13681( 4) - 31-Jul-2014 16:06:43 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 13681 Version: 4 Check-in Time: 31-Jul-2014 16:06:43 STScI Edit Number: 0 Title Fluctuation spectroscopy with the ACS ramp filters: a new way to measure the IMF in elliptical galaxies ------------------------------------------------------------------------------------ Type Cycle GO 22 ------------------------------------------------------------------------------------ Investigators Contact? PI: Prof. Pieter van Dokkum Yale University Y CoI: Dr. Charlie Conroy University of California - Santa Cruz N ------------------------------------------------------------------------------------ Abstract Images of old stellar populations show pixel-to-pixel fluctuations due to Poisson variations in the number of giant stars. These surface brightness fluctuations can be used to study the spectra of stars as a function of their luminosity, by obtaining differential spectroscopy of pixels with high and low fluctuations. If the average number of stars per pixel is sufficiently low, there will be individual pixels that have almost no light from luminous giants, providing sightlines that are dominated by main sequence stars. In this regime the observed spectral response is strongly dependent on the number of cool, low mass stars, and hence the stellar initial mass function (IMF). We propose to observe the nearest elliptical galaxy, Centaurus A, through four narrowband ACS ramp filters tuned to the 0.8 - 0.9 micron range. From the relation between ACS narrowband indices and the amplitude of the surface brightness fluctuation we will be able to obtain quantitative constraints on the IMF from 0.1-1 Solar masses, and distinguish between a Kroupa-like IMF or a bottom-heavy, Salpeter-like IMF, with ~5 sigma significance. We have demonstrated the feasibility of the technique used in this proposal in a Cycle 19 program, where we used the same observational strategy to measure the properties of luminous giants in the Virgo galaxy NGC 4472. ------------------------------------------------------------------------------------ Observations Description ------------------------ We are observing a single target, a field away from the dust lane in the galaxy Centaurus A (NGC 5128), in 4 ACS ramp filters, in the ACS F814W filter, and in 2 WFC3 IR filters. The aim is that the field is imaged in the RAMP-I aperture for all the ACS filters (including F814W). A standard 4-exposure box dither pattern is used. The F814W exposures are a total of 2 orbits but they are split over 2 visits. This is deliberate: by comparing the 2 F814W visits we will get valuable information on the errors in cosmic ray rejection, centroiding, etc. The data can be taken at any ORIENT but it is crucial that all 7 visits are taken at the same ORIENT. After iterating with Norman Grogin we included a post-flash to the ramp filter observations, with FLASH=25. 13681( 4) - 31-Jul-2014 16:06:43 - [ 2] For the IR filters, we are using a 4-point dither pattern and observe in F125W and F160W in a single orbit. In the initial submission we used a 2-point pattern; after iterating with Knox Long we changed it to 4-point box pattern. There is no need to dither over the 'blob' - it is more important to have small dithers so there are no relative astrometric distortions between exposures, and it is important to have optimal resolution (i.e. sample the PSF properly). ------------------------------------------------------------------------------------ 13681( 4) - 31-Jul-2014 16:06:43 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC5128 GALAXY, ELLIPTICAL RA=13H25M37.1000S, J2000 V = 6.84 DEC=-42D59'17.00" Reference Frame: Other: SIMBAD Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. ------------------------------------------------------------------------------------------------------------------------------------ 13681( 4) - 31-Jul-2014 16:06:43 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 3 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-IR-DITHER-BOX-MIN Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.572 Line_Spacing 0.365 Coordinate_Frame POS-TARG Pattern_Orient 18.528 Angle_Between_Sides 74.653 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 4 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.265 Line_Spacing 0.187 Coordinate_Frame POS-TARG Pattern_Orient 20.67 Angle_Between_Sides 69.05 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 13681( 4) - 31-Jul-2014 16:06:43 - [ 5] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC5128 ACS/WFC ACCUM WFC1-IRAM FR853N 8218 FLASH=25.0 1 340 S PATTERN 4 1 P see below (2264 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ NGC5128 1 ACS/WFC ACCUM WFC1-IRA FR853N 8218 1 none none none 1 566.0 S MP NGC5128 1 ACS/WFC ACCUM WFC1-IRA FR853N 8218 2 none none none 1 566.0 S MP NGC5128 1 ACS/WFC ACCUM WFC1-IRA FR853N 8218 3 none none none 1 566.0 S MP NGC5128 1 ACS/WFC ACCUM WFC1-IRA FR853N 8218 4 none none none 1 566.0 S MP 13681( 4) - 31-Jul-2014 16:06:43 - [ 6] Visit: 02 Visit Requirements: SAME ORIENT AS 01 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC5128 ACS/WFC ACCUM WFC1-IRAM FR853N 8354 FLASH=25 1 400 S PATTERN 4 1 P see below (2264 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ NGC5128 1 ACS/WFC ACCUM WFC1-IRA FR853N 8354 1 none none none 1 566.0 S MP NGC5128 1 ACS/WFC ACCUM WFC1-IRA FR853N 8354 2 none none none 1 566.0 S MP NGC5128 1 ACS/WFC ACCUM WFC1-IRA FR853N 8354 3 none none none 1 566.0 S MP NGC5128 1 ACS/WFC ACCUM WFC1-IRA FR853N 8354 4 none none none 1 566.0 S MP 13681( 4) - 31-Jul-2014 16:06:43 - [ 7] Visit: 03 Visit Requirements: SAME ORIENT AS 01 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC5128 ACS/WFC ACCUM WFC1-IRAM FR853N 8548 FLASH=25 1 400 S PATTERN 4 1 P see below (2264 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ NGC5128 1 ACS/WFC ACCUM WFC1-IRA FR853N 8548 1 none none none 1 566.0 S MP NGC5128 1 ACS/WFC ACCUM WFC1-IRA FR853N 8548 2 none none none 1 566.0 S MP NGC5128 1 ACS/WFC ACCUM WFC1-IRA FR853N 8548 3 none none none 1 566.0 S MP NGC5128 1 ACS/WFC ACCUM WFC1-IRA FR853N 8548 4 none none none 1 566.0 S MP 13681( 4) - 31-Jul-2014 16:06:43 - [ 8] Visit: 04 Visit Requirements: SAME ORIENT AS 01 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC5128 ACS/WFC ACCUM WFC1-IRAM FR853N 8787 FLASH=25 1 400 S PATTERN 4 1 P see below (2264 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ NGC5128 1 ACS/WFC ACCUM WFC1-IRA FR853N 8787 1 none none none 1 566.0 S MP NGC5128 1 ACS/WFC ACCUM WFC1-IRA FR853N 8787 2 none none none 1 566.0 S MP NGC5128 1 ACS/WFC ACCUM WFC1-IRA FR853N 8787 3 none none none 1 566.0 S MP NGC5128 1 ACS/WFC ACCUM WFC1-IRA FR853N 8787 4 none none none 1 566.0 S MP 13681( 4) - 31-Jul-2014 16:06:43 - [ 9] Visit: 05 Visit Requirements: SAME ORIENT AS 01 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC5128 ACS/WFC ACCUM WFC1-IRAM F814W 1 400 S PATTERN 4 1 P see below (2288 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ NGC5128 1 ACS/WFC ACCUM WFC1-IRA F814W 1 none none none 1 572.0 S MP NGC5128 1 ACS/WFC ACCUM WFC1-IRA F814W 2 none none none 1 572.0 S MP NGC5128 1 ACS/WFC ACCUM WFC1-IRA F814W 3 none none none 1 572.0 S MP NGC5128 1 ACS/WFC ACCUM WFC1-IRA F814W 4 none none none 1 572.0 S MP 13681( 4) - 31-Jul-2014 16:06:43 - [ 10] Visit: 06 Visit Requirements: SAME ORIENT AS 01 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC5128 ACS/WFC ACCUM WFC1-IRAM F814W 1 400 S PATTERN 4 1 P see below (2288 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ NGC5128 1 ACS/WFC ACCUM WFC1-IRA F814W 1 none none none 1 572.0 S MP NGC5128 1 ACS/WFC ACCUM WFC1-IRA F814W 2 none none none 1 572.0 S MP NGC5128 1 ACS/WFC ACCUM WFC1-IRA F814W 3 none none none 1 572.0 S MP NGC5128 1 ACS/WFC ACCUM WFC1-IRA F814W 4 none none none 1 572.0 S MP 13681( 4) - 31-Jul-2014 16:06:43 - [ 11] Visit: 07 Visit Requirements: SAME ORIENT AS 01 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC5128 WFC3/IR MULTIAC IR F125W NSAMP=14, SAMP-SEQ=SPARS25 1 DEF PATTERN 3 1-2 CUM (1311.756 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC5128 WFC3/IR MULTIAC IR F160W NSAMP=14, SAMP-SEQ=SPARS25 1 DEF CUM (1311.756 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ NGC5128 1 WFC3/IR MULTIAC IR F125W 1 none none none 1 N/A CUM NGC5128 1 WFC3/IR MULTIAC IR F125W 2 none none none 1 N/A CUM NGC5128 1 WFC3/IR MULTIAC IR F125W 3 none none none 1 N/A CUM NGC5128 1 WFC3/IR MULTIAC IR F125W 4 none none none 1 N/A CUM NGC5128 2 WFC3/IR MULTIAC IR F160W 1 none none none 1 N/A CUM NGC5128 2 WFC3/IR MULTIAC IR F160W 2 none none none 1 N/A CUM NGC5128 2 WFC3/IR MULTIAC IR F160W 3 none none none 1 N/A CUM NGC5128 2 WFC3/IR MULTIAC IR F160W 4 none none none 1 N/A CUM 13681( 4) - 31-Jul-2014 16:06:43 - [ 12] Summary Form for Proposal 13681 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR, WFC1-IRAMP ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC, WFC3/IR ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=25, FLASH=25.0, NSAMP=14, SAMP-SEQ=SPARS25 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 3 1-2, PATTERN 4 1, SAME ORIENT AS 01 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F125W, F160W, F814W, FR853N ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC5128 ------------------------------------------------------------------------------------------------------------------------------------