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Are There Dark Galaxies in the Local Group?

Are There Dark Galaxies in the Local Group? Josh Simon Caltech Tim Robishaw (Berkeley) Leo Blitz (Berkeley) Andrew Cole (Minnesota) Martin Weinberg (UMass) Martin Cohen (Berkeley) Outline Missing satellites and HVCs Known or suspected dark galaxies LGS 3 + HVC Complex H

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Are There Dark Galaxies in the Local Group?

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  1. Are There Dark Galaxiesin the Local Group? Josh Simon Caltech Tim Robishaw (Berkeley) Leo Blitz (Berkeley) Andrew Cole (Minnesota) Martin Weinberg (UMass) Martin Cohen (Berkeley)

  2. Outline • Missing satellites and HVCs • Known or suspected dark galaxies LGS 3 + HVC Complex H • High-resolution maps of HVCs Are all HVCs dark galaxies? Ringberg - Dwarf Galaxies as Cosmological Probes

  3. CDM and the Missing Satellites CDM predicts large numbers of subhalos (~300-1000 for a Milky Way-sized galaxy) Milky Way only has ~15 known satellites What happened to the rest of them? Springel et al. 2001 Ringberg - Dwarf Galaxies as Cosmological Probes

  4. CDM and the Missing Satellites CDM predicts large numbers of subhalos (~300-1000 for a Milky Way-sized galaxy) Milky Way only has ~15 known satellites What happened to the rest of them? Springel et al. 2001 Ringberg - Dwarf Galaxies as Cosmological Probes

  5. Are HVCs The Missing Dwarfs? • There are thousands of HVCs in the Local Group, and hundreds of them are compact and isolated • HVCs have the right masses if they are located at distances of several hundred kpc Ringberg - Dwarf Galaxies as Cosmological Probes

  6. Problems with HVCs • Unknown distances and masses • Difficult to study at high resolution Key question: How far away are typical HVCs? Ringberg - Dwarf Galaxies as Cosmological Probes

  7. Problems with HVCs • Unknown distances and masses • Difficult to study at high resolution Key question: How far away are typical HVCs? Do HVCs have dark matter halos? Ringberg - Dwarf Galaxies as Cosmological Probes

  8. Are there dark galaxies in the Local Group? Ringberg - Dwarf Galaxies as Cosmological Probes

  9. Dark Galaxies Yes! But how many? 1. HVC 127-41-330 2. (?) Complex H 3 - 300. ??? Ringberg - Dwarf Galaxies as Cosmological Probes

  10. LGS 3 and HVC 127-41-330 Blitz & Robishaw 2000 Robishaw, Simon, & Blitz 2002 Leiden-Dwingeloo Survey (beam = 36’) Arecibo (beam = 3.3’) Ringberg - Dwarf Galaxies as Cosmological Probes

  11. LGS 3 and HVC 127-41-330 LGS 3 HVC Tidal tails Robishaw, Simon, & Blitz 2002 Leiden-Dwingeloo Survey (beam = 36’) Arecibo (beam = 3.3’) Ringberg - Dwarf Galaxies as Cosmological Probes

  12. HVC Rotation Curve At d=700 kpc, Mdyn = 6MHI At d=100 kpc, Mdyn = 39MHI Ringberg - Dwarf Galaxies as Cosmological Probes

  13. What is HVC 127-41-330? • Cloud of gas in Local Group • Likely at 700 kpc • MHI = 5.5 x 106 M • Dark matter-dominated • No stars Robishaw, Simon, & Blitz 2002 The first dark galaxy! Ringberg - Dwarf Galaxies as Cosmological Probes

  14. Complex H Location in the Galactic plane makes it unique Ringberg - Dwarf Galaxies as Cosmological Probes

  15. Complex H Kinematics Lockman 2003 For b < 15, cosb ≈ 1 and sinb ≈ b Therefore dVLSR/db = Vz Inclined, retrograde, circular orbit at d = 27 kpc fits the data MHI = 2 x 107M Ringberg - Dwarf Galaxies as Cosmological Probes

  16. 8mMSX image 133 126 l 5 b -1 Is Complex H a dwarf galaxy? • In the IR, many sources are visible towards the core of Complex H • CO observations show that they are all in the Milky Way SFR < 5 x 10-4 M yr-1 Simon et al. 2006 Ringberg - Dwarf Galaxies as Cosmological Probes

  17. Is Complex H a dwarf galaxy? • What about an old population? Milky Way main sequence and red giant tracks for d = 2 kpc 2MASS CMD of Complex H Dwarf galaxy tracks for d = 18, 27, 36 kpc M* < 106 M Simon et al. 2006 Ringberg - Dwarf Galaxies as Cosmological Probes

  18. What is Complex H? • Cloud of gas near Milky Way • Likely at 27 kpc • MHI = 2.0 x 107 M • No star formation; MHI/M* > 20 If dark matter If no dark matter The first cold accretion flow? Dark galaxy #2 Ringberg - Dwarf Galaxies as Cosmological Probes

  19. Are many or most HVCs dark galaxies? Ringberg - Dwarf Galaxies as Cosmological Probes

  20. HVC Models Extra/circumgalactic (Oort 1966, Blitz et al. 1999) - d = few hundred kpc - m = 105 - 107 M - dark matter halos - gravitationally bound Hot halo (Maller & Bullock 2004) - d ~ 150 kpc - m = 105 - 107 M - no dark matter - pressure-confined Tidal debris (no formal model) - d = 10 - 50 kpc - m = 103 - 105 M - no dark matter - not bound Questions about the bulk of the HVC population: • Are they gravitationally bound? • Do they have dark matter halos? Ringberg - Dwarf Galaxies as Cosmological Probes

  21. Are HVCs bound? • If not, calculate expansion timescale • 5.3 x 107 yr < t < 2.5 x 108 yr • Not stable for very long • What about dynamical masses? • Assuming virialization: 300 (d/100 kpc)-1 < Mvir/MHI < 2100 (d/100 kpc)-1 Must have dark matter to be bound! Ringberg - Dwarf Galaxies as Cosmological Probes

  22. Audience Quiz Which of these HVCs is not rotating? HVC 018+47 HVC 072-22 HVC 191+29 Ringberg - Dwarf Galaxies as Cosmological Probes

  23. Audience Quiz HVC 018+47 HVC 072-22 HVC 191+29 Ringberg - Dwarf Galaxies as Cosmological Probes

  24. HVC Image Gallery Ringberg - Dwarf Galaxies as Cosmological Probes

  25. Three More Rotating HVCs? HVC 018+47 HVC 072-22 HVC 050-27 Vrot = 14 km s-1 Mdyn/MHI = 78 (d/100 kpc)-1 Vrot = 6 km s-1 Mdyn/MHI = 22 (d/100 kpc)-1 Ringberg - Dwarf Galaxies as Cosmological Probes

  26. Three More Rotating HVCs? HVC 018+47 HVC 072-22 Vrot = 14 km s-1 Mdyn/MHI = 78 (d/100 kpc)-1 Vrot = 6 km s-1 Mdyn/MHI = 22 (d/100 kpc)-1 Ringberg - Dwarf Galaxies as Cosmological Probes

  27. Summary • HVC 127-41 • Cloud kinematics require dark matter, no stars -> dark galaxy • Complex H • Large HI mass, no star formation, no stars -> dark galaxy or cold accretion stream? • Other HVCs • Several also show signs of rotation • If the rotation is real, they are DM-dominated HVCs appear compatible with the dark galaxy hypothesis Ringberg - Dwarf Galaxies as Cosmological Probes

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