Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009a%26a...496...45k&link_type=abstract
Astronomy and Astrophysics, Volume 496, Issue 1, 2009, pp.45-50
Astronomy and Astrophysics
Astrophysics
15
Galaxies: Evolution, Galaxies: High-Redshift, Galaxies:, Ism, Galaxies: Starburst
Scientific paper
Context: Submillimetre galaxies (SMGs) are distant, dusty galaxies undergoing star formation at prodigious rates. Recently there has been major progress in understanding the nature of the bright SMGs (i.e. S850~μ m > 5 mJy). The samples for the fainter SMGs are small and are currently in a phase of being built up through identification studies. Aims: We study the molecular gas content in the two SMGs, SMMJ163555 and SMMJ163541, at redshifts z=1.034 and z=3.187 with unlensed submillimetre fluxes of 0.4 mJy and 6.0 mJy. Both SMGs are gravitationally lensed by the foreground cluster Abell 2218. Methods: We used the IRAM Plateau de Bure Interferometer to obtain observations at 3 mm of the lines CO(2-1) for SMMJ163555 and CO(3-2) for SMMJ163541. Additionally, we obtained CO(4-3) observations for the candidate z=4.048 SMMJ163556 with an unlensed submillimetre flux of 2.7 mJy. Results: The CO(2-1) line was detected for SMMJ163555 at redshift 1.0313 with an integrated line intensity of 1.2±0.2 Jy km s-1 and a line width of 410±120 km s-1. From this a gas mass of 1.6×109 M_&sun; is derived and a star formation efficiency of 440 L_&sun;/M_&sun; estimated. The CO(3-2) line was detected for SMMJ163541 at redshift 3.1824, possibly with a second component at redshift 3.1883, with an integrated line intensity of 1.0±0.1 Jy km s-1 and a line width of 280±50 km s-1. From this a gas mass of 2.2×1010 M_&sun; is derived and a star formation efficiency of 1000 L_&sun;/M_&sun; is estimated. For SMMJ163556, the CO(4-3) is undetected within the redshift range 4.035-4.082 down to a sensitivity of 0.15 Jy km s-1. Conclusions: Our CO-line observations confirm the optical redshifts for SMMJ163555 and SMMJ163541. The CO-line luminosity L'_CO for both galaxies is consistent with the L_FIR-L'_CO relation. SMMJ163555 has the lowest far-infrared luminosity of all SMGs with a known redshift and is one of the few high-redshift LIRGs whose properties can be estimated prior to ALMA.
Based on observations obtained at the IRAM Plateau de Bure Interferometer (PdBI). IRAM is funded by the Centre National de la Recherche Scientifique (France), the Max-Planck Gesellschaft (Germany), and the Instituto Geografico Nacional (Spain). The three spectra cubes (FITS files corresponding to the maps of Fig. 2) are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/496/45
Kneib Jean Paul
Kraiberg Knudsen Kirsten
Neri Roberto.
van der Werf Paul P.
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