Spatially Resolved Spectroscopy of Submillimeter Galaxies at z ≃ 2

Abstract

We present near-infrared integral-field spectroscopic observations targeting Hα in eight submillimeter galaxies (SMGs) at z = 1.3-2.5 using the Very Large Telescope/Spectrograph for Integral Field Observations in the Near Infrared, obtaining significant detections for six of them. The star formation rates derived from the Hα emission are ∼100 M _⊙ yr^-1, which account for only ∼20%-30% of the infrared-derived values, thus suggesting that these systems are very dusty. Two of these systems present [N II]/Hα ratios indicative of the presence of an active galactic nucleus. We mapped the spatial distribution and kinematics of the star-forming regions in these galaxies on kiloparsec scales. In general, the Hα morphologies tend to be highly irregular and/or clumpy, showing spatial extents of ∼3-11 kpc. We find evidence for significant spatial offsets, of ∼0.″1-0.″4 or 1.2-3.4 kpc, between the Hα and the continuum emission in three of the sources. Performing a kinemetry analysis, we conclude that the majority of the sample is not consistent with disk-like rotation-dominated kinematics. Instead, they tend to show irregular and/or clumpy and turbulent velocity and velocity dispersion fields. This can be interpreted as evidence for a scenario in which these extreme star formation episodes are triggered by galaxy-galaxy interactions and major mergers. In contrast to recent results for SMGs, these sources appear to follow the same relations between gas and star-forming rate densities as less luminous and/or normal star-forming galaxies.

Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program IDs 088.A-0452 and 090.A-0464.