies and Ly 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.Item Galaxy Zoo: bars in disc galaxies(Wiley-Blackwell, 2011) Masters, Karen L.; Nichol, Robert C.; Hoyle, Ben; Lintott, Chris; Bamford, Steven P.; Edmondson, Edward M.; Fortson, Lucy; Keel, William C.; Schawinski, Kevin; Smith, Arfon M.; Thomas, Daniel; University of Portsmouth; University of Barcelona; University of Oxford; University of Nottingham; University of Minnesota System; University of Minnesota Twin Cities; University of Alabama Tuscaloosa; Yale UniversityWe 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 13 665 disc 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 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.Item Galaxy Zoo: CANDELS barred discs and bar fractions(Oxford University Press, 2014) Simmons, B. D.; Melvin, Thomas; Lintott, Chris; Masters, Karen L.; Willett, Kyle W.; Keel, William C.; Smethurst, R. J.; Cheung, Edmond; Nichol, Robert C.; Schawinski, Kevin; Rutkowski, Michael; Kartaltepe, Jeyhan S.; Bell, Eric F.; Casteels, Kevin R. V.; Conselice, Christopher J.; Almaini, Omar; Ferguson, Henry C.; Fortson, Lucy; Hartley, William; Kocevski, Dale; Koekemoer, Anton M.; McIntosh, Daniel H.; Mortlock, Alice; Newman, Jeffrey A.; Ownsworth, Jamie; Bamford, Steven; Dahlen, Tomas; Faber, Sandra M.; Finkelstein, Steven L.; Fontana, Adriano; Galametz, Audrey; Grogin, N. A.; Gruetzbauch, Ruth; Guo, Yicheng; Haeussler, Boris; Jek, Kian J.; Kaviraj, Sugata; Lucas, Ray A.; Peth, Michael; Salvato, Mara; Wiklind, Tommy; Wuyts, Stijn; University of Oxford; University of Portsmouth; University of Southampton; University of Minnesota System; University of Minnesota Twin Cities; University of Alabama Tuscaloosa; University of California System; University of California Santa Cruz; Swiss Federal Institutes of Technology Domain; ETH Zurich; National Optical Astronomy Observatory; University of Michigan System; University of Michigan; Institut d'Estudis Espacials de Catalunya (IEEC); University of Barcelona; University of Nottingham; Space Telescope Science Institute; University of Kentucky; University of Missouri System; University of Missouri Kansas City; Pennsylvania Commonwealth System of Higher Education (PCSHE); University of Pittsburgh; University of Texas System; University of Texas Austin; Istituto Nazionale Astrofisica (INAF); Universidade de Lisboa; University of Hertfordshire; Johns Hopkins University; Max Planck Society; European Southern ObservatoryThe formation of bars in disc galaxies is a tracer of the dynamical maturity of the population. Previous studies have found that the incidence of bars in discs decreases from the local Universe to z similar to 1, and by z > 1 simulations predict that bar features in dynamically mature discs should be extremely rare. Here, we report the discovery of strong barred structures in massive disc galaxies at z similar to 1.5 in deep rest-frame optical images from the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey. From within a sample of 876 disc galaxies identified by visual classification in Galaxy Zoo, we identify 123 barred galaxies. Selecting a subsample within the same region of the evolving galaxy luminosity function (brighter than L*), we find that the bar fraction across the redshift range 0.5 <= z <= 2 (f(bar) = 10.7(-3.5)(+6.3) per cent after correcting for incompleteness) does not significantly evolve. We discuss the implications of this discovery in the context of existing simulations and our current understanding of the way disc galaxies have evolved over the last 11 billion years.Item Galaxy Zoo: dust and molecular gas in early-type galaxies with prominent dust lanes(Oxford University Press, 2012) Kaviraj, Sugata; Ting, Yuan-Sen; Bureau, Martin; Shabala, Stanislav S.; Crockett, R. Mark; Silk, Joseph; Lintott, Chris; Smith, Arfon; Keel, William C.; Masters, Karen L.; Schawinski, Kevin; Bamford, Steven P.; Imperial College London; University of Oxford; Institut Polytechnique de Paris; University of Tasmania; University of Alabama Tuscaloosa; University of Portsmouth; Yale University; University of NottinghamWe explore the properties of dust and associated molecular gas in 352 nearby (0.01 < z < 0.07) early-type galaxies (ETGs) with prominent dust lanes, drawn from the Sloan Digital Sky Survey (SDSS). Two-thirds of these dusty ETGs (D-ETGs) are morphologically disturbed, which suggests a merger origin, making these galaxies ideal test beds for studying the merger process at low redshift. The D-ETGs preferentially reside in lower density environments, compared to a control sample drawn from the general ETG population. Around 80 per cent of D-ETGs inhabit the field (compared to 60 per cent of the control ETGs) and less than 2 per cent inhabit clusters (compared to 10 per cent of the control ETGs). Compared to their control-sample counterparts, D-ETGs exhibit bluer ultravioletoptical colours (indicating enhanced levels of star formation) and an active galactic nucleus fraction that is more than an order of magnitude greater (indicating a strikingly higher incidence of nuclear activity). The mass of clumpy dust residing in large-scale dust features is estimated, using the SDSS r-band images, to be in the range 104.5106.5 M?. A comparison to the total (clumpy + diffuse) dust masses calculated using the far-infrared fluxes of 15 per cent of the D-ETGs that are detected by the Infrared Astronomical Satellite (IRAS) indicates that only 20 per cent of the dust is typically contained in these large-scale dust features. The dust masses are several times larger than the maximum value expected from stellar mass loss, ruling out an internal origin. The dust content shows no correlation with the blue luminosity, indicating that it is not related to a galactic scale cooling flow. Furthermore, no correlation is found with the age of the recent starburst, suggesting that the dust is accreted directly in the merger rather than being produced in situ by the triggered star formation. Using molecular gas-to-dust ratios of ETGs in the literature, we estimate that the median current molecular gas fraction in the IRAS-detected ETGs is similar to 1.3 per cent. Adopting reasonable values for gas depletion time-scales and starburst ages, the median initial gas fraction in these D-ETGs is similar to 4 per cent. Recent work has suggested that the merger activity in nearby ETGs largely involves minor mergers (dry ETG + gas-rich dwarf), with mass ratios between 1:10 and 1:4. If the IRAS-detected D-ETGs have formed via this channel, then the original gas fractions of the accreted satellites are between 20 and 44 per cent.Item Galaxy Zoo: Mergers - Dynamical models of interacting galaxies(Oxford University Press, 2016-03-17) Holincheck, Anthony J.; Wallin, John F.; Borne, Kirk; Fortson, Lucy; Lintott, Chris; Smith, Arfon M.; Bamford, Steven; Keel, William C.; Parrish, Michael; George Mason University; Middle Tennessee State University; University of Minnesota System; University of Minnesota Twin Cities; University of Oxford; University of Nottingham; University of Alabama TuscaloosaThe dynamical history of most merging galaxies is not well understood. Correlations between galaxy interaction and star formation have been found in previous studies, but require the context of the physical history of merging systems for full insight into the processes that lead to enhanced star formation. We present the results of simulations that reconstruct the orbit trajectories and disturbed morphologies of pairs of interacting galaxies. With the use of a restricted three-body simulation code and the help of citizen scientists, we sample 105 points in parameter space for each system. We demonstrate a successful recreation of the morphologies of 62 pairs of interacting galaxies through the review of more than 3 million simulations. We examine the level of convergence and uniqueness of the dynamical properties of each system. These simulations represent the largest collection of models of interacting galaxies to date, providing a valuable resource for the investigation of mergers. This paper presents the simulation parameters generated by the project. They are now publicly available in electronic format at http://data.galaxyzoo.org/mergers.html. Though our best-fitting model parameters are not an exact match to previously published models, our method for determining uncertainty measurements will aid future comparisons between models. The dynamical clocks from our models agree with previous results of the time since the onset of star formation from starburst models in interacting systems and suggest that tidally induced star formation is triggered very soon after closest approach.Item Galaxy Zoo: Morphological Classification of Galaxy Images from the Illustris Simulation(IOP Publishing, 2018-02-01) Dickinson, Hugh; Fortson, Lucy; Lintott, Chris; Scarlata, Claudia; Willett, Kyle; Bamford, Steven; Beck, Melanie; Cardamone, Carolin; Galloway, Melanie; Simmons, Brooke; Keel, William; Kruk, Sandor; Masters, Karen; Vogelsberger, Mark; Torrey, Paul; Snyder, Gregory F.; University of Minnesota System; University of Minnesota Twin Cities; University of Oxford; University of Nottingham; University of California System; University of California San Diego; University of Alabama Tuscaloosa; University of Portsmouth; Massachusetts Institute of Technology (MIT); Space Telescope Science InstituteModern large-scale cosmological simulations model the universe with increasing sophistication and at higher spatial and temporal resolutions. These ongoing enhancements permit increasingly detailed comparisons between the simulation outputs and real observational data. Recent projects such as Illustris are capable of producing simulated images that are designed to be comparable to those obtained from local surveys. This paper tests the degree to which Illustris achieves this goal across a diverse population of galaxies using visual morphologies derived from Galaxy Zoo citizen scientists. Morphological classifications provided by these volunteers for simulated galaxies are compared with similar data for a compatible sample of images drawn from the Sloan Digital Sky Survey (SDSS) Legacy Survey. This paper investigates how simple morphological characterization by human volunteers asked to distinguish smooth from featured systems differs between simulated and real galaxy images. Significant differences are identified, which are most likely due to the limited resolution of the simulation, but which could be revealing real differences in the dynamical evolution of populations of galaxies in the real and model universes. Specifically, for stellar masses M-star less than or similar to 10(11) M-circle dot, a substantially larger proportion of Illustris galaxies that exhibit disk-like morphology or visible substructure, relative to their SDSS counterparts. Toward higher masses, the visual morphologies for simulated and observed galaxies converge and exhibit similar distributions. The stellar mass threshold indicated by this divergent behavior confirms recent works using parametric measures of morphology from Illustris simulated images. When M-star less than or similar to 10(11) M-circle dot, the Illustris data set contains substantially fewer galaxies that classifiers regard as unambiguously featured. In combination, these results suggest that comparison between the detailed properties of observed and simulated galaxies, even when limited to reasonably massive systems, may be misleading.Item Galaxy Zoo: the environmental dependence of bars and bulges in disc galaxies(Wiley-Blackwell, 2012) Skibba, Ramin A.; Masters, Karen L.; Nichol, Robert C.; Zehavi, Idit; Hoyle, Ben; Edmondson, Edward M.; Bamford, Steven P.; Cardamone, Carolin N.; Keel, William C.; Lintott, Chris; Schawinski, Kevin; University of Arizona; University of Portsmouth; Case Western Reserve University; Institut d'Estudis Espacials de Catalunya (IEEC); University of Barcelona; Helsinki Institute of Physics; University of Helsinki; University of Nottingham; Massachusetts Institute of Technology (MIT); Brown University; University of Alabama Tuscaloosa; University of Oxford; Yale UniversityWe 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 x 10(10) 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 colourmagnitude 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 barenvironment correlation, and barred disc galaxies show a bulgeenvironment 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 barenvironment correlation were likely inhibited by small number statistics. We demonstrate that approximately half of the barenvironment 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 barenvironment 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.