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 alpha 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 alpha luminosity of 2.1 x 10(44) 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-mu m bands. The LAB's optical spectrum shows clumpy structures and tantalising hints of a sharp red cut-off and shear within the Lyman alpha emission line. Studies of the LAB's surface brightness profile and of the continuum counterpart's spectral energy distribution indicate that the profuse Lyman alpha emission is consistent with being powered by cold gas accreting onto a massive dark matter halo.