Transcript Slides R. Bower

What determines the gas
content of galaxies?
Galaxy formation - a reminder
of the puzzle
• The fraction of
baryons that are
“cold” (stars+cold
gas) is small.
• ~10% overall.
• Rising to 25% in
MW haloes.
Guo et al 2010; Trujillo-Gomez et al 2010
Galaxies are part of the bigger
picture
• In groups we
can make a
complete
baryon census
• The cold
fraction is
~10%
• Hot gas is
~20% in
groups rising to
70% in clusters
McCarthy et al 2009
The “new” consensus
• The supply of new gas is
limited by halo growth.
• Galaxies recycle their gas
into the halo many times.
• Wind loading suppresses the
formation of dwarf galaxies.
– Winds and recycling
timescale determine galaxy
formation efficiency, not star
formation.
• At high masses, the gas
supply is shut off.
• things you have to give
up!
– The supply of gas is
limited by cooling
– Galaxies accrete their
gas and slowly consume
it.
– Star formation efficiency
needs to be understood
Some Questions
• How do galaxies get their gas?
• What determines the balance of inflow
and outflow?
• Where are the baryons in galaxies?
• Are galaxies part of a bigger picture?
How do galaxies get their
gas?
• Hot accretion aka “cooling
flows”
– Not relevant when we talk
about real galaxies.
– Shutdown with AGN
feedback?
• rapid accretion aka “cold
flows”
– Flows that never heat up?
– So what?
• Reionisation
– Not part of today’s story.
• Recycled gas
– Need to get the velocity and
mass loading right!
• Fixed wind speed destroys
L* galaxies
• SA models need  ~ v-2 to v-3
– Galactic fountains or superwinds?
• Is there any evidence for
high mass loading?
– Reheated gas cools again or does it?
• High velocity clouds?
• Hot gas in groups and galaxy
haloes?
• DLA abundance?
What cooling+feedback
Formation of faint
need to do!
galaxies supressed
by Sne energy
feedback has
successfully
depressed galaxy
formation in
small haloes
The same problem is
seen in simulations:
Balogh et al., 2001;
Springel & Hernquist
2003
dark matter mass
function (fixed
M/L)
NB: exacerbated
by the high value
of WMAP Ωb
but cooling is now
too effective
in high mass
haloes (there's
more gas left over)
Benson et al 2003;
Keres et al 2009
What cooling+feedback
Formation of faint
need to do!
galaxies supressed
by Sne energy
feedback has
successfully
depressed galaxy
formation in
small haloes
The same problem is
seen in simulations:
Balogh et al., 2001;
Springel & Hernquist
2003
GIMIC simulation (Crain et
al 2010)
dark matter mass
function (fixed
M/L)
NB: exacerbated
by the high value
of WMAP Ωb
but cooling is now
too effective
in high mass
haloes (there's
more gas left over)
Benson et al 2003;
Keres et al 2009
Fountains or SuperWinds?
MW galaxy 0.2~0.1
Dwarf galaxy 0.2~1
Schaye & Dalla
Vecchia 2008, Mitchel
et al 2010
Where are the Baryons?
How did they get there?
Bower et al 2008
McCarthy et al 2010
What determines the balance
of inflow and outflow?
• Star formation efficiency
– Probably the least important
– Galaxies are self regulated
(which why we stand a chance!)
• Evolution of SSFR
• The end of down-sizing
• Supernova “Feedback”
– Wind loading and energetics
– Galactic fountains vs superwinds
Evolution of star formation
rates - just cosmology?
The end of “Down-Sizing”?
Z=0.9
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Z=0.1
Roles+DEEP2 (Gilbank et
al 2010)
Factor 3.5+ increase in normalisation, but
no change of shape. No “down-sizing”!
What form is the gas?
• “sub-grid” models vs molecular cooling
– The role of pressure
– The role of the Toomre criterion?
– Predicting observations
A bigger picture?
• Galaxy haloes are not “closed boxes”
– Most of the baryons are missing
– How and why?
Cooled Gas Mass
Default Sne feedback
“star formation
efficiency
puzzle”
But where does
the low entropy
gas go?
Data: Lin etal 2003
 No feedback
Too many
stars!
 default
 High energy winds
 AGN driven winds
McCarthy et al., 2009
Gas Expelled
from system
no feedback
BCG Star Formation Rate
 “the cooling flow
crisis”
 Voit & Bryan
process seems to
work!
 But where does
the low entropy
gas go?




Default Sne feedback
No feedback
Too many
stars!
default
High energy winds
Gas Expelled
AGN driven winds
from system
no feedback
But…
• No evidence for cold flows.
• Why do you believe outflows? Even
M82 only ~ SFR.
• What is the mass budget of galaxies?
How many baryons are there in the
MW’s halo?
And…
•
•
•
•
•
•
•
Clusters. 80% why not more.
Triggered star formation in jets?
IMF varied. Why? Submm? Obscurred?
Alpha-enhanced. Why?
How do these winds get out.
Measure 300 km/s blueshift. Grav lens?
Environment. Solved?
Franx et al. 1999
Lya
OII
HST ACS BVI composite
SiII
SFROII ~ 42+/-8Mo/yr
M* ~ 2+/-1x109Mo
MDyn ~ 3+/-1x109Mo
M*/SFR ~ 42Myr
voutflow ~ 150km/s
toutflow ~ 10Myr
NIFS OII white light image
NICMOS JH
3”