The CO line SED and atomic carbon in IRAS F 10214 + 4724 ⋆

Using the IRAM 30m telescope and the Plateau de Bure interferometer we have detected the C I(P2 →P1) and the CO 3−2, 4−3, 6−5, 7−6 transitions as well as the dust continuum at 3 and 1.2 mm towards the distant luminous infrared galaxy IRAS F10214+4724 at z = 2.286. The C I(P2 →P1) line is detected for the first time towards this source and IRAS F10214+4724 now belongs to a sample of only 3 extragalactic sources at any redshift where both of the carbon fine structure lines have been detected. The source is spatially resolved by our C I(P2 →P1) observation and we detect a velocity gradient along the east-west direction. The CI line ratio allows us to derive a carbon excitation temperature of 42+12 −9 K. The carbon excitation in conjunction with the CO ladder and the dust continuum constrain the gas density to n(H2)= 10 cm and the kinetic temperature to Tkin = 45–80 K, similar to the excitation conditions found in nearby starburst galaxies. The rest-frame 360 μm dust continuum morphology is more compact than the line emitting region, which supports previous findings that the far infrared luminosity arises from regions closer to the active galactic nucleus at the center of this system.