The KMOS Kinematic Survey (K2S)
The peak in the volume averaged star-formation rate in galaxies occurs in the redshift range z ~ 1-2. At this epoch, the star formation rate in typical galaxies is an order of magnitude higher than in the local Universe. This is the era when most of the stars (and also black holes) in the Universe were formed. The task is now to address "how" and "why" the Universe is so different.
A picture is emerging in which galaxy formation at this epoch is very different to that in the local Universe. Rather than the quiescent formation of stars that is the norm in today's Universe, violent episodes of star formation are dominated by the formation of super-star clusters. However, the origin of these differences is controversial: the conventional picture is that they are driven by an increase in the galaxy merger rate, but some recent theories have suggested that the difference is driven by the higher rate of gas accretion expected in the high-redshift Universe.
Addressing "how" and "why" requires us to look inside galaxies by resolving the motion of the stars and gas clouds within them (to understand their structure, whether they are chaotic mergers or rotating disks) and map the distribution of new stars and metals within these galaxies. These observations would in turn determine the dynamical state of galaxies and hence directly address the cause of their elevated star formation and so test the scenarios by which early systems mature into the regular galaxies we see today. To undertake such a study would require spatially-resolved spectroscopy of hundreds of faint galaxies, beyond the capabilities of standard instruments until the recent development of KMOS near-infrared multi-integral-field-unit (IFU) spectrograph. KMOS comprises 24 IFUs which are deployable across a 7.2-arcmin field of view. Each IFU has a 3×3 arcsecond field and the spectrograph can operate between 0.8 and 2.5um. KMOS was constructed by a UK-German consortium, led by Durham University, and is installed on UT1 of ESO's Very Large Telescope.
We plan to exploit KMOS to undertake a substantial survey of distant galaxies: the KMOS Kinematic Survey - K2S. K2S is a joint project between Durham and Oxford Universities, with contributions from the Advanced Technology Centre at the Royal Observatory Edinburgh. The project exploits the significant award of Guaranteed Time made to the KMOS consortium. The goal of K2S is to map the kinematics and structure of star-forming galaxies at z~1-2 (around half the age of the Universe) to investigate the processes responsible for the strong variation in star formation in the Universe over this time period.
Data from commissioning observations of K2S target galaxies obtained with KMOS in early 2013 are show in the figure. This illustrates that the instrument is capable of simultaneously measuring resolved velocity fields in large numbers of faint galaxies, providing a 20× multiplex advantage over previous facilities.
The K2S project expects to use around 40 nights of telescope time. K2S is coordinated by Richard Bower in Durham and Martin Bureau in Oxford and is the overall project is led in its initial stages by Ray Sharples (KMOS instrument PI). The survey is a collaboration between Richard Bower, Andy Bunker, Martin Bureau, Matt Jarvis, Ian Smail and Mark Swinbank, as well as associated postdocs (John Stott) and students.
Richard Bower, R.G.Bower [at] durham.ac.uk