[논문 리뷰] UNCOVER: A NIRSpec Census of Lensed Galaxies at z=8.50-13.08 Probing a High AGN Fraction and Ionized Bubbles in the Shadow

Seiji Fujimoto, Bingjie Wang외 34명|arXiv (Cornell University)|2023. 08. 22.

Galaxies: Formation, Evolution, Phenomena인용 수 18

한 줄 요약

JWST/NIRSpec prism spectroscopy of lensed galaxies behind Abell 2744는 z≥8.5에서 10개의 은하가 확인되었음을 확인하고, 무시할 수 없는 AGN 비율에 대한 증거를 드러내며, z=8.5에서 거대 이온화 버블을 식별하여 AGN이 재이온화에 기여할 수 있음을 시사한다.

ABSTRACT

We present JWST NIRSpec prism spectroscopy of gravitationally lensed galaxies at $z\gtrsim9$ found behind the massive galaxy cluster Abell 2744 in the UNCOVER Cycle 1 Treasury Program. We confirm the source redshift via emission lines and/or the Ly$α$ break feature for ten galaxies at z=8.50-13.08 down to $M_{ m UV}=-17.3$. We achieve a high confirmation rate of 100\% for $z>9$ candidates reported in Atek et al. (2023). Using six sources with multiple emission line detections, we find that the offset of the redshift estimates between the lines and the Ly$α$ break alone with prism can be as large as $\pm0.2$, raising caution in designing future follow-up spectroscopy for the break-only sources with ALMA. With spec-$z$ confirmed sources in UNCOVER and the literature, we derive lower limits on the rest-frame ultraviolet (UV) luminosity function (LF) at $z\simeq9$-12 and find these lower limits to be consistent with recent photometric measurements. We identify at least two unambiguous and several possible active galactic nucleus (AGN) systems based on X-ray emission, broad line (BL) H$β$, high ionization line (e.g., NIV]1487, CIV1549) detections, and excess in UVLF. This requires the AGN LFs at $z\simeq$ 9-10 to be comparable or even higher than the X-ray AGN LF estimated at $z\sim6$ and indicates a plausible cause of the high abundance of $z>9$ galaxies claimed in recent photometric studies may be AGNs. One UV-luminous source is confirmed at the same redshift as a dusty BL AGN at $z=8.50$ with a physical separation of 380 kpc in the source plane. These two sources show blueward Ly$α$ line or continuum emission, suggesting that they reside in the same ionized bubble with a radius of $7.69\pm0.18$ pMpc. Our results imply that AGNs have a non-negligible contribution to cosmic reionization.

연구 동기 및 목표

• UNCOVER behind Abell 2744에서 JWST NIRSpec prism spectroscopy를 이용해 z≥8.5 은하 후보의 적분적 적분 적분 redshift를 확인한다.
• spectroscopic redshifts를 포함한 z≈9–12에서의 UV 광도 함수와 렌즈링으로 보정된 faint 은하들을 평가한다.
• AGN 서명(넓은 선, 높은 이온화 선, X-선 연결)을 식별하고 재이온화 동안의 이온화 예산에 대한 영향을 평가한다.
• Lyα Break 동작 및 선 방출에서 추론된 고적 고-z 소스 주변의 이온화 버블의 존재와 특성을 조사한다.

제안 방법

• UNCOVER의 JWST NIRCam 이미징을 사용해 렌즈링 증가가 있는 z≥9 은하 후보를 선택한다.
• 일곱 개의 MSA 마스크에서 NIRSpec prism MOS 관측을 수행해 다수의 고-z 후보의 저해상도 스펙트럼을 얻는다.
• 데이터를 JWST 파이프라인과 msaexp로 감소시키고, 맞춤 보정 및 역분산 가중치를 사용해 1D 스펙트럼을 추출한다.
• z=0.1–20에 대해 eazy 기반 템플릿 적합으로 z_spec를 결정하고, redshift 의존성 SFH, 먼지 감쇠, IGM 감쇠 날개를 포함한다.
• Lyα break 및 약한 발산선(SNR ≥ 2.5)을 식별해 적합한 redshift를 확보하고, 다중선 소스의 z_line과 z_break를 비교한다.

Figure 1: NIRCam RGB (R: F444W, G: F356W, B: F277W) map of A2744 taken in UNCOVER (Bezanson et al. 2022 ) . The white-shaded region indicates the highly magnified area with magnifications of $\geq 2$ (Furtak et al. 2023c ) . The yellow squares show the positions of the 10 sources that are spectrosco

실험 결과

연구 질문

• RQ1 UNCOVER에서 Abell 2744 뒤에 있는 z≥8.5 은하의 분광적 redshift 분포는 무엇인가?
• RQ2 spectroscopically 확인된 소스들을 포함해, 렌즈링된 faint 은하들을 포함한 z≈9–12에서의 UV 광도 함수는 무엇인가?
• RQ3 고적 고-z 소스에 AGN 활동의 징후가 나타나는가, 그리고 이것이 재이온화 중 이온화 예산에 어떤 영향을 미치는가?
• RQ4 가까운 근접 고-z 소스 주위에 거대 이온화 버블의 증거가 있으며, 이것이 그들의 이온화 소스에 대해 무엇을 시사하는가?

주요 결과

• Ten galaxies are spectroscopically confirmed at z≥8.5, with UV magnitudes down to M_UV≈−17.3 after lensing correction.
• At least two unambiguous AGN systems are identified based on X-ray, broad Hβ, and high-ionization lines (e.g., N IV], C IV, He II), suggesting AGN LFs at z≈9–10 may be comparable to or higher than the z∼6 X-ray AGN LF.
• One UV-luminous source at z=8.50 is physically associated with a broad-line AGN at z=8.50 with a 380 kpc separation in the source plane, and they exhibit emission blueward of Lyα, indicating a giant ionized bubble with radius 7.69±0.18 pMpc.
• Several sources show unusually high [O III] 5008/Hβ ratios (e.g., >10, up to 16.3+21.8−5.9) that may indicate AGN activity or strong radiation fields; some results persist under various background subtraction methods.
• The z_phot–z_spec comparison for four A23 sources shows agreement within ~1–2σ, and z_phot estimates generally do not overestimate redshifts as strongly as some prior studies; breaks and lines yield consistent redshift constraints for most sources.
• Redshift offsets between z_line and z_break for multi-line sources are small (Δz′ ≈ −0.2 to +0.2), implying Lyα break-based redshift estimates can have ~±0.2 uncertainty

Figure 2: Zoom-in $3\mbox{\kern 0.55974pt.\kern-4.09024pt\arcsec\kern-0.43057pt}6\times 3\mbox{\kern 0.55974pt.\kern-4.09024pt\arcsec\kern-0.43057pt}6$ NIRCam RGB (R: F444W, G: F356W, B: F277W) cutouts of the 10 sources whose spec- $z$ are successfully confirmed. The rectangles show the shutter conf