Tracers of Dense Gas in the Outer Galaxy
Tracers of Dense Gas in the Outer Galaxy
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DOI：
10.3847/1538-3881/ac83af
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发表时间：
2022-07
期刊：
影响因子：
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通讯作者：
Sudeshna Patra;N. Evans;Kee-Tae Kim;M. Heyer;J. Kauffmann;J. Jose;Manash R. Samal;S. Das
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文献类型：
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作者：
Sudeshna Patra;N. Evans;Kee-Tae Kim;M. Heyer;J. Kauffmann;J. Jose;Manash R. Samal;S. Das
我们利用Taeduk射电天文台的14米射电望远镜对银河系外（银心距离>9.5 kpc）的7个恒星形成区（12+log[O/H]从8.34到8.69）的HCN和HCO+（J = 1 → 0）谱线进行了测绘。我们比较了这两条分子谱线与其他传统的致密气体示踪剂、尘埃的毫米波连续辐射和由13 CO谱线数据推断的消光阈值（AV ≥ 8 mag）。HCN和HCO+与毫米波辐射的相关性比与消光判据的相关性好。对于所有的云来说，大量的光度来自于低于消光标准和毫米团之外的区域。在A-V ≥ 8等的区域内，HCN的平均光度分数为0.343 ± 0.225;在毫米辐射区域，它为0.478 ± 0.149。通过与Herschel柱密度图的比较，HCN和HCO+在高柱密度区比13 CO更好地追踪致密气体。HCO+是集中比HCN外星系的目标，与内星系样品相比，这表明金属丰度可能会影响致密气体示踪剂的解释。当在整个云上积分时，致密气体质量（M致密）和HCN和HCO+的线光度之间的转换因子与河外研究中使用的因子相当。
We have mapped HCN and HCO+ (J = 1 → 0) line emission toward a sample of seven star-forming regions (with 12+log[O/H] ranging from 8.34 to 8.69) in the outer Milky Way (Galactocentric distance >9.5 kpc), using the 14 m radio telescope of the Taeduk Radio Astronomy Observatory. We compare these two molecular lines with other conventional tracers of dense gas, millimeter-wave continuum emission from dust and extinction thresholds (A V ≥ 8 mag), inferred from the 13CO line data. HCN and HCO+ correlate better with the millimeter emission than with the extinction criterion. A significant amount of luminosity comes from regions below the extinction criterion and outside the millimeter clump for all the clouds. The average fraction of HCN luminosity from within the regions with A V ≥ 8 mag is 0.343 ± 0.225; for the regions of millimeter emission, it is 0.478 ± 0.149. Based on a comparison with column density maps from Herschel, HCN and HCO+ trace dense gas in high column density regions better than does 13CO. HCO+ is less concentrated than HCN for outer Galaxy targets, in contrast with the inner Galaxy sample, suggesting that metallicity may affect the interpretation of tracers of dense gas. The conversion factor between the dense gas mass (M dense) and line luminosities of HCN and HCO+, when integrated over the whole cloud, is comparable to factors used in extragalactic studies.