Title Weak lensing using ALMA Pi A. Blain Time 100 hrs 1. Name of program and authors Weak lensing using ALMA Andrew Blain 2. One short paragraph with science goal(s) Gravitational lensing by large-scale structure in the Universe produces systematic distortions in the shapes of galaxies at moderate and high redshifts (by about 0.1-1% for z>0.2). These distortions can be used to map the distribution of dark matter along the line of sight to the lensed object. Currently, this effect is detected statistically with samples of over 10,000 galaxies detected in optical survey fields at least 10 square arcmin in extent. Although ALMA will have exquisite spatial resolution, it will not be able to cover large enough fields to match this work. The ALMA archive would allow this science to be pieced together in field observed for other deep science investigations. There is however, a possible unique niche for ALMA to study weak lensing, along with the astrophysics of gas emission from galaxies at moderate redshifts. By imaging disk galaxies that are close to each other on the sky (separated by an arcmin or less), and by measuring their rotation fields very accurately the distortion can perhaps be detected (Blain 2002 ApJ 570 L54). The most promising way to probe this should be to detect the CO(3-2) line from z~0.5, at which there should be a significant amount of excited gas present, and yet the distance is such that the galaxy is neither too small nor too faint. z~0.5 line-emitting galaxies may also be important for galaxy evolution science. This project may be possible in parallel. 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) 1 trial pair of z~0.5 spiral galaxies separated by up to about 1 arcmin on sky (perhaps pre-selected from a deep ALMA survey region). Program could be extended, combining examples in an interconnected web to build up a map of the distortion 1 arcmin at a time. 4. Coordinates: 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) Could be anywhere near ALMA latitude in dec. 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) None 5. Spatial scales: 5.1. Angular resolution (arcsec): Angular resolution (arcsec): 0.03-0.1" at 230 GHz. Best possible resolution is essential to resolve the rotation curve 5.2. Range of spatial scales/FOV (arcsec): (optional: indicate whether single-field, small mosaic, wide-field mosaic...) 0.03"=10". Pair of single fields. 5.3. Required pointing accuracy: (arcsec) 1 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) N/A 6.2. Stand-alone ACA: no/beneficial/required No 6.3. Cross-correlation of 7m ACA and 12m baseline-ALMA antennas: no/beneficial/required Possibly, as it would help sensitivity a little, which is required to be excellent; but, owing to lack of mosaicking, it'll have no benefit for imaging quality. 6.4. Subarrays of 12m baseline-ALMA antennas: yes/no No. Sensitivity crucial. 7. Frequencies: 7.1. Receiver band: Band 3, 4, 5, 6, 7, 8, or 9 6 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.) CO(3-2) redshifted to 230GHz 7.3. Spectral resolution (km/s): 7.4. Bandwidth or spectral coverage (km/s or GHz): 1-2 km/s 8. Continuum flux density: 8.1. Typical value (Jy): (take average value of set of objects) (optional: provide range of fluxes for set of objects) 0.1mJy 8.2. Required continuum rms (Jy or K): N/A - line observation 8.3. Dynamic range within image: Not a problem. Bright nearby objects will be avoided (from 7.1 and 7.2, but also indicate whether, e.g., weak objects next to bright objects) 8.4. Calibration requirements: absolute ( 1-3% / 5% / 10% / n/a ) repeatability ( 1-3% / 5% / 10% / n/a ) relative ( 1-3% / 5% / 10% / n/a ) 10% 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) 0.4 Jy km/s integrated over 300 km/s, i.e 1.3 mJy line flux. Point by point probably a 10 km/s wide line. 9.2. Required rms per channel (K or Jy): Approx. 0.13mJy to give 100-sigma on whole line. 9.3. Spectral dynamic range: Modest - 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%. 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): 0.13 mJy. RMS in 2 km/s channel in 1 hr is 0.93 mJy, so 51 hours. 2 pointings, 100 hours. Corresponding brightness sensitivity is 1.2 K at 0.05" resolution. 12. Total integration time for program (hr): 100 hrs on a carefully considered target pair of z~0.5 galaxies 13. Comments on observing strategy : (optional) (e.g. line surveys, Target of Opportunity, Sun, ...):