Why are we here

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Why are we here?
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Why are we here?
Plato
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Why are we here?
Plato
Confucius
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Why are we here?
Plato
Confucius
Descartes
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Why are we here?
Plato
Confucius
Descartes
Neitszche
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Why are we here?
Plato
Confucius
Descartes
Neitszche
Dave Barry
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Why are we here?
Plato
Confucius
Descartes
Neitszche
Dave Barry
Ringberg Workshop 2006 Dwarf Galaxies as
Astrophysical and Cosmological Probes
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Why are we interested in dwarf galaxies?
Most common galaxies Simple
systems Building blocks of larger
galaxies Nearest galaxies

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Why are we interested in dwarf galaxies?
Most common galaxies . . . but not
common enough! Simple systems . . .
ha, ha, ha. Building blocks of larger
galaxies . . . yes, no, maybe.
Nearest galaxies . . . true, but in a
highly biased way!
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Must be their looks . . . (MW dSph)
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A brief history 1781 M32 discovered by Le
Gentil. 19th Century NGC, IC includes
dwarfs 1938 Sculptor and Fornax discovered

Slope 0.5 galaxy/yr
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Brief history, continued Prior to 1980
Structure, discovery, oddities? Since 1980
Darkest, closest DM halos
Sources of streams Complex
SFHs Abundance patterns
Surveys well beyond LG A golden
time for dwarf galaxy research.
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Outline of this introduction. ORIGINS a.k.a.
the missing satellite problem INTERACTIONS
parent-dwarf
dwarf-dwarf TRANSFORMATIONS Relations, if
any, between dwarf galaxy types. A lot of
cross-talk implicit here . . .
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ORIGINS
Generally, the idea is to suppress the baryons,
not try to suppress the smallest halos.
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Observational Constraints All dwarfs so studied
have ancient stars (gt 10 Gyr)
LeoA Dolphin et al.
IC1613 Dolphin et al.
M32 Alonso et al.
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Heavy element abundance distributions often
exhibit a large spread, even in systems with
little or no intermediate age populations
Flat dispersion profiles and rotation curves
imply rc gt 20 km/s M gt 108 MO
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ORIGINS trying to solve the missing satellite
problem
Low mass, early origin Self external
reionization We see lightest that retain gas
Bullock et al. 2000
High mass Late formation since can retain gas
through reionization. Visible mass central.
Stoer et al. 2001
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Massive at reionization Forms stars to z3 Tidal
interactions with parent (allows bursty
behavior).
Kravtsov et al. 2004
Hybrid Low mass form early (dSph) More massive
later (dI)
Ricotti and Gnedin 2005
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ORIGINS Questions
Whats wrong with supressing the DM halos
at low masses (warm enough DM?) What
about those baryonless halos? Are they
cannonballs or are they harmless? Could we
see them intereact with visible galaxies? At
what rate?
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Is the planar distribution of the MW and
(somewhat) M31 dwarfs a comparable problem?
(Kroupa et al. 2005) Is having gt 4 solutions
a solution? . . . the missing satellites
are still a problem.
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INTERACTIONS
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We know dwarfs are injecting stars, clusters, DM
into halos today.
Sgr, Majewski et al. 2002
M31, Ibata et al. 2004
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Such strong interactions must have been common
early as the bulge and disk formed, as models
and the longevity of the MW bulge and disk
attest. Surviving dwarfs and building
block dwarfs may be very different. Were
the building blocks really ever independent
entities?
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Less extreme interactions?
LeoI, Mateo et al. 2006
And dwarfs, McConnachie and Irwin 2005
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Dwarf-dwarf interactions?
LMC/Sgr Collision about 3 Gyr ago Zhao 1998,
Majewski et al. 2006
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Substructure primordial or evidence of
hierarchical structure formation?
Sextans, Walker et al 2006
UMi, Wilkenson et al. 2002
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Evidence of capture in Fornax?
1.4 Gyr old Olszewski et al. 2006
Coleman and Da Costa 2003
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INTERACTIONS Questions
How can we account for mild interactions in
kinematic studies to derive M(r) ? Do
present-day dwarfs still show signs of the
mergers that formed them? How common are
dwarf-dwarf and dwarf-halo interactions?
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TRANSFORMATIONS Different types of dwarfs
dE dSph dI
Hybrid/Transition cases (eg, LGS3, Phoenix)

different scaling relations in r, M, L, SB, etc
(Kormendy 1985 Kormendy and Freeman 2004).
What are the evolutionary relationships here?
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We know environment matters
Morphology-density relation for LG dwarfs
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dI/dSph properties differ such that dIs cannot
passively evolve into dSph
Grebel et al. 2004
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Tidal Stirring (Mayer et al. 2001, 2005) may
help, though the metallicity offset between dSph
and dI may be more puzzling.
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dEs may show the relic structures of their dI
past.
Geha et al. 2003
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TRANSFORMATIONS Questions Where is the
gas? What about objects such as Tucana and
Cetus? Exceptions (objects that formed all
stars rapidly)? Or only single pass (need
some orbit information)? Significance of
60-70 kpc (closest small dwarfs survive) and
250 kpc (closest small dIs found)? Role of
detailed environment (MW and M31 do differ)?
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Many more environments out there just getting
started . . .
451 Galaxies D lt 10 Mpc or V lt 550
km/s Nearly all dwarfs
Karachentsev, Karachentseva, Hutchmeier and
Makarov 2004
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Other groups Scl, Cen, M81, Leo Clusters
Virgo, Fornax Better statistics comparative
studies.
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So, why are we here?
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To understand these in the widest context.
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