Spectral Energy Distribution Fitting Techniques Spectral Energy Distribution The Spectral Energy Distribution (SED) is the energy emitted by an object as a function of the wavelength • The flux detected by an observer on the ground can be altered because of 1. The medium around the object (circumstellar material) 2. The Interstellar Medium (ISM) 3. The earth’s atmosphere Spectral Energy Distribution • Overview about SED fitting of Galaxies http://www.sedfitting.org/ • ARIADNE (spectrAl eneRgy dIstribution bAyesian moDel averagiNg fittEr): https://github.com/jvines/astroARIADNE • sedkit: https://github.com/hover2pi/SEDkit • VO SED Analyzer: http://svo2.cab.inta-csic.es/theory/vosa/ Spectral Energy Distribution - Fluxes • To build the SED, we need fluxes, but we observe, normally magnitudes in a certain filter • We need to transform the magnitudes to fluxes • Our standard stars in this respect are the Sun, Vega and Sirius • Review: Hayes, 1985, IAUS, 111, 225 • Cookbook: Gray, 1998, AJ, 116, 482S • Also needed for Gaia: Altavilla et al., 2021, MNRAS, 501, 2848 Black Body Radiation Black Body Radiation Spectral Energy Distribution - Stars Pickles, 1998, PASP, 110, 863 Spectral Energy Distribution - Stars Labadie et al., 2014, Proceedings of the SPIE, Volume 9146, id. 91462T 11 Young star with a disk Spectral Energy Distribution - Stars Whelan et al., 2021, AJ, 161, 67 Spectroscopic binary system Spectral Energy Distribution - Quasars Tanya Urrutia et al., 2012, ApJ, 757, 125 Circles are the observed values Lines are different components of the models Spectral Energy Distribution - Galaxies Brown et al., 2014, ApJS, 212, 18 Red circles are the observed values Black lines are the models Spectral Energy Distribution - Galaxies • Review articles: • Baes, 2020, IAUS, 341, 26 • Leitherer, 2005, AIPC, 761, 39 • Walcher et al., 2011, Ap&SS, 331, 1 • Ingredients: 1. Stellar Population(s) – Initial Mass Function and Stellar Evolution 2. ISM – dust and gas – composition, temperature, amount, emission 3. Galaxy evolution 4. Redshift Open cluster Ahumada et al., 2000, A&AS, 141, 79 Bica & Alloin, 1986, A&A, 162, 21 Age Integrated spectra Z Same age Spectral Energy Distribution - Galaxies Vazquez & Leitherer, 2005, 621, 695 Two different isochrone grids uses Spectral Energy Distribution - Galaxies • Amount of dust in a galaxy regulates star formation • Dust is also the most important contributor to extinction and reddening in the ISM due to absorption and scattering of the stellar light • The absorbed light by dust is re-emitted in the infrared (IR) as thermal radiation (modified black body), reshaping the galaxy spectral energy distribution • Massive star forming regions and starbursts galaxies are often observed in IR, enshrouded in dust cocoons, since the strong UV emission of young stars is reprocessed in dust clouds • High mass galaxies have most of their star formation obscured by dust, while low mass ones tends to have most of the star formation unobscured • So we need to know the composition, formation and evolution of the dust component in a galaxy Spectral Energy Distribution - Galaxies Barbosa-Santos et al, 2020, MNRAS, 499, 1701 Change of the dust mass over time for different gas masses and star forming efficiencies Spectral Energy Distribution - Galaxies •Some commonly used models: • Code for Investigating GALaxy Evolution (CIGALE) https://cigale.lam.fr/ • GRAphite-SILicate approach (GRASIL) https://adlibitum.oats.inaf.it/silva/grasil/grasil.html • Multiwavelength Analysis of Galaxy PHYSical properties (MAGPHYS) http://www.iap.fr/magphys/ Spectral Energy Distribution - Galaxies Hunt et al., 2019, A&A, 621, A51 Spectral Energy Distribution - Galaxies Hunt et al., 2019, A&A, 621, A51 NSD … New Star-forming Disks NSS … New Star-forming Spheroids SFH … Star Formation History SFR … Star Formation Rate Spectral Energy Distribution - Galaxies Hunt et al., 2019, A&A, 621, A51 Spectral Energy Distribution - Methods Dobbles et al., 2020, A&A, 634, A57 Machine Learning algorithm Sawicki, 2012, PASP, 124, 1208 Han & Han, 2014, ApJS, 215, 2