Estimación del desplazamiento al rojo para las galaxias en el Southern H-ATLAS Regions Ks-band Survey

Abstract

This project focuses on obtaining the photometric redshift (photo-z) for galaxies in the first data release (DR1) of the Southern H-ATLAS Regions Ks Band Survey (SHARKS). In particular, we will study the effect of incorporating the Ks-band in the photo-z estimates. A limiting factor in obtaining the redshift by photometric means is the lack of spectral coverage, especially when the SHARKS data are only in the Ks-band. Because of this, we will make use of an astronomical catalog that covers the same region of the sky in the optical range, the Dark Energy Survey (DES), in particular DES-DR2. Before proceeding to the photo-z calculation, we study the calibration of the SHARKS-DR1 data. For this purpose, we will proceed with a near-infrared astronomical catalog that will act as a reference, 2MASS. In this section of the project, using a linear regression between the magnitudes of both catalogs, we will measure the calibration difference between them. In this case, we expect only to measure the difference between the calibration in the Vega and AB system. As for the photometric redshift, it is noteworthy that since this is the first time that these are calculated with SHARKS data, we have focused on a subsample where we have selected only galaxies with a distinct SHARKS-DES detection. For the selection of galaxies, we will use color-color space separation that occurs when using infrared bands. The calculation of the photometric redshift has been performed using the Lephare software. Before the execution, we must define the library of galaxy model templates that we will use (SEDs, Spectral Energy Distribution), here we will use a library of 8 templates. For their subsequent convolution, we will also introduce the filters with which we took the measurements, i.e. those of the DECam and VIRCAM cameras. Then, we proceed to calculate the magnitudes as a function of the redshift for the templates, and finally, we perform a minimization of the reshift for the templates. Finally, a minimization by the 2 fitting method is carried out to obtain the redshift and the template that best fits the observed galaxy. To validate the results, we calculate statistical metrics of the bias and dispersion of the photo-z, concerning a small calibration sample with spectroscopic redshift, limited to low redshift. Next, we compare the overall redshift distributions obtained with and without using the Ks-band and look at some examples of outliers. In general, we find that using SHARKS Ks-band improves the photo-z estimates, compared to the similar estimates using only DES data, through a decrease in the number of catastrophic results (outliers).