6553( 6) - 04/22/96 13:53 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6553 Version: 6 Check-in Date: 22-Apr-1996 13:51:00 1.Proposal Title: Dissecting 3C 324: Anatomy of an Aligned Radio Galaxy at z = 1.206 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle AGN GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Mark Dickinson Space Telescope Science Institute CoI: Arjun Dey Kitt Peak National Observatory N CoI: Hyron Spinrad University of California, Berkeley N CoI: Wil van Breugel Institute of Geophysics and Planetary N Physics, LLNL ------------------------------------------------------------------------------------ 6. Abstract In Cycle 4, we obtained deep images of 3C324 (z=1.206), a prototypical example of the radio galaxy `alignment effect', wherein the spatial orientation of the rest- frame UV continuum emission is closely aligned with the major axis of the FRII radio source. In Cycle 5, we will obtain WFPC2 imaging polarimetry of 3C324 to map out the distribution of the scattering regions. In this Cycle, we propose to obtain WFPC2 emission line imaging, FOS emission line spectroscopy and WFPC2 UV continuum imaging of 3C324 in order to complete our detailed study of this object, and to finally understand the origin of its spectacular, aligned morphology. This target qualifies for such a detailed investigation because of existing deep HST imaging and Keck spectroscopy; the high resolution imaging capability and access to the vacuum ultraviolet provided by HST will allow us to obtain the data required to determine the physical properties of the continuum and emission line emitting regions and the physical mechanism responsible for the alignment effect. ------------------------------------------------------------------------------------ 6553( 6) - 04/22/96 13:53 - [ 2] Observations Description ------------------------ noindent WFPC2 LRF Imaging:\\\\\\\\\\\\\\\\ The O II emission line in 3C 324 is redshifted to 8223Angstrom, and is observable with the FR868N18 linear ramp filter. The total extent of the galaxy continuum is ~ 5", so that co--spatial OII emission should fit well within the ~10" patch of sky covered monochromatically by the LRF. The precise spatial distribution of the emission line gas at HST resolution is unknown in advance, making it impossible to determine OII surface brightnesses a priori. Our ground--based narrow-- band images and long slit spectra do not show evidence for much OII emission extending beyond the optical continuum, however, so we are encouraged to believe that the emission line gas will be highly clumped like the continuum. We estimate our exposure times by using the integrated OII flux determined from our 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. The integrated OII flux from 3C 324 is 2 * 10^-15 erg s^-1 cm^-2. Using the LRF transmission (~75\\\\\\\\\\\\\\\\% at these wavelengths), the WFPC2+OTA throughput plotted in the WFPC2 Instrument Handbook, and the collecting area of the telescope, we estimate that the total LRF count rate will be 1.53 e^-/sec integrated over the entire galaxy, or ~3700 e^- per 2400 second orbit. The observations will be read--noise limited, and we plan to use the WFC in order to maximize surface brightness sensitivity, and to take full--orbit exposures (i.e. without CR-- SPLIT). First, we consider a compact but resolved clump of OII emission with size typical of the continuum blobs in 3C 324 (0\\\\\\\\\\\\\\\\secspt3 FWHM, or 7 WFC pixels area). We assume nominal values for the gain, readout noise and dark current. An OII clump with 5\\\\\\\\\\\\\\\\% of the total galaxy flux, and with half of that flux (i.e. 2.5\\\\\\\\\\\\\\\\%) within a 7 pixel area, would be detected with S/N~5 in a single 2400 second orbit, and S/N~14 with the 8 orbits planned here. Diffuse, low surface--brightness emission is much more difficult to measure, however. If the OII is distributed over a total area of ~3 arcsec^2 (like the continuum), in 8 orbits we will detect emission with the average OII surface brightness at S/N~5 per WFC pixel. Diffuse emission with 10\\\\\\\\\\\\\\\\% of the average surface brightness can be detected with S/N~5 when averaged over an area of 1 arcsec^2. noindent FOS Spectroscopy:\\\\\\\\\\\\\\\\ Since we do not yet know the spatial 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 324, aiming for regions where our Keck spectra indicate substantially different ionization states are found, and using small FOS apertures (e.g. 0\\\\\\\\\\\\\\\\secspt5 or 0\\\\\\\\\\\\\\\\secspt3) to obtain ``pure,'' spatially isolated measurements. The LRF images will trace the low--ionization gas and provide a measure of the line flux within our spectroscopic apertures. 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. For each position, we will use FOS/RD to cover the spectrum from Ly Alpha in the UV to the red-- sensitivity limit of the instrument, using 3 grating settings (G270H, G400H and G570H) to observe NVLambda1240, CIVLambda1549, HeIILambda1640, CIIILambda1909, CIILambda2326, NeIVLambda2424, and MgIILambda2800. The LRF images will provide the OII flux within the same aperture. Since we cannot definitively predict the fluxes or line ratios for lines unobservable from the ground (e.g., Ly Alpha, CIV, and He II) we simply assume the canonical ratios for the ``average'' radio galaxy of McCarthy (1993), scaled to the line fluxes measured in our Keck spectrum. Each aperture/pointing will be chosen to encompass ~10\\\\\\\\\\\\\\\\% of the galaxy's line 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. Assuming ``standard'' radio galaxy ratios for LyAlpha:CIV:OII of 8.5:1:1, and assuming an OII flux of 2 * 10^-16 erg s^-1 cm^-2 per targeted aperture (i.e. 10\\\\\\\\\\\\\\\\% of the galaxy total for 3C 324), we obtain count rates of 0.54/sec for Ly Alpha and 0.07/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=10 integrated over the line in one 2400s orbit. With G270H, one orbit should should be sufficient to detect faint broad wings in Ly Alpha and to reach S/N~4 for NV. We therefore request single orbit exposures in each setting and at each pointing. Because we wish to use the small science apertures with FOS, acquisition overhead will be high. Our target is too faint for direct acquisition, and thus we must offset from a nearby star. Because WFPC2 images including this star are already available, a separate early acquisition image is not needed. We will use a four --stage peak--up procedure to acquire the offset star, which requires 50 or 61 minutes depending on the choice of (small) apertures. Thereafter, simple telescope offsets between the star and the target, and between blobs within the radio galaxy, will suffice and require little overhead. Altogether ~6 orbits are required for the science observations, plus ~60 minutes for the offset star acquisition, plus assorted overhead for guide star acquisition and the telescope offset, for a total of 8 orbits with the FOS. noindent WFPC2 Continuum Imaging:\\\\\\\\\\\\\\\\ 3C 324 is too faint for continuum spectroscopy with HST. We therefore request time to obtain a blue image to go with our existing F702W data and F555W imaging polarimetry in order to measure the colors of each galaxy subcomponent. Practically, the F450W filter is the shortest bandpass we can use to obtain adequate S/N in a reasonable allocation of orbits -- the galaxy's spectrum is quite red (Figure 2), and WFPC2 UV throughput is low. F450W images the radio galaxy at ~2000Angstrom\\\\\\\\\\\\\\\\ in its rest--frame. The only significant line emission in this band is CIII1909 and CII2326, which are fairly weak in 3C 324. We cannot hope to reach the depth of our 32--orbit F702W image, but fortunately the majority of the flux comes from bright, high--surface--brightness clumps, requiring only modest exposure times. In order to match our existing data on 3C 324, the F450W image should be taken on the PC with the same pointing and roll angle as was used in Cycle 4. This will also allow spatially resolved colors to be measured for many of the faint galaxies in the surrounding field for which we have spectroscopy from the Keck multislit system. We have estimated our exposure times using the fluxes in our Cycle 4 data and integrated colors obtained from our spectrophotometry (and verified by older ground--based imaging photometry). The flux density measured in the F702W image was scaled by the observed continuum spectral index (f_Nu ~ nu^-2), and simulated F450W images were produced. We conclude that 6 orbits (no CR--SPLIT) is sufficient to provide adequate signal--to--noise for most components within the galaxies (assuming this average color), while providing enough separate exposures to permit reasonable cosmic ray rejection. As with our Cycle 4 observations, we will employ half--pixel substepping to permit image reconstruction on the undersampled WFC detectors. Real Time Justification ----------------------- None. vspace-0.2in In Cycle 4, Dickinson Etal (GO--5465) obtained an extremely deep Planetary Camera (PC) image of 3C 324 , in part to study extremely faint galaxies in a cluster surrounding the radio source. In Cycle 5 we will collect WFPC2 imaging polarimetry on 3C 324 in order to study the polarization properties on kiloparsec scales (W. van Breugel, P.I.). In 1994--1995, we have also obtained very deep spectroscopy and spectropolarimetry of the radio galaxy with the Keck LRIS 9,11, as well as LRIS multislit spectroscopy of the surrounding cluster (Dickinson Etal 1995 in prep.). A deep infrared K--band observation with the NIRC camera at Keck is also in hand, with further IR imaging planned for 1996. We have recently obtained an extremely deep 8 GHz VLA map with resolution matching that of HST, and have time scheduled for a comparably deep, equally high resolution 1.4 GHz map with the MERLIN array. In addition, we have obtained an extremely deep (72.1 ksec) Rosat HRI exposure which has demonstrated that the x--ray emission from 3C 324 (previously detected in our Rosat PSPC observation) is spatially resolved with a scale of ~ 0.5 Mpc, arising from the surrounding cluster rather than the AGN itself. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6553( 6) - 04/22/96 13:53 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6553( 6) - 04/22/96 13:53 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 3C324 GALAXY,RADIO RA=15H 49M 48.808S +/- J2000 Z = V = 21.5+/-0.5 GALAXY,BRIGHTEST 0.5",DEC=21D 25' 37.90" +/- 0.5" 1.206 F-LINE(3727)=2+/-0.5e-15 CLUSTER MEMBER,HIGH Z GAL,CLUSTER OF 6553( 6) - 04/22/96 13:53 - [ 5] Visit: 01 Visit Requirements: ORIENT 173.2D TO 173.4D On Hold Comments: Additional Comments: F450W exposures on the 3C 324 field. The telescope ORIENT angle and POS TARG positions are chosen to match as nearly as possible the PI's HST Cycle 4 observations of this field through the F702W filter. If there are scheduling problems because of the tight ORIENT restrictions, please contact the PI. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 3C324 WFPC2 IMAGE PC1-FIX F450W CR-SPLIT=NO 1 2300S POS TARG -10.50,-10.50 Comments: First dither position of two. Three exposures (full orbit length) to be taken here, with no CR-SPLIT. ------------------------------------------------------------------------------------------------------------------------------------ 2 3C324 WFPC2 IMAGE PC1-FIX F450W CR-SPLIT=NO 3 2500S POS TARG -10.50,-10.50 Comments: First dither position of two. Three exposures (full orbit length) to be taken here, with no CR-SPLIT. ------------------------------------------------------------------------------------------------------------------------------------ 4 3C324 WFPC2 IMAGE PC1-FIX F450W CR-SPLIT=NO 3 2500S POS TARG -11.048,-11.048 Comments: Second dither position of two. Three exposures (full orbit length) to be taken here, with no CR-SPLIT. ------------------------------------------------------------------------------------------------------------------------------------ 6553( 6) - 04/22/96 13:53 - [ 6] Visit: 02 Visit Requirements: ORIENT 175D TO 180D On Hold Comments: Additional Comments: LRF observations of the [OII] emission line in 3C324, redshifted to 8228A. Any telescope ORIENT angle is suitable. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 3C324 WFPC2 IMAGE LRF LRF 8228 CR-SPLIT=NO 1 2300S POS TARG -0.25,-0.25 Comments: First dither position for LRF observations ------------------------------------------------------------------------------------------------------------------------------------ 2 3C324 WFPC2 IMAGE LRF LRF 8228 CR-SPLIT=NO 3 2500S POS TARG -0.25,-0.25 Comments: First dither position for LRF observations ------------------------------------------------------------------------------------------------------------------------------------ 5 3C324 WFPC2 IMAGE LRF LRF 8228 CR-SPLIT=NO 3 2500S POS TARG 0.25,0.25 Comments: Second dither position for LRF observations. ------------------------------------------------------------------------------------------------------------------------------------ 6553( 6) - 04/22/96 13:53 - [ 7] Summary Form for Proposal 6553 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category AGN ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 173.2D TO 173.4D POS TARG -10.50,-10.50 POS TARG -11.048,-11.048 ORIENT 175D TO 180D POS TARG -0.25,-0.25 POS TARG 0.25,0.25 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F450W LRF ------------------------------------------------------------------------------------------------------------------------------------ Target Names 3C324 ------------------------------------------------------------------------------------------------------------------------------------