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. We characterize the physical properties of the Perseus molecular cloud at ≥5000 AU scales by mapping the diagnostic molecular lines. Methods. We used Nobeyama 45m Radio Observatory (NRO) on-the-fly maps of HCN, HNC, HCO + , and N 2 H + ( J =1–0) toward five subregions in Perseus, complemented with single-pointing Atacama Pathfinder Experiment (APEX) observations of HNC ( J = 4–3), to derive the physical parameters of the dense gas. The spatial resolutions of both observations were ~18″, which is equivalent to ~5000 AU scales at the distance of Perseus. The kinetic gas temperature was derived from the I (HCN)/ I (HNC) J ratio, and the H 2 density was obtained from the HNC J =4–3/ J =1–0 ratio. These parameters were used to obtain the N 2 H + (cold) and HCO + (warm) gas masses. The inferred and derived parameters were then compared to source the parameters, including protostellar multiplicity, bolometric luminosity, and dust envelope mass. Results. The inferred mean kinetic gas temperature ( I (HCN)/ I (HNC) J =1–0 ratio; ranging between 15 and 26 K), and H 2 volumetric density (HNC J =4–3/ J =1–0; 10 5 −10 6 cm −3 ) are not correlated with multiplicity in Perseus. The derived gas and dust masses, 1.3 to 16 × 10 −9 M ⊙ for the cold-gas mass (N 2 H + ), 0.1 to 25 M ⊙ for the envelope dust masses (850 μm), and 0.8 to 10 × 10 −10 M ⊙ for the warm-gas mass (HCO + ), are correlated to multiplicity and to the number of protostellar components. The warm-gas masses are lower by a factor of 16 than the cold-gas masses. Conclusions. The 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, the H 2 density and kinetic gas temperature are not correlated with multiplicity.