Astronomy and Astrophysics, volume 434, 819-825 (2005/5-2)
Molecular gas in a z∼2.5 triply-imaged, sub-mJy submillimetre galaxy typical of the cosmic far-infrared background.
KNEIB J.-P., NERI R., SMAIL I., BLAIN A., SHETH K., VAN DER WERF P. and KNUDSEN K.K.
Abstract (from CDS):
We present the results of observations from the Plateau de Bure IRAM interferometric array of the submillimetre (submm) galaxy SMM J16359+6612 lying at z=2.516 behind the core of the massive cluster A2218. 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 f850µm=0.8mJy - 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 1.3mm 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 220km/s and separated by 280km/s. We estimate the dynamical mass of the system to be ∼1.5x1010M☉ and an H2 gas mass of 4.5x109M☉. 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 ∼3kpc 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 3kpc, 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.
gravitational lensing - cosmology: observations - galaxies: clusters: individual: A2219 - galaxies: high-redshift - infrared: galaxies - galaxies: individual: SMM J16359+6612
p.820: MS 0451-05 is a misprint for MS 0451.6-0305 = ClG 0451-03. Table 1: components SMM 1-A, 1-B, 1-C = [KVK2004] SMM-A, B, C in SIMBAD.
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