COSMOS2020: Manifold learning to estimate physical parameters in large galaxy surveys

Creators: Davidzon, I.¹; Jegatheesan, K.^{2, 3}; Ilbert, O.^{3, 4, 5}; de la Torre, S.³; Leslie, S. K.⁶; Laigle, C.^{7, 8}; Hemmati, S.^{9, 4}; Masters, D. C.^{9, 4}; Blanquez-Sese, D.^{1, 10}; Kauffmann, O. B.³; Magdis, G. E.^{1, 10}; Małek, K.^{11, 3}; McCracken, H. J.^{7, 8}; Mobasher, B.¹²; Moneti, A.^{7, 8}; Sanders, D. B.^{13, 1}; Shuntov, M.^{7, 8}; Toft, S.¹; Weaver, J. R.¹

1. University of Copenhagen
2. Diego Portales University
3. Aix Marseille Univ., CNRS, CNES, LAM, Marseille, France
4. California Institute of Technology
5. Jet Propulsion Lab
6. Leiden University
7. Sorbonne University
8. Institut d'Astrophysique de Paris
9. Infrared Processing and Analysis Center
10. Technical University of Denmark
11. National Centre for Nuclear Research
12. University of California, Riverside
13. University of Hawaii at Manoa

Abstract

We present a novel method for estimating galaxy physical properties from spectral energy distributions (SEDs) as an alternative to template fitting techniques and based on self-organizing maps (SOMs) to learn the high-dimensional manifold of a photometric galaxy catalog. The method has previously been tested with hydrodynamical simulations in Davidzon et al. (2019, MNRAS, 489, 4817), however, here it is applied to real data for the first time. It is crucial for its implementation to build the SOM with a high-quality panchromatic data set, thus we selected "COSMOS2020" galaxy catalog for this purpose. After the training and calibration steps with COSMOS2020, other galaxies can be processed through SOMs to obtain an estimate of their stellar mass and star formation rate (SFR). Both quantities resulted in a good agreement with independent measurements derived from more extended photometric baseline and, in addition, their combination (i.e., the SFR vs. stellar mass diagram) shows a main sequence of star-forming galaxies that is consistent with the findings of previous studies. We discuss the advantages of this method compared to traditional SED fitting, highlighting the impact of replacing the usual synthetic templates with a collection of empirical SEDs built by the SOM in a "data-driven" way. Such an approach also allows, even for extremely large data sets, for an efficient visual inspection to identify photometric errors or peculiar galaxy types. While also considering the computational speed of this new estimator, we argue that it will play a valuable role in the analysis of oncoming large-area surveys such asEuclidof the Legacy Survey of Space and Time at theVera C. RubinTelescope.

Copyright and License

Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Acknowledgement

The authors are grateful to the referee for the thorough and constructive comments they provided. I.D. would like to thank Eric Bell, Micol Bolzonella, Rebecca Bowler, Ivan Delvecchio, Joel Leja, Vihang Mehta for useful discussions. The authors are grateful to Joel Leja also for providing Prospector data in a convenient digital format. This work started during a meeting in Marseille, founded by the French Agence Nationale de la Recherche for the project “SAGACE”. This research is also partly supported by the Centre National d’Etudes Spatiales (CNES). I.D., J.R.W., K.J., and O.I. made use of the CANDIDE Cluster at the Institut d’Astrophysique de Paris and made possible by grants from the PNCG, CNES and the DIM-ACAV. The Cosmic Dawn Center is funded by the Danish National Research Foundation under grant No. 140. I.D. has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 896225. J.R.W. acknowledges support from the European Research Council (ERC) Consolidator Grant funding scheme (project ConTExt, grant No. 648179). K.M. is grateful for support from the Polish National Science Centre via grant UMO-2018/30/E/ST9/00082. G.E.M. acknowledges the Villum Fonden research grant 13160 “Gas to stars, stars to dust: tracing star formation across cosmic time” and grant 37440 “The Hidden Cosmos”. D.B.S. is grateful to Danmarks Nationalbank for their generous hospitality in the Nyhavn 18 residence during his extended visit to Copenhagen. We warmly acknowledge the contributions of the entire COSMOS collaboration consisting of more than 100 scientists. The HST-COSMOS program was supported through NASA grant HST-GO-09822. More information on the COSMOS survey is available at https://cosmos.astro.caltech.edu. A significant portion of this project took place during the COVID-19 global pandemic; the authors would like to thank all those who made sacrifices in order for us to safely continue our research.

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