Volume 522, November 2010
|Number of page(s)||4|
|Published online||29 October 2010|
Letter to the Editor
Discovery of an extremely bright submillimeter galaxy at z = 3.93
Observatoire de Paris, LERMA, CNRS, 61 Av. de l’Observatoire, 75014
2 Institut d’Astrophysique de Paris, UMR 7095, CNRS, UPMC Univ. Paris 06, 98bis Boulevard Arago, 75014, Paris, France
3 Argelander Institute for Astronomy, University of Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
4 Laboratoire AIM Paris-Saclay, CEA/IRFU/SAp - CNRS, Université Paris Diderot, 91191 Gif-sur-Yvette Cedex, France
Accepted: 13 October 2010
Serendipitously we have discovered a rare, bright submillimeter galaxy (SMG) with a flux density of 30 ± 2 mJy at λ = 1.2 mm, using MAMBO2 at the IRAM 30-m millimeter telescope. Although no optical counterpart is known for MM18423+5938, we were able to measure the redshift z = 3.92960 ± 0.00013 from the detection of CO lines using the IRAM Eight MIxer Receiver (EMIR). In addition, by collecting all available photometric data in the far-infrared and radio to constrain its spectral energy distribution, we derive the FIR luminosity 4.8 × 1014/mL⊙ and mass 6.0 × 109/m M⊙ for its dust, allowing for a magnification factor m caused by a probable gravitational lens. The corresponding star-formation rate is 8.3 × 104/mM⊙/yr. The detection of three lines of the CO rotational ladder, and a significant upper limit for a fourth CO line, allow us to estimate an H2 mass of between 1.9 × 1011/m M⊙ and 1.1 × 1012/m M⊙. The two lines C I and C I were clearly detected and yield a [C I]/[H2] number abundance of between 1.4 × 10-5 and 8.0 × 10-5. Upper limits are presented for emission lines of HCN, HCO+, HNC, H2O, and of other molecules. The moderate excitation of the CO lines is indicative of an extended starburst, and excludes the dominance of an AGN in heating this high-z SMG.
Key words: galaxies: evolution / galaxies: high-redshift / galaxies: ISM / infrared: galaxies / submillimeter: galaxies
© ESO, 2010
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