The Masses and Metallicities of the

Least Luminous Galaxies

The Masses and Metallicities of the

Least Luminous Galaxies

Josh SimonCarnegie Observatories

Josh SimonCarnegie Observatories

Marla Geha (Yale)

Beth Willman (Haverford) Joe Wolf (UC Irvine)Manoj Kaplinghat (UC Irvine)James Bullock (UC Irvine)Louie Strigari (Stanford)

Erik Tollerud (UC Irvine) Anna Frebel (Harvard)Evan Kirby (Santa Cruz)

Marla Geha (Yale)

Beth Willman (Haverford) Joe Wolf (UC Irvine)Manoj Kaplinghat (UC Irvine)James Bullock (UC Irvine)Louie Strigari (Stanford)

Erik Tollerud (UC Irvine) Anna Frebel (Harvard)Evan Kirby (Santa Cruz)

Or, Why Segue 1 Is Not a Star Cluster

• Galaxy formation– Dwarf galaxies are astrophysically simple systems

• Dark matter– Dwarf galaxies are the closest and densest dark matter-dominated objects

(Aaronson 1983; Mateo et al. 1993)

• First stars– Dwarf galaxies may be the best places to look for the most metal-poor stars

(Kirby et al. 2008; Frebel et al. 2009; Muñoz et al. 2009)

• Galaxy formation– Dwarf galaxies are astrophysically simple systems

• Dark matter– Dwarf galaxies are the closest and densest dark matter-dominated objects

(Aaronson 1983; Mateo et al. 1993)

• First stars– Dwarf galaxies may be the best places to look for the most metal-poor stars

(Kirby et al. 2008; Frebel et al. 2009; Muñoz et al. 2009)

The Faintest Dwarfs Tell Us About:

The Faintest Dwarfs Tell Us About:

• Galaxy formation– Dwarf galaxies are astrophysically simple systems

• Dark matter– Dwarf galaxies are the closest and densest dark matter-dominated objects

(Aaronson 1983; Mateo et al. 1993)

• First stars– Dwarf galaxies may be the best places to look for the most metal-poor stars

(Kirby et al. 2008; Frebel et al. 2009; Muñoz et al. 2009)

• Galaxy formation– Dwarf galaxies are astrophysically simple systems

• Dark matter– Dwarf galaxies are the closest and densest dark matter-dominated objects

(Aaronson 1983; Mateo et al. 1993)

• First stars– Dwarf galaxies may be the best places to look for the most metal-poor stars

(Kirby et al. 2008; Frebel et al. 2009; Muñoz et al. 2009)

not as #%@#$ complicated as bigger galaxiesnot as #%@#$ complicated as bigger galaxies

The Faintest Dwarfs Tell Us About:

The Faintest Dwarfs Tell Us About:

Dwarf Galaxy Scaling Relations

Dwarf Galaxy Scaling Relations

Geha et al. (2009)

The Least Luminous GalaxiesThe Least Luminous Galaxies

Strigari et al. (2008b)

These dwarfs:

(1) Control the missing satellite problem (Tollerud et al. 2008; Koposov et al. 2009; Busha et al. 2009)

(2) Will be the brightest DM annihilation sources (Strigari et al. 2008a; Geha et al. 2009)

(3) Are the most vulnerable to systematics (Simon & Geha 2007; Niederste-Ostholt et al. 2009)

The Least Luminous GalaxiesThe Least Luminous Galaxies

These dwarfs:

(1) Control the missing satellite problem (Tollerud et al. 2008; Koposov et al. 2009; Busha et al. 2009)

(2) Will be the brightest DM annihilation sources (Strigari et al. 2008a; Geha et al. 2009)

(3) Are the most vulnerable to systematics (Simon & Geha 2007; Niederste-Ostholt et al. 2009)

Segue 1 (d=23 kpc)Segue 1 (d=23 kpc)

Bootes II (d=42 kpc)Bootes II (d=42 kpc)ComBer (d=44 kpc)ComBer (d=44 kpc)

UMa II (d=32 kpc)UMa II (d=32 kpc)

Strigari et al. (2008b)

Boo II KinematicsBoo II Kinematics

• 21 members, v = -126.2 km/s, = 7.6 ± 1.5 km/s• M1/2 = 2.5 106 M

• [Fe/H] = -2.49 ± 0.07, metallicity spread = 0.50 dex

• 21 members, v = -126.2 km/s, = 7.6 ± 1.5 km/s• M1/2 = 2.5 106 M

• [Fe/H] = -2.49 ± 0.07, metallicity spread = 0.50 dex

+1.8–1.0

Simon et al. (in prep)

Boo IIBoo II

foregroundforeground

An ExperimentAn Experiment

• Search for effects of tidal interaction

• Ideal target would be:– Close to MW (to maximize tidal force)– Compact (to search out to large relative radii)

– Well-separated from MW velocity (for clean member selection)

• Search for effects of tidal interaction

• Ideal target would be:– Close to MW (to maximize tidal force)– Compact (to search out to large relative radii)

– Well-separated from MW velocity (for clean member selection)

An ExperimentAn Experiment

• Search for effects of tidal interaction

• Ideal target would be:– Close to MW (d = 23 kpc)– Compact (r = 4.4')– Well-separated from MW velocity (v = 207 km s-1)

• Search for effects of tidal interaction

• Ideal target would be:– Close to MW (d = 23 kpc)– Compact (r = 4.4')– Well-separated from MW velocity (v = 207 km s-1)

Segue 1

A Complete Survey of Segue 1

A Complete Survey of Segue 1

• Keck/DEIMOS spectroscopy of every photometric member candidate in Segue 1 out to r = 10' (67 pc)

– If Segue 1 does not have an extended DM halo, its tidal radius should be less than 50 pc

• Keck/DEIMOS spectroscopy of every photometric member candidate in Segue 1 out to r = 10' (67 pc)

– If Segue 1 does not have an extended DM halo, its tidal radius should be less than 50 pc

almost

29 pc29 pc59 pc59 pc88 pc88 pc

A Complete Survey of Segue 1

A Complete Survey of Segue 1

• Velocity and metallicity separate Milky Way foreground stars

• Velocity and metallicity separate Milky Way foreground stars

A Complete Survey of Segue 1

A Complete Survey of Segue 1

• 65 members, v = 208 km/s, = 5.4 ± 0.8 km/s• M1/2 = 9.0 105 M

• [Fe/H] ~ -2.4, metallicity spread large

• 65 members, v = 208 km/s, = 5.4 ± 0.8 km/s• M1/2 = 9.0 105 M

• [Fe/H] ~ -2.4, metallicity spread large

+3.7–2.8

Simon et al. (in prep)

A Complete Survey of Segue 1

A Complete Survey of Segue 1

• Signs of tidal disruption?– Velocity gradient – Excess of stars at large radii– Velocity dispersion increasing with radius

• Signs of tidal disruption?– Velocity gradient – Excess of stars at large radii– Velocity dispersion increasing with radius

NoNo

No

The Least Evolved Galaxies

The Least Evolved Galaxies

Abundances in the Ultra-Faint Dwarfs

Abundances in the Ultra-Faint Dwarfs

• members HIRES targets• nonmembers

UMa II

Coma

• High-resolution spectroscopy– Accurate abundances for many elements– Requires bright targets + long integrations

• High-resolution spectroscopy– Accurate abundances for many elements– Requires bright targets + long integrations

Frebel et al. (2009)

• MW disk (Venn04)• MW halo (Venn04) dSphs (Venn04, from Shetrone, etc.) ultra-faint dSphs

Metallicities in the SDSS Dwarfs

Metallicities in the SDSS Dwarfs

Frebel et al. (2009)

Is the metal-poor component of the MW halo made up of destroyed

ultra-faint dwarfs?

Metallicities in the SDSS Dwarfs

Metallicities in the SDSS Dwarfs

Frebel et al. (2009)

• Low abundances of neutron-capture species

• Large scatter within individual galaxies

( age spread)

• Low abundances of neutron-capture species

• Large scatter within individual galaxies

( age spread)• MW disk (Venn04)• MW halo (Venn04/Barklem05) dSphs (Venn04, from Shetrone, etc.) ultra-faint dSphs

Our Conclusions:

• New measurements confirm that Bootes II and Segue 1 have large velocity dispersions

• New measurements confirm that Bootes II and Segue 1 have large velocity dispersions• No evidence supporting tidal disruption for either system

• No evidence supporting tidal disruption for either system• Segue 1 is therefore a key target for dark matter studies

• Segue 1 is therefore a key target for dark matter studies• Ultra-faint dwarfs have halo-like abundances• Ultra-faint dwarfs have halo-like abundances