Title: Dwarf galaxies as gastrophysical laboratories
1Dwarf galaxies as gastrophysical laboratories
ringberg march 2006
2gastrophysics the big challenge
- in order to reconcile CDM with galaxy
observations, there must be a strongly non-linear
relationship between DM halo mass and baryonic
mass - achieved in semi-analytic models via scaling laws
for star formation and feedback - feedback from stars and AGN probably play a role
-- relative importance still poorly understood!
DM halos
stars
3merger history determines galaxy morphology
1.0E14
1.0E12
4primordial power spectrum
BH formation, AGN feedback
galaxy observables
5gas cools onto central galaxy... (satellites
dont get any new gas)
rcool
6stars form and metals are produced (n.b. gas
recycling is included) cold gas (and metals)
heated and ejected from the galaxy either
retained in the halo or ejected entirely ejected
gas returns to the halo when larger scale
collapses
rvir
rturnaround
7star formation
- dm/dt mcold/t0 tdyn(V0/Vc)a?
- t0 controls the fraction of gas turned into stars
- with ?0, equivalent to Kennicutt Law
(more efficient SF occurs in merger-triggered
bursts)
8Martin-Heckman Law
SN feedback what do observations tell us?
- reheating rate few times SFR, no strong Vc
dependence - gas escapes from galaxies with Vc
Martin 1999
9Efficiency of SN-driven outflows
detailed hydrodynamic simulations
mass ejection efficiency very low for Mg107
Mo blow-out only for very small masses, Mgejection of metals much more efficient
70-100 ejected for MgMac Low Ferrara 1999
10MacLow Ferrara 1999
11SN feedback and gas ejection
the standard semi-analytic treatment
reheated gas ejected from halo
-reheated mass times SFR typically assumed to be
a strong function of Vc -treatment of reheated
gas varies from model to model --
important! -here, reheated gas ejected from
halo when VcSilk see also Woo Dekel)
reheating rate/SFR
12supernova feedback
- dmrh/dt b(Vc) dm/dt
- b(Vc) eSN (V0,SN/Vc)arh
- energetics arguments predict arh 2
- gas ejected from halo if VcVej
- ejected gas re-enters halo on mass doubling
timescale
13photoionization squelching
- after reionization, ionizing background prevents
gas from collapsing in halos less than the
filtering mass scale, 30-50 km/s
filtering mass
Gnedin 2000
14Local Group Luminosity function
consensus that squelching solves the
substructure problem? what about the star
formation histories of dwarfs?
rss 2002
15constraints on the (coldstar) baryon fraction of
halos
from size-mass relation of disk galaxies in
SDSS (Shen et al. 2003)
from Halo Occupation analysis (Kravtsov et al.
2004 N-body Zheng et al. 2005 semi-analytic)
16no SN feedbackhot gas 0.3 solar
purple dots median baryonic mass
fraction yellow stars median stellar mass
fraction orange dotsbaryons, central
galaxies cyan dotsbaryons, satellite galaxies
Milky Way (Klypin et al. 2002)
K04 baryons K04 stars
17model 0
Kennicutt SF law ?rh2, ?SN1, Vej100 km/s
purple dots median baryonic mass
fraction yellow stars median stellar mass
fraction orange dotsbaryons, central
galaxies cyan dotsbaryons, satellite galaxies
Milky Way (Klypin et al. 2002)
K04 baryons K04 stars
18model 0
Kennicutt SF law ?rh2, ?SN1, Vej100 km/s
large box (L171 Mpc) smallest host halo 1011
Msun small box (L25 Mpc) smallest host halo 20
km/s
dominated by satellites
19gas fraction vs. stellar mass
all galaxies
20gas fraction vs. stellar mass
central galaxies
21model 1
introducing...
tilted Kennicutt Law (?2.5) SN FB just like
model 0
central galaxies only
all galaxies
22model 1
tilted Kennicutt Law (?2.5) SN FB just like
model 0
big box
small box
23model 1r
tilted Kennicutt Law (?2.5) ?rh2, ?SN1,
Vej0 km/s
gas retained
gas ejected
24model 2
tilted Kennicutt Law (?2.5) ?rh0, ?SN3,
Vej100 km/s
(based on Martin 99 recipe)
model 2 (small box)
model 1 (small box)
25low mass galaxies have higher specific SFR than
massive galaxies
present/past averaged star formation rate
log stellar mass
Brinchmann et al. 2004
26model 0
standard Kennicutt Law
central satellite
Brinchmann et al. 2004
problem too many low- mass galaxies with little
or no gas hence little or no SF
27model 1
tilted Kennicutt Law
central satellite
problem remains now the galaxies have gas, but
their SF efficiencies are lower by design! SFE
function of mass z redshift (or
other variable)???
28model 0
metallicity of cold gas
standard Kennicutt
Tremonti et al.
central satellite
big box
Lee et al.
observed dispersion for dwarfs 0.12 dex
small box
29model 1
tilted Kennicutt
observed dispersion for dwarfs 0.12 dex
30model 2
?rh0 (Martin99 FB)
31model 1
model 0
closed box
Lee data
Garnett data
model 2
32stellar metallicity distribution in MW M31
these scaling laws have consequences for big
galaxies too...
MW
M31
Rothberg, rss, Whitmore in prep
model 0
model 2
33and, of course, they also change the redshift
dependence of all sorts of quantities
34an aside reducing small scale power to get rid
of small DM halos has important consequences at
high redshift
M5x105 1/h Msun
T104 K
rss, Bullock Livio 2003
35-RSI/WDM models have trouble producing enough
early star formation even at z2-6 -may have
trouble producing enough photons to
reionize the universe by z15 -fewer old stars
in galaxies at z1-3 -galaxy live in smaller
mass, less clustered halos
LCDM
RSI
36where does this leave us?
- was star formation less efficient in dwarf
galaxies in the past? - threshold? ionizing background? metallicity?
- does mrh/dt /dm/dt scale with Vc?
- models seem to require this, but not seen in
observations - is there a critical velocity threshold for gas
ejection, and where is it? - Vej100 km/s seems to produce a break in the
wrong place
37what do we need?
- compilations of stellar mass, magnitude, circular
velocity, gas content, metallicity, star
formation indicators, size, etc, spanning the
full range of galaxy masses from dwarfs to giants - more information about dwarf properties at
moderate and high redshift - age metallicity distributions in giant and
dwarf galaxies from resolved stellar population
studies - systematic, detailed comparisons with model
predictions for all of these kinds of data
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39star formation SN feedback
??rh
reheated gas ejected if VcVej km/s
- major mergers (41) trigger bursts of star
formation - Bruzual Charlot 2003 multi-metallicity stellar
- population models w/Chabrier IMF (eq. to
Kroupa/Kennicutt)
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41no SN feedback
purple dots median baryonic mass
fraction yellow stars median stellar mass
fraction orange dotsbaryons, central
galaxies cyan dotsbaryons, satellite galaxies
K04 baryons K04 stars