arXiv subjects

M. S. Brotherton

Publications and source records attributed to M. S. Brotherton.

45 records · Page 3Linked to original sources

arXiv1998

The PG X-Ray QSO Sample: Links among X-ray, UV & Optical Spectra

A unique, essentially complete sample of 22 QSOs, with high quality soft X-ray spectra from ROSAT, as well as HST and optical spectrophotometry from below Ly-alpha to above H-alpha, is being used to investigate the relationships among the ionizing continuum and the optical and UV continuum, emission and absorption lines. Here we present a first analysis showing that optical `Eigenvector 1' linking steeper soft X-ray spectra with increasing optical Fe II strength, decreasing [O III] 5007 emission, and narrower BLR H-beta emission, extends to the UV emission lines, and is manifested by weaker C IV 1549 emission, stronger Si III] 1892/C III] 1909 ratio, and narrower C III] 1909 emission. Steeper soft X-ray spectra have been linked to higher L/L_Edd ratios, thus apparently linking BLR densities, high and low ionization gas, and kinematics, to the accretion process.

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arXiv1998

Discovery of Radio-loud Broad Absorption Line Quasars Using Ultraviolet Excess and Deep Radio Selection

We report the discovery of five broad-absorption-line (BAL) QSOs in a complete sample of 111 ultraviolet excess (UVX) QSO candidates also detected in the NRAO VLA Sky Survey. All five BAL QSOs, which include two high-ionization BAL QSOs and three low-ionization BAL QSOs, are formally radio-loud. Of QSOs with z > 0.4, 3+/-2% show low-ionization BALs, and of QSOs with z > 1.5, all radio-loud, 9+/-5% show BALs; these frequencies are consistent with those of optical surveys. While the first reported radio-loud BAL QSO, FIRST J155633.8+351758, is likely to be heavily dust reddened and thus less radio-loud than indicated by its observed radio-to-optical luminosity, these QSOs are UVX selected and probably free of significant dust along the line of sight. We point out unusual features in two of the BAL QSOs and discuss the significance finding these heretofore rare objects.

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arXiv1998

Discovery of an Ultra-Steep Spectrum, Highly Polarized Red Quasar at z = 1.462

We report the discovery of WN J0717+4611, a highly polarized red quasar at z=1.462, selected from a sample of faint (S_{1.4GHz} > 10 mJy) ultra steep spectrum (alpha < -1.3) radio sources. VLA observations at 4.85 GHz show that the radio source is dominated by a 21 mJy core. Using the Keck telescopes, we obtained spectra with a combined wavelength range covering 4000 Angstroms to 1.6 microns, and spectropolarimetric observations between 4000 Angstroms and 9000 Angstroms. We identify WN J0717+4611 as a quasar based on broad emission of Mg II 2799 (FWHM ~ 11,000 km/s), a stellar R_S band Lick image and the high luminosity of the object (M_B = -24.2). The optical linear polarization is wavelength-independent at 15% in both the continuum and the emission lines, with the polarization angle orthogonal to the radio jet axis. We argue that the polarization mechanism is scattering of quasar light by surrounding small dust grains or electrons. WN J0717+4611 appears highly reddened for a core-dominated quasar.

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arXiv1998

Spectropolarimetry of 3CR 68.1: A Highly Inclined Quasar

We present Keck spectropolarimetry of the highly polarized radio-loud quasar 3CR 68.1 (z=1.228, V=19). The polarization increases from 5 in the red (4000 A rest-frame) to >10% in the blue (1900 A rest-frame). The broad emission lines are polarized the same as the continuum, which shows that 3CR 68.1 is not a blazar as it has sometimes been regarded in the past. We also present measurements of the emission lines and a strong, blueshifted, associated absorption line system, as well as a detection at the emission-line redshift of Ca II K absorption, presumably from stars in the host galaxy. 3CR 68.1 belongs to an observationally rare class of highly polarized quasars that are neither blazars nor partially obscured radio-quiet QSOs. Taking into account 3CR 68.1's other unusual properties, such as its extremely red spectral energy distribution and its extreme lobe dominance, we explain our spectropolarimetric results in terms of unified models. We argue that we have a dusty, highly inclined view of 3CR 68.1, with reddened scattered (polarized) quasar light diluted by even more dust-reddened quasar light reaching us directly from the nucleus.

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arXiv1997

Spectropolarimetry of FIRST BAL QSOs

We present Keck spectropolarimetry of two rare low-ionization broad absorption line (BAL) QSOs, FIRST J084044.5+363328 and FIRST J155633.8+351758, that also exhibit narrow absorption lines from metastable excited levels of Fe II (``Iron Lo-BALs''). These QSOs were discovered in optical follow-ups to a deep radio survey; FIRST J155633.8+351758 is radio-loud, the first BAL QSO so identified. FIRST J084044.5+363328 is highly polarized and exhibits many features found in other BAL QSOs, and the polarization and its position angle vary in a complicated manner across the metastable Fe II absorption lines, suggesting that more than one mechanism is at work, or that the system geometry is complex. FIRST J155633.8+351758 may be the most highly polarized BAL QSO known, and exhibits other unusual polarization properties compared to other highly polarized BAL QSOs. Currently available data cannot yet discriminate among the possible lines of sight to BAL QSOs (edge-on, pole-on, or random).

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arXiv1997

Spectropolarimetry of FIRST 0840+3633

We present Keck spectropolarimetry of a rare ``Iron Lo-BALQSO,'' FIRST 0840+3633. The continuum is 4% polarized near 2000 angstroms rest-frame, but falls to 2% at longer wavelengths, and maintains a relatively constant position angle of 50 degrees. The emission lines are unpolarized. The polarization increases up to 8% in the low-ionization absorption troughs of Mg II 2800 and Al III 1860. The polarization and its position angle vary in a complicated manner across the metastable Fe II absorption lines, suggesting that more than one mechanism is at work or that the system geometry is complex.

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arXiv1996

Jets and QSO Spectra

QSOs' emission lines arise from highest velocity (approximately 10000 km/s), dense gas within approximately 0.1 parsec of the central engine, out to low-velocity, low-density gas at great distances from the host galaxy. In radio-loud QSOs there are clear indications that the distribution and kinematics of emission-line gas are related to the symmetry axis of the central engine, as defined by the radio jet. These jets originate at nuclear distances < 0.1 pc --- similar to the highest-velocity emission line gas. There are two ways we can investigate the different environments of radio-loud and radio-quiet QSOs, i.e., those with and without powerful radio jets. One is to look for optical-UV spectroscopic differences between radio-loud and radio-quiet QSOs. The other is to investigate dependences of spectroscopic properties on properties of the powerful jets in radio-loud QSOs. Here we summarize the spectroscopic differences between the two classes, and present known dependences of spectra on radio core-dominance, which we interpret as dependences on the angle of the central engine to the line-of-sight. We speculate on what some of the differences may mean.

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arXiv1995

The Profiles of H-Beta and [OIII] 5007 in Radio-Loud Quasars

Moderate-resolution spectra of the H$β$--[O III] $λ$5007 region have been obtained for 41 radio-loud quasars in order to investigate relationships among their broad- and narrow-line profiles, radio structures, and X-ray properties. Spectra from the literature have been included to form a data set of 60 radio-loud quasars. A variety of statistical analyses have been performed, identifying several strong, related trends. The FWHM, equivalent width, and degree of redward asymmetry of H$β$ increase with decreasing radio core dominance (an orientation indicator), whereas the FWHM of [O III] $λ$5007 increases with luminosity and $α_{ox}$. These and other effects are briefly discussed.

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arXiv1995

AN IMPROVED MEASURE OF QUASAR ORIENTATION

Radio core dominance, usually measured by R, the rest frame ratio of core to lobe flux density, has been used as an indicator of Doppler boosting of quasars' radio jets and hence the inclination of the central engine's spin axis to the line of sight. The use of lobe flux density as a means of normalizing the boosted core flux density to the available intrinsic power of the central engine introduces scatter. This is because the emission from the radio lobes depends strongly on the interaction of the jet with the environment at distances beyond several Kpc from the nucleus. Total kinetic power in the extended radio emission is approximately proportional to emission line luminosity, and emission line luminosity is proportional to the luminosity of AGNs' featureless continua -- both over 4 orders of magnitude. Thus, quasars' optical luminosity may be an excellent measure of available intrinsic jet power. Therefore we define a new core dominance parameter, R$_V$, the ratio of radio core to optical (rest frame V band) continuum luminosity, that is not directly dependent on jet interactions with the super-Kpc-scale environment. We show that the use of R$_V$, rather than R, results in significantly improved inverse correlations with the beaming angle as deduced from apparent superluminal velocities and inverse Compton scattered X-ray emission, and with the FWHM of quasars' broad H$β$ emission line. We discuss some implications and applications of the new parameter.

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