Sgr A East is the supernova remnant closest to the centre of the Milky Way. Its age has been estimated to be either very young, around 1-2 kyr, or about 10 kyr, and its exact origin remains unclear. We aspire to create a simple model of a supernova explosion that reproduces the shape, size, and location of Sgr A East. Using a simplified hydrodynamical code, we simulated the evolution of a supernova remnant in the medium around the Galactic centre. The latter consists of a nearby massive molecular cloud with which Sgr A East is known to be interacting and a wind from the nuclear star cluster. Our preferred models of the Sgr A East remnant are compatible with an age of around 10 kyr. We also find suitable solutions for older ages, but not for ages younger than 5 kyr. Our simulations predict that the supernova exploded at a distance of about 3.5 pc from the Galactic centre, below the Galactic plane, slightly eastwards from the centre and 3 pc behind it.
We present high-resolution multiwavelength radio continuum images of the region within 150$"$ of Sgr A*, revealing a number of new extended features and stellar sources in this region. First, we detect a continuous 2" east-west ridge of radio emission, linking Sgr A* and a cluster of stars associated with IRS 13N and IRS 13E. The ridge suggests that an outflow of east-west blob-like structures is emerging from Sgr A*. We also find arc-like features within the ridge with morphologies suggestive of photoevaporative protoplanetary disks. We use near-IR fluxes to show that the emission has similar…
A New Perspective on the Radio Active Zone at The Galactic Center - Feedback from Nuclear Activities
基于我们使用Jansky VLA在6 cm处观察到的宽带数据的Sgr A的深度图像，我们提出了银河系中心无线电亮区的新观点。我们进一步展示了X射线炮弹的无线电探测，一个与银河系中心SNR Sgr A东相关的候选中子星。射电图像与钱德拉X射线图像进行了比较，以显示双极X射线叶的射电对应物的详细结构。双极波瓣可能是由Sgr A West内部活动产生的风产生的，它可能是由CND中气体的惯性或Sgr A* 的动量驱动而准直的;极向磁场可能在准直中起重要作用。与NW波瓣相比，SE波瓣的准直度较低，这可能是由于Sgr A东SN可能局部地将磁场重新配置为朝向负银河纬度。与X射线观测结果相一致，估算的最外层射电环的~ $1\times10^4$年时间尺度似乎与推断的Sgr A East SNR的年龄相当。
We study the structure and kinematics of the OH-streamer and the +80 km/s cloud and their interactions with the circumnuclear disk (CND) and with other molecular clouds in the vicinity of the Galactic centre (GC), and we map OH absorption at about 6" resolution at R $\le$ 10 pc from the GC, with about 9 km/s velocity resolution. The VLA was used to map OH line absorption at the 1665 and 1667 MHz lambda doublet main lines towards the Sagittarius A complex. Strong OH absorption was found in the OH-streamer, the southern streamer (SS), the +20, +50, and +80 km/s molecular clouds, the molecular be…
New observations of Sgr A have been carried out with the VLA using the broadband (2 GHz) continuum mode at 5.5 GHz, covering the central 30 pc region of the RBZ at the Galactic center. Using the MS-MFS algorithms in CASA, we have imaged Sgr A with a resolution of 1", achieving an rms 8 $μ$Jy/beam, and a dynamic range 100,000:1.The radio image is compared with X-ray, CN emission-line and Paschen-$α$ images obtained using Chandra, SMA and HST/NICMOS, respectively. We discuss several prominent radio features. The "Sgr A West Wings" extend 5 pc from the NW and SE tips of the ionized "Mini-spiral" …
Being one of the most abundant atomic/molecular species observed in dense molecular gas, atomic carbon ($\mathrm{C}^0$) is a potential good tracer of molecular gas mass in many chemical/physical environments, though the $\mathrm{C^0}$ abundance variation outside the Galactic disk region is yet to be fully known. This paper presents a wide-field 500 GHz [CI] map of the Galactic central molecular zone (CMZ) obtained with the ASTE 10-m telescope. Principal component analysis and non-LTE multi-transition analysis have shown that the [CI] emission predominantly originates from the low-excitation ga…
Early stage massive star formation near the Galactic Center: Sgr C
我们对最近发现的一个高质量恒星形成地点进行了近红外光谱以及1毫米线和连续谱观察，该地点可能位于Sgr C附近的中央分子区。该区域位于与Sgr C相关的大规模演化的HII区域的外围，其特征是一个尺寸约为10”（0.4 pc）的扩展绿色物体，其观测特征表明存在嵌入的大质量原恒星驱动外流。我们的数据证实，早期恒星形成发生在Sgr C HII区域的外围，检测到两个原恒星核心和几个结的H2和Brackett伽马发射以及先前检测到的紧凑的射电源。我们计算出核心的联合质量约为10^3兆太阳，柱密度为1-2 x 10^24 cm-2。我们发现，主分子云含有约10^5兆太阳质量的气体和尘埃，温度和柱密度有利于大质量恒星的形成，但是，在EGO之外没有恒星形成的证据，这表明云主要是静止的。考虑到它的质量、密度和温度，这片云可以与其他著名的非恒星形成云相媲美，比如东CMZ的G0.253。
Propagation of fast-mode magnetohydrodynamic (MHD) compression waves is traced in the Galactic Center with a poloidal magnetic cylinder. MHD waves ejected from the nucleus are reflected and guided along the magnetic field, exhibiting vertically stretched fronts. The radio threads and non-thermal filaments are explained as due to tangential views of the waves driven by sporadic activity in Sgr A$^*$, or by multiple supernovae. In the latter case, the threads could be extremely deformed relics of old SNRs exploded in the nucleus.
We analyze the gas and dust emission in the immediate vicinity of the supermassive black hole Sgr~A* at the Galactic center (GC) with the ESO VLT (Paranal/Chile) instruments SINFONI and VISIR. The SINFONI H+K data cubes show several emission lines with related line map counterparts. From these lines, the Br$γ$ emission is the most prominent one and appears to be shaped as a bar extending along the North-South direction. With VISIR, we find a dusty counterpart to this filamentary emission. In this work, we present evidence that this feature can be most likely connected to the mini-spiral and po…
We have performed the observation of the "Galactic Center Mini-spiral(GCMS)" in H42alpha recombination line as a part of the first large-scale mosaic observation in the Sagittarius A complex using Atacama Millimeter/sub-millimeter Array (ALMA). We revealed the kinematics of the ionized gas streamers of the GCMS. We found that the ionized gas streamers of the Northern Arm(NA) and Eastern Arm(EA) in their outer regions somewhat deviate from the Keplerian orbits which were derived previously from the trajectories in the inner regions. In addition, we found that the streamer corresponding to the B…
A supermassive black hole SgrA* with the mass ~4x10^6 Msun resides at the centre of our galaxy. Building up such a massive black hole within the ~10^10 year lifetime of our galaxy would require a mean accretion rate of ~4x10^-4 Msun/yr. At present, X-ray observations constrain the rate of hot gas accretion at the Bondi radius (10^5 R_Sch = 0.04 pc at 8kpc) to \dot{M}_Bondi ~ 3x10^-6 Msun/yr, and polarization measurements constrain it near the event horizon to \dot{M}_horizon ~ 10^{-8} Msun/yr. A range of models was developed to describe the accretion gas onto an underfed black hole. However, t…
We report on a 95 GHz ($8_0-7_1$ A$^{+}$) methanol (CH$_3$OH) emission survey with the Purple Mountain Observatory Delingha 13.7 m telescope. Eight supernova remnants (SNRs) with angular size $\lesssim$ 10' were observed, but emission was only detected in three SNRs near the Galactic center (Sgr A East, G 0.1-0.1, and G 359.92-0.09). CH$_3$OH emission mainly surrounds the SNRs and can be decomposed into nine spatial peaks with velocity range of eight peaks being (-30, 70) km s$^{-1}$, and the other (70, 120) km s$^{-1}$. They are probably excited by interaction with these SNRs and adjacent mol…
Dust formation in supernova ejecta is currently the leading candidate to explain the large quantities of dust observed in the distant, early Universe. However, it is unclear whether the ejecta-formed dust can survive the hot interior of the supernova remnant (SNR). We present infrared observations of ~0.02 $M_\odot$ of warm (~100 K) dust seen near the center of the ~10,000 yr-old Sgr A East SNR at the Galactic center. Our findings signify the detection of dust within an older SNR that is expanding into a relatively dense surrounding medium ($n_e$ ~ 100 $\mathrm{cm}^{-3}$) and has survived the …
We present results from calculations of the physical conditions necessary for the occurrence of 36.169 ($4_{-1}-3_{0}\, E$), 44.070 ($7_{0}-6_{1}\,A^+$), 84.521 ($5_{-1}-4_{0}\,E$), and 95.169 ($8_{0}-7_{1}\,A^+$) GHz methanol (CH$_3$OH) maser emission lines near supernova remnants (SNRs), using the MOLPOP-CEP program. The calculations show that given a sufficient methanol abundance, methanol maser emission arises over a wide range of densities and temperatures, with optimal conditions at $n\sim 10^4-10^6$ cm$^{-3}$ and $T>60$ K. The 36~GHz and 44~GHz transitions display more significant maser…
