Infrared Excess Sources: Compton Thick QSOs, low luminosity Seyferts or starbursts?

A. Georgakakis; M. Rowan-Robinson; K. Nandra; J. Digby-North; P. G. Perez-Gonzalez; G. Barro

doi:10.1111/j.1365-2966.2010.16727.x

paper

Infrared Excess Sources: Compton Thick QSOs, low luminosity Seyferts or starbursts?

arXiv:1003.5218 · doi:10.1111/j.1365-2966.2010.16727.x

Abstract

We explore the nature of Infrared Excess sources (IRX), which are proposed as candidates for luminous L_X(2-10keV)>1e43erg/s Compton Thick (N_H>2e24cm^{-2} $) QS O s a t z 2. L o w er r e d s hi f t, z 1, ana l o g u eso f t h e d i s t an t I R X p o p u l a t i o na r e i d e n t i f i e d b y f i r s tl y r e d s hi f t in g t oz = 2 t h e S E D so f a l l so u r ces w i t h sec u r es p ec t r osco p i cr e d s hi f t s in t h e A E G I S (6488) an d t h e GO O D S - N or t h (1784) s u r v ey s an d t h e n se l ec t in g t h ose t ha tq u a l i f y a s I R X so u r ces a tt ha t r e d s hi f t . A t o t a l o f 19 g a l a x i es a r ese l ec t e d . T h e m e an r e d s hi f t o f t h es am pl e i s$ z\approx1 $. W e d o n o t f in d s t r o n g e v i d e n ce f or C o m pt o n T hi c k QS O s in t h es am pl e . F or 9 so u r ces w i t h X - r a y co u n t er p a r t s, t h e X - r a y s p ec t r aa r eco n s i s t e n tw i t h C o m pt o n T hin A GN . O n l y 3 o f t h e m s h o w t e n t a t i v ee v i d e n ce f or C o m pt o n T hi c k o b sc u r a t i o n . T h e S E D so f t h e X - r a y u n d e t ec t e d p o p u l a t i o na r eco n s i s t e n tw i t h s t a r b u r s t a c t i v i t y . T h er e i s n oe v i d e n ce f or ah o t d u s t co m p o n e n t a tt h e mi d - in f r a r e d a ssoc ia t e d w i t h A GN h e a t e dd u s t . I f t h e X - r a y u n d e t ec t e d so u r ces h os t A GN, an u pp er l imi t o f L_{X} (2 - 10 k e V) = 1 e 43 er g / s i ses t ima t e df or t h e i r in t r in s i c l u min os i t y . W e p r o p ose t ha t a l a r g e f r a c t i o n o f t h e$ z\approx2$ IRX population are not Compton Thick QSOs but low luminosity [L_X(2-10keV)<1e43erg/s], possibly Compton Thin, AGN or dusty starbursts. It is shown that the decomposition of the AGN and starburst contribution to the mid-IR is essential for interpreting the nature of this population, as star-formation may dominate this wavelength regime.

Accepted by MNRAS

Infrared Excess Sources: Compton Thick QSOs, low luminosity Seyferts or starbursts?

Abstract

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