A Lyαblob andz_abs ≈ z_emdamped Lyαabsorber in the dark matter halo of the binary quasar Q 0151+048

Abstract

Context. Q 0151+048 is a physical quasar (QSO) pair at z ∼ 1.929 with a separation of 3.3 arcsec on the sky. In the spectrum of the brighter member of this pair, Q 0151+048A, a damped Lyα absorber (DLA) is observed at a higher redshift. We have previously detected the host galaxies of both QSOs, as well as a Lyα blob whose emission surrounding Q 0151+048A extends over 5× 3.3 arcsec. Aims. We seek to constrain the geometry of the system and understand the possible relations between the DLA, the Lyα blob, and the two QSOs. We also aim at characterizing the former two objects in more detail. Methods. To study the nature of the Lyα blob, we performed low-resolution, long-slit spectroscopy with the slit aligned with the extended emission. We also observed the whole system using the medium-resolution VLT/X-shooter spectrograph and the slit aligned with the two QSOs. The systemic redshift of both QSOs was determined from rest-frame optical emission lines redshifted into the NIR. We employed line-profile fitting technique, to measure metallicities and the velocity width of low-ionization metal absorption lines associated to the DLA and photo-ionization modeling to characterize the DLA further. Results. We measure systemic redshifts of z em(A) = 1.92924 ± 0.00036 and z em(B) = 1.92863 ± 0.00042 from the H β and H α emission lines, respectively. In other words, the two QSOs have identical redshifts within 2σ. From the width of Balmer emission lines and the strength of the rest-frame optical continuum, we estimate the masses of the black holes of the two QSOs to be 10 9.33 M and 10 8.38 M for Q 0151+048A and Q 0151+048B, respectively. We then use the correlation between black hole mass and dark matter halo mass to infer the mass of the dark matter halos hosting the two QSOs: 10 13.74 M and 10 13.13 M for Q 0151+048A and Q 0151+048B, respectively. We observe a velocity gradient along the major axis of the Lyα blob consistent with the rotation curve of a large disk galaxy, but it may also be caused by gas inflow or outflow. We detect residual continuum in the DLA trough, which we interpret as emission from the host galaxy of Q 0151+048A. The derived H 0 column density of the DLA is log N H 0 = 20.34 ± 0.02 cm −2 . Metal column densities are also determined for a number of low-ionization species resulting in an overall metallicity of 0.01 Z . We detect C ii * , which allows us to make a physical model of the DLA cloud. Conclusions. From the systemic redshifts of the QSOs, we conclude that the Lyα blob is associated with Q 0151+048A rather than with the DLA. The DLA must be located in front of both the Lyα blob and Q 0151+048A at a distance greater than 30 kpc and has a velocity relative to the blob of 640 ± 70 km s −1 . The two quasars accrete at normal Eddington ratios. The DM halo of this double quasar will grow to the mass of our local supercluster at z = 0. We point out that those objects therefore form an ideal laboratory to study the physical interactions in a z = 2 precursor of our local supercluster.

A connection between extremely strong damped Lyman-αsystems and Lyman-αemitting galaxies at small impact parameters

“…We indeed observe a non-zero emission on both sides of the Ly α peak which, in addition to light from the DLA galaxy, could also result from residual sky light emission (Pâris et al 2012) or FUV light from the galaxy hosting the background QSO (see Cai et al 2014;Finley et al 2013;Zafar et al 2011). By coadding QSO spectra with high-redshift Lyman-breaks, Cai et al put an upper-limit to the sky residual to F λ < 3×10 −19 erg s −1 Å −1 in the wavelength range of interest for us, which could explain the continuum emission observed here.…”

Witnessing galaxy assembly in an extended z≈3 structure

“…Fynbo et al 1999;Zafar et al 2011;Kashikawa et al 2014). In particular, while the system reported in Fynbo et al (1999) and Zafar et al (2011) lies in proximity to a quasar, the object presented by Kashikawa et al (2014) is a close analogue to the system discussed here, being associated to an intervening DLA with a luminosity of ≈ 10 42 erg s −1 and a size of ≈ 15 kpc as measured in a 2D spectrum at a depth of 2.5 × 10 −19 erg s −1 cm −2 Å −1 .…”

A glance at the host galaxy of high-redshift quasars using strong damped Lyman-αsystems as coronagraphs

“…Indeed, Zafar et al (2011) suggest that this possibility could account for the trough of the associated DLA towards Q0151+048A not going to zero.…”

“…Zafar et al (2011) determined that a Lyα blob located more than ∼30 kpc from Q0151+048A is both the source of Lyα emission in the DLA trough and associated with the quasar host galaxy. With long slit spectroscopy, we could pinpoint the location of the narrow Lyα emission relative to the quasar and investigate the extent of emission regions in quasar host galaxies.…”