TY - JOUR
T1 - The line polarization within a giant Lyα nebula
AU - Prescott, Moire K.M.
AU - Smith, Paul S.
AU - Schmidt, Gary D.
AU - Dey, Arjun
N1 - Funding Information:
The authors are very grateful to a number of people for assistance with the imaging polarimetry observations, in particular Joseph Scumaci in the Steward Observatory Machine Shop for manufacturing the custom-designed filter shim and Heidi Schweiker at NOAO for tracing the narrowband filter bandpass on short notice, allowing us to measure the index of refraction. We thank Tony Misch, Mike Bolte, Buell Jannuzi, and the University of California/Lick Observatory for their assistance in making the narrowband filter available for these polarimetric observations. The authors are grateful to Kristian Finlator, Mark Dijkstra, and an anonymous referee for many helpful discussions and suggestions that improved the paper. The authors also thank Mark Dijkstra for sending his theoretical model results. M.K.M.P. was supported by an NSF Graduate Research Fellowship and a TABASGO Prize Postdoctoral Fellowship. Partial support for M.K.M.P. was provided by NASA, through a grant (for program GO10591) from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA) under NASA contract NAS 5-26555. A.D.’s research is supported by NOAO, which is operated by AURA under cooperative agreement with the National Science Foundation.
PY - 2011/4/1
Y1 - 2011/4/1
N2 - Recent theoretical work has suggested that Lyα nebulae could be substantially polarized in the Lyα emission line, depending on the geometry, kinematics, and powering mechanism at work. Polarization observations can therefore provide a useful constraint on the source of ionization in these systems. In this Letter, we present the first Lyα polarization measurements for a giant Lyα nebula at z ≈ 2.656. We do not detect any significant linear polarization of the Lyα emission: P Lyα = 2.6% ±2.8% (corrected for statistical bias) within a single large aperture. The current data also do not show evidence for the radial polarization gradient predicted by some theoretical models. These results rule out singly scattered Lyα (e.g., from the nearby active galactic nucleus, AGN) and may be inconsistent with some models of backscattering in a spherical outflow. However, the effects of seeing, diminished signal-to-noise ratio, and angle averaging within radial bins make it difficult to put strong constraints on the radial polarization profile. The current constraints may be consistent with higher density outflow models, spherically symmetric infall models, photoionization by star formation within the nebula or the nearby AGN, resonant scattering, or non-spherically symmetric cold accretion (i.e., along filaments). Higher signal-to-noise ratio data probing to higher spatial resolution will allow us to harness the full diagnostic power of polarization observations in distinguishing between theoretical models of giant Lyα nebulae.
AB - Recent theoretical work has suggested that Lyα nebulae could be substantially polarized in the Lyα emission line, depending on the geometry, kinematics, and powering mechanism at work. Polarization observations can therefore provide a useful constraint on the source of ionization in these systems. In this Letter, we present the first Lyα polarization measurements for a giant Lyα nebula at z ≈ 2.656. We do not detect any significant linear polarization of the Lyα emission: P Lyα = 2.6% ±2.8% (corrected for statistical bias) within a single large aperture. The current data also do not show evidence for the radial polarization gradient predicted by some theoretical models. These results rule out singly scattered Lyα (e.g., from the nearby active galactic nucleus, AGN) and may be inconsistent with some models of backscattering in a spherical outflow. However, the effects of seeing, diminished signal-to-noise ratio, and angle averaging within radial bins make it difficult to put strong constraints on the radial polarization profile. The current constraints may be consistent with higher density outflow models, spherically symmetric infall models, photoionization by star formation within the nebula or the nearby AGN, resonant scattering, or non-spherically symmetric cold accretion (i.e., along filaments). Higher signal-to-noise ratio data probing to higher spatial resolution will allow us to harness the full diagnostic power of polarization observations in distinguishing between theoretical models of giant Lyα nebulae.
KW - Galaxies: evolution
KW - galaxies: formation
KW - galaxies: high-redshift
KW - techniques: polarimetric
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U2 - 10.1088/2041-8205/730/2/L25
DO - 10.1088/2041-8205/730/2/L25
M3 - Article
AN - SCOPUS:79953652394
SN - 2041-8205
VL - 730
JO - Astrophysical Journal Letters
JF - Astrophysical Journal Letters
IS - 2 PART II
M1 - L25
ER -