Credit: Subaru Telescope

Galactic Archaeology with
the Prime Focus Spectrograph

Miho N. Ishigaki (Tohoku University)
Galaxy Evolution workshop, June 5-7th 2019
University of Tokyo,
Kashiwa Library Media Hall

The PFS GA teamMasashi Chiba (PI, Tohoku University)
Judy Cohen (Caltech)
Rosemary Wyse (John Hopkins University)
Evan Kirby (Caltech)
Kohei Hayashi (ICRR)
Yutaka Komiyama (NAOJ)& GA Science working group
Instrumentation & Software teams

Special thanks to inspiring discussions/conversation with theorists and observers

Outstanding questions in galaxy evolution•Beginning•Formation and physical properties of the very first galaxies•Growth•Merging history of large spiral galaxies like the Milky Way and the M31•Present•Distribution of dark and luminous matter in galaxies•Chemical evolution•Production of metals by supernovae of various generations of stars
This talk: How GA help answering these questions, Why PFS is usefulWhat makes PFS unique?
Subaru telescope (8.2 m)+Moderately wide field of view (1.3 deg2)➡ Faint and distant stellar populations (i<22)
Dwarf satellites

https://www.naoj.org/Gallery/

Outer Milky Way(halo/disk/streams)

Andromeda (M31)https://www.naoj.org/Gallery/

NASA / JPL-Caltech / R. Hurt, SSC & Caltech.

Field-of-view comparison
Gemini: GMOS-N/S
5.5x5.5 arcmin

Keck: DEIMOS
16.7x5.0 arcmin

VLT: FLAMES
25 arcmin diameter

Subaru: PFS 1.3 deg diameter• The widest FoV among
optical multi-object
spectrographs at 8-10m
telescopes• Complementary to the4m projects
2
4MOST:
4deg•• WEAVE: 3deg2
2DESI:
7deg•Mock PFS spectra for a red-giant star
PFS simulator (K. Yabe, C. Hirata et al.) for gmag=20, 21, 22 stars, Exposure time = 3hours

Absorption lines produced by singly ionized calcium
σVlos ~ 1km/s

σVlos ~ 2km/s

σVlos ~ 5km/s+ measurement ofelemental abundancesof Fe, Mg, Si, Ca, and Ti

Outstanding questions in galaxy evolution•Beginning•Formation and physical properties of the very first galaxies•Growth•Merging history of large spiral galaxies like the Milky Way and the M31•Present•Distribution of dark and luminous matter in galaxies•Chemical evolution•Production of metals by supernovae of various generations of stars
This talk: How GA help answering these questions, Why PFS is useful

The beginning of galaxy formation
Formation of the first (PopIII) stars at z>15

Supernovae of the first stars ejecting metals
Ritter et al. 2012

Hirano et al. 2014

Open questions•How massive the first stars were?
•How does their supernovae impact to the IGM?
•How did the ejected metals mix with IGM?
•When did the first galaxies form?
Direct observations are not feasible➡ Galactic Archaeology is the key

Ultra-faint dwarf galaxies as a fossil of the first galaxies
Bootes I Ultra-faint dwarf galaxyOkamoto et al. 2012

4mPFS

6
VeryfaintM~-5.8,
Dynamicalmass~10M◎V•• Age greater than 13 Gyrs, spread < 1 Gyr• Velocity and chemical analysis with PFS (1 pointing)will reveal its full chemodynamical evolution

Metallicity of the faint dSphs hint at stochastic
chemical enrichments
Simon & Geha 2007

Globular clusters

L (M*) -metallicity relation

UFDs
Local group dSphs
Break down?

Hint at stochastic chemical enrichments by the first generations of stars in the early Universe

Outstanding questions in galaxy evolution•Beginning•Formation and physical properties of the very first galaxies•Growth•Merging history of large spiral galaxies like the Milky Way and the M31•Present•Distribution of dark and luminous matter in galaxies•Chemical evolution•Production of metals by supernovae of various generations of stars
This talk: How GA help answering these questions, Why PFS is usefulGrowth of large spiral galaxies
Font et al. 2006

Merging history isencoded in spatial,
kinematic andchemical distributionsof old stars
Outer halo of the Milky Wayand M31 are particularly
importantSubstructuresassociated with thecosmological merging
eventsAllLow-[α/Fe]

Wide-field spectroscopic surveys of M31
4m limit

M31RGBPFS limitMerging history of M31
When did the accretion occur?, how massive the accreted galaxy was?
➡ Line-of-sight velocity and metal abundance ([Fe/H], [alpha/Fe]) are the keys

Komiyama et al. 2018

The mechanism of galaxy mergers probed by SgrChiba-san’s slide( the PFS collaboration meeting 2018)

Laporte et al. 2018

Outstanding questions in galaxy evolution•Beginning•Formation and physical properties of the very first galaxies•Growth•Merging history of large spiral galaxies like the Milky Way and the M31•Present•Distribution of dark and luminous matter in galaxies•Chemical evolution•Production of metals by supernovae of various generations of stars
This talk: How GA help answering these questions, Why PFS is usefulParticle nature of dark matter
Searches for γ-rays from dark matter annihilation
Fermi satellite

Plot by Hayashi & Chiba

Hayashi et al. 2016

Fornax dwarf galaxy, Credit: ESO/Degitized Sky Survey 2

Dwarf satellites stellar sample will be increased

V magPFS depthWalker et al. 2009, AJ, 137, 3100; Walker et al. 2009, ApJS, 171, 389

PFS fieldof-view

PFS-GA-plan(@12/2018):
Sculptor
FornaxDracoBootesI
Ursa MinorSextans

Stellar streams
Tracer of the gravitational potential of the Milky Way’s dark matter halo
Known streams in the north (Grilmair et al. 2016)

Stellar stream gaps as probes of missing satellites
Yoon et al. 2011
Gaps in a simulated stellar
stream orbiting in a host halowith the dark matter subhalo
mass distribution consistent
with the ΛCDM prediction
No subhalos

Top: stellar density, middle: line-of-sightvelocity dispersion, bottom: line-ofsight velocity

Subhalos with different masses

Distantstreams
byPFS➡ less affected by disk/bulge
Diffuse➡ e.g. ~ 10-30 stars/deg2 (g<22)

PFS field-of-view

Deeper than MSTO
➡ Clear separation of the streamstars from contaminating field stars
based on [Fe/H]

Mock CMD
for Pal5 stream

Shallow(g<20)

Deep(g<22)

Outstanding questions in galaxy evolution•Beginning•Formation and physical properties of the very first galaxies•Growth•Merging history of large spiral galaxies like the Milky Way and the M31•Present•Distribution of dark and luminous matter in galaxies•Chemical evolution•Production of metals by supernovae of various generations of stars
This talk: How GA help answering these questions, Why PFS is usefulChemical abundance ratios
Kirby et al. 2011

Core-collapse
supernovae
Core-collapse
supernovae
Core-collapse +Type Ia
supernovae
Core-collapse +Type Ia
supernovae

Observed chemical abundances

Chemical evolution modelMeasuring C in PFS spectra
Synthetic spectra for a typical halo subgiant; Teff=5800K, logg=3.5, [Fe/H]=-2(Calculated by the code developed by W. Aoki-san; Kurucz model + VALD line list)
Solar abundance

CEMP ([C/Fe]≥1.0)
PFS ETC/simulator developed by K. Yabe & PFS project officeg=20.0 (d◉~25kpc)
S/N~30 (2 hours of exposure)Searches for stars with pristine chemistry in theouter Milky Way halo
Carbonicity ([C/Fe]) map from the SDSS/SEGUE survey (Lee et al. 2017)High [C/Fe] ratios may be originated from supernovae of the Pop III starsOuter• Chemistry ([Fe/H], [α/Fe], and [C/Fe]) in the outer stellar halo hints atnucleosynthesis in the early Universe• Making constraints on surviving (low-mass) Pop III stars (Ishiyama et al. 2016;Hartwig et al. 2016)

Created by M. Chiba•Beginning

PFS GA summary•Faint dwarf satellite galaxies, which are the potential candidate of surviving first galaxies,
provide a unique opportunity to observational probe the cosmic dark ages

•Growth•Kinematics and chemistry of substructures/streams in the outer stellar halos of the Milky Way andM31 allow for reconstructing the merging history of large spiral galaxies•Present•Present-day distribution of dark matter in dwarf satellites puts stringiest constraints on the natureof dark matter•Chemical evolution•Detailed chemical abundances in dSphs are powerful in constraining formation history of thesegalaxies. Chemistry in the outer MW stellar halos can be used as a signature of nucleosynthesisby the progenitor Pop III stars.

PFS has an advantage in all of these science cases because of
its large FoV and faint limiting magnitudes

Subaru 20th anniversary conference
November 17-22 @Waikoloa Beach, Hawaii
https://www.subarutelescope.org/subaru20anniv/index.html
Abstract submission deadline: June 15th

There will also be the “PFS session”!

Keynote & Invited Speaker
Vasily Belokurov (U. of Cambridge)
Brent R. Tully (UH-IfA)
Eric Peng (PKU-KIAA)
Karoline Gilbert (STScI)Kim Venn (U. of Victoria)
Laura Ferrarese (CNRC-NRC)
Masashi Chiba (Tohoku U.)
Michael Rich (UCLA)