The Nature of the Least Luminous Galaxies
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Transcript of The Nature of the Least Luminous Galaxies
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The Nature of the Least Luminous Galaxies
The Nature of the Least Luminous Galaxies
Josh SimonCarnegie Observatories
Josh SimonCarnegie Observatories
Marla Geha (Yale)
Quinn Minor (SUNY Oneonta)
Greg Martinez (UC Irvine)
Manoj Kaplinghat (UC Irvine)
James Bullock (UC Irvine)
Louie Strigari (Stanford)
Beth Willman (Haverford) Evan Kirby (Caltech)
Marla Geha (Yale)
Quinn Minor (SUNY Oneonta)
Greg Martinez (UC Irvine)
Manoj Kaplinghat (UC Irvine)
James Bullock (UC Irvine)
Louie Strigari (Stanford)
Beth Willman (Haverford) Evan Kirby (Caltech)
Or, Looking for Dark Matter in All the Right Places
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Where To Look For Dark Matter
Where To Look For Dark Matter
• Galactic Center– Nearby (8 kpc)– Probably high concentration of DM– Horrendous backgrounds
• Galactic Center– Nearby (8 kpc)– Probably high concentration of DM– Horrendous backgrounds
S. Guisard/Wang et al.
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Where To Look For Dark Matter
Where To Look For Dark Matter
• Galactic Center– Nearby (8 kpc)– Probably high concentration of DM– Horrendous backgrounds
• Galactic Center– Nearby (8 kpc)– Probably high concentration of DM– Horrendous backgrounds
Y. Beletsky
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Where To Look For Dark Matter
Where To Look For Dark Matter
• Galactic halo– Also nearby– Less dark matter, but lots of sky– Backgrounds, but anisotropies may
help
• Galactic halo– Also nearby– Less dark matter, but lots of sky– Backgrounds, but anisotropies may
help
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Where To Look For Dark Matter
Where To Look For Dark Matter
• Dwarf galaxies– Farther away (24 – 250 kpc)– Plenty of DM– No backgrounds
• Dwarf galaxies– Farther away (24 – 250 kpc)– Plenty of DM– No backgrounds
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Which Galaxies?Which Galaxies?
• The closest and densest– Ursa Minor (69 kpc)– Draco (76 kpc)– Ultra-faints (28-42 kpc)
• The closest and densest– Ursa Minor (69 kpc)– Draco (76 kpc)– Ultra-faints (28-42 kpc)
Strigari et al. (2008a)Martinez et al. (2009)Abdo et al. (2010)
Ursa Minor
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The Ultra-Faint DwarfsThe Ultra-Faint Dwarfs
Strigari et al. (2008b)
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What Is Segue 1?What Is Segue 1?
• Globular cluster?
• Globular cluster?
• Globular cluster?
• Globular cluster?
• Galaxy?
• Galaxy?
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• 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 would be ~30 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 would be ~30 pc
A Complete Survey of Segue 1
A Complete Survey of Segue 1
almost
29 pc29 pc59 pc59 pc88 pc88 pc
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Galaxy or Star Cluster?Galaxy or Star Cluster?
• Spectra of Segue 1 red giants
– [Fe/H] range of 1.7 dex– 2 stars near [Fe/H] = -3.4
• Spectra of Segue 1 red giants
– [Fe/H] range of 1.7 dex– 2 stars near [Fe/H] = -3.4
Metal-richMetal-rich
Metal-poorMetal-poor
Simon et al. (2010)Norris et al. (2010)
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A Complete Survey of Segue 1
A Complete Survey of Segue 1
• 71 members (multiple epochs on 33), = 3.7
km s-1
• M1/2 = 5.8 105 M
• 71 members (multiple epochs on 33), = 3.7
km s-1
• M1/2 = 5.8 105 M
+8.2–3.1
+1.4–1.1
Simon et al. (2010)
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Correcting for Binary StarsCorrecting for Binary Stars
• Binaries increase by ~12%• Prior on binary periods has minimal
effect
• Binaries increase by ~12%• Prior on binary periods has minimal
effect
Simon et al. (2010)Martinez et al. (2010)
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Contamination by the Sgr Stream?
Contamination by the Sgr Stream?
Belokurov et al. (2006)
Segue 1
Sagittarius streamright position
wrong velocity
Orphan stream
wrong positionright velocity
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Could Segue 1 be Tidally Disrupting?
Could Segue 1 be Tidally Disrupting?
• No obvious tails/morphological distortion
• No obvious tails/morphological distortion
Simon et al. (2010)
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Could Segue 1 be Tidally Disrupting?
Could Segue 1 be Tidally Disrupting?
• No obvious tails/morphological distortion
• No velocity gradient
• Tidal radius from M1/2 ~ 250 pc
– Needs pericenter <4 kpc to get rtidal ~ r1/2
• If it is not bound, lifetime is few 107 yr
• No obvious tails/morphological distortion
• No velocity gradient
• Tidal radius from M1/2 ~ 250 pc
– Needs pericenter <4 kpc to get rtidal ~ r1/2
• If it is not bound, lifetime is few 107 yr
Simon et al. (2010)
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Ursa Major IIUrsa Major II
• Very close (32 kpc), apparently high mass (7.9 106 M)
• Very close (32 kpc), apparently high mass (7.9 106 M)
+5.6–3.1
Wolf et al. (2010)
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Ursa Major IIUrsa Major II
• Very close (32 kpc), apparently high mass (7.9 106 M)
BUT:• Unusually elongated
• Very close (32 kpc), apparently high mass (7.9 106 M)
BUT:• Unusually elongated
Muñoz et al. (2010)
+5.6–3.1
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Ursa Major IIUrsa Major II
• Very close (32 kpc), apparently high mass (7.9 106 M)
BUT:• Power-law density profile
• Very close (32 kpc), apparently high mass (7.9 106 M)
BUT:• Power-law density profile
Muñoz et al. (2010)
+5.6–3.1
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Ursa Major IIUrsa Major II
• Very close (32 kpc), apparently high mass (7.9 106 M)
BUT:• Unusually high
• Very close (32 kpc), apparently high mass (7.9 106 M)
BUT:• Unusually high
Simon & Geha (2007)
+5.6–3.1
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Ursa Major IIUrsa Major II
• Very close (32 kpc), apparently high mass (7.9 106 M)
BUT:• Velocity gradient?
• Very close (32 kpc), apparently high mass (7.9 106 M)
BUT:• Velocity gradient?
Geha et al. (in prep)
+5.6–3.1
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Ursa Major IIUrsa Major II
• Very close (32 kpc), apparently high mass (7.9 106 M)
BUT:• Velocity gradient?• 11.5 km s-1 E-W (34.5 km s-1 deg-1)
• Very close (32 kpc), apparently high mass (7.9 106 M)
BUT:• Velocity gradient?• 11.5 km s-1 E-W (34.5 km s-1 deg-1)
Geha et al. (in prep)
+5.6–3.1
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Willman 1Willman 1
• Also nearby (38 kpc), large velocity dispersion (4.3 km s-1)
• Also nearby (38 kpc), large velocity dispersion (4.3 km s-1)
Willman et al. (2010)
Like Segue 1, significant metallicity spread
Like Segue 1, significant metallicity spread
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Willman 1Willman 1
• Also nearby (38 kpc), large velocity dispersion (4.3 km s-1)
• Also nearby (38 kpc), large velocity dispersion (4.3 km s-1)
Willman et al. (2010)
WTF?WTF?
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Coma BerenicesComa Berenices
• Farther away (42 kpc), but very regular
• Farther away (42 kpc), but very regular
Muñoz et al. (2010)
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Coma BerenicesComa Berenices
Geha et al. (in prep)
• Repeat measurements of 13 RGB stars: 1 binary– Indicates that binaries inflate by ~7% (Minor et al.
2010)
• Marginal evidence for a small velocity gradient
• Repeat measurements of 13 RGB stars: 1 binary– Indicates that binaries inflate by ~7% (Minor et al.
2010)
• Marginal evidence for a small velocity gradient
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Conclusions
• Assessing the evidence: Segue 1 - galaxy, no tides, no binaries UMa II - galaxy, tides Willman 1 - galaxy, tides?? Bootes II - galaxy Coma Berenices - galaxy, no tides, no binaries
• Assessing the evidence: Segue 1 - galaxy, no tides, no binaries UMa II - galaxy, tides Willman 1 - galaxy, tides?? Bootes II - galaxy Coma Berenices - galaxy, no tides, no binaries
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Conclusions
• Assessing the evidence: Segue 1 - galaxy, no tides, no binaries UMa II - galaxy, tides Willman 1 - galaxy, tides?? Bootes II - galaxy Coma Berenices - galaxy, no tides, no binaries
• Assessing the evidence: Segue 1 - galaxy, no tides, no binaries UMa II - galaxy, tides Willman 1 - galaxy, tides?? Bootes II - galaxy Coma Berenices - galaxy, no tides, no binaries
Likely good targets: Not recommended:Ursa Minor Willman 1Draco UMa IISegue 1Coma Berenices. . .