This second-generation instrument will be an invaluable tool to investigate the physical and environmental processes which shape the formation and evolution of galaxies over cosmic time. In fact, its high multiplex capability (up to 24 sources observed simultaneously) is ideal to follow-up large statitistical samples of distant galaxies.
The synergy between multi-wavelength imaging surveys and KMOS deep, near-IR integral field spectroscopy will be essential to map the variations in star-formation history, spatially resolved star-formation properties, merger rates and dynamical masses of galaxies at z>1 across a wide range of environments, allowing us to delineate the mass assembly history of galaxies as a function of redshift.
KMOS is being designed and built by a consortium including:
The instrument design employs 24 configurable arms that position pick-off mirrors at user-specified locations in the Nasmyth focal plane. The light collected by these pick-off arms is then fed to 24 advanced image slicer integral-field units (IFUs) and then dispersed by three cryogenic grating spectrometers which generate 14x14 spectra for each of the 24 independent sub-units. The patrol field of the pick-off arms is 7.2 arcmin in diameter, which is the diameter of the unvignetted field at the VLT Nasmyth focus. Each IFU has a square field of view of 2.8x2.8 arcsec, large enough to allow local sky-subtraction for compact high-redshift targets, doubling the effective multiplex gain over systems which require beam-switching.
In addition to observing multiple individual sources, KMOS has the capability for integral field mapping of contiguous areas (~1.0 sq. arcmin) in a 24-point dither pattern. This mode would be useful for very extended sources or blank-field surveys for emission-line sources (e.g. Ly alpha at z>7). The spectral resolution of R~3500 provides velocity resolution for studies of low-mass objects and is optimal for OH-avoidance in the J & H bands. Lower resolution modes are also possible and would allow simultaneous coverage of two adjacent bands.
The instrument has just completed formal acceptance testing prior to shipping release to Chile in July 2012. Commissioning work at the VLT site in Paranal is scheduled to start in September 2012. The UK-ATC has a major role in the KMOS project, being responsible, amongst others, for the construction of the cryostat, the robotic pick-off arms, the cable co-rotator and the final assembly and test of the complete instrument.
We have added information and pictures for some of the interesting details about the project on the KMOS updates and photos page.
For more information about KMOS please contact Michele Cirasuolo or visit the University of Durham KMOS (link opens in a new window) website.