论文标题
向下但没有：在剥离的处女座簇早期型Galaxy NGC4526中的分子气体的特性
Down but not out: properties of the molecular gas in the stripped Virgo Cluster early-type galaxy NGC4526
论文作者
论文摘要
我们介绍了3mm连续发射，CO同位素（12CO，13CO，C18O）和高密度分子示踪剂（HCN，HCO+，HNC，HNC，HNCO，CS，CN和CH3OH）的ALMA数据。这些数据使得在处女座群集的长期居民中对分子气体的物理特性进行了详细研究；与更常见的螺旋星系的比较为群集环境中分子气体的处理提供了有趣的提示。 NGC4526中的许多分子线比，以及我们推断的丰度和CO/H2转化因子，与附近螺旋中的分子比率相似。一个惊人的例外是非常低的观察到的12CO/13CO（1-0）线比，$ 3.4 \ pm0.3 $，对于螺旋的螺旋形，它的螺旋形异常低，尽管不是处女座群集早期型星系。我们使用一些存档（2-1）数据对CO同位素学进行了辐射转移模型，并使用Markov Chain Monte Carlo Techniques使用贝叶斯分析来推断共发气体的物理性质。 We find surprisingly low [12CO/13CO] abundance ratios of $7.8^{+2.7}_{-1.5}$ and $6.5^{+3.0}_{-1.3}$ at radii of 0.4 kpc and 1 kpc.高密度示踪剂HCN，HCO+，HNC，CS和CN发射的发射也相对较明亮，CN在NGC4526的内部中异常厚。这些特征暗示，在群集环境中的加工可能已经去除了银河系相对弥漫的大部分，光学上更薄的分子气及其原子气。角动量转移到周围的簇内培养基中也可能导致磁盘收缩，从而放大了径向梯度，例如我们在[13CO/C18O]中发现的。更详细的化学演化建模将很有趣，以探索不寻常的[12CO/13CO]丰度比完全是一种环境效应，或者它是否也反映了这个早期型星系中相对较旧的恒星种群。
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 striking exception is the very low observed 12CO/13CO(1-0) line ratio, $3.4\pm0.3$, which is unusually low for spirals though not for Virgo Cluster early-type galaxies. We carry out radiative transfer modeling of the CO isotopologues with some archival (2-1) data, and we use Bayesian analysis with Markov chain Monte Carlo techniques to infer the physical properties of the CO-emitting gas. We find surprisingly low [12CO/13CO] abundance ratios of $7.8^{+2.7}_{-1.5}$ and $6.5^{+3.0}_{-1.3}$ at radii of 0.4 kpc and 1 kpc. The emission from the high-density tracers HCN, HCO+, HNC, CS and CN is also relatively bright, and CN is unusually optically thick in the inner parts of NGC4526. These features hint that processing in the cluster environment may have removed much of the galaxy's relatively diffuse, optically thinner molecular gas along with its atomic gas. Angular momentum transfer to the surrounding intracluster medium may also have caused contraction of the disk, magnifying radial gradients such as we find in [13CO/C18O]. More detailed chemical evolution modeling would be interesting in order to explore whether the unusual [12CO/13CO] abundance ratio is entirely an environmental effect or whether it also reflects the relatively old stellar population in this early-type galaxy.
