We determine the cosmic abundance of molecular hydrogen (H2) in the local universe from the xCOLD GASS survey. To constrain the H2 mass function at low masses and correct for the effect of the lower stellar mass limit of 10^9 Msun in the xCOLD GASS survey, we use an empirical approach based on an observed scaling relation between star formation rate and gas mass. We also constrain the HI and HI+H2 mass functions using the xGASS survey, and compare it to the HI mass function from the ALFALFA survey. We find the cosmic abundance of molecular gas in the local Universe to be Omega_H2=(5.34+/-0.47)x10^-5 h^-1. Molecular gas accounts for 19.6 +/- 3.9% of the total abundance of cold gas, Omega_HI+H2=(4.66+/-0.70)x10^-4 h^-1. Galaxies with stellar masses in excess of 10^9 Msun account for 89% of the molecular gas in the local Universe, while in comparison such galaxies only contain 73% of the cold atomic gas as traced by the HI 21cm line. The xCOLD GASS CO, molecular gas and cold gas mass functions and Omega_H2 measurements provide constraints for models of galaxy evolution and help to anchor blind ALMA and NOEMA surveys attempting to determine the abundance of molecular gas at high redshifts.
Molecular oxygen has been the subject of many observational searches as chemical models predicted it to be a reservoir of oxygen. Although it has been detected in two regions of the interstellar medium, its rarity is a challenge for astrochemical models. In this paper, we have combined the physical conditions computed with smoothed particle hydrodynamics (SPH) simulations with our full gas-grain chemical model Nautilus, to study the predicted O2 abundance in interstellar material forming cold cores. We thus follow the chemical evolution of gas and ices in parcels of material from the diffuse i…
Chemical models predict that in cold cores gas-phase methanol is expected to be abundant at the outer edge of the CO depletion zone, where CO is actively adsorbed. CO adsorption correlates with volume density in cold cores, and, in nearby molecular clouds, the catastrophic CO freeze-out happens at volume densities above 10$^4$ cm$^{-3}$. The methanol production rate is maximized there and its freeze-out rate does not overcome its production rate, while the molecules are shielded from UV destruction by gas and dust. Thus, in cold cores, methanol abundance should generally correlate with visual …
Complex organic molecules (COMs) have been detected in a variety of interstellar sources. The abundances of these COMs in warming sources can be explained by syntheses linked to increasing temperatures and densities, allowing quasi-thermal chemical reactions to occur rapidly enough to produce observable amounts of COMs, both in the gas phase, and upon dust grain ice mantles. The COMs produced on grains then become gaseous as the temperature increases sufficiently to allow their thermal desorption. The recent observation of gaseous COMs in cold sources has not been fully explained by these gas-…
In the cold neutral medium, high out-of-equilibrium temperatures are created by intermittent dissipation processes, including shocks, viscous heating, and ambipolar diffusion. The high-temperature excursions are thought to explain the enhanced abundance of CH$^{+}$ observed along diffuse molecular sight-lines. Intermittent high temperatures should also have an impact on H$_2$ line luminosities. We carry out simulations of MHD turbulence in molecular clouds including heating and cooling, and post-process them to study H$_2$ line emission and hot-gas chemistry, particularly the formation of CH$^…
Carbon Abundances in Starburst Galaxies of the Local Universe
碳是宇宙中第四丰富的元素，它的宇宙起源并不为人所知，也是一个激烈争论的问题。我们研究了C/O转化为O/H的行为，以约束碳的产生机制。我们在太空望远镜成像光谱仪（STIS）长缝光谱上测量了本地宇宙中18个星暴星系在1600至10000 Å光谱范围内的发射线强度。我们通过传统的星云分析确定化学丰度，并使用马尔可夫链蒙特卡罗（MCMC）方法来确定我们的碳和氧丰度在参数空间中的位置。我们的结论是，我们的C和O丰度测量是合理的。我们在[C/O] vs. [O/H]图中分析了我们的样本相对于其他天体的行为，如DLAs，中性ISM测量，以及盘和晕星，发现每种类型的天体似乎都位于图的特定区域。我们的样本显示了一个陡峭的C/O与O/H的斜率相对于其他样本，这表明，大质量恒星的贡献更多的生产C比N在较高的金属丰度，只有在物体的大质量恒星是众多的;否则，中等质量的恒星占主导地位的C和N的生产。
The supernova explosion increases cosmic ray and x-ray fluxes in the surrounding interstellar medium. Cosmic ray particles and x-ray radiation penetrate nearby molecular clouds and affect the chemical and thermal evolution of the gas. Here we study chemical changes in the dense molecular gas influenced by a sudden increase of the ionization rate that may be caused by the supernova explosion. At the cloud core density $2 \times 10^4$ cm$^{-3}$, the H atom abundance reaches the equilibrium value at about $3 \times 10^4$ yr after the change in irradiation conditions. The response time of abundanc…
Cold cores are an early step of star formation, characterized by densities > 10$^4$ cm$^{-3}$, low temperatures (< 15 K), and very low external UV radiation. We investigate the physico-chemical processes at play to tracing the origin of molecules that are predominantly formed via reactions on dust grain surfaces. We observed the cold core LDN 429-C with the NOEMA interferometer and the IRAM 30m single dish telescope in order to obtain the gas-phase abundances of key species, including CO and CH$_3$OH. Comparing the observed gas phase of methanol to its solid phase previously observed with Spit…
We present the first identification in interstellar space of the propargyl radical (CH2CCH). This species was observed in the cold dark cloud TMC-1 using the Yebes 40m telescope. The six strongest hyperfine components of the 2,0,2-1,0,1 rotational transition, lying at 37.46~GHz, were detected with signal-to-noise ratios in the range 4.6-12.3 sigma. We derive a column density of 8.7e13 cm-2 for CH2CCH, which translates to a fractional abundance relative to H2 of 8.7e-9. This radical has a similar abundance to methyl acetylene, with an abundance ratio CH2CCH/CH3CCH close to one. The propargyl ra…
In this paper, we present preliminary results illustrating the effect of cosmic rays on solid-phase chemistry in models of both TMC-1 and several sources with physical conditions identical to TMC-1 except for hypothetically enhanced ionization rates. Using a recent theory for the addition of cosmic ray-induced reactions to astrochemical models, we calculated the radiochemical yields, called $G$ values, for the primary dust grain ice-mantle constituents. We show that the inclusion of this non-thermal chemistry can lead to the formation of complex organic molecules from simpler ice-mantle consti…
Abundance of chemical elements in the stars provides important clues regarding galaxy formation. The most powerful diagnostics is the relative abundance of α-elements (O, Mg, Si, S, Ca, and Ti) with respect to iron (Fe), [α/Fe], each of which is produced by different kinds of supernovae. The existence of two distinct groups of stars in the solar neighbourhood, one with high [α/Fe] and another with low [α/Fe], suggests that the stars in the solar vicinity have two different origins. However, the specific mechanism of the realization of this bimodality is unknown. Here, we show that the cold flo…
(Abridged) The aim of this study is to investigate the chemical evolution from the prestellar phase to the formation of the disk, and to determine the impact that the chemical composition of the cold and dense core has on the final composition of the disk. We performed 3D nonideal magneto-hydrodynamic (MHD) simulations of a dense core collapse using the adaptive-mesh-refinement RAMSES code. For each particle ending in the young rotationally supported disk, we ran chemical simulations with the three-phase gas-grain chemistry code Nautilus. Two different sets of initial abundances, which are cha…
The Next-Generation Very Large Array (ngVLA) will revolutionize our understanding of the Early Universe by tracing the coldest phase of molecular gas -the raw ingredient for star formation- in the most distant galaxies and galaxy-clusters. The km-scale core of the ngVLA will be densely packed with antennas, making it a prime instrument for imaging low-surface-brightness emission from large-scale molecular gas in the high-z circum- and inter-galactic medium (CGM/IGM). Recent studies indicate that large amounts of cold molecular gas are hiding in the 10s-100 kpc environments of distant galaxies,…
Aims. We study the effect of large scale dynamics on the molecular composition of the dense interstellar medium during the transition between diffuse to dense clouds. Methods. We followed the formation of dense clouds (on sub-parsec scales) through the dynamics of the interstellar medium at galac- tic scales. We used results from smoothed particle hydrodynamics (SPH) simulations from which we extracted physical parameters that are used as inputs for our full gas-grain chemical model. In these simulations, the evolution of the interstellar matter is followed for ~50 Myr. The warm low-density in…
Hyperfine excitation of N$_2$H$^+$ by H$_2$: Toward a revision of N$_2$H$^+$ abundance in cold molecular clouds
星际云中分子发射光谱的建模需要碰撞速率系数的知识。在通常观察到的物种中，N $_2$ H $^+$是特别感兴趣的，因为它被证明是冷分子云物理条件的良好探针。因此，我们计算了N $_2$ H $^+$（X $^1Σ^+$）的超精细结构分辨激发速率系数H $_2(j=0)$，在冷星际介质中最丰富的碰撞伙伴。计算是基于一个新的势能面，从高度相关的{ \it从头计算}计算。计算了温度从5 K到70 K范围内第一超精细能级之间的态-态速率系数。通过与以前发表的N $_2$ H $^+$ -He速率系数的比较，我们发现了显着的差异，不能由一个简单的缩放关系再现。作为第一个应用程序，我们还进行了辐射转移计算，典型的冷分子云的物理条件。我们发现，模拟线强度显着增加时，使用新的H $_2$率系数，通过与基于He率系数的预测相比。特别是，我们重新审视了在LDN 183核心的N $_2$ H $^+$发射的建模，使用新的碰撞数据，并发现，所有三个密度，气体动力学温度和N $_2$ H $^+$丰度必须进行修改。
Methanol and complex organic molecules have been found in cold starless cores, where a standard warm-up scenario would not work because of the absence of heat sources. A recent chemical model attributed the presence of methanol and large organics to the efficient chemical desorption and a class of neutral-neutral reactions that proceed fast at low temperatures in the gas phase. The model calls for a high abundance of methanol ice at the edge of the CO freeze-out zone in cold cloud cores. We performed medium resolution spectroscopy toward 3 field stars behind the starless core L1544 at 3 $μ$m t…
Aims: Interstellar molecules form early in the evolutionary sequence of interstellar material that eventually forms stars and planets. To understand this evolutionary sequence, it is important to characterize the chemical composition of its first steps. Methods: In this paper, we present the result of a 2 and 3 mm survey of five cold clumps identified by the Planck mission. We carried out a radiative transfer analysis on the detected lines in order to put some constraints on the physical conditions within the cores and on the molecular column densities. We also performed chemical models to rep…
We devise a physical model of formation and distribution of molecular gas clouds in galaxies. We use the model to predict the intensities of rotational transition lines of carbon monoxide (CO) and the molecular hydrogen (H$_{\rm 2}$) abundance. Using the outputs of Illustris-TNG cosmological simulations, we populate molecular gas clouds of unresolved sizes in individual simulated galaxies, where the effect of the interstellar radiation field with dust attenuation is also taken into account. We then use the publicly available code DESPOTIC to compute the CO line luminosities and H$_{\rm 2}$ den…
Partitioning of elemental nitrogen in star-forming regions is not well constrained. Most nitrogen is expected to be partitioned among atomic nitrogen, molecular nitrogen (N2), and icy N-bearing molecules, such as ammonia (NH3) and N2. Atomic nitrogen is not directly observable in the cold gas. In this paper, we propose an indirect way to constrain the amount of atomic nitrogen in the cold gas of star-forming clouds, via deuteration in ammonia ice, the [ND2H/NH2D]/[NH2D/NH3] ratio. Using gas-ice astrochemical simulations, we show that if atomic nitrogen remains as the primary reservoir of nitro…
Chemical evolution of the Universe at 0.7 < z < 1.6 derived from abundance diagnostics of the broad-line region of quasars
我们提出了一个分析Mg II $\lambda2798$和Fe II紫外线发射线的档案斯隆数字巡天（SDSS）类星体，探索诊断镁铁丰度比在宽线区域云。我们的样本由17,432个类星体组成，这些类星体是从SDSS数据发布7中选出的，红移范围为$0.72 < z < 1.63$。Mg II等效宽度（EW）和爱丁顿比之间存在较强的正相关关系，而Fe II EW和爱丁顿比之间仅存在较弱的正相关关系。为了调查镁II和铁II发射线的这些不同的行为的起源，我们已经进行了光电离计算，使用云代码，其中考虑了最近的混响映射研究的约束。计算结果表明，Mg Ⅱ和Fe Ⅱ的发射谱线出现在光电离云的不同区域，它们与爱丁顿比的EW相关可以通过改变云的气体密度来解释。这些结果表明，Mg II/Fe II通量比，这已被用作一阶代理的Mg/Fe丰度比的化学演化研究类星体发射线，在很大程度上取决于云气体密度。通过校正这种密度依赖性，我们提出了新的诊断的Mg/Fe丰度比的宽线区域云。比较得出的Mg/Fe丰度比与化学演化模型，我们认为，$α$富集的质量损失，从贫金属的中等质量的恒星发生在$z\sim2$或更早。
We perform a stacking analysis of the neutral \nad\,$λλ$5889,5895\,Å ISM doublet using the SDSS DR7 spectroscopic data set to probe the prevalence and characteristics of cold (T\,$\lesssim$\,10$^{4}$\,K) galactic-scale gas flows in local (0.025$\leqslant z\leqslant$0.1) inactive and AGN-host galaxies across the SFR-M$_{*}$ plane. We find low-velocity outflows to be prevalent in regions of high SFRs and stellar masses (10 $\lesssim$log M$_{*}$/M$_{\odot}$ $\lesssim$ 11.5), however we do not find any detections in the low mass (log M$_{*}$/M$_{\odot}$ $\lesssim$ 10) regime. We also find tentativ…
Extragalactic Planetary Nebulae (xPNe). Chemical evolution and assembly histories of nearby galaxies using Oxygen and Argon abundances. From the local universe to cosmic dawn
Studies measuring the chemical abundances of the neutral gas in star-forming galaxies (SFGs) require ionization correction factors (ICFs) to accurately measure their metal contents. In the work presented here we calculate newly improved ICFs for a sample of SFGs. These new corrections include both the contaminating ionized gas along the line of sight (ICF$_{\rm ionized}$) and unaccounted higher ionization stages in the neutral gas (ICF$_{\rm neutral}$). We make use of recently acquired spectroscopic observations taken with the Cosmic Origins Spectrograph (COS) on board Hubble to measure column…
We report the first detailed measurement of the shape of the CO luminosity function at high redshift, based on $>$320 hr of the NSF's Karl G. Jansky Very Large Array (VLA) observations over an area of $\sim$60 arcmin$^2$ taken as part of the CO Luminosity Density at High Redshift (COLDz) survey. COLDz "blindly" selects galaxies based on their cold gas content through CO($J$=1$\to$0) emission at $z$$\sim$2-3 and CO($J$=2$\to$1) at $z$$\sim$5-7 down to a CO luminosity limit of log($L'_{\rm CO}$/K km s$^{-1}$ pc$^2$)$\simeq$9.5. We find that the characteristic luminosity and bright end of the CO …
The extreme astrophysical processes and conditions that characterize the early Universe are expected to result in young galaxies that are dynamically different from those observed today. This is because the strong effects associated with galaxy mergers and supernova explosions would lead to most young star-forming galaxies being dynamically hot, chaotic and strongly unstable. Here we report the presence of a dynamically cold, but highly star-forming, rotating disk in a galaxy at redshift ($z$) 4.2, when the Universe was just 1.4 billion years old. Galaxy SPT-S J041839-4751.9 is strongly gravit…
The cold interstellar medium (ISM) plays a central role in the galaxy evolution process. It is the reservoir that fuels galaxy growth via star formation, the repository of material formed by these stars, and a sensitive tracer of internal and external processes that affect entire galaxies. Consequently, significant efforts have gone into systematic surveys of the cold ISM of the galaxies in the local Universe. This review discusses the resulting network of scaling relations connecting the atomic and molecular gas masses of galaxies with their other global properties (stellar masses, morphologi…
Abundance Profiling of Extremely Metal-Poor Stars and Supernova Properties in the Early Universe
在大爆炸核合成之后，宇宙中第一次重元素富集是由一颗人口（Pop）III恒星（Pop III SN）的超新星（SN）爆炸造成的。从Pop III SNe产生的元素丰度比记录在极贫金属（EMP）星的丰度模式中。对越来越多的EMP星的观测使得有可能在统计上限制Pop III SNe的爆炸特性。我们提出了Pop III SN模型，其核合成结果很好地再现了48个贫金属星的丰度模式，如[Fe/H] $\mathrel{\rlap{\lower 4pt \hbox{$ \sim $}}\raise 1pt \hbox {$ < $}}-3.5$。然后我们推导出EMP星的丰度比与Pop III SNe的某些爆炸性质之间的关系：较高的[（C+N）/Fe]和[（C+N）/Mg]比值分别对应于较小的喷射Fe质量和较大的致密残余质量。利用这些关系，EMP星的丰度比的分布被转换为Pop III SNe的爆炸性质的分布。与现代SNe爆炸性质的分布进行了比较：Pop III SNe的Fe质量分布与现代SNe的Fe质量分布有相同的峰值，但有一个延伸到$\sim10^{-2}-10^{-5}M_\odot$的尾部，Pop III SNe致密残骸的质量分布与现代恒星质量黑洞的质量分布一样宽。我们的研究结果表明，正在进行的和未来的EMP恒星调查和随后的高色散光谱观测，澄清在早期宇宙的波普III SNe的性质获得的大样本…
We investigate the dependence of elemental abundances on physical constants, and the implications this has for the distribution of complex life for various proposed habitability criteria. We consider three main sources of abundance variation: differing supernova rates, alpha burning in massive stars, and isotopic stability, and how each affects the metal-to-rock ratio and the abundances of carbon, oxygen, nitrogen, phosphorus, sulfur, silicon, magnesium, and iron. Our analysis leads to several predictions for which habitability criteria are correct by determining which ones make our observatio…
Gaseous CO Abundance---An Evolutionary Tracer for Molecular Clouds
普朗克冷团是研究分子云演化的初始条件最有希望的对象之一。本文利用普朗克卫星观测的尘埃释放数据和紫金山天文台13.7 m望远镜观测的$^{12}$ CO/ $^{13}$ CO（1-0）谱线数据，研究了早期冷芯（ECC）样品中674个团簇的CO丰度、CO贫化和CO到H的$_{2}$转换因子。CO丰度的中值和平均值分别为0.89 $\times10^{-4}$和1.28 $\times10^{-4}$。CO消耗因子的平均值和中位数分别为1.7和0.9。整个样本的$X_{CO-to-H_{2}}$的中值为$2.8\times10^{20}$ cm $^{-2}$ K $^{-1}$ km $^{-1}$ s。CO丰度、CO贫化因子和CO-H $_{2}$转换因子与其他物理参数（如尘埃温度、尘埃发射率光谱指数、柱密度、体积密度和发光质量比）有很强的（反）相关性。总之，气态CO丰度可以用作分子云演化的示踪剂。
We describe the CO Luminosity Density at High-z (COLDz) survey, the first spectral line deep field targeting CO(1-0) emission from galaxies at $z=1.95-2.85$ and CO(2-1) at $z=4.91-6.70$. The main goal of COLDz is to constrain the cosmic density of molecular gas at the peak epoch of cosmic star formation. By targeting both a wide ($\sim$51 arcmin$^2$) and a deep area ($\sim$9 arcmin$^2$), the survey is designed to robustly constrain the bright end and the characteristic luminosity of the CO(1-0) luminosity function. An extensive analysis of the reliability of our line candidates, and new techni…
