Our CMB Motion: The Local Void influence
Voids Devoid of Dwarfs:
Cosmology or Gastrophysics?
Brent Tully
Institute for Astronomy
University of Hawaii
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
Fact 2: The Dwarfs in Dynamically Evolved Regions are Overwhelmingly dE
N5353/4 Group
N5846 Group Local Group
radius
velocity
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
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
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
hundreds of 5%
distances within 6 Mpc
marginal at 5 Mpc
OK at 8 Mpc
good at 3 Mpc
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
Where is the Local Filament
going?
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
what does nothing look like?
SGX SGY
S G Z
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
Bulk Peculiar Velocities
Virgo
Leo Spur
local velocity anomaly
56
o45
o36
o7.8 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
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
(again)
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
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.
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.
