An Evolutionary Model for Collapsing Molecular Clouds and Their Star Formation Activity
Manuel Zamora-Aviles, Enrique Vázquez-Semadeni, Pedro Colín
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Version accepted for publication in ApJ. At referee's suggestion, includes comparison with numerical models in addition to comparison with observational data
We present an idealized, semi-empirical model for the evolution of gravitationally contracting molecular clouds (MCs) and their star formation rate (SFR) and efficiency (SFE). The model assumes that the instantaneous SFR is given by the mass above a certain density threshold divided by its free-fall time. The instantaneous number of massive stars is computed assuming a Kroupa IMF. These stars feed back on the cloud through ionizing radiation, eroding it. The main controlling parameter of the evolution turns out to be the maximum cloud mass, $\Mmax$. This allows us to compare various properties of the model clouds against their observational counterparts. A giant molecular cloud (GMC) model ($\Mmax \sim 10^5 \Msun$) adheres very well to the evolutionary scenario recently inferred by Kawamura et al. (2009) for GMCs in the Large Magellanic Cloud. A model cloud with $\Mmax \approx 2000 \Msun$ evolves in the Kennicutt-Schmidt diagram first passing through the locus of typical low- to-intermediate mass star-forming clouds, and then moving towards the locus of high-mass star-forming ones over the course of $\sim 10$ Myr. Also, the stellar age histograms for this cloud a few Myr before its destruction agree very well with those observed in the $ρ$-Oph stellar association, whose parent cloud has a similar mass, and imply that the SFR of the clouds increases with time. Our model thus agrees well with various observed properties of star-forming MCs, suggesting that the scenario of gravitationally collapsing MCs, with their SFR regulated by stellar feedback, is entirely feasible and in agreement with key observed properties of molecular clouds.
S2D2: Small-scale Significant substructure DBSCAN Detection II. Tracing episodes and gradients of star formation activity
Universidad Internacional de Valencia (VIU)(瓦伦西亚国际大学);Univ. Grenoble Alpes, CNRS, IPAG(格勒诺布尔阿尔卑斯大学、法国国家科学研究中心、IPAG);Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS(波尔多大学天体物理实验室、波尔多大学、法国国家科学研究中心)
The evolutionary tracks of young massive star clusters
恒星大多数是由几十到几万个成员组成的群体。30年来,理论模型提供了一个基本的概念,这些星团是如何形成和发展的:它们起源于坍缩分子云的气体和尘埃。从气体到恒星的转换是不完全的,剩余的气体被排出,导致星系团膨胀,恒星变得不受束缚。在观测上,这一过程的直接确认已被证明是难以捉摸的,这是由于形成团簇的性质的多样性。在这里,我们考虑到,真正的集群质量和大小被掩盖,最初的表面密度的背景,后来仍然存在的未绑定的恒星。基于最近的观测发现,在一个给定的恒星形成区域的恒星形成效率取决于当地的气体密度,我们使用的分析方法结合\mbox{N-body simulations, to reveal}演化轨迹的年轻大质量集群覆盖的第一个10万年。就像赫兹-罗素图是恒星演化的度量一样,这些轨道为星团提供了等价的信息。像恒星一样,大质量星团的形成和发展速度比它们的低质量同行更快,这解释了为什么很少发现大质量星团的祖先。
Aims. We investigate the role of selective dissociation in the process of star formation by comparing the physical parameters of protostellar-prestellar cores and the distinct regions with the CO isotope distributions in photodissociation regions. We seek to understand whether there is a better connection between the evolutionary age of star forming regions and the effect of selective dissociation Methods. Wide-field observations of the $\rm ^{12}CO$, $\rm ^{13}CO$, and $\rm C^{18}O$ ( J = 1 - 0) emission lines are used to study the ongoing star formation activity in the Aquila molecular regio…
Context. The formation processes of massive stars are still unclear but a picture is emerging involving accretion disks and molecular outflows in what appears to be a scaled-up version of low-mass star formation. A census of outflow activity towards massive star-forming clumps in various evolutionary stages has the potential to shed light on massive star formation (MSF). Aims. We conducted an outflow survey towards ATLASGAL clumps using SEDIGISM data and aimed to obtain a large sample of clumps exhibiting outflows in different evolutionary stages. Methods. We identify the high-velocity wings o…
Evolution in the Black Hole - Galaxy Scaling Relations and the Duty Cycle of Nuclear Activity in Star-Forming Galaxies
本文测量了69个Herschel探测到的宽线活动星系核(BLAGN)在M_BH-M_* 平面上的位置和演化矢量。BLAGN选自COSMOS和CDF-S场,并且跨越红移范围0.2< z<2.1。黑洞质量的计算使用档案光谱学和单历元维里质量估计,和星系总恒星质量的计算通过拟合光谱能量分布(减去BLAGN分量)。分别使用Chandra/XMM-牛顿X射线和Herschel远红外数据计算了黑洞和星系的质量增长率,这些数据是BLAGN吸积和星系恒星形成率的可靠测量。我们使用蒙特卡罗模拟来解释我们的样本中的偏差,由于选择限制和星系恒星质量分布的大质量末端的陡峭斜率。我们发现我们的样本与M_BH-M_* 关系从z~2到z~0没有演化是一致的。BLAGN和它们的宿主星系如果偏离了黑洞质量星系总恒星质量的关系,则它们的演化矢量往往与它们的质量比反相关:也就是说,具有超大质量(欠大质量)黑洞的星系往往具有低(高)的比吸积率与比恒星形成率之比。我们还使用测量的增长率来估计我们的星系的首选AGN占空比,以最一致地演变到本地M_BH-M_Bul关系。在恒星形成历史呈指数下降的合理假设下,数据表明恒星形成星系中的BLAGN占空比为10%(z 1时1 σ范围为1-42%<1 and 2-34% at z>)。