Giuseppina Battaglia Chemo-dynamics of galaxies from resolved stellar population studies in the surroundings of the Milky Way and beyond Fellow Symposium 2009, 8-10 June, Garching

Main interest: Local Group dwarf galaxies Dwarf irregular (dIrr) Dwarf spheroidal (dSph ) Transition type (dI/dSph) Ultra faint LeoA FornaxPhoenixCanes Venatici D > 400 kpc from large spiralsD < 250 kpc from large spirals They can be studied in great detail Galaxy formation and evolution on the smallest scales Most dark-matter dominated galaxies (M/L up 100s) => potentially good testing grounds for dark matter theories

Data (mainly from DART Large Progr. at ESO) DARTDART (Dwarf galaxies Abundances & Radial velocities Team): E.Tolstoy, A. Helmi, M.Irwin, V.Hill, G.Battaglia, B.Letarte, P.Jablonka, E.Starkenburg, T.de Boer, M.Tafelmeyer, Y.Revaz, K.Venn, M.Shetrone, N.Arimoto, F.Primas, A.Kaufer, P.François, T.Szeifert, T.Abel, K.Sadakane SAMPLE (Milky Way dSphs)SAMPLE (Milky Way dSphs) Sextans, Fornax, Sculptor (80 < d [kpc] < 140) DATA DATA -ESO/WFI V and I photometry -VLT/FLAMES spectroscopy of Red Giant Branch stars: Intermediate resolution around CaII triplet (R ~ 6500, Å) CaT [Fe/H] (±0.15dex) and l.o.s.velocities (±2 km/s) for hundreds probable members over a large area

Large scale metallicity properties MR MP 470 members (3-  ) Rcore Rtidal Metallicity variation w radius: Metal poor stars found throughout the galaxy. Metal rich stars mostly found at smaller radii 562 members (2.5-  ) MR MP RcoreRtidal Rcore Rtidal Battaglia et al.2006, A&A Tolstoy et al.2004, ApJL Fornax Sculptor

Chemo-dynamics: Sculptor Link between metallicity and kinematics Velocity dispersion profiles for mass determination Explored cored and cusped dark matter profiles (for a range of core radii and concentration parameters) Best fit: isothermal halo with core radius 0.5 kpc and mass(<1.8kpc)= 3.4 ± 0.7 x 10 8 Msun (M/L = 158 ± 33) Battaglia et al.2006, A&A “Metal Rich”“Metal Poor” MR MP Battaglia et al. 2008, ApJL

Substructures: Sculptor Metallicity range, dispersion and luminosity estimate make it consistent with being a disrupted stellar cluster Indications of kinematic substructures have been found in several dSphs (Sextans: Walker et al. 2006, UrsaMinor: Kleyna et al. 2003; Fornax: Battaglia et al. 2006)

Rotation: Sculptor Battaglia et al. 2008, ApJL, 681, 13 a 470 probable members on the basis of simple kinematic selection Velocities are corrected for the Local Standard of Rest and Sun motions Velocity gradient of km/s/deg along the projected major axis of Scl (confirmed by other studies, e.g. Walker et al. 2009). This gradient is likely due to INTRINSIC ROTATION => first time for a dSph in the Milky Way halo

Exploring possible links between dwarf types Phoenix is relatively close (about 400 kpc) It has similar luminosity to Sculptor and it shows hints of age gradients (e.g. Martinez- Delgado, Gallart and Aparicio 1999, wide area but shallow photometry) P83 observations with FORS2 in order to acquire: -wide-area imaging (out to the tidal radius) down to below the horizontal branch -> quantification of stellar population gradients, down to the oldest component) -MXU spectroscopy in the CaT region for about 200 RGB stars over a large area -> internal kinematics and metallicity properties

And beyond the Local Group? To carry out similar studies for a variety of galaxy types (e.g. spirals, ellipticals…) and environments (e.g. clusters) we need to go out to the Virgo cluster => MUCH larger telescope needed!

The European Extremely Large Telescope Design Reference Mission at ESO: Simulate data for a set of selected observing proposals => (i) assess the extent to which the E-ELT addresses key scientific questions and (ii) to assist in critical trade-off decisions. Resolved stellar populations out to Virgo is one of these selected cases (PI: Tolstoy) and I’m working on the intermediate resolution spectroscopy part E-ELT VLT E-ELT: Diameter = 42m Fully adaptive Decision to build expected for late 2010 Start of operations planned for 2018

Can we perform similar studies out to the distance of the Virgo cluster with the E-ELT? Main points to address: Larger distances Crowding: effect of stellar background in the spatial resolution element (spaxel) on the properties of target RGB star -> to which extent will the CaT [Fe/H] and velocity derived from the integrated spectrum resemble the ones of the target RGB star? => Can we derive accurate [Fe/H] and line-of-sight velocities from the CaT lines for large numbers (about 1000) of individual RGB stars in a “reasonable” observing time?

Methodology Create the integrated spectrum (due to target RGB star + stellar background) in a spaxel of 50mas x 50 mas a) decide characteristics of the target RGB star (magnitude, color, [Fe/H], [alpha/Fe], velocity) b) create the stellar background using a stellar population code developed by Joe Liske & E.Tolstoy c) associate to each star the appropriate spectrum (from Munari et al synthetic spectra library) d) sum up the spectra and include technical effects Derive line-of-sight velocity and CaT [Fe/H] from the integrated spectrum Compare to the input line-of-sight velocity and CaT [Fe/H] for the target star -> If they agree within 30 km/s and 0.3 dex, then OK!

Explored parameter space SCIENTIFIC PARAMETERS Distances: 800kpc (ngc205), 4 Mpc (CenA), 17 Mpc (Virgo) Projected radii: 1,2,3.5,5 effective radii Stellar population: constant SFH between Gyr; MR: [Fe/H]=-1.0 & MP: [Fe/H]=-1.8 TECHNICAL PARAMETERS Exposure time (20min to 50h) Site (Paranal-like; High&Dry) Mirror coating (bare Al; Ag/Al)

Example: CenA 1 Re  6 kpc 5 Re  30 kpc 5” Tip of the RGB (I = 23.7) 50 mas x 50 mas Tip of the RGB (I = 23.7) 5h exposure time, Paranal-like, Ag/Al