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Resolving the Optical Emission Lines of Ly$\alpha$ Blob ``B1'' at z = 2.38: Another Hidden Quasar

Overzier, R.A.; Nesvadba, N.P.H.; Dijkstra, M.; Hatch, N.A.; Lehnert, M.D.; Villar-Martín, M.; Wilman, R.J.; Zirm, A.W.

Resolving the Optical Emission Lines of Ly$\alpha$ Blob ``B1'' at z = 2.38: Another Hidden Quasar Thumbnail


R.A. Overzier

N.P.H. Nesvadba

M. Dijkstra

N.A. Hatch

M.D. Lehnert

M. Villar-Martín

A.W. Zirm


We have used the SINFONI near-infrared integral field unit on the Very Large Telescope to resolve the optical emission line structure of one of the brightest (L Lyα ≈ 1044 erg s–1) and nearest (z ≈ 2.38) of all Lyα blobs (LABs). The target, known in the literature as object "B1", lies at a redshift where the main optical emission lines are accessible in the observed near-infrared. We detect luminous [O III] λλ4959, 5007 and Hα emission with a spatial extent of at least 32 × 40 kpc (4'' × 5''). The dominant optical emission line component shows relatively broad lines (600-800 km s–1, FWHM) and line ratios consistent with active galactic nucleus (AGN) photoionization. The new evidence for AGN photoionization, combined with previously detected C IV and luminous, warm infrared emission, suggest that B1 is the site of a hidden quasar. This is confirmed by the fact that [O II] is relatively weak compared with [O III] (extinction-corrected [O III]/[O II] of about 3.8), which is indicative of a high, Seyfert-like ionization parameter. From the extinction-corrected [O III] luminosity we infer a bolometric AGN luminosity of ~3 × 1046 erg s–1, and further conclude that the obscured AGN may be Compton-thick given existing X-ray limits. The large line widths observed are consistent with clouds moving within the narrow-line region of a luminous QSO. The AGN scenario is capable of producing sufficient ionizing photons to power the Lyα, even in the presence of dust. By performing a census of similar objects in the literature, we find that virtually all luminous LABs harbor obscured quasars. Based on simple duty-cycle arguments, we conclude that AGNs are the main drivers of the Lyα in LABs rather than the gravitational heating and subsequent cooling suggested by cold stream models. We also conclude that the empirical relation between LABs and overdense environments at high redshift must be due to a more fundamental correlation between AGNs (or massive galaxies) and environment.


Overzier, R., Nesvadba, N., Dijkstra, M., Hatch, N., Lehnert, M., Villar-Martín, M., …Zirm, A. (2013). Resolving the Optical Emission Lines of Ly$\alpha$ Blob ``B1'' at z = 2.38: Another Hidden Quasar. Astrophysical Journal, 771, Article 89.

Journal Article Type Article
Acceptance Date May 10, 2013
Online Publication Date Jun 20, 2013
Publication Date Jun 20, 2013
Deposit Date Apr 9, 2018
Publicly Available Date Jun 28, 2018
Journal Astrophysical Journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 771
Article Number 89
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Published Journal Article (692 Kb)

Copyright Statement
© The American Astronomical Society.

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