Mapping the Clumpy Structures within Submillimeter Galaxies using Laser-Guide Star Adaptive Optics Spectroscopy

TL;DR

This study uses laser-guide star adaptive optics spectroscopy to spatially resolve the clumpy star-forming regions in high-redshift submillimeter galaxies, revealing complex kinematics and merger signatures that challenge the disk galaxy model.

Contribution

First integral-field spectroscopic observations of high-redshift SMGs with LGS-AO, showing detailed clumpy structures and kinematics inconsistent with simple disk models.

Findings

SMGs host high star-formation rate surface densities similar to local extreme sources.

Extended H-alpha emission over 4-16 kpc indicates large-scale intense activity.

Large velocity offsets suggest merging systems rather than ordered disks.

Abstract

We present the first integral-field spectroscopic observations of high-redshift submillimeter-selected galaxies (SMGs) using Laser Guide Star Adaptive Optics (LGS-AO). We target H-alpha emission of three SMGs at redshifts z~1.4-2.4 with the OH-Suppressing Infrared Imaging Spectrograph (OSIRIS) on Keck. The spatially-resolved spectroscopy of these galaxies reveals unresolved broad H-alpha line regions (FWHM>1000 km/s) likely associated with an AGN and regions of diffuse star formation traced by narrow-line H-alpha emission (FWHM<500 km/s) dominated by multiple Halpha-bright stellar clumps, each contributing 1-30% of the total clump-integrated H-alpha emission. We find that these SMGs host high star-formation rate surface densities, similar to local extreme sources, such as circumnuclear starbursts and luminous infrared galaxies. However, in contrast to these local environments, SMGs appear to be undergoing such intense activity on significantly larger spatial scales as revealed by extended H-alpha emission over 4-16 kpc. H-alpha kinematics show no evidence of ordered global motion as would be found in a disk, but rather large velocity offsets (~few x 100 km/s) between the distinct stellar clumps. Together with the asymmetric distribution of the stellar clumps around the AGN in these objects, it is unlikely that we are unveiling a clumpy disk structure as has been suggested in other high-redshift populations of star-forming galaxies. The SMG clumps in this sample may correspond to remnants of originally independent gas-rich systems that are in the process of merging, hence triggering the ultraluminous SMG phase.