To determine foreground and background contamination by star-forming galaxies, AGNs, shock emission, and extended PAH emission, as well as field stars, we performed the infrared color selection method described in Gutermuth et al. (2009). In Phase I of this method, we used only GLIMPSE sources that have photometry in all four IRAC bands, and have photometric uncertainties σ  0.2 mag in all four bands, which corresponds to a total of 2723 sources. In Figure 4 we show CCDs from the first step of the Phase I selection method, that allowed us to identify contamination from star-forming galaxies and AGNs. Then, we proceeded to the elimination of shock emission and extended PAH emission contamination, as well as YSO class selection as shown on Figure 5. This procedure resulted in a total of 2702 Spitzer/GLIMPSE sources without contamination. We obtained a total of 42 sources classified as Class I, and 177 sources classified as Class II. We continued with a process similar to the Phase II selection method described by Gutermuth et al. (2009), which we slightly modified due to the use of VISTA/VVV data instead of 2MASS data used in the Gutermuth et al. (2009) paper. In this step, both Spitzer/GLIMPSE and VISTA/VVV data were used. Specifically, the Phase II selection method is applied to Spitzer/GLIMPSE sources that lack [5.8] and/or [8.0] detections. The Spitzer/GLIMPSE sources were first matched with their VISTA/VVV counterparts. We only selected high-quality VISTA/VVV detections with σ  0.1 mag, and Spitzer/GLIMPSE detections with photometric uncertainties σ  0.2 mag in the detected bands for this analysis. A cross-match of both catalogs was done using a search radius of 1″, to create a matched list of 13,309 sources. A further selection on these sources was done using their VISTA/VVV magnitudes. We excluded stars with saturated photometry (Soto et al. 2013), by limiting the magnitudes of the detected VISTA/VVV sources to 13.8, 12.8, and 12.8, for the J, H, and KS bands, respectively. A total of 9974 non-saturated sources were selected. Whenever possible we checked for contamination using similar color–color criteria as described for Phase I in Gutermuth et al. (2009), and ended up with a total of 9844 sources without contamination. We selected this sample of 9844 stars where objects with infrared excesses are expected to be found. To select these infrared excess sources, we used the dereddened color selection criteria detailed in Gutermuth et al. (2009) with [K–[3.6]]0 and [[3.6]–[4.5]]0 colors. Displaying the position of all the new infrared excess candidates showed that they are uniformly distributed in the region, thus we consider that our selected data set might still suffer contamination by foreground sources. To eliminate any possible chance of selecting any contaminant, we therefore applied additional selection criteria to these infrared excess sources candidates, as described in Winston et al. (2011) and Megeath et al. (2012), by plotting two CCDs, as shown in Figure 6. The first selection was done using the CCD J–H versus H–[4.5], with the slope of the reddening band 





 (Chen et al. 2013). The second color selection was done using the CCD H–KS versus KS–[4.5] with the slope of the reddening band 





 (Chen et al. 2013). We defined as YSOs all sources passing the selection criteria of the first or of the second CCD, and found a total of 1566 YSOs. Initial inspection of this selection indicated that there was still contamination by normally reddened stars, and the limits were moved by 0.2 mag toward the red compared with the formulas given by Winston et al. (2007) and and Jose et al. (2016). To then isolate Class I and Class II YSOs from these sources, we used the Phase II color selection from Gutermuth et al. (2009), with the CCD [KS–[3.6]]0 versus [[3.6]–[4.5]]0 as shown in Figure 7. We obtained a total of 32 Class I YSOs and a total of 385 Class II YSOs.
Citation: Soto et al. 2013
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