Physical properties and chemical composition of the cores in the California molecular cloud^★

¹ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, PR China,
e-mail: zgyin@nao.cas.cn, wangjj@nao.cas.cn
² University of Chinese Academy of Sciences, Beijing 100049, PR China
³ Ural Federal University, Ekaterinburg, Russia
⁴ Engineering Research Institute “Ventspils International Radio Astronomy Centre” of Ventspils University of Applied Sciences, Inženieru 101, Ventspils 3601, Latvia
⁵ Department of Chemistry, Ludwig Maximilian University, Butenandtstr. 5-13, 81377 München, Germany
⁶ Max Planck Institute for Astronomy, Königstuhl 17, 69117, Heidelberg, Germany
⁷ Niels Bohr International Academy, Niels Bohr Institute, Blegdamsvej 17, 2100 Copenhagen Ø, Denmark
⁸ Korea Astronomy and Space Science Institute, 776 Daedeokdaero, Yuseong-gu, Daejeon 34055, Republic of Korea
⁹ East Asian Observatory, 660 N. A’ohoku Place, Hilo, HI 96720, USA
¹⁰ Institute of Astronomy and Astrophysics, Academia Sinica. 11F of Astronomy-Mathematics Building, AS/NTU No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan
¹¹ Kavli Institute for Astronomy and Astrophysics, Peking University, 5 Yiheyuan Road, Haidian District, Beijing 100871, PR China
¹² European Southern Observatory (ESO) Headquarters, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
¹³ CAS Key Laboratory of FAST, NAOC, Chinese Academy of Sciences, Beijing 100101, PR China
¹⁴ College of Physics, Guizhou University, Guiyang 550025, PR China
¹⁵ Xinjiang Astronomical Observatory, CAS, 150, Science 1-street, Urumqi, Xinjiang 830011, PR China
¹⁶ School of Physics and Astronomy, Sun Yat-Sen University, Zhuhai, 519082, Guangdong, PR China

Received: 12 June 2018
Accepted: 19 October 2018

Abstract

Aims. We aim to reveal the physical properties and chemical composition of the cores in the California molecular cloud (CMC), so as to better understand the initial conditions of star formation.

Methods. We made a high-resolution column density map (18.2′′) with Herschel data, and extracted a complete sample of the cores in the CMC with the fellwalker algorithm. We performed new single-pointing observations of molecular lines near 90 GHz with the IRAM 30m telescope along the main filament of the CMC. In addition, we also performed a numerical modeling of chemical evolution for the cores under the physical conditions.

Results. We extracted 300 cores, of which 33 are protostellar and 267 are starless cores. About 51% (137 of 267) of the starless cores are prestellar cores. Three cores have the potential to evolve into high-mass stars. The prestellar core mass function (CMF) can be well fit by a log-normal form. The high-mass end of the prestellar CMF shows a power-law form with an index α = −0.9 ± 0.1 that is shallower than that of the Galactic field stellar mass function. Combining the mass transformation efficiency (ε) from the prestellar core to the star of 15 ± 1% and the core formation efficiency (CFE) of 5.5%, we suggest an overall star formation efficiency of about 1% in the CMC. In the single-pointing observations with the IRAM 30m telescope, we find that 6 cores show blue-skewed profile, while 4 cores show red-skewed profile. [HCO⁺]/[HNC] and [HCO⁺]/[N₂H⁺] in protostellar cores are higher than those in prestellar cores; this can be used as chemical clocks. The best-fit chemical age of the cores with line observations is ~5 × 10⁴ yr.