Karoline Gilbert Space Telescope Science Institute Andromeda: The - PowerPoint PPT Presentation

Karoline Gilbert Space Telescope Science Institute

Andromeda: The Benefits of a Good Neighbor Brown et al. 2009 Hamren et al. 2015 Williams et al. 2015 N$ PAndAS$M31$Map$ (McConnachie$et$al.)$ N147$ N185$ E$ Komiyama et al., 2018 30$kpc$ 60$kpc$ 90$kpc$ 150$kpc$ M31$ Giant$Southern$ Stream$ M31$dSphs$ M31$Halo$Fields$ M33$ Dwarf$Galaxy$Fields$

What Can We Learn About Galaxy Formation From Studying Stellar Halos? N$ PAndAS$M31$Map$ (McConnachie$et$al.)$ N147$ N185$ E$ 30$kpc$ 60$kpc$ 90$kpc$ 150$kpc$ M31$ Giant$Southern$ Stream$ M31$dSphs$ M31$Halo$Fields$ M33$ Dwarf$Galaxy$Fields$

Global Properties: Accretion History Inner Halo: In Situ Population • Luminosity Function, Time of Accretion of destroyed dwarf • Constraints on Formation Avenues galaxy population • Relative importance of in situ and • Relative Importance of major/minor mergers over time accretion N$ PAndAS$M31$Map$ Tidal Debris Mass of Halo: (McConnachie$et$al.)$ N147$ Features: Recent Comparing N185$ E$ Accretion Events Observations with • Stellar Simulated Halos properties of recently Key Observables: accreted stellar density, 30$kpc$ 60$kpc$ 90$kpc$ 150$kpc$ M31$ satellites chemical • Modeling of abundances, stellar collision: time velocities, star of accretion, Giant$Southern$ formation histories Stream$ mass of progenitor and host galaxy M31$dSphs$ • Orbits of satellites M31$Halo$Fields$ M33$ Dwarf$Galaxy$Fields$

SPLASH Spectroscopic Survey of the M31 System N$ PAndAS$M31$Map$ (McConnachie$et$al.)$ N147$ N185$ Over 20,000 M31 RGB E$ spectra in disk, halo, and dwarf galaxies More than 50 spectroscopic fields throughout M31’s 30$kpc$ 60$kpc$ 90$kpc$ 150$kpc$ M31$ stellar halo Spectra of more than 1500 M31 halo stars Giant$Southern$ Stream$ Keck+DEIMOS Medium Resolution Spectroscopy M31$dSphs$ R ~ 6000 M31$Halo$Fields$ M33$ Dwarf$Galaxy$Fields$

Global Properties of M31’s Halo: Implications for M31’s Merger History Surface Brightness Profile to 180 kpc Gilbert et al. 2012; also Ibata et al. 2014 (PAndAS) Observed: Lack of break in surface density Surface Brightness profile, Increased variation at large radii Implication: Large number of recent low-mass accretions at large radii Bullock & Johnston (2005) models Cohen et al. submitted Radius (kpc)

Global Properties of M31’s Halo: Implications for M31’s Merger History Metallicity Profile to 180 kpc Gilbert et al. 2014; see also Ibata et al. 2014 (PAndAS) Observed: Significant metallicity gradient to large 0 radii, even after removal of GSS -1 Implication: M31 halo built largely from one to a few [Fe/H] Phot early, relatively massive (>10 9 M sun ) accretion events -2 Tissera 2014, Cooper 2010 Metallicity Secure M31 RGB Stars, Fit to All Stars Substructure Removed -3 Median [Fe/H] Fit Without Substructure 0 50 100 150 200 Radius Radius (kpc)

Global Properties: Accretion History Gilbert et al. 2012, 2014; also Ibata et al. 2014 (PAndAS) • Relative Importance of major/minor mergers over time • Bulk of stellar mass: one to a few early, relatively massive (>10 9 M sun ) accretion events • Many recent low-mass accretions at large radii N$ PAndAS$M31$Map$ (McConnachie$et$al.)$ N147$ N185$ E$ 30$kpc$ 60$kpc$ 90$kpc$ 150$kpc$ M31$ Giant$Southern$ Stream$ M31$dSphs$ M31$Halo$Fields$ M33$ Dwarf$Galaxy$Fields$

Detailed Dissection of Past Collision Events What Can This Exercise Teach Us? Radius Time since collision Angular momentum Velocity of stars: Trajectory of progenitor Progenitor stellar mass: ~ LMC Fardal et al. 2013 Disruption: ~ 750 Myr Fardal et al. 2012 Gilbert et al. 2007 M31 mass: Fardal et al. 2007 M 200 ~ 2 x 10 12 Msun Ratio of stars: density gradient along stream But see also Hammer et al. 2018

Global Properties: Accretion History Gilbert et al. 2012, 2014; also Ibata et al. 2014 (PAndAS) • Relative Importance of major/minor mergers over time • Bulk of stellar mass: one to a few early, relatively massive (>10 9 M sun ) accretion events • Many recent low-mass accretions at large radii N$ PAndAS$M31$Map$ Mass of Halo: Tidal Debris Features: (McConnachie$et$al.)$ N147$ Recent Accretion Fardal et al. 2007, N185$ E$ 2012, 2013 Events • Modeling GSS Gilbert et al. 2007, Fardal disruption et al. 2007, 2012, 2013 event • Giant Southern Stream Related constrains M31 30$kpc$ 60$kpc$ 90$kpc$ 150$kpc$ M31$ virial mass Debris found throughout the inner halo Giant$Southern$ • Likely contributed by Stream$ ~ LMC mass progenitor, disruption ~750 Myr M31$dSphs$ ago M31$Halo$Fields$ M33$ Dwarf$Galaxy$Fields$

Towards an Independent Mass Estimate: What is the Velocity Dispersion of Andromeda’s Stellar Halo? Gilbert, Tollerud et al., 2018 50 spectroscopic fields throughout M31’s stellar halo Simultaneously Model: N$ • MW Distribution: PAndAS$M31$Map$ (McConnachie$et$al.)$ N147$ N185$ E$ • Thin Disk • Thick Disk • Halo • M31 Distribution: 30$kpc$ 60$kpc$ 90$kpc$ 150$kpc$ M31$ • Kinematically hot halo Giant$Southern$ Stream$ • Kinematically cold tidal debris M31$dSphs$ features M31$Halo$Fields$ M33$ Dwarf$Galaxy$Fields$ Prior Information: • Probability of M31/MW membership • Number, properties of tidal debris features Velocity

Characterizing the M31 Halo Velocity Dispersion to 120 kpc Gilbert et al., 2018 Sample from posterior distributions for stellar halo velocity dispersion with distance from M31’s center… Velocity Dispersion To parameterize dispersion with radius as a power-law with slope -0.11 +/- 0.5 Distance from M31’s center

Global Properties: Accretion History Gilbert et al. 2012, 2014; also Ibata et al. 2014 (PAndAS) • Relative Importance of major/minor mergers over time • Bulk of stellar mass: one to a few early, relatively massive (>10 9 M sun ) accretion events • Many recent low-mass accretions at large radii N$ PAndAS$M31$Map$ Mass of Halo: Tidal Debris Features: (McConnachie$et$al.)$ N147$ Recent Accretion Fardal et al. 2007, N185$ E$ 2012, 2013; Gilbert Events et al. 2018 Gilbert et al. 2007, Fardal • Modeling GSS et al. 2007, 2012, 2013 disruption • Giant Southern Stream Related event 30$kpc$ 60$kpc$ 90$kpc$ 150$kpc$ M31$ constrains M31 Debris found virial mass throughout the inner • Towards an halo Giant$Southern$ Independent • Likely contributed by Stream$ ~ LMC mass measurement of mass from progenitor, halo stars disruption ~750 Myr M31$dSphs$ ago M31$Halo$Fields$ M33$ Dwarf$Galaxy$Fields$

Global Properties: Accretion History Gilbert et al. 2012, 2014; also Ibata et al. 2014 (PAndAS) Inner Halo: In Situ Population • Relative Importance of major/minor mergers over time Dorman et al. 2012, 2013 • Bulk of stellar mass: one to a few early, relatively • Inner region of M31’s halo has a massive (>10 9 M sun ) accretion events significant population of stars that • Many recent low-mass accretions at large radii once belonged to the disk N$ PAndAS$M31$Map$ Mass of Halo: Tidal Debris Features: (McConnachie$et$al.)$ N147$ Recent Accretion Fardal et al. 2007, N185$ E$ 2012, 2013; Gilbert Events et al. 2018 Gilbert et al. 2007, Fardal • Modeling GSS et al. 2007, 2012, 2013 disruption • Giant Southern Stream Related event 30$kpc$ 60$kpc$ 90$kpc$ 150$kpc$ M31$ constrains M31 Debris found virial mass throughout the inner • Towards an halo Giant$Southern$ independent • Likely contributed by Stream$ ~ LMC mass measurement of mass from progenitor, halo stars disruption ~750 Myr M31$dSphs$ ago M31$Halo$Fields$ M33$ Dwarf$Galaxy$Fields$

Towards an M31 Accretion Profile e.g., Gilbert et al. 2009, Lee et al. 2015 Stellar Image Credit Sanjib Sharma Surface Density Luminosity Function of Accreted Satellites Metallicity [Fe/H] Time of Accretion Alpha Element Abundances [α/Fe]

Increasing the Census of Chemical Abundances in M31 N$ Existing data PAndAS$M31$Map$ (McConnachie$et$al.)$ Coadd low SNR N147$ N185$ E$ spectra ➤ Mean [Fe/H], [ α /Fe] abundances in individual lines of Jennifer Wojno sight 30$kpc$ 60$kpc$ 90$kpc$ 150$kpc$ M31$ New Spectroscopic Campaign Obtain deep data in Giant$Southern$ Stream$ strategic dSph and halo fields Ivanna Escala ➤ Distributions of [Fe/H], [ α /Fe] M31$dSphs$ abundances in M31$Halo$Fields$ individual lines of sight M33$ Dwarf$Galaxy$Fields$ NSF AST-1614569 and AST-1614081 Evan Kirby