The factors that influence protostellar multiplicity I: Gas temperature, density, and mass in Perseus with Nobeyama

Context. Protostellar multiplicity is common at all stages and mass ranges. However, the factors that determine the multiplicity of
protostellar systems have not been systematically characterized through their molecular gas.
Aims. This work seeks to characterize the physical properties of the Perseus Molecular Cloud at ≥5000 AU scales through mapping
of diagnostic molecular lines.
Methods. Nobeyama 45m Radio Observatory (NRO) on-the-fly maps of HCN, HNC, HCO+ , and N2 H+ (J = 1–0) toward five sub-
regions in Perseus, complemented with single pointing Atacama Pathfinder EXperiment (APEX) observations of HNC (J = 4–3) are
used to derive physical parameters of the dense gas. Both observations have spatial resolutions of ∼18′′ , equivalent to ∼5000 AU
scales at the distance of Perseus. Kinetic gas temperature is derived from the I(HCN)/I(HNC) J ratio, and H2 density is obtained
from the HNC J=4–3/J=1–0 ratio. These parameters are used to obtain the N2 H+ (cold) and HCO+ (warm) gas masses. The inferred
and derived parameters are then compared to source parameters, including protostellar multiplicity, bolometric luminosity and dust
envelope mass.
Results. Inferred mean kinetic gas temperature (I(HCN)/I(HNC) J=1–0 ratio; ranging between 15 and 26 K), and H2 volumetric
density (HNC J=4–3/J=1–0; 10^5 – 10^6 cm^−3 ) do not show correlations with multiplicity in Perseus. The derived gas and dust masses,
1.3 to 16 × 10^−9 M⊙ for the cold gas mass (N2 H+ ), 0.1 to 25 M⊙ for envelope dust masses (850 μm), and 0.8 to 10 × 10^−10 M⊙ for the
warm gas mass (HCO+ ), are correlated to multiplicity and number of protostellar components. The warm gas masses are a factor of
16 lower than the cold gas masses.
Conclusions. This work shows that gas and dust mass is correlated to multiplicity at ∼5000 AU scales in Perseus. Higher order
multiples tend to have higher gas and dust masses in general, while close binaries (separations ≤7′′ ) and single protostars have
similar gas and dust mass distributions. On the other hand, H2 density and kinetic gas temperature do not show any correlation with
multiplicity.