DENSE MOLECULAR GAS EXCITATION AT HIGH REDSHIFT: DETECTION OF HCO+(J = 4 → 3) EMISSION IN THE CLOVERLEAF QUASAR
DENSE MOLECULAR GAS EXCITATION AT HIGH REDSHIFT: DETECTION OF HCO+(J = 4 → 3) EMISSION IN THE CLOVERLEAF QUASAR
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DOI：
10.1088/0004-637x/726/1/50
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发表时间：
2010-11
期刊：
影响因子：
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通讯作者：
D. Riechers;F. Walter;C. Carilli;P. Cox;A. Weiss;F. Bertoldi;K. Menten
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作者：
D. Riechers;F. Walter;C. Carilli;P. Cox;A. Weiss;F. Bertoldi;K. Menten
我们报道了用IRAM高原de Bure干涉仪在z = 2.56的三叶草类星体中探测到HCO+（J = 4→3）的发射。HCO+发射是一个类似HCN的恒星形成标志，可以在恒星形成的分子云内追踪到致密的分子氢气（n(H2)≃105 cm−3）。我们得到了K km s−1 pc2的透镜校正HCO+（J = 4→3）线光度，对应于HCO+（J = 1→0）光度的48%和CO（J = 3→2）光度的约4%。因此，在J = 4→3跃迁中，HCO+的激发明显是亚热的。对HCO+线辐射传输的模拟表明，HCO+辐射来自一个物理性质与CO线辐射相当的区域，但气体密度高2倍。这表明，HCO+和CO谱线都可以追踪到恒星形成活跃的温暖、密集的分子气体。HCO+谱线的宽度只有CO谱线的2/3，这可能表明密度最大的气体在空间上更集中。与z = 3.91类星体APM 08279+5255相比，三叶草星云中的致密气体激发与纯粹的碰撞一致，而不是被辐射过程增强。因此，三叶草星云中致密气体成分的物理性质与附近星暴星系的核心一致。这表明，在像三叶草这样的早期宇宙时期，活跃的星系核-星暴系统中密集的恒星形成气体的条件主要受星暴本身的影响，而不是中心活跃的黑洞。
We report the detection of HCO+(J = 4 → 3) emission in the Cloverleaf Quasar at z = 2.56, using the IRAM Plateau de Bure Interferometer. HCO+ emission is a star formation indicator similar to HCN, tracing dense molecular hydrogen gas (n(H2) ≃ 105 cm−3) within star-forming molecular clouds. We derive a lensing-corrected HCO+(J = 4 → 3) line luminosity of K km s−1 pc2, which corresponds to only 48% of the HCO+(J = 1 → 0) luminosity, and ≲4% of the CO(J = 3 → 2) luminosity. The HCO+ excitation thus is clearly subthermal in the J = 4 → 3 transition. Modeling of the HCO+ line radiative transfer suggests that the HCO+ emission emerges from a region with physical properties comparable to that exhibiting the CO line emission, but 2× higher gas density. This suggests that both HCO+ and CO lines trace the warm, dense molecular gas where star formation actively takes place. The HCO+ lines have only ∼2/3 the width of the CO lines, which may suggest that the densest gas is more spatially concentrated. In contrast to the z = 3.91 quasar APM 08279+5255, the dense gas excitation in the Cloverleaf is consistent with being purely collisional, rather than being enhanced by radiative processes. Thus, the physical properties of the dense gas component in the Cloverleaf are consistent with those in the nuclei of nearby starburst galaxies. This suggests that the conditions in the dense, star-forming gas in active galactic nucleus–starburst systems at early cosmic times like the Cloverleaf are primarily affected by the starburst itself, rather than the central active black hole.