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The Riddle of Cooling Flows Meeting Summary? Joel N. Bregman. Thanks to the organizers for a great meeting. The basic cooling flow picture what parts are ok what parts need to be changed What would an outsider think? X-ray peak is on a cD galaxy (seems like it must be involved)
Joel N. Bregman
what parts are ok
what parts need to be changed
What would an outsider think?
X-ray peak is on a cD galaxy
(seems like it must be involved)
dT/dr is similar from cluster to cluster
Metallicity and entropy gradients
azimuthal properties (T)
Occam’s razor: keep it simple
A counterpart to Occam’s razor
minimize Trips to the Tooth Fairy (TTF)
The “Classic” Picture
Gas cools in the center of a cluster at 100 Msolar/yr
Gas either accumulates or forms into low mass stars
missing intermediate temperature X-ray lines (OVII, FeXVII)
little evidence for the very high rate of star formation
Save the Picture (little enthusiasm expressed)
have the gas “jump” over the 1 keV range
(OVII, Fe XVII not produced)
(i.e., mixing with cold gas lost from stars)
might gain support if OVI seen in several clusters
The consensus view:
Reduce Mdot by heating the gas as it tries to cool
Energy budget considerations
plenty of energy (infinite thermal bath)
Energy transfer rate
good enough for the hot clusters
a bit low for cool clusters
Big Problem: how is the conduction so “smart” (major TTF)
conduction coefficient needs to be 19% of κSpitzer for
one cluster, 41% for another, etc.
otherwise, observed dT/dr would be wiped out
add in the stellar mass loss from stars in cD
this gas is at 1 keV after themalization (provides Tmin)
the gas is flowing outward into the cluster
T will rise from Tmin to Tcluster in all cases,
but the shape varies with κSpitzer
not sensitive to κSpitzer as long as it is sufficiently large
produces a significant dT/dr that would be similar from
cluster to cluster
don’t get the intermediate temperature cooling lines
what about all that CO?
It’s just mass lost from a galaxy
how about that AGN activity?
It’s not the dominant heat source
is conduction ruled out by cool fronts?
Not if they are magnetically separate
can this work in cooler clusters
Maybe not, but Mdot is not large
didn’t Brighenti and Mathew show this doesn’t work?
Comments: Thomas; Brighenti; Sparks; Soker, …..
Low power radio lobes create acoustic noise that is damped
seems inadequate for most systems (by 10x)
poster by Birzan-Rafferty et al.
Can the energy be distributed azimuthally? (1 TTF)
How did the AGN get to be so smart?
dT/dr so similar from system to system
it puts just the right amount of energy into the system
Goldilocks: not too hot, not too cold; just right
Feed the AGN with cooling gas
If the gas cools too much, the AGN gets fed more until
the heating shuts off cooling
Requires a good match in the timescales
Feeding rate must adjust faster than the energy generation rate.
Not obvious that this requirement is met.
If hot gas has angular momentum, it doesn’t reach the
center once it cools.
Feeding may be by stars scattered into the AGN, not by
the hot gas (no feedback in this case).
If feeding were by cooled gas, do you get the observed
number distribution with redishift?
If the lobe is heating the surroundings, it should be hotter close to the lobe than further away.
Observations can test this.
Discussion: Blanton; Nulsen; Böhringer; Begelman, …..
Does an AGN initiate star formation or are they both part of one phenomenon related to a disturbance, possibly by a passing galaxy?
There seems to be an association between these events in a galaxy cluster:
Hα emitting gas
AGN (radio lobe) activity
“classic” X-ray cooling flow structure
One interpretation of this is within the Cooling Flow paradigm (at reduced Mdot):
Cooling Flow → Cooled Gas (Hα + CO) → star formation (possibly triggered by AGN)
Late-type galaxy passes by cluster core
loses its cold ISM (CO)
shock and disturbance in this gas triggers
star formation (Hα)
disturbance with central galaxy ignites the AGN
In this second picture, X-ray emission has little to do with this
(thermal exchange with Hα gas)
Discussion: Crawford; Baum; McNamara; Edge; Salom, …
Mass of cold gas in clusters
CO to H2 conversion is problematic
dust masses (decent measure of gas mass)
Give HI another try (GBT)
Mass of cooling gas in clusters
is OVI emission common? (5 more CFs scheduled)
In-depth studies of the few best objects.
A test of the heating picture from AGNs.
Observations That We Don’t Need More Of
another X-ray spectrum (RGS) showing the same thing as the first 13 objects
> 50 clusters already observed with XMM
Calculations from first principles (minimize TTF).
Models involving AGN heating
Predictions, that if not verified, invalidates model.
Location and magnitude of the heating.
Apparent conflict with average KE too low.
Distribution of quantities (dT/dr)
Further developments of magnetic heating.
(it’s important in the Sun)
Continued calculations with conduction (ongoing).
A resolution to the Cooling Flow mystery by the next meeting
“Cooling Flows Reloaded”
A little more “love” from the rest of the community.