CO observations towards a sample of nearby galaxies

作     者：Fa-Cheng Li Yuan-Wei Wu Ye Xu 

作者机构：Purple Mountain Observatory & Key Laboratory for Radio Astronomy Chinese Academy of Sciences University of Chinese Academy of Sciences 

出 版 物：《Research in Astronomy and Astrophysics》 (天文和天体物理学研究（英文版）)

年 卷 期：2015年第15卷第6期

页      面：785-801页

核心收录：

学科分类：07[理学] 070401[理学-天体物理] 0704[理学-天文学] 

主　　题：galaxies: ISM -- molecules galaxies -- millimeter lines ISM -- star formation ISM 

摘      要：We have simultaneously observed 12CO, laCO and clSo （J = 1 - 0） rotational transitions in the centers of a sample of 58 nearby spiral galaxies using the 13.7-m millimeter-wave telescope administered by Purple Mountain Observatory. Forty-two galaxies were detected in 13CO emission, but there was a null detection for C180 emission with a cr upper limit of 2 mK. The central beam ratios, R, of 12CO and 13CO range mostly from 5 to 13, with an average value of 8.1 ±4.2, which is slightly lower than previous estimates for normal galaxies. Clear correlations are found between ^12CO and ^13CO luminosities. An average X factor of 1.44± 0.84 × 10^20 cm^-2 （K km s-l）-1 is slightly lower than that in the Milky Way.