Evidence of boosted 13CO/12CO ratio in early-type galaxies in dense environments
Katherine Alatalo, Alison F. Crocker, Susanne Aalto, Timothy A. Davis, Kristina Nyland, Martin Bureau, Pierre-Alain Duc, Davor Krajnovic, Lisa M. Young
We present observations of $^{13}$CO(1-0) in 17 Combined Array for Research in Millimeter Astronomy (CARMA) Atlas3D early-type galaxies (ETGs), obtained simultaneously with $^{12}$CO(1-0) observations. The $^{13}$CO in six ETGs is sufficiently bright to create images. In these 6 sources, we do not detect any significant radial gradient in the $^{13}$CO/$^{12}$CO ratio between the nucleus and the outlying molecular gas. Using the $^{12}$CO channel maps as 3D masks to stack the $^{13}$CO emission, we are able to detect 15/17 galaxies to $>3σ$ (and 12/17 to at least 5$σ$) significance in a spatially integrated manner. Overall, ETGs show a wide distribution of $^{13}$CO/$^{12}$CO ratios, but Virgo cluster and group galaxies preferentially show a $^{13}$CO/$^{12}$CO ratio about 2 times larger than field galaxies, although this could also be due to a mass dependence, or the CO spatial extent ($R_{\rm CO}/R_{\rm e}$). ETGs whose gas has a morphologically-settled appearance also show boosted $^{13}$CO/$^{12}$CO ratios. We hypothesize that this variation could be caused by (i) the extra enrichment of gas from molecular reprocessing occurring in low-mass stars (boosting the abundance of $^{13}$C to $^{12}$C in the absence of external gas accretion), (ii) much higher pressure being exerted on the midplane gas (by the intracluster medium) in the cluster environment than in isolated galaxies, or (iii) all but the densest molecular gas clumps being stripped as the galaxies fall into the cluster. Further observations of $^{13}$CO in dense environments, particularly of spirals, as well as studies of other isotopologues, should be able to distinguish between these hypotheses.
Very Compact Dense Galaxy Overdensity with δ ~ 130 Identified at z ~ 8: Implications for Early Protocluster and Cluster-Core Formation
我们报告了在$z\sim8$上首次发现的致密致密星系超密度，被命名为A2744 z 8 OD。A2744 z 8 OD由八个$Y$ -dropout星系组成，位于Abell 2744后面，最初由哈勃前沿场研究确定。然而，到目前为止，还没有研究得出结构形成的基本物理量或与理论模型进行比较。我们从八个像A2744 z 8 OD数据一样深的哈勃遗留图像的场数据中获得了$z\sim8$的辍学星系的均匀样本。利用该样本，我们发现A2744 z 8 OD的星系表面过密度值非常高，即$δ\simeq130$，其中$δ$是由$6"$（$\simeq30$ physical kpc）半径的小圆圈内的过密度定义的。由于迄今为止尚未报告高$z$过密度的如此大的$δ$值，因此A2744 z 8 OD是一种与先前高$z$过密度研究中发现的系统明显不同的系统。在Henriques et al.（2015）的星系+结构形成模型中，存在一个非常相似的过密度模型Modelz 8 OD，它由$6"$半径圆中$z\sim8$处的8个模型脱落星系组成。Modelz 8 OD是今天的$10^{14}M_\odot$星系团的前身，七个Modelz 8 OD星系中有一半以上合并成星系团中最亮的星系团（BCG）。如果Modelz 8 OD是A2744 z 8 OD的对应物，模型表明A2744 z 8 OD可能是今天的$10^{1…
Early phases of star formation with SKAO: synchrotron emission from dense starless cores in molecular clouds
Observatoire de Paris, Université PSL, Sorbonne Université（巴黎天文台，巴黎文理研究大学，索邦大学）；Sapienza University of Rome（罗马智慧大学）；Institute of Structure of Matter (ISM-CNR), Consiglio Nazionale delle Ricerche（物质结构研究所（ISM-CNR），意大利国家研究委员会）；Niels Bohr Institute, University of Copenhagen（尼尔斯·玻尔研究所，哥本哈根大学）；Haystack Observatory, Massachusetts Institute of Technology（海斯塔克天文台，麻省理工学院）
Dust Production in a Thin Dense Shell in Supernovae with Early Circumstellar Interactions
在超新星（SNe）中，光变曲线显示出喷出物和星周物质（CSM）之间强烈和早期相互作用的证据，估计新尘埃的形成发生在前向（FS）和反向激波（RS）之间的致密气体壳层中。在这项研究中，首次模拟了这种致密壳层中粉尘形成的机制。考虑到喷出物质量的变化和爆炸前的质量损失率，一组9种情况下，考虑到不同的相互作用，在这样的SNe报告的性质。对于一个单一的主序星质量，喷出物质量的变化表现为恒星的H壳层质量的变化，由于爆炸前的质量损失而损失。我们发现，在致密壳层的尘埃质量范围在10 $^{-3}$ M $_{\odot}$和0.8 M $_{\odot}$，由富O和富C的颗粒，其相对比例由相互作用的性质决定。冲击波后气体中尘埃形成的特征是逐渐产生的速率，大部分在$^{-1}$每天10 $^{-6}$到10 $^{-3}$ M $_{\odot}$之间，这种速率可能在爆炸后持续十年。更高的质量损失率导致更大的尘埃质量，而较小的喷出物质量（较小的剩余H-壳层）增加了这种SNe中的尘埃生产效率。正如我们的计算所示，在RS后面形成的尘埃不受FS或RS的破坏，因此可能比喷出物中形成的尘埃有更大比例存活下来。
