Hanny's Voorwerp

Rampadarath, H.; Garrett, M. A.; Józsa, G. I. G.; Muxlow, T. W. B.; Oosterloo, Thomas; Paragi, Z.; Beswick, R.; Arkel, H. van; Keel, William C.; Schawinski, Kevin

doi:10.1051/0004-6361/201014782

Cited by 32 publications

(40 citation statements)

References 14 publications

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“…This has been interpreted as a light echo ionized by an AGN (Rampadarath et al 2010) which faded dramatically within the last ∼ 10 5 yr. This was the first evidence for such a time scale of AGN variability.…”

Section: Introductionmentioning

confidence: 93%

“…This was the first evidence for such a time scale of AGN variability. To explain the nuclear starburst of IC 2497 (Rampadarath et al 2010), the huge reservoir of H i around the galaxy (Józsa et al 2009), the discrepancy between the level of ionization of the cloud and both the luminosity of the AGN and the nature of the X-ray emission (Lintott et al 2009;Sartori et al 2016), Keel et al (2012b) suggested the following sequence of events. A major merger produced the massive tail of H i surrounding both the galaxy and Hanny's Voorwerp and triggered the AGN activity.…”

Section: Introductionmentioning

confidence: 99%

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An Interacting Galaxy Pair at the Origin of a Light Echo

Merluzzi

Busarello

Dopita

et al. 2018

ApJ

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In a low-density region of the Shapley supercluster we identified an interacting galaxy pair at redshift z = 0.04865 in which the Seyfert-2 nucleus of the main galaxy (ShaSS 073) is exciting an extended emission line region (EELR, ∼ 170 kpc 2 ) in the disk of the less massive companion (ShaSS 622). New integral-field spectroscopy and the multi-band data-set, spanning from far-ultraviolet to far-infrared and radio wavelengths, allowed us to obtain a detailed description of the ShaSS 622-073 system. The gas kinematics shows hints of interaction, although the overall velocity field shows a quite regular rotation in both galaxies, thus suggesting that we are observing their first encounter as confirmed by the estimated distance of 21 kpc between the two galaxy centers. The detected ∼ 2 − 3 kpc AGN outflow and the geometry of the EELR in ShaSS 622 support the presence of a hollow bi-cone structure. The status and sources of the ionization across the whole system have been analysed through photoionization models and a Bayesian approach which prove a clear connection between the AGN and the EELR. The luminosity of the AGN (2.4 × 10 44 erg s −1 ) is a factor 20 lower than the power needed to excite the gas in the EELR (4.6×10 45 erg s −1 ) indicating a dramatic fading of the AGN in the last 3 × 10 4 yr. ShaSS 073-622 provides all the ingredients listed in the recipe of a light echo where a high-ionised region maintains memory of a preceding more energetic phase of a now faded AGN. This is the first case of a light echo observed between two galaxies.

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Section: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

An Interacting Galaxy Pair at the Origin of a Light Echo

Merluzzi

Busarello

Dopita

et al. 2018

ApJ

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“…Line widths and electron temperature indicate that the gas is photoionized rather than shock excited, while a combination of ionization‐parameter and recombination arguments bound the required nuclear ionizing luminosity to be erg s. However, X‐ray spectroscopy shows the nucleus of IC 2497 to be only modestly absorbed, with ionizing luminosity only erg s (Schawinski et al 2010b). It is difficult to avoid the conclusion that the nucleus of IC 2497 was in fact a QSO (the nearest known luminous QSO) until roughly years before our current view, and has faded dramatically in the interim; radio and Hubble Space Telescope ( HST ) observations offer hints that some of its energy output may have switched to kinetic forms over this time span (Josza et al 2009; Rampadarath et al 2010; Schawinski et al 2010b; Keel et al, in preparation). The unlikeliness of the nearest QSO showing highly unusual behaviour suggests that such variations maybe common among AGN, prompting us to re‐examine the incidence and properties of extended ionized clouds around nearby AGN.…”

Section: Introductionmentioning

confidence: 98%

The Galaxy Zoo survey for giant AGN-ionized clouds: past and present black hole accretion events

Keel¹,

Chojnowski²,

Bennert³

et al. 2011

Monthly Notices of the Royal Astronomical Society

144

194

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Some active galactic nuclei (AGN) are surrounded by extended emission‐line regions (EELRs), which trace both the illumination pattern of escaping radiation and its history over the light travel time from the AGN to the gas. From a new set of such EELRs, we present evidence that the AGN in many Seyfert galaxies undergo luminous episodes 0.2–2 years in duration. Motivated by the discovery of the spectacular nebula known as Hanny’s Voorwerp, ionized by a powerful AGN which has apparently faded dramatically within years, Galaxy Zoo volunteers have carried out both targeted and serendipitous searches for similar emission‐line clouds around low‐redshift galaxies. We present the resulting list of candidates and describe spectroscopy identifying 19 galaxies with AGN‐ionized regions at projected radii kpc. This search recovered known EELRs (such as Mrk 78, Mrk 266 and NGC 5252) and identified additional previously unknown cases, one with detected emission to kpc. One new Sy 2 was identified. At least 14/19 are in interacting or merging systems, suggesting that tidal tails are a prime source of distant gas out of the galaxy plane to be ionized by an AGN. We see a mix of one‐ and two‐sided structures, with observed cone angles from 23 to 112. We consider the energy balance in the ionized clouds, with lower and upper bounds on ionizing luminosity from recombination and ionization‐parameter arguments, and estimate the luminosity of the core from the far‐infrared data. The implied ratio of ionizing radiation seen by the clouds to that emitted by the nucleus, on the assumption of a non‐variable nuclear source, ranges from 0.02 to ; 7/19 exceed unity. Small values fit well with a heavily obscured AGN in which only a small fraction of the ionizing output escapes to be traced by surrounding gas. However, large values may require that the AGN has faded over tens of thousands of years, giving us several examples of systems in which such dramatic long‐period variation has occurred; this is the only current technique for addressing these time‐scales in AGN history. The relative numbers of faded and non‐faded objects we infer, and the projected extents of the ionized regions, give our estimate (0.2–2 years) for the length of individual bright phases.

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“…Observations in the optical, ultraviolet, and X-ray indicate that this unusual object near the spiral galaxy IC 2497 contains highly ionized gas [80]. The emission-line properties, and lack of X-ray emission from IC 2497, seem to indicate this spiral galaxy is a highly obscured AGN with a novel geometry arranged to allow photoionization of Hanny's Voorwerp but not the galaxy's own circumnuclear gas [81], or alternatively the luminosity of the central source has decreased dramatically within the last 10 5 yr [82]. Should this be the case, Hanny's Voorwerp may exemplify the first detection of a quasar light echo.…”

Section: Dormant Black Holes After a Shining Pastmentioning

confidence: 94%

Ultrahigh energy cosmic ray nuclei from remnants of dead quasars

Moncada

Colon

Guerra

et al. 2017

Journal of High Energy Astrophysics

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We re-examine the possibility of ultrahigh energy cosmic rays being accelerated in nearby dormant quasars. We particularize our study to heavy nuclei to accommodate the spectrum and nuclear composition recently reported by the Pierre Auger Collaboration. Particle acceleration is driven by the Blandford-Znajek mechanism, which wires the dormant spinning black holes as Faraday unipolar dynamos. We demonstrate that energy losses are dominated by photonuclear interactions on the ambient photon fields. We argue that the local dark fossils of the past quasar activity can be classified on the basis of how source parameters (mass of the central engine and photon background surrounding the accelerator) impact the photonuclear interaction. In this classification it is possible to distinguish two unequivocal type of sources: those in which nuclei are completely photodisintegrated before escaping the acceleration region and those in which photopion production is the major energy damping mechanism. We further argue that the secondary nucleons from the photodisintegrated nuclei (which have a steep spectral index at injection) can populate the energy region below "the ankle" feature in the cosmic ray spectrum, whereas heavy and medium mass nuclei (with a harder spectral index) populate the energy region beyond "the ankle", all the way to the high energy end of the spectrum. In addition, we show that five potential quasar remnants from our cosmic backyard correlate with the hot-spot observed by the Telescope Array.

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Hanny's Voorwerp

Cited by 32 publications

References 14 publications

An Interacting Galaxy Pair at the Origin of a Light Echo

An Interacting Galaxy Pair at the Origin of a Light Echo

The Galaxy Zoo survey for giant AGN-ionized clouds: past and present black hole accretion events

Ultrahigh energy cosmic ray nuclei from remnants of dead quasars

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