We use cookies to ensure that we give you the best experience on our website. You can change your cookie settings at any time. Otherwise, we'll assume you're OK to continue.

Durham University

Department of Physics

Staff profile

Publication details for Professor Ian Smail

Livermore, R.C., Jones, T., Richard, J., Bower, R.G., Ellis, R.S., Swinbank, A.M., Rigby, J.R., Smail, I., Arribas, S., Rodriguez Zaurin, J., Colina, L., Ebeling, H. & Crain, R.A. (2012). Hubble Space Telescope Hα imaging of star-forming galaxies at z ≃ 1–1.5 evolution in the size and luminosity of giant H ii regions. Monthly notices of the Royal Astronomical Society 427(1): 688-702.

Author(s) from Durham


We present Hubble Space Telescope/Wide Field Camera 3 narrow-band imaging of the Hα emission in a sample of eight gravitationally lensed galaxies at z = 1–1.5. The magnification caused by the foreground clusters enables us to obtain a median source plane spatial resolution of 360 pc, as well as providing magnifications in flux ranging from ∼10× to ∼50×. This enables us to identify resolved star-forming H ii regions at this epoch and therefore study their Hα luminosity distributions for comparisons with equivalent samples at z ∼ 2 and in the local Universe. We find evolution in the both luminosity and surface brightness of H ii regions with redshift. The distribution of clump properties can be quantified with an H ii region luminosity function, which can be fit by a power law with an exponential break at some cut-off, and we find that the cut-off evolves with redshift. We therefore conclude that ‘clumpy’ galaxies are seen at high redshift because of the evolution of the cut-off mass; the galaxies themselves follow similar scaling relations to those at z = 0, but their H ii regions are larger and brighter and thus appear as clumps which dominate the morphology of the galaxy. A simple theoretical argument based on gas collapsing on scales of the Jeans mass in a marginally unstable disc shows that the clumpy morphologies of high-z galaxies are driven by the competing effects of higher gas fractions causing perturbations on larger scales, partially compensated by higher epicyclic frequencies which stabilize the disc.