@article{6c1d9974415342269f1efb08964e3dd7,
title = "About AGN ionization echoes, thermal echoes and ionization deficits in low-redshift Lyα blobs",
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.",
keywords = "Galaxies: active, Galaxies: evolution, Radiative transfer, Ultraviolet: galaxies",
author = "Mischa Schirmer and Sangeeta Malhotra and Levenson, {Nancy A.} and Hai Fu and Davies, {Rebecca L.} and Keel, {William C.} and Paul Torrey and Bennert, {Vardha N.} and Anna Pancoast and Turner, {James E H}",
note = "Funding Information: MSthanks hiswife Karianne and his children Hendrik and Jakob for their patience over the last four years. Carrie Bridge, Gary Ferland, Pascale Hibon, Kohei Ichikawa, Lia Sartori, Mark Schartmann, Peter Schneider, IsakWold, Yujin Yang and the anonymous referee helped to improve this paperwith discussions and comments. Carrie Bridge, Yuichi Matsuda and IsakWold shared unpublished data for which he is very grateful. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. They are most fortunate to have the opportunity to conduct observations from this mountain. Author Contributions. MS obtained all data, performed the scientific analysis and wrote the manuscript; SM pointed out the delayed Lya escape times with respect to the hydrogen recombination timescale; ultimately, that led to the solution of the LAB ionization deficit problem; NAL reduced the Chandra data and extracted the X-ray fluxes; HF first suggested the possibility that GBs might be low-z LAB analogues; MS, RLD, HF, WCK and PT discussed AGN ionization echoes in depth; VNB, AP and WCK provided missing redshifts for two GBs using the Lick observatory; JEHT doublechecked the flux calibration of the 3D GMOS-S data cube. Support for this work was provided by the National Aeronautics and Space Administration through Chandra Award Number GO4-15110X (PI: M. Schirmer) issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060. VNB gratefully acknowledges assistance from a National Science Foundation (NSF) Research at Undergraduate Institutions (RUI) grant AST-1312296. Note that findings and conclusions do not necessarily represent views of the NSF. The scientific results reported in this paper are based in part on observations made by the Chandra X-ray Observatory, and on data obtained from the Chandra Data Archive. The authors also made use of the software provided by the Chandra X-ray Center (CXC) in the application packages CIAO. Based on observations obtained at the GeminiObservatory,which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnolog{\'i}a e Innovac{\'i}on Productiva (Argentina) and Minist{\'e}rio da Ci{\^e}ncia, Tecnologia e Inova{\c c} {\~a}o (Brazil). Based on observations made with the NASA Galaxy Evolution Explorer. GALEX is a NASA Small Explorer launched in 2003 April. The authors gratefully acknowledge NASA's support for the construction, operation and science analysis for the GALEX mission, developed in cooperation with the Centre National d'Etudes Spatiales of France and theKorean Ministry of Science and Education. Based on data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France and the University of Hawaii. Based on observations made with the European Southern Observatory under programme 287.B-5008, Chile. Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Minist {\'e}rio da Ci{\^e}ncia, Tecnologia, e Inova{\c c} {\~a}o (MCTI) da Reṕublica Federativa do Brasil, the US National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC) and Michigan State University (MSU). This research has also made use of NASA's Astrophysics Data System Bibliographic Services; the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration; the PYTHON MATPLOTLIB package (Hunter 2007). Publisher Copyright: {\textcopyright} The Authors 2016. Published by Oxford University Press on behalf of The Royal Astronomical Society.",
year = "2016",
month = dec,
day = "1",
doi = "10.1093/mnras/stw1819",
language = "English (US)",
volume = "463",
pages = "1554--1586",
journal = "Monthly Notices of the Royal Astronomical Society",
issn = "0035-8711",
publisher = "Oxford University Press",
number = "2",
}