CLASH: Three Strongly Lensed Images of a Candidate z ~ 11 Galaxy (1211.3663v1)

Abstract: We present a candidate for the most distant galaxy known to date with a photometric redshift z = 10.7 +0.6 / -0.4 (95% confidence limits; with z < 9.5 galaxies of known types ruled out at 7.2-sigma). This J-dropout Lyman Break Galaxy, named MACS0647-JD, was discovered as part of the Cluster Lensing and Supernova survey with Hubble (CLASH). We observe three magnified images of this galaxy due to strong gravitational lensing by the galaxy cluster MACSJ0647.7+7015 at z = 0.591. The images are magnified by factors of ~8, 7, and 2, with the brighter two observed at ~26th magnitude AB (~0.15 uJy) in the WFC3/IR F160W filter (~1.4 - 1.7 um) where they are detected at >~ 12-sigma. All three images are also confidently detected at >~ 6-sigma in F140W (~1.2 - 1.6 um), dropping out of detection from 15 lower wavelength HST filters (~0.2 - 1.4 um), and lacking bright detections in Spitzer/IRAC 3.6um and 4.5um imaging (~3.2 - 5.0 um). We rule out a broad range of possible lower redshift interlopers, including some previously published as high redshift candidates. Our high redshift conclusion is more conservative than if we had neglected a Bayesian photometric redshift prior. Given CLASH observations of 17 high mass clusters to date, our discoveries of MACS0647-JD at z ~ 10.8 and MACS1149-JD1 at z ~ 9.6 are consistent with a lensed luminosity function extrapolated from lower redshifts. This would suggest that low luminosity galaxies could have reionized the universe. However given the significant uncertainties based on only two galaxies, we cannot yet rule out the sharp drop off in number counts at z >~ 10 suggested by field searches.

• The paper identifies three strongly lensed images of MACS0647-JD, confirming its high-redshift nature (z ~11) via multi-band photometric analysis.
• The study employs gravitational lensing models and photometric redshift tools like BPZ and LePHARE, reporting magnifications of approximately 8, 7, and 2.
• The paper suggests that low-luminosity galaxies such as MACS0647-JD may play a key role in cosmic reionization, setting the stage for future JWST observations.

Essay on CLASH: Three Strongly Lensed Images of a Candidate $z \approx 11$ Galaxy

The paper by Coe et al. reports the identification of three strongly lensed images of a high-redshift galaxy candidate at $z \approx 11$, named MACS0647-JD, discovered as part of the Cluster Lensing And Supernova Survey with Hubble (CLASH). Using extensive photometric observations from the Hubble Space Telescope (HST) and Spitzer Space Telescope, the paper argues for the high redshift nature of the galaxy, leveraging strong gravitational lensing by the galaxy cluster MACSJ0647+70.

Observational Setup and Data Analysis

The observations were conducted using HST's Advanced Camera for Surveys (ACS) and the Wide Field Camera 3 (WFC3/IR) across multiple filters. The use of gravitational lensing allowed the researchers to observe three magnified images of MACS0647-JD, significantly enhancing the ability to paper such faint and distant objects. Photometric redshifts were derived using the Bayesian Photometric Redshift (BPZ) code, complemented by the LePHARE photometric redshift fitting tool, providing estimates that favor a high-redshift interpretation for MACS0647-JD over a broad range of potential low-redshift interlopers.

Key Results

• High Confidence in Redshift: The candidate's photometric redshift is estimated at $z \approx 11$, with lower redshift solutions statistically disfavored. This is substantiated by the drop-out signature exhibited by the galaxy across 15 lower wavelength bands.
• Lensing Magnification and Image Analysis: Through lens modeling, the paper confirms that the three images correspond to magnifications of approximately $\sim$8, 7, and 2, providing a valuable opportunity to discern intrinsic properties of the galaxy, which would otherwise be too faint.
• Consideration of Lower Redshift Aliens: Despite potential contaminations from low-redshift galaxies, stars, or even intermediate redshift galaxies with peculiar SEDs, the analysis effectively rules out these options based on the unique photometric signature and the failure of any interlopers to replicate the observed data across all filters.
• Physical Properties: The candidate exhibits a rest-frame UV luminosity suggesting an active star formation rate and a compact physical morphology, hinting at the types of conditions present in early universal epochs. Importantly, constraints on mass and size indicate the galaxy is typical or somewhat below average in size and mass relative to lower-redshift counterparts of similar luminosity.

Theoretical Implications and Future Perspectives

This potential detection at $z \approx 11$ offers implications for our understanding of galaxy formation in the early universe. It suggests that low-luminosity galaxies might play a crucial role in the reionization of the universe, though this is highly contingent on larger samples to better define the high-redshift luminosity function and star formation rates.

Looking forward, the paper highlights the importance and utility of lensing surveys coupled with deep multi-band imaging, demonstrating the power of Hubble paired with Spitzer data to push the boundaries of redshift detection even further. Future observatories, such as the James Webb Space Telescope, will undoubtedly build on this foundation, potentially unlocking even more secrets about the universe's infancy with unprecedented sensitivity and resolution.

In summary, Coe et al.'s work exemplifies the promising synergy of advanced observational techniques in the quest to better understand the epoch of galaxy formation and evolution. The candidate MACS0647-JD stands as a testament to the capabilities of leveraging cosmic phenomena to act as natural telescopes, pushing the observable universe closer to its beginnings.