the regulation of star formation by agn feedback
DESCRIPTION
The Regulation of Star Formation by AGN Feedback. D AVID R AFFERTY (Penn State / Ohio U.). Collaborators: Brian McNamara (Waterloo) and Paul Nulsen (CfA). Star Formation & the ICM. Indirect evidence links the ICM to star formation in the central galaxy. For example: - PowerPoint PPT PresentationTRANSCRIPT
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The Regulation of Star Formation by AGN Feedback
DAVID RAFFERTY
(Penn State / Ohio U.)
Collaborators: Brian McNamara (Waterloo) and Paul Nulsen (CfA)
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Star Formation & the ICM• Indirect evidence links the ICM to star formation
in the central galaxy. For example:• Indicators of star formation correlate with properties
of the cooling flow (e.g., Heckman et al. 1981, McNamara & O’Connell 1989, Cardiel et al. 1995)
• Optical line emission seen only in BCGs at the cores of cooling flows (e.g., Edwards et al. 2007)
• Cooling and star formation rates are in rough agreement
• If star formation is fueled by the cooling ICM, there should be some relation between the presence of SF and the central cooling time/entropy of the ICM
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Identifying Star Formation
• Indicators of star formation:• Optical line emission from ionized gas• Far-IR emission from heated dust• Excess blue/UV emission, beyond that
expected from the underlying population:
A1068
McNamara et al. (2004)
A2597
Koekemoer et al. (1999)
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Optical Data • Sample: 46 systems in the
Chandra archive with a wide range of central cooling time
• U, R, and I imaging• Search for excess blue
emission in color profiles:
Radius (arcsec)
U-I
U+I images of A2390 taken at the MDM observatory
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• Star formation (indicated by positive gradients) occurs only where cooling times are short (t ≤ 7-8×108 yr), whereas
• Red systems have a wide range of cooling times• This threshold may correspond to onset of thermal instabilities in the
ICM (see Voit et al. 2008, also Soker 2008)
Results – The Cooling-time / Entropy Threshold
≈ 8108 yr ≈ 30 keV cm2
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• Star formation seen only in systems with small separations between X-ray and CDG cores
• However, small separations and short cooling times are necessary, but not sufficient, conditions
• Why do some systems lack star formation?
Results – CDG Location and Star Formation
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AGN Feedback• Systems with
excess AGN heating: Cooling is
quenched Little active star
formation
• Systems that are underheated:Some cooling
proceeds Active star
formation MS 0735.6+7421 Chandra X-ray (blue): B. R. McNamaraVLA Radio (red): L. Bîrzan
HST Optical: B. R. McNamara
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• Systems in which the AGN quenches cooling:
Generally, no recent star formation
• Systems in which the AGN does not quench cooling :
Tendency for recent star formation
Results – Feedback and Star Formation
€
Pcav
LICM
≥1
€
Pcav
LICM
<1 Quenched
Net cooling +Star formation
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• Many cooling flows have central galaxies with active star formation
• Star formation found only in systems where: 1. Central cooling times are short (tcool < 5 108 yr) or
entropies are low (S < 30 keV cm2)
2. The galaxy is very near the cluster core (r < 20 kpc)
3. The ratio of AGN heating rate to cooling luminosity is approximately less than unity
1. Cooling, regulated by AGN heating, leads to star formation in the central galaxy
Summary
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Thermal Instability• Cooling and star
formation may be driven by thermal instabilities in the hot gas:• A blob of cooling gas
becomes unstable to cooling when growth rate of instabilities exceeds damping rate from conduction
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Radio Luminosity• Galaxies with active
star formation have larger radio luminosities:Evidence that star
formation and AGN activity both fueled by the cooling ICM?