| Issue |
A&A
Volume 496, Number 1, March II 2009
|
|
|---|---|---|
| Page(s) | 45 - 50 | |
| Section | Extragalactic astronomy | |
| DOI | https://doi.org/10.1051/0004-6361:200810876 | |
| Published online | 20 January 2009 | |
New CO detections of lensed submillimetre galaxies in A2218: probing molecular gas in the LIRG regime at high redshift *,**
1
Argelander-Institut für Astronomie, Auf dem Hügel 71, 53123 Bonn, Germany e-mail: knudsen@astro.uni-bonn.de
2
Institut de Radio Astronomie Millimétrique (IRAM), 300 rue de la Piscine, Domaine Universitaire de Grenoble, St. Martin d'Hères 38406, France
3
Laboratoire d'Astrophysique de Marseille, OAMP, Université Aix-Marseille & CNRS, 38 rue F. Joliot-Curie, 13388 Marseille Cedex 13, France
4
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
Received:
28
August
2008
Accepted:
25
November
2008
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. 
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 
and 
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
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 
Jy km s-1 and a line width of
km s-1. From this a gas mass of 
is
derived and a star formation efficiency of 440 
/
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 
Jy km s-1 and a line width of 
km s-1. From
this a gas mass of 
is derived and a star
formation efficiency of 1000 / is estimated. For
SMMJ163556, the CO(4–3) is undetected within the redshift range 
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 
for both galaxies is
consistent with the 
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.
Key words: galaxies: evolution / galaxies: high-redshift / galaxies: ISM / galaxies: starburst
© ESO, 2009
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