论文标题
解决附近宇宙中的尘埃与金属比和二$ _2 $转换因子
Resolving the Dust-to-Metals Ratio and CO-to-H$_2$ Conversion Factor in the Nearby Universe
论文作者
论文摘要
我们在五个附近星系中以〜2 kpc的分辨率(IC342,M31,M33,M33,M101和NGC628)调查了尘埃与金属比(D/M)(D/M)和局部星际介质环境之间的关系。具有破碎的幂律发射率的改良黑体模型用于对赫歇尔观察到的尘埃发射从100到500 UM进行建模。我们利用尽可能在HII区域的极光线测量的金属梯度。档案和新的CO旋转线和HI 21厘米地图均采用用于计算气体表面密度,包括来自IRAM和VLA的IC342的新宽场CO和HI地图。我们尝试了几种Co-to-H $ _2 $转换因子的处方,并比较所得的D/M金属性和D/M密度相关性,这两种相关性预计在耗尽研究中都是不负的。 D/M对转换因子的选择敏感。基于金属性的转化因子处方仅在IC342中心产生过多的分子气体,以获得预期的相关性。在测试的处方中,产生预期相关性的处方取决于金属性和表面密度。派生的D/m的1- $σ$范围跨度为0.40-0.58。与化学演化模型相比,我们的测量结果表明,尘埃生长时间尺度比尘埃破坏时间尺度短得多。测得的D/M与源自红外灰尘发射的星系集成研究中的D/M一致。同时,测得的D/M系统地高于从吸收中得出的D/M,这可能表明两种方法之间的系统偏移。
We investigate the relationship between the dust-to-metals ratio (D/M) and the local interstellar medium environment at ~2 kpc resolution in five nearby galaxies: IC342, M31, M33, M101, and NGC628. A modified blackbody model with a broken power-law emissivity is used to model the dust emission from 100 to 500 um observed by Herschel. We utilize the metallicity gradient derived from auroral line measurements in HII regions whenever possible. Both archival and new CO rotational line and HI 21 cm maps are adopted to calculate gas surface density, including new wide field CO and HI maps for IC342 from IRAM and the VLA, respectively. We experiment with several prescriptions of CO-to-H$_2$ conversion factor, and compare the resulting D/M-metallicity and D/M-density correlations, both of which are expected to be non-negative from depletion studies. The D/M is sensitive to the choice of the conversion factor. The conversion factor prescriptions based on metallicity only yield too much molecular gas in the center of IC342 to obtain the expected correlations. Among the prescriptions tested, the one that yields the expected correlations depends on both metallicity and surface density. The 1-$σ$ range of the derived D/M spans 0.40-0.58. Compared to chemical evolution models, our measurements suggest that the dust growth time scale is much shorter than the dust destruction time scale. The measured D/M is consistent with D/M in galaxy-integrated studies derived from infrared dust emission. Meanwhile, the measured D/M is systematically higher than the D/M derived from absorption, which likely indicates a systematic offset between the two methods.