Observational constraints on galaxy properties in the first four billion years

Identifying the first galaxies that formed, their ubiquity and basic properties (such as masses and star formation rates) remains one of the key challenges for observational astrophysics in the next decade.  The galaxies were likely to be responsible for the bulk of the ionising radiation that resulted in the reionisation around redshift z~8–10 and so studying their basic properties has defined many of the science drivers for the construction of the next generation ground- and space-based telescopes (e.g., James Webb Space Telescope (JWST) and E-ELT).

MUSE BV(I+Ly-alpha) colour image of the  cluster core of RCS 0224 at z=0.9 generated from a ~6hr observation with VLT.  The highly amplified, giant red arc at z=4.9 can clearly be seen, but we also identify a number of lensed Ly-alpha emitters between z=4.8--6.6 (Ly-alpha images of ten of these are shown in the outer panels). Most of these emitters do not have continuum counterparts in the HST imaging to an unlensed limit  of mi=29.5 (see also  Bacon et al. 2015).

As these galaxies evolve into the era immediately after reionisation, they also become critically important for galaxy formation models suggest this is the epoch when most of the stars in the massive spheroids and bulges of today's spirals were formed.  One successful route to identifying intrinsically faint galaxies at these redshifts is to exploit the deep gravitational potential of massive foreground galaxy clusters which magnify the images of distant galaxies that serendipitously lie behind them.  This phenomenum provides two significant advantages over unlensed studies. First, the flux of the background source is increased, making it possible to detect intrinsically faint, high-redshift galaxies that would otherwise be undetectable.  Second, the image of the background galaxy is magnified, allowing us to spatially resolve structures which would otherwise require the next generation of telescopes.

Our programme exploits gravitational lensing by massive galaxy clusters to spectroscopically identify and study star-forming galaxies seen through massive clusters, as they emerge from reionisation and then measure the dynamics of lensed star-forming galaxies at z~3--5 to study the growth of their disks, as well as measuring the properties of the star-forming clumps within the ISM in these structures on scales approaching ~100pc. This observational program exploits observations with the Hubble Space Telescope, multi-IFU KMOS and MUSE integral field spectrographs, and ALMA.

The staff members working on this project are Renske Smit, Mark Swinbank, Ian Smail and Richard Bower.