The Spitzer Survey of Interstellar Clouds in the Gould Belt. V. Ophiuchus North Observed with IRAC and MIPS

Abstract

We present Spitzer IRAC (2.1 deg^2) and MIPS (6.5 deg^2) observations of star formation in the Ophiuchus North (Oph N) molecular clouds. This fragmentary cloud complex lies on the edge of the Sco-Cen OB association, several degrees to the north of the well-known ρ Oph star-forming region, at an approximate distance of 130 pc. The Oph N clouds were mapped as part of the Spitzer Gould Belt project under the working name "Scorpius." In the regions mapped, selected to encompass all the cloud with visual extinction A_V > 3, 11 young stellar object (YSO) candidates are identified, 8 from IRAC/MIPS color-based selection and 3 from Two Micron All Sky Survey (2MASS) K_S /MIPS colors. Adding to one source previously identified in L43, this increases the number of YSOcs identified in Oph N to 12. During the selection process, four color-based YSOcs were rejected as probable asymptotic giant branch stars and one as a known galaxy. The sources span the full range of YSOc classifications from Class 0/1 to Class III, and starless cores are also present. Twelve high extinction (A_V > 10) cores are identified with a total mass of ~100 M_☉. These results confirm that there is little ongoing star formation in this region (instantaneous star formation efficiency <0.34%) and that the bottleneck lies in the formation of dense cores. The influence of the nearby Upper Sco OB association, including the 09V star ζ Oph, is seen in dynamical interactions and raised dust temperatures but has not enhanced levels of star formation in Oph N.

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