![]() We observe differences in the flux ratios of PAHs in the stacked spectra of IR-luminous galaxies with redshift or luminosity, which cannot be attributed to extinction effects since both the depth and the profile of the silicate absorption feature at 9.7 μm remain the same at z < 1 and z ⩾ 1. Spectral stacking leads to the detection of weak features such as the 3.3 μm PAH, the H 2 0–0 S(1) and S(3) lines, and the line. Moreover, an increase in the AGN activity is observed with increasing z and luminosity, based on the decreasing EW of PAHs and the increasing / ratio. Several intermediate and high z starbursts have higher PAH EW than local ULIRGs, which could be indicative of an elevated star formation activity. For this classification, we used the equivalent width (EW) of the 11.3 μm polycyclic aromatic hydrocarbon (PAH) feature. ![]() The number of sources with spectra that are dominated by an active galactic nucleus (AGN) continuum is 49, while 39 sources have strong, star formation related features. ![]() It primarily comprises ultraluminous IR galaxies (ULIRGs) at z ≳ 1 and luminous IR galaxies at z < 1, as estimated from their monochromatic rest-frame 14 μm luminosities. ![]() The sample is selected to be brighter than ∼0.9 mJy at 24 μm and it has a redshift distribution in the range, with a peak at z = 1. We present a catalog of mid-infrared (MIR) spectra of 150 infrared (IR) luminous galaxies in the Spitzer extragalactic first look survey obtained with the IR spectrograph on board the Spitzer Space Telescope. ![]()
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