Are There Dark Galaxies in the Local Group? - PowerPoint PPT Presentation

JasminFlorian
are there dark galaxies in the local group l.
Skip this Video
Loading SlideShow in 5 Seconds..
Are There Dark Galaxies in the Local Group? PowerPoint Presentation
Download Presentation
Are There Dark Galaxies in the Local Group?

play fullscreen
1 / 27
Download Presentation
Are There Dark Galaxies in the Local Group?
331 Views
Download Presentation

Are There Dark Galaxies in the Local Group?

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  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