[C II] LINE EMISSION IN MASSIVE STAR-FORMING GALAXIES AT <i>z</i> = 4.7

Abstract

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations\nof the [CII] 157.7micron fine structure line and thermal dust continuum\nemission from a pair of gas-rich galaxies at z=4.7, BR1202-0725. This system\nconsists of a luminous quasar host galaxy and a bright submm galaxy (SMG),\nwhile a fainter star-forming galaxy is also spatially coincident within a 4"\n(25 kpc) region. All three galaxies are detected in the submm continuum,\nindicating FIR luminosities in excess of 10^13 Lsun for the two most luminous\nobjects. The SMG and the quasar host galaxy are both detected in [CII] line\nemission with luminosities, L([CII]) = (10.0 +/- 1.5)x10^9 Lsun and L([CII]) =\n(6.5+/-1.0)x10^9 Lsun, respectively. We estimate a luminosity ratio,\nL([CII])/L(FIR) = (8.3+/-1.2)x10^-4 for the starburst SMG to the North, and\nL([CII])/L(FIR) = (2.5+/-0.4)x10^-4 for the quasar host galaxy, in agreement\nwith previous high-redshift studies that suggest lower [CII]-to-FIR luminosity\nratios in quasars than in starburst galaxies. The third fainter object with a\nflux density, S(340GHz) = 1.9+/-0.3 mJy, is coincident with a Ly-Alpha emitter\nand is detected in HST ACS F775W and F814W images but has no clear counterpart\nin the H-band. Even if this third companion does not lie at a similar redshift\nto BR1202-0725, the quasar and the SMG represent an overdensity of massive,\ninfrared luminous star-forming galaxies within 1.3 Gyr of the Big Bang.\n