Paper detail

A Magnified View of the Kinematics and Morphology of RCSGA 032727-132609: Zooming in on a Merger at z=1.7

We present a detailed analysis of multi-wavelength HST/WFC3 imaging and Keck/OSIRIS near-IR AO-assisted integral field spectroscopy for a highly magnified lensed galaxy at z=1.70. This young starburst is representative of UV-selected star-forming galaxies (SFG) at z~2 and contains multiple individual star-forming regions. Due to the lensing magnification, we can resolve spatial scales down to 100pc in the source plane of the galaxy. The velocity field shows disturbed kinematics suggestive of an ongoing interaction, and there is a clear signature of a tidal tail. We constrain the age, reddening, SFR and stellar mass of the star-forming clumps from SED modelling of the WFC3 photometry and measure their H-alpha luminosity, metallicity and outflow properties from the OSIRIS data. With strong star formation driven outflows in four clumps, RCSGA0327 is the first high redshift SFG at stellar mass <10^10 M_sun with spatially resolved stellar winds. We compare the H-alpha luminosities, sizes and dispersions of the star-forming regions to other high-z clumps as well as local giant HII regions and find no evidence for increased clump star formation surface densities in interacting systems, unlike in the local Universe. Spatially resolved SED modelling unveils an established stellar population at the location of the largest clump and a second mass concentration near the edge of the system which is not detected in H-alpha emission. This suggests a picture of an equal-mass mixed major merger, which has not triggered a new burst of star formation or caused a tidal tail in the gas-poor component.