Seeds of Life in Space (SOLIS).VII. Discovery of a cold dense methanol
  blob toward the L1521F VeLLO system
  The SOLIS (Seeds Of Life In Space) IRAM/NOEMA Large Program aims at studying
a set of crucial complex organic molecules in a sample of sources, with
well-known physical structure, covering the various phases of Solar-type star
formation. One representative object of the transition from the prestellar core
to the protostar phases has been observed toward the Very Low Luminosity Object
(VeLLO) called L1521F. This type of source is important to study to make the
link between prestellar cores and Class 0 sources and also to constrain the
chemical evolution during the process of star formation. Two frequency windows
(81.6-82.6 GHz and 96.65-97.65 GHz) were used to observe the emission from
several complex organics toward the L1521F VeLLO. Only 2 transitions of
methanol (A+, E2) have been detected in the narrow window centered at 96.7 GHz
(with an upper limit on E1) in a very compact emission blob (~7'' corresponding
to ~1000au) toward the NE of the L1521F protostar. The CS 2-1 transition is
also detected within the WideX bandwidth. Consistently, with what has been
found in prestellar cores, the methanol emission appears ~1000au away from the
dust peak. The location of the methanol blob coincides with one of the
filaments previously reported in the literature. The Tex of the gas inferred
from methanol is (10$\pm$2) K, while the H2 gas density (estimated from the
detected CS 2-1 emission and previous CS 5-4 ALMA obs.) is a factor >25 higher
than the density in the surrounding environment (n(H2) >10$^{7}$ cm$^{-3}$).
From its compactness, low excitation temperature and high gas density, we
suggest that the methanol emission detected with NOEMA is either a cold and
dense shock-induced blob, recently formed ($\leq$ few hundred years) by
infalling gas or a cold and dense fragment that may have just been formed as a
result of the intense gas dynamics found within the L1521F VeLLO system.
