N₂H⁺(1–0) survey of massive molecular cloud cores

¹ Institute of Applied Physics of the Russian Academy of Sciences, Ulyanova 46, 603950 Nizhny Novgorod, Russia
² Nizhny Novgorod University, Gagarin Av. 23, 603950 Nizhny Novgorod, Russia
³ Helsinki University Observatory, Tähtitorninmäki, PO Box 14, 00014 University of Helsinki, Finland
⁴ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁵ Onsala Space Observatory, 43992 Onsala, Sweden
⁶ Harvard-Smithsonian Center of Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

Corresponding author: L. Pirogov, pirogov@appl.sci-nnov.ru

Received: 5 February 2003
Accepted: 18 April 2003

Abstract

We present the results of N₂H⁺(1–0) observations of 35 dense molecular cloud cores from the northern and southern hemispheres where massive stars and star clusters are formed. Line emission has been detected in 33 sources, for 28 sources detailed maps have been obtained. Peak N₂H⁺ column densities lie in the range:  cm^-2. Intensity ratios of (01–12) to (23–12) hyperfine components are slightly higher than the LTE value. The optical depth of (23–12) component toward peak intensity positions of 10 sources is ~. In many cases the cores have elongated or more complex structures with several emission peaks. In total, 47 clumps have been revealed in 26 sources. Their sizes lie in the range 0.3–2.1 pc, the range of virial masses is ~. Mean N₂H⁺ abundance for 36 clumps is . Integrated intensity maps with axial ratios <2 have been fitted with a power-law radial distribution ~ convolved with the telescope beam. Mean power-law index for 25 clumps is close to 1.3. For reduced maps where positions of low intensity are rejected mean power-law index is close to unity corresponding to the ~ r^-2 density profile provided N₂H⁺ excitation conditions do not vary inside these regions. In those cases where we have relatively extensive and high quality maps, line widths of the cores either decrease or stay constant with distance from the center, implying an enhanced dynamical activity in the center. There is a correlation between total velocity gradient direction and elongation angle of the cores. However, the ratio of rotational to gravitational energy is too low (–) for rotation to play a significant role in the dynamics of the cores. A correlation between mean line widths and sizes of clumps has been found. A comparison with physical parameters of low-mass cores is given.