About AGN ionization echoes, thermal echoes and ionization deficits in low-redshift Lyα blobs

Mischa Schirmer; Sangeeta Malhotra; Nancy A Levenson; Hai Fu; Rebecca L Davies; William C Keel; Paul Torrey; Vardha N Bennert; Anna Pancoast; James E. H Turner

doi:10.1093/mnras/stw1819

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About AGN ionization echoes, thermal echoes and ionization deficits in low-redshift Lyα blobs

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About AGN ionization echoes, thermal echoes and ionization deficits in low-redshift Lyα blobs

Mischa Schirmer, Sangeeta Malhotra, Nancy A Levenson, Hai Fu, Rebecca L Davies, William C Keel, Paul Torrey, Vardha N Bennert, Anna Pancoast and James E. H Turner

Monthly notices of the Royal Astronomical Society, Vol.463(2), pp.1554-1586

12/01/2016

DOI: 10.1093/mnras/stw1819

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Abstract

We report the discovery of 14 Lyα blobs (LABs) at z ∼ 0.3, existing at least 4–7 billion years later in the Universe than all other LABs known. Their optical diameters are 20–70 kpc, and GALEX data imply Lyα luminosities of (0.4–6.3) × 1043 erg s−1. Contrary to high-z LABs, they live in low-density areas. They are ionized by AGN, suggesting that cold accretion streams as a power source must deplete between z = 2 and 0.3. We also show that transient AGN naturally explain the ionization deficits observed in many LABs. Their Lyα and X-ray fluxes decorrelate below ≲106 years because of the delayed escape of resonantly scattering Lyα photons. High Lyα luminosities do not require currently powerful AGN, independent of obscuration. Chandra X-ray data reveal intrinsically weak AGN, confirming the luminous optical nebulae as impressive ionization echoes. For the first time, we also report mid-infrared thermal echoes from the dusty tori. We conclude that the AGN have faded by three to four orders of magnitude within the last 104–5 years, leaving fossil UV, optical and thermal radiation behind. The host galaxies belong to the group of previously discovered Green Bean galaxies (GBs). Gemini optical imaging reveals smooth spheres, mergers, spectacular outflows and ionization cones. Because of their proximity and high flux densities, GBs are perfect targets to study AGN feedback, mode switching and the Lyα escape. The fully calibrated, co-added optical FITS images are publicly available.

ultraviolet: galaxies

galaxies: active

galaxies: evolution

radiative transfer

Details

Title: Subtitle: About AGN ionization echoes, thermal echoes and ionization deficits in low-redshift Lyα blobs
Creators: Mischa Schirmer - 1Gemini Observatory, Casilla 603, La Serena, Chile
Sangeeta Malhotra - Arizona State University
Nancy A Levenson - 1Gemini Observatory, Casilla 603, La Serena, Chile
Hai Fu - University of Iowa
Rebecca L Davies - Australian National University
William C Keel - University of Alabama
Paul Torrey - Massachusetts Institute of Technology
Vardha N Bennert - California Polytechnic State University
Anna Pancoast - Harvard University
James E. H Turner - 1Gemini Observatory, Casilla 603, La Serena, Chile
Resource Type: Journal article
Publication Details: Monthly notices of the Royal Astronomical Society, Vol.463(2), pp.1554-1586
DOI: 10.1093/mnras/stw1819
ISSN: 0035-8711
eISSN: 1365-2966
Publisher: Oxford University Press
Grant note: DOI: 10.13039/100000104, name: National Aeronautics and Space Administration, award: GO4-15110X; DOI: 10.13039/100000104, name: National Aeronautics Space Administration, award: NAS8-03060; name: National Science Foundation (NSF) Research at Undergraduate Institutions (RUI), award: AST-1312296; DOI: 10.13039/501100004604, name: European Southern Observatory, award: 287.B-5008
Language: English
Date published: 12/01/2016
Academic Unit: Physics and Astronomy
Record Identifier: 9984199848502771

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