A highly magnified candidate for a young galaxy seen when the Universe was 500 Myrs old (1204.2305v1)

Abstract: The early Universe at redshift z\sim6-11 marks the reionization of the intergalactic medium, following the formation of the first generation of stars. However, those young galaxies at a cosmic age of \lesssim 500 million years (Myr, at z \gtrsim 10) remain largely unexplored as they are at or beyond the sensitivity limits of current large telescopes. Gravitational lensing by galaxy clusters enables the detection of high-redshift galaxies that are fainter than what otherwise could be found in the deepest images of the sky. We report the discovery of an object found in the multi-band observations of the cluster MACS1149+22 that has a high probability of being a gravitationally magnified object from the early universe. The object is firmly detected (12 sigma) in the two reddest bands of HST/WFC3, and not detected below 1.2 {\mu}m, matching the characteristics of z\sim9 objects. We derive a robust photometric redshift of z = 9.6 \pm 0.2, corresponding to a cosmic age of 490 \pm 15Myr (i.e., 3.6% of the age of the Universe). The large number of bands used to derive the redshift estimate make it one of the most accurate estimates ever obtained for such a distant object. The significant magnification by cluster lensing (a factor of \sim15) allows us to analyze the object's ultra-violet and optical luminosity in its rest-frame, thus enabling us to constrain on its stellar mass, star-formation rate and age. If the galaxy is indeed at such a large redshift, then its age is less than 200 Myr (at the 95% confidence level), implying a formation redshift of zf \lesssim 14. The object is the first z>9 candidate that is bright enough for detailed spectroscopic studies with JWST, demonstrating the unique potential of galaxy cluster fields for finding highly magnified, intrinsically faint galaxies at the highest redshifts.

• The paper demonstrates that gravitational lensing by MACS J1149.6+2223 magnified MACS1149-JD1 by roughly 15 times, enabling its detection.
• The paper uses multi-band photometry to achieve a robust redshift estimate of z = 9.6 ± 0.2 and to derive the galaxy’s stellar mass and star formation rate.
• The paper underscores MACS1149-JD1 as a prime target for JWST spectroscopy to explore early galactic conditions and the reionization epoch.

Analysis of a Gravitationally Lensed High-Redshift Galaxy Candidate

The astrophysical research presented elucidates the discovery of a highly magnified galaxy candidate, denoted as MACS1149-JD1, positioned at a redshift of approximately $z = 9.6$. This redshift corresponds to a cosmic age of roughly 490 million years post-Big Bang, offering an opportunity to observe the universe in its formative epochs. The paper utilizes the gravitational lensing effect of the massive galaxy cluster MACS J1149.6+2223, which serves as a natural telescope, enhancing the brightness of the distant galaxy by a factor of approximately 15, facilitating its detection with currently available space-based observatories.

Key Findings

1. Photometric Redshift Estimation:
   • The paper achieves a robust photometric redshift estimate of $z = 9.6 \pm 0.2$, utilizing an overview of multiple observational bands. The credibility of such an elevated redshift derives from detections in the infrared spectrum while registering non-detections in wavelengths below 1.2 μm, consistent with high-redshift sources.
2. Lensing and Magnification:
   • Exploiting the gravitational lensing provided by MACS J1149.6+2223, the paper employs sophisticated modeling techniques, yielding a magnification estimate of $\mu = 14.5^{+4.2}_{-1.0}$. This significant magnification allows for the detailed analysis of a galaxy that would otherwise remain beyond detection limits.
3. Physical Properties and Implications:
   • The paper estimates a stellar mass of approximately $1.5 \times 10^8$ solar masses and a star formation rate around $1.2$ solar masses per year. The galaxy's likely formation redshift $z_f$ suggests that stellar activity commenced at $z < 14.2$, contributing to the reionization epoch.
4. Spectroscopic Potential:
   • MACS1149-JD1 represents a prime target for follow-up spectroscopic observations with the James Webb Space Telescope (JWST). Its brightness and significant lensing effect provide a rare opportunity to understand the physical conditions and processes in early universe galaxies.

Implications and Future Prospects

The discovery of MACS1149-JD1 offers substantial implications for the paper of cosmic reionization and early galaxy formation. The galaxy's physical characteristics imply that even in extreme early epochs, rapid assembly and star formation activities were underway, playing a critical role in reionizing the intergalactic medium. The magnification by the foreground galaxy cluster underscores the utility of gravitational lenses in probing the distant universe, emphasizing the necessity of such approaches in cosmological investigations.

Looking forward, the analytical techniques and observational methodologies developed in this paper pave the way for similar discoveries using more advanced telescopes. The precise spectroscopic paper of MACS1149-JD1 by JWST could unveil detailed insights into its chemical composition, dust content, and ionizing capabilities, augmenting our understanding of primordial star-forming environments. Additionally, integrating similar lensing surveys with systematic modeling will advance the field of high-redshift astronomy, potentially uncovering an extensive population of faint, early-universe galaxies.

In conclusion, this research exemplifies the synergy of gravitational lensing and advanced imaging capabilities in unveiling the remote universe, enhancing our comprehension of galaxy evolution during the nascent phases of cosmic history.