  We present measurements of the auto- and cross-frequency correlation power
spectra of the cosmic (sub)millimeter background at: 250, 350, and 500 um
(1200, 860, and 600 GHz) from observations made with the Balloon-borne Large
Aperture Submillimeter Telescope, BLAST; and at 1380 and 2030 um (218 and 148
GHz) from observations made with the Atacama Cosmology Telescope, ACT. The
overlapping observations cover 8.6 deg^2 in an area relatively free of Galactic
dust near the south ecliptic pole (SEP). The ACT bands are sensitive to
radiation from the CMB, the Sunyaev-Zel'dovich (SZ) effect from galaxy
clusters, and to emission by radio and dusty star-forming galaxies (DSFGs),
while the dominant contribution to the BLAST bands is from DSFGs. We confirm
and extend the BLAST analysis of clustering with an independent pipeline, and
also detect correlations between the ACT and BLAST maps at over 25sigma
significance, which we interpret as a detection of the DSFGs in the ACT maps.
In addition to a Poisson component in the cross-frequency power spectra, we
detect a clustered signal at >4sigma, and using a model for the DSFG evolution
and number counts, we successfully fit all our spectra with a linear clustering
model and a bias that depends only on redshift and not on scale. Finally, the
data are compared to, and generally agree with, phenomenological models for the
DSFG population. This study represents a first of its kind, and demonstrates
the constraining power of the cross-frequency correlation technique to
constrain models for the DSFGs. Similar analyses with more data will impose
tight constraints on future models.

Cosmology and Nongalactic Astrophysics