科研之友
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摘要
Context. Q0151+048 is a physical quasar (QSO) pair at z similar to 1.929 with a separation of 3.3 arcsec on the sky. In the spectrum of the brighter member of this pair, Q0151+048A, a damped Ly alpha absorber (DLA) is observed at a higher redshift. We have previously detected the host galaxies of both QSOs, as well as a Ly alpha blob whose emission surrounding Q0151+048A extends over 5x3.3 arcsec.
Aims. We seek to constrain the geometry of the system and understand the possible relations between the DLA, the Ly alpha blob, and the two QSOs. We also aim at characterizing the former two objects in more detail.
Methods. To study the nature of the Ly alpha 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 beta and H alpha emission lines, respectively. In other words, the two QSOs have identical redshifts within 2 sigma. 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-circle dot and 10(8.38) M-circle dot for Q0151+048A and Q0151+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-circle dot and 10(13.13) M-circle dot for Q0151+048A and Q0151+048B, respectively. We observe a velocity gradient along the major axis of the Ly alpha 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 Q0151+048A. The derived H-0 column density of the DLA is log N-H0 = 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(circle dot). We detect CII*, which allows us to make a physical model of the DLA cloud.
Conclusions. From the systemic redshifts of the QSOs, we conclude that the Ly alpha blob is associated with Q0151+048A rather than with the DLA. The DLA must be located in front of both the Ly alpha blob and Q0151+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.
- 出版日期2011-8
