1. Name of program and authors A deep search for new molecular absorption line systems Wiklind T., Combes F. 2. One short paragraph with science goal(s) Observations of molecular absorption lines offer the only way to obtain detailed information of the physical and chemical parameters of the molecular interstellar medium in distant galaxies. The sensitivity is essentially only given by the strength of the background continuum source, independent of the distance. Four molecular absorption line systems at redshifts between z=0.25-0.89 have previously been detected using single dish telescope, and allowed a detailed study of the astrochemistry of these systems, including molecular species never before observed from the ground. In addition, since molecular absorption is biased towards diffuse and therefore excitationally cold gas, the observations have made it possible to measure the temperature of the Cosmic Microwave Background radiation at the redshift of the absorber. In order to make a comparative study of the chemical and physical status of the molecular gas at earlier epochs it is necessary to increase the number of known systems. Molecular absorption line systems are rare, about 100 times less common than damped Lyman-alpha systems. They are also difficult to detect since continuum fluxes of the background sources are relatively weak at mm/submm wavelenghts. Also, the mere presence of obscuration means that redshift information is lacking. This was the case for one of the known absorption systems and it was detected by the technique of frequency scanning, looking for absorption of high-opacity molecules such as CO and HCO+ (actually, the line first detected in this case turned out to be a HNC(2-1) line). By observing the frequency range 86-116 and 226-260 GHz, the entire redshift space is covered for CO and HCO+ lines. These are the lines with the highest opacities. In this project we propose a search for molecular absorption towards ~70 selected radio loud AGNs with mm continuum fluxes greater than 50mJy. The targets will be prioritized according to a few criteria which enhances the probability for the presence of obscuration; such as gravitational lensing (small impact parameter to the lens), suppressed soft X-ray flux, optically weak and indications of reddening. In order to circumvent the missing or uncertain redshift information, we will search for absorption over the entire redshift range using the technique of frequency scanning. Noise rms limits have been chosen such that band 3, which covers z=0-0.34 and z>0.54,m absorption lines with depth of 5% of the continuum flux can be detected at 5sigma. In band 6, covering z=0.34-0.54, the limits have been set to 10% at 3sigma in order to enable a large number of sources to have complete redshift coverage. With the velocity resolution given below, these limits corresponds to column densities of CO and HCO+ of 710E14 and 8E11 cm-2, respectively. 3. Number of sources (e.g., 1 deep field of 4'x4', 50 YSO's, 300 T Tauri stars with disks, ...; do NOT list individual sources or your "pet object", except in special cases like LMC, Cen A, HDFS) 60 flat spectrum radio continuum sources 4. Coordinates: 4.1. Rough RA and DEC (e.g., 30 sources in Taurus, 30 in Oph, 20 in Cha, 30 in Lupus) Source list can be selected such that there is any desired spread in RA and DEC. Indicate if there is significant clustering in a particular RA/DEC range (e.g. if objects in one particular RA range take 90% of the time) NO 4.2. Moving target: yes/no (e.g. comet, planet, ...) NO 4.3. Time critical: yes/no (e.g. SN, GRB, ...) NO 5. Spatial scales: 5.1. Angular resolution (arcsec): All targets are point sources for which the angular resolution does not really matter. 5.2. Range of spatial scales/FOV (arcsec): (optional: indicate whether single-field, small mosaic, wide-field mosaic...) Single field per source. 5.3. Single dish total power data: yes/no NO 5.4. ACA: yes/no NO 5.5. Subarrays: yes/no NO 6. Frequencies: 6.1. Receiver band: Band 3, 6, 7, or 9 Band 3 and 6 6.2. Lines and Frequencies (GHz): (approximate; do NOT go into detail of correlator set-up but indicate whether multi-line or single line; apply redshift correction yourself; for multi-line observations in a single band requiring different frequency settings, indicate e.g. "3 frequency settings in Band 7" without specifying each frequency (or give dummies: 340., 350., 360. GHz). For projects of high-z sources with a range of redshifts, specify e.g. "6 frequency settings in Band 3". Apply redshift correction yourself) The aim is redshifted CO and HCO+ lines. By using the entire frequency range of band 3 (86-116 GHz) and part of band 6 (226-260 GHz), the entire redshift range is covered. 6.3. Spectral resolution (km/s): Band 3: ~6 km/s Band 6: ~5 km/s 6.4. Bandwidth or spectral coverage (km/s or GHz): Band 3: 4x1 GHz = 4 GHz, 512 channels, ~6 km/s (9 tunings for entire band) Band 6: 8x1 GHz = 8 GHz, 256 channels, ~5 km/s (5 tunings for 226-260 GHz) 7. Continuum flux density: 7.1. Typical value (Jy): (take average value of set of objects) (optional: provide range of fluxes for set of objects) 10 sources with fluxes 50 - 100 mJy 30 sources with fluxes 100 - 200 mJy 30 sources with fluxes >200 mJy 7.2. Required continuum rms (Jy or K): We aim at being able to detect an absorption at 5sigma at 5% of the continuum level in band 3 and at 10% and 3sigma in band 6. For a source with a background continuum of 100 mJy this corresponds to a 1sigma noise rms of 1 mJy. The continuum rms is defined as the limit in percentage of the source continuum flux where an absorption line can be detected at 5sigma: 7.3. Dynamic range within image: (from 7.1 and 7.2, but also indicate whether e.g. weak objects next to bright objects) no imaging is needed. 8. Line intensity: 8.1. Typical value (K or Jy): (take average value of set of objects) (optional: provide range of values for set of objects) See 7.2 8.2. Required rms per channel (K or Jy): See 7.2 8.3. Spectral dynamic range: 100 9. Polarization: yes/no (optional) no 9.1. Required Stokes total intensity only 9.2. Total polarized flux density (Jy) N/A 9.3. Required polarization rms and/or dynamic range N/A 9.4. Polarization fidelity N/A 10. Integration time for each observing mode/receiver setting (hr): Below are integration times to reach a 5sigma rms of 5% of the background source continuum for band 3, and a 3sigma of 10% of the continuum in band 6. The targets are divided into approximately 10 sources with flux densities in the range 50-100 mJy, 30 sources with 100-200 mJy and 30 sources with 100-200 mJy. Flux 50 mJy band 3: 0.9h/tuning, 9 tunings/source, ~9 hours/source band 6: 1.0h/tuning, 5 tunings/source, ~5 hours/source Flux 100 mJy band 3: 0.2h/tuning, 9 tunings/source, ~1.8 hours/source band 6: 0.3h/tuning, 5 tunings/source, ~1.5 hours/source Flux 200 mJy band 3: 0.06h/tuning, 9 tunings/source, ~0.5 hours/source band 6: 0.07h/tuning, 5 tunings/source, ~0.4 hours/source Average total integration times : 50-100 mJy: 5 hours per source, total = 50 hours 100-200 mJy: 2 hours per source, total = 60 hours >200 mJy : 0.5 hours per source, total = 15 hours 11. Total integration time for program (hr): 125 hours + over-head 12. Comments on observing strategy (e.g. line surveys, Target of Opportunity, Sun, ...): (optional) Targets will be radio loud AGNs with one or more of the following indications of possible obscuration along the line of sight (either intervening or intrinsic) (i) optically weak or blank field, (ii) indication of reddening, (iii) gravitationally lensed, (iv) suppressed soft X-ray flux, (v) observed galaxy along the line of sight. The observations are self-calibrated using the background continuum source. The pointing accuracy needs to be than 5". *************************************************************************** Review Pierre Cox: This proposal is a complement to 1.3.1, in which the idea is to search for CO and HCO+ in absorption in weaker sources in order to determine the redshift of the absorbing high-z gas. The time estimates and the observing strategy are correct.