A spectroscopically confirmed z=1.327 galaxy-scale deflector magnifying a z~8 Lyman-Break galaxy in the Brightest of Reionizing Galaxies survey

Abstract

We present a detailed analysis of an individual case of gravitational lensing of a $z\sim 8$ Lyman-Break 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 ($m_{AB}=25.8$) $Y_{098}$-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-$\alpha$, H-$\beta$, [OIII] and [OII] 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 broadband flux in $H_{160}$ band at $70\sigma$, allowing us to exclude the $z\sim 8$ candidate as a low redshift interloper with broadband 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 $z\sim 8$ objects, and we make a marginal detection of a demagnified secondary image in the deepest ($J_{125}$) 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 $\mu =4.3\pm 0.2$. The reconstructed source in the best-fitting model is consistent with luminosities and morphologies of $z\sim 8$ LBGs in the literature. The lens model yields a group mass of $9.62\pm 0.31\times 10^{11}{M}_{\odot }$ and a stellar mass-to-light ratio for the brightest deflector galaxy of $M_{\star }/L_B=2.3_{-0.6}^{+0.8}{M}_{\odot }/L_{\odot }$ within its effective radius. The foreground galaxies' redshifts would make this one of the few strong lensing deflectors discovered at $z>1$.

Accepted for publication in MNRAS. 16 pages, 11 figures, 3 tables

References in corpus (31)

• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• Planck 2013 results. I. Overview of products and scientific results
• UV Luminosity Functions at redshifts z~4 to z~10: 10000 Galaxies from HST Legacy Fields
• Cosmic Reionization and Early Star-Forming Galaxies: A Joint Analysis of New Constraints from Planck and Hubble Space Telescope
• The Evolution of the Galaxy Rest-Frame Ultraviolet Luminosity Function Over the First Two Billion Years
• New Constraints on Cosmic Reionization from the 2012 Hubble Ultra Deep Field Campaign
• Galaxies in the Hubble Ultra Deep Field: I. Detection, Multiband Photometry, Photometric Redshifts, and Morphology
• Size evolution of the most massive galaxies at 1.7<z<3 from GOODS NICMOS survey imaging
• The Structure & Dynamics of Massive Early-type Galaxies: On Homology, Isothermality and Isotropy inside one Effective Radius
• The HST eXtreme Deep Field XDF: Combining all ACS and WFC3/IR Data on the HUDF Region into the Deepest Field Ever
• z~7-10 Galaxies in the HUDF and GOODS fields, and their UV Luminosity Functions
• Probing the Dawn of Galaxies at z~9-12: New Constraints from HUDF12/XDF and CANDELS Data
• A Rapidly Star-forming Galaxy 700 Million Years After the Big Bang at z=7.51
• Spectroscopic detection of CIV in a galaxy at z=7.045: Implications for the ionizing spectra of reionization-era galaxies
• The UV Luminosity Function of star-forming galaxies via dropout selection at redshifts z ~ 7 and 8 from the 2012 Ultra Deep Field campaign
• A Spectroscopic Redshift Measurement for a Luminous Lyman Break Galaxy at z=7.730 using Keck/MOSFIRE
• Spectroscopic detections of CIII]1909 at z~6-7: A new probe of early star forming galaxies and cosmic reionisation
• The changing Lya optical depth in the range 6<z<9 from MOSFIRE spectroscopy of Y-dropouts
• Dynamical masses of early-type galaxies at z~2: Are they truly superdense?
• The SL2S Galaxy-scale Lens Sample. II. Cosmic evolution of dark and luminous mass in early-type galaxies
• The Luminosity Function at z~8 from 97 Y-band dropouts: Inferences About Reionization
• Measurement of Galaxy Clustering at z~7.2 and the Evolution of Galaxy Bias from 3.8<z<8 in the XDF, GOODS-S AND GOODS-N
• The Mass Assembly History of Spheroidal Galaxies: Did Newly-Formed Systems Arise Via Major Mergers?
• The luminosity and stellar mass functions of GRB host galaxies: Insight into the metallicity bias
• The Evolving Faint-End of the Luminosity Function
• The Impact of Strong Gravitational Lensing on Observed Lyman-Break Galaxy Numbers at 4<z<8 in the GOODS and the XDF Blank Fields
• Lensview: Software for modelling resolved gravitational lens images
• Discovery of a Strong Lensing Galaxy Embedded in a Cluster at z = 1.62
• Distortion of the luminosity function of high-redshift galaxies by gravitational lensing
• Verifying the Identity of High-Redshift Massive Galaxies Through the Clustering of Lower Mass Galaxies Around Them
• Morphologies of ~190,000 Galaxies at z=0-10 Revealed with HST Legacy Data I. Size Evolution

Cited by in corpus (5)

• Correcting the z~8 Galaxy Luminosity Function for Gravitational Lensing Magnification Bias
• The Impact of Strong Gravitational Lensing on Observed Lyman-Break Galaxy Numbers at 4<z<8 in the GOODS and the XDF Blank Fields
• Galaxy candidates at z ~ 10 in archival data from the Brightest of Reionizing Galaxies (BoRG[z8]) survey
• Semi analytical description of formation of galaxies and clusters of galaxies
• Optical+NIR analysis of a Newly Confirmed Einstein ring at z$\sim$1 from the Kilo-Degree Survey: Dark matter fraction, total and dark matter density slope and IMF