arXiv 0707.26362007-07-18astro-ph

NGC 6946中的CO（1-0）、CO（2-1）和中性气体：晚型富气螺旋星系中的分子气体

CO(1-0), CO(2-1) and Neutral Gas in NGC 6946: Molecular Gas in a Late-Type, Gas Rich, Spiral Galaxy

Lucian Crosthwaite, Jean Turner

DOI：: 10.1086/521645

摘要：

我们呈现了NGC 6946的10' X 10'区域的CO（1-0）和CO（2-1）排放的“On The Fly”图。使用我们的CO地图和VLA HI观测档案，我们创建了NGC 6946的总气体表面密度图Sigma_gas。主要的分子内部气体盘平滑地过渡到原子外部气体盘，在R = 3.5'（6 kpc）处具有相等的原子和分子气体表面密度。我们估计H2的总质量为3 × 10^9 Mo，大约是星际氢气质量的1/3，大约是我们假设的距离为6 Mpc时星系动力学质量的2%。CO（2-1）/CO（1-0）线比率的值在0.35至2的范围内;地图的50%被非常高的比率（>1）的气体覆盖。非常高的比率主要来自臂间区域，似乎表明存在广泛分布的光学薄气体。恒星形成示踪剂与总中性气体盘的相关性比与分子气体本身的相关性更好，这意味着SFR与Sigma_gas成正比。使用NGC 6946的100 FIR和21 cm连续谱作为恒星形成示踪剂，我们得到了2.8 Gyr的气体消耗时标，这在整个磁盘上相对均匀。核心的高恒星形成率似乎是由于分子气体的大量积累，而不是恒星形成效率的大幅增加。NGC 6946的HI外臂（R > 10 kpc）的中面气压接近我们观测到的CO盘径向极限（10 kpc）的值。如果中平面气压是形成分子云的一个因素，那么这些外部HI气体臂应该包含我们看不到的分子气体，因为它们超出了我们的检测极限。

英文摘要：

We present "On The Fly" maps of the CO(1-0) and CO(2-1) emission covering a 10' X 10' region of the NGC 6946. Using our CO maps and archival VLA HI observations we create a total gas surface density map, Sigma_gas, for NGC 6946. The predominantly molecular inner gas disk transitions smoothly into an atomic outer gas disk, with equivalent atomic and molecular gas surface densities at R = 3.5' (6 kpc). We estimate that the total H2 mass is 3 X 10^9 Mo, roughly 1/3 of the interstellar hydrogen gas mass, and about 2% of the dynamical mass of the galaxy at our assumed distance of 6 Mpc. The value of the CO(2-1)/CO(1-0) line ratio ranges from 0.35 to 2; 50% of the map is covered by very high ratio, >1, gas. The very high ratios are predominantly from interarm regions and appear to indicate the presence of wide-spread optically thin gas. Star formation tracers are better correlated with the total neutral gas disk than with the molecular gas by itself implying SFR is proportional to Sigma_gas. Using the 100 FIR and 21 cm continuum from NGC 6946 as star formation tracers, we arrive at a gas consumption timescale of 2.8 Gyr, which is relatively uniform across the disk. The high star formation rate at the nucleus appears to be due to a large accumulation of molecular gas rather than a large increase in the star formation efficiency. The mid-plane gas pressure in the outer (R > 10 kpc) HI arms of NGC 6946 is close to the value at the radial limit (10 kpc) of our observed CO disk. If the mid-plane gas pressure is a factor for the formation of molecular clouds, these outer HI gas arms should contain molecular gas which we do not see because they are beyond our detection limit.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

摘要：

英文摘要：

相关论文