Distances & Stellar population properties using SBF

Michele Cantiello

• INAF Oss. Astronomico di TeramoStellar 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)

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!

SBF method (2)• Measure the Amplitude of the spatial fluctuations

(SBF) +• Calibration of the absolute SBF magnitude =

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• Distances

mSBF – MSBF= DM• Stellar population properties’ analysisMeasured

Calibrated

TEramo-SPoT group: SBF measurement

1) Mask the dust patches, saturated stars and other bright objects (if any)

2) Model the galaxy profile (that’s why the “smooth profile”)3) Mask the globular clusters, bkgrnd galaxies, foreground

stars, etc.4) Get the power spectrum of the residual frame & match/fit it

with the PSF power spectrum SBF amplitudesWe developed a SBF measurement procedure

specifically optimized to detect/analyse SBF gradients5) Once you get mSBF (usually: ), you need MSBF m

TEramo-SPoT group: SBF calibrationEmpirical 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 synthesisSPoT models (Raimondo et al. 2005)In the Figure: Ages in the range 3-14 GyrMetallicity range: [Fe/H]=-1.8 to 0.3 dex

Example calibration derived: MSBF,I=-1.6+4.5[(V-I)-1.15]

Problems

Need DMs from other distance indicators. Reliable?

One single filter!

Good No DM neededAll filters you can/want do in one single shot!

ProblemsModels suffer for uncertainties as well!

TEramo-SPoT group: SBF DistancesSBF-based distances have been derived from few-kpc up to ~ 150 Mpc

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 MpcWith such distances we got H0~75 (see Biscardi et al. Poster’s - #1)

mSBF – MSBF DM as usual

Measured

Calibrated Nearly 5 orders of magnitude with one single distance indicator! Quite uncommon…

SBF and Stellar population properties Absolute SBF mags.If the DM is known – fromanother D.I. – then: MSBF =mSBF - DM

e.g. Age and t comparing data with models

SBF colorsNo 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 gradientsGradients 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

SummaryTeramo 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