The influence of AGN nuclear parameters on the FRI/FRII dichotomy

We have investigated the influence of nuclear parameters such as black hole mass and photoionizing luminosity on the FRI/FRII transition in a sample of nearby (z<0.2) radio galaxies from the 3CR catalogue. The sample was observed with medium-resolution, optical spectroscopy and contains some galaxies with unpublished velocity dispersion measurements and emission-line fluxes. The measured velocity dispersions for the sample lie in the range 130-340 km s^(-1) with a mean of 216 km s^(-1). Using the M-σ relation, we convert to black hole mass and find that the black hole mass distribution is identical for FRI and FRII galaxies, with a mean of ≈ 2.5 × 10^8 M_☉. We determine narrow emission-line luminosities from [O III] and [O III] in our spectra, as well as from the literature, and convert them to photoionizing luminosities under the assumption that the gas is ionized by the nuclear UV continuum. Most of the galaxies with FRI morphology and/or low-excitation emission-line spectra have progressively lower black hole masses at lower photoionizing (and jet) luminosities. This agrees with the well-known Ledlow-Owen relation which states that the radio luminosity at the FRI/FRII transition depends on the optical luminosity of the host, L_(radio) ∝ L^(1.8)_(optical), because these two luminosities relate to AGN nuclear parameters. When recasting the Ledlow-Owen relation into black hole mass versus photoionizing luminosity and jet luminosity, we find that the recasted relation describes the sample quite well. Furthermore, the FRI/FRII transition is seen to occur at approximately an order of magnitude lower luminosity relative to the Eddington luminosity than the soft-to-hard transition in X-ray binaries. This difference is also consistent with the Ledlow-Owen relation, which predicts a weak black hole mass dependence in the transition luminosity in Eddington units. We conclude that the FRI/FRII dichotomy is caused by a combination of external and nuclear factors, with the latter dominating

The Influence of Black Hole Mass and Accretion Rate on the FRI/FRII Radio Galaxy Dichotomy

We use medium resolution optical spectra of 3CR radio galaxies to estimate their black hole masses and accretion rates. Black hole masses are found from central stellar velocity dispersions and accretion rates are derived from narrow emission-line luminosities. The sample covers both Fanaroff-Riley (FR) classes; the more powerful FRIIs and the less powerful FRIs. We find that FRIs and FRIIs separate in diagrams of black hole mass versus radio luminosity and narrow-line luminosity. This suggests that, at a given black hole mass, the FRIIs accrete more efficiently, or accrete more matter, than FRIs.Comment: 2 pages, 1 figure. Contribution to the proceedings of the conference "Growing Black Holes", Garching, Germany, June 21-24, 2004. Eds. A. Merloni, S. Nayakshin, R. Sunyae

QSO environments at intermediate redshifts

We have made a survey of quasar environments at 0.5 < z < 0.8, using a sample of both radio-loud and radio-quiet quasars matched in B-band luminosity. Our observations include images of background control fields to provide a good determination of the field galaxy counts. About 10 per cent of the quasars appear to live in rich clusters, whereas approximately 45 per cent live in environments similar to that of field galaxies. The richness of galaxies within a 0.5 Mpc radius around the radio-quiet quasars is found to be indistinguishable from the richness around the radio-loud quasars, corresponding on average to groups or poorer clusters of galaxies. Comparing the galaxy richness in the radio-loud quasar fields with quasar fields in the literature, we find no evidence of an evolution in the environment with epoch. Instead, a weak, but significant correlation between quasar radio luminosity and environmental richness is present. It is thus possible that the environments of quasars, at least the powerful ones, do not evolve much between the present epoch and z \approx 0.8.Comment: 6 pages, 4 figures, to appear in the proc. of the workshop `QSO hosts and their environments', IAA, Granada 10-12 Jan, 200

An Economic Analysis of Replacing Existing Bermudagrass Stands with Tifton 85 Bermudagrass for Beef Cow-Calf, Stocker and Hay Production

Comparisons of simulated NPV for Coastal and Tifton 85 bermuda-grass using experimental data, current input prices and historical hay and feeder cattle prices indicates that many producers would benefit by adopting this new cultivar. Cow-calf producers would benefit the most followed by stocker/replacement heifer producers and finally hay producers. When risk-aversion is introduced into the model, all cow-calf and stocker producers regardless of the level of risk-aversion should consider adopting T85. Moderately or extremely risk-averse hay producers would consider adopting T85, while those that are slightly risk-averse would be indifferent.Crop Production/Industries, Risk and Uncertainty,

The radio luminosity function of radio-loud quasars from the 7C Redshift Survey

We present a complete sample of 24 radio-loud quasars (RLQs) from the new 7C Redshift Survey. Every quasar with a low-frequency (151 MHz) radio flux-density S_151 > 0.5 Jy in two regions of the sky covering 0.013 sr is included; 23 of these have sufficient extended flux to meet the selection criteria, 18 of these have steep radio spectra (hereafter denoted as SSQs). The key advantage of this sample over most samples of RLQs is the lack of an optical magnitude limit. By combining the 7C and 3CRR samples, we have investigated the properties of RLQs as a function of redshift z and radio luminosity L_151. We derive the radio luminosity function (RLF) of RLQs and find that the data are well fitted by a single power-law with slope alpha_1=1.9. We find that there must be a break in the RLQ RLF at log_10(L_151 / W Hz^-1 sr^-1) < 27, in order for the models to be consistent with the 7C and 6C source counts. The z-dependence of the RLF follows a one-tailed gaussian which peaks at z=1.7. We find no evidence for a decline in the co-moving space density of RLQs at higher redshifts. A positive correlation between the radio and optical luminosities of SSQs is observed, confirming a result of Serjeant et al. (1998). We are able to rule out this correlation being due to selection effects or biases in our combined sample. The radio-optical correlation and best-fit model RLF enable us to estimate the distribution of optical magnitudes of quasars in samples selected at low radio frequencies. We conclude that for samples with S_151 < 1 Jy one must use optical data significantly deeper than the POSS-I limit (R approx 20), in order to avoid severe incompleteness.Comment: 28 pages with 13 figures. To appear in MNRA

Host Galaxies of Young Dust-Reddened Quasars

We present results on a multiwavelength campaign to identify the nature of dust-reddened Type 1 quasars. These quasars were selected by matching FIRST, 2MASS and very red optical counterparts with r' − K > 5. We find a very high fraction of Low Ionization Broad Absorption Line Quasars (LoBALs) among AGN selected with this method, perhaps a sign of quasar feedback. From X-ray observations and Balmer decrement measurements, the obscuring dust is most likely located in a cold absorber such as the host galaxy, rather than from a torus near the AGN. Hubble ACS imaging of a sub-sample of these sources showed a very high fraction of interacting and merging systems. The quasars appear to be very young in which dust from the merging galaxies is still settling in. Spitzer IRS and MIPS data show star formation signatures and deep Silicate absorption features in these objects, but overall the quasar is the dominant source in the Mid-infrared

Large amounts of optically-obscured star formation in the host galaxies of some type-2 quasars

We present Hubble Space Telescope images, and spectral energy distributions from optical to infrared wavelengths for a sample of six 0.3<z<0.8 type-2 quasars selected in the mid-infrared using data from the Spitzer Space Telescope. All the host galaxies show some signs of disturbance. Most seem to possess dusty, star-forming disks. The disk inclination, estimated from the axial ratio of the hosts, correlates with the depth of the silicate feature in the mid-infrared spectra, implying that at least some of the reddening towards the AGN arises in the host galaxy. The star formation rates in these objects, as inferred from the strengths of the PAH features and far-infrared continuum, range from 3-90 Msun/yr, but are mostly much larger than those inferred from the [OII]3727 emission line luminosity, due to obscuration. Taken together with studies of type-2 quasar hosts from samples selected in the optical and X-ray, this is consistent with previous suggestions that two types of extinction processes operate within the type-2 quasar population, namely a component due to the dusty torus in the immediate environment of the AGN, and a more extended component due to a dusty, star forming disk.Comment: 5 pages, 3 figures. Accepted by ApJ Letter