TY - JOUR
T1 - A spectroscopically confirmed z = 1.327 galaxy-scale deflector magnifying a z ~ 8 Lyman-break galaxy in the Brightest of Reionizing Galaxies survey
AU - Barone-Nugent, R. L.
AU - Sonnenfeld, A.
AU - Wyithe, J. S.B.
AU - Trenti, M.
AU - Treu, T.
AU - Schmidt, K. B.
AU - Oesch, P. A.
AU - Bradley, L.
AU - Puzia, T.
N1 - Publisher Copyright:
© 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.
PY - 2015/11/1
Y1 - 2015/11/1
N2 - We present a detailed analysis of an individual case of gravitational lensing of a z ~ 8 Lymanbreak galaxy (LBG) in a blank field, identified in Hubble Space Telescope imaging obtained as part of the Brightest of Reionizing Galaxies survey. To investigate the close proximity of the bright (mAB = 25.8) Y098-dropout to a small group of foreground galaxies, we obtained deep spectroscopy of the dropout and two foreground galaxies using VLT/X-Shooter. We detect H a, H β, [O III] and [O II] emission in the brightest two foreground galaxies (unresolved at the natural seeing of 0.8 arcsec), placing the pair at z = 1.327. We can rule out emission lines contributing all of the observed broad-band flux in H160 band at 70σ, allowing us to exclude the z ~ 8 candidate as a low-redshift interloper with broad-band photometry dominated by strong emission lines. The foreground galaxy pair lies at the peak of the luminosity, redshift and separation distributions for deflectors of strongly lensed z ~ 8 objects, and we make a marginal detection of a demagnified secondary image in the deepest (J125) filter. We show that the configuration can be accurately modelled by a singular isothermal ellipsoidal deflector and a Sérsic source magnified by a factor of μ = 4.3 ± 0.2. The reconstructed source in the best-fitting model is consistent with luminosities and morphologies of z ~ 8 LBGs in the literature. The lens model yields a group mass of 9.62 ± 0.31 × 1011 M⊙ and a stellar mass-to-light ratio for the brightest deflector galaxy of M*/LB = 2.3+0.8-0.6 M⊙/L⊙ within its effective radius. The foreground galaxies' redshifts would make this one of the few strong lensing deflectors discovered at z > 1. Deeper imaging would allow for confirmation of the existence of the secondary image and elongation in the primary image, verifying multiple imaging and producing more robust estimations of the image magnifications.
AB - We present a detailed analysis of an individual case of gravitational lensing of a z ~ 8 Lymanbreak galaxy (LBG) in a blank field, identified in Hubble Space Telescope imaging obtained as part of the Brightest of Reionizing Galaxies survey. To investigate the close proximity of the bright (mAB = 25.8) Y098-dropout to a small group of foreground galaxies, we obtained deep spectroscopy of the dropout and two foreground galaxies using VLT/X-Shooter. We detect H a, H β, [O III] and [O II] emission in the brightest two foreground galaxies (unresolved at the natural seeing of 0.8 arcsec), placing the pair at z = 1.327. We can rule out emission lines contributing all of the observed broad-band flux in H160 band at 70σ, allowing us to exclude the z ~ 8 candidate as a low-redshift interloper with broad-band photometry dominated by strong emission lines. The foreground galaxy pair lies at the peak of the luminosity, redshift and separation distributions for deflectors of strongly lensed z ~ 8 objects, and we make a marginal detection of a demagnified secondary image in the deepest (J125) filter. We show that the configuration can be accurately modelled by a singular isothermal ellipsoidal deflector and a Sérsic source magnified by a factor of μ = 4.3 ± 0.2. The reconstructed source in the best-fitting model is consistent with luminosities and morphologies of z ~ 8 LBGs in the literature. The lens model yields a group mass of 9.62 ± 0.31 × 1011 M⊙ and a stellar mass-to-light ratio for the brightest deflector galaxy of M*/LB = 2.3+0.8-0.6 M⊙/L⊙ within its effective radius. The foreground galaxies' redshifts would make this one of the few strong lensing deflectors discovered at z > 1. Deeper imaging would allow for confirmation of the existence of the secondary image and elongation in the primary image, verifying multiple imaging and producing more robust estimations of the image magnifications.
KW - Cosmology: observations
KW - Galaxies: high-redshift
KW - Gravitational lensing: strong
UR - http://www.scopus.com/inward/record.url?scp=84947815826&partnerID=8YFLogxK
U2 - 10.1093/mnras/stv1872
DO - 10.1093/mnras/stv1872
M3 - Article
AN - SCOPUS:84947815826
SN - 0035-8711
VL - 453
SP - 3068
EP - 3081
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 3
ER -