The formation of active protoclusters in the Aquila Rift: A millimeter
  continuum view
  Abridged -- We present an analysis of the Aquila Rift complex which addresses
the questions of the star formation rate (SFR), star formation efficiency (SFE)
and typical lifetime of the Class 0 protostellar phase in two nearby
cluster-forming clumps: the Serpens South and W40 protoclusters. We carried out
a 1.2 mm dust continuum mapping of the Aquila Rift complex with the MAMBO
bolometer array on the IRAM 30m telescope. We perform a systematic source
extraction in our millimeter continuum map. Based on complementary data from
the Herschel Gould Belt survey and Spitzer maps, we characterize the SEDs of
the 77 mm continuum sources detected with MAMBO and estimate their evolutionary
stages. Taking advantage of the comprehensive dataset available for the Serpens
South region, spanning wavelengths from 2 microns to 1.2 mm, we estimate the
numbers of young stellar objects (YSOs) at different evolutionary stages and
find a ratio of Class 0 to Class I protostars N(0)/N(I)=0.19-0.27. This low
ratio supports a scenario of relatively fast accretion at the beginning of the
protostellar phase, and leads to a Class 0 lifetime of ~4-9x10^{4} yr. We also
show that both the Serpens South and W40 protoclusters are characterized by
large fractions of protostars and high SFRs ~20-50 Msun.Myr^{-1}pc^{-2}, in
agreement with the idea that these two nearby clumps are active sites of
clustered star formation currently undergoing bursts of star formation, and
have the potential ability to form bound star clusters. While the formation of
these two protoclusters is likely to have been initiated in a very different
manner, the resulting protostellar populations are observed to be very similar.
This suggests that after the onset of gravitational collapse, the detailed
manner in which the collapse has been initiated does not affect much the
ability of a clump to form stars.
