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27 April 2024 |
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About AGN ionization echoes, thermal echoes, and ionization deficits in low redshift Lyman-alpha 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
; | | Date: |
21 Jul 2016 | | Abstract: | We report the discovery of 14 Lyman-alpha 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 Ly-alpha luminosities of
(0.4-6.3)x10^43 erg/s. 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 z=0.3. We also show that transient AGN
naturally explain the ionization deficits observed in many LABs: Their Ly-alpha
and X-ray fluxes decorrelate below 10^6 years because of the delayed escape of
resonantly scattering Ly-alpha photons. High Ly-alpha 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 3-4
orders of magnitude within the last 10^(4-5) 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 Ly-alpha escape. The fully calibrated, coadded
optical FITS images are publicly available. | | Source: | arXiv, 1607.6481 | | Services: | Forum | Review | PDF | Favorites | |
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