Cooling Flows in Clusters of Galaxies. A.C. Fabian ARAA 32, 277-318 (1994) and recent progress. The Origins of “ Cooling Flows ”. Clusters discovered to be extended X-ray sources (Gursky et al. 1971, UHURU; Kellogg et al. 1972; Forman et al. 1972)
A.C. Fabian ARAA 32, 277-318 (1994)
and recent progress
X-ray luminosity 1043-1045 erg/s
radius: 1-2 Mpc, core radius: 0.3-0.5 Mpc
number density: 10-4-10-2cm-3
total gas mass 5*1013-5*1014 Msolar (in rich cluster)
chemical abundance: Fe ~0.3 times solar unit
See also: Hubble & Humason 1931
filamentary structure are clearly seen
Zoomed in view of the very central regions of NGC 1275, showing the freshly formed clusters of stars and dusty regions which are probably a result of the collision.
X-ray image of Perseus A taken with the Chandra telescope, showing a central bright source, two “bubbles” above and below this source, and the shadow of an infalling galaxy (top right). The remaining emission is from the central part of a cooling flow (the inward flow of hot gas into the potential well of the elliptical) which is losing energy (i.e. cooling) via thermal bremsstrahlung emission in the X-ray region.
T>3e7, thermal bremsstrahlung is the main radiation mechanism.
X-ray Luminosity is
Extra assumptions: atomic physics determines L and T,
Locally Maxwellian, no absorption, metal distribution,
Exact prediction for mdot depends on grav. potential
The central luminosity is extraordinary high.
Other clustersVoigt & Fabian 03
Allen et al 01
The central part is cooler due to high number density
4 actual cooling flows
Mukai, Kinkhabwala, Peterson, Kahn, Paerels 2003
Optical: Crawford et al 99
UV: Oergerle et al 01
CO: Edge 02
Dust: Edge et al 99
More than 30-50% of the clusters have surface brightness tcool<H0-1 within central 100 kpc.
Cooling flow condition also occur in large, isolated elliptical galaxies.
Sakelliou et al 02
Gas drops to Tmin~0.3Tvir
Chandra spectra consistent
Peterson et al 01,02
McNamara et al ; David et al ; Allen et al; Blanton et al ; Buote et al………
then and now:
at constant P
Why, and how, is the cooling of gas below Tvir/3 suppressed?
The stellar/gaseous parts of galaxies are due to the cooling of gas in their DM potential wells
Cooling in clusters and groups should be an observable example of this process.
The suppression of cooling in these objects may explain the upper mass cutoff of galaxies.
─ from centre (AGN)
Voigt et al 03
seems inadequate for most systems (by 10x).
It maybe not the dominant heat source
Voigt & F 03
conduction coefficient needs to be 19% of KSpitzer for one cluster, 41% for another, etc.
Voigt & Fabian 03
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
Three-colour image of the Perseus cluster from Fabian et al (2000). Red indicates regions of low-energy emission, blue indicates high-energy emission. Visible in dark green above the centre is an infalling dwarf galaxy, shown by absorption of high-energy X-rays.
Chandra 200 ks observation of the Perseus cluster.
Fluctuations in the Perseus cluster caused by sound waves generated from the central black hole.
about 57 octaves lower than middle-C.
Temperature map of the Perseus cluster.
Weak shock to NE
K~108T 5/2n -1
Viscous heating=rad. cooling in inner 50 kpc of Perseus
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)
Chandra + VLA
A correlation is found between the cooling flow rate and the maximum Faraday rotation measures. Magnetic fields of strength 10–40 μG are found
to be common to the centres of clusters with strong cooling flows, and somewhat lower field
strengths of 2–10 μG are found in the non cooling-flow clusters.
G. B. Taylor et al. MNRAS (2002) 334,769