Our CMB Motion: The Local Void influence Voids Devoid of Dwarfs: Cosmology or Gastrophysics?

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Our CMB Motion: The Local Void influence

Voids Devoid of Dwarfs:

Cosmology or Gastrophysics?

Brent Tully

Institute for Astronomy

University of Hawaii

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Fact 1: Gastrophysics must be important

because

the faint end of the luminosity function of

galaxies depends on environment

More dynamically evolved regions

have steeper faint-end luminosity

functions

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Fact 2: The Dwarfs in Dynamically Evolved Regions are Overwhelmingly dE

N5353/4 Group

N5846 Group Local Group

radius

velocity

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Fact 2: The Dwarfs in Dynamically Evolved Regions are Overwhelmingly dE

Show me a concentration of dE galaxies and I’ll show you a place with large M/L

N5353/4 Group

N5846 Group Local Group

radius

velocity

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Fact 3: Groups of Dwarfs - Evidence for Dark Halos

All-sky census of dwarf galaxies and follow up observations with HST/ACS:

 most dwarfs are in groups

 most of the mass in small groups is invisible

gastrophysics inhibits the collection of gas and star formation

in low mass halos or low density regions

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Fact 4: The Local Void

- a void extending 60 Mpc begins at the edge of the Local Group

HI Parkes All Sky Survey

Time Allocation Committees could have inferred the existence of the Local Void

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hundreds of 5%

distances within 6 Mpc

marginal at 5 Mpc

OK at 8 Mpc

good at 3 Mpc

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Fact 5: we are traveling with the Local Filament as a unit

• co-moving motion of the

Local Group w.r.t. 159 galaxies at 1.1 < d < 7 Mpc

is 9 km/s negligible!!

• velocity dispersion about the local expansion of groups and galaxies outside of groups

is ~40 km/s

within the Local Filament

(Karachentsev et al. 2003, AA, 398, 479)

cold flow!!

green/yellow Vpec~0 red Vpec > +100 blue Vpec < -100

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Where is the Local Filament

going?

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vector decompositions 1

Assume component toward Virgo Cluster:

~200 km/s => l = 282.9 sgl = 102.7 b = 74.5 sgb = -2.3 Subtract from Local Supercluster vector:

~211 km/s => l = 213 sgl = 12 b = -3 sgb = -75

attributed primarily to evacuation of Local Void

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what does nothing look like?

SGX SGY

S G Z

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A galaxy in the void

The lonely dwarf galaxy ESO461-36 = KK246 at 9 Mpc within the Local Void has a peculiar velocity toward us of -216 km/s

Our peculiar motion in the Local Supercluster of 298 km/s is almost in the same direction, so the peculiar motion out of the void of ESO461-36 = KK246 is at least 500 km/s with

respect to the Local Supercluster

TRGB HI

KK246

MB=-14

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Bulk Peculiar Velocities

Virgo

Leo Spur

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local velocity anomaly

56

o

45

o

36

o

7.8 Mpc

8.9 Mpc 9.5 Mpc

-400 km/s

-540 km/s -285 km/s -260 km/s

-510 km/s -260 km/s

local filament

Leo spur

~6 Mpc

Local Void

UGC 3974

D634-03

NGC 2903 milky way

211 km/s

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vector decompositions 2

A s s u m e c o m p o n e n t t o w a r d V ir g o C l u s t e r :

~ 2 0 0 k m / s

=

>

l

= 2 8 2 . 9 s g l

= 1 0 2 . 7 b

= 7 4 . 5 s g b

= - 2 . 3 S u b t r a c t f r o m L o c a l S u p e r c l u s t e r v e c t o r :

~ 2 1 1 k m / s

=

>

l

= 2 1 3 s g l

= 1 2 b

= - 3 s g b

= - 7 5 a tt ri b u t e d p ri m a ri l y t o e v a c u a ti o n o f L o c a l V o i d

CMB motion

Local Group frame: 619 km/s

 l = 275.2 b = 28.7

 sgl = 140.2 sgb= -32.2

Subtract

Local Supercluster vector leaves large-scale structure component: ~446 km/s

 l = 300 b = 15

 sgl = 163 sgb = -15

Attributed to structure on

scales > 3,000 km/s

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Where is the Local Filament going?

~200 km/s

~211 km/s

~446 km/s

attractors on large scales

Kocevski & Ebeling 2006, ApJ, 645, 1043

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Conclus ions:

1. The ratio of dwarf to giant galaxies is highest in high density, dynamically evolved

environments. In the standard hierarchical clustering paradigm, the ratio of low to high halo mass is higher in low density, dynamically unevolved regions. Either the paradigm is wrong or gas & stars are preferentially excluded from low mass halos in low density regions.

2. The evident existence of groups of dwarfs with extreme M/L suggest that gas & stars are excluded in these locals. It must be considered likely that the paucity of dwarfs in voids is due to the inability of halos to collect or retain gas in those environments.

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Conclus ions:

1. The ratio of dwarf to giant galaxies is highest in high density, dynamically evolved

environments. In the standard hierarchical clustering paradigm, the ratio of low to high halo mass is higher in low density, dynamically unevolved regions. Either the paradigm is wrong or gas & stars are preferentially excluded from low mass halos in low density regions.

2. The evident existence of groups of dwarfs with extreme M/L suggest that gas & stars are excluded in these locals. It must be considered likely that the paucity of dwarfs in voids is due to the inability of halos to collect or retain gas in those environments.

3. The Local Filament within 7 Mpc is moving as a unit with low internal dispersion. The bulk

motion of the filament is decomposed cleanly into 3 quasi-orthogonal components: a motion of ~200 km/s away from the Local Void, a motion of ~200 km/s toward the Virgo Cluster, and a motion of

~450 km/s toward clustering on large scales in the direction of Centaurus.

4. While we are moving toward -SGZ, the adjacent filament south of the supergalactic equator

called Leo Spur has a bulk peculiar motion toward +SGZ and consequently is converging with our

filament (in co-moving coordinates).

5. The lonely dwarf galaxy ESO 461-36 lies 9 Mpc

away, 8 Mpc deep into the Local Void. The galaxy appears to be a normal dIrr, with HI and

leisurely ongoing star formation. The galaxy has a LARGE peculiar velocity toward the boundary of the void of over 500 km/s.

Figure

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