论文标题
沿M 82的主要轴的致密分子气的性质
Properties of dense molecular gas along the major axis of M 82
论文作者
论文摘要
致密气体对于星系进化和恒星形成很重要。光学上薄的密集示踪剂，例如HCN，HCO+等的同位素，对诊断致密分子气的激发条件非常有帮助。然而，由于灵敏度和角度分辨率有限，对光学薄致密的气体示踪剂的先前研究主要集中在整个星系的平均特性上。 M82是附近的原型Starburst Galaxy，为单次望远镜的空间分辨研究提供了独特的案例。使用IRAM 30 m望远镜，我们观察到J = 1-0 H13CN，HC15N，H13CO+，HN13C，HN13C，H15NC和SIO J = 2-1，HC3N J = 10-9，H2CO J = 2-9，H2CO J = 2-1沿M82的主要轴沿五个位置朝着五个位置。 I（HCN）/I（H13CN）和I（HCO+）/I（H13CO+）的强度比显示出沿主要轴的显着空间变化，中央区域的值比磁盘上的值低，表明中部地区的光学深度较高。发现HCO+线的光学深度在所有位置的系统上比HCN线的光学深度高。 futhermore，我们发现14N/15N的比率从中心到外盘的梯度增加。
Dense gas is important for galaxy evolution and star formation. Optically-thin dense-gas tracers, such as isotopologues of HCN, HCO+, etc., are very helpful to diagnose excitation conditions of dense molecular gas. However, previous studies of optically-thin dense-gas tracers were mostly focusing on average properties of galaxies as a whole, due to limited sensitivity and angular resolution. M82, a nearby prototype starburst galaxy, offers a unique case for spatially-resolved studies with single-dish telescopes. With the IRAM 30-m telescope, we observed the J = 1 - 0 transition of H13CN, HC15N, H13CO+, HN13C, H15NC, and SiO J = 2 - 1, HC3N J= 10 - 9, H2CO J = 2 - 1 toward five positions along the major axis of M82. The intensity ratios of I(HCN)/I(H13CN) and I(HCO+)/I(H13CO+) show a significant spatial variation along the major axis, with lower values in the central region than those on the disk, indicating higher optical depths in the central region. The optical depths of HCO+ lines are found to be systematically higher than those of HCN lines at all positions. Futhermore, we find that the 14N/15N ratios have an increasing gradient from the center to the outer disk.
