The accretion mechanism in low power radio-galaxies Ranieri D. Baldi 1, Barbara Balmaverde 2 &...

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

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

PB - PJ: hot gas accretion responsible of nuclear activity.


Heinze et al (2007): PJ from empirical relation with radio core luminosity.


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


The Core Galaxies are miniature radio-galaxies

(Balmaverde & Capetti 06).


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



Deprojection of X-ray spectra Deprojection of surface brightness profiles

•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:


• PB – PJ correlation: efficiency conversion

• Mbh,ne,kT depedence

PB – PJ is a primary relation!

Scatter:0.4 dex



• 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

• 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?)


• 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.


The accretion mechanism in low power radio-galaxies Ranieri D. Baldi 1, Barbara Balmaverde 2 &...

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