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Transcript
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 • • • 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