Prof Chris Lintott

Abstract:

Analysis of galaxies with overlapping images offers a direct way to probe the distribution of dust extinction and its effects on the background light. We present a catalog of 1990 such galaxy pairs selected from the Sloan Digital Sky Survey (SDSS) by volunteers of the Galaxy Zoo project. We highlight subsamples which are particularly useful for retrieving such properties of the dust distribution as UV extinction, the extent perpendicular to the disk plane, and extinction in the inner parts of disks. The sample spans wide ranges of morphology and surface brightness, opening up the possibility of using this technique to address systematic changes in dust extinction or distribution with galaxy type. This sample will form the basis for forthcoming work on the ranges of dust distributions in local disk galaxies, both for their astrophysical implications and as the low-redshift part of a study of the evolution of dust properties. Separate lists and figures show deep overlaps, where the inner regions of the foreground galaxy are backlit, and the relatively small number of previously-known overlapping pairs outside the SDSS DR7 sky coverage.

Abstract:

We report the discovery and confirmation of a transiting circumbinary planet (PH1b) around KIC 4862625, an eclipsing binary in the Kepler field. The planet was discovered by volunteers searching the first six Quarters of publicly available Kepler data as part of the Planet Hunters citizen science project. Transits of the planet across the larger and brighter of the eclipsing stars are detectable by visual inspection every ~137 days, with seven transits identified in Quarters 1-11. The physical and orbital parameters of both the host stars and planet were obtained via a photometric-dynamical model, simultaneously fitting both the measured radial velocities and the Kepler light curve of KIC 4862625. The 6.18 +/- 0.17 Earth radii planet orbits outside the 20-day orbit of an eclipsing binary consisting of an F dwarf (1.734 +/- 0.044 Solar radii, 1.528 +/- 0.087 Solar masses) and M dwarf (0.378+/- 0.023 Solar radii, 0.408 +/- 0.024 Solar masses). For the planet, we find an upper mass limit of 169 Earth masses (0.531 Jupiter masses) at the 99.7% confidence level. With a radius and mass less than that of Jupiter, PH1b is well within the planetary regime. Outside the planet's orbit, at ~1000 AU,a previously unknown visual binary has been identified that is likely bound to the planetary system, making this the first known case of a quadruple star system with a transiting planet.

Abstract:

We present a new catalogue of 5106 infrared bubbles created through visual classification via the online citizen science website 'The Milky Way Project'. Bubbles in the new catalogue have been independently measured by at least five individuals, producing consensus parameters for their position, radius, thickness, eccentricity and position angle. Citizen scientists - volunteers recruited online and taking part in this research - have independently rediscovered the locations of at least 86 percent of three widely used catalogues of bubbles and Hii regions whilst finding an order of magnitude more objects. 29 percent of the Milky Way Project catalogue bubbles lie on the rim of a larger bubble, or have smaller bubbles located within them, opening up the possibility of better statistical studies of triggered star formation. Also outlined is the creation of a 'heat map' of star formation activity in the Galactic plane. This online resource provides a crowd-sourced map of bubbles and arcs in the Milky Way, and will enable better statistical analysis of Galactic star formation sites. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Abstract:

We use Galaxy Zoo 2 visual classifications to study the morphological signatures of interaction between similar-mass galaxy pairs in the Sloan Digital Sky Survey. We find that many observable features correlate with projected pair separation; not only obvious indicators of merging, disturbance and tidal tails, but also more regular features, such as spiral arms and bars. These trends are robustly quantified, using a control sample to account for observational biases, producing measurements of the strength and separation scale of various morphological responses to pair interaction. For example, we find that the presence of spiral features is enhanced at scales < 70 h^-1 kpc, probably due to both increased star formation and the formation of tidal tails. On the other hand, the likelihood of identifying a bar decreases significantly in pairs with separations < 30 h^-1 kpc, suggesting that bars are suppressed by close interactions between galaxies of similar mass. We go on to show how morphological indicators of physical interactions provide a way of significantly refining standard estimates for the frequency of close pair interactions, based on velocity offset and projected separation. The presence of loosely wound spiral arms is found to be a particularly reliable signal of an interaction, for projected pair separations up to ~100 h^-1 kpc. We use this indicator to demonstrate our method, constraining the fraction of low-redshift galaxies in truly interacting pairs, with M_* > 10^9.5 M_Sun and mass ratio < 4, to be between 0.4 - 2.7 per cent.

Abstract:

We present Hubble Space Telescope imaging and spectroscopy for the extended high-ionization cloud known as Hanny's Voorwerp, near the spiral galaxy IC 2497. WFC3 images show complex dust absorption near the nucleus of IC 2497. STIS spectra show a type 2 Seyfert AGN of rather low luminosity. The ionization parameter log U = -3.5 is in accord with its weak X-ray emission. We find no high-ionization gas near the nucleus, adding to evidence that the AGN is currently at low radiative output (perhaps now dominated by kinetic energy). The nucleus is accompanied by an expanding ring of ionized gas 500 pc in projected diameter on the side opposite Hanny's Voorwerp, with Doppler offset 300 km/s from the nucleus (kinematic age < 7 x10^5 years). [O III] and H-alpha + [N II] images show fine structure in Hanny's Voorwerp, with limb-brightened sections and small areas where H-alpha is strong. We identify these as regions ionized by recent star formation, in contrast to the AGN ionization of the entire cloud. These candidate "normal" H II regions contain blue continuum objects, whose colors are consistent with young stellar populations; they appear only in a 2-kpc region toward IC 2497 in projection. The ionization-sensitive ratio [O III]/H-alpha shows no discernible pattern near the prominent "hole" in the ionized gas. The independence of ionization and surface brightness suggests that substantial spatial structure remains unresolved, to such an extent that the surface brightness sample the number of denser filaments rather than the characteristic density in emission regions. These results fit with our picture of an ionization echo from an AGN whose ionizing luminosity has dropped by a factor > 100 (and possibly much more) within the last 1-2 x 10^5 years; we suggest a sequence of events and discuss implications of such rapid fluctuations for AGN demographics. (Abridged)