Publications by Chris Lintott

Tidal dwarf galaxies in the nearby Universe

Monthly Notices of the Royal Astronomical Society 419 (2012) 70-79

S Kaviraj, D Darg, C Lintott, K Schawinski, J Silk

We present a statistical observational study of the tidal dwarf (TD) population in the nearby Universe by exploiting a large, homogeneous catalogue of galaxy mergers compiled from the Sloan Digital Sky Survey. 95percent of TD-producing mergers involve two spiral progenitors (typically both in the blue cloud), while most remaining systems have at least one spiral progenitor. The fraction of TD-producing mergers where both parents are early-type galaxies is less than 2percent, suggesting that TDs are unlikely to form in such mergers. The bulk of TD-producing mergers inhabit a field environment and have mass ratios greater than ~1:7 (the median value is 1:2.5). TDs forming at the tidal-tail tips are ~4 times more massive than those forming at the base of the tails. TD stellar masses are less than 10percent of the stellar masses of their parents (the median is 0.6percent) and lie within 15 optical half-light radii of their parent galaxies. The TD population is typically bluer than the parents, with a median offset of ~0.3mag in the (g-r) colour and the TD colours are not affected by the presence of active galactic nuclei (AGN) activity in their parents. An analysis of their star formation histories indicates that TDs contain both newly formed stars (with a median age of ~30Myr) and old stars drawn from the parent discs, each component probably contributing roughly equally to the stellar mass of the object. Thus TDs are not formed purely through gas condensation in tidal tails but host a significant component of old stars from the parent discs. Finally, an analysis of the TD contribution to the observed dwarf-to-massive galaxy ratio in the local Universe indicates that ~6percent of dwarfs in nearby clusters may have a tidal origin, if TD production rates in nearby mergers are representative of those in the high-redshift Universe. Even if TD production rates at high redshift were several factors higher, it seems unlikely that the entire dwarf galaxy population today is a result of merger activity over the lifetime of the Universe. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Galaxy Zoo: Building the low-mass end of the red sequence with local post-starburst galaxies

Monthly Notices of the Royal Astronomical Society 420 (2012) 1684-1692

OI Wong, K Schawinski, S Kaviraj, KL Masters, RC Nichol, C Lintott, WC Keel, D Darg, SP Bamford, D Andreescu, P Murray, MJ Raddick, A Szalay, D Thomas, J Vandenberg

Spheroidal post-mergers in the local Universe

Monthly Notices of the Royal Astronomical Society 420 (2012) 2139-2146

A Carpineti, S Kaviraj, D Darg, C Lintott, K Schawinski, S Shabala

Galaxy merging is a fundamental aspect of the standard hierarchical galaxy formation paradigm. Recently, the Galaxy Zoo project has compiled a large, homogeneous catalogue of 3373 mergers, through direct visual inspection of the entire Sloan Digital Sky Survey spectroscopic sample. We explore a subset of galaxies from this catalogue that are spheroidal 'post-mergers' (SPMs) - where a single remnant is in the final stages of relaxation after the merger and shows evidence for a dominant bulge, making them plausible progenitors of early-type galaxies. Our results indicate that the SPMs have bluer colours than the general early-type galaxy population possibly due to merger-induced star formation. An analysis using optical emission-line ratios indicates that 20 of our SPMs exhibit LINER or Seyfert-like activity (68 per cent), while the remaining 10 galaxies are classified as either star forming (16 per cent) or quiescent (16 per cent). A comparison to the emission-line activity in the ongoing mergers from Darg et al. indicates that the active galactic nuclei (AGN) fraction rises in the post-mergers, suggesting that the AGN phase probably becomes dominant only in the very final stages of the merger process. The optical colours of the SPMs and the plausible mass ratios for their progenitors indicate that, while a minority are consistent with major mergers between two early-type galaxies, the vast majority are remnants of major mergers where at least one progenitor is a late-type galaxy. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Observational Tracking of the 2D Structure of Coronal Mass Ejections Between the Sun and 1 AU

Solar Physics (2012) 1-19

NP Savani, JA Davies, CJ Davis, D Shiota, AP Rouillard, MJ Owens, K Kusano, V Bothmer, SP Bamford, CJ Lintott, A Smith

Galaxy Zoo: Building the low-mass end of the red sequence with local post-starburst galaxies

Monthly Notices of the Royal Astronomical Society 420 (2012) 1684-1692

OI Wong, K Schawinski, S Kaviraj, KL Masters, RC Nichol, C Lintott, WC Keel, D Darg, SP Bamford, D Andreescu, P Murray, MJ Raddick, A Szalay, D Thomas, J Vandenberg

We present a study of local post-starburst galaxies (PSGs) using the photometric and spectroscopic observations from the Sloan Digital Sky Survey and the results from the Galaxy Zoo project. We find that the majority of our local PSG population have neither early- nor late-type morphologies but occupy a well-defined space within the colour-stellar mass diagram, most notably, the low-mass end of the 'green valley' below the transition mass thought to be the mass division between low-mass star-forming galaxies and high-mass passively evolving bulge-dominated galaxies. Our analysis suggests that it is likely that local PSGs will quickly transform into 'red', low-mass early-type galaxies as the stellar morphologies of the 'green' PSGs largely resemble that of the early-type galaxies within the same mass range. We propose that the current population of PSGs represents a population of galaxies which is rapidly transitioning between the star-forming and the passively evolving phases. Subsequently, these PSGs will contribute towards the build-up of the low-mass end of the 'red sequence' once the current population of young stars fade and stars are no longer being formed. These results are consistent with the idea of 'downsizing' where the build-up of smaller galaxies occurs at later epochs. © 2012 CSIRO Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Planet Hunters: The first two planet candidates identified by the public using the Kepler public archive data

Monthly Notices of the Royal Astronomical Society 419 (2012) 2900-2911

DA Fischer, ME Schwamb, K Schawinski, C Lintott, J Brewer, M Giguere, S Lynn, M Parrish, T Sartori, R Simpson, A Smith, J Spronck, N Batalha, J Rowe, J Jenkins, S Bryson, A Prsa, P Tenenbaum, J Crepp, T Morton, A Howard, M Beleu, Z Kaplan, N vanNispen, C Sharzer, J Defouw, A Hajduk, JP Neal, A Nemec, N Schuepbach, V Zimmermann

Planet Hunters is a new citizen science project designed to engage the public in an exoplanet search using NASA Kepler public release data. In the first month after launch, users identified two new planet candidates which survived our checks for false positives. The follow-up effort included analysis of Keck HIRES spectra of the host stars, analysis of pixel centroid offsets in the Kepler data and adaptive optics imaging at Keck using NIRC2. Spectral synthesis modelling coupled with stellar evolutionary models yields a stellar density distribution, which is used to model the transit orbit. The orbital periods of the planet candidates are 9.8844 ± 0.0087d (KIC 10905746) and 49.7696 ± 0.00039d (KIC 6185331), and the modelled planet radii are 2.65 and 8.05R ⊕. The involvement of citizen scientists as part of Planet Hunters is therefore shown to be a valuable and reliable tool in exoplanet detection. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

The Galaxy Zoo survey for giant AGN-ionized clouds: Past and present black hole accretion events

Monthly Notices of the Royal Astronomical Society 420 (2012) 878-900

WC Keel, SD Chojnowski, VN Bennert, K Schawinski, CJ Lintott, S Lynn, A Pancoast, C Harris, AM Nierenberg, A Sonnenfeld, R Proctor

Some active galactic nuclei (AGN) are surrounded by extended emission-line regions (EELRs), which trace both the illumination pattern of escaping radiation and its history over the light travel time from the AGN to the gas. From a new set of such EELRs, we present evidence that the AGN in many Seyfert galaxies undergo luminous episodes 0.2-2years in duration. Motivated by the discovery of the spectacular nebula known as Hanny's Voorwerp, ionized by a powerful AGN which has apparently faded dramatically withinyears, Galaxy Zoo volunteers have carried out both targeted and serendipitous searches for similar emission-line clouds around low-redshift galaxies. We present the resulting list of candidates and describe spectroscopy identifying 19 galaxies with AGN-ionized regions at projected radiikpc. This search recovered known EELRs (such as Mrk 78, Mrk 266 and NGC 5252) and identified additional previously unknown cases, one with detected emission tokpc. One new Sy 2 was identified. At least 14/19 are in interacting or merging systems, suggesting that tidal tails are a prime source of distant gas out of the galaxy plane to be ionized by an AGN. We see a mix of one- and two-sided structures, with observed cone angles from 23to 112. We consider the energy balance in the ionized clouds, with lower and upper bounds on ionizing luminosity from recombination and ionization-parameter arguments, and estimate the luminosity of the core from the far-infrared data. The implied ratio of ionizing radiation seen by the clouds to that emitted by the nucleus, on the assumption of a non-variable nuclear source, ranges from 0.02 to; 7/19 exceed unity. Small values fit well with a heavily obscured AGN in which only a small fraction of the ionizing output escapes to be traced by surrounding gas. However, large values may require that the AGN has faded over tens of thousands of years, giving us several examples of systems in which such dramatic long-period variation has occurred; this is the only current technique for addressing these time-scales in AGN history. The relative numbers of faded and non-faded objects we infer, and the projected extents of the ionized regions, give our estimate (0.2-2years) for the length of individual bright phases. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

The distribution of interplanetary dust between 0.96 and 1.04 au as inferred from impacts on the STEREO spacecraft observed by the heliospheric imagers

Monthly Notices of the Royal Astronomical Society 420 (2012) 1355-1366

CJ Davis, JA Davies, OC St Cyr, M Campbell-Brown, A Skelt, M Kaiser, N Meyer-Vernet, S Crothers, C Lintott, A Smith, S Bamford, EML Baeten

The distribution of dust in the ecliptic plane between 0.96 and 1.04 au has been inferred from impacts on the two Solar Terrestrial Relations Observatory (STEREO) spacecraft through observation of secondary particle trails and unexpected off-points in the heliospheric imager (HI) cameras. This study made use of analysis carried out by members of a distributed web-based citizen science project Solar Stormwatch. A comparison between observations of the brightest particle trails and a survey of fainter trails shows consistent distributions. While there is no obvious correlation between this distribution and the occurrence of individual meteor streams at Earth, there are some broad longitudinal features in these distributions that are also observed in sources of the sporadic meteor population. The different position of the HI instrument on the two STEREO spacecraft leads to each sampling different populations of dust particles. The asymmetry in the number of trails seen by each spacecraft and the fact that there are many more unexpected off-points in the HI-B than in HI-A indicates that the majority of impacts are coming from the apex direction. For impacts causing off-points in the HI-B camera, these dust particles are estimated to have masses in excess of 10 -17 kg with radii exceeding 0.1μm. For off-points observed in the HI-A images, which can only have been caused by particles travelling from the anti-apex direction, the distribution is consistent with that of secondary 'storm' trails observed by HI-B, providing evidence that these trails also result from impacts with primary particles from an anti-apex source. Investigating the mass distribution for the off-points of both HI-A and HI-B, it is apparent that the differential mass index of particles from the apex direction (causing off-points in HI-B) is consistently above 2. This indicates that the majority of the mass is within the smaller particles of this population. In contrast, the differential mass index of particles from the anti-apex direction (causing off-points in HI-A) is consistently below 2, indicating that the majority of the mass is to be found in larger particles of this distribution. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Galaxy Zoo: Bar lengths in local disc galaxies

Monthly Notices of the Royal Astronomical Society (2011)

B Hoyle, KL Masters, RC Nichol, EM Edmondson, AM Smith, C Lintott, R Scranton, S Bamford, K Schawinski, D Thomas

Reinventing Discovery: The New Era of Networked Science

NATURE 478 (2011) 320-321

C Lintott

Technology: The inspiration exchange

Nature 478 (2011) 320-321

C Lintott

Galaxy Zoo: Multimergers and the Millennium Simulation

Monthly Notices of the Royal Astronomical Society 416 (2011) 1745-1755

DW Darg, S Kaviraj, CJ Lintott, K Schawinski, J Silk, S Lynn, S Bamford, RC Nichol

We present a catalogue of 39 multiple mergers, found using the mergers catalogue of the Galaxy Zoo project for z < 0.1, and compare them to corresponding semi-analytical galaxies from the Millennium Simulation. We estimate the (volume-limited) multimerger fraction of the local Universe using our sample and find it to be at least 2 orders of magnitude less than binary mergers - in good agreement with the simulations (especially the Munich group). We then investigate the properties of galaxies in binary mergers and multimergers (morphologies, colours, stellar masses and environment) and compare these results with those predicted by the semi-analytical galaxies. We find that multimergers favour galaxies with properties typical of elliptical morphologies and that this is in qualitative agreement with the models. Studies of multimergers thus provide an independent (and largely corroborating) test of the Millennium semi-analytical models. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Galaxy Zoo: Bar lengths in local disc galaxies

Monthly Notices of the Royal Astronomical Society 415 (2011) 3627-3640

B Hoyle, KL Masters, RC Nichol, EM Edmondson, AM Smith, C Lintott, R Scranton, S Bamford, K Schawinski, D Thomas

We present an analysis of bar length measurements of 3150 local galaxies in a volume-limited sample of low-redshift (z < 0.06) disc galaxies. Barred galaxies were initially selected from the Galaxy Zoo 2 project, and the lengths and widths of the bars were manually drawn by members of the Galaxy Zoo community using a Google Maps interface. Bars were measured independently by different observers, multiple times per galaxy (≥3), and we find that observers were able to reproduce their own bar lengths to 3 per cent and each others' to better than 20 per cent. We find a colour bimodality in our disc galaxy population with bar length, i.e. longer bars inhabit redder disc galaxies and the bars themselves are redder, and that the bluest galaxies host the smallest galactic bars (<5h-1kpc). We also find that bar and disc colours are clearly correlated, and for galaxies with small bars, the disc is, on average, redder than the bar colours, while for longer bars the bar then itself is redder, on average, than the disc. We further find that galaxies with a prominent bulge are more likely to host longer bars than those without bulges. We categorize our galaxy populations by how the bar and/or ring are connected to the spiral arms. We find that galaxies whose bars are directly connected to the spiral arms are preferentially bluer and that these galaxies host typically shorter bars. Within the scatter, we find that stronger bars are found in galaxies which host a ring (and only a ring). The bar length and width measurements used herein are made publicly available for others to use. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Galaxy Zoo Supernovae

Monthly Notices of the Royal Astronomical Society 412 (2011) 1309-1319

AM Smith, S Lynn, M Sullivan, CJ Lintott, PE Nugent, J Botyanszki, M Kasliwal, R Quimby, SP Bamford, LF Fortson, K Schawinski, I Hook, S Blake, P Podsiadlowski, J Jönsson, A Gal-Yam, I Arcavi, DA Howell, JS Bloom, J Jacobsen, SR Kulkarni, NM Law, EO Ofek, R Walters

This paper presents the first results from a new citizen science project: Galaxy Zoo Supernovae. This proof-of-concept project uses members of the public to identify supernova candidates from the latest generation of wide-field imaging transient surveys. We describe the Galaxy Zoo Supernovae operations and scoring model, and demonstrate the effectiveness of this novel method using imaging data and transients from the Palomar Transient Factory (PTF). We examine the results collected over the period 2010 April-July, during which nearly 14000 supernova candidates from the PTF were classified by more than 2500 individuals within a few hours of data collection. We compare the transients selected by the citizen scientists to those identified by experienced PTF scanners and find the agreement to be remarkable - Galaxy Zoo Supernovae performs comparably to the PTF scanners and identified as transients 93 per cent of the ∼130 spectroscopically confirmed supernovae (SNe) that the PTF located during the trial period (with no false positive identifications). Further analysis shows that only a small fraction of the lowest signal-to-noise ratio detections (r > 19.5) are given low scores: Galaxy Zoo Supernovae correctly identifies all SNe with ≥8σ detections in the PTF imaging data. The Galaxy Zoo Supernovae project has direct applicability to future transient searches, such as the Large Synoptic Survey Telescope, by both rapidly identifying candidate transient events and via the training and improvement of existing machine classifier algorithms. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Moon Zoo: Citizen science in lunar exploration

Astronomy and Geophysics 52 (2011)

K Joy, I Crawford, P Grindrod, C Lintott, S Bamford, A Smith, A Cook, M Zoo

The Moon Zoo Team describe how citizen scientists can get involved and explore the Moon online. © 2011 Royal Astronomical Society.

Moon Zoo: citizen science in lunar exploration

ASTRONOMY & GEOPHYSICS 52 (2011) 10-12

KH Joy, IA Crawford, PM Grindrod, C Lintott, S Bamford, A Smith, A Cook, MZ Team

The sudden death of the nearest quasar

Astrophysical Journal Letters 724 (2010)

K Schawinski, DA Evans, S Virani, CM Urry, WC Keel, P Natarajan, CJ Lintott, A Manning, P Coppi, S Kaviraj, SP Bamford, GIG Józsa, M Garrett, H Van Arkel, P Gay, L Fortson

Galaxy formation is significantly modulated by energy output from supermassive black holes at the centers of galaxies which grow in highly efficient luminous quasar phases. The timescale on which black holes transition into and out of such phases is, however, unknown. We present the first measurement of the shutdown timescale for an individual quasar using X-ray observations of the nearby galaxy IC 2497, which hosted a luminous quasar no more than 70,000 years ago that is still seen as a light echo in "Hanny's Voorwerp," but whose present-day radiative output is lower by at least two, and more likely by over four, orders of magnitude. This extremely rapid shutdown provides new insight into the physics of accretion in supermassive black holes and may signal a transition of the accretion disk to a radiatively inefficient state. © 2010. The American Astronomical Society. All rights reserved.

Galaxy Zoo: Dust in spiral galaxies

Monthly Notices of the Royal Astronomical Society 404 (2010) 792-810

KL Masters, R Nichol, S Bamford, M Mosleh, CJ Lintott, D Andreescu, EM Edmondson, WC Keel, P Murray, MJ Raddick, K Schawinski, A Slosar, AS Szalay, D Thomas, J Vandenberg

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. © 2010 The Authors. Journal compilation © 2010 RAS.

Galaxy Zoo: Reproducing galaxy morphologies via machine learning

Monthly Notices of the Royal Astronomical Society 406 (2010) 342-353

M Banerji, O Lahav, CJ Lintott, FB Abdalla, K Schawinski, SP Bamford, D Andreescu, P Murray, MJ Raddick, A Slosar, A Szalay, D Thomas, J Vandenberg

We present morphological classifications obtained using machine learning for objects in the Sloan Digital Sky Survey DR6 that have been classified by Galaxy Zoo into three classes, namely early types, spirals and point sources/artefacts. 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 and parameters associated with profile fitting are reasonable in separating the objects into three classes. However, these results are considerably improved when adding adaptive shape parameters as well as concentration and texture. The adaptive moments, concentration and texture parameters alone cannot distinguish between early type galaxies and the point sources/artefacts. Using a set of 12 parameters, the neural network is able to reproduce the human classifications to better than 90 per cent for all three morphological classes. We find that using a training set that is incomplete in magnitude does not degrade our results given our particular choice of the input parameters to the network. 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. © 2010 The Authors. Journal compilation © 2010 RAS.

Galaxy Zoo: Passive red spirals

Monthly Notices of the Royal Astronomical Society 405 (2010) 783-799

KL Masters, M Mosleh, AK Romer, RC Nichol, SP Bamford, K Schawinski, CJ Lintott, D Andreescu, HC Campbell, B Crowcroft, I Doyle, EM Edmondson, P Murray, MJ Raddick, A Slosar, AS Szalay, J Vandenberg

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{black star} < 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. © 2010 The Authors. Journal compilation © 2010 RAS.