CO J = 3--2 Emission in the Radio Galaxy 53W002 at it Z = 2.394

August 1997 • 1997ApJ...485L..21S

Authors • Scoville, N. Z. • Yun, M. S. • Windhorst, R. A. • Keel, W. C. • Armus, L.

Abstract • We report a sensitive search for redshifted CO J = 3-2 emission from the weak radio galaxy 53W002 at z = 2.394. Maps at resolutions of 3" and 235 km s^-1 show a significant emission peak within 0.5" of the optical and radio continuum peaks. The measured narrowband flux is approximately 10 times the extrapolated centimeter-wavelength nonthermal radio continuum expected at 101.9 GHz and exhibits a spectral profile implying a 540 km s^-1 width (FWHM) at a systemic redshift z = 2.394 +/- 0.001 for CO (3-2). This emission has a total integrated flux of 1.51 +/- 0.2 Jy km s^-1, approximately 4 times weaker than that previously seen in the lensed systems FSC 10214+4724 and the Cloverleaf QSO. For a Galactic CO-to-H₂ conversion ratio, the implied molecular gas mass is 7.4 × 10¹⁰ M_solar (H₀ = 75 km s^-1 Mpc^-1 and q₀ = 0.5). The CO emission is elongated at P.A. = 120° with a deconvolved major-axis radius of 15 kpc (2.8"). This extension is along a similar direction to that seen in the centimeter-wave radio continuum and in the optical, but approximately 3 times larger. A velocity gradient is seen along the major axis, and if this structure is a (forming) disk, the implied dynamical mass is (9-22) × 10¹⁰ M_solar at r <= 15 kpc, assuming inclination i = 0° (edge-on). The magnitude of these masses and the similarity of the high gas-mass fraction are consistent with the host galaxy of 53W002 being a young galactic system but the metallicity (probably >=0.1 Z_solar in order to produce the CO lines) implies significant heavy-element production prior to z = 2.4. This constitutes the first high redshift molecular gas detected in emission where there is probably no gravitational magnification.

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Lee Armus

Senior Scientist