Observations of two H$_2$CO ($3_{03}-2_{02}$ and $3_{21}-2_{20}$) lines and continuum emission at 1.3 mm towards Sgr B2(N) and Sgr B2(M) have been carried out with the SMA. The mosaic maps of Sgr B2(N) and Sgr B2(M) in both continuum and lines show a complex distribution of dust and molecular gas in both clumps and filaments surrounding the compact star formation cores. We have observed a decelerating outflow originated from the Sgr B2(M) core, showing that both the red-shifted and blue-shifted outflow components have a common terminal velocity. This terminal velocity is 58$\pm$2 km s$^{-1}$. It provides an excellent method in determination of the systematic velocity of the molecular cloud. The SMA observations have also shown that a large fraction of absorption against the two continuum cores is red-shifted with respect to the systematic velocities of Sgr B2(N) and Sgr B2(M), respectively, suggesting that the majority of the dense molecular gas is flowing into the two major cores where massive stars have been formed. We have solved the radiative transfer in a multi-level system with LVG approximation. The observed H$_2$CO line intensities and their ratios can be adequately fitted with this model for the most of the gas components. However, the line intensities between the higher energy level transition H$_2$CO ($3_{21}-2_{20}$) and the lower energy level transition H$_2$CO ($3_{03}-2_{02}$) is reversed in the red-shifted outflow region of Sgr B2(M), suggesting the presence of inversion in population between the ground levels in the two K ladders (K$_{-1}$= 0 and 2). The possibility of weak maser processes for the H$_2$CO emission in Sgr B2(M) is discussed.
Observations of H$_{2}$CO lines and continuum at 1.3 mm towards Sgr B2(N) and Sgr B2(M) cores were carried out with the SMA. We imaged H$_{2}$CO line absorption against the continuum cores and the surrounding line emission clumps. The results show that the majority of the dense gas is falling into the major cores where massive stars have been formed. The filaments and clumps of the continuum and gas are detected outside of Sgr B2(N) and Sgr B2(M) cores. Both the spectra and moment analysis show the presence of outflows from Sgr B2(M) cores. The H$_{2}$CO gas in the red-shifted outflow of Sgr B…
We present maps of seven sources selected from Klaassen & Wilson (2007a) in SiO (J=8-7) and HCO$^+$ and H$^{13}$CO$^+$ (J=4-3) which were obtained using HARP-B on the James Clerk Maxwell Telescope. We find that four out of our seven sources have infall signatures based on their HCO$^+$ emission profiles. From our maps, we have determined the extent of both the outflowing and infalling regions towards these sources, and constrained the amount of infalling and outflowing mass as well as the mass infall rate for each massive star forming region. From our SiO observations, we estimate the source l…
Low angular momentum accretion-outflow model of flares from Sgr A$^*$
我们采用一个低角动量吸积外流方案来模拟从Sgr A $^*$中心区域发出的耀斑。在Sgr A $^*$中央SMBH上吸积物质的主要施主被认为是WR星ISR 13 E3。我们分析计算的比能量和角动量密度的恒星风起源于ISR 13 E3和研究的动力学风非常接近的中央SMBH的Sgr A $^*$。我们表明，在通往银河系中心的路上，这种风喂吸积可能会遇到站立的冲击，这种冲击驱动器流出的SMBH附近。计算了这种外流的物质含量，并认为这种外流是银河系中心耀斑产生的原因。然后，我们自洽地计算光度${\cal L}_j$和持续时间尺度$τ$的耀斑，作为一个函数的基本吸积参数。我们对${\cal L}_j$和$τ$的理论计算与观测结果符合得很好。
We present single pointing observations of SiO, HCO$^+$ and H$^{13}$CO$^+$ from the James Clerk Maxwell Telescope towards 23 massive star forming regions previously known to contain molecular outflows and ultracompact HII regions. We detected SiO towards 14 sources and suggest that the non-detections in the other nine sources could be due to those outflows being older and without ongoing shocks to replenish the SiO. We serendipitously detected SO$_2$ towards 17 sources in the same tuning as HCO$^+$. We detected HCO$^+$ towards all sources, and suggest that it is tracing infall in nine cases. F…
The formation of the massive young stars surrounding SgrA* is still an open question. In this paper, we simulate the infall of an isothermal, turbulent molecular cloud towards the Galactic Centre (GC). As it spirals towards the GC, the molecular cloud forms a small and dense disc around SgrA*. Efficient star formation (SF) is expected to take place in such a dense disc. We model SF by means of sink particles. At ~6x10^5 yr, ~6000 solar masses of stars have formed, and are confined within a thin disc with inner and outer radius of 0.06 and 0.5 pc, respectively. Thus, this preliminary study show…
Despite significant strides made towards understanding accretion, outflow, and emission processes in the Galactic Center supermassive black hole Sagittarius A*, the presence of jets has neither been rejected nor proven. We investigate here whether the combined spectral and morphological properties of the source at radio through near infrared wavelengths are consistent with the predictions for inhomogeneous jets. In particular, we construct images of jets at a wavelength of 7mm based on models that are consistent with the spectrum of Sgr A*. We then compare these models through closure quantiti…
On 2004 Dec. 27, the soft gamma repeater (SGR) 1806-20 emitted the brightest giant flare (GF) ever detected from an SGR, with an (isotropic) energy release $\sim 100$ times greater than the only two other known SGR GFs. It was followed by a very bright, fading radio afterglow. Extensive follow-up radio observations provided a wealth of information with unprecedented astrometric precision, revealing the temporal evolution of the source size, along with densely sampled light curves and spectra. Here we expand on our previous work on this source, by explaining these observations within one self-c…
Infall, Outflow, Rotation, and Turbulent Motions of Dense Gas within NGC 1333 IRAS 4
NGC 1333 IRAS 4是英仙座中一组高度嵌入的年轻恒星天体，它的毫米波观测揭示了其两个最明亮的连续体天体4A和4 B周围致密气体的流入，流出，旋转和湍流运动。这些数据的最佳角分辨率约为2”（0.0034 pc），最佳速度分辨率为0.13 km/s。在H2 CO 3_12-2_11中观察到的逆天鹅座P-Cygni剖面中，可以看到朝向这两个天体的入流运动，也可以在CS 3-2和N2 H + 1-0中观察到朝向4A的入流运动，为这种朝向低质量原恒星天体的运动提供了最不明确的证据。流出运动由在4A和4 B的位置偏移处观察到的H2 CO 3_12-2_11和CS 3-2的亮线翼探测，可能追踪致密的空腔壁。稠密气体的旋转运动是由N2 H+线速度的系统变化来追踪的，并且这种变化在4A附近而不是在4 B附近被发现。湍流运动似乎随着尺度的减小而减小，因为4A和4 B周围的N2 H+线宽比单碟观测窄2或3倍。观测到的最小线宽约为0.2公里/秒，这为IRAS 4的母核速度色散提供了一个新的下限，并表明星团恒星形成区域内的湍流可以显着减少。在区域4 B '中的第三个连续体物体在任何观察到的分子种类中都没有显示出可检测的线发射。
HH 212 is a highly collimated jet discovered in H2 powered by a young Class 0 source, IRAS 05413-0104, in the L1630 cloud of Orion. We have mapped around it in 1.33 mm continuum, 12CO ($J=2-1$), 13CO ($J=2-1$), C18O ($J=2-1$), and SO ($J_K = 6_5-5_4$) emission at $\sim$ \arcs{2.5} resolution with the Submillimeter Array. A dust core is seen in the continuum around the source. A flattened envelope is seen in C18O around the source in the equator perpendicular to the jet axis, with its inner part seen in 13CO. The structure and kinematics of the envelope can be roughly reproduced by a simple edg…
Both gas accretion (infall) and winds (outflow) change a galaxy's metallicity and gas fraction, lowering the effective yield. Low effective yields in galaxies with rotation speeds < 120 km/s have been widely interpreted as the onset of SN-driven winds below a characteristic galaxy mass, but gas accretion is also a viable explanation. However, calculations presented here prove: (1) that metal-enriched outflows are the only mechanism that can significantly reduce the effective yield, but only for gas-rich systems; (2) that it is nearly impossible to reduce the effective yield of a gas-poor syste…
为银河系中心区域制作了氨排放的VLA图。NH_3（1，1）和NH_3（2，2）跃迁分别出现在3个2'× 2'视场中，它们覆盖了Sgr A ~* 及其以南3'区域，在围绕Sgr A ~* 的中央3秒差距区域，我们发现了与环核盘（CND）有关的发射，无论是从形态学上还是从运动学上都是如此。这个中心发射连接到一个长的，狭窄的2 pc x 10 pc的cluerous分子气体流光位于南部，这似乎是携带气体从附近的20公里/秒的巨大分子云（GMC）的环核区域。我们发现沿流光的速度梯度，随着气体接近Sgr A*，速度逐渐变高。流光在CND的位置处停止，其中NH3发射的线宽急剧增加。这可能是吸积到CND上的运动学特征。NH3（2，2）/NH3（1，1）发射的比率表明气体在位于CND东部边缘内的流光的北端被加热。气体的形态学、运动学和温度梯度都表明南部流光位于银河系中心，并与环核区域相互作用。
The multi-wavelength observations of the 2004 December~27 Giant Flare (GF) from SGR 1806-20 and its long-lived radio afterglow are briefly reviewed. The GF appears to have been produced by a dramatic reconfiguration of the magnetic field near the surface of the neutron star, possibly accompanied by fractures in the crust. The explosive release of over 10^46 ergs (isotropic equivalent) powered a one-sided mildly relativistic outflow. The outflow produced a new expanding radio nebula, that is still visible over a year after the GF. Also considered are the constraints on the total energy in the G…
We present the detection of infall, rotation and outflow kinematic signatures towards both a protostellar source, VLA 1623 and what was initially thought to be a pre-protostellar core, SM1N, in the rho-Ophiuchus A region. The kinematic signatures of early star formation were detected in the dense molecular gas surrounding the embedded sources using high signal-to-noise millimeter and submillimeter data. Centroid velocity maps made with HCO+ J=4->3 and J=1->0 line emission exhibit the blue bulge signature of infall, which is predicted to be seen when infall motion dominates over rotational moti…
The brightest giant flare from the soft $γ$-ray repeater (SGR) 1806-20 was detected on 2004 December 27. The isotropic-equivalent energy release of this burst is at least one order of magnitude more energetic than those of the two other SGR giant flares. Starting from about one week after the burst, a very bright ($\sim 80$ mJy), fading radio afterglow was detected. Follow-up observations revealed the multi-frequency light curves of the afterglow and the temporal evolution of the source size. Here we show that these observations can be understood in a two-component explosion model. In this mod…
We present an investigation into the absorber in front of the z=2.63 radio galaxy MRC 2025-218, using integral field spectroscopy obtained at the Very Large Telescope, and long slit spectroscopy obtained at the Keck II telescope. The properties of MRC 2025-218 are particularly conducive to study the nature of the absorbing gas, i.e., this galaxy shows bright and spatially extended Ly-alpha emission, along with bright continuum emission from the active nucleus. Ly-alpha absorption is detected across ~40x30 kpc^2, has a covering factor of ~1, and shows remarkably little variation in its properti…
A model for gas outflows is proposed which simultaneously explains the correlations between the (i) equivalent width of low ionization and Ly-alpha lines, (ii) outflow velocity, and (iii) star formation rate observed in Lyman Break Galaxies (LBGs). Our interpretation implies that LBGs host short-lived (30 +/- 5 Myr) starburst episodes observed at different evolutionary phases. Initially, the starburst powers a hot wind bound by a denser cold shell, which after about 5 Myr becomes dynamically unstable and fragments; afterwards the fragment evolution is approximately ballistic while the hot bubb…
The protostar B335 was observed in the 1.3 mm continuum and in the H2CO 312 - 211 line with an angular resolution of about 8 arcsec. The mass of the inner envelope detected by the dust continuum emission is about 0.02 Msun. The H2CO spectrum at the protostellar position shows a blue-skewed double peak profile, suggesting that the kinematics of the inner envelope is dominated by infall motion. When the blueshifted and the redshifted peaks were imaged separately, however, there is a small east-west displacement between the maximum positions. This displacement suggests that some part of the H2CO …
CO isotopes are able to probe the different components in protostellar clouds. These components, core, envelope and outflow have distinct physical conditions and sometimes more than one component contributes to the observed line profile. In this study we determine how CO isotope abundances are altered by the physical conditions in the different components. We use a 3D molecular line transport code to simulate the emission of four CO isotopomers, 12CO J=2-1, 13CO J=2-1, C18O J=2-1 and C17O J=2-1 from the Class 0/1 object L483, which contains a cold quiescent core, an infalling envelope and a cl…
The fate of massive cold clumps, their internal structure and collapse need to be characterised to understand the initial conditions for the formation of high-mass stars, stellar systems, and the origin of associations and clusters. We explore the onset of star formation in the 75 M_sun SMM1 clump in the region ISOSS J18364-0221 using infrared and (sub-)millimetre observations including interferometry. This contracting clump has fragmented into two compact cores SMM1 North and South of 0.05 pc radius, having masses of 15 and 10 M_sun, and luminosities of 20 and 180 L_sun. SMM1 South harbours a…
We have obtained velocity-resolved spectra of the H_2 v=1-0 S(1) (lambda = 2.1218 micron) emission line at 2 arcsec angular resolution (or 0.08 pc spatial resolution) in four regions within the central 10 pc of the Galaxy where the supernova-like remnant Sgr A East is colliding with molecular clouds. To investigate the kinematic, physical, and positional relationships between the important gaseous components in the center, we compared the H_2 data cube with previously published NH_3 data. The projected interaction-boundary of Sgr A East is determined to be an ellipse with its center offset 1.5…
We present observations of IRAS 16293-2422 using the Submillimeter Array (SMA) at 300 GHz, and the Very Large Array (VLA) at frequencies from 1.5 to 43 GHz. This source was already known to be a binary system with components A and B separated by ~5". The new SMA data now separate source A into two submm continuum components, denoted Aa and Ab. The strongest of these, Aa, peaks between the cm radio sources A1 and A2. Archival VLA data show proper motion of sources A and B of 17 mas/yr, associated with motion of the rho Ophiuchi cloud. We also find relative motion between A1 and A2 which exclude…
The radio source Sagittarius A* (Sgr A*) is believed to be a hot, inhomogeneous, magnetized plasma flowing near the event horizon of the 3 million solar mass black hole at the galactic center. At a distance of 8000 parsecs the black hole would be among the largest black holes as judged by angular size. Recent observations are consistent with the idea that the millimeter and sub-millimeter photons are dominated by optically thin, thermal synchrotron emission. Anticipating future Very Long Baseline Interferometry (VLBI) observations of Sgr A* at these wavelengths, we present here the first dynam…
We present high resolution (0.''12 x 0.''079) observations of the ultracompact HII region G10.6-0.4 in 23 GHz radio continuum and the NH3(3,3) line. Our data show that the infall in the molecular material is largely spherical, and does not flatten into a molecular disk at radii as small as 0.03 pc. The spherical infall in the molecular gas matches in location and velocity the infall seen in the ionized gas. We use a non-detection to place a stringent upper limit on the mass of an expanding molecular shell associated with pressure driven expansion of the HII region. These data support a scenari…
