Journal Article

<i>Hubble Space Telescope</i> Hα imaging of star-forming galaxies at <i>z</i> ≃ 1–1.5: evolution in the size and luminosity of giant H <span class="smallCaps">ii</span> regions

R. C. Livermore, T. Jones, J. Richard, R. G. Bower, R. S. Ellis, A. M. Swinbank, J. R. Rigby, Ian Smail, S. Arribas, J. Rodriguez-Zaurin, L. Colina, H. Ebeling and R. A. Crain

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 427, issue 1, pages 688-702
Published in print November 2012 | ISSN: 0035-8711
Published online November 2012 | e-ISSN: 1365-2966 | DOI:
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

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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.

Keywords: gravitational lensing: strong; galaxies: high-redshift; galaxies: star formation

Journal Article.  9761 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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