What is an ultra-faint Galaxy? UCSB KITP Feb 16 2012 Beth Willman (Haverford College) ~ 1/10 Milky Way luminosity Large Magellanic Cloud, MV = -18 image credit: Yuri Beletsky (ESO) and APOD NGC 205, MV = -16.4 ~ 1/40 Milky Way luminosity image credit: www.noao.edu Image credit: David W. Hogg, Michael R. Blanton, and the Sloan Digital Sky Survey Collaboration ~ 1/300 Milky Way luminosity MV = -14.2 Image credit: David W. Hogg, Michael R. Blanton, and the Sloan Digital Sky Survey Collaboration ~ 1/2700 Milky Way luminosity MV = -11.9 Image credit: David W. Hogg, Michael R. Blanton, and the Sloan Digital Sky Survey Collaboration ~ 1/14,000 Milky Way luminosity MV = -10.1 ~ 1/40,000 Milky Way luminosity ~ 1/1,000,000 Milky Way luminosity Ursa Major 1 Finding Invisible Galaxies bright faint blue red Willman et al 2002, Walsh, Willman & Jerjen 2009; see also e.g. Koposov et al 2008, Belokurov et al. Finding Invisible Galaxies Red, bright, cool bright Blue, hot, bright V-band apparent brightness V-band faint Red, faint, cool blue red From ARAA, V26, 1988 Willman et al 2002, Walsh, Willman & Jerjen 2009; see also e.g. Koposov et al 2008, Belokurov et al. Finding Invisible Galaxies Ursa Major I dwarf 1/1,000,000 MW luminosity Willman et al 2005 ~ 1/1,000,000 Milky Way luminosity Ursa Major 1 CMD of Ursa Major I Okamoto et al 2008 Distribution of the Milky Wayʼs dwarfs -14 Milky Way dwarfs 107 -12 -10 classical dwarfs V -8 5 10 Sun M L -6 ultra-faint dwarfs Canes Venatici II -4 Leo V Pisces II Willman I 1000 -2 Segue I 0 50 100 150 200 250 300 Distance from Milky Way (kpc) Luminosities and sizes of nearby dwarf galaxies 5 7 1000 LSun 10 LSun 10 LSun 3.5 MW dwarfs M31 dwarfs 3.0 Sextans Fornax Canes Venatici I Ursa Minor Leo I Ursa Major I (pc)) 2.5 Sculptor Carina HerculesBootes I half Draco Leo II Ursa Major II Leo IV log(r 2.0 Leo T Canes Venatici II Coma Berenices Pisces II Leo V Bootes II Segue II 1.5 Segue I Willman I 0 -2 -4 -6 -8 -10 -12 -14 MV MW dwarf galaxy discovery papers: Willman et al 05a,b; Zucker et al 06a,b; Belokurov et al 06,07,08,09,10; Walsh et al 07, Irwin et al 07; Detection limits: Walsh, Willman & Jerjen 2009, Koposov et al 2008 Luminosities and sizes of nearby dwarf galaxies 5 7 1000 LSun 10 LSun 10 LSun 3.5 MW dwarfs M31 dwarfs 3.0 Sextans Fornax Canes Venatici I Ursa Minor Leo I Ursa Major I (pc)) 2.5 Sculptor Carina HerculesBootes I half Draco Leo II undetectableUrsa Major II Leo IV log(r 2.0 Leo T Canes Venatici II Coma Berenices Pisces II Leo V Bootes II Segue II 1.5 Segue I Willman I 0 -2 -4 -6 -8 -10 -12 -14 MV MW dwarf galaxy discovery papers: Willman et al 05a,b; Zucker et al 06a,b; Belokurov et al 06,07,08,09,10; Walsh et al 07, Irwin et al 07; Detection limits: Walsh, Willman & Jerjen 2009, Koposov et al 2008 Luminosities and sizes of nearby dwarf galaxies 5 7 1000 LSun 10 LSun 10 LSun 3.5 MW dwarfs M31 dwarfs 3.0 Sextans Fornax Canes Venatici I Ursa Minor Leo I Ursa Major I (pc)) 2.5 Sculptor Carina HerculesBootes I half Draco Leo II Ursa Major II Leo IV log(r 2.0 Leo T Canes Venatici II Coma Berenices Pisces II Leo V Bootes II Segue II 1.5 Local Segue I Group limit of Willman I searches outside the the outside 0 -2 -4 -6 -8 -10 -12 -14 MV MW dwarf galaxy discovery papers: Willman et al 05a,b; Zucker et al 06a,b; Belokurov et al 06,07,08,09,10; Walsh et al 07, Irwin et al 07; Detection limits: Walsh, Willman & Jerjen 2009, Koposov et al 2008 Luminosities and sizes of nearby dwarf galaxies 4 6 100 LSun 10 LSun 10 LSun 3.0 2.5 2.0 undetectable (pc)) 1.5 Segue I Willman I half 1.0 log(r 0.5 Segue III 0.0 globular clusters 0 -2 -4 -6 -8 -10 -12 MV “I know it when I see it” is no longer a sufficient definition for galaxy Luminosities and sizes of nearby dwarf galaxies 4 6 100 LSun 10 LSun 10 LSun 3.0 2.5 2.0 undetectable (pc)) 1.5 Segue I Willman I half 1.0 log(r 0.5 Segue III 0.0 globular clusters 0 -2 -4 -6 -8 -10 -12 MV A self-bound stellar system whose properties cannot be explained by baryons + Newton’s laws Willman & Strader in prep Kinematics donʼt reveal huge dark matter reservoirs Segue 3: Magellan/ 12 Gyr [Fe/H] = -1.7 IMACS photometry + Keck/DEIMOS spectroscopy d ~ 17 kpc, MV ~ -0.1, rhalf ~2 pc +1.5 σvel = 1.5 -1.0 km/sec Fadely, Willman, Geha, Walsh et al 2011 Kinematics donʼt reveal huge dark matter reservoirs Segue 3: Magellan/ 12 Gyr [Fe/H] = -1.7 IMACS photometry + Keck/DEIMOS (probably) NOT A GALAXYspectroscopy d ~ 17 kpc, MV ~ -0.1, rhalf ~2 pc +1.5 σvel = 1.5 -1.0 km/sec Fadely, Willman, Geha, Walsh et al 2011 Kinematic studies reveal huge dark matter reservoirs +1.4 σ = 3.7 -1.1 km/sec (incl. binary correction) 5 Mass within 30 pc ~ 6 x 10 MSun, M/L ~ 3000 6 stars with [Fe/H] estimates from -1.7 to -3.3 Keck/DEIMOS observations of Segue 1 Simon, Geha ... Kirby... 99% complete sample of stars with r < 22 within 2 Willman et al (2011) reff (60 pc) Kinematic studies reveal huge dark matter reservoirs +1.4 σ = 3.7 -1.1 km/sec (incl. binary correction) 5 Mass within 30 pc ~ 6 x 10 MSun, M/L ~ 3000 DWARF 6GALAXY stars with [Fe/H] estimates from -1.7 to -3.3 Keck/DEIMOS observations of Segue 1 Simon, Geha ... Kirby... 99% complete sample of stars with r < 22 within 2 Willman et al (2011) reff (60 pc) Kinematic studies complicated by irregular dynamics 10 probable members Running vsys (9 star window) high [Fe/H] candidates probable members including high [Fe/H] 0 ï10 [km/sec] helio v ï20 ï30 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 projected distance from center [rhalf,ell] 10 0 ï10 [km/sec] helio v ï20 ï30 50 0 ï50 projected majorïaxis distance from center [pc] Keck/DEIMOS and KPNO observations of Willman, Geha... Simon, Willman I (MV ~ -2, d ~ 38 kpc) Kirby et al (2011) [Fe/H] spread can distinguish galaxies from clusters Willman & Strader in preparation Dwarf data from: Kirby et al 08, 10; Norris et al 10, Simon et al 11, Willman et al 11; GC data from: Carretta et al 06,07,09,10, Johnson & Pilachowski 2010, Cohen et al 2010, Gratton et al 07, Marino et al 11 [Fe/H] spread can distinguish galaxies from clusters: Willman 1 filled ï candidate Wil 1 members open ï MW stars 16 18 0 r 20 22 bright RGB faint RGB MS/BHB ï0.5 0.0 0.5 1.0 (g ï r) 0 Willman, Geha... Simon, Kirby et al (2011) Keck/DEIMOS and KPNO Two red giant branch star members observations of Willman I There is an [Fe/H] ([Ca/Fe]) spread: -1.7 (MV ~ -2, d ~ 38 kpc) and -2.7 (-0.4 and +0.1) [Fe/H] spread can distinguish galaxies from clusters: Willman 1 filled ï candidate Wil 1 members open ï MW stars 16 18 0 r 20 DWARF GALAXY? 22 bright RGB faint RGB MS/BHB ï0.5 0.0 0.5 1.0 (g ï r) 0 Willman, Geha... Simon, Kirby et al (2011) Keck/DEIMOS and KPNO Two red giant branch star members observations of Willman I There is an [Fe/H] ([Ca/Fe]) spread: -1.7 (MV ~ -2, d ~ 38 kpc) and -2.7 (-0.4 and +0.1) Distribution of the Milky Wayʼs dwarfs -14 Milky Way dwarfs 107 -12 -10 V -8 5 10 Sun M Low luminosity from nurture or L nature? -6 Canes Venatici II -4 Leo V Pisces II Willman I 1000 -2 Segue I 0 50 100 150 200 250 300 Distance from Milky Way (kpc) see e.g. Willman et al 2002; Walsh, Willman & Jerjen 2009 Outer halo dwarfs: Nature vs Nurture Leo V, Pisces II, CVn II Morphological evidence for tidal evolution? Sand, Strader, Willman et al submitted Hints of disturbed structure: 2d distribution Sand, Strader, Willman et al submitted Hints of disturbed structure: 2d distribution Leo V 10 5 0 d ~ 190 kpc Dec (arcmin) -5 To Leo IV -10 10 5 0 -5 -10 RA (arcmin) Sand, Strader, Willman et al submitted Hints of disturbed structure: 2d distribution 10 5 0 -5 -10 10 5 0 -5 -10 10 5 0 -5 -10 10 5 0 -5 -10 10 5 0 -5 -10 10 5 0 -5 -10 Sand, Strader, Willman et al submitted Hints of disturbed structure: 2d distribution Pisces II 10 5 0 d ~ 170 kpc Dec (arcmin) -5 -10 10 5 0 -5 -10 RA (arcmin) Sand, Strader, Willman et al submitted Hints of disturbed structure: 2d distribution CVn II 10 5 0 d ~ 160 kpc -5Dec (arcmin) -10 15 10 5 0 -5 -10 -15 RA (arcmin) Sand, Strader, Willman et al submitted Hints of disturbed structure: Ellipticity eSDSS = 0.44 +/- 0.05 eclassical = 0.32 +/- 0.03 Sand, Strader, Willman et al submitted Hints of disturbed structure: Orientation CVn II 10 5 0 -5Dec (arcmin) -10 15 10 5 0 -5 -10 -15 RA (arcmin) Sand, Strader, Willman et al submitted Challenging pathological explanations: Luminosity-[Fe/H] relation Segue 1 (7 stars): -2.7 +/- 0.4 dex Wil 1 (3 stars): -2.1 +/- 0.4 dex Kirby et al 2011 Connecting observations to theory: How many dwarfs vs subhalos Corrections for SDSS footprint and luminosity bias suggest ~100-300 dwarfs (e.g.