6563( 13) - 04/15/97 10:55 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6563 Version: 13 Check-in Date: 15-Apr-1997 10:30:13 1.Proposal Title: The Helical Jet/ISM Interaction in NGC 4258 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle AGN GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: GERALD CECIL UNIVERSITY OF NORTH CAROLINA CoI: Chris De Pree National Radio Astronomy Observatory N CoI: Michael Dopita Australian National University N CoI: Lincoln Greenhill Center for Astrophysics N CoI: James Moran Center for Astrophysics N ------------------------------------------------------------------------------------ 6. Abstract NGC 4258 is a nearby active spiral with famous jets visible in radio continuum, visual emission lines, and soft x-rays. It is the best galaxy for study of entrainment, confinement, and stability of jets because its jets emerge perpendicular to a pc-scale accretion disk of known orientation. The disk rotates around a compact central mass of density >4*10^9 Msubsun pc^-3. The jets flow for several arc-minutes near the disk plane, and include >10^7/n_e Msun of ionized gas in intertwined strands of diameter <=0sec point9 (<30 pc). The strands twist helically; the twisting is also seen in Fabry- Perot spectra as velocity oscillations of +/-350 kms down the jet, suggesting that the gas flow is itself helical. The emission lines have flux ratios consistent with those of a 300 -400 kms photoionizing shock. Most of the x-rays in NGC 4258 coincide with the jets, are thermal, with kT = 0.3 keV as expected for gas behind a 400 kms shock. The shocks likely arise when molecular clumps --- stripped from cloud complexes known to be adjacent to the jet --- are entrained into the flow. A deep WFPC2 image is proposed to study the jet/ISM interaction away from the nucleus, the time history of the outflow, and correlations with the hot x-ray gas, thermal gas, and relativistic particles in the jets, on a much smaller scale (2 pc) than is possible in powerful radio galaxies. A FOS UV spectrum of a jet knot or the nucleus, along the rotation axis of the accretion disk, will assess the roles of nuclear beaming and in situ photoionization by high-velocity shocks. ------------------------------------------------------------------------------------ 6563( 13) - 04/15/97 10:55 - [ 2] Observations Description ------------------------ NOTE: The observing strategy has been updated from that below in that the imaging is no longer EARLY ACQ imaging. A suitable archival WFPC2 image was found to serve that purpose. The WFPC2 imaging is still being done for scientific reasons. It has just been functionally decoupled from the spectroscopy in the implementation of the program. It was decided not to dither with WFPC2 since the extended structure of the galaxy is diffuse on WF scales as seen in Holland Ford's WFPC2 data. POS TARGs are also not needed for the general placement of the field on the chips since the PI's final choice of the combination of the new target coords measured by him from Ford's image, plus the choice of an absolute ORIENT combined with the PC1-FIX aperture are calculated by the PI so as to align the galaxy over the WFPC2 field of view as desired. Comments added 11/11/96 based on PI's expressed choices during visit to STScI in May/June 1996. - Ray Lucas - 11/11/96 Also note updated flux info below from the PI as of 25 November, 1996. Here is the missing flux estimate for my FOS observation in program GO 6563. I used the archive WFPC2 images (PC chip) to derive the continuum-subtracted [N II]6548+Halpha WFPC2 count rate through F656N, obtaining 30 e/s summed over the square 0.86x0.86" centered on the FOS target position (the nucleus). From my KPNO long-slit spectra that intersect the nucleus, I obtain [N II]6548/Ha \\approx 0.25, so 24 e/s comes from Ha alone. But the Halpha line-width averaged over the nucleus is 900 km/s FWHM, = 20 Ang FWHM, and systemic velocity is 468 km/s = 6573 A. This puts the red wing of the line on the red tail of the F656N filter. So I use 0.07 as an average of the system throughput (vs 0.104 peak). Crudely speaking, the nucleus is a point source, so I have S/t = 2.28e12 lambda T F e/s, solving to get F(Ha) = 2.2e-14 erg/s/cm^2 for the H-alpha flux. Assume modest reddening averaged over nucleus such that f(Ha)/f(Hb) = 4 rather than 2.87, and I have for the integrated Hb flux through the 1.0-PAIR aperture centered on the nucleus F(Hb) = 4.5e-15 erg/s/cm^2 The nucleus is surely fairly blue before this reddening, so a flat continuum is probably a good first estimate. Original text follows, below. - RAL - 11/25/96 A WFPC2 1000 s F791W exposure will remove galaxy starlight. Our long-slit and FP spectrophotometry show that the line flux lies between redshifts of 300 -- 700 kms (CWT), and that the flux ratio N IILambda6583/H Alpha ~ 0.8 along the jets. These velocities are perfectly located on the flat top of filter F658N, while H Alpha comes through on the blue wing at ~1/3 strength to augment the ``N II" flux by 40\\%. (F658N provides better throughput than observing H Alpha\\ on the red wing of F656N.) To estimate the N II exposure from our spectra, we assume that the measured H Alpha jet flux of 6.9times10^-13 erg s^-1 cm^-2 (CWD) comes from 5 twisted strands (3 to the SE, 2 to the NW) of 0sec point9 diameter (an upper limit). Fig.\\ 1c shows that the line emission extends for ~2' on each side of the nucleus, so the total area of the visually emitting jets is 5*0sec point9*2min point5 (to account for their twists) = 675 square arcseconds. The jet H Alpha surface brightness is fairly uniform, so in each WFC pixel we expect on average 9.7x10^-18 erg s^-1 cm^-2 from N IILambda6583 and another 40\\% of this from H Alpha. One N II photon = 3times10^-12 erg, so we collect 0.2 photons s^-1 WFCpix^-1 with the unobstructed telescope area of 45239 cm^2. The system throughput conversion to detected electrons for F658N is 0.12 for the velocity range of NGC 4258. So in this filter, the detected e^- count rate r = 0.024 e^- s^-1 WFCpix^-1. The pixel dark rate is small compared to this (0.003 e^- s^-1 in the WF2 chip at -88degrees C.) The sky, at mag = 22.7- 0.22+(5 for WFC) or (from eq. 6.1, Tables 6.1 and 6.2) 0.012 e^- s^-1, is also quite small. In 3 orbits we get 1000 s (1st orbit) + 2*3100 s = 7,200 s total exposure after overhead. The summed readout and quantization noise is 3*5.5^2 e^- because we do not CR-SPLIT these multiple exposures. In each WFC pixel, the S/N ratio = 9 after 3 orbits. noindent FOS Much of the science can be done now with the 1.0- PAIR aperture of FOS. G160L spans LambdaLambda 0.11 --- 0.25 micron at 7 Angstrom/diode, a region with lines diagnostic of photoionizing shocks (Dopita & Sutherland 1995a.) From CWD we find that knot ``d" emits 4.5\\% of the total H Beta flux of 1.3x10^-13 ergs s^-1 cm^-2 Angstrom^-1. We assume that most of this flux passes through the 1.0-PAIR aperture, and that this region is reddened like the rest of the SE jet by A_V <~ 0.8 (CMV). Using the inverse sensitivity from Table 1- 6, we obtain 0.7 counts/s per H Beta photon from the knot. Our simulations (Fig. 4) provide line fluxes in counts scaled from the number of H Beta photons. If the FOS/BL dark rate of 0.007 count/s is the only noise source, after the background galaxy starlight is subtracted by aperture switching, we get 35 dark counts in each diode after 5000s exposure on target, and ~3400 H Beta photons. Our model spectra show that this provides sufficient S/N for us to distinguish between AGN and shock photoionization. We are aware that BL/G160L is plagued by scattered light at the blue end of the spectrum, so we will restrict our continuum analysis to the red end. This will not affect the emission lines much. Acquisition strategy: the knot and observing aperture are large enough that a WFPC2- assisted offset with <1" uncertainty would be successful. Moreover, the short archival WFPC2 F658N image will be public in 3/96, and will also be used for a precise offset. At that point we`ll also confirm that the nucleus rather than jet knot is our prime target. We propose to use the 1st orbit for the 3-stage ACQ/PEAK of FOS/BL. In the 2nd orbit we'll start with 1200s in G160L, then switch to the PRISM for ~10m to fill out the orbit. This spectrum will link the UV to ground- based spectra. Orbits 3-5 continue with long G160L integrations. All FOS observations will be through the 1.0-PAIR aperture, to obtain the spectrum of galaxy starlight for continuum subtraction. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6563( 13) - 04/15/97 10:55 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: ------------------------------------------------------------------------------------ 6563( 13) - 04/15/97 10:55 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4258-JETS GALAXY, Spiral, RA=12H 18M 57.19S +/-0.2S, 2000 V=465 V = 8 Seyfert, Radio galaxy DEC=+47D 18' 8.5" +/-2", PLATE- ID=024D 2 NGC4258-NUC GALAXY, Spiral, RA=12H 18M 57.469S +/-0.2S, 2000. V=600 V = 8 Seyfert, Radio galaxy DEC=+47D 18' 14.4" +/-2", PLATE- ID=024D 6563( 13) - 04/15/97 10:55 - [ 5] Visit: 01 Visit Requirements: ORIENT 251D TO 275D On Hold Comments: Additional Comments: ORIENT is absolute preferred ORIENT. This is NOT an EARLY ACQ image. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4258-JET WFPC2 IMAGE PC1-FIX F791W 1 1000 S S ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC4258-JET WFPC2 IMAGE PC1-FIX F658N CR-SPLIT=NO 1 1400 S EXPAND S ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC4258-JET WFPC2 IMAGE PC1-FIX F658N CR-SPLIT=NO 1 2900 S EXPAND S ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC4258-JET WFPC2 IMAGE PC1-FIX F658N CR-SPLIT=NO 1 2900 S EXPAND S ------------------------------------------------------------------------------------------------------------------------------------ 6563( 13) - 04/15/97 10:55 - [ 6] Visit: 02 Visit Requirements: ORIENT 250D TO 345D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4258-NUC FOS/BL ACQ/PEA 4.3 MIRROR SEARCH-SIZE-X=1,SEARCH-SIZE-Y=3, 1 5 S ONBOARD ACQ FOR 2 K SCAN-STEP-X=0,SCAN-STEP-Y=1.23 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC4258-NUC FOS/BL ACQ/PEA 1.0-PAI MIRROR SEARCH-SIZE-X=6,SEARCH-SIZE-Y=2, 1 7 S ONBOARD ACQ FOR 3 K R-A SCAN-STEP-X=0.61,SCAN-STEP-Y=0.61 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC4258-NUC FOS/BL ACQ/PEA 0.25-PA MIRROR SCAN-STEP-X=0.17,SCAN-STEP-Y=0.17 1 12 S ONBOARD ACQ FOR 4-5 K IR-A ,SEARCH-SIZE-X=5,SEARCH-SIZE-Y=5 Comments: CRITICAL PEAKUP STAGE ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC4258-NUC FOS/BL ACCUM 1.0-PAI PRISM STEP-PATT=OBJ-OBJ 1 630 S MAX DUR 630S R-A ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC4258-NUC FOS/BL ACCUM 1.0-PAI G160L STEP-PATT=OBJ-OBJ 1 9040 S R-A Comments: A = TARGET, B = BACKGROUND GALAXY STARLIGHT ------------------------------------------------------------------------------------------------------------------------------------ 6563( 13) - 04/15/97 10:55 - [ 7] Summary Form for Proposal 6563 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 FOS/BL ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO SCAN-STEP-Y=1.23 SCAN-STEP-Y=0.61 SEARCH-SIZE-Y=5 STEP-PATT=OBJ-OBJ ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category AGN ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 251D TO 275D EXPAND ORIENT 250D TO 345D ONBOARD ACQ FOR 2 ONBOARD ACQ FOR 3 ONBOARD ACQ FOR 4-5 MAX DUR 630S ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F791W F658N MIRROR PRISM G160L ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC4258-JETS NGC4258-NUC ------------------------------------------------------------------------------------------------------------------------------------