AI 中文总结
在 MACS J0308.9+2645 中发现引力弧候选体 A1，通过 JWST/NIRCam 成像及六波段测光得出其红移为 4.4，利用透镜模型给出相关距离和放大率等数据，还有较暗候选体 A2，该发现需光谱红移测定和专门建模确认。
AI 中文摘要
我们报告了在大规模再电离透镜星系团调查（RELICS）中的 MACS J0308.9+2645（红移 z_l = 0.356）中发现的一个强引力弧（A1），它是在 GO-5293 计划的公开 JWST/NIRCam成像中识别出来的。A1 是一个延伸的、弯曲的、切向排列的源，离星系团 X 射线中心 50.9 角秒。其六波段（1.15 - 4.10 微米）测光给出红移 z_phot = 4.4（+0.1/-0.3），P(z > 3) = 0.99。利用公开的 Zitrin-LTM-Gauss 透镜模型，A1 离红移为 4.4 的源的切向临界曲线的投影中值距离为 4.6 角秒，预计中值绝对放大率|μ| = 7。还报告了一个较暗的弧状小天体（A2）作为次要候选体。A1 不在该星系团已发表的多重成像清单以及 SIMBAD、NED 和 VizieR 数据库中。需要光谱红移测定和专门的透镜建模来确认。
英文摘要
We report a previously uncatalogued gravitational arc candidate (A1) in the massive RELICS cluster MACS J0308.9+2645 (z_l = 0.356), identified in public JWST/NIRCam imaging from programme GO-5293 through a transparent catalogue-based selection of extended, elongated, tangentially aligned sources. A1 has axis ratio a/b ~ 6.5, isophotal extent ~ 5.1 arcsec, and lies 50.9 arcsec from the cluster X-ray centre, tangentially aligned to within 1.4 +/- 3.0 deg. We show that the catalogue aper_total_abmag photometry, designed for unresolved sources, is invalid for this extended arc: the aperture captures only a few per cent of the isophotal flux and, because its radius grows with wavelength, imposes ~ 1.4 mag of spurious red colour that would drive a spurious high-redshift solution. Extended-source photometry (isophotal, fixed matched apertures, curve-of-growth) combined with archival HST/RELICS forced photometry in seven bands yields z ~ 1.4 (range 1.2-1.7). A significant HST/ACS F435W detection independently excludes the high-redshift solution, which would require a complete Lyman-limit dropout. At z ~ 1.4 the public Zitrin-LTM-Gauss lens model places A1 near the tangential critical curve in the single-image regime: full-map ray-tracing predicts no counter-images for z < 2, consistent with the absence of any counterpart, whereas a z = 4.4 source would require a counter-image of m ~ 22.7 where none is observed. The most probable interpretation is a singly lensed galaxy at z ~ 1.4 behind the cluster. The arc's curvature is concave toward the cluster centre (radius ~ 19 arcsec) but of marginal, method-dependent significance once correlated noise is accounted for. A fainter arclet (A2) is retained as a secondary candidate. Spectroscopy and a dedicated lens model are required for confirmation.
CommentsSubmitted to the Publications of the Astronomical Society of Japan (PASJ). 6 pages, 4 figures, 3 tables
