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
Abstract
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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- November 2012
- DOI:
- 10.1111/j.1365-2966.2012.21900.x
- arXiv:
- arXiv:1209.5741
- Bibcode:
- 2012MNRAS.427..688L
- Keywords:
-
- gravitational lensing: strong;
- galaxies: high-redshift;
- galaxies: star formation;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 16 pages, 9 figures, 2 tables, accepted for publication in MNRAS