Studies of Warm and Diffuse Gas and High Ionization Rate Near the Galactic Center Using Infrared Spectra of H3+ and CO

Oka博士和他的团队通过测量(H3)+和CO对中央分子带的红外吸收来研究银河系中心温暖的弥漫气体的特性。质子化的分子氢(H3)+是含有该分子离子的大区域的密度、温度、电离速率和体积填充因子的示踪剂。它也是在漫射星际介质中难以测量的其他多原子分子的示踪剂。（H3）+的发现和沿着14条视线的观测表明，温暖的弥漫气体（温度约为250 K，密度为每立方厘米100-1000个粒子）表明存在温暖的弥漫成分，而已知的致密分子，热电离和超热等离子体成分则更久。研究人员发现，这些气体的体积填充系数似乎非常高，在银河系中心附近的这些视线中，温暖的扩散气体的电离率比这些区域的预期值高一个数量级。目前的工作利用从斯皮策瞥见（银河遗产红外中层巡天）数据库和CO观测中选择的新背景恒星来研究朝向银河系中心的更多视线。这些数据与新的赫歇尔(H2O)+观测数据以及CO的射电和红外光谱进行了比较，以充分表征银河系中心复杂和动态区域中温暖弥漫气体和其他成分的物理性质。本项目培养1名观测红外天文学和分子天体物理学方向博士后。

Dr. Oka and his team study the properties of warm, diffuse gas in the Galactic center by measuring (H3)+ and CO infrared absorption towards the Central Molecular Zone. Protonated molecular hydrogen, (H3)+, is a tracer of the density, temperature, ionization rate, and volume filling factor of the large regions containing this molecular ion. It is also a tracer for other polyatomic molecules that are difficult to measure in the diffuse interstellar medium. The (H3)+ discovery and observations along 14 sight lines showed that warm diffuse gas (T about 250 K, density of 100-1000 particles per cubic centimeter) indicates the presence of a warm, diffuse component to the longer known components of dense-molecular, hot-ionized, and ultra-hot plasma. The researchers found that the volume filling factor of this gas appears to be very high, and the ionization rate for the warm diffuse gas an order of magnitude higher values for these sight lines near the Galactic Center than expected for these regions. The present work investigates more sight lines towards the Galactic center using new background stars that are selected from the Spitzer GLIMPSE (Galactic Legacy Infrared Mid-Plane Survey Extraordinaire) database and CO observations. The data are compared with new Herschel observations of (H2O)+ and radio and infrared spectra of CO to fully characterize the physical properties of the warm diffuse gas and the other components in the complex and dynamical regions at the Galactic center. This project trains a post-doctoral fellow in observational infrared astronomy and molecular astrophysics.