Galaxy Zoo: 'Hanny's Voorwerp', a quasar light echo?

By Chris J. Lintott, Kevin Schawinski, William Keel, H. V. Arkel, N. Bennert, E. Edmondson, D. Thomas, Daniel J B Smith, P. Herbert, M. Jarvis and 10 more. 2009

249 citations recorded by the source corpus.

We report the discovery of an unusual object near the spiral galaxy IC 2497, discovered by visual inspection of the Sloan Digital Sky Survey (SDSS) as part of the Galaxy Zoo project. The object, known as Hanny’s Voorwerp, is bright in the SDSS g band due to unusually strong [O III]4959, 5007 emission lines. We present the results of the first targeted observations of the object in the optical, ultraviolet and X-ray, which show that the object contains highly ionized gas. Although the line ratios are similar to extended emission-line regions near luminous active galactic nucleus (AGN), the source of this ionization is not apparent. The emission-line properties, and lack of X-ray emission from IC 2497, suggest either a highly obscured AGN with a novel geometry arranged to allow photoionization of the object but not the galaxy’s own circumnuclear gas, or, as we argue, the first detection of a quasar light echo. In this case, either the luminosity of the central source has decreased dramatically or else the obscuration in the system has increased within 10 5 yr. This object may thus represent the first direct probe

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/ef16fb52fceae9639ebfaddb45d94ea0ba99e83b

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Citations in the corpus

BLACK HOLE VARIABILITY AND THE STAR FORMATION–ACTIVE GALACTIC NUCLEUS CONNECTION: DO ALL STAR-FORMING GALAXIES HOST AN ACTIVE GALACTIC NUCLEUS? (2013, background): “…echoes in the form of large [O III]-emitting clouds have been discovered on the outskirts of several galaxies without clear evidence of ongoing AGN activity (Lintott et al. 2009; Schawinski et al. 2010; Keel et al. 2012b,a) or as ultraluminous galaxy-wide narrow-line regions (Schirmer et al. 2013).”
Galaxy Zoo: the fraction of merging galaxies in the SDSS and their morphologies (2009, background): “…2009), the relationships between environment, morphology and colour (Bamford et al. 2008a; Skibba et al. 2008), to study optically blue early-type galaxies at very low redshift (Schawinski et al. 2009) and has also lead to some serendipitous discoveries (Lintott et al. 2009; Cardamone et al. 2009).”
Galaxy Zoo 1: data release of morphological classifications for nearly 900 000 galaxies (2010, background): “Its usefulness is demonstrated both by the catalogue presented here, but also by the serendipitous discovery of unusual objects and classes of object discussed el - where (e.g. Lintott et al. 2009; Cardamone et al. 2009).”
The Milky Way Project First Data Release: a bubblier Galactic disc (2012, methodology): “This has been shown by the serendipitous discovery of Hanny’s Voorwerp (Lintott et al. 2009) and the case of the Galaxy Zoo ‘Green Peas’ (Cardamone et al. 2009).”
OpenML: networked science in machine learning (2014, background): “…observations are reported and discussed on an online forum, and have already resulted in the serendipitous discovery of the previously unknown ‘green pea’ galaxies [9], ‘passive red spirals’ [26], and other objects such as ‘Hanny’s Object’ [23], named after the volunteer who discovered it.”
The green valley is a red herring: Galaxy Zoo reveals two evolutionary pathways towards quenching of star formation in early-and late-type galaxies (2014, background): “…al. 2009; Skibba et al. 2009), mergers (Darg et al. 2010a, b; Kaviraj et al. 2012; Teng et al. 2012), unusual galaxy types (Cardamone et al. 2009; Lintott et al. 2009; Keel et al. 2012) and specific morphological features such as bars (e.g. Hoyle et al. 2011; Masters et al. 2011, 2012; Skibba et…”
Rotation-invariant convolutional neural networks for galaxy morphology prediction (2015, methodology): “…from the Galaxy Zoo projects have already been used in a wide variety of studies on galaxy structure, formation and evolution (Bamford et al. 2009; Lintott et al. 2009; Schawinski et al. 2009; Skibba et al. 2009; Darg et al. 2010; Masters et al. 2010, 2011; Simmons et al. 2013; Melvin et al.…”