This is a resubmission of a Cycle 20 proposal. APT claims it has been previously submitted, which is not the case for Cycle 21. Clear ID# button had no discernable effect. 2130921745 Assigned ID: 1636 ----- Attempting Submission 2 (Fri Mar 01 18:53:44 GMT 2013) ----- Exposure warnings (use of PATTERN with ramp filters) not relevant since small shift dither pattern used Updated to eliminate post-flash following recommendation of instrument scientist -2053940679 ----- Attempting Submission 1 (Wed Jun 26 18:54:25 GMT 2013) ----- ----- Attempting Submission 2 (Mon Aug 12 14:57:04 GMT 2013) ----- Warnings disregarded since dither pattern uses small shifts The formation of binary supermassive black holes (BBH) in galaxy centers appears to be an inevitable consequence of hierarchical structure formation. General Relativity predicts that, when a BBH coalesces, the merged SMBH recoils with a velocity that may reach several 1000 km/s. The luminous quasar E1821+643 is one of only 3 SMBH recoil candidates that have been identified via Doppler shifting of emission lines from the retained gas. This case is unique in that the Doppler shift is seen in both direct and scattered light, allowing us to infer a relative velocity of 2100 km/s between the quasar nucleus and host galaxy. By itself, this does not exclude alternative models such as a BBH or anisotropic wind, but follow-up spectroastrometric measurements reveal a relative displacement between the nucleus and the gas emitting the [OIII]4959,5007 lines that is consistent with the recoil hypothesis. The apparent displacement, however, could also be due to an asymmetric circum-nuclear distribution of the [OIII] emission. In order to distinguish between these two possibilities we propose ACS/WFC ramp filter imaging in [OIII] to map the distribution of narrow-line emission on sub-arcsecond scales. The observations will also allow us to study the relationship between the narrow-line gas and the arcsecond-scale radio source, which has morphological features that may relate to precession in a BBH system, or a "spin-flip" following coalescence. With this modest investment of HST time we will take a key step in establishing the nature of the E1821+643 system, which may ultimately yield direct observational evidence for BBH coalescence and high velocity gravitational recoils. We propose to obtain high resolution (0.1") ACS/WFC images of the [OIII]4959, 5007 emission lines using the narrow (2% bandpass) ramp filter FR656N set to a central wavelength of 6460A. At the redshift of our target, E1821+643 (z=0.297), the filter bandwidth will comfortably include both [OIII] lines. We will also obtain short exposures with same filter at a central wavelength 6305A, centered on the broad Hbeta line, in order to characterize the quasar PSF. In addition, observations in FR647M, centered at 7300A, will be used for continuum subtraction. The [OIII] emission line region of our target extends over ~ 5 arcsec, and as described in the science case we are primarily interested in the structure in the central ~1 arcsec, so the smaller field of view of the ramp filters is perfectly suited to our investigation. As our science goals require mapping the spatial distribution of the [OIII] emission both within the inner arcsec and over the fainter, more diffuse extended region we will use a combination of short exposures to obtain high signal:noise (~100) but unsaturated images of the nucleus and longer exposures to map the extended structure on ~5 arcsec scales (signal:noise ~3-10). All exposures will be dithered to allow removal of hot pixels, cosmetic defects and cosmic rays. We used the HST ACS ETC for ramp filters to estimate exposure times based on measurements from our Gemini data. The quasar nucleus has a continuum flux density 4.3E-15 erg s-1 cm-2 A-1 at 6614A (5100A rest wavelength). Using the ETC with an uploaded GEMINI/GMOS longslit spectrum of the nucleus and the default extraction aperture we estimate that we will obtain S/N~260 in FR656N with a total exposure time of 20s at both wavelength settings. We will reach a comparable S/N ratio in a total exposure time of 8s in the FR647M filter. The exposure times needed for the extended structure were based on obtaining a S/N ratio ~10 at a radial offset of 2 arcsec from the nucleus. Exposure times were estimated using average fluxes measured from 1" apertures offset 2" E, N, W and S of the nucleus. The average continuum flux density is 1.5E-17 erg s-1 cm-2 A-1 at 6614 A (5100A rest) and the total integrated flux in both [OIII] lines is 1.9E-15 erg s-1 cm-2. For ETC calculation we used Elliptical galaxy template 2 and added emission lines representing [OIII]4959,5007. For a 2x2 aperture, the ETC indicates that we will reach S/N ~7 in FR656N for a total exposure time of 400s. A total exposure time of 200s will yield a comparable S/N ratio in the FR647M filter. The end product will be a high resolution map of the [OIII] emission around the nucleus of E1821+643 spanning ~0.1" to ~ 5". The 2-D surface brightness distribution will be used as input data for a code that simulates spectroastrometric displacement measurements for specified combinations of point source and extended emission components. Given the input [OIII] surface brightness distribution and a point source which has a quasar spectrum (continuum and broad emission lines), we will use this code to generate simulated displacement spectra for cases where (1) the point source is located at the photocenter of the extended light distribution and (2) is offset by different distances from the photocenter (Fig. 4). These simulations will enable us to estimate the extent to which any anisotropies in the [OIII] surface brightness distribution contribute to the measured spectroastrometric displacement in [OIII] and thus determine if the observed displacement indicates gravitional recoil of the SMBH or can be entirely explained by asymmetric [OIII] emission. We will also combine the [OIII] images with archival radio data to investigate interactions between the arcsec-scale radio jets and the extended emission line gas. Allowing for overheads associated with acquisition, instrument and repositioning overheads, we request 1 orbit for these observations. AGN/QUASARS 12 false false 0.0 0.0 false false false SUPPORTED GALAXY ELLIPTICAL NLR QSO This object was generated by the targetselector and retrieved from the SIMBAD database. IRAS18216+6418 H1821+643 J2000 J2000 nucleus continuum flux density 4.3E-15 erg s-1 cm-2 A-1 at 5100A (rest wavelength); average [OIII]4959+5007 flux = 1.9E-15 erg s-1 cm-2 in 1 arcsec aperture offset 2 arcsec from nucleus ACS/WFC RampFilter No No FR656N ACS/WFC RampFilter No No FR647M POS-TARG DITHER 0.146 LINE false false 2 47.17 ACS-WFC-DITHER-LINE 1 false 1376317788023 /Users/axrsps/Research/Cycle21/E1821/OP-cache/E1821_C21_phaseii_v4-v01.xml The scheduling data was generated by CASM 21.2. CASM was run in Phase II mode. 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