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HST Observaqons of Hanny's Voorwerp and IC 2497

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HST Observaqons of Hanny's Voorwerp and IC 2497 The History And Environment Of A Faded Quasar: HST Observaons Of Hanny's Voorwerp And IC 2497 William C. Keel1, C. Linto2, K. Schawinski3, V. Bennert4, D. Thomas5, A. Manning1, S. D. Chojnowski6, H. van Arkel7, S. Lynn8, Galaxy Zoo team 1Univ. of Alabama, 2Adler Planetarium, 3Yale Univ., 4UCSB, 5Univ. of Portsmouth, UK, 6Texas Chrisan Univ., 7CITAVERDE College, NL, 8Oxford Univ., UK. Perhaps the signature discovery of the Galaxy Zoo cizen‐science project has been Hanny's Voorwerp, a high‐ionizaon cloud extending 45 kpc from the IC 2497 and Hanny’s Voorwerp spiral galaxy IC 2497. It must be ionized by a luminous yet unseen AGN. We Previous results: explore this system using HST imaging and spectroscopy. The disk of IC 2497 Voorwerp has high‐ionizaon opcal spectrum, at z=0.05 matching IC 2497 45 is warped, with complex dust absorpon near the nucleus; the near‐IR peak Gas requires ionizing luminosity ~4x10 erg/s coincides closely with the VLBI core. STIS spectra show the AGN as a low‐ Extent to 45 kpc in projecon 10 luminosity LINER, matching its weak X‐ray emission, and accompanied by an Part of 300‐kc H I tail with nearly 10 solar masses expanding loop of ionized gas ~500 pc in diameter (expansion age < 7 x 105 Connuum with substanal recombinaon component 42 years). We find no high‐ionizaon gas near the core, further evidence that Galaxy nucleus is a LINER, with implied (and X‐ray) luminosity ~10 erg/s the AGN has indeed faded. [O III] and Ηα+[N II] images show fine structure in Summary: IC 2497 hosted a quasar‐luminosity AGN, either obscured to an Hanny's Voorwerp, with limb‐brightened secons suggesng mild interacon enormous extent or recently (and dramacally) faded. Either case is important with a galacc oulow. We idenfy small regions ionized by recent star for AGN demographics; these observaons were planned to disnguish them. formaon, unlike the AGN ionizaon of the overall cloud. These are projected closest to IC 2497, suggesng that the star formaon was triggered by compression from an oulow. Ionizaon traced by [O III]/Hα shows broad bands across the object, and no discernible paern with emission‐line structures or near the prominent “hole” in the ionized gas. These results fit with our picture of an ionizaon echo from an AGN whose ionizing luminosity has dropped by a factor >100 within the last 2x105 years. We acknowledge support from NASA through STScI grant HST‐GO‐11620.01‐A, and support for Galaxy Zoo from the Jim Gray Research Fund at Microso, and the Leverhulme Trust. New data and treatment Instrument Filter/grang Exposure (s) ACS data are severely affected by CR ACS Ha ramp 2750 events and banding. We deal with [O III] ramp 2570 these via spaal filtering, using WFC3 F225W 2952 ground‐based data to restore low‐ F814W 2952 surface‐brightness structures. F160W 2698 STIS F430L 2750 F750L 2000 GALEX NUV image 6193 NUV spec 17798 FUV image 6193 FUV spec 17798 WIYN B 1200 V 1200 I 600 Nucleus: weak AGN with oulow STIS spectra show a LINER nucleus (log U=‐3.5) with no higher‐ionizaon lines (hence no gas seeing an extant quasar). It is accompanied by a 0.5” (500‐pc) loop of gas to its north, redshied by 300 km/s from the nucleus. This feature has kinemac age < 7 x 105 years depending on orientaon. It might represent a switch to kinecally‐ dominated accreon output, but does not lie along the weak radio jet. Structure in the gas Triggered star formaon A 2‐kpc region shows blue connuum knots and disnct line raos indicang star formaon (red above). This area is roughly aligned with the oulow seen at 20 cm and the small nuclear jet At right: pure jet‐induced star formaon in Minkowski’s object. The extent of star formaon is similar, but this has 4x the SFR and the radio source has 6x the power. Also, the gas is seen streaming Base: Hubble Legacy Archive V+I. outward interacng with the jet; Contours: Hα, SARA 0.6m such features are at most localized No ionizaon or morphological clue as to origin of the hole (a shadow?) and subtle in Hanny’s Voorwerp. Ionizaon decoupled from surface brightness (unresolved structures vary in number rather than density?) Skew bands of higher ionizaon – echo of history in thin layer? How common are faded quasars? A suggested meline Inspired by the discovery of Hanny’s Voorwerp, we have begun searches for related objects, bearing on the history and obscuraon of luminous AGN: Interacon launches gas tail (original galaxy is unclear) ‐ SDSS color search by Galaxy Zoo volunteers (see adjacent poster, Chojnowski et al) QSO lights up (perhaps encouraged by interacon), ionizes cone of gas ‐ [O III] imaging of known AGN, H ‐ rich fields, luminous non‐AGN QSO starts oulow (view epoch – 106 years) ‐ X‐ray followup of galaxies with giant high‐ionizaon nebulae QSO shuts down (view epoch ‐200,000 years) .
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