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Star Formation in the Outer Galaxy: Identification and Characterization of Young Stellar Objects in the Cma OB1 Association

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Star Formation in the Outer Galaxy: Identification and Characterization of Young Stellar Objects in the Cma OB1 Association Star Formation in the Outer Galaxy: Identification and Characterization of Young Stellar Objects in the CMa OB1 Association Marta Sewiło (NASA/GSFC), Barbara Whitney (Space Science Institute), Thomas Robitaille, Davide Elia (INAF-IAPS), Remy Indebetouw (NRAO/U. of Virginia), Brian Babler (UW-Madison), Marilyn Meade (UW-Madison), Martha Boyer (NASA/GSFC), William Fischer (NASA/GSFC), Deborah Padgett (NASA/GSFC) Figure 1 – Left: The three-color composite image of the region in Canis Abstract Major (CMa; d ~ 1 kpc) analyzed here (L224o), combining the WISE 12 µm (red), GLIMPSE360 4.5 µm (green), and 3.6 µm (blue) images. The We present a preliminary analysis of the ~34 square degrees region (L220) in the Outer Galaxy with galactic white square enclosed the area with the large concentration of outflows longitudes from l=215° to l=227° and the full galactic latitude extent of the Spitzer Space Telescope GLIMPSE360 as traced by the 4.5 µm emission – see the zoom in on the outflow area (bottom). The contour corresponds to N(H ) of 4 x 1021 cm-2. The circle survey (-2.3° < b < 0.5°; PI B. Whitney) at these longitudes. L220 is home to a very young star-forming complex that is 2 the most concentrated source of outflows in the Spitzer GLIMPSE360 survey. Our goal is to uncover and characterize a represent the ``empty field''. previously unstudied population of intermediate- and low-mass Young Stellar Objects (YSOs) in L220. We are performing a census of YSOs using color-color and color-magnitude selection criteria and modeling of spectral energy distributions (SEDs), combined with the visual inspection of multi-wavelength images. The L220 region samples three different spiral arms and inter-arm regions. This provides an opportunity to study both very active and more quiescent areas. With the kinematic information from the CO data, we will be able to associate YSO candidates with spiral arms and study star formation properties as a function of Galactocentric radius (thus metallicity). Our analysis is mostly based on the Spitzer GLIMPSE360 3.6 and 4.5 µm data combined with the near-infrared photometry from 2MASS, and AllWISE 12 and 22 µm data. The results of our study on L220 will be a valuable complement to the Herschel Space Observatory Hi-GAL study of this region (Elia et al. 2013). In our preliminary analysis of L220, we concentrate on the most active region in Canis Major (CMa) OB1 association (we dubbed it L224o), which encompasses the area harboring clusters of YSOs with outflows. The YSO Selection Method: Spitzer + 2MASS Spitzer / WISE and Herschel View of L220 We first select sources using a combination of the Spitzer and 2MASS data. We select the reddened sources in 3 CCDs that combine [4.5] and two 2MASS bands and then apply a series of filters to remove the contaminants The 12° x 2.8° region L220 contains portions of the Local (d ~ 0.8 kpc, RGC ~ 9 kpc), the (e.g., background galaxies). Perseus (d ~ 4 kpc, RGC ~10 kpc), and the Outer (d ~ 9 kpc, RGC > 14 kpc; Fig. 2) spiral arms. L220 was covered by the 13CO(J=1-0) survey with the NANTEN telescope (Kim et al. 2004) at 1) Color-color cuts using the GLIMPSE360 and 2MASS data 2.6' resolution. They detected two large molecular cloud complexes; one coincides with the CMa OB1 association, another one is located ~3° to the west (G220.8-1.7; see Fig. 3). The analysis of the region in the Outer Galaxy provides us an opportunity to study star formation in a significantly different environment than in the Inner Galaxy (e.g., lower metallicity and lower star formation activity). Our study will provide for the first time information on the YSO Figure 2 - The position of content in L220 for a range of evolutionary stages. The mass limits are estimated to be ~0.1 L220 in the Galactic plane. Msun (at 3 kpc) to ~2 Msun (at 8 kpc). Area rich in outflows (as traced by the Figure 6 – An example Spitzer+2MASS CCD used to select reddened sources. The distribution of all GLIMPSE360 catalog 4.5 µm emission) sources is shown as a Hess diagram. Overplotted are: left – Gould Belt YSO candidates from Dunham et al. (2015); middle – normal galaxies and AGNs (Kochanek et al. 2012), and evolved stars; right – Robitaille et al. (2006) YSO models (orange) and GLIMPSE360 sources from the ``empty field'' that represents the background. The red solid line is parallel to the reddening vector and originates at the position of the K0 dwarf. Dashed lines represent a 1σ uncertainty in color. We select sources rightward from the dashed line on the right in any of the three Spitzer+2MASS CCDs. 2) SED fitting with the stellar photosphere models – remove well-fit sources . Contamination from evolved stars is negligible; this was estimated based on the TRILEGAL stellar population Figure 3 - The 3-color composite image combining WISE 12 μm (red; 6.5'' resolution), GLIMPSE360 IRAC 4.5 μm (green; ~2''), and synthesis code (Girardi et al. 2005), updated with the latest COLIBRI TP-AGB models, including circumstellar dust IRAC 3.6 μm (blue; ~2'') images. The molecular cloud complexes CMa OB1 and G220.8-1.7 are indicated with white squares (Kim et (Marigo et al. 2013). To remove a contamination from background galaxies, we select sources brighter than 13.5 mag in al. 2004). The green square indicates the area rich in outflows that is shown in Fig.1. Note: CMa OB1 extends from b=-3.4° to +0.7° the 3.6 µm band. and from l = 222° to 226°. CMa OB1 association is ~3 Myr old and is 1.15 kpc away (Claria 1974). 3) Visual inspection of multi-wavelength images - environment, artifacts, etc. Based on the Herschel/Hi-GAL data, Elia et al. (2013) revealed that the area rich in outflows is very bright at far-IR/ 4) Spectral energy distribution (SED) fitting using a new set of the 2D radiative transfer YSO models (T. Robitaille, in submm wavelengths, indicating the earliest stages of star formation. The bright Herschel emission and faint mid-IR prep.) - physical parameters and classification emission (with the exception of the 4.5 μm outflows) are indicators of very young low- to intermediate-mass star ● several components: a star, disk, infalling envelope, bipolar cavities, and an ambient medium formation. ● computed as several sets of models with increasing complexity (from 2 to 12 parameters) ● significant improvements over Robitaille et al. (2006) models: - do not depend on highly model-dependent parameters (such as the stellar age and mass) which depend on stellar evolutionary tracks, but they are defined using parameters that have a direct impact on the radiative transfer; L224o - cover a much wider and more uniform region of parameter space; - the envelope outer radius for envelope models are now large enough to include 10-20 K dust that is essential for modeling far-IR and submm observations. Figure 7 - Example SEDs of sources well-fit with the YSO models. The solid black line in each plot shows the best fit YSO model. Filled circles and triangles are valid flux values and flux upper limits, respectively. - Final Spitzer+2MASS YSO candidates list: 186 - low- and intermediate-mass YSOs - Stage I and Stage II Figure 4 - Figure 1 from Elia et al. (2013). The 3-color composite image combining SPIRE 500 μm (red), SPIRE 250 μm (green), and PACS 160 μm (blue) images from the Herschel/Hi-GAL survey. The cyan contour delimits the area covered by both PACS and SPIRE. The spatial resolution of the 500 μm, 250 μm, and 160 μm images is 36'', 18'', and 12'', respectively. The green box as in Fig. 3 shows the region rich in outflows. Spitzer + AllWISE To select YSO candidates with no 2MASS data, we use the CMD and CCD that combine the Spitzer and AllWISE 12 µm data. The color-color and color-magnitude cuts separate YSO candidates from background galaxies (e.g, Koenig & Leisawitz 2014; Fischer et al., in prep.). Region L224o: Clusters of YSOs with Outflows in Canis Major . We have been developing a YSO identification method based on the subregion of L220 that includes the area rich in outflows (Fig. 1 and a yellow rectangle in Fig. 4). We dubbed this region L224o; its boundaries were selected based on the H2 column density map derived by Elia et al. (2013) using the 160-500 µm Herschel data. It 21 -2 encloses a high column density ring-like structure (as traced by the 4 x 10 cm contour in Figs. 1 and 5); the western side of this structure is formed by the two brightest Herschel filaments in the region (Schisano et al. 2014) that coincide with the outflows. Figure 8 – The [3.6]-[4.5] vs. [4.5]-[12] CCD (3 plots at the left) and the [3.6] vs. [3.6]-[12] CMD (right) used to select YSO candidates with no 2MASS data. The symbols are the same as in Fig. 6. We remove sources located in the area outlined with the blue lines in the CCD and to the left of the blue line in the CMD; these sources are likely background galaxies. The subsequent analysis includes the visual inspection of the images and the SED fitting with the YSO models (see above). Using this method, we identified additional 19 YSO candidates (mostly Stage I). Spatial Distribution of the YSO Candidates Figure 5 – The WISE 12 µm (left) and H2 column density (right) image of the CMa region. L224o is indicated with a black rectangle.
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