7275( 5) - 04/16/99 13:37 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7275 Version: 5 Check-in Date: 16-Apr-1999 13:37:14 1.Proposal Title: Kinematics of the Helical Jets in the Seyfert Galaxy ESO428-G14 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Andrew Wilson University of Maryland CoI: Heino Falcke University of Maryland N ------------------------------------------------------------------------------------ 5. Abstract An increasing number of synchrotron-emitting jets from AGN are found to have helical morphologies. Such helical structures may arise in a number of ways, such as precession or lateral oscillations of the axis of the jet's source, causing helical patterns in both heavy (ballistic) and light jets (the latter through Kelvin- Helmholtz surface instabilities), and truly helical propagation along magnetic flux tubes. We have recently found from HST images that the emission-line jets in the Seyfert 2 galaxy ESO 428-G14 have a helical structure. We propose to measure the velocities of HAlpha and neighboring lines along and across the helix. Such measurements permit an unambiguous distinction between ballistic (``garden hose'' model) and truly helical motion. The results will impact on models involving orbital/precessional motions of the axis of the jet's source, on ideas concerning the propagation of jets from magnetised accretion disks, and on the role of MHD instabilities in jets. We feel it is important to resolve the ballistic/true helical motion issue for a galaxy in which the helix is seen in emission lines (thus allowing direct measurement of velocities), as the vast majority of helical structures are visible in jets which are seen in only synchrotron radiation. ------------------------------------------------------------------------------------ 7275( 5) - 04/16/99 13:37 - [ 2] Observations Description ------------------------ We propose to perform long slit observations covering essentially all the bright strands of the jet -- 6 contiguous slit positions in p.a. 115^circ+/- 10^degrees (see Fig. 1). In an attempt to better isolate the important velocities at the ``crossover points'' of the NW helix, we will use the 0.1^ slit down the middle of this helix (we are open to the possibility of changing to the 0.2^ slit if the committee or STScI feels strongly about this). At all other locations, the 0.2^ slit will be used. The net area covered is thus 1.1^prime *51^ . The choice between OIIILambda5007 and HAlpha regions was not an easy one. OIIILambda5007 with G430M would give slightly better spectral resolution (25 -- 67 km s^-1, depending on whether the emission is point-like or fills the slit) than HAlpha with G750M (40 - 100 km s^-1). Although OIIILambda5007 is the brighter line, the exposure times are slightly longer because of the lower throughput. We have chosen to observe the HAlpha region because: a) We have the high resolution PC image for HAlpha+NIILambdaLambda 6548, 6583, and can thus directly compare our long slit spectra with this image to define the precise locations of the slits with respect to the spatial structure after the spectroscopic observations have been made. This is important because we may not be able to position our slits to better than ~ 0.1^ with respect to the emission-line image with the standard peak-up. 2) The lines OILambda6300, 6363, HAlpha, NIILambdaLambda 6548, 6583 and SIILambdaLambda 6717 6731 will all be included within the 570 Angstrom covered at one grating setting. This will provide valuable information on the spatial variation of the excitation and density of the gas. From the PC image, the brightnesses of HAlpha+NIILambdaLambda 6548 6583 in faint regions to be observed outside the jet, in a knot at the SE end of the jet, and in the bright ``figure eight'' pattern to the NW are 8times10^-14, 2times10^-13, and 8times10^-13 erg cm^-2 s^-1 (arc sec)^-2, respectively. Most of the strands are resolved transverse to their lengths in the PC image with sizes 0.1 - 0.2^ . Thus the 0.2^ slit will give higher throughput than the 0.1^ . We have used the spectroscopy of Bergvall et al. (A&A, 166, 92 1986) to derive an average HAlpha/HAlpha+NIILambdaLambda 6548 6583 flux ratio of 0.4, and assume a line width at each location of 400 km s^-1, which is the line width at the nucleus in ground based observations (Wilson & Baldwin 1989). In reality, the lines at HST resolution may be narrower and the S/N ratio higher than derived below. For grating G750M with the 0.2^ slit, the sensitivity is given as 1.2times10^13 counts s^-1 pix_lambda^-1 pix_s^-1 at 6600Angstrom for an incident flux of 1 erg cm^-2 s^-1 AA^-1 (arc sec)^-2 (Table 13.2, STIS manual). For the intermediate brightness region, which is typical of the fainter strands to the SE, we would obtain a S/N of 12 per pixel in HAlpha in a 10 minute integration. This exposure time will give a S/N per pixel ~eq 25 for the bright parts of the NW helix and ~eq 7 for the faint regions outside the jet. Velocity accuracy will thus be a small fraction of the intrinsic FWHM of the line. For the slit covering the outer, fainter parts, we may use on chip binning to improve the S/N ratio, as the gas is expected to change its velocity only slowly with position outside the jet, so the highest spatial resolution is not needed. For the one observation with the 0.1^ slit, we will obtain a S/N of 18 for the bright parts of the NW helix in a 10 minute integration. Depending on the advice of STScI, we may also take a short direct image to aid in registering the STIS and PC observations. Orbital visibility is 53 minutes and we request 2 orbits. Orbit 1 will be broken up as follows: GS Acq. 9 mins; Target Acq 8 mins; Acq Peakup 5 mins; Small offset to central slit location 10 secs; First spectroscopic exposure overhead 5 mins; Science exposure with 0.1^ slit (crsplit = 2 for all science integrations) 2 * 5 min; Readout time 74 secs; Change slit to 0.2^ 1.0 mins; New wavecal 1.5 mins; Offset to new target position 10 secs; Science exposure 2 * 5 mins + 74 secs readout. noindent Total Orbit 1 = 52.3 mins (note that we have assumed that we can go directly from the 0.1^ slit to the 0.2^ slit without a second peak-up; if this is not true, a slight reduction in science time will be necessary) Orbit 2 will be broken up as follows: GS Reacq 6 mins; Offset slit to new target position 10 secs; Science exposure 2 * 5 mins + 74 secs readout; Offset slit to new target position 10 secs; Science exposure 2 * 5 mins + 74 secs readout; Offset slit to new target position 10 secs; Science exposure 2 * 5 mins + 74 secs readout; Offset slit to new target position 10 secs; Science exposure 2 * 5.5 mins + 74 secs readout; noindent Total Orbit 2 = 52.6 mins Real Time Justification ----------------------- None The only currently available radio maps of ESO 428-G14 are from VLA snapshots at 6 and 20 cm made over 11 years ago (Ulvestad & Wilson ApJ 343, 659 1989; note that the galaxy is called 0714-2914 in this paper). They have poor sensitivity and the best resolution achieved was 0.3^ * 0.6^ , much worse than the HST images. We have therefore proposed to obtain long integrations of this galaxy with the VLA in `A' configuration at 3.6 and 2 cm, which will attain resolutions of factors of at least 2 and 3 times better, respectively. This proposal was approved (nr. AW446) and the observations will be made on Nov 3 and 4 1996. These new radio maps will have the resolution and sensitivity to separate and detect the individual emission-line strands in the HST image, and thus allow us to check whether the magnetic field is stronger in and around the strands than elsewhere, and to estimate its strength using the usual equipartition assumption. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 7275( 5) - 04/16/99 13:37 - [ 3] Data Distribution Paper Products: YES Media: DAT Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7275( 5) - 04/16/99 13:37 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 ESO428-G14 GALAXY, SEYFERT, RA=07H 16M 31.280S +/- 0.5", J2000 V = 20 SPIRAL, EMISSION LINE DEC=-29D 19' 29.3" +/- 0.5", F-CONT(6598)=1.5e-17 NEBULA PLATE-ID=0164 F-LINE(6599)=1.94e-15 7275( 5) - 04/16/99 13:37 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 168D TO 176D 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 ESO428-G14 STIS/C ACQ F28X50L MIRROR ACQTYPE=DIFFUSE,CHECKBOX=5, 1 10 S ONBOARD ACQ FOR 30 CD P DIFFUSE-CENTER=FLUX-CENTROID ------------------------------------------------------------------------------------------------------------------------------------ 20 ESO428-G14 STIS/C ACQ/PEA 52X0.1 MIRROR 1 20 S ONBOARD ACQ FOR 30 CD K ------------------------------------------------------------------------------------------------------------------------------------ 30 ESO428-G14 STIS/C ACCUM 52X0.1 G750M 6581 CR-SPLIT=3 1 10 M CD ------------------------------------------------------------------------------------------------------------------------------------ 40 ESO428-G14 STIS/C ACCUM 52X0.2 G750M 6581 CR-SPLIT=3 1 9 M POS TARG -0.35, 0 CD ------------------------------------------------------------------------------------------------------------------------------------ 50 ESO428-G14 STIS/C ACCUM 52X0.2 G750M 6581 CR-SPLIT=3 1 9 M POS TARG -0.15, 0 CD ------------------------------------------------------------------------------------------------------------------------------------ 60 ESO428-G14 STIS/C ACCUM 52X0.2 G750M 6581 CR-SPLIT=3,PATTERN=PERP-TO-SLIT, 1 9 M POS TARG 0.15, 0 CD NUM-POS=3,STEP-SIZE=0.2, PATTERN-DIRECTION=PLUS ------------------------------------------------------------------------------------------------------------------------------------ 7275( 5) - 04/16/99 13:37 - [ 6] Summary Form for Proposal 7275 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 52X0.1 52X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=DIFFUSE CHECKBOX=5 DIFFUSE-CENTER=FLUX-CENTROID CR-SPLIT=3 PATTERN-DIRECTION=PLUS ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 168D TO 176D ONBOARD ACQ FOR 30 POS TARG -0.35, 0 POS TARG -0.15, 0 POS TARG 0.15, 0 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G750M ------------------------------------------------------------------------------------------------------------------------------------ Target Names ESO428-G14 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 6581 ------------------------------------------------------------------------------------------------------------------------------------