Title A deep search for new molecular absorption line systems Pi T. Wiklind Time 260 hrs 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 60 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. Since we want to discover absorption systems with unknown redshift, 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, where absorption lines with depth of 5% of the continuum flux can be detected at 5sigma. In band 4, covering z=0.09-2.69, and in particular the z=0.34-0.54 gap in band 3, the limits have been set to 5% at 5sigma as well. To enable a larger number of sources to have complete redshift coverage, these detection limits could be raised to 10% at 5sigma. 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) 50 flat spectrum radio continuum sources 4. Coordinates: Source list can be selected such that there is any desired spread in RA and DEC. 4.1. Rough RA and DEC (e.g., 30 sources in Taurus, 30 in Oph, 20 in Cha, 30 in Lupus) 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) 4.2. Moving target: yes/no (e.g. comet, planet, ...) NO 4.3. Time critical: yes/no (e.g. SN, GRB, ...) NO 4.4. Scheduling constraints: (optional) 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...) 5.3. Required pointing accuracy: (arcsec) 5" 6. Observational setup 6.1. Single dish total power data: no/beneficial/required NO Observing modes for single dish total power: (e.g., nutator switch; frequency switch; position switch; on-the-fly mapping; and combinations of the above) Nutator 6.2. Stand-alone ACA: no/beneficial/required NO 6.3. Cross-correlation of 7m ACA and 12m baseline-ALMA antennas: no/beneficial/required NO 6.4. Subarrays of 12m baseline-ALMA antennas: yes/no NO (possible for stronger sources, but not considered here) 7. Frequencies: 7.1. Receiver band: Band 3, 4, 5, 6, 7, 8, or 9 3 + 4 7.2. 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 band 4 (125-162 GHz), the entire redshift range is covered. 7.3. Spectral resolution (km/s): 5 km/s 7.4. Bandwidth or spectral coverage (km/s or GHz): Band 3: 2x1 GHz = 2 GHz Band 4: 2x1 GHz = 2 GHz 8. Continuum flux density: 8.1. Typical value (Jy): 5 sources with fluxes 50 - 100 mJy 20 sources with fluxes 100 - 200 mJy 35 sources with fluxes >200 mJy (take average value of set of objects) (optional: provide range of fluxes for set of objects) 8.2. 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 band 4. The sources are assumed to have 50mJy, 100mJy and 200mJy at 90GHz, with a spectral index S_nu \propto S_nu^-0.7 (see ALMA Memo #543). The required exposure time has been calculated for each tuning for band 3 and 4, where the continuum rms is defined as the limit in percentage of the source continuum flux where an absorption line with a depth of 5% of the continuum can be detected at 5sigma. 8.3. Dynamic range within image: (from 7.1 and 7.2, but also indicate whether, e.g., weak objects next to bright objects) n/a 8.4. Calibration requirements: absolute ( 1-3% / 5% / 10% / n/a ) 10% repeatability ( 1-3% / 5% / 10% / n/a ) 5% relative ( 1-3% / 5% / 10% / n/a ) 5% 9. Line intensity: 9.1. Typical value (K or Jy): (take average value of set of objects) (optional: provide range of values for set of objects) See 8.2 9.2. Required rms per channel (K or Jy): See 8.2 9.3. Spectral dynamic range: 100 9.4. Calibration requirements: absolute ( 1-3% / 5% / 10% / n/a ) repeatability ( 1-3% / 5% / 10% / n/a ) relative ( 1-3% / 5% / 10% / n/a ) 10. Polarization: yes/no (optional) No 10.1. Required Stokes parameters: 10.2. Total polarized flux density (Jy): 10.3. Required polarization rms and/or dynamic range: 10.4. Polarization fidelity: 10.5. Required calibration accuracy: 11. Integration time for each observing mode/receiver setting (hr): Band 3 50mJy at 90GHz : 2.2 hours + overhead 100mJy : 1.7 hours + overhead 200mJy : 1.9 hours + overhead Band 4 50mJy at 90GHz : 4.2 hours + overhead 100mJy : 2.9 hours + overhead 200mJy : 2.9 hours + overhead 12. Total integration time for program (hr): 260 hours + overhead (10 sources at 50mJy, 20 sources at 100mJy 20 sources at 200mJy) This estimate is based on a bandwidth of 2GHz. If 4GHz is available, with the required velocity resolution, the exposure times will be significantly lower (almost factor 2). 13. Comments on observing strategy : (optional) (e.g. line surveys, Target of Opportunity, Sun, ...): The 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 v2.0: quasarexgal_2 = 1.3.2. A deep search for new molecular absorption line systems Wiklind T., Combes F. Ok.