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)

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Dwarf spheroidal (dSph)

Transition type (dI/dSph) Ultra faint

LeoA FornaxPhoenix

Canes Venatici

D > 400 kpc from large spirals D < 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)• DART DART (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, 8000-9000 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

Rcore Rtidal

Rcore Rtidal

Battaglia et al.2006, A&A

Tolstoy et al.2004,

ApJL

FornaxFornax

SculptorSculptor

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 108 Msun (M/L = 158 ± 33)

Battaglia et al.2006, A&A

“Metal Rich”

“Metal Poor”

MR

MP

Battaglia et al. 2008,

ApJL

Rotation: Sculptor

Battaglia et al. 2008, ApJL, 681, 13a

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 7.6+3.3-2.2

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

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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

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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. 2005 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!

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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 12-14 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;

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Example: CenA

1 Re 6 kpc 5 Re 30 kpc

5”

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Tip of the RGB (I = 23.7)

50 mas x 50 mas

50 mas x 50 mas

Tip of the RGB (I = 23.7)

5h exposure time, Paranal-like, Ag/Al