![]() ![]() ![]() Spectra are classified into five mid-infrared classes, ranging from active galactic nuclei (class-4) and star-forming nuclei (class-3), to transition class-2 (with PAHs) and class-1 (no-PAHs), to passively evolving nuclei (class-0).Ī demographic study of mid-infrared spectra shows that Es are significantly more passive than S0s: 46 |$^$| per cent have PAH ratios typical of star-forming galaxies. For each galaxy, we provide the fully reduced and calibrated spectrum and the intensity of nebular and molecular emission lines as well as of the polycyclic aromatic hydrocarbons (PAHs) after a template spectrum of a passively evolving ETG has been subtracted. We recover 91 spectra out of 363 galaxies classified as ETGs in the catalogue: 56 E (E0–E6), 8 mixed E/S0+S0/E and 27 S0 (both normal and barred – SB0) plus mixed types SB0/Sa+SB0/SBa. From the Spitzer Heritage Archive we extract ETGs in the Revised Shapley–Ames Catalog of Bright Galaxies having an IRS SL and/or LL spectrum. Es and S0s), in order to build a reference sample in the mid-infrared window. We produce an atlas of homogeneously reduced and calibrated low-resolution IRS spectra of the nuclear regions of nearby early-type galaxies (ETGs, i.e. ![]()
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