WISE J044232.92+322734.9: A star-forming galaxy at redshift 1.1 seen through a Galactic dust clump?

Abstract

Context. Physically unassociated background or foreground objects seen towards submillimetre sources are potential contaminants of both the studies of young stellar objects embedded in Galactic dust clumps and multiwavelength counterparts of submillimetre galaxies (SMGs). Aims. We aim to search for and characterise the properties of a potential extragalactic object seen in projection towards a Galactic dust clump. Methods. We employed the near-infrared (3.4 μm and 4.6 μm) and mid-infrared (12 μm and 22 μm) data from the Wide-field Infrared Survey Explorer (WISE) and the submillimetre data from the Planck satellite. Results. We uncovered a source, namely the WISE source J044232.92+322734.9 (hereafter J044232.92), which is detected in the W1–W3 bands of WISE, but undetected at 22 μm (W4), and whose WISE infrared (IR) colours suggest that it is a star-forming galaxy (SFG). This source is seen in projection towards the Planck-detected dust clump PGCC G169.20-8.96, which likely belongs to the Taurus-Auriga cloud complex, at a distance of 140 pc. We used the MAGPHYS+photo-z spectral energy distribution (SED) code to derive the photometric redshift and physical properties of J044232.92. The redshift was derived to be zphot = 1.132−0.165+0.280, while, for example, the stellar mass, IR (8–1000 μm) luminosity, and star formation rate were derived to be M⋆ = 4.6−2.5+4.7 × 1011 M⊙, LIR = 2.8−1.5+5.7 × 1012 L⊙, and SFR = 191−146+580 M⊙ yr−1 (or 281−155+569 M⊙ yr−1 when estimated from the IR luminosity). The derived value of LIR suggests that J044232.92 could be an ultraluminous IR galaxy, and we found that it is consistent with a main sequence SFG at a redshift of 1.132. Conclusions. The estimated physical properties of J044232.92 are comparable to those of SMGs, except that the derived stellar mass of J044232.92 appears somewhat higher (by a factor of 4–5) than the average stellar masses of SMGs. However, the stellar mass difference could just reflect the poorly sampled SED in the ultraviolet, optical, and near-IR regimes. Indeed, the SED of J044232.92 could not be well constrained using the currently available data (WISE only), and hence the derived redshift of the source and its physical properties should be taken as preliminary estimates. Further observations, in particular high-resolution (sub-)millimetre and radio continuum imaging, are needed to better constrain the redshift and physical properties of J044232.92 and to see if the source really is a galaxy seen through a Galactic dust clump, in particular an SMG population member at z ∼ 1.1.