Distances & Stellar population properties using SBF Michele Cantiello

1. Distances & Stellar population properties using SBFMichele Cantiello • INAF Oss. Astronomico di Teramo Stellar POpulations Tools - SPoT - group • Gabriella Raimondo • Michele Cantiello • Enzo Brocato • Ilaria Biscardi (Univ. “Tor Vergata”) • with: • John P. Blakeslee - Herzberg Institute of Astronomy (Canada) • Massimo Capaccioli - Università degli Studi di Napoli (Italy) • Simona Mei - Observatoire de Paris Meudon (France)

2. SBF method (1) • Tonry & Schneider (1988): Distance indicator for ellipticals up to 20 Mpc • Today: D.I. for unresolved and resolved stellar systems with regular brightness profiles, ellipticals+bulges of spirals+dwarfs+cDs+globular clusters … distances’ range: few kpc up to hundred of Mpc • where “regular” means (nearly) dust free and smooth profiles > Nearby mottled/granulous > Far smooth The “mottling” correlates with the distance! M32 @ 0.75 Mpc N7768 @ 100 Mpc

3. SBF method (2) • Measure the Amplitude of the spatial fluctuations (SBF) + • Calibration of the absolute SBF magnitude = ________________________ • Distances mSBF – MSBF= DM • Stellar population properties’ analysis Measured Calibrated

4. TEramo-SPoT group: SBF measurement • Mask the dust patches, saturated stars and other bright objects (if any) • Model the galaxy profile (that’s why the “smooth profile”) • Mask the globular clusters, bkgrnd galaxies, foreground stars, etc. • Get the power spectrum of the residual frame & match/fit it with the PSF power spectrum  SBF amplitudes We developed a SBF measurement procedure specifically optimized to detect/analyse SBF gradients • Once you get mSBF (usually: ), you need MSBF  

5. Empirical methods Galaxies with known distance moduli (DM) then: MSBF=mSBF-DM Tonry & collaborators: MSBF is not constant. It is more or less correlated to the integrated color, i.e. the stellar population content of the galaxy, depending on the wavelength interval used Example calibration: MSBF,I=-1.58+4.5 x [(V-I)-1.15] from Tonry et al. (2001) + Jensen et al. (2003) Stellar population synthesis SPoT models (Raimondo et al. 2005) In the Figure: Ages in the range 3-14 Gyr Metallicity range: [Fe/H]=-1.8 to 0.3 dex Example calibration derived: MSBF,I=-1.6+4.5[(V-I)-1.15] TEramo-SPoT group: SBF calibration Problems • Need DMs from other distance indicators. Reliable? • One single filter! Good • No DM needed • All filters you can/want do in one single shot! Problems • Models suffer for uncertainties as well!

6. TEramo-SPoT group: SBF Distances mSBF – MSBF  DM as usual SBF-based distances have been derived from few-kpc up to ~ 150 Mpc Measured Calibrated Nearly 5 orders of magnitude with one single distance indicator! Quite uncommon… SPoT (1): SBF for young & old stellar clusters in the Magellanic Clouds at ~ 50 kpc (Raimondo et al. 2005) SPoT (2): Using high resolution data (ACS@HST), & the theoretical calibrations from the SPoT models, we derived the first distances of 4 ellipticals @ 55-110 Mpc With such distances we got H0~75(see Biscardi et al. Poster’s - #1)

7. SBF and Stellar population properties Absolute SBF mags. If the DM is known – from another D.I. – then: MSBF =mSBF - DM  e.g. Age and t comparing data with models SBF colors No DM is required. Some examples Cool…but you need the right color choice. Best results with B-K or I-H, i.e. optical to near-IR colors (last slide) SBF gradients Gradients allow a relative comparison between galaxies, e.g. C05: Models&data tell us that most of the observed grads are driven by metallicity changes, except for NGC1344 that is probably an “age-gradient” dominated

8. Summary Teramo SPoT group distances & stellar population properties with SBF • Refined SSP models (also) for the specific purpose of SBF analysis • SBF measurements • a) Multi-annuli SBF data and/or • b) Multi color SBF measurements • c) SBF measurements for very distant galaxies  H0 Future works  multi-color SBF to help remove the t-Z degeneracy