The Giant Herbig–Haro Flow HH 212 and Associated Star Formation

The bipolar jet HH 212 is one of the finest collimated jets known. It has up to now been detected only in near-infrared H2 emission, but here we present deep optical images that show that two of the major bow shocks are weakly detected in optical [S ii] emission, as expected for a bona fide Herbig–Haro jet. We also present widefield H2 images that reveal two more bow shocks located symmetrically to the north and south around the source and along the main jet axis. Additionally, examination of Spitzer 4.5 μm images reveals yet another bright bow shock further to the north along the jet axis; no corresponding bow shock is seen to the south. In total, the HH 212 flow has an extent of 1050″, corresponding to a projected dimension of 2.0 pc. HH 212 thus joins the growing group of parsec-scale Herbig–Haro jets. Proper motion measurements indicate a velocity of about 170 km s−1, highly symmetric around the source, with an uncertainty of ∼30 km s−1, suggesting a probable age of the giant HH 212 flow of about 7000 yr. The jet is driven by a deeply embedded source, known as IRAS 05413–0104. We draw attention to a Spitzer near- and mid-infrared source, which we call IRS-B, located only 7″ from the driving source, toward the outskirts of the dense cloud core. Infrared photometry and spectroscopy suggests that IRS-B is a K-type star with a substantial infrared excess, except that for an extinction of AV = 44 the star would have only a weak infrared excess, and so in principle it could be a K-giant at a distance of about 2 kpc. Finally, we have identified a Class II source and a Class I source about 2 1/2′ SSW of IRAS 05413–0104, indicating that additional star formation has taken place in the cloud, and that the HH 212 star-forming event is not as isolated as sometimes considered.