Milky Way Satellites: Cosmologically Useful Or Just for Astrophysics?

Milky Way Satellites: Cosmologically Useful or Just For Astrophysics?

Josh Simon Carnegie Observatories

Primary Collaborators: Anna Frebel (MIT) Tom Brown (STScI) Evan Kirby (Caltech) Marla Geha (Yale) Asteroseismologists: Why You Should Pay Attention

Image credit: NASA, ESA, A. Sarajedini, & G. Piotto Asteroseismologists: Why You Should Pay Attention • Galaxies are the defining constituents of the universe • Dwarf galaxies are the best probes of the dark matter distribution • (Old) stellar populations and chemical evolution can be observed most cleanly in dwarfs Asteroseismologists: Why You Should Pay Attention

Dwarf galaxies are the smallest, oldest, most metal-poor, most DM-dominated stellar systems in the universe Segue 1: An Unevolved Fossil

Frebel, Simon, & Kirby (2014) Universal Early Chemical Evolution?

[Mg/Fe] [Ca/Fe]

[Ti/Fe] [Cr/Fe]

MV = -20.5 MV = -5.7 3.9-8 < MV < -14 MV = - M = -6.6 M = - 3.8V V Data from Cayrel, Frebel, M = -6.3 M = - 1.5V V Norris, Shetrone, Simon, etc. Finding the Most Metal-Poor Stars in dSphs • Complete, magnitude limited survey (to V~20) of southern dSphs • Uses IMACS spectrograph at Magellan CCKSUMOMPSDG (Complete Ca K SUrvey for the MOst Metal-Poor Stars in Dwarf Galaxies) IMACS Survey Data

[Fe/H] = -1.5 [Fe/H] = -2.5 [Fe/H] = -3.8 Chemical Fingerprints of the First Supernovae

Simon et al. (2014) Chemical Fingerprints of the First Supernovae • Low alpha abundances can only be produced with ≤ 4 SNe

10 SNe 1 SN Ca Ca Mg Mg

Simon et al. (2014) HST Survey of Ultra-Faint Dwarfs

+ Hercules, Leo IV, and UMa I Boo I Can Ven II Coma Ber • Absolute magnitudes -3.8 to -6.2 • Distances 38-160 kpc • S/N = 100 at the main sequence turnoff – Goal: ages to better than 1 Gyr Brown et al. (2012) Leo IV

16 orbits faint limit V~28.5 MST O star V=24.9 MST O star V=24.8 24 Hercules ACS CMD

Hercules 25 Reaches down to I=29 (M2 dwarf at 133 kpc)

)

(

1 8 m 27

29 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 m606-m814 (STMAG) Brown et al. (2014) 24 Leo IV ACS CMD

Hercules 25 Leo IV (Shifted to distance/reddening of Hercules)

)

(

1 8 m 27

29 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 m606-m814 (STMAG) Brown et al. (2014) 24 CVn II ACS CMD

Hercules 25 Leo IV CVn II (Shifted to distance/reddening of Hercules)

)

(

1 8 m 27

29 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 m606-m814 (STMAG) Brown et al. (2014) 24 UMa I ACS CMD

Hercules 25 Leo IV CVn II (Shifted to UMa I distance/reddening of Hercules)

)

(

1 8 m 27

29 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 m606-m814 (STMAG) Brown et al. (2014) 24 Boötes I ACS CMD

Hercules 25 Leo IV CVn II (Shifted to UMa I Boo I distance/reddening of Hercules)

)

(

1 8 m 27

29 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 m606-m814 (STMAG) Brown et al. (2014) 24 ComBer ACS CMD

Hercules 25 Leo IV CVn II All 6 ultra-faint dwarfs UMa I Boo I have nearly identical Com Ber CMDs, with ages as old 26

) as M92

(

4 1

8 SFHs are consistent with m 27 >80% of stars formed by z=6 (12.8 Gyr ago)

29 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 m606-m814 (STMAG) Brown et al. (2014) Limiting Factors on Age Accuracy

• Stellar isochrones (Dage ~ 1 Gyr)

• Distance (Dage ~ 500 Myr)

• [O/Fe] ratio (Dage ~ 500 Myr) Planes of Satellites

• MW plane first identified by Lynden-Bell (1976) and Kunkel & Demers (1976) Planes of Satellites

• Planes now found around both Milky Way and M31 M31 Milky Way

Ibata et al. (2014) Planes of Satellites

• Planes now found around both Milky Way and M31

Pawlowski et al. (2012) Pawlowski et al. (2013) Planes of Satellites

Planes are common in Planes are extremely ΛCDM rare in ΛCDM D’Onghia & Lake (2008) Metz et al. (2009) Libeskind et al. (2009) Pawlowski et al. (2012) Deason et al. (2011) Pawlowski et al. (2014) Lovell et al. (2011) Ibata et al. (2014a) Wang et al. (2013) Ibata et al. (2014b) Goerdt et al. (2013) Bahl & Baumgardt (2014) Sawala et al. (2014) The Cusp/Core Problem

• Navarro, Frenk, & White (1996) 1 ρ(r) ~ 2 (r/rs)(1 + r/rs)

cusp/core dSph Density Profile Results

• Fornax – (Walker & Penarrubia 2011) – core (Jardel & Gebhardt 2012) – core or cusp (Breddels & Helmi 2013) • Sculptor – core or cusp (Battaglia et al. 2008) – (Walker & Penarrubia 2011) – core (Amorisco & Evans 2012) – g = 0 ± 1.2 (Breddels et al. 2013) – core or cusp (Breddels & Helmi 2013) – g = 0 or 1.2 (Richardson & Fairbairn 2014) Stellar + Gas Velocity Fields of 7 Dwarfs

NGC 959 UGC 2259 NGC 2552 UGC 11707

NGC 2976 NGC 5204 NGC 5949

Adams et al. (2014) Stars vs. Gas

• Initial suggestions of disagreement

between stars and gas, now resolved

star g

*,R Adams et al. (2012) - stars

Simon et al. (2003) - gas Adams et al. (2014) Observed Distribution of Central Slopes

Galaxy sample: Adams et al. (2014) + Simon et al. (2005) + Oh et al. (2011)

Simulations: Diemand et al. (2004)

Average DM profile has  = 0.63 ±

0.28 Adams et al. (2014) Summary

• Early chem evolution similar in all galaxies – Second generation stars discovered in Sculptor • Faintest dwarfs have ages >12 Gyr – Consistent with SF shut off by reionization • Both Milky Way and M31 satellites appear to be concentrated in planar structures • Density profiles less problematic than thought – Careful sample selection and high quality data are key