Near-field Cosmology from the Andromeda galaxy and subgroupNear-field Cosmology from the

Andromeda galaxy and subgroup

Scott C. Chapman

IoA, University of Cambridge

With: R.Ibata, M.Irwin, G.Lewis, A.Ferguson, N.Tanvir, N.Martin, A.McConnachie, J. Penarrubia, M. Collins, D. Trethewey

Scott C. Chapman

IoA, University of Cambridge

With: R.Ibata, M.Irwin, G.Lewis, A.Ferguson, N.Tanvir, N.Martin, A.McConnachie, J. Penarrubia, M. Collins, D. Trethewey

OutlineOutline

The M31 outer disk

The M31 outer halo: The “first” galaxy

(later:) Dwarf galaxy satellites of M31 (and the Milky Way) Is And-XII a “true” fossil? Minimum DM halo mass?

The M31 outer disk

The M31 outer halo: The “first” galaxy

(later:) Dwarf galaxy satellites of M31 (and the Milky Way) Is And-XII a “true” fossil? Minimum DM halo mass?

Context: Hierarchical Galaxy Formation - Little galaxies merge to make big galaxies …- How/when are the galaxy components assembled?

Context: Hierarchical Galaxy Formation - Little galaxies merge to make big galaxies …- How/when are the galaxy components assembled?

Big Bang … Cosmic Microwave Background …

… Galaxy Formation and Evolution … Fossil Records today!Big Bang … Cosmic Microwave Background …

… Galaxy Formation and Evolution … Fossil Records today!

Local galaxies (MW, Andromeda) are ideal laboratories to study archeology.

Bullock et al. (2005) Model/Approach:

3. Embed stars in the center of accreted dark matter halo.

1. Construct accretion histories for Milky-Way type halos using semi-analytic “merger tree”.

2. For each accreted system, model its previous star formation history based onexpected mass growth history

4. Follow evolution within the (growing) host halo

Observational Requirements:

1.) Spatial coverage. 2.) Radial velocities. 3.) Chemical distribution. 4.) Ages ??

Bullock+2005, Font+2006 Predictions:

1.) Substructure in halo. 2.) Chemically distinct outer halo.

Bullock+2005, Font+2006 Predictions:

1.) Substructure in halo. 2.) Chemically distinct outer halo.

Bullock+,Font+,Johnston+ model is our best current prediction for MW/M31.

(Changing with Aquarius -- Springel et al. 2008)

Bullock+,Font+,Johnston+ model is our best current prediction for MW/M31.

(Changing with Aquarius -- Springel et al. 2008)

Observational Tests: Local Galaxy Archeology

(Milky Way, Andromeda, satellites)

Observational Tests: Local Galaxy Archeology

(Milky Way, Andromeda, satellites)

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Dissecting the history of a galaxy by digging up its stars 1 by 1:

Near-Field cosmology-where are missing satellites-are DM profiles universal? (cuspy NFW?)-DM: extent, nature, spatial distribution-how were MW and M31 constructed: typical disks?-role of accretion in formation of halo, disk, bulge?

-stars maintain birth statistical pattern-chemical evolution proceeds in 1 direction

Imaging and Spectroscopic study of Andromeda -- M31

Imaging and Spectroscopic study of Andromeda -- M31

M31 (M33) Fossil Record of Galaxy Formation:

M31 (M33) Fossil Record of Galaxy Formation:

Using the Keck 10m / DEIMOS spectrograph:

… dissect components & piece together the evolutionary history

(Ibata+ 04,05,06; Chapman+ 04,05,06; McConnachie+04,06)

Classical (Palomar) view of M31

Modern (wide-field CCD) view of M31: a train wreck! (Irwin+05)

6 degrees

(12 full moons)

100 kpc

age in Gyr

mass

fra

ctio

nAbadi, Navarro, Steinmetz & Eke 2003

Fine structure of simulated galaxies

thin

dis

kth

ick

dis

ksp

hero

id

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Building the Spheroid (Bullock+06)Building the Spheroid (Bullock+06)

Imaging Surveys:INT2.5m widefield survey of M31CFHT/MegaCam halo survey of entire M31 halo out to 150kpc

Initiated w/ Keck/DEIMOS: Sept 2002Status Nov, 2008 Number of Nights : 21 (70% usable)Number of Fields : 75 Limiting I-mag < 22Candidate M31 Spectra: ~14,000(and ~6000 Milky Way foreground stars)

Data products:~5-10km/s velocity determination, (Calcium Triplet, cross-correlation)

[Fe/H] measurement by EWs of CaTFainter lines of other species …

Ibata et al. (2004,2005); Chapman et al. (2005,2006,2008)

M31 Kinematics and Metallicity ExperimentM31 Kinematics and Metallicity Experiment

Surprise! the “messy halo” of stars surrounding M31 is actually a giant rotating disk! (not a train wreck halo)

Surprise! the “messy halo” of stars surrounding M31 is actually a giant rotating disk! (not a train wreck halo)

(Ibata et al. 2005)

DEIMOS spectraDEIMOS spectra

Technique: Sort stars by kinematicsTechnique: Sort stars by kinematics

disk

halo

Velocity distribution of all stars 1hour Keck exposures Apply disk model (flat rotation

curve to >70kpc)

A new ``extended disk'' galaxy component

Discovered that all structures participate in giant rotating disk

Separation of outer disk/halo in velocitySeparation of outer disk/halo in velocity

disk

Outer disk of stars rotates like the inner disk

~15% of light of inner disk>40% of angular momentum!

Irregular morphology, lots of substructure … transitory?(Ibata+2005, Chapman+2006)

Star velocities in giant disk

Distance (Major Axis)40kpc 40kpc

Separation of outer disk/halo in velocitySeparation of outer disk/halo in velocity

disk

What’s left? A primeval “Halo” of stars!-few heavy metals (formed early) -An relic of M31’s beginning

v = 125 km/s Monotonic decrease in v(R)No rotation. Detectable “spikey” substructure?(Chapman, et al. 2006; 2009 in prep)

halo

Mass of M31 from Halo starsMass of M31 from Halo starsFirst assume simple rotating isothermal halo:

not rotating, and 125km/s v

Then ignore rotation and allow v to decrease linearly with projected R.

Monotonic decline in v with radius … better fit.

Mass of M31 from Halo starsMass of M31 from Halo starsMonotonic decline in sigma_v with radius - ignore stream spikes … (Trethewey+08)

Fit to an NFW dark matter halo (assuming the stars are a reasonable tracer of the halo:And taking Klypin et al. 2002 limit for concentration (caveats)M_virial > 9e11 Msun, 99% confidence.

Consistent with other estimates of M31’s DM halo mass (satellites - Evans&Wilkinson, giant stream - Ibata,Chapman et al. 2004)

All fields have similar average metallicities [Fe/H] ~ -1.0 [sigma=0.4] - More metal rich than MW halo.

Average “extended disk” star from 15kpc - 70kpc probing similar global star population!

Compare HALO and DISK chemistry:R~70kpc Extended Disk -

Metallicities

Compare HALO and DISK chemistry:R~70kpc Extended Disk -

MetallicitiesAverage spectrum at each Keck position

fields have average metallicities [Fe/H] = -1.4 [=0.2]

Stars selected like those in MW halo (non-rotating), have similar metallicity and velocity distribution.

NFW model fit => 10^12 Msun

Solves “puzzle” of metal-rich halo in M31!

R=10-70kpc Stellar Halo: Metallicities

R=10-70kpc Stellar Halo: Metallicities

Average spectrum at each Keck position

Metal Poor halo: no abundance gradient

Metal Poor halo: no abundance gradient

Halo radial Fe/H constant: detect the metal-poor halo component from 50kpc right up to 17kpc

… as opposed to minor axis where velocities of all components overlap in the M31 systemic velocity range.

consistent with Koch et al. 2007

Giant stream

Koch et al. (2007): M31 minor axis from 10-120kpc

combined M.Rich & S.Chapman Keck-DEIMOS data

Koch et al. (2007): M31 minor axis from 10-120kpc

combined M.Rich & S.Chapman Keck-DEIMOS data

Abundance transition at 20kpc: metal-rich to metal-poor

… inconsistent with previous sparsely sampled minor axis study (Kalirai et al. 2006).

M33 (1/10 the mass of M31 and MW) kinematically selected halo

M33 (1/10 the mass of M31 and MW) kinematically selected halo

Keck/DEIMOS M31 halo study … on edge of disk/halo transition from Ibata et al. (2007)

Keck spectra find: 1) Metal poor halo Fe/H = -1.5 2) Extended disk3) Unknown “stream”

(McConnachie+06, Trethewey+09)

“Mouhcine plot”VERY HARD to see metal-poor primordial halos in more

distant galaxies without kinematics!

“Mouhcine plot”VERY HARD to see metal-poor primordial halos in more

distant galaxies without kinematics!

L vs Fe/H correlated in spiral galaxy halos? (Mouhcine+05)

Kinematically selected Halos in M31 (Chapman+06)M33 (McConnachie+06)MW (Chiba&Beers+00,01)… all Fe/H ~ -1.5

Are we comparing apples with apples in distant (10Mpc) spiral galaxies?

Dots are Renda+05 model

ConclusionsConclusions

In halos of big (L*) Spiral galaxies (M31), extended rotating components may be common => difficult to interpret more distant galaxies without kinematics

Beginning to understand the primeval halo of M31 (and the MW …), versus later accretions. More work required to understand substructure and mass

function of first accretions

In halos of big (L*) Spiral galaxies (M31), extended rotating components may be common => difficult to interpret more distant galaxies without kinematics

Beginning to understand the primeval halo of M31 (and the MW …), versus later accretions. More work required to understand substructure and mass

function of first accretions

Halo stars in front of M31, outer edge of the MW halo Growing discoveries of dSph galaxies (and their characterizations) are an excellent testbed of galaxy evolution and cosmology.

Halo stars in front of M31Halo stars in front of M31

CDM Has a Missing Satellite ProblemCDM Has a Missing Satellite Problem

V.Springel et al. 2001

CDM predicts large numbers of subhalos (~100-1000 for a Milky Way-sized galaxy)

Milky Way only has 23 known satellites

M31 has 25 satellitesWhat happened to the rest of them?

CDM predicts large numbers of subhalos (~100-1000 for a Milky Way-sized galaxy)

Many never form stars

V.Springel et al. 2001

CDM Has a Missing Satellite ProblemCDM Has a Missing Satellite Problem

What is a dwarf Fossil*?What is a dwarf Fossil*?*defined by Ricotti & Gnedin (2005)

Survivors (M > 109 M) * star formation started after reionization * mostly dIrr, some dE

LMC M32

Polluted fossils (M ~ 106 - 108/9 M) * significant star formation after reionization * tidal effects from host cause additional bursts * dSph and dE

Pegasus

True fossils (M ~ 106 - 108/9 M) * < 30% of stars formed after reionization * never accreted gas from the IGM * dSph

Cetus (Whiting et al. 1999)

Fossil PropertiesFossil Properties

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Ricotti & Gnedin (2005), Bovill et al. (2007)

R02a,b predictions.

Known survivorsKnown polluted fossils

Known true fossilsNew ultra-faint dwarfs

~ Scatter in Z due to: - pollution from nearby halos - multiple bursts of star formation (ie. Stinson et al (2007))

~ Fossil properties at z = 0 are simply related to their properties at reionization.

Formation and Evolution of dwarf galaxiesFormation and Evolution of dwarf galaxies Environment of dwarfs severely affects their properties.

Most dwarfs have been orbiting around our Local environment for most of the age of the Universe (>10 Billion years)

Environment of dwarfs severely affects their properties.

Most dwarfs have been orbiting around our Local environment for most of the age of the Universe (>10 Billion years)

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McConnachie & Irwin 2005

CDM predicts late accreting DM halosCDM predicts late accreting DM halos

But we’ve never seen one …

have any of them formed stars?

Dwarf Galaxies still bringing in primeval material?

But we’ve never seen one …

have any of them formed stars?

Dwarf Galaxies still bringing in primeval material?

Late accretions:Late accretions:

Objects that accrete late do so from larger average distances than those that accrete early.

late accreting objects interesting both observationally and theoretically

spent the majority of their lives in different environments,

far from the disruptive tidal forces of larger galaxies,

a direct prediction of the theoretical CDM model for structure formation.

Objects that accrete late do so from larger average distances than those that accrete early.

late accreting objects interesting both observationally and theoretically

spent the majority of their lives in different environments,

far from the disruptive tidal forces of larger galaxies,

a direct prediction of the theoretical CDM model for structure formation.

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4% today

Ludlow et al. 2009

Dwarf Galaxies still bringing in primeval material?

Dwarf Galaxies still bringing in primeval material?

DISCOVERY of AndXII, a faint Dwarf galaxy building up the Local Group environment: falling in for the first time!Direct observational evidence for the hierarchical formation of the Local Group.Insights into processes responsible for the dynamical evolution of dwarfs?

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(Chapman et al. 2007)

“Mateo” Plot“Mateo” Plot Simplest possible model: equilibrium, spherical, isotropic systems where M follows L

(c.f. Strigari et al. 2007)

Do all dwarfs live in similar halos? Is there a minimum mass for dwarfs?

Simplest possible model: equilibrium, spherical, isotropic systems where M follows L (c.f. Strigari et al. 2007)

Do all dwarfs live in similar halos? Is there a minimum mass for dwarfs?

Kinematics in dwarfs:

MW: Martin+07; Simon+07

M31: Chapman+05,07; Collins+08; Letarte+08

And more to be studied/discovered …

And17,18,19,20,21 (Irwin+08, McConnachie+08)

Globular star clusters, no DM

And12

And13

And11 And16

And15

Two basic sets of possible solutions:

Modifications to CDM What modifications? Power spectrum,

DM particle mass/decay/interaction cross-section?

Astrophysics prevents stars from forming in most low-mass halos

Reionization, feedback, winds …

Two basic sets of possible solutions:

Modifications to CDM What modifications? Power spectrum,

DM particle mass/decay/interaction cross-section?

Astrophysics prevents stars from forming in most low-mass halos

Reionization, feedback, winds …

What Does This Problem Tell Us?What Does This Problem Tell Us?

Angular Momentum (J) CatastropheAngular Momentum (J) Catastrophe Sizes of galactic disks linked to J of parent DM halos (Fall & Efstathiou 1980)• distribution of halo spin parameters ( N-body simulations, e.g. Bullock+ 2001)• baryons and dark matter initially share the same distribution of specific angular momentum, j, within the halos (e.g. van den Bosch etal. 2002)• j is conserved as the baryons contract to form the disk (e.g. Mestel 1963).

Disk sizes with these assumptions, roughly comparable to those observed.

But, Hydrodynamics shows this process is invalid.=> significant fraction of J of the baryons *is* transferred to DM,… disk sizes 10x too small! (Navarro & Steinmetz 2000)

SOLUTION? Feedback … remove incoming dwarf galaxy low-j baryons(Maller&Dekel 2003)

Forming the EdiskForming the Edisk

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How to further increase angular moomentum by 50% ???

Accretion origin to extended disk?(Penarrubia+06)

BUT: Requires specialized conditions; large in-plane accretion(s);

… would be consistent with observations

Evolving Fossils to z = 0Evolving Fossils to z = 0

Fossil properties at z = 0 are simply related to their properties at reionization.

Properties of the new Sloan and M31 dwarfs agree well with predictions for primordial galaxies

Fossil properties at z = 0 are simply related to their properties at reionization.

Properties of the new Sloan and M31 dwarfs agree well with predictions for primordial galaxies