Title: Submillimeter Galaxy Number Counts in a Semi-analytic Model: the "Count  
Matching" Approach

Abstract:
Fitting submillimeter galaxies (SMGs) into the current theory of galaxy 
formation has been a challenge since their discovery, even though they are the 
most luminous star-forming sources at the epoch where galaxy formation peaks. 
Recent ALMA observations of the Extended Chandra Deep Field South (for which 
LABOCA detections are available) show that the bright end of the LABOCA number 
counts is actually comprised by emission from multiple fainter sources, given 
the high sensitivity and resolution of ALMA maps compared to LABOCA.
With the aim of exploring the properties of SMGs, and in analogy to the now-
standard abundance matching approach, we perform a "Count Matching" approach 
through lightcones drawn from a semi-analytic model. We choose various physical 
galaxy properties given by the model as proxies for their submillimeter fluxes, 
assuming a monotonic relationship so that the combined LABOCA plus bright-end 
ALMA observed number counts are reproduced. After turning the catalogs of 
galaxy positions and fluxes given by the different proxies into submillimeter 
maps that include a modeling of the observational process, we perform a source 
extraction as done for maps obtained through observations. With this we study 
the effects of the observational process in the recovered counts, as well as 
the galaxy properties derived from the detected sources for each proxy.
The difference between the counts with and without the beam of LABOCA can 
be used to find the best proxy: sources with the highest submm fluxes will 
have different clustering depending on the assumed proxy, since the sources 
with the highest value of a given property will be clustered in a particular 
way; the best proxy then will be such that the clustering measured from the 
model galaxies is the same that the one given by the ALMA sources, while 
the recovered clustering from the simulated maps is the same that the one 
given by the LABOCA SMGs. This can also be confirmed exploring other 
statistics like redshift, morphology, stellar mass and host halo mass 
distributions.