13385( 3) - 12-Aug-2013 15:11:43 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 13385 Version: 3 Check-in Time: 12-Aug-2013 15:11:43 STScI Edit Number: 0 Title Is there a kicked supermassive black hole in E1821+643? ------------------------------------------------------------------------------------ Type Cycle GO 21 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Andrew Robinson Rochester Institute of Technology Y CoI: Dr. Rachel Louise Curran Rochester Institute of Technology N CoI: Prof. Alessandro Marconi Universita di Firenze N CoI: Dr. Alessandro Capetti Osservatorio Astronomico di Torino N ------------------------------------------------------------------------------------ Abstract 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. ------------------------------------------------------------------------------------ Observations Description ------------------------ 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 13385( 3) - 12-Aug-2013 15:11:43 - [ 2] 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. Real Time Justification ----------------------- Calibration Justification ------------------------- 13385( 3) - 12-Aug-2013 15:11:43 - [ 3] Additional Comments ------------------- ------------------------------------------------------------------------------------ 13385( 3) - 12-Aug-2013 15:11:43 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 E1821+643 GALAXY, ELLIPTICAL, RA=18H21M57.2365S +/- 0.1", J2000 Z = V = 14.24 +/- 0.1 nucleus continuum NLR, QSO DEC=+64D20'36.23" +/- 0.1" 0.297 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 Reference Frame: Other: J2000 Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. ------------------------------------------------------------------------------------------------------------------------------------ 13385( 3) - 12-Aug-2013 15:11:43 - [ 5] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.146 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 47.17 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 13385( 3) - 12-Aug-2013 15:11:43 - [ 6] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 E1821+643 ACS/WFC ACCUM WFC1-MRAM FR656N 6460 1 200 S (400 PATTERN 1 1-2 PQ S) ------------------------------------------------------------------------------------------------------------------------------------ 2 E1821+643 ACS/WFC ACCUM WFC1-MRAM FR656N 6460 1 25 S (50 PQ S) ------------------------------------------------------------------------------------------------------------------------------------ 3 E1821+643 ACS/WFC ACCUM WFC1-MRAM FR656N 6305 1 20 S (40 PATTERN 1 3 PQ S) ------------------------------------------------------------------------------------------------------------------------------------ 4 E1821+643 ACS/WFC ACCUM WFC1-IRAM FR647M 7300 1 100 S (200 PATTERN 1 4-5 PQ S) ------------------------------------------------------------------------------------------------------------------------------------ 5 E1821+643 ACS/WFC ACCUM WFC1-IRAM FR647M 7300 1 9 S (18 S) PQ ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ E1821+643 1 ACS/WFC ACCUM WFC1-MRA FR656N 6460 1 none none none 1 N/A MPQ E1821+643 1 ACS/WFC ACCUM WFC1-MRA FR656N 6460 2 none none none 1 N/A MPQ E1821+643 2 ACS/WFC ACCUM WFC1-MRA FR656N 6460 1 none none none 1 N/A MPQ E1821+643 2 ACS/WFC ACCUM WFC1-MRA FR656N 6460 2 none none none 1 N/A MPQ E1821+643 3 ACS/WFC ACCUM WFC1-MRA FR656N 6305 1 none none none 1 N/A MPQ E1821+643 3 ACS/WFC ACCUM WFC1-MRA FR656N 6305 2 none none none 1 N/A MPQ E1821+643 4 ACS/WFC ACCUM WFC1-IRA FR647M 7300 1 none none none 1 N/A MPQ E1821+643 4 ACS/WFC ACCUM WFC1-IRA FR647M 7300 2 none none none 1 N/A MPQ E1821+643 5 ACS/WFC ACCUM WFC1-IRA FR647M 7300 1 none none none 1 N/A MPQ E1821+643 5 ACS/WFC ACCUM WFC1-IRA FR647M 7300 2 none none none 1 N/A MPQ 13385( 3) - 12-Aug-2013 15:11:43 - [ 7] Summary Form for Proposal 13385 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC1-IRAMPQ, WFC1-MRAMPQ ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1-2, PATTERN 1 3, PATTERN 1 4-5 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements FR647M, FR656N ------------------------------------------------------------------------------------------------------------------------------------ Target Names E1821+643 ------------------------------------------------------------------------------------------------------------------------------------