Dark matter properties of dwarf galaxies in the GAIA era Louis E. Strigari (Texas A&M University) Small Galaxies, Cosmic Questions Durham University July 30, 2019
Astrometry + dark matter
Astrometry + dark matter Proper motion
Astrometry + dark matter Proper motion • Now able to measure 3 velocity components of stars in dSphs
Astrometry + dark matter Proper motion • Now able to measure 3 velocity components of stars in dSphs • What can this tell us about dark matter?
Dark matter properties of dwarf satellites Velocity dispersion [km/s] Simon & Geha 2007 • Jeans-based equilibrium models • Corrections from non-spherical potentials • Self-consistent distribution function-based models • Orbit-based models • Action/angles • Integrated mass within characteristic radius is well- Walker et al. 2007 measured
Multiple stellar populations in dwarf galaxies Battaglia et al 2008 • Some dwarf galaxies (Sculptor, ANDII) show evidence for multiple stellar populations • Some kinematic studies disfavor NFW for Sculptor (Walker & Penarrubia 2011; Amorisco & Evans: Agnelle & Evans 2012) • Some studies show NFW cannot be ruled out for Sculptor (Breddels & Helmi 2014; Strigari, Frenk, White 2014)
Multiple stellar populations in dwarf galaxies 12 10 Velocity dispersion [km/s] 8 6 4 Battaglia et al 2008 2 0 0 0.1 0.2 0.3 0.4 0.5 0.6 Radius [kpc] • Some dwarf galaxies (Sculptor, ANDII) show evidence for multiple stellar populations • Some kinematic studies disfavor NFW for Sculptor (Walker & Penarrubia 2011; Amorisco & Evans: Agnello & Evans 2012) • Some studies show NFW cannot be ruled out for Sculptor (Breddels & Helmi 2014; Strigari, Frenk, White 2014)
Internal proper motions with HST 0.2 0.2 0.2 0.2 Draco dSph (b) Sculptor dSph (b) − − − − Piatek et al. (2006) − 0.0 − 0.0 − 0.0 − 0.0 − − − − µ N (mas/yr) µ N (mas/yr) − − − − This study This study − 0.2 − 0.2 − 0.2 − 0.2 − − − − Pryor et al. (2015) Casetti − Dinescu (2016) − 0.4 − 0.4 − 0.4 − 0.4 − − − − − − − − − 0.6 − 0.6 − 0.6 − 0.6 − − − − − − − − − 0.2 − 0.2 0.0 0.0 0.2 0.2 0.4 0.4 − − − − − − − − − 0.6 − 0.6 − 0.4 − 0.4 − 0.2 − 0.2 − 0.0 − 0.0 0.2 0.2 µ W (mas/yr) µ W (mas/yr) Sculptor requires PMs ~ 22 micro-arcsec/year • Positional accuracy of 0.003 ACS/WFC per epoch • For N exposures, the positional accuracy per exposure is 0.003 sqrt(N) • For N ~5-19, positional accuracy per exposure is ~ 0.01 pixel • Sohn, Patel et al. 2017
Internal stellar proper motions Draco Sculptor ith this high-quality dataset we determined be σ R = 11 . 0 + 2 . 1 � 1 . 5 km / s, σ T = 9 . 9 + 2 . 3 d σ R = 11 . 5 ± 4 . 3 km s − 1 d σ T = 8 . 5 ± 3 . 2 km s − 1 � 3 . 1 km / s This results in a velocity anisotropy β 0 . 28 Massari et al. 2018, 2019
Sculptor multiple stellar populations & proper motions 15 15 15 NFW Burkert ● σ LOS (km/s) 10 10 10 σ R (km/s) σ T (km/s) ● ● ● ● ● ● 5 5 5 0 0 0 0.1 1 0.1 1 0.1 1 Radius (kpc) Radius (kpc) Radius (kpc)
Sculptor multiple stellar populations & proper motions 15 15 15 NFW Burkert ● σ LOS (km/s) 10 10 10 σ R (km/s) σ T (km/s) ● ● ● ● ● ● 5 5 5 0 0 0 0.1 1 0.1 1 0.1 1 Radius (kpc) Radius (kpc) Radius (kpc) Require transverse velocity dispersions to ~ 1 km/s (LS, Frenk, White 2018)
Kinematics of the Sagittarius dwarf galaxy
Sagattarius velocity samples • Several samples of velocity in the central core of Sagittarius (Majewski et al. 2012; Frinchaboy et al. 2012; McDonald et al. 2012) • Evidence of a ``cold spot” in the center
Sagittarius velocity dispersion • To resolve the internal dispersion, need stars with tangential errors less than 12 km/s • Sample contains Red Giant stars; Gaia PMs cross matched with previous spectroscopic samples • F12 sample extends well beyond the core; equilibrium model likely not valid. Andrew Pace & LS 2019
Sagittarius: NFW and Burkert fits • Central region strongly dark matter-dominated (under equilibrium assumption) • Assuming spherical jeans model, fits to entire data set unable to distinguish between core and cusp • Circular orbits strongly preferred from combined data Andrew Pace & LS 2019
Sagittarius: NFW and Burkert fits • Central region strongly dark matter-dominated (under equilibrium assumption) • Assuming spherical jeans model, fits to entire data set unable to distinguish between core and cusp • Circular orbits strongly preferred from combined data Andrew Pace & LS 2019
RR Lyrae in Dark Energy Survey Stringer et al. 2019
RR Lyrae in Dark Energy Survey Sculptor Stringer et al. 2019
RR Lyrae in Dark Energy Survey Fornax Sculptor Stringer et al. 2019
RR Lyrae in the core of Sagittarius Peter Ferguson et al. 2019
Orbits of dwarfs in simulations Fornax analogues in APSOTLE show a range tidal disruption possibilities (Mei-Yu • Wang, Azi Fattahi et al. 2017) Difficult to match the kinematics & the orbital dynamics simultaneously • Best model: Stream with surface brightness ~ 32 mag/arcsec^2 (DES, LSST?) •
Stellar streams around dwarf galaxies? Fornax: Wang et al. (DES Collaboration) 2018
Omega Centauri
Omega Centauri 5 -38 -40 -42 Centaurus A Declination [degrees] -44 -46 ω Cen -48 -50 -52 -54 -56 220 215 210 205 200 195 190 185 Right ascension [degrees]
ω � � � � Omega Centauri Brown et al. 2019 a 25 10 -11 V elocity dispersion [km/s] a n n i r h e i l t a t t a i o m n k r a D No dark matter Gamma ray emission [ erg / cm / s ] 2 20 10 -12 M i l l i s e c o n d p u 15 l s a 10 -13 r s 0.1 1.0 6.0 Radius [pc] 1.0 Residuals 10 12 b 0.5 0.0 • Best fit dark matter spectrum: 31 GeV -0.5 -1.0 ω Cen’s half-light radius [M ] 0.1 1 10 100 • Sensitivity to much lower annihilation cross Photon energy [GeV] sections that dSphs or Galactic center Reynosa-Cordova et al. 2019 • Deeper radio observations Stellar mass-to-light ratio [M /L ]
In the upcoming years • Obtain velocity dispersions from Gaia DR3? • 6D view of Sagittarius and other dSphs? • Revisit possibility of dark matter in globular clusters 5 -38 -40 -42 Centaurus A Declination [degrees] -44 -46 ω Cen -48 -50 -52 -54 -56 220 215 210 205 200 195 190 185 Right ascension [degrees]
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