Spatially resolved physical conditions of molecular gas and potential star formation tracers in M 83, revealed by the Herschel SPIRE FTS
Spatially resolved physical conditions of molecular gas and potential star formation tracers in M 83, revealed by the Herschel SPIRE FTS
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DOI：
10.1051/0004-6361/201423847
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发表时间：
2014-12
影响因子：
6.5
通讯作者：
R. Wu;S. Madden;F. Galliano;C. Wilson;J. Kamenetzky;Min-Young Lee;M. Schirm;S. Hony;V. Lebouteiller;L. Spinoglio;D. Cormier;J. Glenn;P. Maloney;M. Pereira-Santaella;A. R'emy-Ruyer;M. Baes;A. Boselli;F. Bournaud;I. D. Looze;T. Hughes;P. Panuzzo;N. Rangwala
中科院分区：
文献类型：
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作者：
R. Wu;S. Madden;F. Galliano;C. Wilson;J. Kamenetzky;Min-Young Lee;M. Schirm;S. Hony;V. Lebouteiller;L. Spinoglio;D. Cormier;J. Glenn;P. Maloney;M. Pereira-Santaella;A. R'emy-Ruyer;M. Baes;A. Boselli;F. Bournaud;I. D. Looze;T. Hughes;P. Panuzzo;N. Rangwala
我们研究了m83中分子和电离气体的物理性质，以及它们与恒星形成和尘埃性质的关系，基于亚毫米成像光谱，从星爆核周围的中心3.5 '（直径约4 kpc）。观测使用了赫歇尔空间天文台上的光谱和光度成像接收器（SPIRE）的傅立叶变换光谱仪（FTS）。新观测到的光谱线包括[CI] 370 μm， [CI] 609 μm, [NII] 205 μm， CO从J = 4−3跃迁到J = 13−12。结合先前观测到的J = 1−0到J = 3−2跃迁，利用非局部热平衡（non-LTE）辐射传输模型RADEX，将CO谱线能量分布转化为空间分解的物理参数，即CO柱密度N（CO）和分子气体热压Pth。结果表明，[NII] 205 μm的空间分辨强度与恒星形成速率（SFR）的表面密度ΣSFR之间存在一定的关系。与超发光红外星系（ulrgs）的综合性质相比，这一关系呈现出不同的斜率，因为[NII] 205 μm分布比SFR更宽。另一方面，空间分辨率[CI] 370 μm与ΣSFR呈线性关系，可能是一种很好的SFR示踪剂。与来自宽频带图像的尘埃特性相比，我们发现CO在J = 1−0跃迁中的发射率与星际辐射场（ISRF）的平均强度⟨U⟩之间存在正趋势。这一趋势意味着当⟨U⟩增加时CO-to-H2转换因子XCO的减少。我们估计m83中心2 kpc内的气体-尘埃质量比为77±33，中心4 kpc内的气体-尘埃质量比为93±19，这意味着m83观测区域内的星系尘埃-金属质量比。估计m83核的气体耗尽时间为1.13±0.6 Gyr，比文献中发现的附近螺旋星系的值（~2.35 Gyr）短，很可能是由于年轻的核恒星爆发。Pth和⟨U⟩产生的辐射压力Prad之间的线性关系被发现为Pth≈30 Prad，这表明单独的ISRF不足以维持观察到的CO跃迁。Pth的空间分布揭示了一个压力梯度，这与观测到的星暴活动的传播和射电源（可能是背景）的对齐一致。我们发现分子气体体积密度的偏心峰（来自光核）与相对芳香特征强度的最小值吻合得很好，表明它们的载流子可能被破坏。我们得出的结论是，观测到的CO跃迁很可能与机械加热过程有关，而机械加热过程与最近的核恒星爆发直接或间接相关。
We investigate the physical properties of the molecular and ionized gas, and their relationship to the star formation and dust properties in M 83, based on submillimeter imaging spectroscopy from within the central 3.5′ (~4 kpc in diameter) around the starburst nucleus. The observations use the Fourier Transform Spectrometer (FTS) of the Spectral and Photometric Imaging REceiver (SPIRE) onboard the Herschel Space Observatory. The newly observed spectral lines include [CI] 370 μm, [CI] 609 μm, [NII] 205 μm, and CO transitions from J = 4−3 to J = 13−12. Combined with previously observed J = 1−0 to J = 3−2 transitions, the CO spectral line energy distributions are translated to spatially resolved physical parameters, column density of CO, N(CO), and molecular gas thermal pressure, Pth, with a non-local thermal equilibrium (non-LTE) radiative transfer model, RADEX. Our results show that there is a relationship between the spatially resolved intensities of [NII] 205 μm and the surface density of the star formation rate (SFR), ΣSFR. This relation, when compared to integrated properties of ultra-luminous infrared galaxies (ULIRGs), exhibits a different slope, because the [NII] 205 μm distribution is more extended than the SFR. The spatially resolved [CI] 370 μm, on the other hand, shows a generally linear relationship with ΣSFR and can potentially be a good SFR tracer. Compared with the dust properties derived from broad-band images, we find a positive trend between the emissivity of CO in the J = 1−0 transition with the average intensity of interstellar radiation field (ISRF), ⟨ U ⟩. This trend implies a decrease in the CO-to-H2 conversion factor, XCO, when ⟨ U ⟩ increases. We estimate the gas-to-dust mass ratios to be 77 ± 33 within the central 2 kpc and 93 ± 19 within the central 4 kpc of M 83, which implies a Galactic dust-to-metal mass ratio within the observed region of M 83. The estimated gas-depletion time for the M 83 nucleus is 1.13 ± 0.6 Gyr, which is shorter than the values for nearby spiral galaxies found in the literature (~2.35 Gyr), most likely due to the young nuclear starbursts. A linear relationship between Pth and the radiation pressure generated by ⟨ U ⟩, Prad, is found to be Pth ≈ 30 Prad, which signals that the ISRF alone is insufficient to sustain the observed CO transitions. The spatial distribution of Pth reveals a pressure gradient, which coincides with the observed propagationof starburst activities and the alignment of (possibly background) radio sources. We discover that the off-centered (from the optical nucleus) peak of the molecular gas volume density coincides well with a minimum in the relative aromatic feature strength, indicating a possible destruction of their carriers. We conclude that the observed CO transitions are most likely associated with mechanical heating processes that are directly or indirectly related to very recent nuclear starbursts.