1. Name of program and authors Spectral line survey in high-z molecular absorption systems Wiklind T., Combes F. 2. One short paragraph with science goal(s) Molecular line absorption in front of a radio continuum sources is a very powerful technique to detect even small quantities of interstellar molecules in external galaxies. It is also complementary to the emission technique: it samples molecules in low excitation state, that would never have been detected in emission. For galaxies at large distances, molecular absorption lines offer the only way to observe rare molecular species. This has been proven through the detection of many molecular species (about 20) at redshifts z=0.25-0.89, using pre-ALMA instrumentation. The sensitivity is largely determined by the strength of the background continuum source, meaning that a large collecting area is the main issue (the sources themselves remain point sources even at high angular resolution). The completion of ALMA makes it possible to make a spectral line survey to an unprecedented level of the molecular interstellar medium in distant galaxies. We propose to carry on a complete molecular line survey (using the available frequency bands) towards 3 remarkable sources at different redshifts, in order to probe the interstellar chemistry and its evolution. Many different molecular species, such as CCH, C3H2, HOC+, SiC, deuterated species etc. are expected to be detected. A complete spectral line survey will allow a detailed comparison of the interstellar chemistry of these three distant sources with that of the Milky Way ISM. In addition, the survey will include several molecular lines which for Milky Way gas are not possible to observe from the ground; such as the ground transition of LiH and water vapor, as well as the elusive molecular oxygen. Noise rms limits have been chosen such that over most of the available frequencies, absorption lines with depth of <1% of the continuum flux can be detected at 5sigma. Over some frequency intervals and for the stronger sources, this limit is set as low as 0.15%. This corresponds to column densities of CO and HCO+ of 910E12 and 1E10, respectively. It is possible that the density of lines will be large, possibly limiting the detections of individual lines through confusion over certain frequency intervals. We propose to do a systematic survey in the 4 priority bands Band 3: 86 GHz - 116 GHz Band 6: 211 GHz - 275 GHz Band 7: 275 GHz - 370 GHz Band 9: 602 GHz - 720 GHz for 3 absorption systems already observed with IRAM and SEST, and visible from Chajnantor: PKS1830-211 (z=0.89) PKS1413+135 (z=0.25) CenA (z=0) 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) 3 sources PKS1830-211, PKS1413+135 and CenA (note that PKS1830-211 gives two sight lines through the intervening galaxy, separated by ~6 kpc). 4. Coordinates: 4.1. Rough RA and DEC (e.g., 30 sources in Taurus, 30 in Oph, 20 in Cha, 30 in Lupus) 1830-211, 1413+135, 1325-43 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 three 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, 6, 7 and 9 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) This is a line survey. We will cover the entire extent of each band falling within atmospheric windows of sufficient transparency. 6.3. Spectral resolution (km/s): 2 - 3 km/s 6.4. Bandwidth or spectral coverage (km/s or GHz): Band 3: 2x1 GHz = 2 GHz, 1024 channels, ~3 km/s (17 tunings for entire band) Band 6: 4x1 GHz = 4 GHz, 512 channels, ~2.5 km/s (18 tunings for entire band) Band 7: 8x1 GHz = 8 GHz, 256 channels, ~3.3 km/s (13 tunings for entire band) Band 9: 8x1 GHz = 8 GHz, 256 channels, ~1.8 km/s (16 tunings for entire band) 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) Variable radio sources, Minimum 0.2 Jy, average around 1 Jy Estimated continuum fluxes used in time calculations: PKS1413 PKS1830 Cen A Band 3: 0.2 2.0 6.0 Band 6: 0.1 1.0 3.0 Band 7: 0.05 0.5 2.0 Band 9: 0.02 0.2 1.0 7.2. Required continuum rms (Jy or K): The continuum rms is defined as the limit in percentage of the source continuum flux where an absorption line can be detected at 5sigma. The values in parenthesis are the actual channel to channel noise rms: PKS1413 PKS1830 Cen A Band 3: 1 (0.4 mJy) 0.1 (0.4 mJy) 0.05 (0.6 mJy) Band 6: 3 (6.0 mJy) 0.5 (1.0 mJy) 0.15 (0.9 mJy) Band 7: 5 (0.5 mJy) 1 (1.0 mJy) 0.5 (2.0 mJy) Band 9: 50 (2.0 mJy) 15 (6.0 mJy) 5 (10.0 mJy) 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) in average 0.02 Jy (but can be much lower) 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 the integration time is given as hour (per tuning/total time). This done for each band and source. Note that PKS1413 will only be observed using band 3 and 6. PKS1413 PKS1830 Cen A Band 3: 1.4/24 1.0/17 0.5/9 Band 6: 1.5/27 1.2/22 1.0/18 Band 7: 5.2/0 1.3/17 0.3/13 Band 9: 8.4/0 1.0/16 0.5/8 11. Total integration time for program (hr): 171 hours + over-head 12. Comments on observing strategy (e.g. line surveys, Target of Opportunity, Sun, ...): (optional) This is a molecular line line survey. The observations are self-calibrated using the central continuum source. The pointing accuracy needs to be than 5". Very good weather conditions are only required for high frequency observations. A homogeneous sensitivity is necessary in order to allow a comparative abundances study of weak lines. The estimated time can be decreased by lowering the target sensitivity or only choosing PKS1830-211 and Cen A as targets. However, given the uniqueness of this data set, we would prompt for a significant time allocation. *************************************************************************** Review Pierre Cox: This is a proposal which aims at probing the molecular content of the interstellar medium along the line of sight towards three high-z continuum sources by exploring systematically the entire frequency range of the four Bands. The time estimate is correct, and the total amoutn of time is not much as compared to the potential scientific outcome of this programme. It should be noted that many more such sources with lower continuum levels will be doable with ALMA. This is the scientific aim of the next programme 1.3.2. where the idea is to search for CO and HCO+ in absorption in order to determine the redshift of the absorbing high-z gas. Here as well the time estimates and the observing strategy are correct.