EDP Sciences
Free Access
Volume 434, Number 3, May II 2005
Page(s) 819 - 825
Section Cosmology (including clusters of galaxies)
DOI https://doi.org/10.1051/0004-6361:20042034
Published online 18 April 2005

A&A 434, 819-825 (2005)
DOI: 10.1051/0004-6361:20042034

Molecular gas in a z $\mathsf{\sim 2.5}$ triply-imaged, sub-mJy submillimetre galaxy typical of the cosmic far-infrared background

J.-P. Kneib1, 2, 3, R. Neri4, I. Smail5, A. Blain2, K. Sheth2, P. van der Werf6 and K. K. Knudsen6

1  Observatoire Midi-Pyrénées, CNRS-UMR5572, 14 avenue E. Belin, 31400 Toulouse, France
    e-mail: jean-paul.kneib@oamp.fr
2  Caltech-Astronomy, MC105-24, Pasadena, CA 91125, USA
3  OAMP, Laboratoire d'Astrophysique de Marseille, traverse du Siphon, 13012 Marseille, France
4  IRAM, 300 rue de la Piscine, 38640 Saint Martin d'Hères, France
5  Institute for Computational Cosmology, University of Durham, South Road, Durham DH1 3LE, UK
6  Leiden Observatory, PO Box 9513, NL - 2300 RA Leiden, The Netherlands

(Received 21 September 2004 / Accepted 10 January 2005)

We present the results of observations from the Plateau de Bure IRAM interferometric array of the submillimetre (submm) galaxy SMMJ16359+6612 lying at z=2.516 behind the core of the massive cluster A 2218. The foreground gravitational lens produces three images with a total magnification of 45 of this faint submm galaxy, which has an intrinsic submm flux of just $f_{850~\mu{\rm
m}}=0.8$ mJy - placing it below the confusion limit of blank-field surveys. The substantial magnification provides a rare opportunity to probe the nature of a distant sub-mJy submm-selected galaxy, part of the population which produces the bulk of the cosmic far-infrared background at submm wavelengths. Our observations detect the CO(3-2) line in all three images, as well as the CO(7-6) line and the dust continuum at 1.3 mm for the brightest image but only at a 3$\sigma$ level. The velocity profile of the CO(3-2) line displays a double-peak profile which is well fit by two Gaussians with FWHM of 220 km s-1 and separated by 280 km s-1. We estimate the dynamical mass of the system to be ~1.5 $\times$ $10^{10}~M_\odot$ and an H2 gas mass of 4.5 $\times$ $10^9~M_\odot$. We identify a spatial offset of ~1'' between the two CO(3-2) velocity components, again benefiting from the magnification due to the foreground lens, modeling of which indicates that the offset corresponds to just ~3 kpc in projection at z=2.516. The spatial and velocity properties of these two components are closely related to features detected in previously published H$\alpha$ spectroscopy. We propose that this source is a compact merger of two typical Lyman-break galaxies with a maximal separation between the two nuclei of about 3 kpc, although a dusty disk explanation is not excluded. This system is much less luminous and massive than other high-redshift submillimetre galaxies studied to date, but it bears a close similarity to similarly luminous, dusty starburst resulting from lower-mass mergers in the local Universe.

Key words: gravitational lensing -- cosmology: observations -- galaxies: clusters: individual: A2219 -- galaxies: high-redshift -- infrared: galaxies -- galaxies: individual: SMM J16359+6612

SIMBAD Objects

© ESO 2005

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.