Transcript Revising the census of low luminosity AGN

REVISING THE CENSUS OF LOW
LUMINOSITY AGN
A. Capetti,
R. Baldi, B. Balmaverde, S. Buttiglione
AGN 10 - Roma 10/09/2012
WHY AN AGN CENSUS?
• A PROPER AGN CENSUS IS NEEDED FOR A VARIETY OF STUDIES,
SUCH AS, E.G. , THE AGN/HOST GALAXY CONNECTION, THE
PROPERTIES OF THE CENTRAL ENGINE, THE AGN LUMINOSITY
FUNCTION …
• THE CENSUS SHOULD BE COMPLETE (OR AT LEAST WITH WELL DEFINED BIASES)
AND INCLUDE THE LEAST NUMBER OF INTERLOPERS
• AGN SHOULD NOT ONLY BE PROPERLY CATALOGUED, BUT WE ALSO
NEED TO ESTIMATE THEIR LUMINOSITY
• HOW DO WE LOOK FOR AGN? MULTI BAND NUCLEAR EMISSION
(RADIO, OPTICAL, X-RAY, …) OR WITH THE EMISSION LINES.
AGN 10 - Roma 10/09/2012
EMISSION LINES GALAXIES
• NARROW EMISSION LINES ARE NOT AFFECTED BY NUCLEAR OBSCURATION
BROAD EMISSION LINES CAN ONLY BE PRODUCED BY AN AGN BUT THEY ARE RARELY SEEN PARTICULARLY AT LOW LUMINOSITIES
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•
•
THEY ARE EASY TO MEASURE AT (ALMOST) ALL REDSHIFTS
THEIR LUMINOSITY IS A GOOD PROXY FOR THE BOLOMETRIC EMISSION.
LINE RATIOS CAN BE USED TO SEPARATE AGN FROM STAR FORMING GALAXIES.
AGN 10 - Roma 10/09/2012
EMISSION LINES IN NEARBY SDSS GALAXIES
GENUINE AGN?
THE [OIII] FLUX CORRELATES WITH THE STELLAR CONTINUUM.
THE EW ARE STRONGLY CLUSTERED AROUND 1 Ᾰ.
VERY HARD TO ACCOUNT IN CASE OF LINES POWERED BY AN AGN
THE CLOSE CONNECTION SUGGESTS A STELLAR ORIGIN, FOR EXAMPLE FROM THE LARGE
POPULATION OF HOT EVOLVED STARS (pAGB) WHICH MIMICS A DISK EMISSION.
AGN 10 - Roma 10/09/2012
WHICH IS THE AGN FRACTION
AMONG EMISSION LINE GALAXIES?
STAR FORMING GALAXIES ARE EXCLUDED
EW < 2 Å
2 A <EW < 3 Å
EW> 3 Å
ONLY A FEW PERCENT! MOST OF THEM HAVE LOW EW AND ARE UNLIKELY TO BE AGN
THE LINE EMISSION IS PRODUCED BY THE HOST GALAXY, NOT BY THE AGN
THE LINERs REGION IS MOSTLY POPULATED BY NON-AGN
THE EW IS A BEST PREDICTOR FOR GENUINE AGN THAN THE DIAGNOSTIC DIAGRAMS
A LOW EW (~1 Å) IS CHARACTERISTIC OF STELLAR PROCESSES
AGN 10 - Roma 10/09/2012
AGN LUMINOSITY FUNCTION
EW < 2 Å
2 A <EW < 3 Å
EW> 3 Å
THE AGN LUMINOSITY FUNCTION IS RADICALLY CHANGED BELOW 1040 erg/s
THE AGN CENSUS BASED ON EMISSION LINES IS NOT RELIABLE FOR LOW LUMINOSITY LINERs
THE HOST GALAXY CONTAMINATES / DOMINATES IN FAINT AGN (or in quiescent galaxies)
AGN 10 - Roma 10/09/2012
THE PALOMAR SURVEY
SPECTROSCOPY OF ~500 NEARBY (D<40 Mpc) BRIGHT GALAXIES
LOOKING FOR FAINTER AGN
REDUCED PHYSICAL SIZE OF THE SPECTRAL APERTURE (FROM ~2 kpc OF SDSS TO ~100 pc)
UPPER LIMITS
THE SAME CONCENTRATION AT LOW EW…
THE LINE CONTAMINATION FROM THE HOST STILL DOMINATES
AGN 10 - Roma 10/09/2012
DIAGNOSTIC DIAGRAMS
EW < 2 Å
2 A <EW < 3 Å
EW> 3 Å
(blue = S.F.)
THE AGN FRACTION IS NOT 40-50% (AS INDICATED BY THE DIAGNOSTIC DIAGRAMS) BUT 10-15%
MOST LINERs ARE NOT AGN (BUT ALSO SOME LOW LUMINOSITY SEYFERT)
AGN 10 - Roma 10/09/2012
THE AGN LUMINOSITY FUNCTION
THE AGN LUMINOSITY FUNCTION IS STRONGLY AFFECTED BELOW 1039 erg/s
AND COMPLETELY UNRELIABLE BELOW 1038 erg/s
(CORRESPONDING TO EDDINGTON RATIOS <10-6)
AGN 10 - Roma 10/09/2012
HOW CAN WE IMPROVE THE AGN CENSUS?
1) REDUCE THE SIZE OF THE APERTURE TO DECREASE THE STELLAR CONTAMINATION
PALOMAR
8 sq”
TNG
0.5 sq”
HST
0.05 sq”
2”
2) COMBINE WITH MULTI-BAND (X-RAY AND RADIO) DATA
AGN 10 - Roma 10/09/2012
HST SPECTRA OF LOW LUMINOSITY AGN
AN EXAMPLE
PALOMAR
HST
THE APERTURE SIZE IS DECREASED BY A FACTOR OF ~160
THE [OIII] EW GROWS FROM ~1 Å TO ~10 Å DUE TO THE REDUCED STELLAR CONTINUUM
THIS IS A GENUINE AGN
AGN 10 - Roma 10/09/2012
A FIRST TEST: THE SUNNS SAMPLE
18 GALAXIES OBSERVED WITH BOTH HST AND CHANDRA
SEYFERT 2
NO LINES
NO X-RAY
HIGH EW LINES
X-RAY
HST AND CHANDRA YIELD CONCORDING RESULTS
ONLY 20-30% OF THE PALOMAR GALAXIES HAVE HST AND/OR CHANDRA OBSERVATIONS,
THE DATA ARE OFTEN OF LOW QUALITY
AGN 10 - Roma 10/09/2012
HOW ABOUT THE RADIO DATA?
AGN
NON AGN
DIFFICULT TO PREDICT THE
EXPECTED LEVEL OF RADIO
EMISSION
RADIO OBSERVATIONS CAN BE
USED TO CONFIRM AGN,
BUT NOT TO FALSIFY THEM.
ALSO THE RADIO SUFFERS FROM CONTAMINATION AT LOW POWER
DATA OF HIGH SENSITIVITY, RESOLUTION MULTI-FREQUENCY ARE NEEDED.
AGN 10 - Roma 10/09/2012
THE TNG SURVEY
A PILOT TEST ON 19 GALAXIES WITH LOW EW (< 2Å) IN THE PALOMAR SURVEY
APERTURE REDUCED FROM 2”X4” TO 0.7”X0.75” (16 TIMES)
HIGH QUALITY SPECTRA “EASY” TO OBTAIN
AGN 10 - Roma 10/09/2012
THE TNG SURVEY 2
THE EW GENERALLY GROWS
(DUE TO THE REDUCED STELLAR
CONTAMINATION)
EW > 1 OBJECTS ARE
ASSOCIATED WITH X-RAY
NUCLEAR SOURCES,
LIKELY GENUINE AGN
AGN 10 - Roma 10/09/2012
CONCLUSIONS
LINES FROM THE HOST CONTAMINATE THE AGN EMISSION
AND STRONGLY AFFECT THE AGN CENSUS
THE DIAGNOSTIC DIAGRAMS ARE NOT SUFFICIENT TO
ESTABLISH THE AGN NATURE
CAREFUL WITH LOW EW LUMINOSITY LINERS
A BETTER AGN PREDICTOR IS THE LINE EW
SPECTRA FROM SMALLER APERTURES REDUCE THE HOST
CONTAMINATION AND IMPROVE THE AGN CENSUS
AGN 10 - Roma 10/09/2012