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

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

Monthly Notices of the Royal Astronomical Society, Volume 427, Issue 1, pp. 688-702.

Advertised on:
11
2012
Number of authors
13
IAC number of authors
1
Citations
104
Refereed citations
94
Description
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.
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