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SUMMARY:Addressing the Missing AGN Problem - Belinda Wilkes (SAO)
DTSTART:20180517T150000Z
DTEND:20180517T160000Z
UID:TALK104491@talks.cam.ac.uk
CONTACT:28811
DESCRIPTION:The complex nuclear structures of active galactic nuclei (AGN)
  \nlead to strong selection effects in most wavebands\, including the X-ra
 y. \nHighly obscured AGN are hard to find\, and identify. Estimating their
  \nnumbers\, a function of luminosity and redshift\, remains a major quest
 \nboth for AGN science\, and in understanding the level of accretion \npow
 er particularly in the early Universe. \n\n\n== Multi-wavelength observati
 ons of the low-frequency\, radio-selected 3CR\nluminous\nAGN sample (z>0.5
 ) largely avoid selection biases\, revealing the obscured\nAGN\, \nand pro
 bing both their intrinsic\, and orientation-dependent properties.\nChandra
 \, Spitzer\, Herschel and multi-wavelength observations confirm that\nthe 
 FIR (> ~ 40um) does not depend on orientation and that ~half the sample \n
 is significantly obscured with ~a quarter being Compton thick. This is a \
 nlarger fraction than typically estimated for optically- or X-ray-selected
 \, \nhigh-luminosity samples. Once the primary X-ray power-law is obscured
 \, AGN \nX-ray spectra are complex\, and detecting and estimating X-ray ob
 scuration \nlevels becomes highly uncertain. This is particularly true for
  sources close\nto the flux limit. The loss or miss-classification of obsc
 ured AGN in\nsurveys \nalso results in large (*10-1000) uncertainties on t
 heir intrinsic\nluminosities.\nThis may explain discrepant obscured fracti
 ons reported for various\noptical- and X-ray-samples\, and may also affect
  the shape of derived\nluminosity\nfunctions. The use of independent measu
 res of the AGN power\, such \nas the low-frequency radio\, or [OIII] emiss
 ion line luminosity\, helps to \ncounteract such problems. ==\n\n\nI will 
 close with a look to the future\, reviewing the science pillars \nand miss
 ion concept of the NASA-funded\, Chandra Successor Mission Study\,\nLynx\,
 \nleading up to the USA Astronomy and Astrophysics Decadel Survey.
LOCATION:Sackler Lecture Theatre\, IoA (tea at 3:30 pm)
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