Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

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.

Abstract:

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.

Abstract:

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.

Abstract:

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

Abstract:

The Galaxies in Cosmological Simulations (galics) semi-analytical model of hierarchical galaxy formation is used to investigate the effects of different galactic properties, including star formation rate (SFR) and outflows, on the shape of the mass-metallicity relation and to predict the relation for galaxies at redshift z= 2.27 and 3.54. Our version of galics has the chemical evolution implemented in great detail and is less heavily reliant on approximations, such as instantaneous recycling. We vary the model parameters controlling both the efficiency and redshift dependence of the SFR as well as the efficiency of supernova feedback. We find that the factors controlling the SFR influence the relation significantly at all redshifts and require a strong redshift dependence, proportional to 1 +z, in order to reproduce the observed relation at the low-mass end. Indeed, at any redshift, the predicted relation flattens out at the high-mass end resulting in a poorer agreement with observations in this regime. We also find that variation in the parameters associated with outflows has a minimal effect on the relation at high redshift but does serve to alter its shape in the more recent past. We thus conclude that the relation is one between the SFR and mass and that outflows are only important in shaping the relation at late times. When the relation is stratified by the SFR, it is apparent that the predicted galaxies with increasing stellar masses have higher SFRs, supporting the view that galaxy downsizing is the origin of the relation. Attempting to reproduce the observed relation, we vary the parameters controlling the efficiency of star formation and its redshift dependence and compare the predicted relations with those of Erb et al. at z= 2.27 and Maiolino et al. at z= 3.54 in order to find the best-fitting parameters. We succeed in fitting the relation at z= 3.54 reasonably well; however, we fail at z= 2.27, our relation lying on average below the observed one at the one standard deviation level. We do, however, predict the observed evolution between z= 3.54 and 0. Finally, we discuss the reasons for the above failure and the flattening at high masses, with regards to both the comparability of our predictions with observations and the possible lack of underlying physics. Several of these problems are common to many semi-analytic/hybrid models and so we discuss possible improvements and set the stage for future work by considering how the predictions and physics in these models can be made more robust in light of our results. © 2010 The Authors Monthly Notices of the Royal Astronomical Society © 2010 RAS.