Title A submm study of strong gravitational lenses Pi T. Wiklind Time 230 hrs 1. Name of program and authors A submm study of strong gravitational lenses Wiklind T. 2. One short paragraph with science goal(s) Strong gravitational lensing offers the possibility to indirectly image the gravitational potential of individual galaxies. Presently this is done using background AGNs, viewed either at optical/NIR wavelengths, or at radio wavelengths. The former case leads to point-like images and, hence, with few constraints on the shape of the lensing potential. The latter case often leads to partially resolved images of the background source. However, the intrinsic shape of the radio loud AGN remains unknown and effectively reduces the number of constraints that can be set on the lens. Dust continuum emission offers an advantage over both optical and radio wavelengths; it has a finite and resolvable distribution and its intrinsic shape, although unknown, is likely to be simple compared to radio jets. With present day instrumentation, it is not possible to reach the low flux levels associated with the extended dust emission, nor to reach the angular resolution needed. Another constraint on the shape of the lensing potential can be obtained from the relative flux ratios of two or more images of the same source point. However, this constraint is rarely usable due to different amount of obscuration along different line of sights in the case of optical imaging, and due to only partially resolved images at radio wavelengths. Observing at submm wavelengths alleviates the obscuration problem, and if sufficient angular resolution can be achieved, the images will be resolved to the extent that flux ratios will provide an additional constraint when solving for the lensing potential. Two projects are proposed: 1) Imaging of known gravitationally lensed radio loud AGNs with the aim of determining accurate positions and relative flux ratios of the lensed components. Lenses can be selected from optical and/or radio surveys. Typical flux levels are in the mJy range. Angular scales are 0.1 - 3 arcsec Number of sources ~ 10 2) High fidelity imaging of gravitational lenses, selected from optical and/or radio surveys, in order to image the lensed components of the host galaxy. Another source of targets is background galaxies strongly lensed by intervening cluster members. The aim is to constrain the total gravitational potential of the lens by resolving the images, determining the shape and location of the Einstein ring caused when parts of the host galaxy passes through the cusp. Typical flux levels are 25 microJy and up Angular scales are 0.1" - 1" Number of sources ~ 5 In addition, observations of CO lines in emission can be used to both determine the physical and chemical status of the gas in the background source and to constrain the lens modeling. However, this aspect of gravitational lensing will not be covered in this proposal as the instrumental parameters needs to be defined specifically for each individual case. Another issue will be searching for new gravitational lenses. Here one can target high redshift AGNs, which are not known to be lensed. The larger extent of the dust emission region could mean that the dust emission consists of multiple components while the AGN remains single, albeit magnified. This aspect is not covered in this proposal, as it will be a 'side product' of other surveys, in particular those concerning weak lensing. A short note on flux density estimates: The actual flux densities from 'typical' high redshift galaxies is essentially unknown at the present. An estimate of the observed flux in a 16 GHz wide band centered on 345 GHz of an unresolved galaxy with a FIR luminosity of 1E10 L_sun (integrated over 10-3000 micron) is : Dust temp z=2 z=4 z=6 K ----------------------------------------------------- 30 35 microJy 33 microJy 22 microJy 50 8 9 10 ----------------------------------------------------- The luminosity and flux density have been estimated using a modified blackbody curve B_nu(T_d) (1 - exp(-tau_nu), where tau_nu = (\nu/\nu_0)**b. The parameter b is set to 1.5 and \nu_0 to 10 microns. Parts of the emission will be magnified with factors >10, while other parts will experience magnification factors much smaller ~2. Hence, ALMA can easily detect unresolved lens components in this particular case, but will run into problems when resolving the emission. An exact time estimate is therefore not possible at the present, and needs to be done on a case-to-case basis. The FIR luminosity chosen for this example may be a conservative estimate for typical targets. It may also prove favorable to use band 9, both from an angular resolution point of view and for an increased sensitivity (basically for any type of dust SED). With this note in mind, the suggested programme is only preliminary and a final decision should await actual receiver performance details. The time estimate has been done in a very conservative manner. 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) 10 radio loud strongly gravitational lensed sources 2 strongly gravitationally lensed AGNs, both radio loud and radio quiet (possibly more sources if time estimate is over-conservative; see below). 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 a 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): Ranging from 0.1" to ~3" (see observing strategy below) 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 7 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) Band 7, continuum observation 6.3. Spectral resolution (km/s): None 6.4. Bandwidth or spectral coverage (km/s or GHz): Band 7, 16 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) 30 microJy - several mJy (due to magnification and resolved images). 7.2. Required continuum rms (Jy or K): 1) 25 microJy (radio loud AGNs) 2) 6 microJy (high fidelity imaging) 7.3. Dynamic range within image: (from 7.1 and 7.2, but also indicate whether e.g. weak objects next to bright objects) ~50-100 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) No 8.2. Required rms per channel (K or Jy): No 8.3. Spectral dynamic range: No 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): 1) Imaging of gravitationally lensed radio loud AGns: estimated rms needed ~50 (correct to 25 EvD) microJy, requiring ~ 0.25 hours per source. For an angular resolution of 0.1", this increases to ~25 hours. Not all lenses are likely to need 0.1" resolution. An estimate is therefore 10x0.25 + 3x25 = 100 hours. (this time estimate can be decreased significantly if a sufficient number of stronger radio loud lensed AGNs become available prior to 2011). 2) High fidelity imaging of lensed AGNs (not necessarily radio loud): estimated rms needed 10 microJy, requiring ~6 hours per source at an angular resolution of 1". At 0.3" the time increases to ~60 hours per source. With 2 sources in total the time amounts to ~130 hours. (If the flux densities are stronger, the same amount of time should/could be used to reach the target angular resolution of 0.1"). 11. Total integration time for program (hr): 230 hours + over-head 12. Comments on observing strategy (e.g. line surveys, Target of Opportunity, Sun, ...): (optional) Targets can be selected from known gravitational lenses. The number of available targets is likely to be significantly larger at the time when ALMA is fully operational than what is the case now. This will likely mean that targets can be chosen that have a FIR luminosity greater than the nominal (and conservative 1.E10 L_sun used here). This will decrease the estimated integration time considerably. Review Chris Carilli: he says he needs an rms of 50 uJy for radio loud AGN in continuum with band 7, and that this will take 0.25hrs. but I get an rms of 25 uJy in 0.25 hrs. in another place in proposal he says 25 uJy, so I guess 50 was just a typo. Comment Ewine: typo corrected to 25 uJy -------------------------------------------------- Review v2.0: 1.2.4 A submm study of strong gravitational lenses (Wiklind) Not revised since DRSP 1.1. Similar to 1.2.2. Scientifically OK, no need for ACA or ACA/12m array cross-correlation. Back then 230 h + overhead, probably similar now.