JWST Potential for Studies of the Local Group

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JWST Potential for Studies of the Local Group
R. Michael Rich, UCLA
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The JWST Observatory Optical Telescope
Following slides, thanks to J. Kriss JWST
project (HST website)
, Diameter 6.5 m
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Observatory Performance Characteristics

• Primary mirror is 18 hexagonal segments, 6.5 m in
  diameter.
• Strehl ratio gt 0.80 at 2 micrometers
• Encircled energy gt 0.74 within 0.15 arc sec at
  1um
• Gold coating ? good response at wavelengths gt 0.6
  micrometers
• Field of regard
• Sun angles of 85135 are permitted, with roll
  of 5.
• ? gt35 sky coverage at any instant
• There is a Continuous Viewing Zone (CVZ) of 5
  about the ecliptic poles.

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Overview of JWST Science Instruments

• NIRCam (Near Infrared Camera)
• 0.62.3 ?m, 2.45.0 ?m. R4, 10, 100.
• Fields of view 2 ? 2.2??2.2? 0.032, 0.065 /pix
• Lyot-mask coronagraphy
• F070W, F090W, F110W, F150W, F200W (short
  wavelength)
• NIRSpec (Near Infrared Spectrometer)
• 0.65.0 ?m for R100. 1.05.0 ?m for R1000,
  3000.
• Micro-shutter array (3??3?), fixed slits, and
  Integral Field Unit (3??3?)
• MIRI (Mid Infrared Instrument)
• 528 ?m. R4, 10, 100, 3000.
• Imager (1.9??1.4?), Coronagraphy, Low Resolution
  Spectrometer, IFU (5??5?)
• FGS-TF (Fine Guidance Sensor-Tunable Filter
  Imager)
• 1.02.1 ?m, 2.14.8 ?m. R70150.
• Field of view 2.2??2.2?
• Coronagraphy

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The JWST Focal Plane
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JWST Limiting Sensitivities

• Sensitivity is limited by background radiation
  from the sky and telescope.
• The limiting flux (10 ?) shown is for a point
  source at the North Ecliptic Pole (minimum
  background) in a 100,000 second exposure.

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Gain in Astronomical Capability with JWST (G.
Rieke)
JWST1
Key issues AB30.7 at S/N5 in 10 h
(1-2.2um) Images at 0.7-1um may be compromised
(50 enc in 0.1)
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The Near Infrared Spectrograph

• R1000 mode
• 1.0 - 5.0 µm
• Micro-shutter array (MSA) or fixed slits
• Covered by three 1st-order gratings
• 1.0 - 1.8 µm
• 1.7 - 3.0 µm
• 2.9 - 5.0 µm
• Sensitivity (10? in 104 s)
• 5.2 ?10-19 erg cm-2 s-1 (emission line)
• R3000 mode
• 1.0 - 5.0 µm
• Fixed slit or integral field unit
• Also uses three 1st-order gratings
• R100 mode
• 0.6 - 5.0 µm
• Micro-shutter array or fixed slits
• Covered by single dual-pass prism

Micro Shutter Array

• 4 x (384 x 185) Shutters
• Slits are 200 mas x 450 mas
• 9 arcmin2 of MSA area
• IFU is 3x3 arcsec2
• HgCdTe FPA is 2 ? (2040 ? 2040)
• Pixels are 0.1 arcsec

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The Mid Infrared Instrument (MIRI) Imager Low
Resolution Spectrometer

• MIRI Imager uses a single 1024?1024 SiAs
  detector
• Scale is 0.11 arcsec/pixel, 1.88?1.41 arcmin2
  FOV.
• Sensitivity (10? in 104 s)
• 10 µm (R5) 0.7 µJy
• 21 µm (R4.2) 8.7 µJy
• LRS uses a fixed slit and a grism at R100

MIRI Imager Filters
?????m) ?????m)
MIRI?IM??? 5.6 1.2
MIRI?IM??? 7.7 2.2
MIRI?IM??? 10 2.0
MIRI?IM??? 11.3 0.7
MIRI?IM??? 12.8 2.4
MIRI?IM??? 15 3.0
MIRI?IM??? 18 3.0
MIRI?IM??? 21 5.0
MIRI?IM??? 25.5 4.0
MIRI?IM??? 25.5 4.0
MIRI Imager, LRS Coronagraphs
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MIRI Integral Field Unit (IFU)

• The MIRI IFU uses two 1024?1024 SiAs detectors
• One third of each channels waveband is dispersed
  onto one half of a 1k x 1k detector, and the four
  channels are mapped onto 2 detectors.
• A full 5 to 28 mm spectrum requires 3 exposures,
  with the dichroic/grating wheels moved between
  each exposure.
• 4 channels x 3 exposures 12 (overlapping)
  spectral segments
• Sensitivity to line emission (10? in 104 s)
• 9.2 µm (R2400) 1.0 ?10-17 erg cm-2 s-1
• 22.5 µm (R1200) 5.6 ?10-17 erg cm-2 s-1

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The Tunable Filter Imager

• The FGS Tunable Filter imager has short and
  long-wave channels
• Short wavelength channel 1.0-2.1 µm, R70150
• Long wavelength channel 2.1-4.8 µm, R70150
• Optics are reflective except for the dichroic
  beamsplitter, the Fabry-Perot etalon assemblies,
  and the order-blocking filters.
• Each channel uses a 2048 ? 2048 HgCdTe detector
• FOV 2.2?2.2 arcmin2
• 0.065 arcsec/pixel
• Lyot coronagraphic occulters are similar to
  NIRCams---bars and spots.
• Sensitivity (10?, R100, 104 s)
• 1.5 ?m 357 nJy (continuum), 7.1 ?10-18 erg cm-2
  s-1 (line)
• 2.0 ?m 325 nJy (continuum), 4.9 ?10-18 erg cm-2
  s-1 (line)
• 3.5 ?m 368 nJy (continuum), 3.2 ?10-18 erg cm-2
  s-1 (line)
• 5.0 ?m 504 nJy (continuum), 3.0 ?10-18 erg cm-2
  s-1 (line)

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Stellar Populations Science Case
Design Reference Mission White dwarf cooling
ages of globular clusters, age of Local Group
populations, Abundances of intergalactic stars in
Virgo. Star Formation History Age,
metallicity, stellar content of streams,
structure, and outer disks of M31, M33 and other
Local Group galaxies and their globular clusters.
Global SF history and gradients for dwarf
galaxies. Streams, satellites, metallicity, and
age constraints for halos of galaxies to 10
Mpc Very long integrations ages of halos, ages
of satellites in Virgo cluster.
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Stellar Populations Goals (contd)
Are the ages of the oldest stars (M92) the same
in all metal poor systems? Did character of star
formation change after reionization? Resolve the
stellar populations in low surface brightness
galaxies and tidal tails out to 15 Mpc. Survey
low luminosity stars and mass function in the
Galactic halo and bulge. Settle problem of white
dwarfs as dark matter. Precise relative ages,
maybe star formation history reconstruction, from
white dwarf cooling sequence. AGB stellar
content of galaxies to Virgo
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Where might we be in 2013? Is science worth
doing? Galaxy evolution and formation major
science aims. The relative roles of gas
accretion, interactions, ingestion of companions
will best be sorted out for nearby
galaxies. Galaxy evolution and formation in the
Local Group may not be representative of either
low or high density environments we will want to
conduct detailed studies of stellar populations
across the Hubble sequence and across
environment.
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The HR diagram and the Age Ladder
AGB 107 yr
Red Giant Branch (RGB) 5x108 yr 100-103
Lsun
Horizontal Branch (HB) 108 yr (He burning) 100
Lsun
UVX?
MS turnoff is most reliable age measure. HB can
indicate Intermediate age vs. old pops. The AGB
tip luminosity still not a reliable indicator of
inter- mediate age stars, especially In metal
rich populations
Main sequence 1010 yr H-burning
1 Lsun
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IR is not as good as optical for measuring
age/metallicitybut useful measurements possible
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Deep IR CMD Simulation by D. Reitzel
Simulate field of globular cluster G1 as imaged
in J and K bands with realistic errors. Mu_v24
mag/sq arcsec. Age sensitivity is less than
optical but theres hope for modeling.
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Optical vs. IR IR superior for low luminosity
stars and obscured populations (e.g. survey of
the inner 100pc of the Galaxy).
Absolute mag in V and K as a function of stellar
mass. Infrared colors have a clear advantage for
this problem. At the Galactic Center, one must
reach K27 to get to the end of the hydrogen
burning stars, whereas one must reach to V36 (!)
to accomplish the same in optical colors. This
problem (and others like it) will be done by
JWST. (models from Baraffe et al. 2002)
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The Fuel Consumption Theorem Renzini Buzzoni
(1986) Renzini 1998

• nj B LTtj

nj is number of stars in evol. stage j B is
specific evolutionary flux, 2x1011 stars/yr L T
is the total bolometric luminosity tj is the
lifetime in yr, in evol. stage j.
The fuel consumption equation can be used to
predict the number of stars in a given
evolutionary stage, per sq. arcsec.
We can solve the FCT to find the maximum surface
brightness at which A stellar population can be
resolved. Surf (V) distance modulus mag
(for main sequence stars) Surf (V) distance
modulus 5 mag (HB stars).
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Reach of large space telescopes to image the
Sun (Mv5). JWST gets a wider range of Hubble
types. (courtesy Tom Brown, STScI)
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Applying the White Dwarf Cooling Sequence to
determine Precision relative ages for the Milky
Way and LMC/SMC Globular Clusters and the
Galactic Bulge
New cooling models by Hansen (1998) show that the
oldest DA white dwarfs become bluer at the end of
their cooling tracks, due to H_2 molecular
opacity, and may be observed at M_V18 HSTACS
will likely observe 3-4 clusters (needs 2 epochs
for proper motion cleaning of CMD 10-50 orbits
per epoch)
JWST can do this problem if it can reach the R
band, but old wd suffer the H_2 opacity in the
IR.
JWST can reach M_1um 34, placing the
bulge (m-M)_V16 and intermediate age LMC/SMC
clusters in reach. The technique has the
potential for relative age dating to /- 1 Gyr
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Color-magnitude diagram of M4 HST/WFPC2
Richer et al. 2002
Full Sample Cluster
Field
120 Orbits with WFPC2 -- 1 Hr with JWST
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Constraining the Age of the Globular Cluster M4
(Hansen et al. 2001)
A powerful age constraint, insensitive to 0.5 mag
distance/reddening error.
Detail of proper-motion cleaned cooling sequence
with selection function and DB cooling track
(red). Note the hint of a blueward hook (DA
track in blue).
Fit of cooling models (including
incomplete- ness, and the wd counts from M4. The
best fit is for 12.5 Gyr. Data in grey area
ignored in fit. Chi-square insensitive to
/-0.5 mag error in distance/reddening.
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Best fit age and formation redshift for M4 and
the disk (constrained from models of WD
luminosity function) Hansen et al. 2001
LDMLiebert Dahn Monet
Hansen et al. 2004
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New results 126 orbits (ACS) on NGC 6397
Richer et al. 2006, Hansen et al. 2006 (in prep)
Potentially can date ages to before/after reioniza
tion
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ACS imaging of M31 halo field (vs. 5 old
globular Clusters spanning -2ltFe/Hlt-0.2)
Brown et al.2003
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Brown et al. 2005 astro-ph/0512001
Kalirai et al. 2005
Rich et al. 06
Rich et al. 2006
STREAM
HALO
stream
halo
Stellar populations in halo and giant stream
identical
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RED
ALL
Ferguson et al. 2002 SNAP could map With actual
MS Turnoff ages!
Int. Age AGB
Blue/Red
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Turnoff Photometry of a large sample of
M31 Globular clusters presently impossible with
HST (100 orbits/cluster). JWST will do this in
5hr per cluster.
Rich et al. 2004 (WFPC2 4 orbits)
Jablonka 1999
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The Andromeda dwarfs range from Fe/H-2 to
-1, and show internal age ranges, but RR Lyrae
stars and BHB demand some old component. They
look like Galactic dwarf spheroidals.
Da Costa et al. 1996, 2000, 2002
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For Local Group, possible to work in the outer
M31, M33 disks measure star formation history to
the main sequence turnoff. Contrast SFH of
disks, halos, dwarf galaxies.
Kent 1989
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Detailed star formation histories and Population
gradients in dwarf galaxies Did star formation
change before/after reionization?
MighellRich 1996
Fornax Buonnano et al.
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One would like to map age, star formation history
of dwarf galaxies - was there a transition in SF
before/after reionization? SF history vs radius?
Fornax Dwarf Galaxy Coleman et al. 2004
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Survey of Omega Cen - Ferraro et al. 2004 ApJ L
Bedin et al.
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Extend studies of metallicities of halo
populations
Haris, Harris, Poole 2001
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Wide field surveys of Local Group halos could
reach to below the horizontal branch and allow
structural and relative star formation history
studies.
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Galaxy halos can be resolved to 10 Mpc. Could
make maps of interaction streamers and dwarf
galaxies over wide range Hubble type and
luminosity
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Spiral Galaxy halos
Mouhcine, Ferguson, Rich, Brown, Smith (2005
ApJ 633, 821) Implication How can halos be
accretion of low mass low metallicity satellites ?
MW
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Intergalactic Stars in Virgo
Virgo IntraCluster Stars (VICS) Ciardullo
Williams 2006
An ideal low surface brightness stellar
population Likely tidal streams, possibly new
(very ancient) stellar population formed in a
high density region JWST can measure the age of
this population, easily reach the HB age will
need 100 hrs (equivalent to M31 halo)
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Antennae Hibbard Galex Team 2005
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Saviane et al. 2004 HST image of tidal dwarf
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A SNAP could do detailed studies of unusual
stellar populations, such as those found in
interacting galaxies, tidal tails, etc. The CMDs
at left from WFPC/2 Imagery of the tidal
dwarf Galaxy candidate in NGC 4038/9 SNAP could
map over whole Field of Antennae.
8 associations in the tidal dwarf galaxy
candidate In the Antennae (NGC 4038/9) Saviane.
Hibbard, Rich 2004
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M31 nucleus with resolved stars and PAH emission
(Spitzer/IRAC Ch4 8um Rich et al. 2006 MIRI
will produce 0.5 diffraction limited images
Virgo Possible since AGB stars are short lived,
luminous, rare.
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M32 with resolved AGB stars 200 resolved stars gt
lifetime 104 yrs
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CONCLUSIONS
JWST will have 10x HST sensitivity, but must
work in IR. Resolution like HST but worse in
optical. mid-IR is diffraction limited. JWST
will be powerful in the study of resolved
populations. However, deep photometry will be
possible only in regions of very low surface
brightness. Major progress likely in white dwarf
cooling ages, resolved populations of halos and
satellites, AGB content of major galaxies in the
Local Group.