arXiv subjects

Beverley J. Wills

Publications and source records attributed to Beverley J. Wills.

34 records · Page 2Linked to original sources

arXiv1999

PKS 1004+13: A High-Inclination, Highly-Absorbed Radio-Loud QSO -- The First Radio-Loud BAL QSO at Low Redshift?

The existence of BAL outflows in only radio-quiet QSOs was thought to be an important clue to mass ejection and the radio-loud - radio-quiet dichotomy. Recently a few radio-loud BAL QSOs have been discovered at high redshift. We present evidence that PKS 1004+13 is a radio-loud BAL QSO. It would be the first known at low-redshift (z = 0.24), and one of the most radio luminous. For PKS 1004+13, there appear to be broad absorption troughs of O VI, N V, Si IV, and C IV, indicating high-ionization outflows up to about 10,000 km/s. There are also two strong, broad (~500 km/s), high-ionization, associated absorption systems that show partial covering of the continuum source. The strong UV absorption we have detected suggests that the extreme soft-X-ray weakness of PKS 1004+13 is primarily the result of absorption. The large radio-lobe dominance indicates BAL and associated gas at high inclinations to the central engine axis, perhaps in a line-of-sight that passes through an accretion disk wind.

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arXiv1999

Introduction to Principal Components Analysis

Understanding the inverse equivalent width - luminosity relationship (Baldwin Effect), the topic of this meeting, requires extracting information on continuum and emission line parameters from samples of AGN. We wish to discover whether, and how, different subsets of measured parameters may correlate with each other. This general problem is the domain of Principal Components Analysis (PCA). We discuss the purpose, principles, and the interpretation of PCA, using some examples from QSO spectroscopy. The hope is that identification of relationships among subsets of correlated variables may lead to new physical insight.

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arXiv1999

The PG X-ray QSO sample: Links between the UV-X-ray Continuum and Emission Lines

The UV to soft X-rays of luminous AGNs dominate their bolometric luminosity, driven by an accretion-powered dynamo at the center. These photons ionize the surrounding gas, thereby providing clues to fueling and exhaust. Two sets of important relationships - neither of them understood - link the continuum and gas properties. (i) Boroson & Green's `eigenvector 1' relationships: Steeper soft X-ray spectra are clearly related to narrower Hbeta emission and stronger optical Fe II emission from the BLR, and weaker [O III] 5007 from the NLR. We show that these relationships extend to UV spectra: narrower C III] 1909, stronger low ionization lines, larger Si III] 1892/C III] 1909 (a density indicator), weaker C IV 1549 but stronger higher-ionization N V 1240. We speculate that high accretion rates are linked to high columns of dense (1e10 - 1e11 cm-3), nitrogen-enhanced, low-ionization gas from nuclear starbursts. Linewidth, inverse Fe II-[O III] and inverse Fe II-C IV relationships hint at the geometrical arrangement of this gas. (ii) The Baldwin effect (inverse equivalent width - luminosity relationships): Our correlation analyses suggest that these are independent of the above eigenvector 1 relationships. The eigenvector 1 relationships can therefore be used in future work, to reduce scatter in the Baldwin relationships, perhaps fulfilling the dream of using the Baldwin effect for cosmological studies.

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arXiv1999

Introduction to Unified Schemes

The differences among apparently diverse classes of AGN are mainly the result of viewing the central engine at different orientations, because dust, which absorbs and scatters the light, partially covers the central source, and because synchrotron emission is highly beamed along the relativistic jet. Also important are factors independent of orientation: the total power output, the unknown mover behind the eigenvector 1 relationships, and the radio-loudness. These other factors may not be independent of the parameters of Unified models, such as intrinsic jet physics, AGN dust content, and torus thickness. We outline the basic evidence for orientation Unified Schemes, and briefly discuss their importance for understanding the mechanisms of the central engine and its relation to the surrounding host galaxy and beyond.

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arXiv1998

Absorption and scattering properties in polarized bright soft X-ray selected ROSAT AGN

We have surveyed the optical linear polarimetric properties of 65 soft X-ray selected ROSAT Active Galactic Nuclei (AGN). Most of these sources show low polarization (<1%) and no optical reddening. This is in agreement with the X-ray results suggesting a direct view on the center. However, two of our AGN show polarization as high as 7--8% and high reddening. This optical reddening suggests a high column of dusty gas, but why does this gas not absorb the soft X-rays? We suggest that the dusty gas is actually ionized. There is evidence for these 'warm' absorbers from X-ray absorption features seen in ROSAT and ASCA spectra.

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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

Optical Polarization of 52 Radio-Loud QSOs and BL Lac Objects

Polarization measurements are presented for 52 radio-loud QSOs and BL Lac objects. For 9 highly polarized (p >3%) AGN, these are the first published polarization measurements. Of these 9, 7 are highly-polarized QSOs (HPQs), one is a BL Lac object and another is a likely BL Lac object. Polarization variability is confirmed for some of these new and previously known highly-polarized AGN. While 6 of the HPQs have flat radio spectra are almost certainly blazars, PKS 1452-217 is probably a new member of the rare class of radio-loud QSOs that show high polarization by scattering, and is therefore important for testing orientation Unified Schemes. In competition for the highest redshift HPQ are the well-observed QSO PKS 0438-43 at z = 2.85, with maximum p = 4.7%, and PKS 0046-315 at z = 2.72, for which we find p = 13%.

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arXiv1998

Does Every Quasar Harbor A Blazar?

Assuming there is a blazar type continuum in every radio-loud quasar, we find that the free-free heating due to the beamed infrared continuum can greatly enhance collisionally excited lines, and thus explain the stronger CIV $λ$1549 line emission observed in radio loud quasars. We further predict that the CIV line should show variability {\it not} associated with observed continuum or Ly$α$ variability.

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arXiv1998

Clues to Outflows: Polarization of IRAS-Selected QSOs

Broad-band polarimetry and spectropolarimetry of a complete sample of 18 luminous AGNs (Lbol > 10^11.5 Lsun), selected in an orientation-independent way by warm infrared flux, shows that an orientation-dust-covering Unified Scheme like that successfully explored for the lower luminosity Seyfert galaxies applies to the luminous QSOs. Broad emission lines and continuum seen in polarized (scattered) light show that hyperluminous infrared galaxies contain buried QSO nuclei and are therefore the `missing' QSO 2s -- the high-luminosity analogs of Seyfert 2 galaxies like NGC1068. Most of the QSOs show significant polarization and reddening. Three are `classical' low-ionization BALQSOs, and several others have narrower, blueshifted, low-ionization absorption. These properties are to be compared with those of the UV-optically selected QSOs, of which only ~1% show low-ionization BALs, and only the BALQSOs show significant polarization. Outflows are therefore much more common than previously suspected.

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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

The Optical Polarization and Warm Absorber in IRAS 17020+4544

We report the detection of ionized absorption in the ASCA spectrum of the narrow-line Seyfert 1 galaxy IRAS 17020+4544. Subsequent optical spectropolarimetry revealed high polarization increasing from 3% in the red to 5% in the blue, indicating electron or dust scattering as a likely origin. The broad emission line H$α$ is somewhat less polarized than the continuum, supporting a location of the polarizing material within the AGN. The Balmer line decrement and reddened optical spectrum support the presence of a dusty warm absorber in this object. We compared the broad band optical polarization and ionized X-ray absorption of a collection of Seyfert 1 and 1.5 galaxies, excluding classes of objects that are likely to have significant neutral X-ray absorption. Warm absorber objects are generally more likely to have high optical polarization than objects with no detected ionized absorption. This result lends additional support to the idea that the warm absorber is associated with dust and implies either that dust transmission is responsible for at least part of the polarization or that the polarization is revealed because of the dimming of the optical spectrum. Spectropolarimetry of Seyfert 1s generally locates the scattering material inside the narrow-line region and often close to or within the broad line region, consistent with estimates of the location of the dusty warm absorber.

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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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arXiv1996

An Interpretation of Radio-loud -- Radio-quiet QSO Differences

Here we speculate on what observations are telling us about the difference between radio-loud and radio-quiet QSOs. The observations are (i) the relation between ultraviolet-optical luminosity and `jet power', (ii) the dependences of emission and absorption line spectra, and the spectral energy distribution, on radio core-dominance, assumed to be an indicator of orientation, (iii) the spectral differences between radio-loud and radio-quiet QSOs, and (iv) the inverse relation between the strength of broad, blended Fe\,II multiplets and [O\,III]\,$λ$5007, and the apparently-related association between Fe\,II strength, reddening, broad absorption lines, and scattering polarization. We present and discuss a picture in which there are two main variables: (i) the inclination of the plane of the host galaxy to the axis of the inner jet (the central engine's rotation axis), and (ii) the angle of the line-of-sight to this rotation axis. The radio-loud QSOs are those with jets aiming away from the plane of the host galaxy.

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arXiv1996

Accretion and Jet Power

In the first of a series of three lectures we discuss ways of measuring the power available to feed the jets in powerful FR II radio sources. For unobscured radio-loud QSOs we present evidence that this power is directly related to the UV-optical luminosity, or probably more accurately, to the power radiated through processes of accretion in a strong gravitational potential. It has been suggested on theoretical grounds that powerful radio jets are a necessary component of the central engine. It then follows, from the similarity of the optical-UV power output, spectral energy distribution, and emission-line spectra of radio-loud and radio-quiet QSOs, that radio-quiet QSOs have the same power available to feed jets as do radio-loud QSOs. This then leaves us with the puzzle of why we do not see the powerful jets in radio-quiet QSOs.

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arXiv1995

THE POLARIZED SPECTRUM OF THE FE II-RICH BAL QSO, IRAS 07598+6508

We present IUE spectrophotometry and optical spectropolarimetry of the ultraluminous, extreme FeII-emitting QSO IRAS 07598+6508. We find broad absorption troughs from high- and low-ionization species, showing that this object is a member of the class of rare low-ionization BAL QSOs. Compared with non-BAL QSOs, the spectral energy distribution is reddened by E(B-V) sim 0.12, and the Halpha/Hbeta ratio even more reddened with E(B - V) sim 0.45. The broad emission lines are unpolarized. We see broad Na I lambda5892 absorption in the unpolarized continuum, but not in the polarized continuum (at the 5-6 sigma level). The polarized continuum rises smoothly towards shorter wavelengths with F_lambda propto lambda{-2}. We argue that a normal QSO continuum is polarized by scattering from a region within, or very near, the Broad Emission Line Region (BELR). Thus there are at least three distinct light paths to the observer: a dusty path from the BELR, a direct path traced by the unpolarized continuum, passing through dust and low-ionization gas (NaI), and another relatively unobscured path followed by scattered continuum. This provides direct evidence that a BAL region and dust only partially cover the central QSO. Ultraluminous AGNs, including IRAS 07598+6508, appear no more IR-luminous than non-IRAS-selected QSOs, and have normal L(IR)/L(opt) ratios when the optical luminosities are corrected for reddening. Reddening and BALs occur only along some sight lines and the parent population of BALQs are `normal' QSOs.

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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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