Galactic Archaeology with Subaru: Prospects for Wide-Field Surveys
Masashi Chiba
(Tohoku University, Sendai)with HSC and PFS science working groups
Outline
Background Wide-field photometric survey with
Hyper Suprime Cam (HSC) Wide-field, fiber-fed multi-object
spectroscopic survey with Prime Focus Spectrograph (PFS)
What do we want to know?Formation of the Galaxy in CDM theory
Bright parts arecentrally concentrated
Dark halo in the GalaxyAssembly of CDMBy Moore
Resolved stars provide fossil recordsof galaxy formation process
By Moore
Then, what data do we need?
Photometry : mag., color ( → color-mag. diagram)
Spectroscopy : metallicity , Vrad (kinematics)abundance pattern ( → SFH & chemical evol.)
Astrometry : proper motion, distance (→ 6d phase space)
⇒ galaxy formation and evolution
Subaru/PFS
Subaru/HSC
Gaia
HSC
HSC
(Hyper Suprime Cam)
FOV: 1.77 sq deg (1.5 deg diameter)Pixel scale: 0”.17/pixFilters: grizy + several NBFirst light: Jan., 2012
Prime focus
International collaboration: Japan, Princeton, Taiwan
Funded since 2006
HSC
Wide-field FoV is essential for mapping stars
Subaru Strategic Program (SSP)with HSC (to be submitted)
(dedicated to a newly commissioned instrument: max: 60 nights/year x 5 years)
1. Wide-field survey over ~ 1,500 deg2
cosmology: primary science driver weak lensing, strong lensing, galaxy clusters
other science incl. galactic archaeology
2. Deep and ultra-deep survey galaxy and QSO/AGN evolution
high-z galaxies, re-ionization, z~7 QSOs
HSC white paper(July, 2011)
Planned GA survey with HSC
1. Wide-field survey of the MW outer haloDiscovery of new ultra-faint dSphs and halo streams3 bands (g, r, i), ~ 26 mag (3 mag deeper than SDSS)~1,500 deg2 (fully utilizing weak-lensing survey data)color-magnitude diagram for old MS + RGB stars in the
outer halo (r = 30 – 250 kpc)
2. Deep and wide-field survey of the M31/M33 halo Detailed mapping of stellar halos in M31/M33Use (DDO51-type) NB515 filter centered @ 515 nm
to distinguish halo RGBs with (g, i) + NB515 imagingNB515 is fully optimized for z=3 BAO as well
(Belokurov+ 2006)
UFDs and substructures revealed by SDSS
20 < r < 22
Tollerud +08
Observed photometric properties of Galactic satellites(SDSS)
Single LSST: rlim = 24.5Co-added LSST: rlim =27.5Subaru/HSC(wide-f. survey): rlim~26
satellites
radius
(Bullock & Johnston 2005)Halo realization
Survey of the MW outer halo with HSC
HSC
HSC
HSC survey over ~1,500 deg2
• ~ 20 new UFDs @ Mv<-3• 3~4 new streams with lim~34 mag/”
Stellar halos in M31/M33using (DDO51-type) NB515 filter
CW: 5145 A, FWHM: 80 A
To separate RGBs in M31/M33 from Galactic dwarfs+ optimized for BAO science using z=3 LAEs
Requirement from BAO science(with Y. Matsuda)
Feasibility for LG science(with M.Tanaka)
giants
dwarfs
130 HSC pointings
Deep and wide-field survey of stellar halos in M31/M33 with HSC
Metallicities and RVs of substructuresand satellites with PFS (+ star clusters)
ITRGB=20.5
Ibata+
PFS
PFS
(Prime Focus Spectrograph)
FOV: 1.5 deg in diameter2400 fiber positionersλ: 380~1,300 nm(3 channels: Blue, Red, IR)R: ~3,000First light: 2016
Led by IPMU (U. of Tokyo) + NAOJ/Subaru community+ Caltech/JPL, Princeton, (JHU), LAM, UK, Brazil, Taiwan
Prime focus
Spectrograph design By Jim Gunn
Red
Blue
IR
Key science with PFS(Science white paper, 1st ver. in Jan 2011)
1. Cosmology: primary science driver BAO, lensing
2. Galaxy evolution Galaxies at z ~ 2 and beyond
3. Galactic archaeology Milky Way and Local Group
4. QSO/AGN evolution QSOs at z < 6
1st version of PFS white paper(Jan, 2011)
SuMIRe=Subaru Measurement of Images and RedshiftsThe project name using both HSC and PFS
Many fibers Merging history
GA science goals with PFS
1. Formation of Galactic structures Merging history of the Milky Way (MW)? Formation of old MW components (thick disk, halo)? Star-formation history of dwarf satellites? Formation of M31: is it different from the MW?
2. The nature of galactic dark matter How is dark matter distributed in the MW? Dark matter of dwarf satellites: is CDM correct?
GA science goals with PFS
All of these information are recorded in stars
1. Space and velocity distributions of ancient stars Past collapse and merging events
Tracer of dark matter profiles
2. Chemical abundance of ancient stars Star formation and chemical evolution
Phase space
Debris of building blocks
A building block
Helmi & de Zeeuw 2000
Freeman & Bland-Hawthorn 2002
Extracting past merging history: how?
Astrometry with Gaia (precise distances and proper motions) + Vrad & [Fe/H] distrib. with PFSwill resolve each of blocksand its chemical evolution
Accretion time of a satellite can be deducedfrom phase-space distribution of stars
(McMillan & Binney 2008, Gomez+ 2010)
7.9 Gyr 8.9 Gyr 7.6 Gyr
r-
Lz
r-
k
P(k)
Orbital freq.
GA survey plan with PFS
1. The Milky Way survey• Sample:
i. Gaia sample: ~ 106 stars with 18<V<20 (Halo ~55%, Thick disk ~40%, Thin disk ~5%)
ii. Faint sample: stars in 8-9 stellar streams and ~ 105 stars in the outer halo with 18<V<21.5
• Total area: 1,000 + 180 deg2 (560 + 100 pointings)• Survey time: ~30 + 20 = 50 nights
2. The M31 halo survey• Sample: RGBs, V < 21.5• Total area: ~ 230 deg2 (~130 pointings)• Survey time: ~ 30 nights
3. Dwarf galaxy survey• Sample: RGBs, V < 21.5• Survey time: ~ 8 nights (can be PI-led programs)
Summary: GA with Subaru next decade
HSC (2012~)• 1.5 deg FOV, gri+NB515, g<26• Discovery of new UFDs and halo
substructures in the MW• Detailed halo structure in M31/M33
PFS (2016~)• R=3,000, ~2,400 fibers, λ=380-1300 nm, 18<V<21.5• Discovery of kinematical substructures and
merger history in the MW • Dark matter and abundance distribution in
Local Group galaxies
TMT
(Thirty Meter Telescope)
WFOS, IRIS, IRMS,HROS, NIRES etc.R~5,000 for mV<26 magR~50,000 for mV<21 mag
Japan will join TMT
GA with TMTScience Working Group (Stars and Local Group)
led by Wako Aoki
1. Exploring stellar activities and explosions
2. Clarifying galaxy formation with resolved stars
Supernovae, GRB, Seismology, First stars,Extremely metal-poor stars, Our Galaxy,Andromeda, The Local Group and beyond …
Summarized in Science Report (2011)