The Big Picture
The figure below illustrates a typical spectral energy distribution of an Ultra-Compact HII region (red curve). The distinctive shape is the product of two emission processes: thermal radiation from warm dust (the 'hump') and thermal free-free radio emission from ionised gas (the 'plateau').
CORNISH is the only survey to image ionised gas in interstellar medium with coverage and resolution (1.5 arcsec) comparable to the surveys below.
The IPHAS survey of the H alpha line and neighbouring continuum is currently being carried out on the 2.5 m Isaac Newton Telescope. This will provide complementary optical views of the ionised gas that will allow the extinction to be measured to compact nebular sources.
A deep JHK survey of the Galactic Plane was completed in 2012 as part of the UK Infrared Deep Sky Survey (UKIDSS) programme. This has a limiting magnitude of 18 - 19 and is thus about one hundred times deeper than the 2MASS survey as well as being about three times higher spatial resolution. It enables unprecedented systematic large-scale studies of young clusters and stellar populations.
The GLIMPSE survey at 4-8 microns was the original motivation for CORNISH and the l=10o to 65o region defines the radio survey area. The depth and resolution is revolutionising our view of star forming regions and evolved stars as unveiled by their hot dust emission. The MIPSGAL survey is also providing longer wavelength data at 24 and 70 microns that allow luminosities to be estimated and earlier stages of star formation to be investigated.
Complementary high resolution far-IR data comes from the latest generation of satellite surveys: HERSCHEL. Observations are now complete and provide the flux data to measure accurate luminosities for star forming regions and evolved sources seen in GLIMPSE. Members of the CORNISH team are involved in the Hi-Gal Key Programme for a HERSCHEL Galactic Plane survey.
The cool dust emission has been probed by the ATLASGAL project on the APEX telescope. This survey has mapped over 400 square degrees at λ=870μm in the inner Galaxy, with a uniform sensitivity of a few solar masses at 1 kpc distance. Selected regions of the Galactic plane will be imaged to a deeper level by the JCMT Legacy Survey using the SCUBA2 camera on the James Clerk Maxwell Telescope. The survey is led by Toby Moore (LJMU) and includes other members of the CORNISH team.
The molecular gas in over half of the GLIMPSE region has been mapped in detail by the BU-FCRAO Galactic Ring Survey. This gives kinematic information on the molecular gas including the kinematic distances to all embedded sources.
These signposts of the early stages of massive star formation have been systematically surveyed by Arecibo in part of the northern plane that is covered by CORNISH. A survey of the Galactic plane for methanol masers using a multi-beam receiver has been completed on the Parkes telescope and now covers the full CORNISH region.
The atomic component of the ISM is being examined by the VLA H I survey. In addition to setting the context for molecular cloud formation it importantly allows the ambiguity in the kinematic distances to be solved in most cases.