2007ApJ...662L..51A

We report on the serendipitous discovery of the brightest Lyman break galaxy (LBG) currently known, a galaxy at z=2.73 that is being strongly lensed by the z=0.38 luminous red galaxy (LRG) SDSS J002240.91+143110.4. The arc of this gravitational lens system, which we have dubbed the ``8 o'clock arc'' due to its time of discovery, was initially identified in the imaging data of the Sloan Digital Sky Survey Data Release 4; followup observations on the Astrophysical Research Consortium (ARC) 3.5 m telescope at Apache Point Observatory confirmed the lensing nature of this system and led to the identification of the arc's spectrum as that of an LBG. The arc has a spectrum and a redshift remarkably similar to those of the previous record-holder for brightest LBG (MS 1512-cB58, also known as cB58), but, with an estimated total magnitude of (g, r, i)=(20.0, 19.2, 19.0) and surface brightness of (µ_g, µ_r, µ_i)=(23.3, 22.5, 22.3) mag/arcsec2, the 8 o'clock arc is thrice as bright. The 8 o'clock arc, which consists of three lensed images of the LBG, is 162° (9.6") long and has a length-to-width ratio of 6:1. A fourth image of the LBG–a counterimage–can also be identified in the ARC 3.5 m g-band images. A simple lens model for the system assuming a singular isothermal ellipsoid yields an Einstein radius of θ_Ein=3.32"±0.16", a total mass for the lensing LRG (within the 12.1±0.6 h^–1 kpc enclosed by the Einstein radius) of 1.35x10¹² h^–1M_☉, and a magnification factor for the LBG of 12.3^+15.0_–3.6. The LBG itself is intrinsically quite luminous (~11L_*) and shows indications of massive recent star formation, perhaps as high as 160 h^–1 M_☉/yr.