Are massive dense clumps truly sub-virial? A new analysis using Gould Belt ammonia data
Ayushi Singh, Christopher D. Matzner, Rachel K. Friesen, Peter G. Martin, Jaime E. Pineda, Erik W. Rosolowsky, Felipe Alves, Ana Chacón-Tanarro, Hope How-Huan C… 展开作者
Ayushi Singh, Christopher D. Matzner, Rachel K. Friesen, Peter G. Martin, Jaime E. Pineda, Erik W. Rosolowsky, Felipe Alves, Ana Chacón-Tanarro, Hope How-Huan Chen, Michael Chun-Yuan Chen, Spandan Choudhury, James Di Francesco, Jared Keown, Helen Kirk, Anna Punanova, Youngmin Seo, Yancy Shirley, Adam Ginsburg, Stella S. R. Offner, Héctor G. Arce, Paola Caselli, Alyssa A. Goodman, Philip C. Myers, Elena Redaelli
Dynamical studies of dense structures within molecular clouds often conclude that the most massive clumps contain too little kinetic energy for virial equilibrium, unless they are magnetized to an unexpected degree. This raises questions about how such a state might arise, and how it might persist long enough to represent the population of massive clumps. In an effort to re-examine the origins of this conclusion, we use ammonia line data from the Green Bank Ammonia Survey and Planck-calibrated dust emission data from Herschel to estimate the masses and kinetic and gravitational energies for dense clumps in the Gould Belt clouds. We show that several types of systematic error can enhance the appearance of low kinetic-to-gravitational energy ratios: insufficient removal of foreground and background material; ignoring the kinetic energy associated with velocity differences across a resolved cloud; and over-correcting for stratification when evaluating the gravitational energy. Using an analysis designed to avoid these errors, we find that the most massive Gould Belt clumps harbor virial motions, rather than sub-virial ones. As a byproduct, we present a catalog of masses, energies, and virial energy ratios for 85 Gould Belt clumps.
The distribution of ultraviolet (UV) radiation field provides critical constraints on the physical environments of molecular clouds. Within 1 kpc of our solar system and fostering protostars of different masses, the giant molecular clouds in the Gould Belt present an excellent opportunity to resolve the UV field structure in star forming regions. We performed spectral energy distribution (SED) fitting of the archival data from the Herschel Gould Belt Survey (HGBS). Dust radiative transfer analysis with the DUSTY code were applied to 23 regions in 14 molecular complexes of the Gould Belt, resul…
We analyze the spatial and kinematic properties of a large sample of young T Tauri type stars in a 500 pc radius solar neighborhood, closely related to the Gould belt. The following parameters of the exponential density distribution have been determined: the average $(z_G)_\odot=-25\pm5$ pc and scale height $h_G=56\pm6$ pc. We propose a method of excluding background stars from the samples, which are located at large heights with respect to the symmetry plane of the Gould belt. We discovered that the expansion effect for the entire star system, $K_G=6\pm1$ km s$^{-1}$ kpc$^{-1}$, is determined…
The JCMT Transient Survey: Identifying Submillimetre Continuum Variability over Several Year Timescales Using Archival JCMT Gould Belt Survey Observations
The Herschel Gould Belt survey mapped the nearby (d < 500 pc) star-forming regions to understand better how the prestellar phase influences the star formation process. Here we report a complete census of dense cores in a 15 deg2 area of the Serpens star-forming region located between d=420 pc and 484 pc. The PACS and SPIRE cameras imaged this cloud from 70micron to 500micron. With the multi-wavelength source extraction algorithm getsources, we extract 833 sources, of which 709 are starless cores and 124 are candidate proto-stellar cores. We obtain temperatures and masses for all the sample, cl…
Hierarchical Star Formation: Stars and Stellar Clusters in the Gould Belt
我们执行的空间和运动学分布的年轻的疏散星团在太阳附近的研究,辨别我们的样本内的绑定集群和瞬态恒星凝聚。然后,我们区分古尔德带(GB)和本地银河系盘(LGD)的成员,使用以前的估计从样本的O-B6依巴谷星获得的两个系统的结构参数。利用这一分类样本,我们分析了GB中集群系统的空间结构和运动学行为。这两个恒星形成区占据主导地位,并使GB具有其特征性的倾斜形状,它们的星团含量显示出显着的差异:虽然Ori OB 1由疏散星团组成,但在Sco OB 2的边界内没有一个星团。这反映在速度空间中,再次转化为运动空间区域中由Ori OB 1成员填充的大量集群,以及与Sco OB 2相关的边缘数量。根据这些结果,我们研究了银河系相对于猎户臂光学段的性质,我们提出,星团的不同内容,在银河平面上的不同高度和不同的剩余速度的Ori OB 1和Sco OB 2可以解释在它们的相对位置的最大密度的本地臂在太阳附近。虽然在形态上很有趣,但GB似乎是我们对局部臂中更大的星团复合体的局部和偏见的结果,这可以用银河系盘的内部动力学来解释。
We present Herschel SPIRE and PACS maps of the Cepheus Flare clouds L1157, L1172, L1228, L1241, and L1251, observed by the Herschel Gould Belt Survey (HGBS) of nearby star-forming molecular clouds. Through modified blackbody fits to the SPIRE and PACS data, we determine typical cloud column densities of 0.5-1.0 $\times$ 10$^{21}$ cm$^{-2}$ and typical cloud temperatures of 14-15 K. Using the getsources identification algorithm, we extract 832 dense cores from the SPIRE and PACS data at 160-500 $μ$m. From placement in a mass vs. size diagram, we consider 303 to be candidate prestellar cores, an…
The Link between Magnetic Fields and Filamentary Clouds: Bimodal Cloud Orientations in the Gould Belt
利用近红外尘埃消光图和光学恒星偏振计资料研究了古尔德带内的对流分子云及其局部ICM(云间介质)磁场的方向。这些对流云的长度在几秒差距到十秒差距之间,我们发现它们的方向倾向于平行或垂直于当地ICM的平均场方向。这种双峰分布是没有发现在云模拟与超Alfvenic湍流,云的方向应该是随机的。ICM磁场在动力学上比惯性范围的湍流和自引力更重要,它可以很容易地解释这两种场丝结构。以前的研究普遍认为,强磁场可以引导引力收缩,并导致纤维垂直于他们,但很少讨论的事实,磁场也可以通道亚阿尔芬湍流,形成与他们对齐的纤维。这种云形成的强场情景也与从ICM到云观测到的恒定场强相一致(Crutcher et al. 2010),并且可以解释“中心-细丝”云结构(Myers 2009)和云重力收缩的密度阈值(Kainulainen et al. 2009)。
Although episodic star formation (SF) had been suggested for nearby SF regions, a panoramic view to the latest episodic SF history in the solar neighborhood is still missing. By uniformly constraining the slope $α$ of infrared spectral energy distributions (SEDs) of young stellar objects (YSOs) in the 13 largest Gould's Belt (GB) protoclusters surveyed by Spitzer Space Telescope, we have constructed a cluster-averaged histogram of $α$ representing YSO evolution lifetime as a function of the $α$ value. Complementary to the traditional SED classification scheme (0, I, F, II, III) that is based o…
The JCMT Legacy Survey of the Gould Belt: a first look at Serpens with HARP
JCMT上的Gould Belt Legacy Survey(GBS)观测到巨蛇座分子云中12 CO J=3- 2发射的260平方角分区域,以及13 CO和C18 O发射的190平方角分子集。我们研究了非流出气体的全局速度结构,并计算了激发温度和不透明度。大规模的质量和能量的区域进行评估,特别考虑到高速气体。我们发现这个云的质量是203个太阳质量,并且受到引力束缚,流出气体的动能大约是云湍流动能的70%。我们确定了该地区一些亚毫米级0/I类源的紧凑流出
Radiative feedback can influence subsequent star formation. We quantify the heating from OB stars in the local star-forming regions in the JCMT Gould Belt survey. Dust temperatures are calculated from 450/850 micron flux ratios from SCUBA-2 observations at the JCMT assuming a fixed dust opacity spectral index $β=1.8$. Mean dust temperatures are calculated for each submillimetre clump along with projected distances from the main OB star in the region. Temperature vs. distance is fit with a simple model of dust heating by the OB star radiation plus the interstellar radiation field and dust cooli…
The dense cores and filamentary structure of the molecular cloud in Corona Australis. Herschel SPIRE and PACS observations from the Herschel Gould Belt Survey
The JCMT Gould Belt Survey: First results from the Corona Australis molecular cloud and evidence of variable dust emissivity indices in the Coronet region