论文标题
灰尘在哪里？：NGC 4725 B中微波排放的加深异常
Where's the Dust?: The Deepening Anomaly of Microwave Emission in NGC 4725 B
论文作者
论文摘要
我们提出了新的Atacama大毫米阵列（ALMA）对NGC 4725 B的观测值，这是一个在附近Galaxy NGC 4725的星形磁盘内一个离散的，紧凑的，光学绘制的区域，该磁盘表现出强烈的微波发射（AME）。这些新的ALMA数据包括以92、133、203和221 GHz为中心的连续观测，并伴随着$^{12} $ CO（$ j = 2 \ rightarrow1 $）线的光谱观测。尽管在203 GHz处的检测是边缘的，但在连续体中都检测到NGC 4725 B。虽然在NGC 4725 B的确切位置未检测到分子气体，但附近有分子气（即$ \ lyssim 100 $ PC），以及相关的散射8 $μM的排放。当与现有非常大的阵列连续数据结合使用1.5、3、5.5、9、14、22、33和44 GHz时，频谱最适合AME，同步加速器和免费发射的组合，免费吸收的免费吸收$ \ sim6 $ GHz。鉴于AME的强度，令人惊讶的是，在$ \ lyseSim $ 6 \ arcsec〜空间尺度上，与ALMA干涉数据的敏感性相关的NGC 4725 B相关的毫米灰尘发射。根据最近分子气体复合物和推断的恒星形成速率的特性，NGC 4725 B与非常年轻的（$ \ sim 3-5 $ Myr）一致，大量（$ \ sillsim 10^{5} m _ {\ odot} $）群集，这是经过活跃的集群反馈。但是，缺乏毫米热灰尘发射很难与30 GHz发射的旋转粉尘起源相协调。另一方面，将NGC 4725 B建模为新的背景射电星系也不令人满意。
We present new Atacama Large Millimeter Array (ALMA) observations towards NGC 4725 B, a discrete, compact, optically-faint region within the star-forming disk of the nearby galaxy NGC 4725 that exhibits strong anomalous microwave emission (AME). These new ALMA data include continuum observations centered at 92, 133, 203, and 221 GHz accompanied by spectral observations of the $^{12}$CO ($J=2\rightarrow1$) line. NGC 4725 B is detected in the continuum at all frequencies, although the detection at 203 GHz is marginal. While molecular gas is not detected at the exact location of NGC 4725 B, there is molecular gas in the immediate vicinity (i.e., $\lesssim 100$ pc) along with associated diffuse 8 $μ$m emission. When combined with existing Very Large Array continuum data at 1.5, 3, 5.5, 9, 14, 22, 33, and 44 GHz, the spectrum is best fit by a combination of AME, synchrotron, and free-free emission that is free-free absorbed below $\sim6$ GHz. Given the strength of the AME, there is surprisingly no indication of millimeter dust emission associated with NGC 4725 B on $\lesssim$6\arcsec~spatial scales at the sensitivity of the ALMA interferometric data. Based on the properties of the nearest molecular gas complex and the inferred star formation rate, NGC 4725 B is consistent with being an extremely young ($\sim 3-5$ Myr) massive ($\lesssim 10^{5} M_{\odot}$) cluster that is undergoing active cluster feedback. However, the lack of millimeter thermal dust emission is difficult to reconcile with a spinning dust origin of the 30 GHz emission. On the other hand, modeling NGC 4725 B as a new class of background radio galaxy is also unsatisfactory.
