Colour matters: the effects of lensing on the positional offsets between optical and submillimetre galaxies in Herschel-ATLAS

Abstract

We report an unexpected variation in the positional offset distributions between Herschel-ATLAS sub-millimetre (submm) sources and their optical associations, depending on both 250-μm signal-to-noise ratio and 250/350-μm colour. We show that redder and brighter submm sources have optical associations with a broader distribution of positional offsets than would be expected if these offsets were due to random positional errors in the source extraction. The observation can be explained by two possible effects: either red submm sources trace a more clustered population than blue ones, and their positional errors are increased by confusion; or red submm sources are generally at high redshifts and are frequently associated with low-redshift lensing structures which are identified as false counterparts. We perform various analyses of the data, including the multiplicity of optical associations, the redshift and magnitude distributions in H-ATLAS in comparison to HerMES, and simulations of weak lensing, and we conclude that the effects are most likely to be explained by widespread weak lensing of Herschel-SPIRE sources by foreground structures. This has important consequences for counterpart identification and derived redshift distributions and luminosity functions of submm surveys.

10 pages, 6 figures. Accepted for publication in MNRAS

References in corpus (54)

• The Sloan Digital Sky Survey: Technical Summary
• The Seventh Data Release of the Sloan Digital Sky Survey
• Herschel Space Observatory - An ESA facility for far-infrared and submillimetre astronomy
• The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory
• The Herschel-SPIRE instrument and its in-flight performance
• Accurate photometric redshifts for the CFHT Legacy Survey calibrated using the VIMOS VLT Deep Survey
• K-corrections and filter transformations in the ultraviolet, optical, and near infrared
• Unveiling Dust-enshrouded Star Formation in the Early Universe: a Sub-mm Survey of the Hubble Deep Field
• A Deep Sub-millimeter Survey of Lensing Clusters: A New Window on Galaxy Formation and Evolution
• Galaxy and Mass Assembly (GAMA): survey diagnostics and core data release
• The 6dF Galaxy Survey: Final Redshift Release (DR3) and Southern Large-Scale Structures
• The Tenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Apache Point Observatory Galactic Evolution Experiment
• Galaxy Clustering in the Completed SDSS Redshift Survey: The Dependence on Color and Luminosity
• The Herschel Multi-tiered Extragalactic Survey: HerMES
• The Herschel ATLAS
• SCUBA-2: The 10000 pixel bolometer camera on the James Clerk Maxwell Telescope
• The Detection of a Population of Submillimeter-Bright, Strongly-Lensed Galaxies
• A median redshift of 2.4 for galaxies bright at submillimetre wavelengths
• Cosmic Variance and Its Effect on the Luminosity Function Determination in Deep High z Surveys
• A Critical Assessment of Photometric Redshift Methods: A CANDELS Investigation
• Deep radio imaging of the SCUBA 8-mJy survey fields: sub-mm source identifications and redshift distribution
• An ALMA survey of submillimeter galaxies in the Extended Chandra Deep Field South: Source catalog and multiplicity
• The SCUBA HAlf Degree Extragalactic Survey (SHADES) - III. Identification of radio and mid-infrared counterparts to submillimetre galaxies
• The Sloan Lens ACS Survey. IX. Colors, Lensing and Stellar Masses of Early-type Galaxies
• An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field South: High resolution 870um source counts
• Astrophysical and Cosmological Information from Large-scale sub-mm Surveys of Extragalactic Sources
• Submillimetre galaxies in a hierarchical universe: number counts, redshift distribution, and implications for the IMF
• Photometric redshifts for the CFHTLS T0004 Deep and Wide fields
• Herschel-ATLAS Galaxy Counts and High Redshift Luminosity Functions: The Formation of Massive Early Type Galaxies
• The 2dF-SDSS LRG and QSO (2SLAQ) Luminous Red Galaxy Survey
• The Herschel Multi-Tiered Extragalactic Survey: Source Extraction and Cross-Identifications in Confusion-Dominated SPIRE Images
• HerMES: Candidate Gravitationally Lensed Galaxies and Lensing Statistics at Submillimeter Wavelengths
• Redshift Distribution of the Faint Submillimeter Galaxy Population
• Radio Constraints on the Identifications and Redshifts of Submm Galaxies
• AzTEC millimeter survey of the COSMOS field - III. Source catalog over 0.72 sq. deg. and plausible boosting by large-scale structure
• The 2dF-SDSS LRG and QSO Survey: The spectroscopic QSO catalogue
• Herschel-ATLAS: First data release of the Science Demonstration Phase source catalogues
• Herschel-ATLAS: counterparts from the UV--NIR in the science demonstration phase catalogue
• Herschel-ATLAS: Dust temperature and redshift distribution of SPIRE and PACS detected sources using submillimetre colours
• The Angular Correlation Function of Galaxies from Early SDSS Data
• A joint analysis of BLAST 250--500um and LABOCA 870um observations in the Extended Chandra Deep Field South
• The first release of data from the Herschel ATLAS: the SPIRE images
• Confusion errors in astrometry and counterpart association
• H-ATLAS: PACS imaging for the Science Demonstration Phase
• Herschel-ATLAS: towards a sample of ~1000 strongly-lensed galaxies
• Effective Models for Statistical Studies of Galaxy-Scale Gravitational Lensing
• The properties of (sub)millimetre-selected galaxies as revealed by CANDELS HST WFC3/IR imaging in GOODS-South
• On the cross-correlation of sub-mm sources and optically-selected galaxies
• HerMES: detection of cosmic magnification of sub-mm galaxies using angular cross-correlation
• Effect of clustering on extragalactic source counts with low-resolution instruments
• Herschel-ATLAS: VISTA VIKING near-IR counterparts in the Phase 1 GAMA 9h data
• Herschel-ATLAS/GAMA: SDSS cross-correlation induced by weak lensing
• Correlations between bright submillimetre sources and low-redshift galaxies
• Submillimetre Source Counts in the Fields of High-Redshift Galaxy Clusters

Cited by in corpus (13)

• ALMA Long Baseline Observations of the Strongly Lensed Submillimeter Galaxy HATLAS J090311.6+003906 at z=3.042
• The East Asian Observatory SCUBA--2 survey of the COSMOS field: unveiling 1147 bright sub-millimeter sources across 2.6 square degrees
• The Herschel-ATLAS Data Release 1 Paper II: Multi-wavelength counterparts to submillimetre sources
• The SCUBA-2 Cosmology Legacy Survey: The EGS deep field - II. Morphological transformation and multi-wavelength properties of faint submillimetre galaxies
• H-ATLAS/GAMA: Magnification Bias Tomography. Astrophysical constraints above $\sim 1$ arcmin
• A search for the lenses in the Herschel Bright Sources (HerBS) Sample
• The second Herschel-ATLAS Data Release - III: optical and near-infrared counterparts in the North Galactic Plane field
• Herschel-ATLAS Data Release III: Near-infrared counterparts in the South Galactic Pole field -- Another 100,000 submillimetre galaxies
• Herschel-ATLAS : The spatial clustering of low and high redshift submillimetre galaxies
• SHALOS: Statistical Herschel-ATLAS Lensed Objects Selection
• ALMA 26 arcmin${}^2$ survey of GOODS-S at one-millimeter (ASAGAO): millimeter properties of stellar mass selected galaxies
• Over-density of SMGs in fields containing z~0.3 galaxies: magnification bias and the implications for studies of galaxy evolution
• Multifrequency filter search for high redshift sources and lensing systems in Herschel-ATLAS