# Publications by Chris Lintott

## Galaxy Zoo: Are bars responsible for the feeding of active galactic nuclei at 0.2 < z < 1.0?

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 447 (2015) 506-516

E Cheung, JR Trump, E Athanassoula, SP Bamford, EF Bell, A Bosma, CN Cardamone, KRV Casteels, SM Faber, JJ Fang, LF Fortson, DD Kocevski, DC Koo, S Laine, C Lintott, KL Masters, T Melvin, RC Nichol, K Schawinski, B Simmons, R Smethurst, KW Willett

## PLANET HUNTERS. VII. DISCOVERY OF A NEW LOW-MASS, LOW-DENSITY PLANET (PH3 C) ORBITING KEPLER-289 WITH MASS MEASUREMENTS OF TWO ADDITIONAL PLANETS (PH3 B AND D)

ASTROPHYSICAL JOURNAL 795 (2014) ARTN 167

JR Schmitt, E Agol, KM Deck, LA Rogers, JZ Gazak, DA Fischer, J Wang, MJ Holman, KJ Jek, C Margossian, MR Omohundro, T Winarski, JM Brewer, MJ Giguere, C Lintott, S Lynn, M Parrish, K Schawinski, ME Schwamb, R Simpson, AM Smith

## Planet Hunters. VI: An Independent Characterization of KOI-351 and Several Long Period Planet Candidates from the Kepler Archival Data

ArXiv (2013)

JR Schmitt, J Wang, DA Fischer, KJ Jek, JC Moriarty, TS Boyajian, ME Schwamb, C Lintott, S Lynn, AM Smith, M Parrish, K Schawinski, R Simpson, D LaCourse, MR Omohundro, T Winarski, SJ Goodman, T Jebson, HM Schwengeler, DA Paterson, J Sejpka, I Terentev, T Jacobs, N Alsaadi, RC Bailey, T Ginman, P Granado, KV Guttormsen, F Mallia, AL Papillon, F Rossi, M Socolovsky

We report the discovery of 14 new transiting planet candidates in the Kepler field from the Planet Hunters citizen science program. None of these candidates overlapped with Kepler Objects of Interest (KOIs) at the time of submission. We report the discovery of one more addition to the six planet candidate system around KOI-351, making it the only seven planet candidate system from Kepler. Additionally, KOI-351 bears some resemblance to our own solar system, with the inner five planets ranging from Earth to mini-Neptune radii and the outer planets being gas giants; however, this system is very compact, with all seven planet candidates orbiting $\lesssim 1$ AU from their host star. A Hill stability test and an orbital integration of the system shows that the system is stable. Furthermore, we significantly add to the population of long period transiting planets; periods range from 124-904 days, eight of them more than one Earth year long. Seven of these 14 candidates reside in their host star's habitable zone.

## The Green Valley is a Red Herring: Galaxy Zoo reveals two evolutionary pathways towards quenching of star formation in early- and late-type galaxies

ArXiv (2014)

K Schawinski, CM Urry, BD Simmons, L Fortson, S Kaviraj, WC Keel, CJ Lintott, KL Masters, RC Nichol, M Sarzi, Ramin, Skibba, E Treister, KW Willett, OI Wong, SK Yi

We use SDSS+\textit{GALEX}+Galaxy Zoo data to study the quenching of star formation in low-redshift galaxies. We show that the green valley between the blue cloud of star-forming galaxies and the red sequence of quiescent galaxies in the colour-mass diagram is not a single transitional state through which most blue galaxies evolve into red galaxies. Rather, an analysis that takes morphology into account makes clear that only a small population of blue early-type galaxies move rapidly across the green valley after the morphologies are transformed from disk to spheroid and star formation is quenched rapidly. In contrast, the majority of blue star-forming galaxies have significant disks, and they retain their late-type morphologies as their star formation rates decline very slowly. We summarize a range of observations that lead to these conclusions, including UV-optical colours and halo masses, which both show a striking dependence on morphological type. We interpret these results in terms of the evolution of cosmic gas supply and gas reservoirs. We conclude that late-type galaxies are consistent with a scenario where the cosmic supply of gas is shut off, perhaps at a critical halo mass, followed by a slow exhaustion of the remaining gas over several Gyr, driven by secular and/or environmental processes. In contrast, early-type galaxies require a scenario where the gas supply and gas reservoir are destroyed virtually instantaneously, with rapid quenching accompanied by a morphological transformation from disk to spheroid. This gas reservoir destruction could be the consequence of a major merger, which in most cases transforms galaxies from disk to elliptical morphology, and mergers could play a role in inducing black hole accretion and possibly AGN feedback.

## Crowd-Sourced Assessment of Technical Skills: a novel method to evaluate surgical performance

Journal of Surgical Research (2013)

C Chen, D Holst, L White, T Kowalewski, R Aggarwal, C Lintott, B Comstock, K Kuksenok, C Aragon, T Lendvay

## Crowd-sourced assessment of technical skills: A novel method to evaluate surgical performance

Journal of Surgical Research 187 (2014) 65-71

C Chen, LW White, TM Kowalewski, R Aggarwal, CJ Lintott, BA Comstock, K Kuksenok, CR Aragon, D Holst, TS Lendvay

## Galaxy Zoo: An independent look at the evolution of the bar fraction over the last eight billion years from HST-COSMOS

ArXiv (2014)

T Melvin, K Masters, C Lintott, RC Nichol, B Simmons, SP Bamford, KRV Casteels, E Cheung, EM Edmondson, L Fortson, K Schawinski, RA Skibba, AM Smith, KW Willett

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 to identify both 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 two, from 22+/-5% at z=0.4 (tlb = 4.2 Gyr) to 11+/-2% at z=1.0 (tlb = 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(Mstar/Msun) > 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%), 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: CANDELS barred discs and bar fractions

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 445 (2014) 3466-3474

BD Simmons, T Melvin, C Lintott, KL Masters, KW Willett, WC Keel, RJ Smethurst, E Cheung, RC Nichol, K Schawinski, M Rutkowski, JS Kartaltepe, EF Bell, KRV Casteels, CJ Conselice, O Almaini, HC Ferguson, L Fortson, W Hartley, D Kocevski, AM Koekemoer, DH McIntosh, A Mortlock, JA Newman, J Ownsworth, S Bamford, T Dahlen, SM Faber, SL Finkelstein, A Fontana, A Galametz, NA Grogin, R Gruetzbauch, Y Guo, B Haeussler, KJ Jek, S Kaviraj, RA Lucas, M Peth, M Salvato, T Wiklind, S Wuyts

## The ultraviolet attenuation law in backlit spiral galaxies Based in part on observations made with the NASA Galaxy Evolution Explorer. GALEX is operated for NASA by the California Institute of Technology under NASA contract NAS5-98034.

Astronomical Journal 147 (2014)

W Keel, AM Manning, BW Holwerda, CJ Lintott, K Schawinski

The effective extinction law (attenuation behavior) in galaxies in the emitted ultraviolet (UV) regime is well known only for actively star-forming objects and combines effects of the grain properties, fine structure in the dust distribution, and relative distributions of stars and dust. We use Galaxy Evolution Explorer, XMM Optical Monitor, and Hubble Space Telescope (HST) data to explore the UV attenuation in the outer parts of spiral disks which are backlit by other UV-bright galaxies, starting with the candidate list of pairs provided by Galaxy Zoo participants. New optical images help to constrain the geometry and structure of the target galaxies. Our analysis incorporates galaxy symmetry, using non-overlapping regions of each galaxy to derive error estimates on the attenuation measurements. The entire sample has an attenuation law across the optical and UV that is close to the Calzetti et al. form; the UV slope for the overall sample is substantially shallower than found by Wild et al., which is a reasonable match to the more distant galaxies in our sample but not to the weighted combination including NGC 2207. The nearby, bright spiral NGC 2207 alone gives an accuracy almost equal to the rest of our sample, and its outer arms have a very low level of foreground starlight. Thus, this widespread, fairly "gray" law can be produced from the distribution of dust alone, without a necessary contribution from differential escape of stars from dense clouds. Our results indicate that the extrapolation needed to compare attenuation between backlit galaxies at moderate redshifts from HST data, and local systems from Sloan Digital Sky Survey and similar data, is mild enough to allow the use of galaxy overlaps to trace the cosmic history of dust in galaxies. For NGC 2207, HST data in the near-UV F336W band show that the covering factor of clouds with small optical attenuation becomes a dominant factor farther into the UV, which opens the possibility that widespread diffuse dust dominates over dust in star-forming regions deep into the UV. Comparison with published radiative-transfer models indicates that the role of dust clumping dominates over differences in grain populations at this coarse spatial resolution. © 2014. The American Astronomical Society. All rights reserved.

## The Ultraviolet Attenuation Law in Backlit Spiral Galaxies

ArXiv (2014)

WC Keel, AM Manning, BW Holwerda, CJ Lintott, K Schawinski

(Abridged) The effective extinction law (attenuation behavior) in galaxies in the emitted ultraviolet is well known only for actively star-forming objects and combines effects of the grain properties, fine structure in the dust distribution, and relative distributions of stars and dust. We use GALEX, XMM Optical Monitor, and HST data to explore the UV attenuation in the outer parts of spiral disks which are backlit by other UV-bright galaxies, starting with candidates provided by Galaxy Zoo participants. Our analysis incorporates galaxy symmetry, using non-overlapping regions of each galaxy to derive error estimates on the attenuation measurements. The entire sample has an attenuation law close to the Calzetti et al. (1994) form; the UV slope for the overall sample is substantially shallower than found by Wild et al. (2011), a reasonable match to the more distant galaxies in our sample but not to the weighted combination including NGC 2207. The nearby, bright spiral NGC 2207 alone gives accuracy almost equal to the rest of our sample, and its outer arms have a very low level of foreground starlight. This "grey" law can be produced from the distribution of dust alone, without a necessary contribution from differential escape of stars from dense clouds. The extrapolation needed to compare attenution between backlit galaxies at moderate redshifts, and local systems from SDSS data, is mild enough to allow use of galaxy overlaps to trace the cosmic history of dust. For NGC 2207, the covering factor of clouds with small optical attenuation becomes a dominant factor farther into the ultraviolet, which opens the possibility that widespread diffuse dust dominates over dust in star-forming regions deep into the ultraviolet. Comparison with published radiative-transfer models indicates that the role of dust clumping dominates over differences in grain populations, at this spatial resolution.

## Ideas for Citizen Science in Astronomy

ArXiv (2014)

PJ Marshall, CJ Lintott, LN Fletcher

We review the relatively new, internet-enabled, and rapidly-evolving field of citizen science, focusing on research projects in stellar, extragalactic and solar system astronomy that have benefited from the participation of members of the public, often in large numbers. We find these volunteers making contributions to astronomy in a variety of ways: making and analyzing new observations, visually classifying features in images and light curves, exploring models constrained by astronomical datasets, and initiating new scientific enquiries. The most productive citizen astronomy projects involve close collaboration between the professionals and amateurs involved, and occupy scientific niches not easily filled by great observatories or machine learning methods: citizen astronomers are most strongly motivated by being of service to science. In the coming years we expect participation and productivity in citizen astronomy to increase, as survey datasets get larger and citizen science platforms become more efficient. Opportunities include engaging the public in ever more advanced analyses, and facilitating citizen-led enquiry by designing professional user interfaces and analysis tools with citizens in mind.

## HST Imaging of Fading AGN Candidates I: Host-Galaxy Properties and Origin of the Extended Gas

ArXiv (2014)

WC Keel, WP Maksym, VN Bennert, CJ Lintott, SD Chojnowski, A Moiseev, A Smirnova, K Schawinski, CM Urry, DA Evans, A Pancoast, B Scott, C Showley, K Flatland

We present narrow- and medium-band HST imaging, with additional supporting ground-based data, for 8 galaxies identified as hosting fading AGN. These have AGN-ionized gas projected >10 kpc from the nucleus, and significant shortfall of ionizing radiation between the distant gas and the AGN, indicating fading AGN on ~50,000-year timescales. Every system shows evidence of ongoing or past interactions; a similar sample of obscured AGN with extended ionized clouds shares this incidence of disturbances. Several systems show multiple dust lanes in different orientations, broadly fit by differentially precessing disks of accreted material ~1.5 Gyr after initial arrival. The gas has lower metallicity than the nuclei; three systems have abundances uniformly well below solar, consistent with an origin in tidally disrupted low-luminosity galaxies, while some systems have more nearly solar abundances (accompanied by such signatures as multiple Doppler components), which may suggest redistribution of gas by outflows within the host galaxies themselves. These aspects are consistent with a tidal origin for the extended gas in most systems, although the ionized gas and stellar tidal features do not always match closely. In contrast to clouds near radio-loud AGN, these are dominated by rotation, in some cases in warped disks. Outflows are important only in localized regions near some of the AGN. In UGC 7342 and UGC 11185, luminous star clusters are seen within projected ionization cones, potentially triggered by outflows. As in the discovery example Hanny's Voorwerp/IC 2497, some clouds lack a strong correlation between H-alpha surface brightness and ionization parameter, indicating unresolved fine structure. Together with thin coherent filaments spanning several kpc, persistence of these structures over their orbital lifetimes may require a role for magnetic confinement. (Abridged)

## Measuring the conceptual understandings of citizen scientists participating in zooniverse projects: A first approach

Astronomy Education Review 12 (2013)

EE Prather, S Cormier, CS Wallace, CJ Lintott, M Jordan Raddick, AM Smith

The Zooniverse projects turn everyday people into "citizen scientists" who work online with real data to assist scientists in conducting research on a variety of topics related to galaxies, exoplanets, lunar craters, and solar flares, among others. This paper describes our initial study to assess the conceptual knowledge and reasoning abilities of citizen scientists participating in two Zooniverse projects: Galaxy Zoo and Moon Zoo. In order to measure their knowledge and abilities, we developed two new assessment instruments, the Zooniverse Astronomical Concept Survey (ZACS) and the Lunar Cratering Concept Inventory (LCCI). We found that citizen scientists with the highest level of participation in the Galaxy Zoo and Moon Zoo projects also have the highest average correct scores on the items of the ZACS and LCCI. However, the limited nature of the data provided by Zooniverse participants prevents us from being able to evaluate the statistical significance of this finding, and we make no claim about whether there is a causal relationship between one's participation in Galaxy Zoo or Moon Zoo and one's level of conceptual understanding or reasoning ability on the astrophysical topics assessed by the ZACS or the LCCI. Overall, both the ZACS and the LCCI provide Zooniverse's citizen scientists with items that offer a wide range of difficulties. Using the data from the small subset of participants who responded to all items of the ZACS, we found evidence suggesting the ZACS is a reliable instrument (α=0.78), although twenty-one of its forty items appear to have point biserials less than 0.3. The work reported here provides significant insight into the strengths and limitations of various methods for administering assessments to citizen scientists. Researchers who wish to study the knowledge and abilities of citizen scientists in the future should be sure to design their research methods to avoid the pitfalls identified by our initial findings. © 2013 The American Astronomical Society.

## Galaxy Zoo: Motivations of Citizen Scientists

ArXiv (2013)

MJ Raddick, G Bracey, PL Gay, CJ Lintott, C Cardamone, P Murray, K Schawinski, AS Szalay, J Vandenberg

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.

## Galaxy Zoo: Observing Secular Evolution Through Bars

ArXiv (2013)

E Cheung, E Athanassoula, KL Masters, RC Nichol, A Bosma, EF Bell, SM Faber, DC Koo, C Lintott, T Melvin, K Schawinski, RA Skibba, KW Willett

In this paper, we use the Galaxy Zoo 2 dataset to study the behavior of bars in disk galaxies as a function of specific star formation rate (SSFR), and bulge prominence. Our sample consists of 13,295 disk galaxies, with an overall (strong) bar fraction of $23.6\pm 0.4\%$, of which 1,154 barred galaxies also have bar length measurements. These samples are the largest ever used to study the role of bars in galaxy evolution. We find that the likelihood of a galaxy hosting a bar is anti-correlated with SSFR, regardless of stellar mass or bulge prominence. We find that the trends of bar likelihood and bar length with bulge prominence are bimodal with SSFR. We interpret these observations using state-of-the-art simulations of bar evolution which include live halos and the effects of gas and star formation. We suggest our observed trends of bar likelihood with SSFR are driven by the gas fraction of the disks; a factor demonstrated to significantly retard both bar formation and evolution in models. We interpret the bimodal relationship between bulge prominence and bar properties as due to the complicated effects of classical bulges and central mass concentrations on bar evolution, and also to the growth of disky pseudobulges by bar evolution. These results represent empirical evidence for secular evolution driven by bars in disk galaxies. This work suggests that bars are not stagnant structures within disk galaxies, but are a critical evolutionary driver of their host galaxies in the local universe ($z<1$).

## An introduction to the Zooniverse

AAAI Workshop - Technical Report WS-13-18 (2013) 103-

AM Smith, S Lynn, CJ Lintott

The Zooniverse (zooniverse.org) began in 2007 with the launch of Galaxy Zoo, a project in which more than 175,000 people provided shape analyses of more than 1 million galaxy images sourced from the Sloan Digital Sky Survey. These galaxy 'classifications', some 60 million in total, have subsequently been used to produce more than 50 peer-reviewed publications based not only on the original research goals of the project but also because of serendipitous discoveries made by the volunteer community. Based upon the success of Galaxy Zoo the team have gone on to develop more than 25 web-based citizen science projects, all with a strong research focus in a range of subjects from astronomy to zoology where human-based analysis still exceeds that of machine intelligence. Over the past 6 years Zooniverse projects have collected more than 300 million data analyses from over 1 million volunteers providing fantastically rich datasets for not only the individuals working to produce research from their projects but also the machine learning and computer vision research communities. The Zooniverse platform has always been developed to be the 'simplest thing that works', implementing only the most rudimentary algorithms for functionality such as task allocation and user-performance metrics. These simplifications have been necessary to scale the Zooniverse so that the core team of developers and data scientists can remain small and the cost of running the computing infrastructure relatively modest. To date these simplifications have been acceptable for the data volumes and analysis tasks being addressed. This situation however is changing: next generation telescopes such as the Large Synoptic Sky Telescope (LSST) will produce data volumes dwarfing those previously analyzed. If citizen science is to have a part to play in analyzing these next-generation datasets then the Zooniverse will need to evolve into a smarter system capable for example of modeling the abilities of users and the complexities of the data being classified in real time. In this session we will outline the current architecture of the Zooniverse platform and introduce new functionality being developed that should be of interest to the HCOMP community. Our platform is evolving into a system capable of integrating human and machine intelligence in a live environment. Data APIs providing realtime access to 'event streams' from the Zooniverse infrastructure are currently being tested as well as API endpoints for making decisions about for example what piece of data to show next to a volunteer as well as when to retire a piece of data from the live system because a consensus has been reached.

## Morphology in the Era of Large Surveys

ArXiv (2013)

C Lintott, K Masters, B Simmons, S Bamford, S Kaviraj

The study of galaxies has changed dramatically over the past few decades with the advent of large-scale astronomical surveys. These large collaborative efforts have made available high-quality imaging and spectroscopy of hundreds of thousands of systems, providing a body of observations which has significantly enhanced our understanding not only of cosmology and large-scale structure in the universe but also of the astrophysics of galaxy formation and evolution. Throughout these changes, one thing that has remained constant is the role of galaxy morphology as a clue to understanding galaxies. But obtaining morphologies for large numbers of galaxies is challenging; this topic, "Morphology in the era of large surveys", was the subject of a recent discussion meeting at the Royal Astronomical Society, and this "Astronomy and Geophysics" article is a report on that meeting.

## A Herschel-ATLAS study of dusty spheroids: probing the minor-merger process in the local Universe

ArXiv (2013)

S Kaviraj, K Rowlands, M Alpaslan, L Dunne, Y-S Ting, M Bureau, S Shabala, CJ Lintott, DJB Smith, TH-ATLAS collaboration

We use multi-wavelength (0.12 - 500 micron) photometry from Herschel-ATLAS, WISE, UKIDSS, SDSS and GALEX, to study 23 nearby spheroidal galaxies with prominent dust lanes (DLSGs). DLSGs are considered to be remnants of recent minor mergers, making them ideal laboratories for studying both the interstellar medium (ISM) of spheroids and minor-merger-driven star formation in the nearby Universe. The DLSGs exhibit star formation rates (SFRs) between 0.01 and 10 MSun yr^-1, with a median of 0.26 MSun yr^-1 (a factor of 3.5 greater than the average SG). The median dust mass, dust-to-stellar mass ratio and dust temperature in these galaxies are around 10^7.6 MSun yr^-1, ~0.05% and ~19.5 K respectively. The dust masses are at least a factor of 50 greater than that expected from stellar mass loss and, like the SFRs, show no correlation with galaxy luminosity, suggesting that both the ISM and the star formation have external drivers. Adopting literature gas-to-dust ratios and star formation histories derived from fits to the panchromatic photometry, we estimate that the median current and initial gas-to-stellar mass ratios in these systems are ~4% and ~7% respectively. If, as indicated by recent work, minor mergers that drive star formation in spheroids with (NUV-r)>3.8 (the colour range of our DLSGs) have stellar mass ratios between 1:6 and 1:10, then the satellite gas fractions are likely >50%.

## Sir Patrick Moore, 'The Sky at Night' and modern astronomy in the UK

ASTRONOMY & GEOPHYSICS 54 (2013) 37-38

P Abel, C Lintott, M Barstow

## Galaxy Zoo 2: detailed morphological classifications for 304,122 galaxies from the Sloan Digital Sky Survey

ArXiv (2013)

KW Willett, CJ Lintott, SP Bamford, KL Masters, BD Simmons, KRV Casteels, EM Edmondson, LF Fortson, S Kaviraj, WC Keel, T Melvin, RC Nichol, MJ Raddick, K Schawinski, RJ Simpson, RA Skibba, AM Smith, D Thomas

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. 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 Galaxy Zoo 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%) 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 .