Resolved spectroscopy of gravitationally lensed galaxies: Global dynamics and star-forming clumps on ~100 pc scales at 1 < z < 4

Abstract

We present adaptive optics-assisted integral field spectroscopy around the Hα or Hβ lines of 12 gravitationally lensed galaxies obtained with VLT/SINFONI,Keck/OSIRIS and Gemini/NIFS. We combine these data with previous observations and investigate the dynamics and star formation properties of 17 lensed galaxies at 1 < z<4. Thanks to gravitational magnification of 1.4-90 times by foreground clusters, effective spatial resolutions of 40-700 pc are achieved. The magnification also allows us to probe lower star formation rates (SFRs) and stellar masses than unlensed samples; our target galaxies feature dust-corrected SFRs derived from Hα or Hβ emission of ~0.8-40M<inf>⊙</inf> yr-1, and stellar masses M<inf>*</inf> ~ 4 × 108-6 × 1010 M<inf>⊙</inf>. All of the galaxies show velocity gradients, with 59 per cent consistent with being rotating discs and a likely merger fraction of 29 per cent, with the remaining 12 per cent classed as 'undetermined'. We extract 50 star-forming clumps with sizes in the range 60 pc-1 kpc from the Hα (or Hβ) maps, and find that their surface brightnesses, Σ<inf>clump</inf> and their characteristic luminosities, L<inf>0</inf>, evolve to higher luminosities with redshift. We show that this evolution can be described by fragmentation on larger scales in gas-rich discs, and is likely to be driven by evolving gas fractions.