在$z\lesssim 0.5$星形成星系的AKARI中红外无狭缝光谱巡天
AKARI mid-infrared slitless spectroscopic survey of star-forming galaxies at $z\lesssim 0.5$
摘要：
深红外巡天观测揭示了许多红移z~<2的强恒星形成星系。它们的MIR通量是由连续谱和PAH排放特征的组合产生的。PAH特征可以支配总MIR通量，但在没有光谱学的情况下难以测量。我们的目标是通过使用MIR波段的盲谱巡天来研究恒星形成星系，以了解它们的恒星形成率（SFR）和比SFR（z~=0.5）的演化，特别关注它们的PAH性质。利用AKARI红外相机（IRC）对北极附近的9 μ m通量选择源（> 0.3mJy）进行了5- 13 μ m的低分辨率（R~=50）无狭缝光谱测量。在用IRC测光法去除11个活动星系核候选星系后，我们确定了48个PAH星系，它们在z<0.5时具有PAH 6.2，7.7和8.6 μ m的特征。利用CFHT和AKARI/IRC成像技术，得到了0.37- 18 μ m的静止坐标系光学-MIR光谱能量分布（SED），并结合PAH光谱进行了分析。我们通过使用7.7um PAH特征与SED的3.5um恒星分量的光度比来定义PAH增强。所有PAH星系的静止坐标系SED具有普遍的形状与恒星和7.7微米的颠簸，除了PAH增强显着变化的PAH光度的函数。在z~>0.35处，我们发现了一个PAH增强的星系群，它的SEDs和光度都是典型的亮红外星系。它们在高光度下表现出特别大的PAH增强，这意味着它们是具有升高的特定SFR的活跃的恒星形成星系。我们的复合星爆模型，结合了一个非常年轻的，光学非常厚的星爆与一个非常古老的人口可以成功地再现他们的SED特性，虽然我们不能确认这个光学厚组件从我们的光谱分析。
英文摘要：
Deep MIR surveys have revealed numerous strongly star-forming galaxies at redshift z~<2. Their MIR fluxes are produced by a combination of continuum and PAH emission features. The PAH features can dominate the total MIR flux, but are difficult to measure without spectroscopy. We aim to study star-forming galaxies by using a blind spectroscopic survey at MIR wavelengths to understand evolution of their star formation rate (SFR) and specific SFR up to z~=0.5, by paying particular attention to their PAH properties. We conducted a low-resolution (R~=50) slitless spectroscopic survey at 5-13um of 9um flux-selected sources (>0.3 mJy) around the North Ecliptic Pole with the Infrared Camera (IRC) onboard AKARI. After removing 11 AGN candidates by using the IRC photometry, we identified 48 PAH galaxies with PAH 6.2, 7.7, and 8.6um features at z<0.5. The rest-frame optical-MIR spectral energy distributions (SEDs) based on CFHT and AKARI/IRC imaging covering 0.37-18um were produced, and analysed in conjunction with the PAH spectroscopy. We defined the PAH enhancement by using the luminosity ratio of the 7.7um PAH feature over the 3.5um stellar component of the SEDs. The rest-frame SEDs of all PAH galaxies have a universal shape with stellar and 7.7um bumps, except that the PAH enhancement significantly varies as a function of the PAH luminosities. We identified a PAH-enhanced population at z~>0.35, whose SEDs and luminosities are typical of luminous infrared galaxies. They show particularly larger PAH enhancement at high luminosity, implying that they are vigorous star-forming galaxies with elevated specific SFR. Our composite starburst model that combines a very young and optically very thick starburst with a very old population can successfully reproduce most of their SED characteristics, although we could not confirm this optically thick component from our spectral analysis.
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