Intergalactic Medium Emission Observations with the Cosmic Web Imager. II. Discovery of Extended, Kinematically-Linked Emission around SSA22 Lyα Blob 2

Abstract

The intergalactic medium (IGM) is the dominant reservoir of baryons, delineates the large scale structure of the universe at low to moderate overdensities, and provides gas from which galaxies form and evolve. Simulations of a Cold Dark Matter (CDM) dominated universe predict that the IGM is distributed in a cosmic web of filaments, and that galaxies should form along and at the intersections of these filaments (Bond, Kofman, & Pogosyan 1994; Miralda-Escude et al. 1996). While observations of QSO absorption lines and the large-scale distribution of galaxies have confirmed the CDM paradigm, the cosmic web of IGM has never been confirmed by direct imaging. Here we report our observation of the Lyα blob-2 (LAB2) in SSA22, with the Cosmic Web Imager. This is an integral field spectrograph optimized for low surface brightness, extended emission. With 22 hours of total on- and off-source exposure, CWI has revealed that LAB2 has extended Lyα emission which is organized into azimuthal zones consistent with filaments. We perform numerous tests with simulations and the data to secure the robustness of this result, which relies on data with modest signal-to-noise ratio. We have developed a smoothing algorithm that permits visualization of data cube slices along image or spectral-image planes. With both raw and smoothed data cubes we demonstrate that the filaments are kinematically associated with LAB2 and display double-peaked profiles characteristic of optically thick Lyα emission. The flux is 10-20 times brighter than expected for the average emission from the IGM but is consistent with boosted fluorescence from a buried QSO or gravitation cooling radiation. Using simple emission models we infer a baryon mass in the filaments of at least 1−4 × 10^(11)M_☉, and the dark halo mass is at least 2 × 10^(12)M_☉. The spatial-kinematic morphology is more consistent with inflow from the cosmic web than outflow from LAB2, although an outflow feature maybe present at one azimuth. LAB2 and the surrounding gas have significant and coaligned angular momentum, strengthening the case for their association.

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