The e-MERLIN Legacy programme
Luminous Infra-Red Galaxy Inventory (LIRGI)
J. E. Conway (Onsala Space Observatory, Sweden) and M. A. Perez-Torres (IAA-CSIC, Granada, Spain)
Susanne Aalto (Onsala Space Observatory, Chalmers, Sweden), Antxon Alberdi (IAA, Granada, Spain), Phil Appleton (NASA Herschel Science Center, Caltech USA), Willem Baan (ASTRON, The Netherlands), Fabien Batejat (Onsala Space Observatory, Chalmers. Sweden), Rob Beswick (JBCA, Manchester), Luis Colina (DAMIR, Madrid, Spain), John Conway (Onsala Space Observatory, Chalmers, Sweden), Phil Diamond (JBCA, Manchester), Denise Gabuzda (University College Cork, Ireland), Simon Garrington (JBCA, Manchester), Rossa Hurley (Onsala Space Observatory, Chalmers Sweden), Hans-Rainer Klockner (Oxford), Carole Mundell (Liverpool, John Moores Univ), Ray Norris (CSIRO, Australia), Miguel Perez-Torres (IAA, Granada, Spain), Rodrigo Parra (Catolica Univ, Santiago, Chile), Ylva Pihlstrom (Univ of New Mexico, USA), Cristina Romero-Canizales (IAA, Spain), Jose-Maria Torrelles (CSIC-IEEC, Barcelona, Spain)
We propose legacy survey observations of 42 of the most luminous northern luminous infra-red galaxies selected from the IRAS revised Bright Galaxy Sample (Sanders et al. 2003). This survey will provide a high spatial resolution radio complement to legacy observations made with the NASA Great Observatories (GOALS program). Additionally it will itself provide legacy data to be combined with upcoming radio/millimetre/submm instruments. Our sample selects sources with L= log(Lir/Lsol) >11.4, which have sizes well matched to eMERLIN spatial resolution. The sample spans the range of FIR luminosities from the upper end of the Luminous Infra-Red Galaxies (LIRGs) to Ultra- Luminous Infra-Red Galaxies (ULIRGs), most of which are merging or post merger systems. Our local (<200 Mpc) targets have properties of area star formation densities, gas and radiation densities similar to star-forming galaxies a high redshift. A major goal of future radio/millimetre instruments is to use these high redshift objects to trace the starformation (and galaxy assembly) history of the universe. Achieving this goal reliably requires understanding the physics of similar local objects. Crucially it is important to understand how accurately radio continuum flux densities can be converted to Star Formation Rates (SFR). If for instance in the warm dense gas environments of (U)LIRGs) the stellar Initial Mass Functions is top-heavy, the calibration of SFR from star-formation tracers can be affected. Definite evidence for non-standard IMFs in extreme environments would also be an important input into understanding star-formation mechanisms in general.
Specific project goals are: (1) To map the size and morphology of diffuse radio emission in each source at two wavelengths (6 cm and 18 cm). These observations will give the best estimate at any waveband of the physical size of the starburst, trace the free-free absorption, look for the predicted upper limits on radio brightness, etc. (2) Use three epoch 6 cm observations on a 25 source subsample to detect powerful core-collapse radio supernovae (RSNe) in order to constrain the high mass star-formation rate and hence the IMF. (3) Make polarisation and rotation measure observations to constrain the magnetic field properties, in order to check whether B fields are weak and in equipartition with relativistic particles, or are strong and in equipartition with the thermal gas. (4) Systematically study the gas dynamics and physical conditions at high angular resolution by observing absorption/megamaser spectral line emission (e.g. HI and four OH lines at L-band and OH and H_2CO at C-band). (5) Check for lobe, jet and core structures consistent from embedded AGNs. (6) Establish a phenomenological sequence and time scale for the evolution of a nuclear starburst using the combined FIR, continuum, and spectral line information provided by this Legacy survey.
Our proposed observations will consist of an initial epoch (semester 1) of quasi-simultaneous observations at L- and C-band of all 42 objects with 5 hrs per source per frequency (total 410 hrs). This will be followed by two additional epochs spaced one year apart (in semesters 3 and 5) of 25 sources at C-band to search for RSNe (total 250 hrs). Hence the total time request is 660 hrs. Our proposal will leave an important legacy to the community: a uniformly observed sample of (U)LIRGs in the nearby universe, done in a timely way that will serve as a reference for future studies to be carried out with forthcoming instruments (ALMA, EVLA, LOFAR, Herschel etc).