AI 中文总结
本研究通过VLT/MUSE和JWST数据，分析z=3-9的小红点（LRDs）的Lyα轮廓，发现宽Lyα发射仅为LRDs中的罕见现象，或对应特定演化阶段，占比约为高红移恒星形成星系的5倍。
AI 中文摘要
我们利用分辨率R~1000-4000的光谱，对红移z=3至9的小红点（LRDs）的莱曼α（Lyα）轮廓开展了初步人口统计学研究。样本包含8个在VLT/MUSE深场与宽场巡天中观测到的LRDs，以及23个来自JADES、CANUCS和含SPURS项目的GO计划、由JWST/NIRSpec光栅光谱观测得到的LRDs。我们在5个MUSE LRDs和9个JWST LRDs中探测到了Lyα发射线；其中仅2个呈现宽Lyα发射（半高全宽FWHM>1000 km s⁻¹），且均为此前已报道的天体。其余探测到Lyα发射的LRDs均呈现窄Lyα发射（FWHM<1000 km s⁻¹），其FWHM大多处于300-600 km s⁻¹区间，与高红移恒星形成星系的FWHM（100-500 km s⁻¹）相当或略大。我们在宽Lyα光度阈值L_{Lyα,broad}=10⁴² erg s⁻¹的条件下，测量了宽Lyα发射体的占比，得到LRDs的占比为0.10⁺⁰·¹²₋₀·⁰⁷，约为高红移恒星形成星系2σ上限（<0.02）的5倍。尽管我们复现了此前对8个LRDs开展堆叠分析所报道的宽Lyα成分（尽管不确定性较大），但在排除2个单独探测到的宽Lyα发射体后，无论是更大样本的JWST堆叠、还是更高分辨率的MUSE堆叠，均未发现宽Lyα发射的证据。这些结果表明，宽Lyα发射并非LRDs的普遍现象；相反，具有宽Lyα发射的LRDs似乎是一个罕见的群体，可能对应某个特定演化阶段，或与异常强烈的外流及其他独特物理条件相关。
英文摘要
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.
Comments23 pages, 12 figures, submitted to ApJ
