HUBBLE SPACE TELESCOPENARROWBAND SEARCH FOR EXTENDED Lyα EMISSION AROUND TWOz> 6 QUASARS

Abstract

We search for extended Lyα emission around two z > 6 quasars, SDSS J1030+0524 (z = 6.309) and SDSS J1148+5251 (z = 6.419) using WFC3 narrow-band filters on board the Hubble Space Telescope. For each quasar, we collected two deep, narrow-band images, one sampling the Lyα line+continuum at the quasar redshifts and one of the continuum emission redwards of the line. After carefully modeling the Point Spread Function, we find no evidence for extended Lyα emission. These observations set 2-σ limits of L(Lyα, extended) < 3.2 × 10 44 erg s −1 for J1030+0524 and L(Lyα, extended) < 2.5 × 10 44 erg s −1 for J1148+5251. Given the star formation rates typically inferred from (rest-frame) farinfrared measurements of z ∼ 6 quasars, these limits are well below the intrinsic bright Lyα emission expected from the recombination of gas photoionized by the quasars or by the star formation in the host galaxies, and point towards significant Lyα suppression or dust attenuation. However, small extinction values have been observed along the line of sight to the nuclei, thus reddening has to be coupled with other mechanisms for Lyα suppression (e.g., resonance scattering). No Lyα emitting companions are found, down to a 5-σ sensitivity of ∼ 1 × 10 −17 erg s −1 cm −2 arcsec −2 (surface brightness) and ∼ 5 × 10 −17 erg s −1 cm −2 (assuming point sources).

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

“…These leakages may be associated with short and extreme bursts of star formation that have been proposed to explain the intrinsically blue rest-frame UV slope observed in dusty, star-forming galaxies (SFR>50 M e yr −1 ) up to z∼5 (e.g., Casey et al 2014). A similar scenario was also proposed by Decarli et al (2012) to explain the lack of extended Lyα emission from the host galaxy of the two highly star-forming z>6 QSOs: SDSSJ1030+0524 and SDSSJ1148+5251 (see also Mechtley et al 2012). …”

“…Resonance scattering may trap Lyα photons and dim the expected luminosity of the extended emission. The bouncing of Lyα photons between optically thick clouds increases the total path length traveled in the dusty medium, incrementing its extinction (see the discussion in Decarli et al 2012 and the Appendix in Hennawi & Prochaska 2013). The relative importance of this effect strongly depends on various QSO host galaxy properties, such as neutral hydrogen column density, neutral fraction, dust-to-gas ratio, and geometry, among others.…”

“…The first search for LAEs around z>5.5 QSOs was performed by Decarli et al (2012) using a combination of narrowband filters of the WFC3 on HST. No companion galaxies were found around the two QSOs SDSSJ1030+0524 and SDSSJ1148+5251.…”

“…In recent years, huge efforts have been made to probe the extended Lyα emission around z∼6 QSOs with contrasting results. Decarli et al (2012), using the Wide Field Camera3 (WFC3) narrowband filters on the Hubble Space Telescope (HST), put strong limits on the Lyα extended emission in the proximity of the highly star-forming host galaxies of the QSOs SDSSJ1148+5251 (z=6.42, L Lya ( ) <2.5×10…”

“…Conversely, the presence of a Lyα nebula has been reported in narrowband Suprime-Cam/ Subaru images of the QSO CFHQSJ2329−0301 at z=6.42 (Goto et al 2009) and subsequently confirmed with long-slit spectroscopy with the Echelle Spectrograph and Imager and with the DEep Imaging Multi-object Spectrograph (DEIMOS) spectrographs at the Keck II telescope (Willott et al 2011;Goto et al 2012). Whereas all of these observations consistently report the presence of a bright Lyα halo extending on scales of 15 kpc in the proximity of CFHQSJ2329−0301, its luminosity is not well-constrained, with values that range from L Lya ( )1.7-7.5×10 43 ergs −1 (Willott et al 2011;Goto et al 2012) up to L Lya ( )=3.6×10 44 ergs −1 (Goto et al 2009; see footnote 10 in Decarli et al 2012). Recently, Roche et al (2014) presented long-slit spectroscopic observations with the Optical System for Imaging and low Resolution Integrated Spectroscopy (OSIRIS) mounted on the Gran Telescopio Canarias of a sample of QSOs at z>2, including one at z=5.95 the radio-loud QSO SDSSJ2228+0110.…”