Observations of the [CI] ($^3P_1$-$^3P_0$) emission toward the massive star-forming region RCW38: further evidence for highly-clumped density distribution of the molecular gas
We present observations of the $^3P_1$-$^3P_0$ fine-structure line of atomic carbon using the ASTE 10 m sub-mm telescope towards RCW38, the youngest super star cluster in the Milky Way. The detected [CI] emission is compared with the CO $J$ = 1-0 image cube presented in Fukui et al. (2016) which has an angular resolution of 40$^{\prime \prime}$ ($\sim$ 0.33 pc). The overall distribution of the [CI] emission in this cluster is similar to that of the $^{13}$CO emission. The optical depth of the [CI] emission was found to be $τ$ = 0.1-0.6, suggesting mostly optically thin emission. An empirical conversion factor from the [CI] integrated intensity to the H$_2$ column density was estimated as $X_{\rm [CI]}$ = 6.3 $\times$ 10$^{20}$ cm$^{-2}$ K$^{-1}$ km$^{-1}$ s (for visual extinction: $A_V$ $\le$ 10 mag) and 1.4 $\times$ 10$^{21}$ cm$^{-2}$ K$^{-1}$ km$^{-1}$ s (for $A_V$ of 10-100 mag). The column density ratio of the [CI] to CO ($N_{\rm [CI]}/N_{\rm CO}$) was derived as $\sim$ 0.1 for $A_V$ of 10-100 mag, which is consistent with that of the Orion cloud presented in Ikeda et al. (2002). However, our results cover an $A_V$ regime of up to 100 mag, which is wider than the coverage found in Orion, which reach up to $\sim$ 60 mag. Such a high [CI]/CO ratio in a high $A_V$ region is difficult to be explained by the plane-parallel photodissociation region (PDR) model, which predicts that this ratio is close to 0 due to the heavy shielding of the ultraviolet (UV) radiation. Our results suggest that the molecular gas in this cluster is highly clumpy, allowing deep penetration of UV radiation even at averaged $A_V$ values of 100 mag. Recent theoretical works have presented models consistent with such clumped gas distribution with a sub-pc clump size (e.g., Tachihara et al. 2018).
Synthetic observations of highly clumped formation of CO and CI clouds in the turbulent interstellar medium; Implications on the seed CO clouds and the CO-dark H$_{2}$ gas
The Large Program "Astrochemical Surveys At IRAM" (ASAI) investigates the emergence of molecular complexity along the different stages of the solar-type star formation process, by carrying out unbiased line surveys of a sample of ten template sources in the range 80-272 GHz with the IRAM 30m telescope. We present here an overview of the main results of the Large Program ASAI.
We present ALMA CO (2-1) detections of 24 star-forming Brightest Cluster Galaxies (BCGs) over $0.2<z<1.2$, constituting the largest and most distant sample of molecular gas measurements in BCGs to date. The BCGs are selected from the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS) to be IR-bright and therefore star-forming. We find that molecular gas is common in star-forming BCGs, detecting CO at a detection rate of 80% in our target sample of 30 objects. We additionally provide measurements of the star formation rate (SFR) and stellar mass, calculated from existing MIPS 24 $μ$…
In order to investigate the role of gas in the demise of star formation on kpc-scales, we compare the resolved molecular gas main sequence (rMGMS: Sigma_* vs Sigma_H2) of star-forming regions to the sequence of `retired' regions that have ceased to form new stars. Using data from the ALMaQUEST survey, we find that retired spaxels form a rMGMS that is distinct from that of star-forming spaxels, offset to lower Sigma_H2 at fixed Sigma_* by a factor of ~5. We study the rMGMS of star-forming and retired spaxels on a galaxy-by-galaxy basis for eight individual ALMaQUEST galaxies. Six of these galax…
Connecting the Dots: Analyzing Synthetic Observations of Star-Forming Clumps in Molecular Clouds
在本文中,我们调查分子云的观测可以正确识别和测量恒星形成团块的程度。我们从一个5000 M $_{\odot}$分子云的模拟坍缩中产生了一个合成柱密度图和一个合成谱线数据立方体。通过将模拟中发现的团块与合成观测中发现的团块相关联,发现来自谱线数据立方体的团块质量非常接近团块的真实物理性质。我们还发现,“观察到的”团块质量函数来自列密度图转移的一个因素~ 3高于真正的团块质量函数,由于低密度材料沿视线的投影。Alves等人(2007年)首先提出,团簇质量函数向更高质量的偏移3倍可以归因于30%的恒星形成效率。我们的研究结果表明,这一发现可能是由于高估了从柱密度观测确定的团块质量。
We perform a joint-analysis of high spatial resolution molecular gas and star-formation rate (SFR) maps in main-sequence star-forming galaxies experiencing galactic-scale outflows of ionised gas. Our aim is to understand the mechanism that determines which galaxies are able to launch these intense winds. We observed CO(1-0) at 1" resolution with ALMA in 16 edge-on galaxies, which also have 2" spatial resolution optical integral field observations from the SAMI Galaxy Survey. Half the galaxies in the sample were previously identified as harbouring intense and large-scale outflows of ionised gas…
We present a study of molecular outflows using six molecular lines (including 12CO/13CO/C18O/HCO+(J = 1-0) and SiO/CS(J = 2-1)) toward nine nearby high-mass star-forming regions with accurate known distances. This work is based on the high-sensitivity observations obtained with the 14-m millimeter telescope of Purple Mountain Observatory Delingha (PMODLH) observatory. The detection rate of outflows (including 12CO, 13CO, HCO+, and CS) is 100\%. However, the emission of SiO was not detected for all sources. The full line widths ($ΔV$) at 3$σ$ above the baseline of these molecular lines have the…
We complement the MALATANG sample of dense gas in nearby galaxies with archival observations of $^{12}\rm CO$ and its isotopologues to determine scaling relations between Wide-field Infrared Survey Explorer (WISE) 12 $μ$m emission and molecular gas tracers at sub-kiloparsec scales. We find that 12 $μ$m luminosity is more tightly correlated with $^{12}\rm CO$ than it is with $^{13}\rm CO$ or dense gas tracers. Residuals between predicted and observed $^{12}\rm CO$ are only weakly correlated with molecular gas mass surface density ($Σ_{\rm mol}$) in regions where $Σ_{\rm mol}$ is very low ($\sim…
CHemical Evolution in MassIve star-forming COres (CHEMICO). II. Molecular ions, electron fraction, and cosmic-ray ionisation rate
INAF - Osservatorio Astrofisico di Arcetri(意大利国家天体物理研究所-阿尔切特里天体物理天文台);Observatoire de Paris(巴黎天文台);PSL Research University(巴黎文理研究大学);CNRS(法国国家科学研究中心);Vrije Universiteit Amsterdam(阿姆斯特丹自由大学)
ATOMS: ALMA Three-millimeter Observations of massive Star-forming regions -XX. Probability distribution function of integrated intensity for dense molecular gas tracers
In the first article of this series, we have used the ergodic theory to assess the validity of a statistical approach to characterize various properties of star-forming molecular clouds (MCs) from a limited number of observations or simulations. This allows the proper determination of confidence intervals for various volumetric averages of statistical quantities obtained form observations or numerical simulations. In this joint paper, we apply the same formalism to a different kind of (observational or numerical) study of MCs. Indeed, as observations cannot fully unravel the complexity of the …
Dynamical Properties of Molecular-forming Gas Clumps in Galaxies at the Epoch of Reionization
利用宇宙学放大模拟研究了分子形成气体团簇(MGCs)在再电离阶段的性质。我们确定MGCs在z=6的原型星系(“Althaea”)使用H2密度为基础的团块发现。我们比较它们的质量,尺寸,速度色散,气体表面密度和维里参数(alpha_vir)的观测。在阿尔泰,典型的MGC质量和大小为Mgas=10^6.5 Msun,R=45-100 pc,与附近的旋涡星系和星暴星系相当。MGCs是高度超音速的,并受到湍流的支持,其均方根速度色散为sigma_gas=20-100 km s^-1,压力为P/k_B=10^7.6 K cm^-3(即,> 1000倍于银河系),类似于在附近和z~2富气体星暴星系中发现的。此外,我们进行稳定性分析,了解的起源和动力学性质的MGCs。我们发现,MGC在蜀葵主盘中是全局稳定的。恒星形成预计发生在云和核心中的更小尺度的区域,反而具有较低的α_vir和Toomre-Q值。因此,对再电离时期恒星形成气体动力学的详细研究需要<40 pc(=0.01”)的空间分辨率,这是阿塔卡马大(亚)毫米阵列和下一代甚大阵列可以达到的。
We present observations of CO(3-2) in 13 main-sequence $z=2.0-2.5$ star-forming galaxies at $\log(M_*/M_{\odot})=10.2-10.6$ that span a wide range in metallicity (O/H) based on rest-optical spectroscopy. We find that CO(3-2)/SFR decreases with decreasing metallicity, implying that the CO luminosity per unit gas mass is lower in low-metallicity galaxies at $z\sim2$. We constrain the CO-to-H$_2$ conversion factor ($α_{\text{CO}}$) and find that $α_{\text{CO}}$ inversely correlates with metallicity at $z\sim2$. We derive molecular gas masses ($M_{\text{mol}}$) and characterize the relations among…