J/MNRAS/493/4276 A search for the lenses in the HerBS sample (Bakx+, 2020)
A search for the lenses in the Herschel Bright Sources (HerBS) sample.
Bakx T.J.L.C., Eales S., Amvrosiadis A.
<Mon. Not. R. Astron. Soc., 493, 4276-4293 (2020)>
=2020MNRAS.493.4276B 2020MNRAS.493.4276B (SIMBAD/NED BibCode)
ADC_Keywords: Gravitational lensing ; Galaxies ; Millimetric/submm sources ;
Optical ; Infrared ; Redshifts
Keywords: gravitational lensing: strong - galaxies: high redshift -
submillimetre: galaxies
Abstract:
Verifying that sub-mm galaxies are gravitationally lensed requires
time-expensive observations with oversubscribed high-resolution
observatories. Here, we aim to strengthen the evidence of
gravitational lensing within the Herschel Bright Sources (HerBS) by
cross-comparing their positions to optical (SDSS) and near-infrared
(VIKING) surveys, in order to search for the foreground lensing galaxy
candidates. Resolved observations of the brightest HerBS sources have
already shown that most are lensed, and a galaxy evolution model
predicts that ∼76 per cent of the total HerBS sources are lensed,
although with the SDSS survey we are only able to identify the likely
foreground lenses for 25 per cent of the sources. With the
near-infrared VIKING survey, however, we are able to identify the
likely foreground lenses for 57 per cent of the sources, and we
estimate that 82 per cent of the HerBS sources have lenses on the
VIKING images even if we cannot identify the lens in every case. We
find that the angular offsets between lens and Herschel source are
larger than that expected if the lensing is done by individual
galaxies. We also find that the fraction of HerBS sources that are
lensed falls with decreasing 500-micron flux density, which is
expected from the galaxy evolution model. Finally, we apply our
statistical VIKING cross-identification to the entire Herschel-ATLAS
catalogue, where we also find that the number of lensed sources falls
with decreasing 500-micron flux density.
Description:
The HerBS sample consists of the brightest sources from the 660 square
degree Herschel-ATLAS survey (Eales et al. 2010PASP..122..499E 2010PASP..122..499E;
Valiante et al. 2016MNRAS.462.3146V 2016MNRAS.462.3146V, Cat. J/MNRAS/462/3146). HerBS
galaxies are selected with SPIRE S500µm>80mJy and photometric
redshifts zphot>2. These photometric redshifts were obtained by
fitting the dust spectral energy distribution that Pearson et al.
(2013MNRAS.435.2753P 2013MNRAS.435.2753P) found was a good fit to the sub-mm flux
densities of high-redshift Herschel sources to the sub-mm flux
densities of each HerBS source. Local galaxies and blazars have been
removed with the use of 850µm SCUBA-2 observations (Bakx et al.
2018MNRAS.473.1751B 2018MNRAS.473.1751B, Cat. J/MNRAS/473/1751). The sample of Negrello et
al. (2017MNRAS.465.3558N 2017MNRAS.465.3558N, Cat. J/MNRAS/465/3558), a sample of
potential lensed sources with S500µm>100mJy, has 63 sources in
common with HerBS.
We carried out our own search for lenses on the VIKING near-infrared
survey, adapting the standard statistical method of finding
counterparts to Herschel sources to allow for the fact that most of
the sources are probably lensed. We found probable lenses for 56 out
of 98 HerBS sources.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 69 98 Table of VIKING counterparts
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See also:
J/MNRAS/462/3146 : Herschel-ATLAS DR1 (HATLAS) (Valiante+, 2016)
II/343 : VIKING catalogue data release 2 (Edge+, 2016)
J/A+A/632/A34 : KiDS+VIKING-450 opt+NIR dataset (Wright+, 2019)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- ID [2/209] HerBS identifier (HerBS NNN in Simbad)
5- 8 F4.2 --- zsubmm Sub-mm and near-infrared redshift
10- 13 F4.2 --- R ? Reliability (1)
15- 19 F5.2 mag Ksmag ? Ks-band magnitude
21- 24 F4.2 mag e_Ksmag ? Error on Ksmag
26- 29 F4.2 arcsec theta ? Angular separation between the Herschel and
VIKING position
31- 39 F9.5 deg RAdeg ? Right ascension (J2000) (2)
41- 49 F9.5 deg DEdeg ? Declination (J2000) (2)
51- 55 F5.3 --- zVIK ? Redshift from VIKING, Wright et al.
(2019A&A...632A..34W 2019A&A...632A..34W, Cat. J/A+A/632/A34)
57- 61 F5.3 --- E_zVIK ? Upper error on zVIK
63- 67 F5.3 --- e_zVIK ? Lower error on zVIK
69 A1 --- f_zVIK [*] Flag on zVIK (3)
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Note (1): We estimate the actual probability (the 'reliability') that a
potential counterpart is associated with a Herschel source by the
weighted combination of the likelihood ratios of all potential
counterparts near to that source:
Rj=Lj/[ΣiLi+(1-Q0)]
The reliability Rj of each potential match, j, is computed as the
ratio of its likelihood ratio (Lj) to the sum of the likelihood
ratios of all potential matches within 10arcsec. An extra term in the
denominator, (1-Q0), accounts for the possibility that the
optical/near-IR counterpart to the Herschel source is not visible on
the images.
Note (2): Positions form VIKING
Note (3): Flag as follows:
* = zVIK is found by using the EAZY package.
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 28-Apr-2023