We present an analysis of multi-wavelength observations from various datasets and Galactic plane surveys to study the star formation process in the W42 complex. A bipolar appearance of W42 complex is evident due to the ionizing feedback from the O5-O6 type star in a medium that is highly inhomogeneous. The VLT/NACO adaptive-optics K and L' images (resolutions ~0".2-0".1) resolved this ionizing source into multiple point-like sources below ~5000 AU scale. The position angle ~15 deg of W42 molecular cloud is consistent with the H-band starlight mean polarization angle which in turn is close to the Galactic magnetic field, suggesting the influence of Galactic field on the evolution of the W42 molecular cloud. Herschel sub-millimeter data analysis reveals three clumps located along the waist axis of the bipolar nebula, with the peak column densities of ~3-5 x10^{22} cm^{-2} corresponding to visual extinctions of AV ~32-53.5 mag. The Herschel temperature map traces a temperature gradient in W42, revealing regions of 20 K, 25 K, and 30-36 K. Herschel maps reveal embedded filaments (length ~1-3 pc) which appear to be radially pointed to the denser clump associated with the O5-O6 star, forming a hub-filament system. 512 candidate young stellar objects (YSOs) are identified in the complex, ~40% of which are present in clusters distributed mainly within the molecular cloud including the Herschel filaments. Our datasets suggest that the YSO clusters including the massive stars are located at the junction of the filaments, similar to those seen in Rosette Molecular Cloud.
We present sensitive observations of NH2D at 110.153599 GHz toward 50 Galactic massive star-forming regions with IRAM 30-m telescope. The NH2D transition is detected toward 36 objects, yielding a detection rate of 72%. Column densities of NH2D, HC3N and C18O for each source are derived by assuming local thermal equilibrium conditions with a fixed excitation temperature. The deuterium ratio of NH$_3$, defined as the abundance ratio of NH2D to NH3, for 19 sources is also obtained with the information of NH3 from the literature. The range of deuterium fractionation bends to be large in the late-s…
EVN observations of 6.7 GHz methanol maser polarization in massive star-forming regions IV. Magnetic field strength limits and structure for 7 additional sources
Overview of the Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX) Project
MYStIX(Massive Young Star-Forming Complex Study in Infrared and X-ray)计划利用钱德拉X射线天文台、斯皮策太空望远镜和英国红望远镜上的成像探测器,对20个以OB-dominated年轻星团及其周围的距离d < 4 kpc的天体进行表征。观测的目标是构建具有明确标准的恒星形成复杂恒星成员的目录,以及星云气体(特别是热X射线发射等离子体)和尘埃的地图。汇编了一个包含数百颗OB星和> 30,000颗低质量前主序星的MYStIX可能复合体成员(MPCMs)星表。这个样本和相关的数据产品将被用来寻求新的经验约束的理论模型的团簇形成和动力学,质量分离,OB星的形成,恒星形成触发的周边HII地区,生存的原行星盘在HII地区。本文介绍了该项目的概况,包括数据分析方法及其在两个恒星形成区NGC 2264和三叉星云中的应用。
The massive star-forming region W75N~(B) is thought to host a cluster of massive protostars (VLA~1, VLA~2, and VLA~3) undergoing different evolutionary stages. In this work, we present radio continuum data with the highest sensitivity and angular resolution obtained to date in this region, using the VLA-A and covering a wide range of frequencies (4-48~GHz), which allowed us to study the morphology and the nature of the emission of the different radio continuum sources. We also performed complementary studies with multi-epoch VLA data and ALMA archive data at 1.3 mm wavelength. We find that VLA…
We performed observations of the HC$_3$N (24-23, 17-16, 11-10, 8-7) lines towards a sample consisting of 19 Galactic massive star-forming regions with the Arizona Radio Observatory 12-m and Caltech Submillimeter Observatory 10.4-m telescopes. HC$_3$N (24-23, 17-16, 11-10, 8-7) lines were detected in sources except for W44, where only HC$_3$N (17-16, 11-10) were detected. Twelve of the nineteen sources showed probable line wing features. The excitation temperatures were estimated from the line ratio of HC$_3$N (24-23) to HC$_3$N (17-16) for 18 sources and are in the range 23-57 K. The line widt…
Massive star-forming regions exhibit an extremely rich and diverse chemistry, which in principle provides a wealth of molecular probes, as well as laboratories for interstellar prebiotic chemistry. Since the chemical structure of these sources displays substantial spatial variation among species on small scales (${\lesssim}10^4$ au), high angular resolution observations are needed to connect chemical structures to local environments and inform astrochemical models of massive star formation. To address this, we present ALMA 1.3 mm observations toward OB cluster-forming region G10.6-0.4 (hereaft…
High Redshift Massive Quiescent Galaxies are as Flat as Star Forming Galaxies: The Flattening of Galaxies and the Correlation with Structural Properties in CANDELS/3D-HST
A catalog of 44 GHz methanol masers in massive star-forming regions. IV. The high-mass protostellar object sample
本文报道了用卡尔G. Jansky甚大阵列(VLA); 56个场中有24个显示出脉泽发射。这些数据使我们能够证明协会,在角秒精度,I类脉泽排放与流出,HII地区,和冲击跟踪4.5微米的排放。我们发现,共有83个脉泽组件的线宽范围从0.17至3.3公里秒$^{-1}$与近平坦的分布和一个中位数值为1.1公里秒$^{-1}$。脉泽相对于宿主云系统速度的相对速度范围从$-$ 2.5到3.1 km s $^{-1}$,分布峰值接近零。我们还研究了脉泽之间的相关性和所谓的扩展绿色物体(EGO)从GLIMPSE调查。在每个领域的多个来源,揭示了从红外图像以及从VLA档案数据厘米连续发射,在大多数情况下,44 GHz脉泽的位置相关的EGO似乎跟踪在外地的年轻来源。我们报告一个可能的情况下,44 GHz脉泽与低质量原恒星。如果得到证实,这个区域将是第五个已知的恒星形成区域,拥有与低质量原恒星相关的I类脉泽。我们讨论三种可能的情况下,微波激射器的可变性。
Forming massive stars launch outflows of magnetic origin, which in fact serve as a marker for finding sites of massive star formation. However, both the theoretical and observational study of the mechanisms that intervene in the formation and propagation of such outflows has been possible only until recent years. With this work, we aim to study in detail the mechanisms that drive highly collimated outflows from early stages of the formation of a massive star, and how those processes are impacted by the properties of the natal environment of the forming massive star. We perform a series of 31 s…
We present the first direct spectroscopic measurement of the stellar velocity dispersion function (VDF) for massive quiescent and star-forming galaxies at $0.6 < z \leq 1.0$. For this analysis we use individual measurements of stellar velocity dispersion from high-S/N spectra from the public Large Early Galaxy Astrophysics Census (LEGA-C) survey. We report a remarkable stability of the VDF for both quiescent and star-forming galaxies within this redshift range, though we note the presence of weak evolution in the number densities of star-forming galaxies. We compare both VDFs with previous dir…
The Comparison of Physical Properties Derived from Gas and Dust in a Massive Star-Forming Region
我们通过比较气体和尘埃各自的物理性质,探索大质量恒星形成区域中气体和尘埃之间的关系。我们比较的温度和柱密度在一个巨大的恒星形成红外暗云(IRDC,G32.02+0.05),它显示了一系列的演化状态,从静止到活跃。利用NH3的(1,1)、(2,2)和(4,4)跃迁在Karl G. Jansky甚大阵列(VLA),而尘埃温度和柱密度的计算使用卷云减去,修改后的黑体适合赫歇尔数据。我们通过比较推导出的柱密度,计算出NH3的丰度为4.6 x 10^-8。在最冷的恒星形成区,我们发现测得的尘埃温度低于测得的气体温度(平均值和标准差T_dust ~ 11.6 +/- 0.2 K vs. T_gas ~ 15.2 +/- 1.5 K),这可能表明气体和尘埃在最年轻的区域没有很好地耦合(~0.5百万年),或者这些观测探测了尘埃和/或气体温度测量不可靠的区域。最后,我们计算毫米通量的基础上的温度和柱密度来自NH3,这表明毫米尘埃连续观测的大规模恒星形成的地区,如Bolocam银河系平面调查或ATLASGAL,可以探测热核心,冷核心,和致密的气体通道,它们形成,一般不占主导地位的最热的核心。
The Evolution of the Fractions of Quiescent and Star-forming Galaxies as a Function of Stellar Mass Since z=3: Increasing Importance of Massive, Dusty Star-forming Galaxies in the Early Universe
利用UltraVISTA DR 1和3D-HST星表,我们构建了一个恒星质量完整的样本,其独特的组合调查的体积和深度,研究的分数的演化的静止星系,适度清晰的恒星形成的星系,尘埃恒星形成的星系作为一个函数的恒星质量在红移间隔$0.2 \le z \le 3.0$。我们发现,尘埃恒星形成星系的整体星系人口中的作用变得更加重要,随着恒星质量的增加,并迅速增长的红移。具体来说,尘埃恒星形成星系占主导地位的星系人口与$\log{(M_{\rm star}/M_{\odot})} \gtrsim 10.3$在$z\gtrsim2$。尘埃和非尘埃恒星形成星系的比例作为恒星质量的函数,随红移的变化很小。尘埃恒星形成星系在$\log{(M_{\rm star}/M_{\odot})} \gtrsim 10.0-10.5$的恒星形成种群中占主导地位,是$\sim$ 3-5的一个因子,而在$\log{(M_{\rm star}/M_{\odot})} \lesssim 10$中,清晰的恒星形成星系占主导地位。在$\log{(M_{\rm star}/M_{\odot})} > 10.5$,红色星系在所有红移$z<3$的星系群中占主导地位,这可能是因为它们处于静止状态(在晚期)或尘埃恒星形成(在早期宇宙)。