The fate of a red nugget: In-situ star formation of satellites around a
  massive compact galaxy
  To study the accretion phase for local massive galaxies, we search accreting
satellites around a massive compact galaxy (M_*~3.9x10^10Msun),
spectroscopically confirmed (z_spec-1.9213) in the eXtreme Deep Field, which
has been originally reported in Szomoru et al. We detect 1369 satellite
candidates within the projected virial radius (rvir~300 kpc) of the compact
galaxy in the all-combined ACS image with 5sigma-limiting magnitude of
mACS~30.6 ABmag, which corresponds to ~1.6x10^7M_sun at the redshift. The
photometric redshift measured with 12 multi-band images confirms 34 satellites
out of the candidates. Most of the satellites are found to have the rest-frame
colors consistent with star forming galaxies. We investigate the relation
between stellar mass and star formation rate (the star formation main
sequence), and find the steeper slope at the low-mass end (<10^8M_sun), while
more massive satellites are consistently on the sequence reported in previous
studies. Within the uncertainties of star formation and photometric redshift,
we conjecture possible scenarios for the compact galaxy which evolves to a
local massive galaxy by way of significant size and mass growth. While merging
of the existing total stellar mass of the satellites is not enough to explain
the mass growth predicted by observations and simulations, the contribution by
in-situ star formation in the satellites would compensate the deficit. Provided
that most satellites keep the observed in-situ star formation and then quench
before they accrete by, e.g., environmental quenching, the compact galaxy would
become a massive early-type galaxy consistent with the local size-mass
relation.
