Evidence for cold accretion onto a massive galaxy at high redshift?

In this Letter we report on the discovery of a z= 2.83 Lyman α Blob (LAB) found in our wide-field narrow-band survey within the Spitzer First Look Survey region. The blob is extended over at least 95 kpc and has a total Lyman α luminosity of 2.1 × 1044 erg s−1. It is only the sixth LAB known of this scale (>50 kpc), and is associated with an embedded continuum source in g′, R, i′, K and 4.5-μm bands. The LAB's optical spectrum shows clumpy structures and tantalising hints of a sharp red cut-off and shear within the Lyman α emission line. Studies of the LAB's surface brightness profile and of the continuum counterpart's spectral energy distribution indicate that the profuse Lyman α emission is consistent with being powered by cold gas accreting onto a massive dark matter halo.