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

SLIDE 1

Karoline Gilbert Space Telescope Science Institute

SLIDE 2

M31$

N185$ N147$

M33$ 30$kpc$ 90$kpc$ 150$kpc$ 60$kpc$ N$ E$ M31$dSphs$

Giant$Southern$ Stream$ M31$Halo$Fields$

PAndAS$M31$Map$ (McConnachie$et$al.)$

Dwarf$Galaxy$Fields$

Andromeda: The Benefits of a Good Neighbor

Komiyama et al., 2018 Hamren et al. 2015 Williams et al. 2015 Brown et al. 2009

SLIDE 3

M31$

N185$ N147$

M33$

30$kpc$

90$kpc$ 150$kpc$

60$kpc$

N$ E$ M31$dSphs$

Giant$Southern$ Stream$ M31$Halo$Fields$

PAndAS$M31$Map$ (McConnachie$et$al.)$

Dwarf$Galaxy$Fields$

What Can We Learn About Galaxy Formation From Studying Stellar Halos?

SLIDE 4

M31$

N185$ N147$

M33$

30$kpc$

90$kpc$ 150$kpc$

60$kpc$

N$ E$ M31$dSphs$

Giant$Southern$ Stream$ M31$Halo$Fields$

PAndAS$M31$Map$ (McConnachie$et$al.)$

Dwarf$Galaxy$Fields$

Inner Halo: In Situ Population

Constraints on Formation Avenues
Relative importance of in situ and

accretion Mass of Halo: Comparing Observations with Simulated Halos Tidal Debris Features: Recent Accretion Events

Stellar

properties of recently accreted satellites

Modeling of

collision: time

f accretion,

mass of progenitor and host galaxy

Orbits of

satellites Key Observables: stellar density, chemical abundances, stellar velocities, star formation histories Global Properties: Accretion History

Luminosity Function, Time of Accretion of destroyed dwarf

galaxy population

Relative Importance of major/minor mergers over time

SLIDE 5

Over 20,000 M31 RGB spectra in disk, halo, and dwarf galaxies More than 50 spectroscopic fields throughout M31’s stellar halo Spectra of more than 1500 M31 halo stars

SPLASH Spectroscopic Survey of the M31 System

Keck+DEIMOS Medium Resolution Spectroscopy R ~ 6000 M31$

N185$ N147$

M33$

30$kpc$

90$kpc$ 150$kpc$

60$kpc$

N$ E$ M31$dSphs$

Giant$Southern$ Stream$ M31$Halo$Fields$

PAndAS$M31$Map$ (McConnachie$et$al.)$

Dwarf$Galaxy$Fields$

SLIDE 6

Gilbert et al. 2012; also Ibata et al. 2014 (PAndAS)

Global Properties of M31’s Halo: Implications for M31’s Merger History

Surface Brightness Profile to 180 kpc Observed: Lack of break in surface density profile, Increased variation at large radii Implication: Large number of recent low-mass accretions at large radii

Bullock & Johnston (2005) models

Surface Brightness Radius (kpc)

Cohen et al. submitted

SLIDE 7

Gilbert et al. 2014; see also Ibata et al. 2014 (PAndAS)

Global Properties of M31’s Halo: Implications for M31’s Merger History

Metallicity Profile to 180 kpc Observed: Significant metallicity gradient to large radii, even after removal of GSS

50 100 150 200 Radius

3
2
1

[Fe/H]Phot

Secure M31 RGB Stars, Substructure Removed Median [Fe/H] Fit to All Stars Fit Without Substructure

Implication: M31 halo built largely from one to a few early, relatively massive (>109 Msun) accretion events

Tissera 2014, Cooper 2010

Radius (kpc) Metallicity

SLIDE 8

M31$

N185$ N147$

M33$

30$kpc$

90$kpc$ 150$kpc$

60$kpc$

N$ E$ M31$dSphs$

Giant$Southern$ Stream$ M31$Halo$Fields$

PAndAS$M31$Map$ (McConnachie$et$al.)$

Dwarf$Galaxy$Fields$

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 (>109 Msun) accretion events

Many recent low-mass accretions at large radii

SLIDE 9

Fardal et al. 2012 Gilbert et al. 2007 Fardal et al. 2007

Radius Velocity

Time since collision Angular momentum

f stars:

Trajectory of progenitor Ratio of stars: density gradient along stream

Detailed Dissection of Past Collision Events

What Can This Exercise Teach Us?

Progenitor stellar mass: ~ LMC Disruption: ~ 750 Myr M31 mass: M200 ~ 2 x 1012 Msun Fardal et al. 2013 But see also Hammer et al. 2018

SLIDE 10

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 (>109 Msun) accretion events

Many recent low-mass accretions at large radii

Tidal Debris Features: Recent Accretion Events Gilbert et al. 2007, Fardal et al. 2007, 2012, 2013

Giant Southern

Stream Related Debris found throughout the inner halo

Likely contributed by

~ LMC mass progenitor, disruption ~750 Myr ago Mass of Halo: Fardal et al. 2007, 2012, 2013

Modeling GSS

disruption event constrains M31 virial mass

M31$

N185$ N147$

M33$

30$kpc$

90$kpc$ 150$kpc$

60$kpc$

N$ E$ M31$dSphs$

Giant$Southern$ Stream$ M31$Halo$Fields$

PAndAS$M31$Map$ (McConnachie$et$al.)$

Dwarf$Galaxy$Fields$

SLIDE 11

Simultaneously Model:

MW Distribution:
Thin Disk
Thick Disk
Halo
M31 Distribution:
Kinematically hot

halo

Kinematically cold

tidal debris features Prior Information:

Probability of M31/MW

membership

Number, properties of

tidal debris features

Gilbert, Tollerud et al., 2018

Towards an Independent Mass Estimate: What is the Velocity Dispersion of Andromeda’s Stellar Halo?

M31$

N185$ N147$

M33$ 30$kpc$ 90$kpc$ 150$kpc$ 60$kpc$ N$ E$ M31$dSphs$

Giant$Southern$ Stream$ M31$Halo$Fields$

PAndAS$M31$Map$ (McConnachie$et$al.)$

Dwarf$Galaxy$Fields$

50 spectroscopic fields throughout M31’s stellar halo

Velocity

SLIDE 12

Characterizing the M31 Halo Velocity Dispersion to 120 kpc

To parameterize dispersion with radius as a power-law with slope -0.11 +/- 0.5

Gilbert et al., 2018

Velocity Dispersion Distance from M31’s center

Sample from posterior distributions for stellar halo velocity dispersion with distance from M31’s center…

SLIDE 13

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 (>109 Msun) accretion events

Many recent low-mass accretions at large radii

Tidal Debris Features: Recent Accretion Events Gilbert et al. 2007, Fardal et al. 2007, 2012, 2013

Giant Southern

Stream Related Debris found throughout the inner halo

Likely contributed by

~ LMC mass progenitor, disruption ~750 Myr ago Mass of Halo: Fardal et al. 2007, 2012, 2013; Gilbert et al. 2018

Modeling GSS

disruption event constrains M31 virial mass

Towards an

Independent measurement

f mass from

halo stars

M31$

N185$ N147$

M33$

30$kpc$

90$kpc$ 150$kpc$

60$kpc$

N$ E$ M31$dSphs$

Giant$Southern$ Stream$ M31$Halo$Fields$

PAndAS$M31$Map$ (McConnachie$et$al.)$

Dwarf$Galaxy$Fields$

SLIDE 14

M31$

N185$ N147$

M33$

30$kpc$

90$kpc$ 150$kpc$

60$kpc$

N$ E$ M31$dSphs$

Giant$Southern$ Stream$ M31$Halo$Fields$

PAndAS$M31$Map$ (McConnachie$et$al.)$

Dwarf$Galaxy$Fields$

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 (>109 Msun) accretion events

Many recent low-mass accretions at large radii

Tidal Debris Features: Recent Accretion Events Gilbert et al. 2007, Fardal et al. 2007, 2012, 2013

Giant Southern

Stream Related Debris found throughout the inner halo

Likely contributed by

~ LMC mass progenitor, disruption ~750 Myr ago Inner Halo: In Situ Population Dorman et al. 2012, 2013

Inner region of M31’s halo has a

significant population of stars that

nce belonged to the disk

Mass of Halo: Fardal et al. 2007, 2012, 2013; Gilbert et al. 2018

Modeling GSS

disruption event constrains M31 virial mass

Towards an

independent measurement

f mass from

halo stars

SLIDE 15

Stellar Surface Density Metallicity [Fe/H] Alpha Element Abundances [α/Fe]

e.g., Gilbert et al. 2009, Lee et al. 2015 Image Credit Sanjib Sharma

Luminosity Function

f Accreted Satellites

Time of Accretion

Towards an M31 Accretion Profile

SLIDE 16

Increasing the Census of Chemical Abundances in M31

M31$

N185$ N147$

M33$

30$kpc$

90$kpc$ 150$kpc$

60$kpc$

N$ E$ M31$dSphs$

Giant$Southern$ Stream$ M31$Halo$Fields$

PAndAS$M31$Map$ (McConnachie$et$al.)$

Dwarf$Galaxy$Fields$

Existing data Coadd low SNR spectra ➤ Mean [Fe/H], [α/Fe] abundances in individual lines of sight New Spectroscopic Campaign Obtain deep data in strategic dSph and halo fields ➤ Distributions of [Fe/H], [α/Fe] abundances in individual lines of sight

Jennifer Wojno Ivanna Escala Evan Kirby

NSF AST-1614569 and AST-1614081

SLIDE 17

Abundances for Individual Stars: Deeper observations: [α/Fe] vs. [Fe/H] distributions per line of sight

0.6 0.8 1.0 flux

Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Ca Ca Ca Ca Ca Ca Ca Ca Ca Ti Ti Ti Ti Teff = 3939 [Fe/H] = −1.00 ± 0.11 Fornax 37716 R = 17.8 Teff = 3939 [Fe/H] = −1.00 ± 0.11 Fornax 37716 R = 17.8

0.6 0.8 1.0 flux

Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Ca Ca Ca Ca Ca Ca Ca Ca Ca Ti Ti Ti Ti Teff = 4241 [Fe/H] = −2.18 ± 0.11 Ursa Minor Bel10019 I = 15.6 Teff = 4241 [Fe/H] = −2.18 ± 0.11 Ursa Minor Bel10019 I = 15.6

0.6 0.8 1.0 flux

Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Ca Ca Ca Ca Ca Ca Ca Ca Ca Ti Ti Ti Ti Teff = 5153 [Fe/H] = −1.67 ± 0.16 Draco 620611 I = 19.7 Teff = 5153 [Fe/H] = −1.67 ± 0.16 Draco 620611 I = 19.7

6400 6450 6500 6550 rest wavelength (Å) 0.6 0.8 1.0 flux

Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Ca Ca Ca Ca Ca Ca Ca Ca Ca Ti Ti Ti Ti Teff = 5002 [Fe/H] = −2.92 ± 0.27 Sextans 919 I = 19.2 Teff = 5002 [Fe/H] = −2.92 ± 0.27 Sextans 919 I = 19.2 Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Mg Mg Mg Mg Mg Mg Mg Mg Si Si Si Si Si Ti Ti Ti Ti Ti Teff = 4127 [Fe/H] = −1.05 ± 0.11 Fornax 40828 R = 17.9 Teff = 4127 [Fe/H] = −1.05 ± 0.11 Fornax 40828 R = 17.9 Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Mg Mg Mg Mg Mg Mg Mg Mg Si Si Si Si Si Ti Ti Ti Ti Ti Teff = 4641 [Fe/H] = −2.03 ± 0.25 Ursa Minor Bel10043 I = 16.8 Teff = 4641 [Fe/H] = −2.03 ± 0.25 Ursa Minor Bel10043 I = 16.8 Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Mg Mg Mg Mg Mg Mg Mg Mg Si Si Si Si Si Ti Ti Ti Ti Ti Teff = 4929 [Fe/H] = −1.89 ± 0.12 Draco 578941 I = 17.8 Teff = 4929 [Fe/H] = −1.89 ± 0.12 Draco 578941 I = 17.8

8700 8750 8800 8850 rest wavelength (Å)

Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Mg Mg Mg Mg Mg Mg Mg Mg Si Si Si Si Si Ti Ti Ti Ti Ti Teff = 4987 [Fe/H] = −2.05 ± 0.16 Sextans 878 I = 19.1 Teff = 4987 [Fe/H] = −2.05 ± 0.16 Sextans 878 I = 19.1

Kirby et al. 2010

Increasing the Census of Chemical Abundances in M31: Spectral Synthesis

SLIDE 18

Kirby et al., in prep

Current sample of Andromeda dSphs have [Fe/H] and [α/Fe] distributions consistent with MW dSphs of similar mass

Comparing M31 and MW dSphs

Increasing the Census of Chemical Abundances in M31

−3 −2 −1 0.0 0.1 0.2 0.3 0.4 Andromeda VII

(1.5 × 10

7 Msun)

Fornax

(2.5 × 10

7 Msun)

−3 −2 −1 Andromeda I

(7.6 × 10

6 Msun)

Leo I

(4.9 × 10

6 Msun)

−3 −2 −1 Andromeda III

(1.8 × 10

6 Msun)

Leo II

(1.2 × 10

6 Msun)

−3 −2 −1 Andromeda V

(6.2 × 10

5 Msun)

Sextans

(6.9 × 10

5 Msun)

−3 −2 −1 Andromeda X

(1.4 × 10

5 Msun)

Canes Venatici I

(3.0 × 10

5 Msun)

[Fe/H] dN / d[Fe/H]

−0.5 0.0 0.5 1.0 Andromeda VII

(1.5 × 10

7 Msun)

Fornax

(2.5 × 10

7 Msun)

−0.5 0.0 0.5 1.0 Andromeda I

(7.6 × 10

6 Msun)

Leo I

(4.9 × 10

6 Msun)

−0.5 0.0 0.5 1.0 Andromeda III

(1.8 × 10

6 Msun)

Leo II

(1.2 × 10

6 Msun)

−0.5 0.0 0.5 1.0 Andromeda V

(6.2 × 10

5 Msun)

Sextans

(6.9 × 10

5 Msun)

−3.5 −3.0 −2.5 −2.0 −1.5 −1.0 [Fe/H] −0.5 0.0 0.5 1.0 Andromeda X

(1.4 × 10

5 Msun)

Canes Venatici I

(3.0 × 10

5 Msun)

[α/Fe]

SLIDE 19

Gilbert et al., in prep

[Fe/H] measurements of M31 outer halo stars appear consistent with stars in M31 dSphs.

Comparing M31 Outer Halo and dSph Stars [Fe/H]

Increasing the Census of Chemical Abundances in M31

SLIDE 20

Gilbert et al., in prep

First direct [Fe/H] measurements of stars in Andromeda’s Giant Southern Stream, and in the inner region of M31’s halo

[Fe/H] Distribution of an M31 Inner Halo Field

Gilbert et al., 2009

GSS ?

Increasing the Census of Chemical Abundances in M31

[Fe/H] Velocity (km/s)

GSS ?

SLIDE 21

Gilbert et al., in prep

First direct [Fe/H] measurements of stars in Andromeda’s Giant Southern Stream, and in the inner region of M31’s halo

[Fe/H] Distribution of an M31 Inner Halo Field [Fe/H] Velocity (km/s)

Increasing the Census of Chemical Abundances in M31

SLIDE 22

Gilbert et al., 2018

[Fe/H] Distribution of an M31 Inner Halo Field

Increasing the Census of Chemical Abundances in M31

To estimate uncertainties on the MDFs, leverage velocity distribution modelling performed to measure the velocity dispersion profile of M31’s stellar halo. Posterior probability distributions for every parameter.

SLIDE 23

Gilbert et al., in prep

Stars in the second kinematically cold peak, of unknown origin, have an indistinguishable [Fe/H] distribution from stars in the GSS.

[Fe/H] [Fe/H] Distribution of an M31 Inner Halo Field

Increasing the Census of Chemical Abundances in M31

Gilbert et al., 2018

SLIDE 24

Global Properties: Accretion History

Bulk of stellar halo mass: one to a few early, relatively massive (>109

Msun) accretion events

Many recent low-mass accretions at large radii
Future: line of sight alpha and iron abundances − luminosity

function and time of accretion of destroyed dwarf galaxy population Inner Halo: In Situ Population

Inner region of M31’s halo has

a significant population of stars that once belonged to the disk.

Future: [Fe/H] and [alpha/Fe]

– constrain origins Mass of Halo:

Modeling GSS

disruption constrains virial mass

Future: Independent

measurement of mass from halo stars

Future: alpha and

iron abundances – more securely identify associated debris to improve constraints on models Tidal Debris Features: Recent Accretion Events

Giant Southern Stream

Related Debris found throughout the inner halo

Full posterior

probability distributions

f substructure

parameters

Future: alpha and

iron abundances – constrain star formation history

M31$

N185$ N147$

M33$ 30$kpc$ 90$kpc$ 150$kpc$ 60$kpc$ N$ E$ M31$dSphs$

Giant$Southern$ Stream$ M31$Halo$Fields$

PAndAS$M31$Map$ (McConnachie$et$al.)$

Dwarf$Galaxy$Fields$