Title Unbiased survey of submm galaxies: line survey 210-275 GHz Pi S.Guilloteau Time 180 hrs 1.1.4: Name -- Unbiased survey of submm galaxies -- -- Part 4 -- Authors: S.Guilloteau 2. Science goal: -- (Generic Science Scope from C.Carilli) -- The discovery of the IR background, and the SCUBA/MAMBO population of dusty, star forming galaxies at high redshift, has transformed our understanding of galaxy formation. It is now clear that a significant fraction (of order 50%) of star formation in the cosmos occurs in galaxies that are heavily obscured by dust, and that this fraction may rise with redshift, possibly corresponding to the formation of spheroidal galaxies in active starbursts. One highly uncertain aspect of the study of submm galaxies is their redshift distribution. Optical redshifts remain problematic for the majority of such sources, and can be misleading due to possible mis-identifications. -- (specific part) An important way to study the history of galaxy formation is to perform an unbiased redshift survey. We propose a unbiased, high sensitivity survey over a 4x4' area of the sky. This survey consists in a 4 main parts, and 2 or 3 complementary observations which are discussed in separate proposals: - Part 1) Continuum survey at 1 mm to reach 0.1 mJy point source sensitivity at the 5 sigma level. - Part 2) Combined line and continuum survey at 3 mm, down to 7.5 microJy at the 5 sigma level. - Part 3) Pointed continuum survey at 650 GHz towards sources detected in Part 1), down to 0.4 mJy at the 5 sigma level - Part 4) Line survey of the 210-275 GHz frequency band, down to 50 microJy for the 8 GHz bandwidth, with some angular resolution (0.4") in order to provide dynamical masses and lens corrections for the detectable sources. The fraction of sources found in Part 1 to be detected in Part 4 is unknown, but should be high (perhaps 50 -- 80 %). The complementary observations include: high resolution imaging to identify lenses and derive dynamical masses, and observations of other lines such as HCN or CI. This proposal covers Part 4). In Part 4), we propose to cover completely in space the same area as covered in Part 1), and in frequency the range 210 to 274 GHz. The frequency coverage can be done in 8 tunings of the Band 6 receivers. We propose to achieve a continuum sensitivity (averaged over the total 64 GHz) of 50 microJy at 5 sigma all over the 4x4' field. Such a field requires about 90 pointings at each frequency tuning (70 at 210 GHz, 110 at 270 GHz). An integration time of 2 hours per pointing (all tunings included) is required to reach this sensitivity level, leading to a total time of 8 days to perform the program. The continuum part of this survey duplicates Part 1: all sources detected in Part 1 will be detected in Part 4. However, Part 4 also allows detection of the CO lines from the sources. Because of the overlap with Part 1, it is conceivable to perform Part 4 with some angular resolution. For this excercise, we assume an angular resolution of 0.4", already better than that of the best images obtained today (July 2003). The continuum brightness sensitivity corresponds to 1 mK (1 sigma) at this angular resolution. Statistics on the strength of the CO lines redshifted to such frequencies are still too scarce to predict a detection rate. The brightness sensitivity of the instrument is then 0.05 K (1 sigma) for 50 km/s resolution. This is well below the typical line strength of CO in nearby galaxies. Even accounting for additional beam dilution, we would thus expect a large number of detections. The highest redshift objects may escape detection, since the high J CO lines may no longer be significantly excited. Conducted as such, Part 4 would allow to obtain sizes of most (but probably not all) of the sources detected in Part 1, as well as dynamical masses for the brighter objects. Lensing correction for the brightest sources may also be possible, as the angular resolution will help in building a first order lens model for the brightest sources. 3. Number of sources: 4. Coordinates: 4.1. Any 4.2. Moving target: no 4.3. Time critical: no 5. Spatial scales: 5.1. Angular resolution: 0.4" 5.2. Range of spatial scales/FOV: scales < 1" , FOV 4x4' 5.3. Single dish: no 5.4. ACA: no 5.5. Subarrays: no 6. Frequencies: 6.1. Receiver band: Band 6 -- 210 to 274 GHz 6.2. Lines and Frequencies 8 adjacent tunings 6.3. Spectral Resolution (km/s) 50 6.4. Bandwidth or spectral coverage: 8 GHz 7. Continuum flux density: 7.1. Typical value: 0.05 - 2 mJy 7.2. Continuum peak value: 4 mJy 7.3. Required continuum rms: 0.01 mJy 7.4. Dynamic range in image: < 100:1 8. Line intensity: 8.1. Typical value: 8.2. Required rms per channel: 8.3. Spectral dynamic range: 9. Polarization: no 10. Integration time per setting: 2 hours per pointing center, shared between 8 tunings, 90 pointings 11. Total integration time for program: Part 4): 180 hours ************************************************************************ Review Pierre Cox: this programme in four parts proposes to explore a 4x4 arcmin^2 field in order to study the submm galaxy population in both the dust and line emission. A few 100-300 sources will be detected providing a census of the population together with first indications on their properties (redshifts, infrared luminosities, gas excitation, and dynamical masses). The time estimates are correct and the overall strategy is robust. Note that in 1.1.2, the current CO detections of submm galaxies indicate that the CO fluxes are about 1-2 Jy km/s for 1.3 mm continuum flux densities of 1-3 mJy rather than the 5-10 mJy which are indicated and which correspond to the 850 microns flux densities. Also at the expected sensitivities, one could perhaps start to detect species other than CO such as HCN which is typically 10 times weaker than CO. -------------------------------------------------- Review v2.0: 1.1.4 Recent exciting reports on the detections of redshifted [CII] 158um emission suggest that this program will allow us to detect CII from many of sources, if there are any SMGs lying in the redshift range of 6 to 8. A minor revision on the time estimation. If 2 hours integration will be shared by 8 tunings (i.e., 900 sec for each setup), a line sensitivity (rms) of 0.5 mJy per 50 km/s channel (or 0.07 K for 0".4 resolution) will be achieved. About 2000 sec integration will be required to achieve 0.05 K rms, which is stated in the text. The total integration time for this program will be around 400 hours in this case.