Multifrequency filter search for high redshift sources and lensing systems in Herschel -ATLAS

We present a new catalog of high-redshift candidate Herschel sources. Our sample is obtained after applying a multifrequency filtering method (?matched multifilter?), which is designed to improve the signal-to-noise ratio of faint extragalactic point sources. The method is tested against already-detected sources from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) and used to search for new high-redshift candidates. The multifilter technique also produces an estimation of the photometric redshift of the sources. When compared with a sample of sources with known spectroscopic redshift, the photometric redshift returned from the multifilter is unbiased in the redshift range 0.8?< ?z?< ?4.3. Using simulated data we reproduced the same unbiased result in roughly the same redshift range and determined the error (and bias above z???4) in the photometric redshifts. Based on the multifilter technique, and a selection based on color, flux, and agreement of fit between the observed photometry and assumed SED, we find 370 robust candidates to be relatively bright high-redshift sources. A second sample with 237 objects focuses on the faint end at high-redshift. These 237 sources were previously near the H-ATLAS detection limit but are now confirmed with our technique as high significance detections. Finally, we look for possible lensed Herschel sources by cross-correlating the first sample of 370 objects with two different catalogs of known low-redshift objects, the redMaPPer Galaxy Cluster Catalog and a catalog of galaxies with spectroscopic redshift from the Sloan Digital Sky Survey Data Release 14. Our search renders a number of candidates to be lensed systems from the SDSS cross-correlation but none from the redMaPPeR confirming the more likely galactic nature of the lenses

Methodological refinement of the submillimeter galaxy magnification bias. Paper iI: cosmological analysis with a single redshift bin

The main goal of this work, the second in a three-paper series, is to test the impact of a methodological improvement in measuring the magnification bias signal on a sample of submillimeter galaxies and its implications for constraining cosmological parameters. The analysis considers the angular cross-correlation function between a foreground sample of GAMA galaxies ($0.2<z<0.8$) and a background sample of H-ATLAS submillimeter galaxies ($1.2<z<4.0$). A refined methodology, discussed extensively in Paper I, is used. By interpreting the weak lensing signal within the halo model and employing an MCMC algorithm, the posterior distribution of the halo occupation distribution (HOD) and cosmological parameters is obtained for a flat $\Lambda$CDM model. The analysis incorporates the foreground angular auto-correlation function to account for galaxy clustering. The results demonstrate a remarkable improvement in uncertainties for both HOD and cosmological parameters compared to previous studies. However, when using the cross-correlation data alone, the estimation of $\sigma_8$ depends on prior knowledge of $\beta$, the logarithmic slope of the background number counts. Assuming a physically motivated prior distribution for $\beta$, mean values of $\Omega_m=0.18^{+0.03}{-0.03}$ and $\sigma_8=1.04^{+0.11}{-0.07}$ are obtained. These results may however be subject to an inherent bias in the data due to anomalous behavior observed in the G15 field. After excluding the G15 region, the mean values shift to $\Omega_m=0.30^{+0.05}{-0.06}$ and $\sigma_8=0.92^{+0.07}{-0.07}$. This becomes more apparent when adding the clustering of the foreground sample, but the dependence on $\beta$ information disappears, mitigating the aforementioned issue. Excluding the G15 region, the joint analysis yields mean values of $\Omega_m=0.36^{+0.03}{-0.07}$, $\sigma_8=0.90^{+0.03}{-0.03}$, and $h=0.76^{+0.14}_{-0.14}$.Comment: This work is the second one of a three-paper series. Submitted to A&