the accretion mechanism in low power radio-galaxies ranieri d. baldi 1, barbara balmaverde 2 &...
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The accretion mechanism in low power radio-galaxies
Ranieri D. Baldi1, Barbara Balmaverde2 & Alessandro Capetti2
1: Università degli Studi di Torino2: Osservatorio Astronomico di Torino
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Baldi Ranieri Torino, 22/05/2008 Baldi Ranieri Torino, 22/05/2008
The fundamental questions:
• when does a galactic nucleus become active?
• why AGN show a huge range of nuclear luminosity?
• what sets the level of activity?
Which quantity best correlates with the level of activity of a radio-loud AGN?
Method: estimates of accretion rate using X-ray images from Chandra archive
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PB - PJ: hot gas accretion responsible of nuclear activity.
Baldi Ranieri Torino, 22/05/2008 Baldi Ranieri Torino, 22/05/2008
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Heinze et al (2007): PJ from empirical relation with radio core luminosity.
Baldi Ranieri Torino, 22/05/2008 Baldi Ranieri Torino, 22/05/2008
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1. Capetti & Balmaverde (2005): 29 Core Galaxies 24/29
2. Chiaberge et al. (99): 33 FR I 22/33
3. Allen et al (2006): 9 radio-galaxies 9/9
CHANDRA DATA
44 objects5 orders of magnitude in LRadio nuc
Elliptical galaxies @ z < 0.2
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The Core Galaxies are miniature radio-galaxies
(Balmaverde & Capetti 06).
Baldi Ranieri Torino, 22/05/2008 Baldi Ranieri Torino, 22/05/2008
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Bondi (1952): spherical accretion onto a black hole
• kT from X-ray spectra and ne from X-ray surface brightness profiles at rB.
• Mbh from literature ( stellar dynamics of empirical relation).
• Errore budget: logMbh = 0.5
2.
cMP BB
2
2
c
GMB
BHr
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Deprojection of X-ray spectra Deprojection of surface brightness profiles
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•Weak sources: 6 objects
•Complex morphology: 3 objects
•Large PB error : 12 objects
44 – 21 = 23 objects
(6 FRI+ 8 CoreG + 9 Allen)
Criteria of exclusion:
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• PB – PJ correlation: efficiency conversion
• Mbh,ne,kT depedence
PB – PJ is a primary relation!
Scatter:0.4 dex
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• CoreG: correlation LR,LO,Lx
• FRI: high polarization of optical nuclei• LX/PB~10-4 – 10-5
Jet origin for the nuclear emission
Upper limit per Paccretion
&
ADAF,ADIOS, CDAF models:
Small accretion rate and low radiative
efficiency
Costraints on the accretion process:
.
.
B
disk
m
mf
Radiative efficiency:
Mass flow in the jet Low X-ray luminosity
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• Homologic shape of Surface Brightness Profiles (SBP)
• S1kpc – PJ: scatter 0.67 dex
Global property of hot coronae – level of AGN activitya change in power requires a global change in the host properties (a merger?)
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• PB - PJ: accrection process from hot gas• Bondi accretion approximation works over 4 orders of magnitude PJ!
• Hot coronae brightness - levels of radio-loud AGN activity
• Accretion process: small rate and low radiative efficiency (ADAF)
• S1kpc – PJ:useful tool for faint and distant objects.
Baldi Ranieri Torino, 22/05/2008 Baldi Ranieri Torino, 22/05/2008