Resolved spectroscopy of gravitationally lensed galaxies: global dynamics and star-forming clumps on ~100pc scales

TL;DR

This study uses adaptive optics-assisted integral field spectroscopy of gravitationally lensed galaxies to analyze their dynamics and star-forming regions at high spatial resolution, revealing evolution in clump properties with redshift.

Contribution

It provides detailed kinematic and star formation data on high-redshift lensed galaxies at unprecedented spatial scales, combining new observations with previous data.

Findings

59% of galaxies are consistent with rotating discs

Star-forming clumps range from 60pc to 1kpc in size

Clump luminosities increase with redshift, driven by gas-rich disc fragmentation

Abstract

We present adaptive optics-assisted integral field spectroscopy around the Ha or Hb 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 z = 1-4. Thanks to gravitational magnification of 1.4 - 90x by foreground clusters, effective spatial resolutions of 40 - 700 pc are achieved. The magnification also allows us to probe lower star formation rates and stellar masses than unlensed samples; our target galaxies feature dust-corrected SFRs derived from Ha or Hb emission of 0.8 - 40Msol/yr, and stellar masses M* ~ 4e8 - 6e10 Msol. All of the galaxies have velocity gradients, with 59% consistent with being rotating discs and a likely merger fraction of 29%, with the remaining 12% classed as 'undetermined.' We extract 50 star-forming clumps with sizes in the range 60pc - 1kpc from the Ha (or Hb) maps, and find that their surface brightnesses and their characteristic luminosities 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.