the apache point observatory galactic evolution experiment · ricardo schiavon cs20, boston, august...
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![Page 1: The Apache Point Observatory Galactic Evolution Experiment · Ricardo Schiavon CS20, Boston, August 1st, 2018. Overview paper: Majewski, Schiavon et al. (2017) APOGEE at a Glance](https://reader034.vdocuments.us/reader034/viewer/2022050518/5fa25064cf06a609ec773347/html5/thumbnails/1.jpg)
The Apache Point Observatory Galactic Evolution Experiment
Ricardo SchiavonCS20, Boston, August 1st, 2018
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Overview paper: Majewski, Schiavon et al. (2017)
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APOGEE at a Glance
• Dual hemisphere spectroscopic survey of MW stellar populations
• Bright time SDSS-III/IV survey, 2011.Q2 to 2020.Q2
• Two 300 fiber, R ≈ 22,500, cryogenic spectrographs, large FOV
• H-band: 1510 – 1690 nm (AH /AV ~ 1/6)
• Typical S/N = 100/pixel @ H=12.2 for 3-hr integration
• RV uncertainty spec < 500 m/s in 3 hr Actual < 100 m/s in 1hr
• Precision abundances for ≈ 20 chemical elements (including C, N, O, Fe, other α, odd-Z, a few neutron-capture)
• 5 x 105, predominantly giant stars, probing all Galactic populations, and those of their Local Group counterparts
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2.5 m SDSS telescope at Apache Point Observatory
2.5 m du Pont telescope at Las Campanas Observatory
The APOGEE-N spectrograph
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APOGEE at a Glance
• Dual hemisphere spectroscopic survey of MW stellar populations
• Bright time SDSS-III/IV survey, 2011.Q2 to 2020.Q2
• Two 300 fiber, R ≈ 22,500, cryogenic spectrographs, large FOV
• H-band: 1510 – 1690 nm (AH /AV ~ 1/6)
• Typical S/N = 100/pixel @ H=12.2 for 3-hr integration
• RV uncertainty spec < 500 m/s in 3 hr Actual < 100 m/s in 1hr
• Precision abundances for ≈ 20 chemical elements (including C, N, O, Fe, other α, odd-Z, a few neutron-capture)
• 5 x 105, predominantly giant stars, probing all Galactic populations, and those of their Local Group counterparts
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Why APOGEE makes a difference
High resolution *
Near Infrared *
4-5x105 giant stars
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Optical Sky
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Near-Infrared Sky
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APOGEE Field Plan
APOGEE DR12 coverage
APOGEE Footprint
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APOGEE 2 Field plan - Zasowski et al. (2017)
APOGEE 2 Footprint
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Target Selection
• Main sample is selected from 2MASS (MIR from Spitzer and WISE for dereddening)
• (J-K)0 ≥ 0.5, 7 < H < 13.8 => giants (RGB, AGB, RC) are 80% of the sample
• Open and globular clusters targeted for science and calibration purposes
• Ancillary science programs cover a variety of science targets (young Galactic clusters, M dwarfs, M31 GCs in integrated light)
• For details, see Zasowski et al. (2013,
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APOGEE Scientific Footprint
• Galactic Archaeology
• Local Group galaxies
• Stars
• Stellar Clusters
• Interstellar Medium
• Sub-stellar Companions
• Spectral Analysis
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APOGEE Scientific Footprint
• Galactic Archaeology
• Local Group galaxies
• Stars
• Stellar Clusters
• Interstellar Medium
• Sub-stellar Companions
• Spectral Analysis
Disk Bulge
Halo{
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• What is the current “structure” of the Galaxy?
• What was the history leading up to it?
• What does that teach us about galaxy formation
The Questions:
Galactic Archaeology
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• What is the current “structure” of the Galaxy?
• What was the history leading up to it?
• What does that teach us about galaxy formation
The Questions:
Galactic Archaeology
Is the Galaxy a typical galaxy?
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The Nearby Stellar DiskBensby et al. 2014
• Precision abundances for 714 F-G dwarfs
• R = 40,000-110,000
• Solar neighborhood
• A bimodal distribution in [α/Fe] (at constant [Fe/H])
• High α stars older, higher zMAX, shorter RMEAN => Inner (thick) disk
• Low α stars younger, lower zMAX, longer RMEAN => reach Outer disk
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• A bimodal distribution in [α/Fe] (at constant [Fe/H])
• High α stars older, higher zMAX, shorter RMEAN => Inner (thick) disk
• Low α stars younger, lower zMAX, longer RMEAN => reach Outer disk
The Nearby Stellar DiskBensby et al. 2014
• Precision abundances for 714 F-G dwarfs
• R = 40,000-110,000
• Solar neighborhood
Hard
to Ex
plain
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“Reverse Engineering” Disk Formation
Andrews et al. 2017
• Devise SFH and chemical enrichment history to produce observations
• Two-infall model (Chiappini et al. 2001), radial migrations (e.g., Schönrich & Binney 2009, Loebman et al. 2011)
• Match data for solar neighborhood with varying degree of success
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The Disk According to APOGEEHayden et al. 2015
• Study [Fe/H] and [α/Fe] for ~70,000 stars along RGB • Data from DR12. Note bimodal [α/Fe]. • 3 < RGC < 15 kpc, |z|< 2 kpc • See also Hasselquist et al. (2018)
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APOGEE vs EAGLEMackereth, Crain, Schiavon
• Understanding bimodality in light of state-of-the-art cosmological numerical simulations
• Some MW-like galaxies show bimodality in the simulations
�0.2�0.1
0.00.10.20.30.40.50.6
[↵/F
e]
3 < Rgc < 7Kpc 7 < Rgc < 11Kpc 11 < Rgc < 15Kpc
�1.5 �1.0 �0.5 0.0 0.5 1.0
[Fe/H]
�0.2�0.1
0.00.10.20.30.40.50.6
[↵/F
e]
3 < Rgc < 7Kpc
�1.0 �0.5 0.0 0.5 1.0
[Fe/H]
7 < Rgc < 11Kpc
�1.0 �0.5 0.0 0.5 1.0
[Fe/H]
11 < Rgc < 15Kpc
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Den
sity
Perc
enti
le
0.0 < |Z| < 1.0Kpc
1.0 < |Z| < 2.0Kpc
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• Main EAGLE movie here
Milky Way analogue at z=0
The EAGLE project Schaye,RAC+15; RAC+15
Cosmological simulations of the galaxy population.
~200 ~L* galaxies, each with 10,000 star particles.
Diverse formation histories & environments
Largest run is a cubic volume of L=100 cMpc
Unknown feedback efficiencies calibrated to reproduce observables.
Abundances of 9 metal species tracked, from:
- AGB stars- Type Ia SNe- Type II SNe
Visualisation by Adrien Thob
Schaye+ 2015, Crain+2015
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Origin of high-/low-α according to EAGLE cosmological simulations
• High- and low-α populations evolve in chemical isolation • No need to concoct schemes to explain chemical evolution
10− 3
10− 2
10− 1
r[pMpc
]30pkpc
high [α/ Fe]low [α/ Fe]
6 3 2 1 0.5 0.1z
0 2 4 6 8 10 12t [Gyr]
0.0
0.5
1.0
1.5
2.0
2.5
t g[Gyr]
τ
t1/ 2
0 2 4 6 8 10 12t [Gyr]
0 2 4 6 8 10 12t [Gyr]
0.0
0.2
0.4
0.6
0.8
1.0
f Fe,SNIa
− 1.5 − 1.0 − 0.5 0.0 0.5[Fe/H]
− 1− 0.2
0.0
0.2
0.4
0.6
[α/Fe]
Distinct accretion episodes…
tg = ⌃g/⌃̇?
…the earlier fosters shorter consumption timescales
…suppressing enrichment of the ISM with Fe from Type Ia SNe
fFe,SNIa : fraction of Fe in the ISM synthesised by Type Ia SNe
Mackereth, Crain, Schiavon, et al. (2018)
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Accretion History
0 2 4 6 8 10 12
t [Gyr]
0
1
2
3
4
5
MD
MO
200
[⇥10
12M
�]
Correa et al. (2015a)
all discs
bimodal
3 2 1 0.5 0.1z
• Only 6/133 MW-like galaxies in EAGLE show bimodal [α/Fe] distributions
• The phenomenon seems to be associated with intense accretion activity at 1<z<2
• The Milky Way may be a rare MW-like galaxy
Mackereth, Crain, Schiavon et al. (2018)
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C/N and Mass of RGB stars
Masseron & Gilmore (2015)
• High-α/thick disk and low-α/thin disk stars have markedly different [C/N] ratios
• This is a by-product of a combination of stellar evolution (mixing), chemical evolution (weakly) and stellar mass
• The mass of an RGB star is directly related to its age!
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Δν2 ~ M/R3
νmax ~ M/R2 T-1/2
=> Can Solve For M and R
Scaling Relations + Spectroscopy = Mass and Age
“Scaling Relations”16 Cyg A Metcalfe+ 2012
RGB masses from asteroseismology
See Pinsonneault et al. (2018), Epstein et al. (2014)
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Ages of field stars
• Use APOKASC sample to fit relation between Mass and [C/N] for fixed stellar parameters
• Invert relation to estimate masses (thus ages) for 52,000 stars • High-α stars ~8-11 Gyr old. Interesting pattern in thin disk. • Spatial distribution interesting, not corrected for selection function • See also Ness et al. (2016)
Martig et al. (2016)
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Low [a/Fe], youngest
populations
Clear broken exponential
recover [Fe/H] gradient
Mackereth et al. (2017)
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Profiles broaden with age
Timescale of radial migration / disk heating?
log
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Fundamental constraint on models for the formation of
the thick disk
Scale-height of both high- and low-α disks
in solar annulus evolved steadily with
time
Evolution of disk scale-height, hZ
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The BulgeSchultheis et al. 2017, García-Pérez et al. 2018
• Mapping spatial structure and detailed chemical composition of bulge stellar populations
0 < |z| < 0.5 kpc0.5 < |z| < 1 kpc
1 < |z| < 1.5 kpc
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Dissolved Globular ClustersSchiavon et al. 2017
• Stars discovered in the Inner Galaxy with GC abundance patterns (C,N,Mg,Al)
• GC destruction deposited 25% of halo stellar mass at RGC < 2 kpc (108 MSun)
• Corresponds to 6-8 times the mass of the entire existing Galactic GC system
• See also Martell et al. (2017), Fernandez-Trincado et al. (2017)
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GCs and DM halos
Hudson et al. 2014
• Total mass in GC systems scales with the total mass of the system
• Only stellar population found to behave that way
• Suggestion that it formed early, before feedback processes became important
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Hudson et al. 2014
• η=MGC/MTOT
• η= (4±1) x 10-5
• ηMW = 9 x10-6 - 5 x10-5
GCs and DM halos
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Accreted vs “In situ” Halo
• Precision abundances for 94 F-G dwarfs
• R = 40,000-54,000
• Distance < 335 pc
• A bimodal distribution in [α/Fe]
• High α stars mostly on prograde orbits => Puffed up disk/bulge
• Low α stars mostly on retrograde orbits => Accreted
Nissen & Schuster (2010)
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Abundance Patterns
Abundance pattern of low α stars indeed similar to that of dwarf galaxies
Hayes et al. (2018)
See also Fernandez-Alvar et al. (2018)
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Gaia-Enceladus
• Gaia DR2 reveals a large population of retrograde stars within 2.5 kpc of Sun
• Low-α abundances (APOGEE)
• Single accretion event
• Distribution on the sky of potential G-E members
• Progenitor system mass estimated at 6 x 108 MSun
Helmi et al. (2018), Kopelman et al. (2018)
See Also Belokurov et al. (2018), Deason et al. (2018)
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The APOGEE view
• Discovery of an accreted population with very high eccentricity (e)
• Makes up for 2/3 of all APOGEE-Gaia sample
• Presence of a “knee” in Mg-Fe plane suggests massive system (MC-like)
• Low e population shows no “knee” => mix of stellar populations
Mackereth et al. (2018b)
�2.5 �2.0 �1.5 �1.0 �0.5 0.0 0.5
[Fe/H]
�0.2
�0.1
0.0
0.1
0.2
0.3
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[Mg/Fe]
accreted halo
high [↵/Fe]
low [↵/Fe] 0.2
0.4
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0.8
e
0.2
0.4
[Mg/
Fe]
high e
�2.0 �1.5 �1.0
[Fe/H]
0.2
0.4
[Mg/
Fe]
low e
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The EAGLE view
• The EAGLE simulations show that only systems accreted at z < 1.5 have such high eccentricity distributions
• Due to cosmology, such systems tend to be more massive (up to 109 MSun)
• Such accretion events happen for only 3/22 of MW-like galaxies. They are rare.
Mackereth et al. (2018b)
0 1 2 3 4 5 6 7 8 9zmerge
0.2
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1.0
med
ian
e
e =0.85
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
log 1
0(M
⇤)[M
�]
0 8 10 12 13tlookback [Gyr]
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M Dwarfs
• Contain most of the stellar mass
• Least studied among cool stars
• Important in search for extra-solar Earths
• TESS and Plato will discover lots of those
• APOGEE has amassed spectra for an astounding 12,000 M dwarfs.
Souto et al. (2018, 2017)
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M Dwarfs
• Contain most of the stellar mass
• Least studied among cool stars
• Important in search for extra-solar Earths
• TESS and Plato will discover lots of those
• APOGEE has amassed spectra for an astounding 12,000 M dwarfs.
Souto et al. (2018, 2017)
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Spectrum synthesis of Ross 128 — Souto et al. (2018) Teff - 3200 K log g = 5 near solar metallicity Abundances of C, O, Mg, Al, K, Ca, Ti, and Fe
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ASPCAPExample: spectral fits around CO lines
For details, see Holtzman et al. (2015), García Pérez et al. (2017), Majewski et al. (2017)
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The Evolution of APOGEE Stellar Parameters
Download DR14 data from: https://www.sdss.org/dr14/irspec/
See Holtzman et al. (2018) and Jönsson et al. (2018)
Credit: Szabolcs Mészaros