8665( 3) - 01/03/01 10:11 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8665 Version: 3 Check-in Date: 03-Jan-2001 10:10:52 1.Proposal Title: The Starburst - AGN Connection: The Nature of the UV-bright Core in NGC 4303 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Luis Colina Instituto de Fisca de Cantabria CoI: Dr. Rosa Gonzalez-Delgado Instituto de Astrof'\i sica de Andaluc'\i N a CoI: Dr. Claus Leitherer Space Telescope Science Institute N CoI: Dr. Miguel Mas-Hesse Laboratorio de Astrof'\i sica Espacial N ------------------------------------------------------------------------------------ 5. Abstract NGC 4303 is to date the best example of the claimed starburst- AGN connection in active galaxies. HST images of NGC 4303 have unveiled the existence of a nuclear mini-bar (250 pc in size), centered on the unresolved (size <= 8 pc) UV-bright core, itself connected with a star-forming mini-spiral (radius ~ 250 pc). The spiral consist of compact clusters (size <= 15 pc) of young stars (5-25 Myrs). The UV- bright core is classified as a Seyfert 2 AGN but its UV luminosity and optical properties are also compatible with the existence of a young (~ 4 Myr) massive (~ 10^5 M_\odot) cluster of stars. We propose to obtain STIS UV spectra of the unresolved core and the brightest knots in the star-forming mini-spiral of NGC 4303. The spectra will be combined with multifrequency data and evolutionary spectral synthesis models to: (1) pin down the nature of the UV-bright core, i.e. AGN versus young massive stellar cluster, (2) quantify the AGN and starburst energy contribution, (3) determine the age and mass of the star-forming knots, and (4) establish an evolutionary sequence of events within the bar - starburst - AGN scenario. The detection of signatures of massive stars in the spectrum of the core of NGC 4303, would demonstrate for the first time ever that a compact (<= 8 pc) massive stellar cluster is located at the core of a Seyfert 2 galaxy and is, perhaps, its dominant energy source. ------------------------------------------------------------------------------------ 8665( 3) - 01/03/01 10:11 - [ 2] Observations Description ------------------------ We plan to observe the core and UV-bright star-forming regions of NGC 4303 using STIS 25^''times0.2^'' long-slit with the MAMA detectors. We have decided to use the 0.2^'' slit for the observations of the core and compact star- forming knots because they appear as bright point-like sources (size ~ 0.1^'') and therefore the resolution will not be significantly degradated by using this slit. For a projected physical size of 0.1^'', the spectral resolution will be degradated to about 2.4Angstrom\ that is sufficient to separate the stellar and interstellar UV absorption lines. The UV range LambdaLambda 1150 - 1740 (G140L) has been selected to include all the relevant massive star spectral features, like NV 1240Angstrom, SiIV 1400Angstrom, CIV 1550Angstrom\ as well as the photospheric lines of O- and B- type stars. vspace2mm centerline UV Observations From our WFPC2 F218W image, the core and brightest individual nuclear star-forming knots have a flux F(2200Angstrom) ~ 0.4 - 2.0 * 10^-15 erg s^-1 cm^-2 AA^-1. Star-forming regions with young stars (age less than 10 Myr) and an internal extinction of E(B-V)= 0.15, have a F(1500Angstrom)/F(2200Angstrom) ratio of 1-2. To be able to do a meaningful comparison of the spectra with model simulations, a S/N ratio of at least 15 is required. Assuming the case of an extended source (MAMA pixels size correspond to 0.^''025) with a 0.1^'' diameter and a ~ 1.0 * 10^-13 erg s^-1 cm^-2 AA^-1 arcsec^-2, a S/N ratio of ~ 20 - 25 per resolution element will be achieved in ~ 120 minutes using G140L. Thus, two full orbits will be needed per position angle to obtain the required S/N. For 4 position angles a total of 9 orbits are required (adding the guide star re-acq. overheads). vspace2mm centerline Target Acquisition and Slit Orientation vspace2mm The Need for an Early Acquision The standard STIS acquisition is not good enough to precisely position the star- forming knots and core of NGC 4303 in the narrow slit. The standard acquisition could have uncertainties of ~ 0.1^'' in the positioning of the slit for large diffuse sources (STIS Handbook). We can not take the risk of having such large uncertainties for the positioning of the narrow 0.2^'' slit and require therefore the use of a peakup. However, since the peakup target acquisition can only be performed in the optical, the slit would be centered where the optical flux peaks. This is not necessarily where the UV flux peaks. Therefore MAMA UV and CCD optical images with STIS should be taken and the offset between the optical and UV flux peak determined. We require one orbit to obtain well exposed optical (F28X50LP) and UV (F25QTZ) images of NGC 4303 as part of an early acquisition. vspace2mm Peakup and Slit Orientation The guide stars plus target peakup acquisition will take no less than 25 minutes. The slit will be positioned along the north-south direction in such a way that the core, the brightest star-forming knots, and part of the diffuse emission connecting them, will be covered. The slit will be first centered on the UV-bright core and then moved to the different UV-bright knots by maneuvering the telescope according to the relative positions measured in our UV images (relative astrometry is better than 0.01^''). The accuracy of the STIS peakup acquisition process is 0.05 times the dimension of the slit (STIS Handbook). However, drift of up to 0.05^'' may occur over a time scale of ~ 12 hours and is attributed to thermal effects as the spacecraft and FGS are heated or cooled. It is therefore recommended to execute a full peakup acquisition after about 4 orbits when using the 0.1^'' narrow slit (HST Cycle 8 Call for Proposals and Phase I Instructions). For this project we require one early acquisition and two full peakup target acquisitions, therefore a total of 2 orbits are needed. The images taken as part of the early acquisition will also be used later on during the scientific analysis of the UV spectra. vspace2mm centerline Observations versus Models: Unveiling the Nature of the UV core The proposed UV spectra will be complemented with the already analised HST images and with ground-based optical spectra. Also, a complete evolutionary synthesis code developed by members of our team (Leitherer et al. 1999, ApJS 123, 3; Mas-Hesse & Kunth 1999, A&A, in press) will be used to interpret the data. These complementary aspects (ground-based optical plus HST observations and spectral synthesis models) are the master keys to identify the nature and properties of the ionizing sources, and have succesfully been applied in the interpretation and dating of the stellar content of extragalactic star-forming regions (Gonzalez Delgado et al. 1999 ApJ 513, 707). The process of unveiling the nature of the UV-bright core will have two steps: beginenumerate em The first one is the detection (or lack of it) of massive stars in the UV spectrum. O-star wind lines are about 10 times as broad as the corresponding interstellar lines and therefore easy to distinguish from them with the high resolution STIS spectra. A positive result would indicate that a young starburst would be the ionizing UV source. In this case, our method will permit to constrain the IMF upper mass limit and age of the star cluster through the fitting of synthetic models to the profiles of the UV lines (NV 1240 Angstrom, SiIV 1400 Angstrom, CIV 1550 Angstrom). The photoionization code will check that the ionizing continuum from this cluster is able to reproduce the HAlpha luminosity and the optical emission line ratios. em The non-detection of massive star features in the UV spectrum would point to a different solution. If strong UV (CIV, SiIV, NV) and optical (ground- based obs.) nebular lines are present at the same spatial location, again we would have two possibilities that will be investigated with photoionization codes: (a) a non-stellar source, (b) ionization originated by shocks, for example if the cluster was evolved enough to contain SN type II. In this case, the UV spectrum would be different from the one coming from a power- law type spectrum, showing carbon and silicon photospheric lines from B-type stars (e.g. the SiIII 1300Angstrom triplet). endenumerate Once the nature of the nuclear source is unveiled, the X-ray and UV luminosity of the stellar cluster best fitting the observed absorption spectral lines can be computed using our synthesis codes. Therefore, we can quantify the relative contribution of the AGN and the starburst to the energy output of the unresolved core. Real Time Justification ----------------------- HST ultraviolet (WFPC2 F218W), optical (WFPC2 F606W) and near-infrared (NICMOS F160W) images of NGC 4303 have already been obtained. The results of the HST UV image have been published (Colina et al. 1997, ApJ 484, L41) and a paper combining the analysis of the HST UV, optical, and near- infrared images with hydrodynamical models is in press (Colina & Wada 1999, ApJ). Ground-based 2D- fiber spectroscopy covering the HBeta - OIII and the HAlpha - SII spectral ranges, have been obtained using the 2D-FIS system. The excitation conditions and velocity field of the ionized gas have been investigated in detail (Colina & Arribas 1999, ApJ 514, 637). Additional ground-based high spatial and spectral long-slit spectra will be obtained in 2000. A CO map with the Plateau de Bure interferometer was taken recently to investigate the gas density and velocity field of the cold nuclear molecular gas (Colina, Planesas & Wada, in preparation). Radio observations with the VLA (A configuration) were requested but not awarded. We plan to resubmit a modified version of this proposal in the future. A proposal to do high resolution X-ray imaging with CHANDRA will be prepared for the next round of proposals. Calibration Justification ------------------------- Real_Time_Justification Additional Comments ------------------- ------------------------------------------------------------------------------------ 8665( 3) - 01/03/01 10:11 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4303-CORE GALAXY, SPIRAL, RA=12H 21M 54.93S +/- 0.2", J2000 Z = V = 9.7+/-0.1 SEYFERT, STARBURST DEC=04D 28' 25.3" +/- 0.2", 0.0052 PLATE-ID=01UQ Coordinate Source: HST_IMAGE Comments: The coordinates for NGC4303-CORE correspond to that of the core of the galaxy as given in table 1 of Colina et al. 1997, ApJ 484, L41. These coordinates were obtained using the WFPC2 F218W image of NGC 4303 obtained for program 6358. 2 NGC4303-SB GALAXY, SPIRAL, RA=12H 21M 54.75S +/- 0.5", J2000 Z = V = 9.7+/-0.1 SEYFERT, STARBURST DEC=04D 28' 24.7" +/- 0.5", 0.0052 PLATE-ID=01UQ Coordinate Source: HST_IMAGE Comments: The coordinates for NGC4303-SB correspond to that of region I as given in table 1 of Colina et al. 1997, ApJ 484, L41. These coordinates were obtained using the WFPC2 F218W image of NGC 4303 obtained for program 6358. These coordinates will be updated when we get the STIS F25QTZ image prior to the STIS spectroscopic observations. 3 NGC4303- GALAXY, SPIRAL, RA=12H 21M 54.93S +/- 0.2", J2000 Z = V = 9.7+/-0.1 OFFSET SEYFERT, STARBURST DEC=04D 28' 25.3" +/- 0.2", 0.0052 PLATE-ID=01UQ Coordinate Source: HST_IMAGE Comments: The coordinates for NGC4303-OFFSET correspond to that of the core of the galaxy as given in table 1 of Colina et al. 1997, ApJ 484, L41. These coordinates were obtained using the WFPC2 F218W image of NGC 4303 obtained for program 6358. These coordinates will be updated when we get the STIS F25QTZ image prior to the STIS spectroscopic observations. 8665( 3) - 01/03/01 10:11 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type STIS-MAMA-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.275 Coordinate_Frame POS-TARG Pattern_Orient 26.6 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type STIS-ALONG-SLIT Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.325 Coordinate_Frame POS-TARG Pattern_Orient 90 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 8665( 3) - 01/03/01 10:11 - [ 5] Visit: 01 Visit Priority: Visit Requirements: BEFORE 01-Dec-2000 On Hold Comments: Additional Comments: Early acquisition ultraviolet and optical images. These images will be used (1) to measure any possible optical to ultraviolet offsets in the position of the core of the galaxy, (2) to update the coordinates for the NGC4303- OFFSET and NGC4303-SB targets, and (3) to refine the values of the position angles (PA) along which the long-slit will be oriented during the spectroscopic observations. These images should be obtained 2 months prior to the execution of the first spectroscopic visit. This time is needed to do the appropiate measurements and update the corresponding parameters (coordinates, position angle of the slit, etc) for visits 2 and 3. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC4303-COR STIS/N ACCUM F25QTZ MIRROR 1 520 S PATTERN 1 10 MAX DUR 100% E UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC4303-COR STIS/C ACCUM F28X50L MIRROR CR-SPLIT=2,GAIN=1 1 210 S MAX DUR 100% E CD P ------------------------------------------------------------------------------------------------------------------------------------ 8665( 3) - 01/03/01 10:11 - [ 6] Visit: 02 Visit Priority: Visit Requirements: ORIENT 85D TO 85D ORIENT 265D TO 265D BETWEEN 01-Feb-2001 AND 01-Mar-2001 AFTER 01 BY 50 D On Hold Comments: Additional Comments: This visit consist of (1) an acquisition using the wide optical filter F28X50LP for a diffuse source and (2) FUV MAMA observations using the 52x0.2 slit along PA40 or PA220 on the sky (corresponds to an ORIENT of PA85 or PA265). The orientation of the slit is such that goes through the core of the galaxy and through region G (brightest UV circumnuclear region; see Colina et al. 1997 ApJ 484, L41). The target + slit orientation constrains are such that the observations can only be scheduled during February 2001, and always after visit 1. The coordinates and PA for the slit (+/- 2 degrees) will be refined after the results of visit 1 had been analysed. A fine lock with two guide stars (GS) is a requirement with the actual structure of the visit. If only one GS is available for the specific ORIENT, we would need to modify the structure of this visit adding a full ACQ or a PEAKUP/ACQ at the beginning of orbit 4. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC4303-COR STIS/C ACQ F28X50L MIRROR ACQTYPE=DIFFUSE,CHECKBOX=7, 1 130 S E CD P DIFFUSE-CENTER=FLUX-CENTROID Comments: This exposure contains the target acquisition using the wide optical filter F28X50LP for a diffuse source. The target acquisition simulator has been used together with the WFPC2 F606W image of NGC 4303 to establish the best acquisition strategy. A checkbox of 11 with a flux-centroid algorithm works fine. The WFPC2 F606W shows a bright point-like source at the center of the galaxy with a diffuse component. A box of 11 STIS-CCD pixels contains 91% of a point source. A checkbox this size optimizes therefore the S/N for the algorithm used in the search of the centroid. ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC4303-COR STIS/F ACCUM 52X0.2 G140L 1425 1 1800 S E UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC4303-COR STIS/F ACCUM 52X0.2 G140L 1425 1 2900 S PATTERN 2 30 E UV-MAM A Comments: A dithering pattern of four points along the slit is used to remove any residual flat-field effects. ------------------------------------------------------------------------------------------------------------------------------------ 8665( 3) - 01/03/01 10:11 - [ 7] Visit: 03 Visit Priority: Visit Requirements: ORIENT 146.5D TO 146.5D ORIENT 326.5D TO 326.5D BETWEEN 01-Apr-2001 AND 01- May-2001 AFTER 01 BY 70 D On Hold Comments: Additional Comments: This visit consist of (1) an acquisition using the wide optical filter F28X50LP for a diffuse source and (2) FUV MAMA observations using the 52x0.2 slit along PA 101.5 or PA281.5 on the sky (corresponds to an ORIENT of PA146.5 or PA326.5). We need first to acquire the offset target which corresponds to the core of the galaxy and then move the telescope (SAM) to target NGC4303-SB (region I in Colina et al. 1997, ApJ 484, L41) The target + slit orientation constrains are such that the observations can be scheduled only during April 2001 and always after visit 1. The coordinates and PA for the slit (+/- 2 degrees) will be refined after the results of visit 1 had been analysed. A fine lock with two guide stars (GS) is a requirement with the present structure of this visit. If only one GS is available for the specific ORIENT, we would need to modify the structure of this visit adding a full ACQ or a PEAKUP/ACQ at the beginning of orbit 4. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC4303-OFF STIS/C ACQ F28X50L MIRROR ACQTYPE=DIFFUSE,CHECKBOX=7, 1 130 S SET CD P DIFFUSE-CENTER=FLUX-CENTROID ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC4303-SB STIS/F ACCUM 52X0.2 G140L 1425 1 1800 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC4303-SB STIS/F ACCUM 52X0.2 G140L 1425 1 2900 S PATTERN 2 30 UV-MAM A Comments: A dithering pattern of four points along the slit is used to remove any residual flat-field effects. ------------------------------------------------------------------------------------------------------------------------------------ 8665( 3) - 01/03/01 10:11 - [ 8] Summary Form for Proposal 8665 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F25QTZ F28X50LP 52X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/NUV-MAMA STIS/CCD STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ACQ ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=2 GAIN=1 DIFFUSE-CENTER=FLUX-CENTROID CHECKBOX=7 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BEFORE 01-Dec-2000 PATTERN 1 10 MAX DUR 100% MAX DUR 100% ORIENT 85D TO 85D ORIENT 265D TO 265D BETWEEN 01-Feb-2001 AND 01-Mar-2001 AFTER 01 BY 50 D PATTERN 2 30 ORIENT 146.5D TO 146.5D ORIENT 326.5D TO 326.5D BETWEEN 01-Apr-2001 AND 01-May-2001 AFTER 01 BY 70 D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC4303-CORE NGC4303-OFFSET NGC4303-SB ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 ------------------------------------------------------------------------------------------------------------------------------------