Publication details for Professor Ian SmailKneib, J.-P., Neri, R., Smail, I., Blain, A., Sheth, K., van der Werf, P. & Knudsen, K.K. (2005). Molecular gas in a z ∼ 2.5 triply-imaged, sub-mJy submillimetre galaxy typical of the cosmic far-infrared background. Astronomy & astrophysics 434(3): 819-825.
- Publication type: Journal Article
- ISSN/ISBN: 0004-6361 (print), 1432-0746 (electronic)
- DOI: 10.1051/0004-6361:20042034
- Keywords: Gravitational lensing, cosmology: observations, galaxies: clusters: individual: A2219, galaxies: high-redshift, infrared: galaxies, galaxies: individual: SMM J16359+6612
- Further publication details on publisher web site
- Durham Research Online (DRO) - may include full text
Author(s) from Durham
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 f850~μm=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 3σ 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 × 1010~M_⊙ and an H2 gas mass of 4.5 × 10^9~M_⊙. 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 Hα 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.