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Published June 2021 | Accepted Version + Published
Journal Article Open

SPICY: The Spitzer/IRAC Candidate YSO Catalog for the Inner Galactic Midplane


We present ~120,000 Spitzer/IRAC candidate young stellar objects (YSOs) based on surveys of the Galactic midplane between ℓ ~ 255° and 110°, including the GLIMPSE I, II, and 3D, Vela-Carina, Cygnus X, and SMOG surveys (613 square degrees), augmented by near-infrared catalogs. We employed a classification scheme that uses the flexibility of a tailored statistical learning method and curated YSO data sets to take full advantage of Spitzer's spatial resolution and sensitivity in the mid-infrared ~3–9 μm range. Multiwavelength color/magnitude distributions provide intuition about how the classifier separates YSOs from other red IRAC sources and validate that the sample is consistent with expectations for disk/envelope-bearing pre–main-sequence stars. We also identify areas of IRAC color space associated with objects with strong silicate absorption or polycyclic aromatic hydrocarbon emission. Spatial distributions and variability properties help corroborate the youthful nature of our sample. Most of the candidates are in regions with mid-IR nebulosity, associated with star-forming clouds, but others appear distributed in the field. Using Gaia DR2 distance estimates, we find groups of YSO candidates associated with the Local Arm, the Sagittarius–Carina Arm, and the Scutum–Centaurus Arm. Candidate YSOs visible to the Zwicky Transient Facility tend to exhibit higher variability amplitudes than randomly selected field stars of the same magnitude, with many high-amplitude variables having light-curve morphologies characteristic of YSOs. Given that no current or planned instruments will significantly exceed IRAC's spatial resolution while possessing its wide-area mapping capabilities, Spitzer-based catalogs such as ours will remain the main resources for mid-infrared YSOs in the Galactic midplane for the near future.

Additional Information

© 2021. The American Astronomical Society. Received 2020 November 12; revised 2020 December 23; accepted 2020 December 24; published 2021 June 2. We thank Robert Benjamin for useful discussions about GLIMPSE and the spiral structure of the Galaxy, and Philip Lucas and Leigh Smith for assistance with the UKIDSS and VVV catalogs. This work is a result of the 6th COIN Residence Program (CRP#6; https://cosmostatistics-initiative.org/residence-programs/crp6) held in Chamonix, France in 2019 August. COIN is financially supported by CNRS as part of its MOMENTUM program over the 2018–2020 period. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. This work has also made use of data from the European Space Agency mission Gaia, processed by the Gaia Data Processing and Analysis Consortium. Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This work is also based in part on observations obtained with the Samuel Oschin 48 inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. This research has made use of the NASA/IPAC Infrared Science Archive, which is funded by the National Aeronautics and Space Administration and operated by the California Institute of Technology. A.K.M. acknowledges support from the Portuguese Fundação para a Ciência e a Tecnologia (FCT) through grants SFRH/BPD/74697/2010, PTDC/FIS-AST/31546/2017 and from the Portuguese Strategic Programme UID/FIS/00099/2013 for CENTRA. M.A.K. acknowledges support from the Chandra grant GO9-20002X for analysis of data related to the Trifid Nebula. Facilities: 2MASS - , Gaia - , Spitzer (IRAC - , MIPS) - , UKIRT - , VISTA/VIRCAM - , WISE - , ZTF - , IRSA. - Software: caret (Kuhn 2015), mclust (Scrucca et al. 2016), hdbscan (McInnes et al. 2017), modeest (Poncet 2019), mclust (Scrucca et al. 2016), PostgreSQL (PostgreSQL Global Development Group 2020), Python, R (Core Team 2019), rjags (Plummer 2017, 2019), SAOImage DS9 (Joye & Mandel 2003), sbgcop (Hoff 2018), TOPCAT & STILTS (Taylor 2005).

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Published - Kuhn_2021_ApJS_254_33.pdf

Accepted Version - 2011.12961.pdf


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August 22, 2023
October 23, 2023