Browsing by Author "Schawinski, K."

Now showing 1 - 4 of 4
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    Galaxy Zoo: building the low-mass end of the red sequence with local post-starburst galaxies
    (Oxford University Press, 2012) Wong, O. I.; Schawinski, K.; Kaviraj, S.; Masters, K. L.; Nichol, R. C.; Lintott, C.; Keel, W. C.; Darg, D.; Bamford, S. P.; Andreescu, D.; Murray, P.; Raddick, M. J.; Szalay, A.; Thomas, D.; VandenBerg, J.; Commonwealth Scientific & Industrial Research Organisation (CSIRO); Yale University; University of Alabama Tuscaloosa; University of Nottingham; Johns Hopkins University; Imperial College London; University of Oxford; University of Portsmouth
    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 colourstellar 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.
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    Hanny's Voorwerp Evidence of AGN activity and a nuclear starburst in the central regions of IC 2497
    (EDP Sciences, 2010) Rampadarath, H.; Garrett, M. A.; Jozsa, G. I. G.; Muxlow, T.; Oosterloo, T. A.; Paragi, Z.; Beswick, R.; van Arkel, H.; Keel, W. C.; Schawinski, K.; Leiden University; Leiden University - Excl LUMC; University of Manchester; Jodrell Bank Centre for Astrophysics; Swinburne University of Technology; University of Groningen; University of Alabama Tuscaloosa; Yale University
    We present high-and intermediate resolution radio observations of the central region in the spiral galaxy IC 2497, performed using the European VLBI Network (EVN) at 18 cm, and the Multi-Element Radio Linked Interferometer Network (MERLIN) at 18 cm and 6 cm. We detect two compact radio sources, with brightness temperatures above 10(5) K, suggesting that they are related to AGN activity. We show that the total 18 cm radio emission from the galaxy is dominated neither by these compact sources nor large-scale emission, but extended emission confined within a sub-kpc central region. IC 2497 therefore appears as a typical luminous infrared galaxy that exhibits a nuclear starburst with a massive star formation rate (M > 5 M(circle dot)) of 12.4 M(circle dot)/yr. These results are in line with the hypothesis that the ionisation nebula "Hanny's Voorwerp" at a distance of similar to 15-25 kpc from the galaxy is ionised by the radiation cone of the AGN.
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    Revealing Hanny's Voorwerp: radio observations of IC 2497
    (EDP Sciences, 2009) Jozsa, G. I. G.; Garrett, M. A.; Oosterloo, T. A.; Rampadarath, H.; Paragi, Z.; van Arkel, H.; Lintott, C.; Keel, W. C.; Schawinski, K.; Edmondson, E.; Leiden University; Leiden University - Excl LUMC; Swinburne University of Technology; University of Groningen; University of Oxford; University of Alabama Tuscaloosa; Yale University; University of Portsmouth
    We present multi-wavelength radio observations in the direction of the spiral galaxy IC 2497 and the neighbouring emission nebula known as "Hanny's Voorwerp". Our WSRT continuum observations at 1.4 GHz and 4.9 GHz reveal the presence of extended emission at the position of the nebulosity, although the bulk of the emission remains unresolved at the centre of the galaxy. e-VLBI 1.65 GHz observations show that on the milliarcsecond-scale, a faint central compact source is present in IC 2497 with a brightness temperature in excess of 4 x 105 K. With the WSRT, we detect a large reservoir of neutral hydrogen in the proximity of IC 2497. One cloud complex with a total mass of 5.6 x 10(9) M(circle dot) to the South of IC 2497 encompasses Hanny's Voorwerp. Another cloud complex is located at the position of a small galaxy group similar to 100 kpc to the West of IC 2497 with a mass of 2.9 x 10(9) M(circle dot). Our data hint at a physical connection between the complexes. We also detect Hi in absorption against the central continuum source of IC 2497. Our observations strongly support the hypothesis that Hanny's Voorwerp is being ionised by an AGN in the centre of IC 2497. In this scenario, a plasma jet associated with the AGN clears a path through the ISM/IGM in the direction of the nebulosity. The large-scale radio continuum emission possibly originates from the interaction between this jet and the large cloud complex in which Hanny's Voorwerp is embedded. The Hi kinematics do not fit regular rotation, thus the cloud complex around IC 2497 is probably of tidal origin. From the Hi absorption against the central source, we derive a lower limit of 2.8 +/- 0.4 x 10(21) atoms cm(-2) to the H I column density. However, assuming non-standard conditions for the detected gas, we cannot exclude the possibility that the AGN in the centre of IC 2497 is Compton-thick.
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    SPATIALLY RESOLVED SPECTRA OF THE "TEACUP" ACTIVE GALACTIC NUCLEUS: TRACING THE HISTORY OF A DYING QUASAR
    (IOP Publishing, 2014) Gagne, J. P.; Crenshaw, D. M.; Kraemer, S. B.; Schmitt, H. R.; Keel, W. C.; Rafter, S.; Fischer, T. C.; Bennert, V. N.; Schawinski, K.; University System of Georgia; Georgia State University; Catholic University of America; United States Department of Defense; United States Navy; Naval Research Laboratory; University of Alabama Tuscaloosa; Technion Israel Institute of Technology; California State University System; California Polytechnic State University San Luis Obispo; Swiss Federal Institutes of Technology Domain; ETH Zurich
    The Sloan Digital Sky Survey (SDSS) Galaxy Zoo project has revealed a number of spectacular galaxies possessing extended emission-line regions (EELRs), the most famous being Hanny's Voorwerp galaxy. We present another EELR object discovered in the SDSS endeavor: the Teacup active galactic nucleus (AGN). Nicknamed for its EELR, which has a "handle"-like structure protruding 15 kpc into the northeast quadrant of the galaxy. We analyze the physical conditions of this galaxy with long-slit, ground-based spectroscopy from the Lowell, Lick, and KPNO observatories. With the Lowell 1.8 m Perkin's telescope we took multiple observations at different offset positions, allowing us to recover spatially resolved spectra across the galaxy. Line diagnostics indicate the ionized gas is photoionized primarily by the AGN. Additionally we are able to derive the hydrogen density from the [S II]lambda 6716/.6731 ratio. We generated two-component photoionization models for each spatially resolved Lowell spectrum. These models allow us to calculate the AGN bolometric luminosity seen by the gas at different radii from the nuclear center of the Teacup. Our results show a drop in bolometric luminosity by more than two orders of magnitude from the EELR to the nucleus, suggesting that the AGN has decreased in luminosity by this amount in a continuous fashion over 46,000 yr, supporting the case for a dying AGN in this galaxy independent of any IR based evidence. We demonstrate that spatially resolved photoionization modeling could be applied to EELRs to investigate long timescale variability.