Mapping the Lyα Emission around a z ∼ 6.6 QSO with MUSE: Extended Emission and a Companion at a Close Separation

Abstract

We utilize the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope to search for extended Lyα emission around the z∼6.6 QSO J0305−3150. After carefully subtracting the point spread function, we reach a nominal 5σ surface-brightness limit of SB 5σ =1.9×10−18 ergs −1 cm −2 arcsec −2 over a 1arcsec 2 aperture, collapsing fivewavelength slices centered at the expected location of the redshifted Lyα emission (i.e., at 9256 Å). Current data suggest the presence (5σ accounting for systematics) of a Lyα nebula that extends for 9 kpc around the QSO. This emission is displaced and redshifted by 155 km s −1 with respect to the location of the QSO host galaxy traced by the [C II] 158 μm emission line. The total luminosity is L Lya ( )=(3.0 ± 0.4)× 10 42 ergs −1 . Our analysis suggests that this emission is unlikely to rise from optically thick clouds illuminated by the ionizing radiation of the QSO. It is more plausible that the Lyα emission is due to the fluorescence of the highly ionized optically thin gas. This scenario implies a high hydrogen volume density of n 6 H~c m −3 . In addition, we detect a Lyα emitter (LAE) in the immediate vicinity of the QSO, i.e., with a projected separation of ∼12.5 kpc and a line-of-sight velocity difference of 560 km s . The probability of finding such a close LAE is one order of magnitude above the expectations based on the QSO-galaxy cross-correlation function. This discovery is in agreement with a scenario where dissipative interactions favor the rapid build-up of supermassive black holes at early cosmic times.

Lyα Halos around z ∼ 6 Quasars

“…an order of magnitude higher, and likewise, J1030+0524, which previously was not reported to display a Lyα halo, now appears with a small halo of moderate luminosity, that is an order of magnitude more luminous than Farina et al (2017). This stresses the need for larger samples of Lyα halos around QSOs at z ∼ 6.…”

“…Using the quasar itself allows us to avoid issues related to PSF variations across the field, and spatial interpolation. Indeed, in the analysis of the z ∼ 6 quasar presented in Farina et al (2017), these two commonly-applied PSF subtraction techniques were tested, and found to be equally reliable.…”

“…With one of the highest SFRs and Eddington ratios above z ∼ 6, this quasar provides an ideal source to target a large gas reservoir surrounding one of the first QSOs. Farina et al (2017) detected a faint Lyα halo around J0305 − 3150 extending ∼ 9 pkpc, offset in velocity by 155 km s −1 , and with a total luminosity of (3.0 ± 0.4) × 10 42 erg s −1 .…”

“…Following its detection in narrow-band imaging, the halo was spectroscopically confirmed in Willott et al (2011) and Goto et al (2012) and in these long-slit studies, the halo around J2329−0301 appeared very similar to J2228+0110 in terms of size and luminosity. Finally, Farina et al (2017) targeted the z = 6.61 QSO J0305−3150 with MUSE. With one of the highest SFRs and Eddington ratios above z ∼ 6, this quasar provides an ideal source to target a large gas reservoir surrounding one of the first QSOs.…”

“…Motivated by these studies, we search for Lyα halos in the deepest available MUSE observations of the highest redshift quasars (z ∼ 6). To reach approximately the surface brightness (SB) level achieved in Farina et al (2017), we queried the ESO archive for observations of exposure time ∼ 2 hours or greater, resulting in a total sample of five objects listed in Table 1. SB levels in the wavelength layer where Lyα emission peaks range between 4.71 × 10 −19 erg s −1 cm −2 arcsec −1 and 8.81 × 10 −19 erg s −1 cm −2 arcsec −1 (see Table 2 for details).…”