Radio Loudness Research Articles

Unusual high-redshift radio broad absorption-line quasar 1624+3758

We present observations of the most radio-luminous broad absorption-line (BAL) quasar known, 1624+3758, at redshift z = 3.377. The quasar has several unusual properties. (1) The Fe II UV191 1787-A emission line is very prominent. (2) The BAL trough (BALnicity index 2990 km s −1 )i sdetached by 21 000 km s −1 and extends to velocity v =− 29 000 km s −1 . There are additional intrinsic absorbers at −1900 and −2800 km s −1 . (3) The radio rotation measure of the quasar, 18 350 rad m −2 ,i sthe second highest known. The radio luminosity is P 1.4 GHz = 4.3 × 10 27 WH z −1 (H 0 = 50 km s −1 Mpc −1 , q 0 = 0.5) and the radio loudness is R ∗ = 260. The radio source is compact ( ∼ 2.8 kpc) and the radio spectrum is GHz-peaked, consistent with it being relatively young. The width of the C IV emission line, in conjunction with the total optical luminosity, implies a black hole mass M BH ∼ 10 9 M� , L/L Eddington ≈ 2. The high Eddington ratio and the radio-loudness place this quasar in one corner of Boroson’s two-component scheme for the classification of active galactic nuclei, implying a very high accretion rate, and this may account for some of the unusual observed properties. The v = −1900 km s −1 absorber is a possible Lyman-limit system, with N (H I) = 4 × 10 18 cm −2 , and a covering factor of 0.7. A complex mini-BAL absorber at v =− 2200 to −3400 km s −1 is detected in each of C IV ,N V and O VI. The blue and red components of the C IV doublet happen to be unblended, allowing both the covering factor and optical depth to be determined as a function of velocity. Variation of the covering factor with velocity dominates the form of the mini-BAL, with the absorption being saturated (e −τ ≈ 0) over most of the velocity range. The velocity dependence of the covering factor and the large velocity width imply that the mini-BAL is intrinsic to the quasar. There is some evidence of line-locking between velocity components in the C IV mini-BAL, suggesting that radiation pressure plays a role in accelerating the outflow. Ke yw ords: galaxies: high-redshift ‐ intergalactic medium ‐ quasars: absorption lines ‐ quasars: emission lines ‐ quasars: general ‐ early Universe.

Was the Narrow Line Seyfert 1 RGB J0044+193 ever radio loud?

We show new radio data and a re-analysis of old data for the Narrow Line Seyfert 1 (NLSy1) galaxy RGB J0044+193. This galaxy has previously been suggested to be both radio loud, and highly variable in the radio. As most NLSy 1 galaxies are radio quiet, this was interpreted as possible evidence that this AGN's jet was beamed toward the observer. This object was probably never either radio loud and nor variable – the one exception to this rule is a marginal detection of the object in the 1987 Green Bank survey, which we argue may have been spurious.

XMM-Newton spectroscopy of an X-ray selected sample of RL AGNs

This paper presents the X-ray spectroscopy of an X-ray selected sample of 25 radio-loud (RL) AGNs extracted from the XBSS sample. The main goal is to study the origin of the X-ray spectral differences usually observed between radio-loud and radio-quiet (RQ) AGNs. To this end, a comparison sample of 53 RQ AGNs has been also extracted from the same XBSS sample and studied together with the sample of RL AGNs. We have focused the analysis on the distribution of the X-ray spectral indices of the power-law component that models the large majority of the spectra in both samples. We find that the mean X-ray energy spectral index is very similar in the 2 samples and close to alpha_X~1. However, the intrinsic distribution of the spectral indices is significantly broader in the sample of RL AGNs. In order to investigate the origin of this difference, we have divided the RL AGNs into blazars and ``non-blazars'', on the basis of the available optical and radio information. We find strong evidence that the broad distribution observed in the RL AGN sample is mainly due to the presence of the blazars. Furthermore, within the blazar class we have found a link between the X-ray spectral index and the value of the radio-to-X-ray spectral index suggesting that the observed X-ray emission is directly connected to the emission of the relativistic jet. This trend is not observed among the ``non-blazars'' RL AGNs. This favours the hypothesis that, in these latter sources, the X-ray emission is not significantly influenced by the jet emission and it has probably an origin similar to the RQ AGNs. Overall, the results presented here indicate that the observed distribution of the X-ray spectral indices in a given sample of RL AGNs is strongly dependent on the amount of relativistic beaming present in the selected sources.

X-ray pre-ionization powered by accretion on the first black holes - II. Cosmological simulations and observational signatures

We use numerical simulations of a cosmological volume to study the X-ray ionization and heating of the intergalactic medium (IGM) by an early population of accreting black holes (BHs). By considering theoretical limits on the accretion rate and observational constraints from the X-ray background and faint X-ray source counts, we find that the maximum value of the optical depth to Thompson scattering which can be produced using these models is τe≃ 0.17, in agreement with previous semi-analytic results. The redshifted soft X-ray background produced by these early sources is important in producing a fully ionized atomic hydrogen in the low-density intergalactic medium before stellar reionization at redshift z∼ 6–7. As a result, stellar re-ionization is characterized by an almost instantaneous ‘overlap phase’ of H ii regions. The background also produces a second He ii re-ionization at about redshift 3 and maintains the temperature of the IGM at about 10 000 K even at low redshifts. If the spectral energy distribution of these sources has a non-negligible high-energy power-law component, the luminosity in the soft X-ray band of the ‘typical’ galaxies hosting intermediate-mass accreting BHs is maximum at z∼ 15 and is about one or two orders of magnitude below the sensitivity limit of the Chandra Deep Field. We find that about a thousand of these sources may be present per square arcmin of the sky, producing potentially detectable fluctuations. We also estimate that a few rare objects, not present in our small simulated volume, could be luminous enough to be visible in the Chandra Deep Field. The XEUS and Constellation-X satellites will be able to detect more of these sources that, if radio loud, could be used to study the 21-cm forest in absorption. A signature of an early X-ray pre-ionization is the production of secondary cosmic microwave background (CMB) anisotropies on small angular scales (<1 arcmin). We find that in these models the power spectrum of temperature fluctuations increases with decreasing angular scale (ΔT∼ 16 μK at ∼1-arcsec scales), while for stellar re-ionization scenarios the power decreases on smaller scales. We also show that the redshifted 21-cm radiation from neutral hydrogen can be marginally detected in emission at redshifts 7 < z < 12. At a redshift of about z∼ 30 a stronger and narrower (in redshift space) signal in absorption against the CMB, that is peculiar to these models, could be detectable.

Average Ultraviolet Quasar Spectra in the Context of Eigenvector 1: A Baldwin Effect Governed by the Eddington Ratio?

We present composite UV spectra for low-redshift type 1 active galactic nuclei binned to exploit the information content of the eigenvector 1 (E1) parameter space. Composite spectra show high enough S/N and spectral resolution to permit a decomposition of the C IV λ1549 line profile: one of the strongest high-ionization lines (HILs), and fundamental in defining E1 space. The simplest C IV λ1549 decomposition into narrow-line region (NLR), broad-line region (BLR), and very broad line region (VBLR) components suggests that different components have an analog in Hβ with two major exceptions. VBLR emission is seen only in population B [FWHM(HβBC) > 4000 km s-1] sources. A blueshifted/asymmetric BLR component is seen only in population A [FWHM(HβBC) ≤ 4000 km s-1] HILs such as C IV λ1549. The blueshifted component is thought to arise in a high-ionization wind or outflow. Our analysis suggests that such a wind can only be produced in population A (almost all radio-quiet, RQ) sources, where the accretion rate is relatively high. We propose a model to account for several differences between low- and high-ionization line profiles. Part of the broad-line emission is attributed to a self-gravitating/fragmented region in an accretion disk. An inner, optically thick, geometrically thin region of the flow may give rise to a wind/outflow and produce the blueshifted HIL spectrum in population A sources. The fragmented region may produce all or most of the broad-line emission in population B, which contains RQ and the majority of radio-loud (RL) quasars. Comparison between broad UV lines in RL and RQ sources in a single, well-populated E1 parameter space bin (B1) shows few significant differences. Clear evidence is found for a significant NLR C IV component in most RL sources. The BLR/VBLR similarity in bin B1 provides circumstantial evidence in favor of black hole (BH) spin, rather than BH mass or accretion rate, as a key trigger in determining whether an object will be RL or RQ. We find a 10-fold decrease in EW C IV λ1549 with Eddington ratio (decreasing from ≈1 to ~0.01), while N V λ1240 shows no change. These trends suggest a luminosity-independent Baldwin effect in which the physical driver may be the Eddington ratio.

Does the dichotomy of active galactic nuclei depend only on black hole spins?

A toy model for jet powers and radio loudness of active galactic nuclei (AGNs) is proposed based on the coexistence of the Blandford-Znajek (BZ) and magnetic coupling (MC) processes (CEBZMC) in black hole (BH) accretion disc. It turns out that both the jet powers and radio-loudness of AGNs are controlled by more than one physical parameter besides the BH spin. The observed dichotomy between radio-loud and radio-quiet AGNs is well interpreted by the two parameters, the BH spin and the power-law index of the variation of the magnetic field on the disc. Furthermore, we discuss the correlation of jet powers with radio loudness of AGNs in terms of the two parameters. It is found that the contours of radio loudness are approximately in accord with those of jet powers for several 3CR radio sources, implying roughly that the stronger jet power corresponds to stronger radio loudness. In addition we discuss the correlation of the jet powers and radio-loudness of AGNs with the position of the inner edge of an accretion disc. These results imply that the spin paradigm for radio loudness of AGNs might be modified by a scenario containing more physical parameters.

Intranight optical variability of BL Lacs, radio-quiet quasars and radio-loud quasars

We report monitoring observations of 20 high-luminosity active galactic nuclei (AGN), 12 of which are radio-quiet quasars (RQQs). Intranight optical variability (INOV) was detected for 13 of the 20 objects, including 5 RQQs. The variations are distinctly stronger and more frequent for blazars than for the other AGN classes. By combining these data with results obtained earlier in our programme, we have formed an enlarged sample consisting of 9 BL Lacs, 19 RQQs and 11 lobe-dominated radio-loud quasars (RLQs). The moderate level of rapid optical variability found for both RQQs and radio lobe-dominated quasars (LDQs) argues against a direct link between INOV and radio loudness. We supplemented the present observations of 3 BL Lacs with additional data from the literature. In this extended sample of 12 well observed BL Lacs, stronger INOV is found for the EGRET detected subset.

SDSS J022119.84+005628.4: A Radio-Loud Narrow-Line Seyfert 1 Galaxy with Star Formation in its Nucleus

The optical spectrum of SDSS J022119.84 + 005628.4 (RA = 02 h 21 m 19.84 s , Dec = 00 o 56' 28.4, J2000; z =0.399785 ± 0.000558) is analyzed by multi-component profile modelling. The small flux ratio of [O III] NC /H β (=0.78) and {FWHM}( {H} beta {BC}})= {1778.1p 85.9 km s -1 } led us to identify SDSS J022119.84 + 005628.4 as a Narrow-line Seyfert 1 galaxy with RFe=1.4 +1.0 -1.0 and intermediate radio loudness, log R =1.93. The continuum low jump at the Balmer limit might be contributed by a starburst component, which suggests that the object is a relatively young AGN with star-formation activity in its inner region. This provides a useful observational test of the AGN evolution. The low flux ratio of the narrow components, [ {i{O}{iii}}]/ {H}β = 1.62, and the prominent [O II]λ3727 emission, [O II]/[O III] = 2.24, suggests that there should be a group of AGNs different from Seyfert 2s when their broad line regions are obscured by the torus on the line of sight. A possible orientation effect is suggested to interpret the observed Seyfert 1.5s-like spectrum of the object. The spectrum features prominent broad blue wings of both [O III] λλ4959 and 5007. After excluding other possible contributions, we conclude that the broad components are emitted by [O III] itself. The material emitting the broad [O III] line is probably situated in a transient line region (with a low electron density, n e 7 cm -3 ) between the broad line region (BLR) and the narrow line region (NLR). The object can be classified as a ``blue outlier'' defined by Zamanov et al., according to its velocity shift upsilon r {([i{O}{iii}])=-293.6p.0 km s -1 }, relative to the systematic velocity.

XMM-Newtonobservations of seven soft X-ray excess quasi-stellar objects

XMM-Newton observations of seven quasi-stellar objects (QSOs) are presented and the EPIC spectra analysed. Five of the active galactic nuclei (AGN) show evidence for Fe Kα emission, with three being slightly better fitted by lines of finite width; at the 99 per cent level they are consistent with being intrinsically narrow, though. The broad-band spectra can be well modelled by a combination of different temperature blackbodies (BBs) with a power law, with temperatures between kT ∼100 and 300 eV. On the whole, these temperatures are too high to be direct thermal emission from the accretion disc, so a Comptonization model was used as a more physical parametrization. The Comptonizing electron population forms the soft excess emission, with an electron temperature of ∼120-680 eV. Power-law, thermal plasma and disc BB models were also fitted to the soft X-ray excess. Of the sample, four of the active galactic nuclei are radio quiet and three radio loud. The radio-quiet QSOs may have slightly stronger soft excesses, although the electron temperatures cover the same range for both groups.

Is there a dichotomy in the radio loudness distribution of quasars?

We present a new approach to tackling the issue of radio loudness in quasars. We constrain a (simple) prescription for the intrinsic distribution of radio-to-optical ratios by comparing properties of Monte Carlo simulated samples with those of observed optically selected quasars. We find strong evidence for a dependence of the radio luminosity on the optical one, even though with a large scatter. The dependence of the fraction of radio-loud quasars on apparent and absolute optical magnitudes results in a selection effect related to the radio and optical limits of current surveys. The intrinsic distribution of the radio-to-optical ratios shows a peak at R*1.4∼ 0.3, with only ≲5 per cent of objects being included in a high-R*1.4 tail, which identifies the radio-loud regime. No lack or deficit of sources — but only a steep transition region — is present between the radio-loud and radio-quiet populations at any R*1.4. Briefly, we discuss possible origins for this behaviour (e.g. an absence of jets in radio-quiet sources, a large range of radiative radio efficiency, different lifetimes for the accretion and jet ejection phenomena, etc.).

Radio-loud Active Galactic Nuclei in the Context of the Eigenvector 1 Parameter Space

We consider the properties of radio-loud (RL) active galactic nuclei in the context of the eigenvector 1 (E1) parameter space. RL sources show a restricted E1 parameter space occupation relative to the radio-quiet (RQ) majority. The Fanaroff-Riley II parent population of relatively unboosted RL sources (median radio/optical flux ratio ~490) shows the most restricted occupation. RL sources have different broad-line properties (and inferred black hole masses and Eddington ratios). FWHM H? for the broad-line component in RL sources are at least twice as large as in the RQ majority. The average broad Fe II ?4570 emission-line strength is also about half that for RQ sources. Our sample suggests that the RL cutoff occurs near RK ? 70 or log P6 cm ~ 32.0 ergs s-1 Hz-1. Sources below this cutoff are RQ, although we cannot rule out the existence of a distinct intermediate population. We show that the Doppler-boosted core-dominated RL sources (median flux ratio ~1000) lie toward smaller FWHM(H?BC) and stronger Fe IIopt in E1, as expected if the lines arise in an accretion disk. Our subsample of superluminal sources, with orientation inferred from the synchrotron self-Compton model, reinforce this general E1 trend and allow us to estimate the role of source orientation in driving E1 domain occupation.

Searching for the physical drivers of eigenvector 1: influence of black hole mass and Eddington ratio

We compute the virial mass (M) of the central black hole and the luminosity-to-mass (L/M) ratio of ≈300 low-z quasars and luminous type 1 Seyfert nuclei. We analyse the following: (1) whether radio-quiet and radio-loud objects show systematic differences in terms of M and L/M; (2) the influence of M and L/M on the shape of the Hβ broad component line profile; and (3) the significance of the so-called ‘blue outliers’, i.e. sources showing a significant blueshift of the [O iii]λλ4959,5007 lines with respect to the narrow component of Hβ, which is used as an estimator of the quasar reference frame. We show that M and L/M distributions for radio-quiet and radio-loud sources are probably different for samples matched in luminosity and redshift, in the sense that radio-quiet sources have systematically smaller masses and larger L/M. However, the L/M ratio distributions become indistinguishable if 8.5 < log M < 9.5. Line profile comparisons for median spectra computed over narrow ranges of M and L/M indicate that a Lorentz function provides a better fit for higher L/M sources and a double Gaussian for lower L/M values. A second (redshifted) Gaussian component at low L/M appears as a red asymmetry frequently observed in radio-loud and radio-quiet sources with broader (full width at half-maximum ≳4000 km s−1) Hβ broad component profiles. This component becomes stronger in larger mass and lower L/M sources. No specific influence of radio loudness on the Hβ broad component profile is detected, although equivalent widths of Hβ broad component and especially of [O iii]λλ4959,5007 are larger for radio-loud sources. We identify five more ‘blue outlier’ sources. Since these sources are, on average, one magnitude brighter than other active galactic nuclei with similar mass, their resulting Eddington ratio is 2–3 times higher. We hint at evolutionary effects that explain some of these results, and reinforce the ‘eigenvector 1’ correlations.

Intranight optical variability of radio-quiet and radio lobe-dominated quasars

We present results of a programme of multi-epoch, intra-night optical monitoring of a sample of non-blazar type AGN, which includes seven radio-quiet QSOs (RQQs) and an equal number of radio-loud, lobe-dominated quasars (LDQs), covering a redshift range from about 0.2 to 2.0. These two sets of optically bright and intrinsically luminous QSOs are well matched in the redshift-optical luminosity ($z - M_B$) plane. Our CCD monitoring covered a total of 61 nights with an average of 6.1 hours of densely sampled monitoring of just a single QSO per night, thereby achieving a typical detection threshold of $\sim 1$% variation over the night. Unambiguous detection of intra-night variability(INOV) amplitudes in the range 1$-$3% on day-like or shorter time scales were thus made for both RQQs and LDQs. Based on these clear detections of INOV, we estimate duty cycles of 17% and 9% for RQQs and LDQs, respectively; inclusion of the two cases of probable variations of LDQs would raise the duty cycle to 15% for LDQs. The similarity in the duty cycle and amplitude of INOV for the RQQs and LDQs suggests, firstly, that the radio loudness alone does not guarantee an enhanced INOV in QSOs and,secondly, that as in LDQs, relativistic jets may also be present in RQQs. We argue that, as compared to BL Lacs, the conspicuously milder, rarer and possibly slower INOV of RQQs and LDQs, can in fact be readily understood in terms of their having optical synchrotron jets which are modestly misaligned from us,but are otherwise intrinsically as relativistic and active as the jets in BL Lacs.

Disc-jet coupling in an atoll-type neutron star X-ray binary: 4U 1728-34 (GX 354-0)

We have analysed 12 simultaneous radio (Very Large Array) and X-ray (RXTE) observations of the atoll-type X-ray binary 4U 1728-34, performed in two blocks in 2000 and 2001. We have found that the strongest and most variable emission seems to be associated with repeated transitions between hard (island) and softer (lower banana) X-ray states, while weaker, persistent radio emission is observed when the source is steadily in the hard X-ray state. There is a significant positive ranking correlation between the radio flux density at 8.46 GHz and the 2-10 keV X-ray flux. Moreover, significant positive ranking correlations between radio flux density and X-ray timing features (i.e. break and low-frequency Lorentzian frequencies) have been found. These correlations represent the first evidence for a coupling between disc and jet in an atoll-type X-ray binary Furthermore, drawing an analogy between the hard (island) state and the low/hard state of black hole binaries, we confirm previous findings that accreting neutron stars are a factor of ∼30 less radio loud' than black holes.

The BeppoSAX High Energy Large Area Survey (HELLAS) -- VI. The radio properties

We present results of a complete radio follow-up obtained with the VLA and ATCA radio telescopes down to a 6 cm flux limit of about 0.3 mJy of all the 147 X-ray sources detected in the BeppoSAX HELLAS survey. We found 53 X-ray/radio likely associations, corresponding to about one third of the X-ray sample. Using the two point spectral index alpha_ro=0.35 we divided all the HELLAS X-ray sources in radio quiet and radio loud. We have 26 sources classified as radio-loud objects, corresponding to about 18% of the HELLAS sample. In agreement with previous results, the identified radio-loud sources are associated mainly with Type 1 AGNs with L(5-10 keV) > 10^44 erg/s, while all the identified Type 2 AGNs and Emission Line Galaxies are radio quiet objects with L(5-10 keV) < 10^44 erg/s. The analysis of the radio spectral index suggests that Type 1 AGNs have a mean radio spectral index flatter than Type 2 AGNs and Emission Line Galaxies.

SDSS J094857.3+002225: A Very Radio Loud, Narrow‐Line Quasar with Relativistic Jets?

We report the identification of a very radio loud, narrow-line quasar, SDSS J094857.3+002225, discovered in the Sloan Digital Sky Survey (SDSS) early data release (EDR). With FWHM (Hβ) ≈ 1500 km s-1 and undetected [O III] λλ 4959, 5007 SDSS J094857.3+002225 is consistent with the conventional definition of narrow-line Seyfert 1 galaxies (NLS1s). Its strong optical Fe II emission [R4570 ≡ f(Fe II λ4570)/f(Hβ) ≈ 1.59] is also typical of NLS1s. With a radio loudness RL ≡ (fν,4.85 GHz/fν,B) ≳ 1000 and radio power of P4.85 GHz ~ (3.6-5.2) × 1026 W Hz-1, it is the first bona fide, very radio loud NLS1. The inverted radio spectrum and very high brightness temperature (≳1013 K) derived from variation of the radio flux suggest the presence of a relativistic jet beaming toward the observer in this NLS1.

Clear Evidence for Intranight Optical Variability in Radio-quiet Quasars

We present new clues to the problem of the radio loudness dichotomy arising from an extensive search for intranight optical variability in seven sets of optically luminous radio-quiet quasars and (radio-loud) BL Lacertae objects, which are matched in optical luminosity and redshift. Our monitoring of radio-quiet quasars has for the first time clearly detected such intranight variability, with peak-to-peak amplitudes ~1%, occurring with a duty cycle of ~. The matched BL Lac objects have both higher variability amplitudes and duty cycles when observed in the same fashion. We show that the much less pronounced intranight variability of the radio-quiet quasars relative to BL Lac objects can be understood in terms of a modest misalignment of the jets in radio-quiet quasars from the line of sight. We thus infer that relativistic particle jets may well also emerge from radio-quiet quasars, but while traversing the short optical-emitting distances, they could be snuffed out, possibly through inverse Compton losses in the nuclear region.

The radio-loud/radio-quiet dichotomy: news from the 2dF QSO Redshift Survey

We present a detailed analysis of a sample of radio-detected quasars, obtained by matching together objects from the FIRST and 2dF Quasar Redshift Surveys. The dataset consists of 113 sources, spanning a redshift range 0.3 < z < 2.2, with optical magnitudes 18.25 < b_J < 20.85 and radio fluxes S_{1.4 GHz} < 1 mJy. These objects exhibit properties such as redshift and colour distribution in full agreement with those derived for the whole quasar population, suggestive of an independence of the mechanism(s) controlling the birth and life-time of quasars of their level of radio emission. The long debated question of radio-loud (RL)/radio-quiet (RQ) dichotomy is then investigated for the combined FIRST-2dF and FIRST-LBQS sample, since they present similar selection criteria. We find the fraction of radio detections to increase with magnitude from < 3% at the faintest levels up to 20% for the brightest sources. The classical RL/RQ dichotomy, in which the distribution of radio-to-optical ratios and/or radio luminosities shows a lack of sources, is ruled out by our analysis. We also find no tight relationship between optical and radio luminosities for sources in the considered sample, result that tends to exclude the mass of the quasar black hole as the physical quantity associated to the level of radio emission.

ChandraSnapshot Observations of Low‐Luminosity Active Galactic Nuclei with a Compact Radio Source

The results of Chandra snapshot observations of 11 LINERs (Low-Ionization Nuclear Emission-line Regions), three low-luminosity Seyfert galaxies, and one HII-LINER transition object are presented. Our sample consists of all the objects with a flat or inverted spectrum compact radio core in the VLA survey of 48 low-luminosity AGNs (LLAGNs) by Nagar et al. (2000). An X-ray nucleus is detected in all galaxies except one and their X-ray luminosities are in the range 5x10^38 to 8x10^41 erg/s. The X-ray spectra are generally steeper than expected from thermal bremsstrahlung emission from an advection-dominated accretion flow (ADAF). The X-ray to Halpha luminosity ratios for 11 out of 14 objects are in good agreement with the value characteristic of LLAGNs and more luminous AGNs, and indicate that their optical emission lines are predominantly powered by a LLAGN. For three objects, this ratio is less than expected. Comparing with properties in other wavelengths, we find that these three galaxies are most likely to be heavily obscured AGN. We use the ratio RX = \nu L\nu (5 GHz)/LX, where LX is the luminosity in the 2-10 keV band, as a measure of radio loudness. In contrast to the usual definition of radio loudness (RO = L\nu(5 GHz)/L\nu(B)), RX can be used for heavily obscured (NH >~ 10^23 cm^-2, AV>50 mag) nuclei. Further, with the high spatial resolution of Chandra, the nuclear X-ray emission of LLAGNs is often easier to measure than the nuclear optical emission. We investigate the values of RX for LLAGNs, luminous Seyfert galaxies, quasars and radio galaxies and confirm the suggestion that a large fraction of LLAGNs are radio loud.

The Independence of Active Galactic Nucleus Black Hole Mass and Radio Loudness

We revisit the issue of whether radio loudness in active galactic nuclei (AGNs) is associated with central black hole mass, as has been suggested in the literature. We present new estimates of black hole mass for 295 AGNs (mostly radio quiet), calculating their radio loudnesses from published radio and optical fluxes, and combine with our previously published values, for a sample of 452 AGNs for which both black hole mass and radio loudness (or upper limits thereto) are known. Among the radio-quiet AGNs, there are now many black holes with mass larger than 109 M?, extending to the same high black hole masses as radio-loud AGNs of the same redshifts. Over the full sample, the black hole masses of radio-loud and radio-quiet AGNs span the same large range, 106-1010 M?. We conclude that radio loudness in AGNs does not depend strongly on central black hole mass.