Discovery of a giant and luminous Lyα+C IV+He II nebula at z = 3.326 with extreme emission line ratios

Abstract

We present the discovery of HLock01-LAB, a luminous and large Lyα nebula at z = 3.326. Medium-band imaging and long-slit spectroscopic observations with the Gran Telescopio Canarias reveal extended emission in the Lyα 1215Å, C iv 1550Å, and He ii 1640Å lines over ∼ 100 kpc, and a total luminosity L Lyα = (6.4±0.1)×10 44 erg s −1 . HLock01-LAB presents an elongated morphology aligned with two faint radio sources contained within the central ∼ 8 kpc of the nebula. The radio structures are consistent to be faint radio jets or lobes of a central galaxy, whose spectrum shows nebular emission characteristic of a type-II active galactic nucleus (AGN). The continuum emission of the AGN at short wavelengths is, however, likely dominated by stellar emission of the host galaxy, for which we derive a stellar mass M * 2.3 × 10 11 M . Our kinematic analysis shows that the ionized gas is perturbed almost exclusively in the inner region between the radio structures, probably as a consequence of jet-gas interactions, whereas in the outer regions the ionized gas appears more quiescent. The detection of extended emission in C iv and C iii] indicates that the gas within the nebula is not primordial. Feedback may have enriched the halo at at least 50 kpc from the nuclear region. Using rest-frame UV emission-line diagnostics, we find that the gas in the nebula is likely heated by the AGN. Nevertheless, at the center of the nebula we find extreme emission line ratios of Lyα/Civ ∼ 60 and Lyα/Heii ∼ 80, one of the highest values measured to date, and well above the standard values of photoionization models (Lyα/Heii ∼ 30 for case B photoionization). Our data suggest that jet-induced shocks are likely responsible for the increase of the electron temperature and, thus, the observed Lyα enhancement in the center of the nebula. This scenario is further supported by the presence of radio structures and perturbed kinematics in this region. The large Lyα luminosity in HLock01-LAB is likely due to a combination of AGN photoionization and jet-induced shocks, highlighting the diversity of sources of energy powering Lyα nebulae. Future follow-up observations of HLock01-LAB will help in revealing in more detail the excitation conditions of the gas induced by jets and investigate the underlying cooling and feedback processes in this unique object.

J-PLUS: Unveiling the brightest end of the Lyαluminosity function at 2.0 <z< 3.3 over 1000 deg2

“…We broadly expect the above findings to hold valid over the much wider area of DR1 (bigger by a factor of ∼ 500), hence to select a mixture of extremely Lyα-bright, rare star-forming galaxies (e.g., Sobral et al 2016;Hartwig et al 2016;Cai et al 2017a;Shibuya et al 2018;Cai et al 2018;Marques-Chaves et al 2019) and luminous AGN/QSOs, numerically dominated by the latter source class. Indeed, our work selects objects showing strong and reliable NB excess, without employing any further criterion to disentangle its nature.…”

Deciphering the Lyman α blob 1 with deep MUSE observations

“…Extended He ii emission is commonly observed within the extended Lyα emitting regions surrounding high-z radio galaxies (e.g. Maxfield et al 2002;Villar-Martín et al 2007a,b;Morais et al 2017;Marques-Chaves et al 2019). Broad line profiles and alignments with the radio-jet axes indicate that He ii is, at least in part, powered by jet-gas interactions in those objects.…”

“…The distinctive observational feature of LABs with respect to similarly extended and luminous high-z Lyα nebulae around radio galaxies (e.g. Morais et al 2017;Vernet et al 2017;Marques-Chaves et al 2019), radio-loud quasars (e.g. Smith et al 2009;Roche et al 2014), or radio-quiet quasars (e.g.…”

The FLASHES Survey. I. Integral Field Spectroscopy of the CGM around 48 z ≃ 2.3–3.1 QSOs

“…A number of studies over the past 5-6 yr have revealed giant Lyα nebulae around individual high-redshift galaxies and QSOs (e.g., Martin et al 2014aMartin et al , 2014bCai et al 2018) as well as connecting pairs of QSOs (Arrigoni Battaia et al 2019b). Multiphase observations of similar nebulae have also begun to emerge (Cantalupo et al 2019;Marques-Chaves et al 2019). However, to fully characterize the morphology, composition, and dynamics of the CGM, large samples with multiwavelength observations are needed.…”