7882( 2) - 11/21/97 08:47 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7882 Version: 2 Check-in Date: 21-Nov-1997 08:46:01 1.Proposal Title: Molecular gas in the centers of Arp220 and NGC6240: nuclear accretion disks? ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: PAUL VAN DER WERF LEIDEN OBSERVATORY CoI: Dr. Alan Moorwood European Southern Observatory N CoI: Dr. Frank Israel Leiden Observatory N ------------------------------------------------------------------------------------ 5. Abstract NIC2 will be used to image the H_2 1-0 S(1) emission in the prototypical ultraluminous infrared galaxies (ULIRGs) Arp220 and NGC6240. In ground-based observations, we have found that the H_2 emission peaks between the two remnant stellar nuclei of the merging galaxies. This is a result of dissipation in shocks in the gas, which makes the gas components merge before the dissipationless stellar components merge. The shock- excited H_2 emission is the direct signature of this dissipation and can be used to trace the flow of molecular gas towards the bottom of the potential well. ULIRGs are suspected to harbour dust-embedded quasars, formed in their dusty centers. The immense concentrations of dissipative material, in a deep potential well, may form ideal birth places for active nuclei. Aim of the HST observations is a determination of the morphology of the molecular concentration, in particular the presence of a molecular accretion disk (as suggested by 1'' resolution CO observations), its radial profile around the central peak, and substructure within the central concentration. Combined with existing ground-based spectroscopy, the HST will provide the information required for understanding the dynamical state of these regions. Since these regions will form the birth places of extreme starbursts or a luminous active nucleus, the programme will have implications on the formation of active nuclei and extreme starbursts in general, and the possible relation between the two. ------------------------------------------------------------------------------------ 7882( 2) - 11/21/97 08:47 - [ 2] Observations Description ------------------------ Here we describe our calculation of integration times for Arp220. From our ground-based observations, we determine an integrated flux over the central 2''*2'' of approximately 4times10^-14 erg s^-1 cm^-2 for the H_2 1-0 S(1) line. The line is redshifted to 2.1602 Mum, where the F216N filter has maximum transmission. The underlying extended continuum (i.e., in regions avoiding the two nuclei) is about 15.2 K- magnitudes per arcsec^2. This gives a line/continuum ratio of typically about 1-2 (but with a significant spread over the image) in the F216N filter. Therefore it is necessary to obtain line-free continuum measurements. Broad-band images are not suitable for this, because of the expected color variations over the surface of the galaxy, due to photospheric absorption (CO bands) in the underlying evolved stellar population, and due to emission by hot dust contributing at the longest wavelengths. Therefore, it is necessary to obtain the reference continuum measurements in a narrow-band filter, as close to the redshifted line wavelength as possible. For Arp220, we will use the F212N filter (which is free of strong emission lines) for the continuum measurement (F215N still has significant transmission at 2.1602 Mum and is thus not line-free). The very different morphology expected for line and continuum will facilitate the removal of the continuum. Due to the two bright nuclei, we need to achieve significant dynamic range and thus need to use MULTIACCUM mode. Finally, since we are observing at long wavelengths, and require accurate continuum subtraction, we need to chop (the NICMOS simulator shows that the expected count rate is dominated by the background). A chop throw of 60'' is required to be sufficiently far from the most luminous parts of the target. We aim for a S/N ratio of 10 in the continuum-free line image. This is done optimally by obtaining equal r.m.s. noises in the line+continuum (F216N) and the continuum (F212N) images. We used the NICMOS exposure simulator to derive an optimal observing strategy. We assume that the line flux is evenly distributed over the central 2''*2'', i.e., an average line surface brightness of 1times10^-14 erg s^-1 cm^-2 arcsec^-2 over this region. The underlying continuum is 0.5,mJy arcsec^ -2 (excepting the two nuclei). Using the exposure calculator we found that for the expected signal strengths given above, we need to integrate 1.5 times longer in F216N than in F212N to achieve equal r.m.s. noises in both filters, due to the line signal and higher background in F216NNull. The required integration time now follows from the need to achieve a S/N of about 20 in F212N on the unchopped continuum signal, which after chopping and continuum subtraction gives a S/N of 10 in the final image. For a typical surface brightness of 0.5,mJy arcsec^-2 in the relevant regions the NICMOS simulator gives an integration time of 3010 seconds in F212N for a S/N of 20. Since we calculated above that the exposure time in F216N should be 1.5 times this to achieve the same r.m.s.noise, the required integration time in F216N is 4500 seconds. Since chopping is needed in both filters, the integration times have to be doubled, and overheads added. The integration time will be built up in exposures of 514 sec (MULTIACCUM sequence MIF512 with NSAMP=25), which ensures that we are still shot-noise limited. This can be done in seven orbits, organized as follows: beginenumerate item acquisition 7.1 min; NICMOS setup 18 sec, F212N exposure 1088 sec, overhead for MULTIACCUM 27 sec (cumulative 26.0 min); chop 80 sec, F212N exposure 1088 sec, overhead for MULTIACCUM 27 sec (cumulative 45.9 min). item identical to orbit 1 except only 5.3 min acquisition and 80 sec overhead for chop back to original position. item identical to orbit 2, completes F212N exposures. item reacquisition 5.3 min, NICMOS setup 18 sec, chop to original position 80 sec, filter change to F216N 18 sec; F216N exposure 1088 sec, overhead for MULTIACCUM 27 sec (cumulative 25.8 min); chop 80 sec, F216N exposure 1088 sec, overhead for MULTIACCUM 27 sec (cumulative 45.7 min). item identical to orbit 2, except that F216N is used in stead of F212N. item identical to orbit 5. item identical to orbit 5, completes F216N exposures. endenumerate This gives an on-source integration time of 4352 sec in F216N and 3264 sec in F212N, sufficiently close to the required integration times of 4500 and 3000 sec calculated above. For NGC6240 the calculations are very similar. For this object the continuum level is very close to that in Arp220, but the line is about twice as bright. However, the line is redshifted to 2.1736 Mum, where the transmission of the F216N filter is 50%; as a result the sensitivity numbers become essentially identical to those in Arp220, with as only difference that for NGC6240 we can use the F215N filter for the continuum measurement. Real Time Justification ----------------------- None. None. Calibration Justification ------------------------- Additional Comments ------------------- In order to avoid the "bars" in NIC2, we also attach parallel exposures in NIC1 and NIC3 (as recommended in one of the NICMOS advisories). NIC2 is always the prime camera.Please note that the number of exposures in every individual orbit must always be EVEN, or else the "on" and "off" exposures get separated. (I have had cases were RPS2 wanted to put 5 exposures into one orbit; this must be AVOIDED - I solved it by increasing the chop offset a bit and that took enough extra time). ------------------------------------------------------------------------------------ 7882( 2) - 11/21/97 08:47 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7882( 2) - 11/21/97 08:47 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 IC4553 GALAXY,ULTRALUMINOUS IR RA=15H 34M 57.25S +/- 1",DEC=23D J2000 V = 5434 SURF-LINE(21602)=10+/-5e-15 GAL,INTERACTING 30' 11.3" +/- 1",PLATE-ID=0280 SURF-BKG(K) = 15+/-2 GALAXY,STARBURST,MULTIP LE NUCLEI,DUST LANE Comments: We center on the bright K-band nuclei. These are in the middle of the dust lane and optically invisible. 2 NGC6240 GALAXY,ULTRALUMINOUS IR RA=16H 52M 58.90S +/- 1",DEC=02D J2000 V = 7335 SURF-LINE(21736)=20+/-5e-15 GAL,INTERACTING 24' 4.0" +/- 1",PLATE-ID=00JO SURF-BKG(K) = 15+/-2 GALAXY,MULTIPLE NUCLEI,DUST Comments: We center on the two nuclei. 7882( 2) - 11/21/97 08:47 - [ 5] TARGET LIST c)Generic Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Selection Criteria | Flux data No | Name | Description | | ------------------------------------------------------------------------------------------------------------------------------------ PARALLEL- UNIDENTIFIED,PARALLEL F(16000)=0+/-0 FIELD FIELD Comments: T <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< his is the generic target for parallel observations with NIC1 and NIC3 (NIC2 is always the prime camera). Its actual pointing is irrelevant. The flux is given in Jy at 1.6 micron. ------------------------------------------------------------------------------------------------------------------------------------ 7882( 2) - 11/21/97 08:47 - [ 6] Visit: 01 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: These are the Arp220 exposures: F216N contains the redshifted H2 1-0 S(1) line, and F212N is the reference continuum measurement (F215N is not suitable for that since it still has significant transmission at the wavelength of the line). The attached parallels are only included for suppressing the "bars" in NIC2, as recommended in one of the NICMOS advisories. NIC2 is always prime. For the attached parallels, pointing and parameters are irrelevant, as long as they take as much time as the prime exposures. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 IC4553 NIC2 MULTIAC NIC2 F212N 21200 CAMERA-FOCUS=DEF,SAMP-SEQ=MIF512, 1 DEF PAR 2-3 WITH 1 CUM NSAMP=25,PATTERN=TWO-CHOP, OFFSET=SAM,CHOP-SIZE=90, PATTERN-ORIENT=0,NUM-POS=12 Comments: This is the exposure on the continuum for Arp220 with NIC2, which is prime. We need to chop because of the large source size. We use per orbit 2 on and 2 off exposures. This is should be frequent enough for chopping, since the expected background counts are typically equal to the expected counts from the target. Note that in some cases RPS2 wanted to put 5 exposures into 1 orbit. This should be AVOIDED, since "on" and "off" exposures must NOT be separated. ------------------------------------------------------------------------------------------------------------------------------------ 2 PARALLEL-FI NIC1 MULTIAC NIC1 F160W 16000 SAMP-SEQ=MIF512,NSAMP=25 1 DEF ELD CUM Comments: These are the NIC1 parallel observations for Arp220, off line. NIC2 is always prime. Parameters and pointing of the parallel observations is irrelevant, they are only meant to suppress the "bars" in NIC2, as recommended in one of the NICMOS advisories, The parallel observations are tailored such that they take just as long as the prime observations. ------------------------------------------------------------------------------------------------------------------------------------ 7882( 2) - 11/21/97 08:47 - [ 7] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 3 PARALLEL-FI NIC3 MULTIAC NIC3 G141 16000 SAMP-SEQ=MIF512,NSAMP=25 1 DEF ELD CUM Comments: These are the NIC3 parallel observations for Arp220, off line. NIC2 is always prime. Parameters and pointing of the parallel observations is irrelevant, they are only meant to suppress the "bars" in NIC2, as recommended in one of the NICMOS advisories, The parallel observations are tailored such that they take just as long as the prime observations. ------------------------------------------------------------------------------------------------------------------------------------ 4 IC4553 NIC2 MULTIAC NIC2 F216N 21600 CAMERA-FOCUS=DEF,SAMP-SEQ=MIF512, 1 DEF PAR 5-6 WITH 4 CUM NSAMP=25,PATTERN=TWO-CHOP, OFFSET=SAM,CHOP-SIZE=90, PATTERN-ORIENT=0,NUM-POS=16 Comments: These are the Arp220 observations on the emission line with NIC2, which is prime. We need to chop because the source is large. Background counts are about equal to counts expected from the target, so chopping with 2 on and 2 off exposures per orbit should be OK. Note that in some cases RPS2 wanted to put 5 exposures into 1 orbit; this should be AVOIDED, since "on" and "off" exposures must not be separated. ------------------------------------------------------------------------------------------------------------------------------------ 5 PARALLEL-FI NIC1 MULTIAC NIC1 F160W 16000 SAMP-SEQ=MIF512,NSAMP=25 1 DEF ELD CUM Comments: These are the NIC1 parallel observations for Arp220, on line. NIC2 is always prime. Parameters and pointing of the parallel observations is irrelevant, they are only meant to suppress the "bars" in NIC2, as recommended in one of the NICMOS advisories, The parallel observations are tailored such that they take just as long as the prime observations. ------------------------------------------------------------------------------------------------------------------------------------ 6 PARALLEL-FI NIC3 MULTIAC NIC3 G141 16000 SAMP-SEQ=MIF512,NSAMP=25 1 DEF ELD CUM Comments: These are the NIC3 parallel observations for Arp220, on line. NIC2 is always prime. Parameters and pointing of the parallel observations is irrelevant, they are only meant to suppress the "bars" in NIC2, as recommended in one of the NICMOS advisories, The parallel observations are tailored such that they take just as long as the prime observations. ------------------------------------------------------------------------------------------------------------------------------------ 7882( 2) - 11/21/97 08:47 - [ 8] Visit: 02 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: These are the NGC6240 exposures. The F216N exposures are on the redshifted H2 1-0 S(1) line and the F215N are the off-line reference exposures. Since the line is on the red side in the F216N filter, F215N will be line-free. NIC2 is always prime. The attached parallels are only for suppressing the "bars" in NIC2, hence the pointing and parameters for the parallels are irrelevant as long as the parallel observations take as long as the prime observations. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6240 NIC2 MULTIAC NIC2 F215N 21500 CAMERA-FOCUS=DEF,SAMP-SEQ=MIF512, 1 DEF PAR 2-3 WITH 1 CUM NSAMP=25,PATTERN=TWO-CHOP, OFFSET=SAM,CHOP-SIZE=90, PATTERN-ORIENT=45,NUM-POS=12 Comments: This is the NGC6240 off-line exposure with NIC2, which is the prime camera. We need to chop, because of the size of the source. Background counts are expected to be about equal to counts from the target, so 2 on and 2 off per orbit should be OK. We chop at an angle of 45 degrees in order to avoid a bright star east of the galaxy. Note that in some cases RPS2 wanted to put 5 exposures into 1 orbit. This should be AVOIDED: "on" and "off" exposures MUST not be separated. ------------------------------------------------------------------------------------------------------------------------------------ 2 PARALLEL-FI NIC1 MULTIAC NIC1 F160W 16000 SAMP-SEQ=MIF512,NSAMP=25 1 DEF ELD CUM Comments: This is the NIC1 parallel exposure for NGC6240, off-line. NIC2 is always prime. Actual pointing and parameters for the parallel observations are irrelevant, since they are only included to suppress the "bars" in NIC2, as recommended in one of the NICMOS advisories. The parallel exposures are tailored such that they take as long as the prime exposures. ------------------------------------------------------------------------------------------------------------------------------------ 3 PARALLEL-FI NIC3 MULTIAC NIC3 G141 16000 SAMP-SEQ=MIF512,NSAMP=25 1 DEF ELD CUM Comments: This is the NIC3 parallel exposure for NGC6240, off-line. NIC2 is always prime. Actual pointing and parameters for the parallel observations are irrelevant, since they are only included to suppress the "bars" in NIC2, as recommended in one of the NICMOS advisories. The parallel exposures are tailored such that they take as long as the prime exposures. ------------------------------------------------------------------------------------------------------------------------------------ 7882( 2) - 11/21/97 08:47 - [ 9] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6240 NIC2 MULTIAC NIC2 F216N 21700 CAMERA-FOCUS=DEF,SAMP-SEQ=MIF512, 1 DEF PAR 5-6 WITH 4 CUM NSAMP=25,PATTERN=TWO-CHOP, OFFSET=SAM,CHOP-SIZE=90, PATTERN-ORIENT=45,NUM-POS=16 Comments: This is the NGC6240 exposure on the redshifted H2 1-0 S(1) line with NIC2, which is the prime camera. We need to chop because of the large source size. The background counts are expected to be about equal to the counts from the target, so 2 on and 2 off exposures per orbit should be OK. We chop at 45 degrees in order to avoid a bright star East of the galaxy. Note that in some cases RPS2 wanted to put 5 exposures into 1 orbit; this must be AVOIDED: the "on" and "off" exposures MUST NOT be separated. ------------------------------------------------------------------------------------------------------------------------------------ 5 PARALLEL-FI NIC1 MULTIAC NIC1 F160W 16000 SAMP-SEQ=MIF512,NSAMP=25 1 DEF ELD CUM Comments: This is the NIC1 parallel exposure on NGC6240 , on-line. NIC2 is always prime, parallel exposures are only included so as to suppress the "bars" in NIC2, as recommended in a NICMOS advisory. Hence pointing and parameters of the parallel exposures are irrelevant, as long as the parallel exposures take as long as the prime exposures. ------------------------------------------------------------------------------------------------------------------------------------ 6 PARALLEL-FI NIC3 MULTIAC NIC3 G141 16000 SAMP-SEQ=MIF512,NSAMP=25 1 DEF ELD CUM Comments: This is the NIC3 parallel exposure on NGC6240 , on-line. NIC2 is always prime, parallel exposures are only included so as to suppress the "bars" in NIC2, as recommended in a NICMOS advisory. Hence pointing and parameters of the parallel exposures are irrelevant, as long as the parallel exposures take as long as the prime exposures. ------------------------------------------------------------------------------------------------------------------------------------ 7882( 2) - 11/21/97 08:47 - [ 10] Summary Form for Proposal 7882 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations NIC2 NIC1 NIC3 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CAMERA-FOCUS=DEF SAMP-SEQ=MIF512 NSAMP=25 PATTERN=TWO-CHOP OFFSET=SAM CHOP-SIZE=90 PATTERN-ORIENT=0 NUM-POS=12 NUM-POS=16 PATTERN-ORIENT=45 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PAR 2-3 WITH 1 PAR 5-6 WITH 4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F212N F160W G141 F216N F215N ------------------------------------------------------------------------------------------------------------------------------------ Target Names IC4553 PARALLEL-FIELD NGC6240 ------------------------------------------------------------------------------------------------------------------------------------