We study the co-existence of star formation and active galactic nucleus
(AGN) activity in Chandra X-ray-selected AGN by analyzing stacked 870
μm submillimeter emission from a deep and wide map of the Extended
Chandra Deep Field South (ECDFS), obtained with the LABOCA instrument at
the APEX telescope. The total X-ray sample of 895 sources with median
redshift z ~ 1 drawn from the combined (E)CDFS X-ray catalogs is
detected at >11σ significance at a mean submillimeter flux of
0.49 ± 0.04 mJy, corresponding to a typical star formation rate
(SFR) around 30 M sun yr-1 for a T = 35 K, β
= 1.5 graybody far-infrared spectral energy distribution. The good
signal-to-noise ratio permits stacking analyses for major subgroups,
splitting the sample by redshift, intrinsic luminosity, and AGN
obscuration properties. We observe a trend of SFR increasing with
redshift. An increase of SFR with AGN luminosity is indicated at the
highest L 2-10 keV >~ 1044 erg s-1
luminosities only. Increasing trends with X-ray obscuration as expected
in some AGN evolutionary scenarios are not observed for the bulk of the
X-ray AGN sample but may be present for the highest intrinsic luminosity
objects with L 2-10 keV >~ 1044 erg
s-1. This behavior suggests a transition between two modes in
the co-existence of AGN activity and star formation. For the bulk of the
sample, the X-ray luminosity and obscuration of the AGN are not
intimately linked to the global SFR of their hosts. The hosts are likely
massive and forming stars secularly, at rates similar to the pervasive
star formation seen in massive galaxies without an AGN at similar
redshifts. In these systems, star formation is not linked to a specific
state of the AGN and the period of moderately luminous AGN activity may
not highlight a major evolutionary transition of the galaxy. The change
indicated toward more intense star formation, and a more pronounced
increase in SFRs between unobscured and obscured AGN reported in the
literature at highest (L 2-10 keV >~ 1044 erg
s-1) luminosities suggests that these luminous AGNs follow an
evolutionary path on which obscured AGN activity and intense star
formation are linked, possibly via merging. Comparison to local hard
X-ray-selected AGN supports this interpretation. SFRs in the hosts of
moderate luminosity AGN at z ~ 1 are an order of magnitude higher than
at z ~ 0, following the increase in the non-AGN massive galaxy
population. At high AGN luminosities, hosts on the evolutionary
link/merger path emerge from this secular level of star formation.