Evolutionary status of dense cores in the NGC 1333 IRAS 4 star-forming region

¹ SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands
e-mail: ev.koumpia@gmail.com
² Kapteyn Institute, University of Groningen, Landleven 12, 9747 AD Groningen, The Netherlands
³ Korea Astronomy and Space Science Institute, 776, Daedeok-Daero, Yuseong-gu, 34055 Daejeon, Korea
⁴ National Radio Astronomy Observatory, Charlottesville, VA 22903, USA
⁵ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁶ Jodrell Bank Centre for Astrophysics & UK ALMA Regional Centre Node, School of Physics & Astronomy, The University of Manchester, Manchester, M13 9PL, UK
⁷ Department of Physics & Astronomy and Institute for Space Imaging Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada
⁸ Korea University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, 34113 Daejeon, Korea

Received: 24 December 2015
Accepted: 25 August 2016

Abstract

Context. Protostellar evolution after the formation of the protostar is becoming reasonably well characterized, but the evolution from a prestellar core to a protostar is not well known, although the first hydrostatic core (FHSC) must be a pivotal step.

Aims. NGC 1333 – IRAS 4C is a potentially very young object that we can directly compare with the nearby Class 0 objects IRAS 4A and IRAS 4B. Observational constraints are provided by spectral imaging from the JCMT Spectral Legacy Survey (330−373 GHz). We present integrated intensity and velocity maps of several species, including CO, H₂CO and CH₃OH. CARMA observations provide additional information with which we can distinguish IRAS 4C from other evolutionary stages.

Methods. We present the observational signatures of the velocity of an observed outflow, the degree of CO depletion, the deuterium fractionation of [DCO⁺]/[HCO⁺], and gas kinetic temperatures.

Results. We report differences between the three sources in four aspects: a) the kinetic temperature as probed using the H₂CO lines is much lower toward IRAS 4C than the other two sources; b) the line profiles of the detected species show strong outflow activity toward IRAS 4A and IRAS 4B, but not toward IRAS 4C; c) the HCN/HNC is <1 toward IRAS 4C, which confirms the cold nature of the source; d) the degree of CO depletion and the deuteration are lowest toward the warmest of the sources, IRAS 4B.

Conclusions. IRAS 4C seems to be in a different evolutionary state than the sources IRAS 4A and IRAS 4B. We can probably exclude the FHSC stage becaues of the relatively low L_smm/L_bol (~6%), and we investigate the earliest accretion phase of Class 0 stage and the transition between Class 0 to Class I. Our results do not show a consistent scenario for either case; the main problem is the absence of outflow activity and the cold nature of IRAS 4C. The number of FHSC candidates in Perseus is ~10 times higher than current models predict, which suggests that the lifespan of these objects is ≥10³ yrs, which might be due to an accretion rate lower than 4 × 10^-5 M_⊙/yr.