Properties of Submillimeter Galaxies in a Semi-analytic Model using the "Count Matching" Approach: Application to the ECDF-S

TL;DR

This paper introduces a novel 'Count Matching' technique to model submillimeter galaxies using semi-analytic galaxy formation models, reproducing observed counts and properties by assigning fluxes based on physical proxies.

Contribution

The paper develops a new method that links galaxy properties to submillimeter luminosities, effectively reproducing observed counts and distributions, including blending effects.

Findings

The 'dust mass × SFR' proxy best reproduces observed properties.

Blended sources are mostly spatially unassociated.

The method matches observed counts even with randomized source positions.

Abstract

We present a new technique for modeling submillimeter galaxies (SMGs): the "Count Matching" approach. Using lightcones drawn from a semi-analytic model of galaxy formation, we choose physical galaxy properties given by the model as proxies for their submillimeter luminosities, assuming a monotonic relationship. As recent interferometric observations of the Extended Chandra Deep Field South show that the brightest sources detected by single-dish telescopes are comprised by emission from multiple fainter sources, we assign the submillimeter fluxes so that the combined LABOCA plus bright-end ALMA observed number counts for this field are reproduced. After turning the model catalogs given by the proxies into submillimeter maps, we perform a source extraction to include the effects of the observational process on the recovered counts and galaxy properties. We find that for all proxies, there are lines of sight giving counts consistent with those derived from LABOCA observations, even for input sources with randomized positions in the simulated map. Comparing the recovered redshift, stellar mass and host halo mass distributions for model SMGs with observational data, we find that the best among the proposed proxies is that in which the submillimeter luminosity increases monotonically with the product between dust mass and SFR. This proxy naturally reproduces a positive trend between SFR and bolometric IR luminosity. The majority of components of blended sources are spatially unassociated.