5966( 22) - 10/08/96 11:45 - [ 0] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 5966 Version: 22 Check-in Date: 08-Oct-1996 11:42:42 1.Proposal Title: The Origin of the Alignment Effect: Spectroscopy and Imaging of Radio Galaxies at z~1.2 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle AGN GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Mark Dickinson SPACE TELESCOPE SCIENCE INSTITUTE CoI: Arjun Dey University of California, Berkeley N CoI: Hyron Spinrad University of California, Berkeley N CoI: Wil van Breugel Institute of Geophysics and Planetary N Physics, Lawrence Livermore National CoI: S. George Djorgovski California Institute of Technology N CoI: Peter Eisenhardt Jet Propulsion Laboratory N ------------------------------------------------------------------------------------ 6. Abstract In Cycle 4, we have obtained deep images of 3C 324 (z=1.206) and 3C 368 (z=1.132), two prototypical examples of the radio galaxy ``alignment effect,'' wherein the rest --frame UV continuum closely shares the orientation of the FR II radio source. These remarkable images reveal complex structures comprised of compact clumps and filaments distributed over tens of kpc. This unprecedentedly detailed view has raised many new questions concerning the origin(s) of this UV light. Polarimetric measurements suggest that much of this continuum may be scattered radiation from the central AGN, but we have no working model to explain all of the observed properties. We propose to conduct a detailed dissection of 3C368, combining WFPC2 emission line and UV continuum imaging with FOS spectroscopy to determine the physical conditions in the emission line gas and continuum substructures on kiloparsec scales. With such data, we can strongly constrain proposed models for the aligned continuum. Our Cycle 4 imaging and (for 3C 368, polarimetry), together with deep Keck spectroscopy and infrared imaging (all in hand), recommends this galaxy as an ideal target for such a detailed investigation. By thoroughly investigating 3C368, we hope to firmly establish the origin and the physics underlying the spectacular morphologies of high redshift radio galaxies. ------------------------------------------------------------------------------------ Observations Description ------------------------ WFPC2 LRF Imaging: The O II emission line is redshifted to 7944 Angstroms for 3C 368. The spatial distribution of the emission line gas at the resolution probed by HST is of course unknown at the present time, making it impossible to determine OII surface brightnesses in advance. We estimate our exposure times by using the integrated OII flux determined from our slit spectroscopy and older ground--based OII images, and roughly dividing it among the various continuum components seen in the HST images. We have also examined the emission line substructure visible in the Keck spectra for this purpose. It is entirely possible and even likely, however, that there may be extended line emission not associated with the continuum, so our calculations are necessarily estimates. Using the LRF transmission (~75\\\\\\\\ throughput plotted in the WFPC2 Instrument Handbook, and the collecting area of the telescope, we estimate an OII count rate of 7.5 e^-/sec from 3C 368 (L_OII = 8.2 * 10^-15 erg/sec). Assuming nominal values for gain, readout noise and dark current, a compact but resolved (~ 0".2 FWHM) clump of OII emission with 2% of this total flux would be detected on the WFC with a S/N~7 in a single 2100 sec orbit (without CR-- SPLIT). Readout and dark noise limitations makes low--surface brightness emission much harder to detect, however. With the 8--orbit exposure planned here, we should be able to detect diffuse O II emission with a surface brightness of a few tenths of the average for the radio galaxy as a whole when integrating over 1 arcsec^2 regions on the WFC. FOS Spectroscopy: Since we do not yet know the distribution of the emission line gas, we wish to schedule the LRF observations far enough in advance of the spectroscopy to be able to use these as ``acquisition images'' to guide aperture placement with the FOS. At present, we intend to observe at two pointings within 3C 368, aiming for regions where our Keck spectra indicate substantially different ionization states are found within the gas. The LRF data will trace the low--ionization gas and provide a measure of the flux in that line within our spectroscopic apertures. Careful comparison of the OII images to our 2-D Keck spectra should give us a close idea where the high--ionization gas is located. The FOS apertures specified in this Phase I proposal would be modified if necessary depending on what we learn from the emission line images; at present, the are designed under the assumption that the OII emission comes primarily from compact regions closely associated with the continuum we observe in our Cycle 4 data. In order to obtain ``pure,'' spatially isolated measurements, we will use FOS/RD with at least two grating settings (G270H and G400H) to measure redshifted Ly-alphaLambda1216, NVLambda1240, CIVLambda1549, HeIILambda1640, and CIIILambda1909, and possibly with a third setting (G570H) to measure CIILambda2326, NeIVLambda2424, and MgIILambda2800. Naturally, we cannot definitively estimate in advance the fluxes or line ratios for lines unobservable from the ground such as Ly Alpha, CIV, and He II. We do so here by simply assuming the canonical ratios for the ``average'' radio galaxy of McCarthy (1993), scaled to the line fluxes measured in our Keck spectrum, and assuming that each aperture/pointing we attempt will be chosen to encompass ~10% of the total emission. Since we already know from the ground--based data that line ratios are positionally variable in these objects, this is clearly an oversimplification, but we believe the numbers allow for a reasonable margin of uncertainty. For example, assuming ``standard'' radio galaxy ratios for LyAlpha:CIV:OII of 8.5:1:1, and assuming an OII flux of 5.5 * 10^-16 erg s^-1 cm^-2 per targeted aperture we obtain count rates of 1.5/sec for Ly Alpha and 0.18/sec for CIV. Assuming a CIV broad line--width of 1350kms for CIV (5 diodes with G400H) and assuming nominal values for the dark count rate, we should achieve S/N=17 integrated over the line in one 2100s orbit. With G270H, one orbit should should be sufficient to detect faint broad wings in Ly Alpha and to reach S/N~10 in NV. We therefore request single orbit exposures in each setting and at each pointing. Exact aperture sizes will be ascertained based on the LRF emission line images. WFPC2 Continuum Imaging: Our target is too faint for continuum spectroscopy. We therefore request time to obtain continuum images through bandpasses other than those we already have in hand in order to measure the colors of each galaxy subcomponent. For 3C 368, our existing polarimetry data provides a total--flux image in F555W. We request an image of 3C 368 through F850LP to provide a long wavelength baseline -- F850LP samples rest--frame wavelengths entirely redward of 4000Angstroms. Our 3C 368 polarimetry was done on the WFC, and we will do that for the new broad--band images as well, primarily to increase our sensitivity to the lower--surface-- brightness continuum which is found in many regions of that galaxy. We have estimated our exposure times using the fluxes in our Cycle 4 data and integrated colors obtained from our spectroscopy and verified by older ground-- based imaging photometry. Again, if clump-- to--clump colors vary, this integrated color for the whole galaxy will not be entirely appropriate, but our exposures should provide useful S/N for all regions of interest unless the colors are truly extreme compared to the mean for the galaxy. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: , ------------------------------------------------------------------------------------ 5966( 22) - 10/08/96 11:45 - [ 1] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 3C368 GALAXY,RADIO RA=18H 2M 45.60S +/- B1950 Z = V = 21.5 GALAXY,HIGH Z GAL 0.5",DEC=11D 1' 13.8" +/- 0.5" 1.132 2 3C368-STAR- GALAXY,RADIO RA=18H 2M 44.80S +/- B1950 V = 15.12+/-0.05 MIDPT GALAXY,HIGH Z GAL,STAR 0.5",DEC=11D 0' 50.0" +/- 0.5" Comments: The target position is midway between 3C 368 and the offset star to be used for FOS spectroscopy acquisition. With HST pointed at this position, both objects will fit easily within one WF CCD, and can be imaged to obtain accurate relative astrometry. 3 3C368-OFFSET STAR RA=18H 5M 04.1507S +/- J2000 V = 15.12+/-0.05 0.03S,DEC=11D 0' 43.0" +/- 0.5" B-V = 1.01+/-0.05 Comments: Offset star for FOS spectroscopy acquisition. The coordinates should be moderately accurate in the guide star reference frame, but we will use a 3-stage acquistion to ensure that we can acquire the offset star even if the coordinates are fairly inaccurate. 4 3C368-POS1 GALAXY,RADIO RA-OFF=2.3405S+/- 0.007S,DEC- J2000 Z = V = 23.78 GALAXY,HIGH Z GAL,KNOT, OFF=33.896"+/- 0.1",FROM 3 1.132 Comments: The offsets used here have been computed from the WFPC2 early acquisition images in F814W. 5 3C368-POS2 GALAXY,RADIO RA-OFF=2.3048S+/- 0.007S,DEC- J2000 Z = V = 24.10 GALAXY,HIGH Z GAL,KNOT, OFF=31.758"+/- 0.1",FROM 3 1.132 Comments: The offsets used here have been computed from the WFPC2 early acquisition images in F814W. 5966( 22) - 10/08/96 11:45 - [ 2] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: These WFPC2 LRF images are a NECESSARY PREREQUISITE to obtaining the FOS spectroscopy. They will be used to determine the distribution of the emission line gas of which we will be obtaining spectra. Visit 03 (the FOS observations) are ON HOLD until Visits 01 and 02 have been completed. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 3C368 WFPC2 IMAGE LRF LRF 7944 CR-SPLIT=NO 1 2000 S EXPAND POS TARG -0.25, -0.25 ------------------------------------------------------------------------------------------------------------------------------------ 2 3C368 WFPC2 IMAGE LRF LRF 7944 CR-SPLIT=NO 3 2100 S EXPAND POS TARG -0.25, -0.25 ------------------------------------------------------------------------------------------------------------------------------------ 3 3C368 WFPC2 IMAGE LRF LRF 7944 CR-SPLIT=NO 3 2100 S EXPAND POS TARG 0.25,0.25 ------------------------------------------------------------------------------------------------------------------------------------ 5966( 22) - 10/08/96 11:45 - [ 3] Visit: 02 Visit Requirements: On Hold Comments: Additional Comments: These WFPC2 broad band images are a NECESSARY PREREQUISITE to obtaining the FOS spectroscopy. They will be used to determine distribution of red continuum light in the galaxy, for comparison with the LRF narrow band data. In addition, they will assist in measuring the spatial offset to be used for the FOS spectroscopy. Visit 03 (the FOS observations) are ON HOLD until Visits 01 and 02 have been completed. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 3C368 WFPC2 IMAGE WFALL F850LP CR-SPLIT=NO 1 2600 S MAX DUR 100% EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 2 3C368 WFPC2 IMAGE WFALL F850LP CR-SPLIT=NO 2 2800 S MAX DUR 100% EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 3 3C368 WFPC2 IMAGE WFALL F850LP CR-SPLIT=NO 3 2800 S MAX DUR 100% EXPAND POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 4 3C368 WFPC2 IMAGE WFALL F850LP CR-SPLIT=NO 1 1800 S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 5 3C368-STAR- WFPC2 IMAGE WF3 F814W CR-SPLIT=NO 1 8 S MIDPT Comments: This is a short exposure to be used for accurately measuring the offset from the FOS acquisition star to the radio galaxy. In 5 seconds, the offset star should remain unsaturated. ------------------------------------------------------------------------------------------------------------------------------------ 6 3C368-STAR- WFPC2 IMAGE WF3 F814W CR-SPLIT=NO 1 300 S EXPAND MIDPT Comments: Longer exposure for measuring offset from the FOS acquisition star to the radio galaxy. The offset star will be saturated. ------------------------------------------------------------------------------------------------------------------------------------ 5966( 22) - 10/08/96 11:45 - [ 4] Visit: 03 Visit Requirements: BETWEEN 01-OCT-96 AND 01-DEC-96 ORIENT 60D TO 80D On Hold Comments: Additional Comments: FOS spectroscopy of extended emission line gas. ORIENT is required to keep sky aperture for PRISM observation away from nearby faint galaxy. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 3C368-OFFSE FOS/RD ACQ/PEA 4.3 MIRROR SCAN-STEP-X=3.3,SCAN-STEP-Y=1.23, 1 1.0 S ONBOARD ACQ FOR 2 T K SEARCH-SIZE-X=2,SEARCH-SIZE-Y=6 Comments: Initial acquisition of offset star ------------------------------------------------------------------------------------------------------------------------------------ 2 3C368-OFFSE FOS/RD ACQ/BIN 4.3 MIRROR 1 6.5 S ONBOARD ACQ FOR 3 T ARY Comments: Second level acquisition of offset star ------------------------------------------------------------------------------------------------------------------------------------ 3 3C368-OFFSE FOS/RD ACQ/PEA 0.3 MIRROR SCAN-STEP-X=0.11,SCAN-STEP-Y=0.11 1 1.0 S ONBOARD ACQ FOR 4-8 T K ,SEARCH-SIZE-X=5,SEARCH-SIZE-Y=5 Comments: Fine acquisition of offset star ------------------------------------------------------------------------------------------------------------------------------------ 4 3C368-POS2 FOS/RD ACCUM 1.0 G270H 1 2400 S Comments: Lyman alpha spectrum of south/central clump ------------------------------------------------------------------------------------------------------------------------------------ 5 3C368-POS2 FOS/RD ACCUM 1.0 G400H 1 4800 S Comments: CIV-HeII-CIII] spectrum of south/central clump ------------------------------------------------------------------------------------------------------------------------------------ 6 3C368-POS1 FOS/RD ACCUM 1.0 G400H 1 2400 S Comments: CIV-HeII-CIII] spectrum of northern clump ------------------------------------------------------------------------------------------------------------------------------------ 7 3C368-POS1 FOS/RD ACCUM 1.0 G270H 1 1200 S Comments: Lyman alpha spectrum of northern clump ------------------------------------------------------------------------------------------------------------------------------------ 8 3C368-POS1 FOS/RD ACCUM 1.0-PAI PRISM STEP-PATT=OBJ-SKY 1 3600 S R-A Comments: Prism spectrum of northern clump and offset sky position ------------------------------------------------------------------------------------------------------------------------------------ 5966( 22) - 10/08/96 11:45 - [ 5] Summary Form for Proposal 5966 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 FOS/RD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ACQ/PEAK ACQ/BINARY ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO SEARCH-SIZE-Y=6 SEARCH-SIZE-Y=5 STEP-PATT=OBJ-SKY ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category AGN ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements EXPAND POS TARG -0.25,-0.25 EXPAND POS TARG 0.25,0.25 MAX DUR 100% EXPAND MAX DUR 100% EXPAND POS TARG 0.5,0.5 BETWEEN 01-OCT-96 AND 01-DEC-96 ORIENT 60D TO 80D ONBOARD ACQ FOR 2 ONBOARD ACQ FOR 3 ONBOARD ACQ FOR 4-8 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements LRF F850LP F814W MIRROR G270H G400H PRISM ------------------------------------------------------------------------------------------------------------------------------------ Target Names 3C368 3C368-STAR-MIDPT 3C368-OFFSET 3C368-POS2 3C368-POS1 ------------------------------------------------------------------------------------------------------------------------------------