AGN Selec)on Techniques Kris)n Kulas Astro 278 Winter 2012
Selec)on Techniques Op)cal X- ray Radio Infrared Variability
X- ray and Radio Physical Processes Detec)on of Sources Benefit of Wavelength Regime Issues Some Results
X- rays Physical Processes Emission extends from ~0.1 - ~300 kev Inverse- Compton scauering from high- energy electrons in hot corona around accre)on disk Obscura)on - > effects emission at lower energies (soz x- rays absorbed more than hard x- rays) 1-5 )mes more luminous in X- rays compared to other galaxies
X- rays Detec)on of Sources Deep surveys with Chandra (0.5-2 kev, 2-8 kev; 0.1-3 ) and XMM- Newton (5-10 kev; 1-3 ) Complementary: Chandra sensi)vity and XMM- Newton FOV >70% of X- ray sources iden)fied as AGN Largest AGN densi)es, ~7,200 deg - 2 at flux limits of 2.5e- 17 erg cm - 2 s - 1 (0.5-2.0 kev), 10-20 )mes higher than op)cal
Why X- rays? Most AGN obscured by gas and dust - > reduces absorp)on bias Minimal dilu)on from host galaxy Selects which galaxies to follow- up with with deep op)cal spectroscopy - > probes further down luminosity func)on
Issues With X- rays 1. S)ll biased against most obscured AGN > Compton- thick (CT) AGN (N H > 10 24 cm - 2 ) > CT AGN ~40% in local universe Ex) NGC 1068 not detectable at z > 0.1 2. Lower bolometric luminosity compared to op)cal - > redshiz confirma)on
Results From Deep X- ray Surveys Brandt & Hasinger 2005 Luminosity Func)on ~ 950 AGN 0.5 2 kev Luminosity and density evolu)on
Results From Deep X- ray Surveys Comoving Space Density AGN space density peaks at lower redshiz with decreasing luminosity Rate of evolu)on slower for lower luminosity Very different from op)cal quasar space density
Emission from 10MHz to 100 GHz Synchrotron radia)on from jets (radio- loud sources) Almost ALL luminous radio sources are AGN Radio Physical Processes
Defining Radio Galaxies Many different defini)ons across the literature Radio luminosity compared to op)cal luminosity: f 5GHz /f B >10 (Kellermann et al, 1989) L 1.4GHz > 10 24 W Hz 1 (Alexander & Hickox, 2011) 4000 Å break [D n (4000)] strength to separate AGN radio emission from star forma)on (Best et al., 2005)
Radio Fanaroff- Riley Classes FR I: - Distorted (not well collimated) jets - Lower radio luminosity; L < 10 25 W Hz - 1 FR II: - Jets that appear smooth and un- distorted - Higher radio luminosity; L > 10 25 W Hz - 1
First quasar discovered was a radio source Most absent of strong emission lines (less the 30% op)cally loud ) Surveys: Radio Detec)on of Sources - FIRST (9,900 deg 2 ) Overlaps SDSS; high angular resolu)on (5 ); limi)ng flux 1mJy - NVSS (En)re sky north of - 40 dec.) Extended radio emission (45 ); limi)ng flux 2.5mJy
Why Radio? Not effected by highly obscured objects Radio- loud sources are predominately AGN Accurate determined posi)on, allowing counterparts in other wavelengths to be iden)fied Image from FIRST Why Not Radio? Only ~10% of AGN are luminous in radio Lower- luminosity radio sources - > star forma)on
Results From Radio Observa)ons Best et al. 2005 Found mostly in galaxies with large BH masses and stellar masses Op)cally selected largely independent of BH mass BH mass important for galaxy to become radio loud
Emission- line Ac)vity Radio and emission- line ac)vity two physically dis)nct and independent phenomena
Environment Radio- loud AGN prefer dense environments
What type of galaxies are we probing with radio observa)ons? Older, massive galaxies Bulge dominated Larger black hole masses Lower accre)on rate Reside in denser environments *Caveat: These conclusions are for lower redshiz, FR I (less luminous) radio galaxies
References Alexander and Hickox, 2011, What Drives the Growth of Black Holes Bauer et al., 2004, The Fall of Ac@ve Galac@c Nuclei and the Rise of Star- forming Galaxies: A Close Look at the Chandra Deep Field X- Ray Number Counts Best et al., 2005a, A sample of radio- loud AGN in the Sloan Digital Sky Survey Best et al., 2005b, The Host Galaxies of Radio- Loud Ac@ve Galac@c Nuclei: Mass Dependences, Gas Cooling, and Ac@ve Galac@c Nuclei Feedback Brandt and Hasinger, 2005, Deep Extragalac@c X- Ray Surveys Mushotzky, 2004, How Are AGN Found? Richardson et al., 2006, The SDSS Quasar Survey: Quasar Luminosity Func@on from Data Release Three Treister and Urry, 2011, The Cosmic History of Black Hole Growth from Deep Mul@- Wavelength Surveys