A gas and dust rich giant elliptical galaxy in the ISOPHOT serendipity survey

We present a multi-wavelength study of the unusual galaxy ISOSS J 15079+7247. With a bolometric luminosity of LFIR ∼ 2 × 1012 L⊙ this object is one of the most luminous galaxies detected by the 170 μm ISOPHOT Serendipity Survey (ISOSS). We have obtained 1.2 mm continuum and CO (1-0) line observations, optical spectra and deep R-band images of the system. The CO emission originates from a giant elliptical galaxy at redshift z = 0.2136, yielding a molecular gas mass of 2.9 × 1010 M⊙. The high gas mass favors the picture that the dust emission is associated with the elliptical galaxy. The nature of the ultraluminous IR emission can be explained by an opaque, hidden starrburst in the center of the elliptical. The huge dust mass of 5 × 108 M⊙ corresponds to a visual extinction of Av ∼ 1000 mag. This is consistent with the non-detection of any optical signatures of a strong starburst in ISOSS J 15079+7247 and the strength of non-thermal radio continuum emission.