Giuseppina Battaglia Instituto de Astrofisica de Canarias Tenerife Credit ESO HHHeyer Credit ESOL Calçada Karachentsev et al 2014 Individual Red Giant Branch stars ID: 388578
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Slide1
Chemo-dynamics of galaxies with resolved stellar populations: now and then
Giuseppina BattagliaInstituto de Astrofisica de Canarias, Tenerife
Credit
: ESO/
H.H.Heyer
Credit
: ESO/L.
Calçada
Karachentsev
et al. 2014Slide2
Individual
Red Giant Branch stars& CaII triplet intermediate resolution spectroscopy
Gallart
et al 2005
Tracers of galaxy evolution from recent epochs back to the oldest times
Bright!
B
rightest feature in old stellar pop.
At low/ intermediate resolution (R ~ 3
000
-6000
) -> short(
ish
) exposure times:
KINEMATICS: Velocities accurate to a few km/s
CHEMISTRY: Calibration
CaT EW – [Fe/H] OVER A WIDE [Fe/H] RANGE (e.g. Rutledge et al. 1997, Cole et al. 2004, Battaglia et al. 2008, Starkenburg et al. 2010, Carrera et al. 2013 etc.)
Starkenburg
et al. 2010Slide3
Credits:
M.Mateo
McConnachie
2012
Dwarf galaxies: even the simplest galaxies are complexSlide4
Credits:
M.Mateo
McConnachie
2012
Milky Way Dwarf
spheroidals
&
VLT/FLAMES
Phoenix transition type &
VLT/FORS
NGC6822 dwarf irregular &
VLT/MUSE
Early-types
Late-types
Figure credits:
McConnachie
2012; Mario Mateo; Stephen
Leshin
; Local Group Survey Team; Lowell Observatory
Dwarf galaxies: even the simplest galaxies are complexSlide5
Spatial variations of
metallicity properties
Sculptor
dSph
(
Tolstoy et al.
2004,
Battaglia et al. 2008)
Fornax
dSph
(
Battaglia
et al.
2006, 2008)
Sextans
dSph
(
Battaglia
et al. 2011)
[Fe/H] from
CaT
lines calculated using the calibration from
Starkenburg
et al. 2010
(see also e.g. Koch et al. 2006;
Faria
et al. 2007;
Gullieuszik
et al. 2009; Kirby et al. 2011)
Phoenix
dT
(
Kacharov
,
Rejkuba
,
Battaglia
et al.
in prep)
r
tid
r
core
r
core
r
tid
r
tid
r
core
r
core
r
tid
180
mem
180
mem
600
mem
850
memSlide6
A
“centrifugal barrier” mechanism?
Phoenix
Pegasus
Leaman
et al. 2013
Non-rotating Rotating
Less massive (
Mdm
~ 5 x 10^8
Msun
)
More massive (
Mdm
~ 3 x 10^9
Msun
)
Schroyen
et al. 2011
Interesting to analyze
dIrrs
and
dTs
as a function of mass and angular momentum; we are starting to populate the parameter spaceSlide7
MP
MR
“
Metal-rich
”
[Fe/H] > -1.5
“
Metal-poor
”
[Fe/H] < -1.7
Multiple stellar components & dark matter:
Sculptor
(found also in
Fornax
and
Sextans
)
Battaglia
et al. (2008)
-
Kinematics of multiple
stellar
components
prefer
a
cored
profile
to
a
cuspy
one
(
Battaglia
et al. 2008)
-
Not
possible
to
make a
distinction
when
treating
the stars as 1 component
-
Results
confirmed
by
other
groups
(Walker &
Peñarrubia
2011;
Amorisco
& Evans 2012)
Cored _____
Cusped - - - -
No selection in [Fe/H]
Line-of-sight velocity dispersion profiles:Slide8
VLT/FORS: Tolstoy et al. 2001
VLT/FLAMES: Tolstoy et al. 2004,
Battaglia
et al. 2006, 2008, 2011,
Starkenburg
et al. 2010
Much wider range of [Fe/H] values within each galaxy than previously thought -> this should give indications on the galaxy
’
s capability to retain its ISM -> potential well
Presence of (rare) extremely metal-poor stars
(see also Kirby et al. 2009,
Frebel
2010,
Tafelmeyer
et al.2010)
Sculptor
Fornax
Large number statistics is important !
Sculptor
FornaxSlide9
Spatially extended
vs centrally concentrated samplesSlide10
Spatially extended
vs centrally concentrated samples
Kirby et al. 2010, 2011Slide11
Can we carry out similar observations out to the distance of the Virgo cluster using the E-ELT + HARMONI ?
GENERAL AIM: [Fe/H] (±0.3dex) and line-of-sight velocities (±20 km/s for large galaxies, 5km/s for dwarfs) from the
CaT
lines for about 1000 individual RGB stars in a
“
reasonable” observing time out to a few Mpc (Virgo?)
In the
E-ELT era: Simulations within the Design Reference Mission
Credit
: ESO/L.
CalçadaSlide12
Objects and Distance range:
Generalities
~1
Mpc
(LG: NGC205) 4
Mpc
(
CenA
) 17
Mpc
(Virgo: M87)
Tip of the RGB
in I-mag at
~
:
20.6 23.9 27.2
Target RGB + stellar background from mock stellar population yielding a given surf. brightness (code by J.
Liske
)
Constant SFH (14-12Gyr)
[Fe/H] = -1.7 (MP)
[Fe/H] = -1.0 (MR)
Spectrum star 1
+ spectrum star 2
+ ……
+ …. Star N
+ sky contribution
& technical effects
= Integrated spectrum
Spectra from the
Munari
et al. 2005 synthetic spectral library Slide13
R = 4000 & 9000
Instantaneous field-of-view = 5
”
x 10
”
Spatial pixel (
spaxel) size = 40 mas x 40 mas35% instrument throughput
18% Encircled Energy in one spaxel in I-band
Instrumental and technical adopted characteristics
INSTRUMENT (adapted to HARMONI)
TECHNICAL PARAMETERS
Exposure time (20min to 50h)
Site (
Paranal
-like;
High&Dry
)
Mirror coating (bare Al;
Ag/Al
)
Zenith & seeing = 0.8”
Diameter = 42m (to be updated to 39m)Slide14
2 Re ≈
12 kpc
(23.7 mag/arcsec^2)
5 Re ≈
30
kpc
(26.3 mag/arcsec^2)
5
”
Centaurus
A
[Fe/H]=-1 ; target RGB 0.5 mag below tip (I= 24.4)
No crowding at these distances at the explored mag.
High&Dry
; Ag/Al
R=4000&9000Slide15
Centaurus
A
[Fe/H] and
vel
requirements fulfilled in 1h considering the flux in only 1
spaxel
!
EE= 18%:
-> seeing 0.6”If EE=9%
-> exp. time x 4
In reality we will recover the flux over multiple
spaxels
Numb RGB stars per pointing (I <= tip – 0.5mag):
1Re = 75
2Re = 16
3.5Re= 4
-> well feasible to observe 1000 target RGBsSlide16
M87/Virgo
[Fe/H]=-1 ; target RGB at the tip (I= 27.2)
Some crowding already at 4Re (22.2 mag/arcsec^2)
Critical to explore options to use more
spaxels
(
ala
Kammann et al.)
Most likely observations limited to a few
pointings
Slide17
Summary
Even small systems like dwarf galaxies are complex (e.g. metallicity gradients, large range of [Fe/H], multiple-stellar components, rotation etc.). Large number statistics and spatial coverage are important (even more so for larger/more complex galaxies)Intermediate res. Spectroscopy of large numbers of individual RGB stars in the nIR
CaT region with E-ELT+HARMONI:
Well feasible out to a few
Mpc (e.g. CenA
) Much more time consuming at the distance of VirgoSlide18
Caveats
Simulations assumed “perfect” data reduction. Only 1-D spectra simulated.No effect of airmass; just one seeingOnly one spaxel considered and for completely resolved stars Restricted range of SFHs/target types (RGBs)/only CaT
Next Steps
HARMONI simulator (DATA CUBES)Explore options to deal with crowding and extract flux from more spaxels (e.g. as Kammann
et al.)
Actual IFU observations of Local Group systemsSlide19
Resolved stellar population studies with IFUs: NGC6822
dIrr @ VLT/MUSE (PI: Mendel)D= 490kpc
Star-forming and g
as-rich
MV= -15.2Pointing:Surf. Bright V ~ 20.8 mag/arcsec^2
~ half-light radius1’ x 1’, 0.2”/pixel (0.3”-0.4” FWHM)R = 1700 (480nm) – 3600 (930nm)1.5h on source
“BVI” MUSE imageSlide20
Resolved stellar population studies with IFUs:
NGC6822 dIrr @ VLT/MUSE (PI: Mendel)
192 sources
288 sources
Data reduction mostly with ESO pipeline
Source extraction/sky-subtraction with
PampelMUSE
(
Kammann et al. 2013)