Resolving the physical scale of star formation in a lensed galaxy at z=2.5

  • Sept. 11, 2017, 2:00 pm US/Central
  • Traci Johnson, University of Michigan

Clumpy substructure in galaxies 1<z<3 is prevalent and forms from gravitational instabilities in the disk as cold gas accretes from the intergalactic medium. These clumps are the launching points of outflows from massive stars, and will merge over time to build up the exponential disks of today’s galaxies. Even with HST, the highest spatial resolution we can achieve at these redshifts is ~1 kpc, and we expect much of the substructure is unresolved. Gravitational lensing breaks down this observational barrier by amplifying the observed sizes of galaxies. I will be presenting my work using the combined power of HST and lensing to resolve the structure of SGAS J1110+6459, a clumpy star-forming galaxy at z=2.481 lensed by a galaxy cluster at z=0.659. We have developed an innovative forward-modeling technique to model the clumpy structure of the galaxy in the source plane, which allows us to effectively deconvolve the source galaxy with the so-called “lensing PSF” arising from asymmetric shear and the instrument PSF. We are able to resolve scales for star forming clumps on the order of 40 pc (HWHM) and recover clumps as small as 10 pc. With our model and exquisite HST imaging, we have measure precise star formation rates on a clump-by-clump basis, confirming the hypothesis of constant star formation surface density from scales of 1 kpc down to the scales of the clumps we measure.