Abstract
Abstract We present an enhanced version of the multiwavelength spectral modeling code MAGPHYS that allows the estimation of galaxy photometric redshift and physical properties (e.g., stellar mass, star formation rate, dust attenuation) simultaneously, together with robust characterization of their uncertainties. The self-consistent modeling over ultraviolet to radio wavelengths in MAGPHYS+photo-z is unique compared to standard photometric redshift codes. The broader wavelength consideration is particularly useful for breaking certain degeneracies in color versus redshift for dusty galaxies with limited observer-frame ultraviolet and optical data (or upper limits). We demonstrate the success of the code in estimating redshifts and physical properties for over 4000 infrared-detected galaxies at 0.4 < z < 6.0 in the COSMOS field with robust spectroscopic redshifts. We achieve high photo-z precision ( ), high accuracy (i.e., minimal offset biases; median(Δz/(1 + z spec)) ≲ 0.02), and low catastrophic failure rates (η ≃ 4%) over all redshifts. Interestingly, we find that a weak 2175 Å absorption feature in the attenuation curve models is required to remove a subtle systematic z phot offset ( ) that occurs when this feature is not included. As expected, the accuracy of derived physical properties in MAGPHYS+photo-z decreases strongly as redshift uncertainty increases. The all-in-one treatment of uncertainties afforded with this code is beneficial for accurately interpreting physical properties of galaxies in large photometric data sets. Finally, we emphasize that MAGPHYS+photo-z is not intended to replace existing photo-z codes, but rather offers flexibility to robustly interpret physical properties when spectroscopic redshifts are unavailable. The MAGPHYS+photo-z code is publicly available online.
Highlights
Obtaining accurate distances to galaxies, typically inferred from cosmological redshift (z; Hogg 1999; Condon & Matthews 2018), is an essential first step in any observational study of cosmology or galaxy evolution
We find that this feature is necessary to reduce systematic residuals between the observations and models in standard Multiwavelength Analysis of Galaxy Physical Properties (MAGPHYS), with an average bump strength of ∼30% the Milky Way (MW) value being necessary for IR-detected galaxies from 0.1 z 3 (Battisti et al in prep.)
We identify and remove active galactic nuclei (AGN) from the main analysis because current public versions of MAGPHYS are intended only for purely star-forming galaxies and properties derived for AGN may be incorrect
Summary
Obtaining accurate distances to galaxies, typically inferred from cosmological redshift (z; Hogg 1999; Condon & Matthews 2018), is an essential first step in any observational study of cosmology or galaxy evolution. The 2175 ̊A absorption bump is a prominent feature in the Milky Way (MW) extinction curve (e.g., Draine 2003), but this feature is typically much weaker in strength or completely absent in dust attenuation curves (e.g., Calzetti et al.1994; Noll et al 2009; Wild et al 2011; Buat et al 2012; Kriek & Conroy 2013; Reddy et al 2015; Scoville et al 2015; Salmon et al 2016; Battisti et al 2017; Salim et al 2018) and for this reason it is often excluded in SED modeling (Charlot & Fall 2000; da Cunha et al 2008) We find that this feature is necessary to reduce systematic residuals between the observations and models in standard MAGPHYS, with an average bump strength of ∼30% the MW value being necessary for IR-detected galaxies from 0.1 z 3 (Battisti et al in prep.). We take our estimates of each parameter to be the median of its likelihood distribution, and the 1σ confidence range to be the 16th to 84th percentile range
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