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亮红外星系核和恒星形成区的高空间分辨率中红外光谱研究

A High Spatial Resolution Mid-Infrared Spectroscopic Study of the Nuclei and Star-Forming Regions in Luminous Infrared Galaxies

T. Diaz-Santos, A. Alonso-Herrero, L. Colina, C. Packham, N. A. Levenson, M. Pereira-Santaella, P. F. Roche, C. M. Telesco

摘要:

利用T-ReCS在Gemini South望远镜上对4个亮红外星系(LIRGs)的核和恒星形成区进行了高空间(衍射极限)分辨率(~0.3”)的中红外(MIR)光谱研究。我们调查的空间变化中看到的N-波段光谱的LIRGs的尺度上的~100 pc的功能,这使我们能够分离的AGN发射的恒星形成(SF)。我们比较我们的双子座T-ReCS核和积分光谱的LIRGs与斯皮策IRS。9.7um硅酸盐的吸收特征在LIRGs的核中比在周围区域中弱。这可能是由于要么cluerous或紧凑的环境,中央AGN或年轻,核星暴。我们发现[NeII]光度面密度与LIRG恒星形成区的Pa-α光度面密度紧密直接相关(斜率为1.00+-0.02)。尽管11.3 um PAH特征也显示了Pa-α的趋势,但这并不常见于所有区域。我们还发现[NeII] \Pa -α比率不依赖于Pa-α等效宽度(EW),即,的年龄的电离恒星星族,这表明,在这里探测的尺度上,[NeII]发射线是一个很好的示踪剂的SF活动的LIRGs。另一方面,11.3 um PAH \Pa -α比率随着Pa-α EW值的减小(年龄的增加)而增加,这表明11.3 um PAH特征也可以由比Pa-α发射更老的恒星激发。额外的高空间分辨率的观测是必不可少的调查,在统计的方式,在最小尺度上的本地LIRGs的恒星形成,并最终探测它们是否共享相同的物理性质的高z LIRGs,ULIRGs和submillimiter星系。

英文摘要:

We present a high spatial (diffraction-limited) resolution (~0.3") mid-infrared (MIR) spectroscopic study of the nuclei and star-forming regions of 4 local luminous infrared galaxies (LIRGs) using T-ReCS on the Gemini South telescope. We investigate the spatial variations of the features seen in the N-band spectra of LIRGs on scales of ~100 pc, which allow us to separate the AGN emission from that of the star formation (SF). We compare our Gemini T-ReCS nuclear and integrated spectra of LIRGs with those obtained with Spitzer IRS. The 9.7um silicate absorption feature is weaker in the nuclei of the LIRGs than in the surrounding regions. This is probably due to the either clumpy or compact environment of the central AGN or young, nuclear starburst. We find that the [NeII] luminosity surface density is tightly and directly correlated with that of Pa-alpha for the LIRG star-forming regions (slope of 1.00+-0.02). Although the 11.3um PAH feature shows also a trend with Pa-alpha, this is not common for all the regions. We also find that the [NeII]\Pa-alpha ratio does not depend on the Pa-alpha equivalent width (EW), i.e., on the age of the ionizing stellar populations, suggesting that, on the scales probed here, the [NeII] emission line is a good tracer of the SF activity in LIRGs. On the other hand, the 11.3um PAH\Pa-alpha ratio increases for smaller values of the Pa-alpha EW (increasing ages), indicating that the 11.3um PAH feature can also be excited by older stars than those responsible for the Pa-alpha emission. Additional high spatial resolution observations are essential to investigate, in a statistical way, the star formation in local LIRGs at the smallest scales and to probe ultimately whether they share the same physical properties as high-z LIRGs, ULIRGs and submillimiter galaxies.

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