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Astron. Astrophys. 359, 900-906 (2000)
ISO observations of a sample of 60 µm peaker galaxies
R.J. Laureijs 1,
D. Watson 2,
L. Metcalfe 1,
B. McBreen 2,
B. O'Halloran 2,
J. Clavel 1,
K. Leech 1,
P. Gallais 1,
P. Barr 1,
M. Delaney 3,
L. Hanlon 2 and
F. Quilligan 2
1 ISO Data Centre, Astrophysics Division, Space Science Department of ESA, Villafranca del Castillo, P.O. Box 50727, 28080 Madrid, Spain
2 Department of Physics, University College, Dublin 4, Ireland
3 Stockholm Observatory, 133 36 Saltsjöbaden, Sweden
Received 2 December 1999 / Accepted 22 April 2000
Abstract
The sample of IRAS galaxies with spectral energy distributions that
peak near 60 µm are called Sixty Micron Peakers (SMPs or
60PKs). Their generally peculiar and amorphous morphologies, hot dust
and lack of a cirrus component have been interpreted as being
indicative of a recent interaction/merger event. Mid-infrared spectra
of eight SMPs, obtained with ISOPHOT-S in the
![[FORMULA]](img1.gif)
2-11 µm 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
6.2 µm, 7.7 µm and 8.6 µm is
ubiquitous in the spectra. The PHOT-S spectrum of the H2 galaxy
IRAS 23446+1519 exhibits a bright 11.04 µm line and an
8.6 µm feature of comparable size to its
7.7 µm feature. [S IV] emission at
10.5 µm was detected in three of four H2 galaxies and in
one Seyfert 2 galaxy. The ratio of the 7.7 µm PAH feature
to the continuum at 7.7 µm (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 µm to the flux at
60 µm is found, similar to that found in ultraluminous
infrared galaxies. Silicate absorption at approximately
9.7 µm 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.
Key words: ISM: dust,
extinction 
ISM: molecules
galaxies: ISM
galaxies:
Seyfert
galaxies:
starburst
infrared: galaxies
Send offprint requests to: D. Watson (dwatson@bermuda.ucd.ie)
Contents
- 1. Introduction
- 2. Observations and data reduction
- 3. Results and discussion
- 3.1. H2 galaxies
- 3.2. Sy2s
- 4. Separation of starbursts and AGN
- 5. Conclusions
- References
© European Southern Observatory (ESO) 2000
Online publication: July 13, 2000
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