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Chemo-dynamics of galaxies
resolved stellar population studies
surroundings of the Milky Way and beyond
Giuseppina Battaglia
Fellow Symposium 2009, 8-10 June, Garching
from
in the
Main interest: Local Group dwarf galaxies
Dwarf irregular (dIrr)
Transition type (dI/dSph)
Dwarf spheroidal (dSph)
Ultra faint
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LeoA
Phoenix
D > 400 kpc from large spirals
Fornax
Canes Venatici
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 (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)
Sextans, Fornax, Sculptor (80 < d [kpc] < 140)
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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
Sculptor
Large scale metallicity properties
MR
MP
Rcore
radius:
•
Metal poor stars found
throughout the galaxy.
Rtidal
562 members (2.5-)
MR
MP
Rcore
Metallicity variation w
Rtidal
Rtidal
Battaglia et al.2006, A&A
Fornax
Rcore
Tolstoy et al.2004, ApJL
470 members (3-)
•
Metal rich stars mostly
found at smaller radii
Chemo-dynamics: Sculptor
Battaglia et al.2006, A&A
MR
•
Link between metallicity and
kinematics
MP
•
•
“Metal Poor”
mass determination
Explored cored and cusped
dark matter profiles (for a range
of core radii and concentration
parameters)
Battaglia et al. 2008, ApJL
“Metal Rich”
Velocity dispersion profiles for
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)
Rotation: Sculptor
Battaglia et al. 2008, ApJL, 681, 13
a
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
470 probable members on the basis of simple
kinematic selection
Velocities are corrected for the Local Standard of Rest
and Sun motions
Exploring possible links between dwarf types
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Phoenix is relatively close (about 400 kpc)
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It has similar luminosity to Sculptor and it shows hints of age gradients (e.g. MartinezDelgado, 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
E-ELT
E-ELT:
Diameter = 42m
Fully adaptive
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VLT
Decision to build
expected for late 2010
Start of operations
planned for 2018
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
Can we perform similar studies out to the distance of
the Virgo cluster with the E-ELT?
=> 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?
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?
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
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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 12-14 Gyr; MR: [Fe/H]=-1.0 &
MP: [Fe/H]=-1.8
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TECHNICAL PARAMETERS
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•
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Exposure time (20min to 50h)
Site (Paranal-like; High&Dry)
Mirror coating (bare Al; Ag/Al)
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Example: CenA
1 Re  6 kpc
5 Re  30 kpc
50 mas x 50 mas
50 mas x 50 mas
5”
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QuickTime™ and a
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Tip of the RGB (I = 23.7)
Tip of the RGB (I = 23.7)
5h exposure time, Paranal-like, Ag/Al