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arXiv 1607.08023astro-ph.GA
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CO近场Galerkin多线成像（COMING）：I.棒旋星系NGC 2903中分子气体的物理性质

CO Multi-line Imaging of Nearby Galaxies (COMING): I. Physical properties of molecular gas in the barred spiral galaxy NGC 2903

Kazuyuki Muraoka, Kazuo Sorai, Nario Kuno, Naomasa Nakai, Hiroyuki Nakanishi, Miho Takeda, Kazuki Yanagitani, Hiroyuki Kaneko, Yusuke Miyamoto, Nozomi Kishida, … 展开作者

Kazuyuki Muraoka, Kazuo Sorai, Nario Kuno, Naomasa Nakai, Hiroyuki Nakanishi, Miho Takeda, Kazuki Yanagitani, Hiroyuki Kaneko, Yusuke Miyamoto, Nozomi Kishida, Takuya Hatakeyama, Michiko Umei, Takahiro Tanaka, Yuto Tomiyasu, Chey Saita, Saeko Ueno, Naoko Matsumoto, Dragan Salak, Kana Morokuma-Matsui

备注：
26 pages, 11 figures, 3 tables, accepted for publication in PASJ
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摘要：

利用野边山射电天文台45米望远镜，在有效角分辨率为20”（或870 pc）的条件下，对附近的棒旋星系NGC 2903的整个星系盘（8'× 5'或20.8 kpc × 13.0 kpc）进行了12 CO、13 CO和C18 O分子J=1-0发射的同步测绘。我们在NGC 2903的盘面上探测到了~（12）CO（J=1-0）辐射。此外，在中心和杆端发现了显著的13 CO（J=1-0）发射，而我们没有检测到任何显著的C18 O（J=1-0）发射。为了提高CO排放的信噪比，获得准确的12 CO（J=2-1）/12 CO（J=1-0）谱线比，（$R_{2-1/1-0}$）和13 CO（J=1-0）/12 CO（J=1-0）（$R_{13/12}$），我们对我们的12 CO（J=1-0），13 CO（J=1-0），和NGC 2903的9个代表性区域的速度轴对准的存档12 CO（J=2-1）光谱。我们成功地获得了三条CO谱线的叠加谱，并且可以测量所有区域具有高显著性的平均$R_{2-1/1-0}$和$R_{13/12}$。我们发现，$R_{2-1/1-0}$和$R_{13/12}$都根据区域而不同，这反映了分子气体物理性质的差异;即，密度（$n_{\rm H_2}$）和动力学温度（$T_K$）。在大速度梯度近似下，用$R_{2-1/1-0}$和$R_{13/12}$确定了$n_{\rm H_2}$和$T_K$。导出的$n_{\rm H_2}$范围为约1000 cm $^{-3}$（在棒、棒端和螺旋臂中）至3700 cm $^{-3}$（在中心处），导出的$T_K$范围为10 K（在棒和螺旋臂中）至30 K（在中心处）。我们研究了恒星形成效率（SFE）对$n_{\rm H_2}$和$T_K$的依赖性，发现SFE和$n_{\rm H_2}$之间呈正相关，最小二乘幂律拟合$R^2$的相关系数为0.50。这表明，分子气体密度控制的空间变化的SFE。

英文摘要：

We present simultaneous mappings of J=1-0 emission of 12CO, 13CO, and C18O molecules toward the whole disk (8' x 5' or 20.8 kpc x 13.0 kpc) of the nearby barred spiral galaxy NGC 2903 with the Nobeyama Radio Observatory 45-m telescope at an effective angular resolution of 20" (or 870 pc). We detected 12CO(J=1-0) emission over the disk of NGC 2903. In addition, significant 13CO(J=1-0) emission was found at the center and bar-ends, whereas we could not detect any significant C18O(J=1-0) emission. In order to improve the signal-to-noise ratio of CO emission and to obtain accurate line ratios of 12CO(J=2-1)/12CO(J=1-0) ($R_{2-1/1-0}$) and 13CO(J=1-0)/12CO(J=1-0) ($R_{13/12}$), we performed the stacking analysis for our 12CO(J=1-0), 13CO(J=1-0), and archival 12CO(J=2-1) spectra with velocity-axis alignment in nine representative regions of NGC 2903. We successfully obtained the stacked spectra of the three CO lines, and could measure averaged $R_{2-1/1-0}$ and $R_{13/12}$ with high significance for all the regions. We found that both $R_{2-1/1-0}$ and $R_{13/12}$ differ according to the regions, which reflects the difference in the physical properties of molecular gas; i.e., density ($n_{\rm H_2}$) and kinetic temperature ($T_K$). We determined $n_{\rm H_2}$ and $T_K$ using $R_{2-1/1-0}$ and $R_{13/12}$ based on the large velocity gradient approximation. The derived $n_{\rm H_2}$ ranges from ~ 1000 cm$^{-3}$ (in the bar, bar-ends, and spiral arms) to 3700 cm$^{-3}$ (at the center) and the derived $T_K$ ranges from 10 K (in the bar and spiral arms) to 30 K (at the center). We examined the dependence of star formation efficiencies (SFEs) on $n_{\rm H_2}$ and $T_K$, and found the positive correlation between SFE and $n_{\rm H_2}$ with the correlation coefficient for the least-square power-law fit $R^2$ of 0.50. This suggests that molecular gas density governs the spatial variations in SFEs.

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