Free-free and H42a emission from the dusty starburst within NGC 4945 as observed by ALMA
Free-free and H42a emission from the dusty starburst within NGC 4945 as observed by ALMA
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ALMA 观测到 NGC 4945 内尘埃星暴的游离态和 H42a 排放
DOI：
10.1093/mnras/stw1659
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发表时间：
2016
影响因子：
4.8
通讯作者：
Bendo G
中科院分区：
文献类型：
--
作者：
Bendo G
我们展示了 NGC 4945 内中心 30 角秒的 85.69 GHz 连续谱发射和 H42α 线发射的观测结果。两种发射源均源自几乎相同的结构，这些结构可以建模为尺度长度为 ∼2.1 角秒（或 ∼40 pc）的指数圆盘。将这些数据与档案数据相结合进行的光谱能量分布分析表明，85.69 GHz 连续谱发射的 84 ± 10% 来自自由发射。电子温度为 5400 ± 600 K，与银河系中心附近测量到的温度相当。基于 H42α 和 85.69 GHz 自由发射（并使用 3.8 Mpc 距离）的恒星形成率 (SFR) 为 4.35 ± 0.25 M⊙yr−1。这与总红外通量的恒星形成率以及之前基于复合线发射的测量结果一致，并且在无线电数据得出的恒星形成率的约 2 倍范围内。斯皮策太空望远镜 24 μm 数据和广域红外勘测探测器 22 μm 数据产生的恒星形成率比阿塔卡马大型毫米/亚毫米阵列测量值低约 10 倍，很可能是因为中红外数据受到相当于 AV= 150 的尘埃衰减的强烈影响。这些结果表明，对于尘埃密集的环核星暴，基于中红外发射的恒星形成率可能非常不准确。
We present observations of the 85.69 GHz continuum emission and H42α line emission from the central 30 arcsec within NGC 4945. Both sources of emission originate from nearly identical structures that can be modelled as exponential discs with scalelengths of ∼2.1 arcsec (or ∼40 pc). An analysis of the spectral energy distribution based on combining these data with archival data imply that 84 ± 10 per cent of the 85.69 GHz continuum emission originates from free–free emission. The electron temperature is 5400 ± 600 K, which is comparable to what has been measured near the centre of the Milky Way Galaxy. The star formation rate (SFR) based on the H42α and 85.69 GHz free–free emission (and using a distance of 3.8 Mpc) is 4.35 ± 0.25 M⊙yr−1. This is consistent with the SFR from the total infrared flux and with previous measurements based on recombination line emission, and it is within a factor of ∼2 of SFRs derived from radio data. TheSpitzer Space Telescope24 μm data andWide-field Infrared Survey Explorer22 μm data yield SFRs ∼10× lower than the Atacama Large Millimeter/submillimeter Array measurements, most likely because the mid-infrared data are strongly affected by dust attenuation equivalent toAV= 150. These results indicate that SFRs based on mid-infrared emission may be highly inaccurate for dusty, compact circumnuclear starbursts.