Nuclear Bar Catalyzed Star Formation: 13CO, C18O, and Molecular Gas Properties in the Nucleus of Maffei 2
Nuclear Bar Catalyzed Star Formation: 13CO, C18O, and Molecular Gas Properties in the Nucleus of Maffei 2
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DOI：
10.1086/524932
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发表时间：
2007-10
期刊：
影响因子：
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通讯作者：
D. Meier;J. Turner;R. Hurt
中科院分区：
文献类型：
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作者：
D. Meier;J. Turner;R. Hurt
我们给出了马菲2中心CO、其同位素和HCN的~3″分辨率图。利用欧文斯谷射电天文台（OVRO）和伯克利-伊利诺伊-马里兰州协会（比马）射电台阵观测到了12 CO、13 CO、C 18 O和HCN的J = 1-0转动谱线，以及13 CO和C 18 O的J = 2-1转动谱线。较低的不透明度的CO同位素给出了更可靠的约束H2柱密度和物理条件比光学厚12 CO。同位素的J = 2-1/1-0线比限制了大部分分子气体起源于低激发的亚热气体。根据大速度梯度（LVG）模拟，我们推断中心巨分子云（GMC）的nH 2为102.75 cm−3，Tk为30 K。连续排放在3.4，2.7，和1.4毫米的映射，以确定H II区域和灰尘的分布和数量。从C18 O和1.4 mm尘埃连续通量导出的柱密度表明，标准的银河系转换因子高估了马菲2中心分子气体的数量，高估了2-4倍。气体形态和位置-速度图中清晰的“π”表明分子气体轨道在核（~220 pc）棒的势内。核酒吧是不同的酒吧，管理大规模形态的马菲2。由于潮汐效应，原子核中的巨分子云是非球形的，并且有很大的线宽。致密气体和星星的形成都集中在核棒的x1-x2轨道交叉点处，这表明星暴是动态触发的。
We present ~3″ resolution maps of CO, its isotopologues, and HCN from in the center of Maffei 2. The J = 1–0 rotational lines of 12CO,13CO, C18O and HCN, and the J = 2–1 lines of 13CO and C18O were observed with the Owens Valley Radio Observatory (OVRO) and Berkeley-Illinois-Maryland Association (BIMA) arrays. The lower opacity CO isotopologues give more reliable constraints on H2 column densities and physical conditions than optically thick 12CO. The J = 2–1/1–0 line ratios of the isotopologues constrain the bulk of the molecular gas to originate in low-excitation, subthermal gas. From large velocity gradient (LVG) modeling, we infer that the central giant molecular clouds (GMCs) have nH2 ∼ 102.75 cm−3 and Tk ∼ 30 K. Continuum emission at 3.4, 2.7, and 1.4 mm was mapped to determine the distribution and amount of H II regions and dust. Column densities derived from C18O and 1.4 mm dust continuum fluxes indicate the standard Galactic conversion factor overestimates the amount of molecular gas in the center of Maffei 2 by factors of ~2-4. Gas morphology and the clear “parallelogram” in the position-velocity diagram shows that molecular gas orbits within the potential of a nuclear (~220 pc) bar. The nuclear bar is distinct from the bar that governs the large-scale morphology of Maffei 2. Giant molecular clouds in the nucleus are nonspherical and have large line widths, due to tidal effects. Dense gas and star formation are concentrated at the sites of the x1-x2-orbit intersections of the nuclear bar, suggesting that the starburst is dynamically triggered.