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arXiv 0903.4017astro-ph.COastro-ph.GA
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亚毫米波星系的中红外光谱:大质量高红移星系中扩展的恒星形成

Mid-Infrared Spectroscopy of Submillimeter Galaxies: Extended Star Formation in Massive High Redshift Galaxies

Karín Menéndez-Delmestre, Andrew W. Blain, Ian Smail, Dave M. Alexander, Scott C. Chapman, Lee Armus, Dave Frayer, Rob J. Ivison, Harry Teplitz

摘要:

利用Spitzer红外光谱仪研究了24个亚毫米波半导体镓的中红外光谱性质和能量学性质。这是斯皮策IRS观测到的最大的SMG样本,涵盖了z ~ 0.65-3.2的红移范围内的SMG的放射性识别种群的全部性质。我们在80%以上的样本中观察到多环芳烃(PAHs)的广泛排放特征。我们发现,中等的中红外光谱可以很好地用一个具有额外幂律的星爆分量Fnu ~ nu^-2来描述,这可能代表活动星系核对辐射热光度的贡献小于32%。因此,我们的研究结果证实,星暴活动占主导地位的太阳黑子的热光度。我们发现SMG在9.7um处的硅酸盐吸收比本地ULIRG弱。我们还发现SMG中的6.2um PAH发射(相对于7.7um PAH特征)比本地核星爆更强,这可能是由于SMG视线沿线的冰消光较低。这表明SMG的连续谱和多环芳烃发射区域比局部星爆和类似发光的低红移ULIRG更不模糊。我们解释这些结果作为证据的冷,暖尘埃在SMG更广泛的分布相比,更紧凑的发射区域在本地ULIRGs和星爆。总之,这些结果表明,SMG不是简单的高红移本地ULIRG或核星暴的类似物,而是它们似乎有类似于在z~0的不太极端的恒星形成环境中看到的恒星形成-这表明它们的强烈活动分布在比本地ULIRG中的~1-kpc核爆发大得多的区域。

英文摘要:

We used the Spitzer Infrared Spectrograph (IRS) to study the mid-IR properties and investigate the energetics of 24 Submillimeter Galaxies (SMGs). This is the largest sample of SMGs observed with Spitzer IRS and covers the full extent of properties of the radio-identified population of SMGs in the redshift range of z ~ 0.65-3.2. We observe broad emission features from Polycyclic Aromatic Hydrocarbons (PAHs) in more than 80% of our sample. We find that the median mid-IR spectrum is well described by a starburst component with an additional power law, Fnu ~ nu^-2, likely representing a < 32% AGN contribution to the bolometric luminosity. Our results thus confirm that starburst activity dominates the bolometric luminosity in SMGs. We find that SMGs show weaker silicate absorption at 9.7um than local ULIRGs. We also find stronger 6.2um PAH emission in SMGs (relative to the 7.7um PAH feature) than in local nuclear starbursts, which may be attributed to lower extinction by ice along the line of sight to SMGs. This suggests that the continuum and PAH emitting regions of SMGs are less obscured than in local starbursts and similarly luminous low-redshift ULIRGs. We interpret these results as evidence for a more extended distribution of cool and warm dust in SMGs compared to the more compact emitting regions in local ULIRGs and starbursts. Together these results suggest that SMGs are not simple high-redshift analogs of local ULIRGs or nuclear starbursts, but instead they appear to have star formation which resembles that seen in less-extreme star-forming environments at z~0 -- suggesting their intense activity is distributed across a far larger region than the ~1-kpc nuclear bursts in local ULIRGs.

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