Dark matter properties of dwarf galaxies in the GAIA era Louis E. - - PowerPoint PPT Presentation

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

• Now able to measure 3 velocity

components of stars in dSphs

Proper motion

Astrometry + dark matter

• Now able to measure 3 velocity

components of stars in dSphs

• What can this tell us about dark matter?

Proper motion

Dark matter properties of dwarf satellites

• 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-

measured

Velocity dispersion [km/s]

Walker et al. 2007 Simon & Geha 2007

Multiple stellar populations in dwarf galaxies

• 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)

Battaglia et al 2008

Multiple stellar populations in dwarf galaxies

• 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)

Radius [kpc] Velocity dispersion [km/s] 0.1 0.2 0.3 0.4 0.5 0.6 2 4 6 8 10 12

Battaglia et al 2008

Internal proper motions with HST

• 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

− − − − − − − − − − − − − − − − − − − − −0.2 0.0 0.2 0.4 −0.6 −0.4 −0.2 −0.0 0.2 −0.2 0.0 0.2 0.4 µW (mas/yr) −0.6 −0.4 −0.2 −0.0 0.2 µN (mas/yr)

Draco dSph

Pryor et al. (2015) Casetti−Dinescu (2016) This study

(b)

− − − − − − − − − − − − − − − − − − − − −0.6 −0.4 −0.2 −0.0 0.2 −0.6 −0.4 −0.2 −0.0 0.2 −0.6 −0.4 −0.2 −0.0 0.2 µW (mas/yr) −0.6 −0.4 −0.2 −0.0 0.2 µN (mas/yr)

Sculptor dSph

Piatek et al. (2006) This study

(b)

Sohn, Patel et al. 2017

Internal stellar proper motions

d σR = 11.5 ± 4.3 km s−1

d σT = 8.5 ± 3.2 km s−1

Massari et al. 2018, 2019 ith this high-quality dataset we determined be σR = 11.0+2.1

1.5 km/s, σT = 9.9+2.3 3.1 km/s

This results in a velocity anisotropy β 0.28

Sculptor Draco

Sculptor multiple stellar populations & proper motions

• NFW

Burkert

5 10 15 0.1 1

Radius (kpc) σT (km/s)

• 5

10 15 0.1 1

Radius (kpc) σR (km/s)

• 5

10 15 0.1 1

Radius (kpc) σLOS (km/s)

Sculptor multiple stellar populations & proper motions

• NFW

Burkert

5 10 15 0.1 1

Radius (kpc) σT (km/s)

• 5

10 15 0.1 1

Radius (kpc) σR (km/s)

• 5

10 15 0.1 1

Radius (kpc) σLOS (km/s)

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

Andrew Pace & LS 2019

• 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

Sagittarius: NFW and Burkert fits

Andrew Pace & LS 2019

• 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

RR Lyrae in Dark Energy Survey

Stringer et al. 2019

RR Lyrae in Dark Energy Survey

Stringer et al. 2019

Sculptor

RR Lyrae in Dark Energy Survey

Stringer et al. 2019

Fornax Sculptor

RR Lyrae in the core of Sagittarius

Peter Ferguson et al. 2019

• 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?)

Orbits of dwarfs in simulations

Stellar streams around dwarf galaxies?

Fornax: Wang et al. (DES Collaboration) 2018

Omega Centauri

Omega Centauri

ω Cen Centaurus A Right ascension [degrees] Declination [degrees] 220 215 210 205 200 195 190 185

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• Best fit dark matter spectrum: 31 GeV
• Sensitivity to much lower annihilation cross

sections that dSphs or Galactic center

• Deeper radio observations

Omega Centauri

b a ωCen’s half-light radius [M ]

Stellar mass-to-light ratio [M /L ] 15 20 25 0.1 1.0 6.0 Velocity dispersion [km/s] Radius [pc] No dark matter

• ω

Residuals 1012 Photon energy [GeV] 0.1 1 10 100 1.0 0.5 0.0

• 0.5
• 1.0

10-11 10-12 10-13 Gamma ray emission [ erg / cm / s ]

2 Mill ise con d p u l s a r s D a r k m a t t e r a n n i h i l a t i

• n

Brown et al. 2019 Reynosa-Cordova et al. 2019

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

ω Cen Centaurus A Right ascension [degrees] Declination [degrees] 220 215 210 205 200 195 190 185

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