Filamentary Star Formation: Observing the Evolution toward Flattened
  Envelopes
  Filamentary structures are ubiquitous from large-scale molecular clouds (few
parsecs) to small-scale circumstellar envelopes around Class 0 sources (~1000
AU to ~0.1 pc). In particular, recent observations with the Herschel Space
Observatory emphasize the importance of large-scale filaments (few parsecs) and
star formation. The small-scale flattened envelopes around Class 0 sources are
reminiscent of the large-scale filaments. We propose an observationally derived
scenario for filamentary star formation that describes the evolution of
filaments as part of the process for formation of cores and circumstellar
envelopes. If such a scenario is correct, small-scale filamentary structures
(0.1 pc in length) with higher densities embedded in starless cores should
exist, although to date almost all the interferometers have failed to observe
such structures. We perform synthetic observations of filaments at the
prestellar stage by modeling the known Class 0 flattened envelope in L1157
using both the Combined Array for Research in Millimeter-wave Astronomy (CARMA)
and the Atacama Large Millimeter/Submillimeter Array (ALMA). We show that with
reasonable estimates for the column density through the flattened envelope, the
CARMA D-array at 3mm wavelengths is not able to detect such filamentary
structure, so previous studies would not have detected them. However, the
substructures may be detected with CARMA D+E array at 3 mm and CARMA E array at
1 mm as a result of more appropriate resolution and sensitivity. ALMA is also
capable of detecting the substructures and showing the structures in detail
compared to the CARMA results with its unprecedented sensitivity. Such
detection will confirm the new proposed paradigm of non-spherical star
formation.
