Tracing the evolution of dust obscured star-formation and accretion back
  to the reionisation epoch with SPICA
  Our current knowledge of star formation and accretion luminosity at
high-redshift (z>3-4), as well as the possible connections between them, relies
mostly on observations in the rest-frame ultraviolet (UV), which are strongly
affected by dust obscuration. Due to the lack of sensitivity of past and
current infrared (IR) instrumentation, so far it has not been possible to get a
glimpse into the early phases of the dust-obscured Universe. Among the next
generation of IR observatories, SPICA, observing in the 12-350 micron range,
will be the only facility that can enable us to make the required leap forward
in understanding the obscured star-formation rate and black-hole accretion rate
densities (SFRD and BHARD, respectively) with respect to what Spitzer and
Herschel achieved in the mid- and far-IR at z<3. In particular, SPICA will have
the unique ability to trace the evolution of the obscured SFRD and BHARD over
cosmic time, from the peak of their activity back to the reionisation epoch
(i.e., 3<z<6-7), where its predecessors had severe limitations. Here we discuss
the potential of both deep and shallow photometric surveys performed with the
SPICA mid-IR instrument (SMI), enabled by the very low level of impact of dust
obscuration in a band centred at 34 micron. These unique unbiased photometric
surveys that SPICA will perform will be followed up by observations both with
the SPICA spectrometers and with other facilities at shorter and longer
wavelengths, with the aim to fully characterise the evolution of AGNs and
star-forming galaxies after re-ionisation.
