Year: 2026
Type: preprint
Abstract: We present an initial demographic study of Ly$α$ profiles in little red dots (LRDs) at $z=3$--9 using $R\sim1000$--4000 spectroscopy. Our sample consists of 8 LRDs observed in the VLT/MUSE Deep and Wide surveys and 23 LRDs observed with JWST/NIRSpec grating spectroscopy from JADES, CANUCS, and GO programs including SPURS. We identify Ly$α$ emission in 5 MUSE LRDs and 9 JWST LRDs. Only two of them exhibit broad Ly$α$ emission (FWHM $>1000\ \mathrm{km\ s^{-1}}$), both reported previously. The other Ly$α$-emitting LRDs show narrow Ly$α$ emission (FWHM $<1000\ \mathrm{km\ s^{-1}}$), with FWHMs mostly in the range 300--600 $\mathrm{km\ s^{-1}}$, comparable to or slightly larger than those of high-redshift star-forming galaxies (100--500 $\mathrm{km\ s^{-1}}$). We measure the fraction of broad Ly$α$ emitters above a broad Ly$α$ luminosity threshold of $L_{\mathrm{Ly}α,\mathrm{broad}}=10^{42}\ \mathrm{erg\ s^{-1}}$, obtaining $0.10^{+0.12}_{-0.07}$ for LRDs, about five times higher than the $2σ$ upper limit of $<0.02$ for high-redshift star-forming galaxies. Although we reproduce the broad Ly$α$ component reported in a previous stacking analysis of eight LRDs, albeit with a large uncertainty, we find no evidence for broad Ly$α$ emission in either the larger JWST stack, after excluding the two individually detected broad Ly$α$ emitters, or the higher-resolution MUSE stack. These results suggest that broad Ly$α$ emission is not ubiquitous among LRDs. Instead, LRDs with broad Ly$α$ emission appear to represent a rare population that may correspond to a particular evolutionary stage, potentially associated with unusually strong outflows or other distinctive physical conditions.
Source: arXiv (Cornell University)
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Aeronautics and Space Administration, Space Telescope Science Institute, National Research Foundation, Ministry of Education, Culture, Sports, Science and Technology, Danmarks Grundforskningsfond, Japan Society for the Promotion of Science, Institute for Cosmic Ray Research, University of Tokyo
Awards: G103270039, G1338664626, ＪＷＳＴとＰＦＳのα/Ｆｅ測定で探る遠方銀河の超新星爆発と天の川銀河の恒星の起源, 徹底的なJWST研究で迫る初代銀河と極金属欠乏初期銀河の統計的性質, 可視・近赤外分光で探る宇宙再電離の起源天体, G256731684, Uncovering Early Cosmic Evolution with JWST and Subaru/PFS Spectroscopy and Theoretical Modeling, Cosmic Dawn Center (DAWN), Investigating the first star formation and reionization process of the Universe by MWA, G5568641063, G6531013582, G6603402766, Comprehensive understanding of the formation history of structures in the Universe, 極金属欠乏銀河のヘリウム組成比で探る宇宙のレプトン非対称性, First galaxy formation probed by thorough analysis of JWST data
OpenAlex ID: W7203633178