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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

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)

outline
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

cdm and the missing satellites
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

cdm and the missing satellites4
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

are hvcs the missing dwarfs
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

problems with hvcs
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

problems with hvcs7
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

slide8
Are there dark galaxies in the Local Group?

Ringberg - Dwarf Galaxies as Cosmological Probes

dark galaxies
Dark Galaxies

Yes!

But how many?

1. HVC 127-41-330

2. (?) Complex H

3 - 300.

???

Ringberg - Dwarf Galaxies as Cosmological Probes

lgs 3 and hvc 127 41 330
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

lgs 3 and hvc 127 41 33011
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

hvc rotation curve
HVC Rotation Curve

At d=700 kpc, Mdyn = 6MHI

At d=100 kpc, Mdyn = 39MHI

Ringberg - Dwarf Galaxies as Cosmological Probes

what is hvc 127 41 330
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

complex h
Complex H

Location in the Galactic plane makes it unique

Ringberg - Dwarf Galaxies as Cosmological Probes

complex h kinematics
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

is complex h a dwarf galaxy

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

is complex h a dwarf galaxy17
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

what is complex h
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

slide19
Are many or most HVCs dark galaxies?

Ringberg - Dwarf Galaxies as Cosmological Probes

hvc models
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

are hvcs bound
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

audience quiz
Audience Quiz

Which of these HVCs is not rotating?

HVC 018+47

HVC 072-22

HVC 191+29

Ringberg - Dwarf Galaxies as Cosmological Probes

audience quiz23
Audience Quiz

HVC 018+47

HVC 072-22

HVC 191+29

Ringberg - Dwarf Galaxies as Cosmological Probes

hvc image gallery
HVC Image Gallery

Ringberg - Dwarf Galaxies as Cosmological Probes

three more rotating hvcs
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

three more rotating hvcs26
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

summary
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