Deep spectroscopy of z~1 6C radio galaxies - II. Breaking the redshift-radio power degeneracy

The results of a spectroscopic analysis of 3CR and 6C radio galaxies at redshift z~1 are contrasted with the properties of lower redshift radio galaxies, chosen to be matched in radio luminosity to the 6C sources studied at z~1, thus enabling the P-z degeneracy to be broken. Partial rank correlations and principal component analysis have been used to determine which of z and P are the critical parameters underlying the observed variation of the ionization state andd kinematics of the emission line gas. [OII]/H-beta is shown to be a useful ionization mechanism diagnostic. Statistical analysis of the data shows that the ionization state of the emission line gas is strongly correlated with radio power, once the effects of other parameters are removed. No dependence of ionization state on z is observed, implying that the ionization state of the emission line gas is solely a function of the AGN properties rather than the hostt galaxy and/or environment. Statistical analysis of the kinematic properties of the emission line gas shows that these are strongly correlated independently withh both P and z. The correlation with redshift is the stronger of the two, suggesting that host galaxy composition or environment may play a role in producing the less extreme gas kinematics observed in the emission line regions of low redshift galaxies. For both the ionization and kinematic properties of thee galaxies, the independent correlations observed with radio size are strongest. Radio source age is a determining factor for the extended emission line regions.Comment: 10 pages, 5 figures, accepted for publication in MNRA

A short survey on nonlinear models of the classic Costas loop: rigorous derivation and limitations of the classic analysis

Rigorous nonlinear analysis of the physical model of Costas loop --- a classic phase-locked loop (PLL) based circuit for carrier recovery, is a challenging task. Thus for its analysis, simplified mathematical models and numerical simulation are widely used. In this work a short survey on nonlinear models of the BPSK Costas loop, used for pre-design and post-design analysis, is presented. Their rigorous derivation and limitations of classic analysis are discussed. It is shown that the use of simplified mathematical models, and the application of non rigorous methods of analysis (e.g., simulation and linearization) may lead to wrong conclusions concerning the performance of the Costas loop physical model.Comment: Accepted to American Control Conference (ACC) 2015 (Chicago, USA

The host galaxies of radio-loud AGN: mass dependencies, gas cooling and AGN feedback

The properties of the host galaxies of a well-defined sample of 2215 radio-loud AGN with redshifts 0.03 < z < 0.3, defined from the SDSS, are investigated. These are predominantly low radio luminosity sources, with 1.4GHz luminosities of 10^23 to 10^25 W/Hz. The fraction of galaxies that host radio-loud AGN with L(1.4GHz) > 10^23 W/Hz is a strong function of stellar mass, rising from nearly zero below a stellar mass of 10^10 Msun to more than 30% at 5x10^11 Msun. The integral radio luminosity function is derived in six ranges of stellar and black hole mass. Its shape is very similar in all of these ranges and can be well fitted by a broken power-law. Its normalisation varies strongly with mass, as M_*^2.5 or M_BH^1.6; this scaling only begins to break down when the predicted radio-loud fraction exceeds 20-30%. There is no correlation between radio and emission line luminosities for the radio-loud AGN in the sample and the probability that a galaxy of given mass is radio-loud is independent of whether it is optically classified as an AGN. The host galaxies of the radio-loud AGN have properties similar to those of ordinary galaxies of the same mass. All of these findings support the conclusion that the optical AGN and low radio luminosity AGN phenomena are independent and are triggered by different physical mechanisms. Intriguingly, the dependence on black hole mass of the radio-loud AGN fraction mirrors that of the rate at which gas cools from the hot atmospheres of elliptical galaxies. It is speculated that gas cooling provides a natural explanation for the origin of the radio-loud AGN activity, and it is argued that AGN heating could plausibly balance the cooling of the gas over time. [Abridged]Comment: Accepted for publication in MNRAS. LaTeX, 16 pages. Figure 10 is in colou

Red galaxy overdensities and the varied cluster environments of powerful radio sources with z~1.6

The environments of a complete subsample of 6 of the most powerful radio-loud AGN at redshifts z~1.6 are investigated, using deep RJK imaging to depths of R~26, J~22.4 and K~20.6. An excess of galaxy counts in the K-band is seen across these fields; these are predominantly associated with red galaxies (R-K>4) of magnitudes 17.5<K<20.5 found within radial distances of ~1 Mpc of the AGN host. These are exactly (though not uniquely) the magnitudes, colours and locations that would be expected of old passive elliptical galaxies in cluster environments at the redshifts of these AGN. Using both an Abell-style classification scheme and investigations of the angular and spatial cross-correlation functions of the galaxies, the average environment of the fields around these AGN is found to be consistent with Abell cluster richness classes 0 to 1. The amplitude of the angular cross-correlation function around the AGN is a strong function of galaxy colour, and is highest when only those galaxies with the colours expected of old elliptical galaxies at these redshifts are considered. The galaxy overdensities are found on two scales around the AGN: (i) pronounced central concentrations on radial scales within 150 kpc; where present, these are composed almost entirely of red (R-K>4) galaxies, suggesting that the morphology-density relation is imprinted into the centres of clusters at a high redshift. (ii) weaker large-scale excesses extending out to between 1 and 1.5 Mpc radius. The presence or absence of galaxy excesses on these two scales, however, differs greatly between the six different fields. The implications of these results for both cluster formation and the nature of high redshift AGN are discussed (abridged).Comment: Accepted for publication in MNRAS. LaTeX, 16 pages, plus 12 additional jpeg figures, 6 in colour. A version with all figures in the postscript file is available from http://www.roe.ac.uk/~pnb/eso_clus.p

Deep LOFAR 150 MHz imaging of the Bo\"otes field: Unveiling the faint low-frequency sky

We have conducted a deep survey (with a central rms of $55\mu\textrm{Jy}$) with the LOw Frequency ARray (LOFAR) at 120-168 MHz of the Bo\"otes field, with an angular resolution of $3.98^{''}\times6.45^{''}$, and obtained a sample of 10091 radio sources ($5\sigma$ limit) over an area of $20\:\textrm{deg}^{2}$. The astrometry and flux scale accuracy of our source catalog is investigated. The resolution bias, incompleteness and other systematic effects that could affect our source counts are discussed and accounted for. The derived 150 MHz source counts present a flattening below sub-mJy flux densities, that is in agreement with previous results from high- and low- frequency surveys. This flattening has been argued to be due to an increasing contribution of star-forming galaxies and faint active galactic nuclei. Additionally, we use our observations to evaluate the contribution of cosmic variance to the scatter in source counts measurements. The latter is achieved by dividing our Bo\"otes mosaic into 10 non-overlapping circular sectors, each one with an approximate area of $2\:\textrm{deg}^{2}.$ The counts in each sector are computed in the same way as done for the entire mosaic. By comparing the induced scatter with that of counts obtained from depth observations scaled to 150MHz, we find that the $1\sigma$ scatter due to cosmic variance is larger than the Poissonian errors of the source counts, and it may explain the dispersion from previously reported depth source counts at flux densities $S<1\,\textrm{mJy}$. This work demonstrates the feasibility of achieving deep radio imaging at low-frequencies with LOFAR.Comment: A\&A in press. 15 pages, 16 figure

Star Formation, Radio Sources, Cooling X-ray Gas, and Galaxy Interactions in the Brightest Cluster Galaxy in 2A0335+096

We present deep emission-line imaging taken with the SOAR Optical Imaging Camera of the brightest cluster galaxy (BCG) in the nearby (z=0.035) X-ray cluster 2A0335+096. We analyze long-slit optical spectroscopy, archival VLA, Chandra X-ray, and XMM UV data. 2A0335+096 is a bright, cool-core X-ray cluster, once known as a cooling flow. Within the highly disturbed core revealed by Chandra X-ray observations, 2A0335+096 hosts a highly structured optical emission-line system. The redshift of the companion is within 100 km/s of the BCG and has certainly interacted with the BCG, and is likely bound to it. The comparison of optical and radio images shows curved filaments in H-alpha emission surrounding the resolved radio source. The velocity structure of the emission-line bar between the BCG nucleus and the companion galaxy provides strong evidence for an interaction between the two in the last ~50 Myrs. The age of the radio source is similar to the interaction time, so this interaction may have provoked an episode of radio activity. We estimate a star formation rate of >7 solar mass/yr based on the Halpha and archival UV data, a rate similar to, but somewhat lower than, the revised X-ray cooling rate of 10-30 solar masses/year estimated from XMM spectra by Peterson & workers. The Halpha nebula is limited to a region of high X-ray surface brightness and cool X-ray temperature. The detailed structures of H-alpha and X-ray gas differ. The peak of the X-ray emission is not the peak of H-alpha emission, nor does it lie in the BCG. The estimated age of the radio lobes and their interaction with the optical emission-line gas, the estimated timescale for depletion and accumulation of cold gas, and the dynamical time in the system are all similar, suggesting a common trigger mechanism.Comment: Accepted AJ, July 2007 publication. Vol 134, p. 14-2

Dust in 3C324

The results of a deep submillimetre observation using SCUBA of the powerful radio galaxy 3C324, at redshift z=1.206, are presented. At 850 microns, emission from the location of the host radio galaxy is marginally detected at the 4.2 sigma level, 3.01 +/- 0.72 mJy, but there is no detection of emission at 450 microns to a 3 sigma limit of 21 mJy. A new 32 GHz radio observation using the Effelsberg 100m telescope confirms that the sub-millimetre signal is not associated with synchrotron emission. These observations indicate that both the mass of warm dust within 3C324, and the star formation rate, lie up to an order of magnitude below the values recently determined for radio galaxies at z = 3 to 4. The results are compared with dust masses and star formation rates derived in other ways for 3C324.Comment: 5 pages LaTeX, including 1 figure. Accepted for publication in MNRA

HST Observations of the Host Galaxies of BL Lacertae Objects

Six BL Lac objects from the complete 1 Jy radio-selected sample of 34 objects were observed in Cycle 5 with the HST WFPC2 camera to an equivalent limiting flux of mu_I~26 mag/arcsec^2. Here we report results for the second half of this sample, as well as new results for the first three objects, discussed previously by Falomo et al. (1997). In addition, we have analyzed in the same way HST images of three X-ray-selected BL Lacs observed by Jannuzi et al. (1997). The ensemble of 9 BL Lac objects spans the redshift range from z=0.19 to ~1. Host galaxies are clearly detected in seven cases, while the other two, at z~0.258 (redshift highly uncertain) and z=0.997, are not resolved. The HST images constitute a homogeneous data set with unprecedented morphological information between a few tenths of an arcsecond and several arcseconds from the nucleus, allowing us in 6 of the 7 detected host galaxies to rule out definitively a pure disk light profile. The host galaxies are luminous ellipticals with an average absolute magnitude of M_I~-24.6 mag (with dispersion 0.7 mag), more than a magnitude brighter than L* and comparable to brightest cluster galaxies. The morphologies are generally smooth and have small ellipticities (epsilon<0.2). Given such roundness, there is no obvious alignment with the more linear radio structures. In the six cases for which we have HST WFPC2 images in two filters, the derived color profiles show no strong spatial gradients and are as expected for K-corrected passively evolving elliptical galaxies. The host galaxies of the radio-selected and X-ray-selected BL Lacs for this very limited sample are comparable in both morphology and luminosity.Comment: 23 pages, including 6 postscript figures and 3 tables (embedded). Latex requires aaspp4.sty and psfig.sty (not included). Accepted for publication in the Astrophysical Journa