Spectroscopy of Spatially Extended Material around High-Redshift Radio-loud Quasars
Abstract
We present the analysis of long-slit optical spectra taken of five high-redshift (z ~ 2-3) radio-loud quasars (QSRs), selected from the imaging survey of Heckman et al. We confirm that the QSRs have Lyα emission is spatially extended by at least several tens of kiloparsecs, with a luminosity of order 10^44^ ergs s^-1^. The gas is very active kinematically. After a subtraction of the seeing-scattered light from the broad-line region (BLR) of the central QSR, we find that line widths in the nebulae are 1000-1500 km s^-1^ (FWHM). The gas does not show any globally organized velocity gradient (i.e., velocities do not change by more than about 500 km s^-1^ over scales of tens of kiloparsecs). The line widths are close to the maximum possible for gas that is freely falling into the potential well of a very massive galaxy. Alternatively, we may be witnessing the explosive ejection of matter on a galactic scale by the QSR. The kinematic properties of the QSR nebulae are broadly similar to those of the nebulae associated with high-redshift radio galaxies. We confirm the suggestion of Foltz et al. that the nuclear He II λ1640 emission line in QSRs is systematically narrower than other nuclear emission lines. We find that this narrow-lined, nuclear He II emission has a strength that correlates with the strength of the spatially extended Lyα emission, and suggest that the former probably arises in the inner (arcsec-scale) part of the Lyα nebula. This is consistent with the fact that the velocity of the spatially extended Lyα emission agrees well with the velocity of the narrow core of the nuclear Lyα profile. Selecting by the presence of strong narrow He II λ1640 lines should be a good way to find high-z quasars with prominent Lyα nebulae. We discuss the implications of these results for the nature of the Z_abs_~Z_em_ systems in high-z QSRs. In three QSRs, the spatially extended Lyα is redshifted by of order 10^3^ km s^-1^ with respect to the C IV λ1549 BLR profile (but exhibits no significant shift in the other two QSRs). We believe that this reflects a blueshift of the C IV lines with respect to QSR systemic velocity. This has implications for the interpretation of the BLR dynamics. We have likely (4-5σ) detections of spatially extended He II λ1640 in one QSR nebulae and C IV λ1549 in another (each at 7%-10% of Lyα). These possible detections and the upper limits on other lines are consistent with the emission-line spectra of high-z radio galaxies. Our data are not good enough either to yield strong constraints on the metallicities in the nebulae or to discriminate decisively between, alternative ionization sources (photoionization by a standard active galactic nucleus continuum, photoionization by hot stars, shock heating, etc.). The probable He II detector is inconsistent with predictions of photoionization models for normal high-mass stars. The probable C IV detection means that at least some galaxy-scale sites in the early universe have nonprimordial chemical abundances. The probable detections of He II and C IV make it unlikely that the bulk of the spatially extended Lyα emission arises via resonant scattering of nuclear Lyα photons by neutral hydrogen surrounding the QSR.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 1991
- DOI:
- 10.1086/170660
- Bibcode:
- 1991ApJ...381..373H
- Keywords:
-
- Quasars;
- Radio Sources (Astronomy);
- Red Shift;
- Astronomical Spectroscopy;
- Lyman Alpha Radiation;
- Nebulae;
- Radio Galaxies;
- Spectral Line Width;
- Astrophysics;
- GALAXIES: FORMATION;
- GALAXIES: INTERNAL MOTIONS;
- QUASARS