CO observations of high-z radio galaxies MRC 2104-242 and MRC 0943-242: spectral-line performance of the Compact Array Broadband Backend

B. H. C. Emonts*, R. P. Norris, I. Feain, G. Miley, E. M. Sadler, M. Villar-Martin, M. Y. Mao, T. A. Oosterloo, R. D. Ekers, J. B. Stevens, M. H. Wieringa, K. E. K. Coppin, C. N. Tadhunter

*Corresponding author for this work

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Abstract

We present the first 7-mm observations of two high-redshift, Ly alpha-bright radio galaxies (MRC 2104-242 and MRC 0943-242) performed with the 2 x 2 GHz instantaneous bandwidth of the Compact Array Broadband Backend (CABB) at the Australia Telescope Compact Array (ATCA). The aim was to search for (CO)-C-12(1-0) emission in these systems and test the millimetre capabilities of CABB for performing spectral line observations at high redshifts. We show that the stable band and enhanced velocity coverage of CABB, combined with hybrid array configurations, provide the ATCA with excellent 7-mm capabilities that allow reliable searches for the ground transition of CO at high redshifts. In this paper we explicitly discuss the calibration procedures used to reach our results. We set a firm upper limit to the mass of molecular gas in MRC 2104-242 (z = 2.5) of M-H2 <2 x 10(10) (alpha(x)/0.8) M-circle dot. For MRC 0943-242 (z = 2.9) we derive an upper limit of M-H2 <6 x 10(10) (alpha(x)/0.8) M-circle dot. We also find a tentative 3 sigma CO detection in the outer part of the giant Ly alpha halo that surrounds MRC 0943-242. The 30-33 GHz radio continuum of MRC 2104-242 and MRC 0943-242 is reliably detected. Both radio sources show a spectral index of alpha approximate to -1.5 between 1.4 and 30 GHz, with no evidence for spectral curvature within this range of frequencies.

Original languageEnglish
Pages (from-to)655-664
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Volume415
Issue number1
DOIs
Publication statusPublished - Jul-2011

Keywords

  • techniques: interferometric
  • galaxies: active
  • galaxies: high-redshift
  • galaxies: individual: MRC 0943-242
  • galaxies: individual: MRC 2104-242
  • galaxies: ISM
  • ULTRALUMINOUS INFRARED GALAXIES
  • STAR-FORMING GALAXIES
  • GALACTIC GAMMA-RAYS
  • HIGH-REDSHIFT
  • MOLECULAR GAS
  • SUBMILLIMETER GALAXIES
  • LUMINOSITY FUNCTION
  • INTERSTELLAR-MEDIUM
  • NUCLEAR ACTIVITY
  • CARBON-MONOXIDE

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