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Home All issues Volume 387 / No 2 (May IV 2002) A&A, 387 2 (2002) 406-411 Abstract
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Issue
A&A
Volume 387, Number 2, May IV 2002
Page(s) 406 - 411
Section Cosmology
DOI http://dx.doi.org/10.1051/0004-6361:20020382


A&A 387, 406-411 (2002)
DOI: 10.1051/0004-6361:20020382

CO and Dust in PSS 2322+1944 at a redshift of 4.12

P. Cox1, A. Omont2, S. G. Djorgovski3, F. Bertoldi4, J. Pety5, C. L. Carilli6, K. G. Isaak7, A. Beelen1, R. G. McMahon8 and S. Castro3, 9

1  Institut d'Astrophysique Spatiale, Université de Paris XI, 91405 Orsay, France
2  Institut d'Astrophysique de Paris, CNRS, 98bis boulevard Arago, 75014 Paris, France
3  Astronomy Department, California Institute of Technology, Pasadena, CA 91125, USA
4  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
5  IRAM, 300 rue de la Piscine, 38406 St-Martin-d'Hères, France
6  National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801, USA
7  Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE, UK
8  Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
9  Infrared Processing and Analysis Center 100-22, Caltech, Pasadena, CA 91125, USA

(Received 11 January 2002 / Accepted 8 March 2002 )

Abstract
Using the IRAM interferometer we have detected $J=4{\rightarrow}3$ and $5{\rightarrow}4$ CO line emission toward the radio quiet quasar PSS 2322+1944. At a redshift of $z_{\rm CO}=4.1199$ this is the fourth and strongest detection of CO at z>4. The velocity-integrated CO $J=4{\rightarrow}3$ and $J=5{\rightarrow}4$ line fluxes are $4.21 \pm 0.40$ and $3.74 \pm 0.56 \rm\thinspace Jy \thinspace km \thinspace s^{-1}$ , and the linewidth is ${\approx} 300 \thinspace \rm km s^{-1}$. The CO $J=10{\rightarrow}9$ was searched for but not detected with an upper intensity limit of 30 mJy. The 1.35 mm (250  $\rm\mu m$ rest wavelength) continuum flux density is $7.5\pm1.3$ mJy, in agreement with previous bolometer measurements at 1.2 mm with the 30-m IRAM telescope. The 3 mm (580  $\rm\mu m$ rest wavelength) continuum is not detected with a 3  $\sigma$ upper limit of 0.7 mJy. We also report observations of the 450  $\rm\mu m$ continuum in PSS 2322+1944 using the SCUBA array at the JCMT. The quasar was detected with a 450  $\rm\mu m$ flux density of $\rm 79 \pm 19 \thinspace mJy$ . At the angular resolution of $4\farcs8 \times 2\farcs1$ at 1.3 mm and $6\farcs2 \times 4\farcs9$ at 3.2 mm, the interferometer observations do not show evidence of spatial extension in the continuum or CO line emission. Assuming no gravitational magnification, we estimate a molecular gas mass of ${\approx} 2.5 \times 10^{11} ~ M_\odot$. The molecular gas is warm ( $\rm 40 {-} 100 \thinspace K$) and dense ( $\rm 10^{3.5} {-} 10^{4.1} \thinspace cm^{-3}$). The infrared-to-CO luminosity ratio is ${\approx} 185 ~ L_\odot \rm \thinspace (K \thinspace km \thinspace s^{-1} \thinspace pc^2)^{-1}$ , comparable to the values found for ultraluminous infrared galaxies. The detection of CO emission in this high redshift QSO provides further evidence that the radio emission and the millimeter to submillimeter continuum emission are predominantly powered by a starburst which is coeval with the AGN activity.


Key words: galaxies: formation -- quasars: emission lines -- quasars: individual: PSS 2322+1944 -- cosmology: observations -- cosmology: early Universe -- radio lines: galaxies

Offprint request: P. Cox, pierre.cox@ias.u-psud.fr

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