J-PAS: Discovery of RaJav, a bright spatially extended Ly$α$ Nebula at z=2.25

TL;DR

RaJav is a giant Ly$\alpha$ nebula at $z=2.245$ discovered around a quasar pair in the J-PAS EDR. It hosts a faint embedded quasar JPAS-9600-10844 at a projected distance of $7.31''$ ($60.2$ kpc) from the bright J1620+4334, with an extended Ly$\alpha$+$CIV$>$ nebula reaching $15.38''$ ($126.7$ kpc) and $L_{Ly\alpha}\approx5.84\times10^{44}$ erg s$^{-1}$, $L_{CIV}\approx3.7\times10^{44}$ erg s$^{-1}$ after continuum subtraction. The nebula shows a bridge between the quasars, metal-enriched CGM traced by CIV, and signs of strong quasar outflows; extended UV continuum indicates concurrent star formation, all within a large-scale overdensity potentially connected to the cosmic web. The findings demonstrate J-PAS's capability to detect rare, massive Ly$\alpha$ nebulae over wide cosmological volumes and motivate deep IFU spectroscopy to map kinematics and disentangle powering mechanisms—photoionization by AGN, shocks from outflows, and star-formation activity—during the peak epoch of galaxy formation.

Abstract

We report the discovery of a massive and potentially largest Ly$α$ Nebula, RaJav, at z=2.25, associated with a quasar pair: the bright SDSS~J162029.07+433451.1 (hereafter J1620+4334) and the faint newly discovered quasar JPAS-9600-10844, at 2.265 $\pm$ 0.021 using the early data release (17 deg$^{2}$) of the J-PAS. The quasar JPAS-9600-10844 embedded in the nebula is located at ~ 60.2 kpc (7.3'') from J1620+4334, and shows a compact structure with broad emission lines (> 3000 km/s), typical of active galactic nuclei. At a 2$σ$ surface brightness (SB) contour of $\sim 1.86 \times 10^{-16}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$, the nebula extends > 100 kpcs and has a total Ly$α$ luminosity of $\sim 5.8 \pm 0.7 \times 10^{44}$ erg s$^{-1}$ signify the presence of a giant Enormous Ly$α$ Nebula (ELAN). The nebula traces an over density of quasars at redshift of 2.2-2.3 consistent with the progenitor of a massive galaxy cluster. The extended CIV emission indicates that the circum-galactic medium (CGM) is metal-enriched and not primordial. The current J-PAS observations suggest photoionization and shocks due to outflows as possible ionization mechanisms. The faint extended FUV and NUV continuum emission likely points to ongoing star formation around the two quasars, suggesting a complex interaction in their environments. These findings provide new insights into the environment of quasars and their role in shaping the dynamics and evolution of the CGM at cosmic noon. Further spectroscopic observations will be required to fully characterize the object's nature and its kinematic properties. This study demonstrates the unique capability of J-PAS to detect massive and rare Ly$α$ nebulae, providing new insights into their properties, environments, and connections to large-scale structures in the cosmic web such as filaments and overdensities in a large cosmological volume.

Figures (6)

• Figure 1: Co-added J-PAS NB image of a) Ly$\alpha$ +continnum (J0390+J0400+J0410), b) CIV +continnum (J0490+J0500+J0510), and c) continuum (J0420+J0440+J0450). Broad band image from d) HSC i-band. SB contours in the panels a and c are from the Ly$\alpha$ image (levels: 1.3$\sigma$, 2$\sigma$,3$\sigma$,10$\sigma$, and 100$\sigma$), in panel b is from HSC g-band (partially including Ly$\alpha$ and CIV) image (levels: 2$\sigma$,3$\sigma$,5$\sigma$,10$\sigma$,20$\sigma$ and 1000$\sigma$) and the panel d overlaid with radio LOFAR 144 MHz contours (levels: 2$\sigma$,2.5$\sigma$,4$\sigma$, 6$\sigma$, 8$\sigma$, and 9.5$\sigma$). The positions of the bright quasar J1620+4334, the faint quasar JPAS-9600-10844, and the Ly$\alpha$ emitting region are labeled as R1, R2, and R3, respectively and RaJav nebula defined in blue contour.
• Figure 2: Upper panel: J-spectra of JPAS-9600-10844. Bottom panel: Normalized photospectra of JPAS-9600-10844 and J1620+4334, along with the normalized SDSS spectrum of J1620+4334.
• Figure 3: Luminosity-size diagram of Ly$\alpha$ nebulae: from 2024Li, around quasar pairs 2024Herwig, ELANe 2014Cantalupo2015Hennawi2017Cai2022Arrigoni2018Arrigoni, and RaJav (yellow star). Colors show the SB depth (2$\sigma$) of each nebula. Fabulous nebula is also shown in J-PAS depth (green square).
• Figure 4: J-PAS NB image of a) J0390, b) J0400, and c) J0410 covering Ly$\alpha$+cont, J0450 covering continuum e) J0490, f) J0500, g) J0510, covering CIV+cont, and h) J0530 covering HeII+cont.
• Figure 5: Radial surface brightness profiles extracted in four angular sectors around J1620+4334 (Left: from coadded Ly$\alpha$+cont, Right: from coadded CIV+cont image). The conical regions (over-plotted on the coadded image is on top right) correspond to position angle intervals of 50$^{\circ}$–120$^{\circ}$ (mint green), 140$^{\circ}$–210$^{\circ}$ (blue), 230$^{\circ}$–300$^{\circ}$ (pink), and 320$^{\circ}$–30$^{\circ}$ (olive). The circularly averaged SB profile are in black. The distances of the quasars from the center of J1620+4334 are indicated by red circles and the grey curve is from the PSF.