6496( 4) - 04/02/96 09:07 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6496 Version: 4 Check-in Date: 02-Apr-1996 09:03:51 1.Proposal Title: Nuclear Rings: Probing the Hearts of Barred Galaxies ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle GALAXIES & CLUSTERS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Ronald Buta University of Alabama CoI: Deborah Crocker University of Alabama N CoI: Gene Byrd University of Alabama N ------------------------------------------------------------------------------------ 6. Abstract We propose to obtain multi-band PC1 images of two ``nuclear rings'' in barred galaxies, chosen on the basis of showing strong star formation and other characteristics in ground- based images. These small rings, less than 10'' in angular radius, are thought to trace the location of the inner Lindblad resonance (ILR), a 2:1 orbital resonance with the bar that is of great importance to the structure and evolution of disk galaxies. We wish to map the detailed structure in and near these rings, such as dust lanes, shock fronts, and star-forming complexes, from the near-UV to the near-IR in order to examine the process of star formation in the resonance region and to connect the morphology to dynamics. We will use the data to address the following questions. (1) What is the rate of massive star formation in these rings? (2) Is the star formation in the rings continuous or episodic, occurring in periodic ``bursts''? (3) What is the luminosity function of star clusters and HII regions in the rings? (4) How are dust lanes distributed around the rings, and what ``feeds'' the gas to the ring region? (5) How does the small-scale structure in the rings connect to periodic orbit characteristics, bar strength, pattern speed, central density, and the stellar distribution? We will interpret the results in terms of sophisticated numerical models (including stars and gas) of the ILR region in a barred galaxy. The observations should have a significant impact on our understanding of nuclear activity, central starbursts, and galaxy morphology. The sample consists of the nuclear rings in NGC 1326 and ESO 565-11. The former nuclear ring is about average in linear size and intrinsic shape, while the latter is unusually large in linear size and extremely oval in intrinsic shape. Together the two rings should provide complementary insights into the nuclear ring phenomenon. ------------------------------------------------------------------------------------ 6496( 4) - 04/02/96 09:07 - [ 2] Observations Description ------------------------ We will image the two nuclear rings in filters F255W (near uv), F336W (Johnson U), F439W (Johnson B), F555W (Johnson V), and F814W (Cousins I), and the ring of NGC 1326 in filter F658N also. To deduce the required exposure times for U, B, V, and I, we use surface brightnesses measured from ground-based CCD images. Using these surface brightnesses, a background sky brightness $\\mu_V$ = 23.0 mag arcsec^-2 (both galaxies have ecliptic latitudes of >30 degrees), a read noise of 5.2 electrons, a median dark count of 0.008/sec, and the information in the WFPC2 handbook, we have deduced exposure times that will allow us to get good signal-to-noise ratios in the background star light in the ring regions. For filter F255W, the exposure time is geared to get good signal-to-noise in the associations, because the stellar background underlying the rings is very faint in the near-uv. The times are contained within three orbits for each galaxy. The nuclear ring in NGC 1326 is very bright, and at an average point (off the associations) has a surface brightness of 19.4, 19.0, 18.1, and 17.0 mag arcsec^-2 in U, B, V, and I, respectively. Our adopted exposure times and signal-to-noise ratios for these filters are: F336W 23.3m S/N per PC pix = 5.8 F439W 23.3m S/N per PC pix = 8.3 F555W 10m S/N per PC pix = 21.5 F814W 10m S/N per PC pix = 29.5 The nucleus of NGC 1326 is very bright, and may saturate in the split 10m exposures we have adopted for F555W and F814W. We have added 60s exposures in these filters to avoid any possible saturation. For filter F255W, we assume that normal ``super star clusters'' are in the ring. These have an absolute V-band magnitude of -12.5 after allowing for 1.5 magnitudes of typical extinction. At the distance of 16.9 Mpc, the apparent magnitudes would be about V=18.5 and our adopted exposure time of 1000s would yield a point source signal -to-noise ratio of about 6. NGC 1326 will also be observed with the F658N filter to detect the HII regions in the ring. The faintest ones detected in ground-based Halpha imaging have an Halpha flux of 1.0e-16 ergs cm^-2 s^-1. Treating these as point sources, the signal-to-noise that would be reached relative to the bright continuum background would be 7.5 in our adopted exposure time of 20m. The nuclear ring of ESO 565-11 has brighter associations than in NGC 1326, but the ring is physically larger and the background continuum star light is fainter. The surface brightness of the continuum star light underlying the ring is 21.1, 21.0, 20.2, and 19.2 mag arcsec^-2 for U, B, V, and I respectively. Our adopted exposure times and signal-to-noise ratios for these filters are: F336W 25m S/N per PC pix = 1.0 F439W 33.3m S/N per PC pix = 2.7 F555W 10m S/N per PC pix = 6.9 F814W 10m S/N per PC pix = 7.8 These exposure times may saturate the brightest associations in the nuclear ring, which have B=18.3, B-V=0.04, and V-I =0.41. In case they are point sources, we have incorporated short exposures in F439W, F555W, and F814W to avoid this possible saturation. The signal-to-noise ratio for the U-band stellar background is low, but the associations in the ring would be point sources for which the ratio would be much higher. The fainter of these associations in the ring have a B-band magnitude of 20, and in 23.3M the signal-to-noise ratio would be ~70 for an estimated color excess of E(B-V)=0.3 and assuming an intrinsic color similar to a B0 star. For the F255W filter, the signal-to-noise ratio was also computed by assuming the fainter associations are point sources having B = 20 and the intrinsic color of a B0 star. For our adopted 23.3m exposure time, the signal-to-noise ratio would be ~25. The radial velocity of ESO 565-11 is large enough to preclude observations at Halpha with the available filters. Real Time Justification ----------------------- None Supporting optical and Fabry-Perot ground-based observations of ESO 565-11 have already been obtained (Buta et al. 1995b). Optical broad-band and \\halpha\\ images of NGC 1326 have been obtained by Garcia-Barreto et al. (1991) and Crocker et al. (1995). For each galaxy, the main complementary ground-based data we plan to obtain are near-IR JHK observations and estimates of extinction via the H\\alpha to H\\beta ratio. These observations will be obtained at the Cerro Tololo Inter-American Observatory. The JHK observations have already been scheduled for the nights of Feb. 7-8, 1996 at CTIO. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6496( 4) - 04/02/96 09:07 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: University of Alabama, Box 870324, Tuscaloosa, AL 35487-0324 Ship Via: UPS Email: buta@sarah.astr.ua.edu , ------------------------------------------------------------------------------------ 6496( 4) - 04/02/96 09:07 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC1326 GALAXY,STARBURST,RING,B RA=3H 23M 56.37S +/- 0.15S,DEC=- J2000 V = 1362 V = 10.5+/-0.1 AR,NUCLEUS, 36D 27' 51.3" +/- 2.0",PLATE- B-V = 0.88+/-0.05 ID=02IW SURF(U) = 19.4+/-0.3 SURF(B) = 19.0+/-0.3 SURF(V) = 18.1+/-0.3 SURF(I) = 17.0+/-0.3 SURF(6563)=5+/-2e-15 E(B-V) = 0.03+/-0.02 2 ESO565-11 GALAXY,STARBURST,RING,B RA=9H 29M 16.28S +/- 0.15S,DEC=- J2000 V = 4775 V = 13.0+/-0.1 AR,NUCLEUS, 20D 22' 44.4" +/- 2.0",PLATE- B-V = 0.85+/-0.05 ID=04LT SURF(U) = 21.1+/-0.3 SURF(B) = 21.0+/-0.3 SURF(V) = 20.2+/-0.3 SURF(I) = 19.2+/-0.3 E(B-V) = 0.05+/-0.02 6496( 4) - 04/02/96 09:07 - [ 5] Visit: 01 Visit Requirements: 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 NGC1326 WFPC2 IMAGE PC1-FIX F439W 4300 CR-SPLIT=DEF 1 1400S ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC1326 WFPC2 IMAGE PC1-FIX F555W 5398 CR-SPLIT=NO 1 60S ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC1326 WFPC2 IMAGE PC1-FIX F555W 5398 CR-SPLIT=0.5,CR 1 600S -TOLERANCE=0.1 ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC1326 WFPC2 IMAGE PC1-FIX F336W 3342 CR-SPLIT=DEF 1 1400S ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC1326 WFPC2 IMAGE PC1-FIX F814W 7921 CR-SPLIT=NO 1 60S ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC1326 WFPC2 IMAGE PC1-FIX F814W 7921 CR-SPLIT=0.5,CR 1 600S -TOLERANCE=0.1 ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC1326 WFPC2 IMAGE PC1-FIX F658N 6590 CR-SPLIT=DEF 1 1200S ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC1326 WFPC2 IMAGE PC1-FIX F255W 2586 CR-SPLIT=DEF 1 1000S ------------------------------------------------------------------------------------------------------------------------------------ 6496( 4) - 04/02/96 09:07 - [ 6] Visit: 02 Visit Requirements: 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 ESO565-11 WFPC2 IMAGE PC1-FIX F439W 4300 CR-SPLIT=NO 1 100S ------------------------------------------------------------------------------------------------------------------------------------ 2 ESO565-11 WFPC2 IMAGE PC1-FIX F439W 4300 CR-SPLIT=DEF 1 1000S ------------------------------------------------------------------------------------------------------------------------------------ 3 ESO565-11 WFPC2 IMAGE PC1-FIX F439W 4300 CR-SPLIT=DEF 1 900S ------------------------------------------------------------------------------------------------------------------------------------ 4 ESO565-11 WFPC2 IMAGE PC1-FIX F336W 3342 CR-SPLIT=DEF 1 1400S ------------------------------------------------------------------------------------------------------------------------------------ 5 ESO565-11 WFPC2 IMAGE PC1-FIX F555W 5398 CR-SPLIT=NO 1 60S ------------------------------------------------------------------------------------------------------------------------------------ 6 ESO565-11 WFPC2 IMAGE PC1-FIX F555W 5398 CR-SPLIT=0.5,CR 1 600S -TOLERANCE=0.1 ------------------------------------------------------------------------------------------------------------------------------------ 7 ESO565-11 WFPC2 IMAGE PC1-FIX F255W 2586 CR-SPLIT=DEF 1 1400S ------------------------------------------------------------------------------------------------------------------------------------ 8 ESO565-11 WFPC2 IMAGE PC1-FIX F814W 7921 CR-SPLIT=NO 1 60S ------------------------------------------------------------------------------------------------------------------------------------ 9 ESO565-11 WFPC2 IMAGE PC1-FIX F814W 7921 CR-SPLIT=0.5,CR 1 600S -TOLERANCE=0.1 ------------------------------------------------------------------------------------------------------------------------------------ 6496( 4) - 04/02/96 09:07 - [ 7] Summary Form for Proposal 6496 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=DEF CR-SPLIT=NO CR-TOLERANCE=0.1 CR-SPLIT=0.5 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category GALAXIES & CLUSTERS ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F439W F555W F336W F814W F658N F255W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC1326 ESO565-11 ------------------------------------------------------------------------------------------------------------------------------------