HERSCHEL-ATLAS: TOWARD A SAMPLE OF ∼1000 STRONGLY LENSED GALAXIES

Abstract

While the selection of strongly lensed galaxies with 500µm flux density S 500 > 100 mJy has proven to be rather straightforward (Negrello et al. 2010), for many applications it is important to analyze samples larger than the ones obtained when confining ourselves to such a bright limit. Moreover, only by probing to fainter flux densities is possible to exploit strong lensing to investigate the bulk of the high-z star-forming galaxy population. We describe HALOS (the Herschel -ATLAS Lensed Objects Selection), a method for efficiently selecting fainter candidate strongly lensed galaxies, reaching a surface density of ≃ 1.5-2 deg −2 , i.e. a factor of about 4 to 6 higher than that at the 100 mJy flux limit. HALOS will allow the selection of up to ∼ 1000 candidate strongly lensed galaxies (with amplifications µ 2) over the full H-ATLAS survey area. Applying HALOS to the H-ATLAS Science Demonstration Phase (SDP) field (≃ 14.4 deg 2 ) we find 31 candidate strongly lensed galaxies, whose candidate lenses are identified in the VIKING near-infrared catalog. Using the available information on candidate sources and candidate lenses we tentatively estimate a ≃ 72% purity of the sample. As expected, the purity decreases with decreasing flux density of the sources and with increasing angular separation between candidate sources and lenses. The redshift distribution of the candidate lensed sources is close to that reported for most previous surveys for lensed galaxies, while that of candidate lenses extends to substantially higher redshifts than found in the other surveys. The counts of candidate strongly lensed galaxies are also in good agreement with model predictions (Lapi et al. 2011). Even though a key ingredient of the method is the deep near-infrared VIKING photometry, we show that H-ATLAS data alone allow the selection of a similarly deep sample of candidate strongly lensed galaxies with an efficiency close to 50%; a slightly lower surface density (≃ 1.45 deg −2 ) can be reached with a ∼ 70% efficiency.

The Herschel Bright Sources (HerBS): sample definition and SCUBA-2 observations

“…A high flux density cut-off (S 500µm > 100 mJy) eliminates a large amount of possible lenses in order to achieve a low contamination rate from unlensed sources (González-Nuevo et al 2012). Lowering the cut-off flux density to 80 mJy was already tested in Wardlow et al (2013).…”

A COMPREHENSIVE VIEW OF A STRONGLY LENSEDPLANCK-ASSOCIATED SUBMILLIMETER GALAXY

“…The lensing boost of the effective angular resolution and sensitivity has allowed us to examine in unprecedented details the properties of a typical starburst galaxy when the universe is only 1/7 of its current age. HATLAS12−00 provides a prelude to a golden age of SMG research, as Herschel is unveiling hundreds of strongly lensed SMGs before the mission completes (e.g., González-Nuevo et al 2012;Wardlow et al 2012).…”

Toward a Tomographic Analysis of the Cross-Correlation Between Planck CMB Lensing and H-Atlas Galaxies

“…However, if a typical rest-frame spectral energy distribution (SED) of H-ATLAS galaxies can be identified, it can be used to estimate the redshifts directly from Herschel photometric data. Lapi et al (2011) andGonzález-Nuevo et al (2012) showed that the SED of SMM J2135-0102, "The Cosmic Eyelash" at z = 2.3 Swinbank et al 2010) is a good template for  z 1. Comparing the photometric redshift obtained with this SED with spectroscopic measurements for the 36 H-ATLAS galaxies at  z 1 for which spectroscopic redshifts were available González-Nuevo et al (2012) found a median value of…”