与著名的50 km/s分子云相关的一组四个紧凑的HII区域是离银河系动力中心最近的正在进行的恒星形成的地点，投影距离约为6 pc。我们提出了一个电离气体的研究的基础上[NeII]（12.8微米）线，以及多频无线电连续，HST Pa阿尔法和斯皮策IRAC观测的最紧凑的成员的HII组，Sgr A东HII D。在6厘米处的射电连续谱图像显示，这个源分裂成两个同样明亮的电离特征，D1和D2。D源的SED与它是由一颗质量为25 \pm 3太阳质量，光度为8 \pm 3 x 10 ^4太阳光度的恒星产生的一致。推断的质量，有效温度的紫外光源和电离率是兼容的年轻的O 9-B 0星。被电离的特征D1和D2被认为是由吸积盘准直的UV辐射电离的。我们认为，中心大质量恒星在3 × 10 ^4年的时间尺度上光蒸发其拱星盘，产生的质量通量约为3 × 10 ^{-5}太阳质量/年，并产生在非均匀介质中膨胀的D1和D2电离物质。电离气体的运动学，跟踪的[Ne II]发射，是很难解释的，但它可以解释的双极射流与周围的气体，以及什么似乎是一个锥形壁的低速气体的相互作用。其他的HII区域，Sgr A East A-C，其形态和运动学更类似于其他紧凑的HII区域中的彗星流，其中气体沿着由恒星风与分子云相互作用形成的抛物面移动。
英文摘要：
A group of four compact HII regions associated with the well-known 50 km/s molecular cloud is the closest site of on-going star formation to the dynamical center of the Galaxy, at a projected distance of ~6 pc. We present a study of ionized gas based on the [NeII] (12.8 micron) line, as well as multi-frequency radio continuum, HST Pa alpha and Spitzer IRAC observations of the most compact member of the HII group, Sgr A East HII D. The radio continuum image at 6cm shows that this source breaks up into two equally bright ionized features, D1 and D2. The SED of the D source is consistent with it being due to a 25\pm3 solar mass, star with a luminosity of 8\pm3x10^4 solar luminosity. The inferred mass, effective temperature of the UV source and the ionization rate are compatible with a young O9-B0 star. The ionized features D1 and D2 are considered to be ionized by UV radiation collimated by an accretion disk. We consider that the central massive star photoevaporates its circumstellar disk on a timescale of 3x10^4 years giving a mass flux ~3x10^{-5} solar mass per yr and producing the ionized material in D1 and D2 expanding in an inhomogeneous medium. The ionized gas kinematics, as traced by the [Ne II] emission, is difficult to interpret, but it could be explained by the interaction of a bipolar jet with surrounding gas along with what appears to to be a conical wall of lower velocity gas. The other HII regions, Sgr A East A-C, have morphologies and kinematics that more closely resemble cometary flows seen in other compact HII regions, where gas moves along a paraboloidal surface formed by the interaction of a stellar wind with a molecular cloud.
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. O…
Sgr E is a massive star formation complex found toward the Galactic center that consists of numerous discrete, compact HII regions. It is located at the intersection between the Central Molecular Zone (CMZ) and the far dust lane of the Galactic bar, similar to "hot spots" seen in external galaxies. Compared with other Galactic star formation complexes, the Sgr E complex is unusual because its HII regions all have similar radio luminosities and angular extents, and they are deficient in ~10micron emission from their photodissociation regions (PDRs). Our Green Bank Telescope (GBT) radio recombin…
This is the fourth paper exploring the infrared properties of giant HII regions with the FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA). Our survey utilizes the census of 56 Milky Way giant HII regions identified by Conti & Crowther (2004), and in this paper we present the 20 and 37 micron imaging data we have obtained from SOFIA for sources Sgr D and W42. Based upon the SOFIA data and other multi-wavelength data, we derive and discuss the detailed physical properties of the individual compact sources and sub-regions as well as the large scale properties of …
We present a study of diffuse extended ionised gas toward three clouds located in the Galactic Centre (GC). One line of sight (LOS) is toward the 20 km s$^{-1}$ cloud (LOS$-$0.11) in the Sgr A region, another LOS is toward the 50 km s$^{-1}$ cloud (LOS$-$0.02), also in Sgr A, while the third is toward the Sgr B2 cloud (LOS+0.693). The emission from the ionised gas is detected from H$nα$ and H$mβ$ radio recombination lines (RRLs). He$nα$ and He$mβ$ RRL emission is detected with the same $n$ and $m$ as those from the hydrogen RRLs only toward LOS+0.693. RRLs probe gas with positive and negative …
Until recently, the strong interstellar scattering observed towards the Galactic center (GC) black hole, Sgr A*, was thought to come from dense gas within the GC region. The pulse broadening towards the transient magnetar SGR J1745-2900 near Sgr A* has shown that the source of the scattering is instead located much closer to Earth, possibly in a nearby spiral arm. We show that a single HII region along the line of sight, 1.5-4.8 kpc away from Earth with density $n_e$ of a few 100 cm$^{-3}$ and radius R = 1.8-3.2 pc can explain the observed angular broadening of Sgr A*. Clouds closer to the GC …
The giant molecular cloud Sagittarius B2 (hereafter SgrB2) is the most massive region with ongoing high-mass star formation in the Galaxy. Two ultra-compact HII (UCHII) regions were identified in SgrB2's central hot cores, SgrB2(M) and SgrB2(N). Our aim is to characterize the properties of the HII regions in the entire SgrB2 cloud. Comparing the HII regions and the dust cores, we aim to depict the evolutionary stages of different parts of SgrB2. We use the Very Large Array in its A, CnB, and D configurations, and in the frequency band C (~6 GHz) to observe the whole SgrB2 complex. Using ancill…
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。
Using data from the Green Bank Telescope, we analyze the radio continuum (free-free) and radio recombination line (RRL) emission of the compact HII region NGC 7538 (Sharpless 158). We detect extended radio continuum and hydrogen RRL emission beyond the photodissociation region (PDR) toward the north and east, but a sharp decrease in emission toward the south and west. This indicates that a non-uniform PDR morphology is affecting the amount of radiation "leaking" through the PDR. The strongest carbon RRL emission is found in the western PDR that appears to be dense. We compute a leaking fractio…
The lines of HOC$^+$, HCO and CO$^+$ are considered good tracers of photon-dominated regions (PDRs) and X-ray dominated regions. We study these tracers towards regions of the Sgr B2 cloud selected to be affected by different heating mechanisms. We find the lowest values of the column density ratios of HCO$^+$ versus HOC$^+$, HCO and CO$^+$ in dense HII gas, where UV photons dominate the heating and chemistry of gas. HOC$^+$, HCO and CO$^+$ abundances and the above ratios are compared with those of chemical modeling, finding that high temperature chemistry, a cosmic-ray ionization rate of 10$^{…
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。
Physical conditions in star forming regions around S235
根据氨谱线观测资料，导出了Sh 2 -235周围恒星形成区的气体密度和温度。这些信息被用来评估形成的情景，并确定年轻的嵌入式集群S235 East 1，S235 East 2和S235 Central的演化阶段。我们还估计了嵌入星团中的气体质量及其与恒星质量的比值。S235 East 1似乎比S235 East 2和S235 Central进化得更少。在S235 East 1中，分子气体质量超过了其他星系团。此外，这个星团比其他两个更嵌入母气云中。与理论模型的比较表明，这三个团簇的形成可能是由Sh 2 -235 HII区（以下简称S235）的膨胀通过收集和塌陷过程刺激的，只要周围气体的密度超过$3\cdot10^3$ cm $^{-3}$，或者通过预先存在的团簇的塌陷。S235的膨胀不可能是S235南部A-B区域恒星形成的原因。然而，这一区域的大质量恒星的形成可能是由大规模的超新星冲击触发的。因此，在所研究的区域中，触发的恒星形成可能有三种，即收集和崩溃和崩溃的预先存在的团块，无论是由当地的HII区域的扩张，并触发外部大规模的冲击。我们认为，C235 A HII区域扩展成一个高度不均匀的介质，密度增加。它太年轻了，无法通过收集和坍缩过程在其附近引发恒星形成。在S235 A-B区域内存在年龄分布。S235 A-B区域的大质量恒星比同一区域的低质量恒星年轻得多。这是根据对它们的年龄和相…
The giant molecular cloud Sagittarius B2 (hereafter SgrB2) is the most massive region with ongoing high-mass star formation in the Galaxy. In the southern region of the 40-pc large envelope of SgrB2, we encounter the SgrB2(DS) region which hosts more than 60 high-mass protostellar cores distributed in an arc shape around an extended HII region. We use the Very Large Array in its CnB and D configurations, and in the frequency bands C (4--8 GHz) and X (8--12 GHz) to observe the whole SgrB2 complex. Continuum and radio recombination line maps are obtained. We detect radio continuum emission in Sg…
Electron temperature and emission measure of HII regions in the central molecular zone (CMZ) from H40 αrecombination line and continuum emissions by ALMA CMZ Exploration Survey - ACES -
Institute of Astronomy, The University of Tokyo（东京大学天文学研究所）；Astrophysics Research Institute, Liverpool John Moores University（利物浦约翰摩尔斯大学天体物理研究所）；CCosmic Origins Of Life (COOL)（宇宙生命起源中心（COOL））；UK ALMA Regional Centre Node, Jodrell Bank Centre for Astrophysics, Oxford Road, The University of Manchester（曼彻斯特大学约德尔银行天体物理学中心英国ALMA区域中心节点）；Department of Astronomy, University of Florida（佛罗里达大学天文学系）；Max Planck Institute for Astronomy（马克斯·普朗克天体物理学研究所）；Center for Astrophysics and Space Astronomy（科罗拉多大学博尔德分校天体物理学与空间天文中心；天体物理与行星科学系）；Department of Astrophysical and Planetary Sciences；University of Colorado, Boulder
We report SOFIA-upGREAT spectroscopic imaging of the [C II] 158um spectral line, as well as a number of [O I] 63um spectra, across a 67x45 pc field toward the Sgr B region in our Galactic center. The fully-sampled and velocity-resolved [C II] images have 0.55 pc spatial and 1 km/s velocity resolutions. We find that Sgr B extends as a coherent structure spanning some 34 pc along the Galactic plane. Bright [C II] emission encompasses Sgr B1 (G0.5-0.0), the G0.6-0.0 HII region, and passes behind and beyond the luminous star forming cores toward Sgr B2 (G0.7-0.0). Sgr B is a major contributor to t…
The distribution of N/O abundance ratios calculated by the detailed modelling of different galaxy spectra at z<4 is investigated. Supernova (SN) and long gamma-ray-burst (LGRB) host galaxies cover different redshift domains. N/O in SN hosts increases due to secondary N production towards low z (0.01) accompanying the growing trend of active galaxies (AGN, LINER). N/O in LGRB hosts decreases rapidly between z>1 and z ~0.1 following the N/H trend and reach the characteristic N/O ratios calculated for the HII regions in local and nearby galaxies. The few short period GRB (SGRB) hosts included in …
We present radio continuum observations of the high-mass young stellar object (HMYSO) G345.4938+01.4677 made using the Australia Telescope Compact Array (ATCA) at 5, 9, 17, and 19 GHz. These observations provide definite evidence that the outer and inner pairs of radio lobes consist of shock ionized material being excited by an underlying collimated and fast protostellar jet emanating from a hypercompact HII region. By comparing with images taken 6 yr earlier at 5 and 9 GHz using the same telescope, we assess the proper motions of the radio sources. The outer West and East lobes exhibit proper…
The Sagittarius C Complex in the Mid-Infrared with SOFIA/FORCAST
Kavli Institute for Particle Astrophysics & Cosmology (KIPAC) and Department of Physics at Stanford University（斯坦福大学粒子天体物理与宇宙学 Kavli 研究所和物理系）；Kavli Institute for Cosmological Physics, The University of Chicago（芝加哥大学宇宙物理 Kavli 研究所）；Department of Physics, The University of Chicago（芝加哥大学物理系）；NSF-Simons AI Institute for the Sky (SkAI)（NSF-Simons 天空人工智能研究所）；Department of Physics & Astronomy, UCLA（加州大学洛杉矶分校物理与天文学系）；Arkansas Tech University（阿肯色理工大学）；SETI Institute（搜寻地外文明研究所）
本研究利用 SOFIA/FORCAST 数据对 Sgr C 复合体的中红外观测展开分析，明确其尘埃特性，推测密度脊中相对论电子的来源，发现 H II 区存在未识别大质量恒星，并分析了相邻区域。
Reconciling 3D Models for the Central 10 parsecs of the Milky Way
University of Kansas（堪萨斯大学）；National Radio Astronomy Observatory（国家射电天文台）；National Sun Yat-Sen University（国立中山大学）；Center of Astronomy and Gravitation, National Taiwan Normal University（国立台湾师范大学天体物理与引力研究中心）；University of Connecticut（康涅狄格大学）；University of Florida（佛罗里达大学）；Università dell’Insubria（因斯布鲁克大学）；Astrophysics Research Institute, Liverpool John Moores University（利物浦约翰摩尔斯大学天体物理研究所）；European Southern Observatory (ESO)（欧洲南方天文台）；Universität Heidelberg（海德堡大学）
We present observations of the H-alpha, H-beta, [SII] 6716, 6731 and [NII] 6583 emission lines in the galactic HII region Sh2-235 with the Mapper of Narrow Galaxy Lines (MaNGaL), a tunable filter at the 1-m telescope of Special Astrophysical Observatory of the Russian Academy of Sciences. We show that the HII region is obscured by neutral material with AV = 2-4 mag. The area with the highest AV is situated to the south-west from the ionizing star and coincides with a maximum detected electron density of >=300 cm(-3). The combination of these results with archive AKARI far-infrared data allows …
Messier 8 (M8), one of the brightest HII regions in our Galaxy, is associated with two prominent massive star-forming regions: M8-Main, the particularly bright part of the large scale HII region (mainly) ionised by the stellar system Herschel 36 (Her 36) and M8 East (M8 E), which is mainly powered by a deeply embedded young stellar object (YSO), a bright infrared (IR) source, M8E-IR. We aim to study the interaction of the massive star-forming region M8 E with its surroundings and to compare the star-forming environments of M8-Main and M8 E. We used the IRAM 30 m telescope to perform an imaging…
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…
We present SiO J=2-1 maps of the Sgr B2 molecular cloud, which show shocked gas with a turbulent substructure comprising at least three cavities at velocities of [10,40] km s$^{-1}$ and an arc at velocities of [-20,10] km s$^{-1}$. The spatial anti-correlation of shocked gas at low and high velocities, and the presence of bridging features in position-velocity diagrams suggest that these structures formed in a cloud-cloud collision. Some of the known compact HII regions spatially overlap with sites of strong SiO emission at velocities of [40,85] km s$^{-1}$, and are between or along the edges …
Sh2-48 is a Galactic HII region located at 3.8 kpc with an O9.5-type star identified at its center. As a part of the FOREST Unbiased Galactic plane Imaging survey using the Nobeyama 45-m telescope (FUGIN) project, we obtained the CO J=1-0 dataset for a large area of Sh2-48 at a spatial resolution of 21"(~0.4 pc), which we used to find a molecular cloud with a total molecular mass of ~3.8x10^4 Mo associated with Sh2-48. The molecular cloud has a systematic velocity shift within a velocity range ~42-47 km/s . On the lower velocity side the CO emission spatially corresponds with the bright 8 μm f…
We present the results of a closure phase analysis of 3 mm very long baseline interferometry (VLBI) measurements performed on Sagittarius A* (Sgr A*). We have analyzed observations made in May 2015 using the Very Long Baseline Array, the Robert C. Byrd Green Bank Telescope and the Large Millimeter Telescope Alfonso Serrano and obtained non-zero closure phase measurements on several station triangles - indicative of a non-point-symmetric source structure. The data are fitted with an asymmetric source structure model in Sgr A*, represented by a simple two-component model, which favours a fainter…
We report the discovery of the first 14NH3 (2,2) maser, seen in the Sgr B2 Main star forming region near the center of the Milky Way, using data from the Very Large Array radio telescope. The maser is seen in both lower resolution (3" or ~0.1 pc) data from 2012 and higher resolution (0''.1 or ~1000 AU) data from 2018. In the higher resolution data ammonia (2,2) maser emission is detected toward 5 independent spots. The maser spots are not spatially or kinematically coincident with any other masers in this region, or with the peaks of the radio continuum emission from the numerous ultracompact …
We use VLBA+VLA observations to measure the sizes of the scatter-broadened images of 6 of the most heavily scattered known pulsars: 3 within the Galactic Centre (GC) and 3 elsewhere in the inner Galactic plane. By combining the measured sizes with temporal pulse broadening data from the literature and using the thin-screen approximation, we locate the scattering medium along the line of sight to these 6 pulsars. At least two scattering screens are needed to explain the observations of the GC sample. We show that the screen inferred by previous observations of SGR J1745-2900 and Sgr A*, which m…
We present new [Ne II] (12.8 micron) IRTF/TEXES observations of the Galactic Center HII regions H1 and H2, which are at a projected distance of ~11 pc from the center of the Galaxy. The new observations allow to map the radial velocity distributions of ionized gas. The high spectroscopic resolution (~4 km/s) helps us to disentangle different velocity components and enables us to resolve previous ambiguity regarding the nature of these sources. The spatial distributions of the intensity and radial velocity of the [Ne II] line are mapped. In H1, the intensity distributions of the Paschen-α(1.87 …
We report on the discovery of linear filaments observed in CO(1-0) emission for a $\sim2'$ field of view toward the Sgr E star forming region centered at (l,b)=(358.720$^\circ$, 0.011$^\circ$). The Sgr E region is thought to be at the turbulent intersection of the ''far dust lane'' associated with the Galactic bar and the Central Molecular Zone (CMZ). This region is subject to strong accelerations which are generally thought to inhibit star formation, yet Sgr E contains a large number of HII regions. We present $^{12}$CO(1-0), $^{13}$CO(1-0), and C$^{18}$O(1-0) spectral line observations from …
Interstellar graphene could be present in the interstellar medium (ISM), resulting from the photochemical processing of polycyclic aromatic hydrocarbon (PAH) molecules and/or collisional fragmentation of graphitic particles. Indeed, by comparing the observed ultraviolet (UV) extinction and infrared (IR) emission of the diffuse ISM with that predicted for graphene, as much as $\sim$ 2% of the total interstellar carbon could have been locked up in graphene without violating the observational constraints. While the possible detection of planar C$_{24}$, a small piece of a graphene sheet, has been…
We present the results of NH3 (1,1), (2,2) and (3,3) and H2O maser simultaneous mapping observations toward the high-mass star-forming region W33 with the Nobeyama 45-m radio telescope. W33 has six dust clumps and one of which, W33 Main, is associated with a compact HII region. To investigate star-forming feedback activity on its surroundings, the spatial distribution of the physical parameters was established. The distribution of the rotational temperature shows a systematic change from west to east in our observed region. The high-temperature region obtained in the region near W33 Main is co…
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…
In this paper we simultaneously fit the orbits and line-of-sight velocities of the ionized gas around the supermassive black hole, Sagittarius A$^{\ast}$ (Sgr A$^{\ast}$), at the center of the Milky Way. The data we use are taken with the K-band Multi Object Spectrograph (KMOS), presented in Feldmeier-Krause et al. (2015) and cover the central $\sim$ 2 pc of the Milky Way. From the brightest gas emission line in the K-band, the Br$γ$ line, we derive the spatial distribution and line-of-sight velocities of the gas in the minispiral. Using the flux distribution and the line-of-sight velocity inf…
