Spectro-polarimetry confirms central powering of a Ly$\alpha$ nebula at z=3.09

Abstract

We present a follow-up study to the imaging polarimetry performed by Hayes et. al. 2011 on LAB1 in the SSA22 protocluster region. Arguably the most well-known Lyman-$\alpha$ "blob", this radio-quiet emission-line nebula likely hosts a galaxy which is either undergoing significant star formation or hosts an AGN, or both. We obtain deep, spatially resolved spectro-polarimetry of the Ly$\alpha$ emission and detect integrated linear polarization of $9$-$13\%\pm 2$-$3\%$ at a distance of approximately 15 kpc north and south of the peak of the Lyman-$\alpha$ surface brightness with polarization vectors lying tangential to the galactic central source. In these same regions, we also detect a wavelength dependence in the polarization which is low at the center of the Ly$\alpha$ line profile and rises substantially in the wings of the profile. These polarization signatures are easily explained by a weak out-flowing shell model. The spectral dependence of the polarization presented here provide a framework for future observations and interpretations of the southern portion of LAB1 in that any model for this system must be able to reproduce this particular spectral dependence. However, questions still remain for the northern-most spur of LAB1. In this region we detect total linear polarization of between $3$ and $20\%$ at the $5\%$ significance level. Simulations predict that polarization should increase with radius for a symmetric geometry. That the northern spur does not suggests either that this region is not symmetric (which is likely) and exhibits variations in columns density, or that it is kinematically distinct from the rest of LAB1 and powered by another mechanism altogether.

11 pages, 7 figures, accepted for publication in ApJ

References in corpus (11)

• A novel estimator of the polarization amplitude from normally distributed Stokes parameters
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• Overturning the Case for Gravitational Powering in the Prototypical Cooling Lyman-alpha Nebula
• An extremely dense group of massive galaxies at the centre of the protocluster at z = 3.09 in the SSA22 field
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• ALMA observations of Lyman-alpha Blob 1: halo sub-structure illuminated from within
• Gas Accretion and Giant Lyman-alpha Nebulae
• Deciphering Lyman $\alpha$ blob 1 with deep MUSE observations
• Revisiting the Gas Kinematics in SSA22 Lyman-$\alpha$ Blob 1 with Radiative Transfer Modeling in a Multiphase, Clumpy Medium
• Unlocking the Full Potential of Extragalactic Ly$\alpha$ through Its Polarization Properties
• CHORUS. III. Photometric and Spectroscopic Properties of Ly$\alpha$ Blobs at $z=4.9-7.0$
• What Makes Ly$\alpha$ Nebulae Glow? Mapping the Polarization of LABd05
• Where Outflows Meet Inflows: Gas Kinematics in SSA22 Lyman-$\alpha$ Blob 2 Decoded by Advanced Radiative Transfer Modelling
• Ly-alpha Radiative Transfer: A Stokes Vector Approach to Ly-alpha Polarization
• Lyman-$\alpha$ Polarization Intensity Mapping
• Mapping the Polarization of the Radio-Loud Ly$\alpha$ Nebula B3 J2330+3927
• Constraining the geometry of the gas surrounding a typical galaxy at $z=3.4$ with Ly$\alpha$ polarization