We present the full catalog of Young Stellar Objects (YSOs) identified in the 18 molecular clouds surveyed by the Spitzer Space Telescope "cores to disks" (c2d) and "Gould Belt" (GB) Legacy surveys. Using standard techniques developed by the c2d project, we identify 3239 candidate YSOs in the 18 clouds, 2966 of which survive visual inspection and form our final catalog of YSOs in the Gould Belt. We compile extinction corrected SEDs for all 2966 YSOs and calculate and tabulate the infrared spectral index, bolometric luminosity, and bolometric temperature for each object. We find that 326 (11%), 210 (7%), 1248 (42%), and 1182 (40%) are classified as Class 0+I, Flat-spectrum, Class II, and Class III, respectively, and show that the Class III sample suffers from an overall contamination rate by background AGB stars between 25% and 90%. Adopting standard assumptions, we derive durations of 0.40 − 0.78 Myr for Class 0+I YSOs and 0.26 − 0.50 Myr for Flat-spectrum YSOs, where the ranges encompass uncertainties in the adopted assumptions. Including information from (sub)millimeter wavelengths, one-third of the Class 0+I sample is classified as Class 0, leading to durations of 0.13−0.26 Myr (Class 0) and 0.27 − 0.52 Myr (Class I). We revisit infrared color-color diagrams used in the literature to classify YSOs and propose minor revisions to classification boundaries in these diagrams. Finally, we show that the bolometric temperature is a poor discriminator between Class II and Class III YSOs.20 Class 0 protostars are the youngest class of YSOs; see §3.1 for the formal definition of this class of objects. 21 The quantity α is defined as the slope of the infrared SED in log(λS λ ) vs. log(λ) and is used to classify YSOs, as discussed in detail in §3.1 and §3.2. While α calculated from extinction corrected photometry is used in later sections, here we use the values calculated from the observed photometry for consistency with the previous studies to which we compare.

We have completed a 1.1 mm continuum survey of 7.5 deg 2 of the Perseus Molecular Cloud using Bolocam at the Caltech Submillimeter Observatory. This represents the largest millimeter or submillimeter continuum map of Perseus to date. Our map covers more than 30,000 31 ′′ (FWHM) resolution elements to a 1σ RMS of 15 mJy/beam. We detect a total of 122 cores above a 5σ point source mass detection limit of 0.18M ⊙ , assuming a dust temperature of T D = 10 K, 60 of which are new millimeter or submillimeter detections. The 1.1 mm mass function is consistent with a broken power law of slope α 1 = 1.3 (0.5M ⊙ < M < 2.5M ⊙ ) and α 2 = 2.6 (M > 2.5M ⊙ ), similar to the local initial mass function slopeNo more than 5% of the total cloud mass is contained in discrete 1.1 mm cores, which account for a total mass of 285M ⊙ . We suggest an extinction threshold for millimeter cores of A V ∼ 5 mag, based on our calculation of the probability of finding a 1.1 mm core as a function Recent estimates of the distance to Perseus range from 220 pc to 350 pc (e. g Černis 1990;Herbig & Jones 1983). Larger values (300 − 350 pc) are often adopted based on the

We have mapped 63 regions forming high-mass stars in CS J ¼ 5 ! 4 using the CSO. The CS peak position was observed in C 34 S J ¼ 5 ! 4 toward 57 cores and in 13 CS J ¼ 5 ! 4 toward the nine brightest cores. The sample is a subset of a sample originally selected toward water masers; the selection on maser sources should favor sources in an early stage of evolution. The cores are located in the first and second Galactic quadrants with an average distance of 5:3 AE 3:7 kpc and were well detected with a median peak signalto-noise ratio in the integrated intensity of 40. The integrated intensity of CS J ¼ 5 ! 4 correlates very well with the dust continuum emission at 350 lm. For 57 sufficiently isolated cores, a well-defined angular size (FWHM) was determined. The core radius (R CS ), aspect ratio [ða=bÞ obs ], virial mass (M vir ), surface density (AE), and the luminosity in the CS J ¼ 5 ! 4 line (LðCS54Þ) are calculated. The distributions of size, virial mass, surface density, and luminosity are all peaked with a few cores skewed toward much larger values than the mean. The median values, l 1/2 , are as follows: l 1/2 ðR CS Þ ¼ 0:32 pc, l 1/2 ðða=bÞ obs Þ ¼ 1:20, l 1/2 ðM vir Þ ¼ 920 M , l 1/2 ðAEÞ ¼ 0:60 g cm À2 , l 1/2 ðLðCS54ÞÞ ¼ 1:9 Â 10 À2 L , and l 1/2 ðL bol =M vir Þ ¼ 165 ðL=MÞ . We find a weak correlation between C 34 S line width and size, consistent with Dv $ R 0:3 . The line widths are much higher than would be predicted by the usual relations between line width and size determined from regions of lower mass. These regions are very turbulent. The derived virial mass agrees within a factor of 2-3 with mass estimates from dust emission at 350 lm after corrections for the density structure are accounted for. The resulting cumulative mass spectrum of cores above 1000 M can be approximated by a power law with a slope of about À0.9, steeper than that of clouds measured with tracers of lower density gas and close to that for the total masses of stars in OB associations. The median turbulent pressures are comparable to those in UCH ii regions, and the pressures at small radii are similar to those in hypercompact H ii regions (P=k $ 10 10 K cm À3 ). The filling factors for dense gas are substantial, and the median abundance of CS is about 10 À9 . The ratio of bolometric luminosity to virial mass is much higher than the value found for molecular clouds as a whole, and the correlation of luminosity with mass is tighter.

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We have undertaken an unprecedentedly large 1.1 millimeter continuum survey of three nearby star forming clouds using Bolocam at the Caltech Submillimeter Observatory. We mapped the largest areas in each cloud at millimeter or submillimeter wavelengths to date: 7.5 deg 2 in Perseus (Paper I), 10.8 deg 2 in Ophiuchus (Paper II), and 1.5 deg 2 in Serpens with a resolution of 31 ′′ , detecting 122, 44, and 35 cores, respectively. Here we report on results of the Serpens survey and compare the three clouds. Average measured angular core sizes and their dependence on resolution suggest that many of the observed sources are consistent with power-law density profiles. Tests of the effects of cloud distance reveal that linear resolution strongly affects measured source sizes and densities, but not the shape of the mass distribution. Core mass distribution slopes in Perseus and Ophiuchus (α = 2.1 ± 0.1 and α = 2.1 ± 0.3) are consistent with recent measurements of the stellar IMF, whereas the Serpens distribution is flatter (α = 1.6 ± 0.2). We also compare the relative mass distribution shapes to predictions from turbulent fragmentation simulations. Dense cores constitute less than 10% of the total cloud mass in all three clouds, consistent with other measurements of low star-formation efficiencies. Furthermore, most cores are found at high column densities; more than 75% of 1.1 mm cores are associated with A V 8 mag in Perseus, 15 mag in Serpens, and 20 − 23 mag in Ophiuchus.