We performed correlation analyses between the $^{12}$CO and $^{13}$CO $J=$1-0 line intensities in order to derive the variability of the CO-to-H$_2$ conversion factor ($X_{\rm CO, iso}$) in the central molecular zone (CMZ) of our Galaxy. New high-resolution $X_{\rm CO, iso}$ maps at a resolution of $\sim 30$" and the longitude-velocity diagram (LVD) at resolution $\sim 30$" $ \times\ 2$ km s$^{-1}$ are presented using the $^{12}$CO and $^{13}$CO archival survey data obtained by the Nobeyama 45 m telescope. We revealed the variation of $X_{\rm CO, iso}$ in the CMZ within the range of $X_{\rm CO, iso} \sim (0.2-1.3) \times 10^{20}\ {\rm cm^{-2}\ (K\ km\ s^{-1})^{-1}}$, if we assume the normalization value of $0.59 \times 10^{20}\ {\rm cm^{-2}\ (K\ km\ s^{-1})^{-1}}$. The mean value is obtained as $X_{\rm CO, iso} = (0.48 \pm 0.15) \times 10^{20}\ {\rm cm^{-2}\ (K\ km\ s^{-1})^{-1}}$ in the CMZ of our Galaxy.
We present simultaneous measurements of emission from dust continuum at 230 GHz and the J=2-1 $^{12}$CO, $^{13}$CO and C$^{18}$O isotopologues at $\sim$ 15 pc resolution from individual Giant Molecular Clouds (GMCs) in the Andromeda galaxy (M31). These observations were obtained in an ongoing survey of this galaxy being conducted with the Submillimeter Array (SMA). Initial results describing the continuum and $^{12}$CO emission were published earlier. Here we primarily analyze the observations of $^{13}$CO and C$^{18}$O emission and compare them to the measurements of dust continuum and $^{12}…
Statistical Properties of Molecular Clouds in the Milky Way: Insights from Three-Isotopologue CO Observations of the MWISP Project
Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台）；State Key Laboratory of Radio Astronomy and Technology, Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台射电天文与技术国家重点实验室）
Trace the Self-Gravitating Gas Using CO Isotopologues
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；University of Chinese Academy of Sciences（中国科学院大学）；Max Planck Institute for Astronomy（马克斯·普朗克天文学研究所）；School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）；Key Laboratory of Modern Astronomy and Astrophysics, Ministry of Education（教育部现代天文与天体物理重点实验室）；School of Physical Science and Technology, Guangxi University（广西大学物理科学与工程学院）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学天文与空间科学研究院）；New Cornerstone Science Laboratory, Department of Astronomy, Tsinghua University（清华大学天文系新基石科学实验室）
We present models of CO(1-0) emission from Milky Way-mass galaxies at redshift zero in the FIRE-2 cosmological zoom-in simulations. We calculate the molecular abundances by post-processing the simulations with an equilibrium chemistry solver while accounting for the effects of local sources, and determine the emergent CO(1-0) emission using a line radiative transfer code. We find that the results depend strongly on the shielding length assumed, which in our models sets the attenuation of the incident UV radiation field. At the resolution of these simulations, commonly used choices for the shie…
The observed star formation rate of the Milky Way can be explained by applying a metallicity-dependent factor to convert CO luminosity to molecular gas mass and a star formation efficiency per free-fall time that depends on the virial parameter of a molecular cloud. These procedures also predict the trend of star formation rate surface density with Galactocentric radius. The efficiency per free-fall time variation with virial parameter plays the major role in bringing theory into agreement with observations for the total star formation rate, while the metallicity dependence of the CO luminosit…
The Three-mm Ultimate Mopra Milky Way Survey. III. Data Release 6, An Atlas of Physical Conditions, Global Mass Conversion Laws, and 3D Physical Architecture of the Molecular ISM in the Fourth Quadrant
A new catalog of homogenised absorption line indices for Milky Way globular clusters from high-resolution integrated spectroscopy
我们对24个银河系球状星团进行了综合光谱分析。从一个核心半径的光谱观察到每个集群与高波长分辨率~2.0 A的FWHM。结合Puzia et al.（2002）和Schiavon et al.（2005）的两个现有数据集，我们构建了一个包含53个银河系球状星团的Lick光谱指数的大型数据库，这些球状星团具有广泛的金属丰度范围，-2.4 < [Fe/H] < 0.1，以及各种水平分支形态。经验指数到金属丰度的转换关系提供了20舔指数用于推导金属丰度的远程，未解决的恒星系统。
The Milky Way Joins the Extragalactic World: I. PHANGS
The University of Texas at Austin（德克萨斯大学奥斯汀分校）；INAF-IAPS（意大利国家天体物理研究所空间天文与物理学中心）；INAF, Sezione di Lecce（意大利国家天体物理研究所莱切分部）；University of Kentucky（肯塔基大学）；National Astronomical Observatory of Japan（日本国立天文台）；Max Planck Institute for Radio Astronomy（马克斯·普朗克射电天文研究所）；The Ohio State University（俄亥俄州立大学）
We present polynomial conversions between each of 11 different strong line gas-phase metallicity calibrations, each based on $\sim$ 1.1 million star-forming spaxels in the public Sloan Digital Sky Survey (SDSS) Data Release 15 (DR15) Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. For this sample, which is $\sim$ 20 times larger than previous works, we present 5th order polynomial fits for each of 110 possible calibration conversions, for both Small Magellanic Cloud (SMC)-type and Milky Way (MW)-type dust corrections. The typical $2σ$ scatter around our polynomial fits is 0…
Carbon monoxide (CO) provides crucial information about the molecular gas properties of galaxies. While $^{12}$CO has been targeted extensively, isotopologues such as $^{13}$CO have the advantage of being less optically thick and observations have recently become accessible across full galaxy discs. We present a comprehensive new dataset of $^{13}$CO(1-0) observations with the IRAM 30-m telescope of the full discs of 9 nearby spiral galaxies from the EMPIRE survey at a spatial resolution of $\sim$1.5kpc. $^{13}$CO(1-0) is mapped out to $0.7-1r_{25}$ and detected at high signal-to-noise through…
To trace chemical evolution in a prototypical starburst environment, we spatially resolve the carbon and oxygen isotope ratios across the central molecular zone (full size ~$\sim 600$ pc) in the nearby starburst galaxy NGC 253. We imaged the emission of the optically thin isotopologues $^{13}$CO, C$^{18}$O, C$^{17}$O, $^{13}$C$^{18}$O at a spatial resolution $\sim50$ pc, comparable to the typical size of giant molecular associations. Optical depth effects and contamination of $^{13}$C$^{18}$O by C$_4$H is discussed and accounted for to derive column densities. This is the first extragalactic d…
The molecular clouds in a section of the third Galactic quadrant: observational properties and chemical abundance ratio between CO and its isotopologues
基于 MWISP 对第三银河象限 7069 个分子云的 CO 同位素观测，本文量化了角面积、流量与丰度比关系，发现 LTE 下相关比值近似恒定，并指出其受化学分馏、选择性离解和自屏蔽共同控制。
The CO-to-H$_2$ conversion factor ($α_\rm{CO}$) is critical to studying molecular gas and star formation in galaxies. The value of $α_\rm{CO}$ has been found to vary within and between galaxies, but the specific environmental conditions that cause these variations are not fully understood. Previous observations on $\sim$kpc scales revealed low values of $α_\rm{CO}$ in the centers of some barred spiral galaxies, including NGC 3351. We present new ALMA Band 3, 6, and 7 observations of $^{12}$CO, $^{13}$CO, and C$^{18}$O lines on 100 pc scales in the inner $\sim$2 kpc of NGC 3351. Using multi-lin…
CO-dark gas and molecular filaments in Milky Way type galaxies
我们使用移动网格代码AREPO耦合到一个含时的化学网络来研究分子气体在模拟的螺旋星系中的形成和破坏。这使我们能够确定CO排放不跟踪的气体的特性。我们的极高分辨率AREPO模拟使我们能够捕捉光盘的化学演变，而无需求助于参数化的“聚集因子”。我们通过我们模拟的盘星系计算了H2和CO柱密度，并估算了CO发射和CO-H2转换因子。我们发现，在类似的条件下，在当地的星际介质，大约42%的总分子质量应该在CO暗区，在合理的协议与观测估计。这部分是几乎不敏感的CO积分强度阈值用于区分CO亮和CO暗气体，只要这个阈值是小于10 K km/s。CO暗分子气体主要存在于极长（>100 pc）的细丝中，这些细丝被星系切变拉伸在旋臂之间。只有这些细丝的中心在CO中是明亮的，这表明在银河系中观察到的非连续分子云可能只是更大结构的一小部分。CO暗分子气体主要存在于部分分子相中，占总圆盘质量预算的很大一部分。在环境紫外线场较高或表面密度较低的模拟中，暗气体比例较高，这意味着具有这些条件的外部星系可能具有更大比例的暗气体。
We present ALMA data on the 3mm continuum emission, CO isotopologues (12CO, 13CO, C18O), and high-density molecular tracers (HCN, HCO+, HNC, HNCO, CS, CN, and CH3OH) in NGC4526. These data enable a detailed study of the physical properties of the molecular gas in a longtime resident of the Virgo Cluster; comparisons to more commonly-studied spiral galaxies offer intriguing hints into the processing of molecular gas in the cluster environment. Many molecular line ratios in NGC4526, along with our inferred abundances and CO/H2 conversion factors, are similar to those found in nearby spirals. One…
We utilize a modified astrochemistry code which includes cosmic ray attenuation in-situ to quantify the impact of different cosmic-ray models on the CO-to-H$_2$ and CI-to-H$_2$ conversion factors, $X_{\rm CO}$ and $X_{\rm CI}$, respectively. We consider the impact of cosmic rays accelerated by accretion shocks, and show that clouds with star formation efficiencies greater than 2\% have $X_{\rm CO} = (2.5 \pm 1)\times10^{20}$ cm$^{-2}$(K km s$^{-1}$)$^{-1}$, consistent with Milky Way observations. We find that changing the cosmic ray ionization rate from external sources from the canonical $ζ\a…
We construct a semi-analytic model to study the effect of far-ultraviolet (FUV) radiation on gas chemistry from embedded protostars. We use the Protostellar Luminosity Function (PLF) formalism of Offner & McKee (2011) to calculate the total, FUV, and ionizing cluster luminosity for various protostellar accretion histories and cluster sizes. We compare the model predictions with surveys of Gould Belt star-forming regions and find the Tapered Turbulent Core model matches best the mean luminosities and the spread in the data. We combine the cluster model with the photo-dissociation region astroch…
Being one of the most abundant atomic/molecular species observed in dense molecular gas, atomic carbon ($\mathrm{C}^0$) is a potential good tracer of molecular gas mass in many chemical/physical environments, though the $\mathrm{C^0}$ abundance variation outside the Galactic disk region is yet to be fully known. This paper presents a wide-field 500 GHz [CI] map of the Galactic central molecular zone (CMZ) obtained with the ASTE 10-m telescope. Principal component analysis and non-LTE multi-transition analysis have shown that the [CI] emission predominantly originates from the low-excitation ga…
We present new ${ }^{12}$CO(J=1-0) observations of Henize 2-10, a blue compact dwarf galaxy about 8.7 Mpc away, taken with the Atacama Large Millimeter Array. These are the highest spatial and spectral resolution observations, to date, of the molecular gas in this starburst galaxy. We measure a molecular mass of $1.2\times10^8 M_\odot$ in Henize 2-10, and most of the molecular gas is contained within a region having a size of about 310 pc. We use the CPROPS algorithm to identify 119 resolved giant molecular clouds distributed throughout the galaxy, and the molecular gas contained within these …
We present the results of $^{12}$CO($J$=1-0) mosaicing observations of the cD galaxy NGC 1316 at kpc-resolution performed with the Morita Array of the Atacama Large Millimeter/submillimeter Array (ALMA). We reveal the detailed distribution of the molecular gas in the central region for the first time: a shell structure in the northwest, a barely resolved blob in the southeast of the center and some clumps between them. The total molecular gas mass obtained with a standard Milky-Way CO-to-H$_2$ conversion factor is $(5.62 \pm 0.53)\times10^8$ M$_\odot$, which is consistent with previous studies…
We present $^{12}$CO, $^{13}$CO, and C$^{18}$O data as the next major release for the CHaMP project, an unbiased sample of Galactic molecular clouds in $l$ = 280$^{\circ}$-300$^{\circ}$. From a radiative transfer analysis, we self-consistently compute 3D cubes of optical depth, excitation temperature, and column density for $\sim$300 massive clumps, and update the $I_{\rm CO}$-dependent CO$\rightarrow$H$_2$ conversion law of Barnes et al (2015). For $N$ $\propto$ $I^p$, we find $p$ = 1.92$\pm$0.05 for the velocity-resolved conversion law aggregated over all clumps. A practical, integrated conv…
