ISO observations of a sample of 60 micron peaker galaxies

The sample of IRAS galaxies with spectral energy distributions that peak near 60 m are called Sixty Micron Peakers (SMPs or 60PKs). Their generally peculiar and amor- phous morphologies, hot dust and lack of a cirrus component have been interpreted as being indicative of a recent interac- tion/merger event. Mid-infrared spectra of eight SMPs, obtained with ISOPHOT-S in the 2-11 m band are presented. Four of the observed sources are H II region-like (H2) galaxies, three are Seyfert 2 and one is unclassified. Emission attributed to Polycyclic Aromatic Hydrocarbons (PAHs) at 6.2m, 7.7 m and 8.6 m is ubiquitous in the spectra. The PHOT-S spectrum of the H2 galaxy IRAS 23446+1519 exhibits a bright 11.04m line and an 8.6 m feature of comparable size to its 7.7 m fea- ture. (S IV) emission at 10.5 m was detected in three of four H2 galaxies and in one Seyfert 2 galaxy. The ratio of the 7.7 m PAH feature to the continuum at 7.7 m (PAH L/C) divides the eight SMPs at a ratio greater than 0.8 for H2 and less than 0.8 for Seyfert galaxies. An anti-correlation between PAH L/C and the ratio of the continuum flux at 5.9 m to the flux at 60 mi s found, similar to that found in ultraluminous infrared galaxies. Silicate absorption at approximately 9.7 m was observed in the Seyfert 2 galaxy, IRAS 04385-0828 and in IRAS 03344-2103. The previously unclassified SMP galaxy IRAS 03344-2103 is probably a Seyfert 2.