A Single Line-Emitter Identified in an Unbiased Search with JWST/NIRSpec: Multi-Object Coronagraphy for Slitless Spectroscopy

@misc{huberty2026single,
  title = {{A Single Line-Emitter Identified in an Unbiased Search with JWST/NIRSpec: Multi-Object Coronagraphy for Slitless Spectroscopy}},
  author = {Mason S. Huberty and Claudia Scarlata and Matthew J. Hayes and Alaina Henry and Danielle A. Berg and Vieri Cammelli and Richard Ellis and Anne E. Jaskot and Yu-Heng Lin and Vihang Mehta and Matilde Mingozzi and Pierluigi Monaco and Alberto Saldana-Lopez and Aayush Saxena and Jonathan C. Tan and Alice Young},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.12553},
  eprint = {2610.12553},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.12553},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - A Single Line-Emitter Identified in an Unbiased Search with JWST/NIRSpec: Multi-Object Coronagraphy for Slitless Spectroscopy
AU  - Mason S. Huberty
AU  - Claudia Scarlata
AU  - Matthew J. Hayes
AU  - Alaina Henry
AU  - Danielle A. Berg
AU  - Vieri Cammelli
AU  - Richard Ellis
AU  - Anne E. Jaskot
AU  - Yu-Heng Lin
AU  - Vihang Mehta
AU  - Matilde Mingozzi
AU  - Pierluigi Monaco
AU  - Alberto Saldana-Lopez
AU  - Aayush Saxena
AU  - Jonathan C. Tan
AU  - Alice Young
PY  - 2026
DA  - 2026/10/08
PB  - arXiv
DO  - 10.48550/arxiv.2610.12553
UR  - https://arxiv.org/abs/2610.12553
AB  - We report the detection of a previously unknown object with a single emission line within the Hubble Ultra Deep Field, using a new JWST NIRSpec technique called Multi-Object Coronagraphy for Slitless Spectroscopy (MOCSS) with the G140M/F100LP observing mode. The MOCSS technique involves opening almost all the shutters on the NIRSpec microshutter array, while simultaneously closing the shutters that lie on top of known low redshift objects, facilitating a wide field slitless spectroscopic search without contamination from bright objects. This observational technique has enabled the detection of a strong emission line in four different dither positions and in two position angles, and thus cannot be artificial. This line is detected at 1.60 μm with a line flux of [2.5± 0.3]×10^−18 erg s^−1 cm^−2 and a FWHM of 13.2±2.0Å, and does not correspond to any known source with some of the deepest HST and JWST imaging in existence. Based upon the absence of imaging detection, we place a lower limit on the observed frame equivalent width (EW) of 7620Å on this object, which strongly limits the number of possible lines that this line can be. Given the wavelength, an EW limit that is near the ceiling of expectation, and the lack of other lines in the bandpass, this line cannot be easily explained by [OII] at z=3.29, [OIII] at z=2.20, Hα at z=1.44, and Lyα at z=12.16. We discuss possible AGN and transient phenomena that could explain the finding.
ER  -