  [Abridged] We make use of a semi-analytic cosmological model that includes
simple prescriptions for dust attenuation and emission to make predictions for
the observable and physical properties of galaxies that may be detected by the
recently launched Herschel Space Observatory in deep fields such as
GOODS-Herschel. We compare our predictions for differential galaxy number
counts in the PACS (100 & 160) and SPIRE (250, 350, and 500 micron) bands with
available observations. We find very good agreement with the counts in the PACS
bands, for the overall counts and for galaxies binned by redshift at z< 2. At z
> 2 our model underpredicts the number of bright galaxies by a factor of ten.
The agreement is much worse for all three SPIRE bands, and becomes
progressively worse with increasing wavelength. We discuss a number of possible
reasons for these discrepancies, and hypothesize that the effect of blending on
the observational flux estimates is likely to be the dominant issue. We note
that the PACS number counts are relatively robust to changes in the dust
emission templates, while the predicted SPIRE number counts are more template
dependent. We present quantitative predictions for the relationship between the
observed PACS 160 and SPIRE 250 micron fluxes and physical quantities such as
halo mass, stellar mass, cold gas mass, star formation rate, and total infrared
(IR) luminosity, at different redshifts. We also present quantitative
predictions for the correlation between PACS 160 micron flux and the
probability that a galaxy has experienced a recent major or minor merger.
Although our models predict a strong correlation between these quantities, such
that more IR-luminous galaxies are more likely to be merger-driven, we find
that more than half of all high redshift IR-luminous galaxies detected by
Herschel are able to attain their high star formation rates without enhancement
by a merger.
