INFRARED SEARCH FOR YOUNG STARS IN H-I HIGH-VELOCITY CLOUDS

We have searched the IRAS Point Source Catalog and HIRES maps for youn g stellar objects (YSOs) in the direction of five H I high-velocity cl ouds (HVCs). In agreement with optical searches in the halo, no eviden ce was found for extensive star formation activity inside the high-lat itude HVCs. Specifically, we have found no signs of star formation or YSOs in the direction of the A IV cloud or in the very high velocity c louds HVC 110-07-465 and HVC 114-10-440. We have identified only one y oung star in the direction of the M I.1 cloud, which shows almost perf ect alignment with a knot of HI emission. Because of the small number of early-type stars observed in the halo, the probability of such a po sitional coincidence is low; thus this young; star appears to be physi cally associated with the M I.1 cloud. We have also identified a good YSO candidate in the H I shell-like structure observed in the core reg ion of the low-latitude cloud complex H (HVC 131+01-200). This region could be a supernova remnant with several other YSO candidates formed along the shock front produced by the explosion. In agreement with rec ent theoretical estimates, these results point to a low but significan t star formation rate in intermediate and high Galactic latitude HVCs. For M I.1 in particular, we estimate that the efficiency of the star formation process is M(YSO)/M(H I)greater than or similar to 10(-4) to 10(-3) by mass. Such efficiency is sufficient to account for (1) the existence of the few young blue stars whose ages imply that they were born in the Galactic halo and (2) the nonprimordial metallicities infe rred for some HVCs if their metal content proves to be low.