Transcript Origin of radio emission from nearby low luminosity active
Origin of Radio Emission from Nearby Low
－
Luminosity Active Galactic Nuclei Qingwen Wu & Xinwu Cao [email protected]
Shanghai Astronomical Observatory
1.
Background
Radio emission from Low-Luminosity Active Galactic Nuclei(LLAGNs) is unclear.
(I)
Radiatively inefficient accretion flows
(
RIAF
, e.g.,
ADAF, ADIOS, CDAF
) Radio emission comes from Synchrotron radiation from hot thermal electrons . The spectrum can described by ADAF/ADIOS model very well (e.g., Sgr A* Narayan&Yi 1994) (II)
Compact-jet model
(Falcke 2000, Yuan et al. 2002)
Where is the radio emission coming from in LLAGNs --- jet or RIAF ???
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2.Sample
The sample includes nearby inactive and Seyfert nuclei which have the most up-to-date BH mass and high angular resolution optical
（
HST
）
and radio
（
VLA
）
measurements ( Ho, 2002, ApJ). X-ray data were taken from the literature.
Our sample includes 62 sources, of which 57 have measured optical nuclei, 60 have measured radio nuclei, and 57 have measured X-ray emission.
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3. Spectra of ADAF / ADIOS
Spectra of ADAFs (Advection Dominated Accretion Flows) can described by four parameters:
M BH
, , ,
P gas P tot al
( Mahadevan 1997). Spectra of ADIOS (Advection Dominated Inflow Outflow Solutions) In ADIOS model, the wind blows away the matter that .
flowing into black hole, so is not constant . We can calculate the ADIOS spectrum in a similar way 4
4. Results
1. Relation between
M BH
L
M BH
L
( 5
GHz
)
M BH
L
(
B
)
M BH
L
( 2
keV
)
Triangle sources: Circle sources:
L obs
( 5
GHz
)
L ADAF
, max ( 5
GHz
)
L obs
(
B
)
L ADAF
, max (
B
)
Radio emission for triangle sources—jet or RIAF?
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2) Test ADAF model (triangle sources) There are 15 triangle sources in our sample, 10 of them have optical, radio and X-ray data. The relation of and are
Edd
calculated for both ADAF model and the radio-weak sources.
M BH
10 8
Msun
is adopted in our calculation.
1
B
2 /
P total
1 2020/5/1 0 .
1 6
3) Test ADIOS model (triangle sources) mild wind (p ＝ 0.4) Strong wind (p ＝ 0.99) 1 1 2020/5/1 7
5. Discussion and Summary
I)
The radio emission of most of the LLAGNs may be dominated by the jet ( the square and circle sources).
II) Can radio emission from triangle sources be explained by RIAF models(ADAF/ADIOS) ???
In ADAF/ADIOS state with very weak magnetic field strength .
Can ADAF exist with such weak magnetic field strength ???
---this maybe difficult (Pan , Lu & Gu 2002)!!!
6 of 10 sources have radio emission higher than maximal radio luminosity predicted by pure ADAF with the weak magnetic field strength that required for spectral calculations.
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III)
Other possible model for radio-weak LLAGNs
ADAF+SD ----
our conclusions are unchanged.
CDAF model—very faint, as accretion rate is much smaller than non-convecting ADAF
The radio emission may be dominated by jet in these LLAGNs , not RIAFs( ADAF / ADIOS / CDAF) --- RIAFs+jet model for LLAGNs
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Circle sources:
table1
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2) Square sources: 2020/5/1 12
Radio-weak sources: 2020/5/1 13
II)
Edd
may indicate different accretion modes (Standard cold disk and RIAF).
Future high sensitivity Square Kilometer Array(SKA) observation on these LLAGNs to verify the origin of radio emission of these radio-weak LLAGNs since their radio flux densities are always sub millijansky.
The maximal luminosity of ADAFs can be calculated as a function of , 2020/5/1
BH
is a critical accretion rate for ADAF. owing to luminosity 14
2)
Distribution of
l
L B
/
L Edd
bimodal.
A KMM test shows that its distribution is non unimodal(P value=0.003<0.05) which is similar to Marchesini et al （ astro- ph 0403272 ） for a samples of radio galaxies and RL quasar. Begelman & Celotti (a-ph 0406607) proposed that lower accretion rate population should be in ADAF/ADIOS state. So the lower population in our sample may in ADAF/ADIOS state .
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