1. SBF with HST Previous ACS & Future WFC3 measurements Michele Cantiello INAF Osservatorio Astronomico di Teramo –Gabriella Raimondo –Enzo Brocato –Ilaria Biscardi »with: John P. Blakeslee - Herzberg Institute of Astronomy (Canada) Massimo Capaccioli - Università degli Studi di Napoli (Italy) Simona Mei - Observatoire de Paris (France)

2. Credits J. Jensen NGC 7768 (100 Mpc)M 32 (0.77 Mpc) Surface Brightness Fluctuations (SBF) 101 Tonry & Schneider (1988, TS88): distance indicator for ellipticals up to 20 Mpc …20 years later… SBF: distance indicator for a much larger family of objects (Galactic and MC star clusters, dwarfs, bulges of spirals, cDs …) distances reached up to now: from few Kpc up to ~130 Mpc Basic idea : nearby  mottled/granulous Far  smooth The mottling correlates with distance! TS88 quantify: SBF ~ ≡ Spatial fluctuations of the Surface Brightness / average Brightness SBF ≡  i n i f i 2 /  n i f i Ratio of the 2° to the 1° moment of the stellar LF SBF also a Tracer of Stellar Population Properties Integrated colors & “classical” mags ≡ first moment of the LF SBF mags: also 2° LF moment, more sensitive to the bright stellar component

3. Our Results (1) Theoretical modeling since 1997 (Brocato et al., 1997) 2003-2005: SPoT models (Raimondo et al., 2005) (available at: www.oa-teramo.inaf.it/spot) Applications to stellar pops, as an example: SBF gradients? Images for SBF analysis: High S/N High resolution Large FoV …ACS! 8 ellipticals (6 bright Es + NGC1344 + 1 local dwarf) from the ACS archive (Cantiello et al., 2005) STELLAR POPULATION ANALYSIS 6 bright Es: SBF vs color gradient ~ mainly due to [Fe/H] variations NGC1344: [Fe/H]+age? Local dwarf (NGC404) no gradients Z=0.01 Z=0.02 t=5-15 Gyr Z=0.04

4. Our Results (2) First B-band SBF at D>10 Mpc B-I SBF color… nice, but… Why? Standard SSP SSP including “extra hot stars” (Cantiello et al. 2003, Cantiello et al. 2007a) Composite SP t= 5,7,9,11,13,14 Gyr

5. Our Results (3) SBF from archival ACS data 14 very different galaxies (dwarfs, shells, giants…) Very different physical properties (Cantiello et al., 2007b) SBF color vs integrated colorAbsolute SBF vs color… M=m-DM (!) t= 5,7,9,11,13,14 Gyr

6. see Raimondo et al. Poster at this conference Possible applications with WFC3 STELLAR POPULATIONS Stellar population studies based on SBF require wide wavelength coverage. Optical to near-IR colors will be perfect! WFC3/UVIS+IR: large FoVs + high resolution + high efficiency = SBF color gradients? DISTANCES We have done SBF distances for ellipticals, not discussed here: Biscardi et al. (2008): D~100 Mpc Raimondo et al. (2005) D~50 Kpc Using also SBF gradients  high accuracy (Cantiello et al., 2005) Farthest SBF distance up to now ~130 Mpc with NICMOS (Jensen et al. 2001) WFC3/IR channel distances farther than 130 Mpc? If so then: SBF more then 10 4 range of distances!