The spectral characteristics of the 2dFGRS-NVSS galaxies

We have analysed the 2dF spectra of a sample of galaxies common to the 2dF galaxy redshift survey (2dFGRS, Colless 1999) and the NRAO VLA sky survey (NVSS, Condon et al. 1998). Our sample comprises 88 galaxies selected by Sadler et al. (1999) from 30 2dFGRS fields observed in 1998. In this paper we discuss how this and future, much larger, samples of 2dFGRS-NVSS galaxies can be interpreted via analysis of those galaxies with strong narrow emission lines. Using diagnostic line ratio measurements we confirm the majority of the eyeball classifications of Sadler et al. (1999), although many galaxies show evidence of being `composite' galaxies - a mixture of AGN plus starburst components.Comment: 11 pages, 5 figures, accepted for publication in PAS

Long-term optical photometric monitoring of the quasar SDSS J153259.96-003944.1

We report optical Cousins R and I band monitoring observations of the high redshift (z = 4.67) QSO SDSS J153259.96-003944.1 that does not show detectable emission lines in its optical spectrum. We show this object varies with a maximum amplitude of ~0.4 mag during a year and three months of monitoring. Combined with two other epochs of photometric data available in the literature, we show the object has gradually faded by ~0.9 mag during the period June 1998 - April 2001. A linear least squares fit to all available observations gives a slope of ~0.35 mag/yr which translates to ~1.9 mag/yr in the rest frame of the quasar. Such a variability is higher than that typically seen in QSOs but consistent with that of BL Lacs, suggesting that the optical continuum is Doppler boosted. Alternatively, within photometric errors, the observed lightcurve is also consistent with the object going through a microlensing event. Photoionization model calculations show the mass of the Broad Line Region to be few tens of solar mass similar to that of low luminosity Seyfert galaxies, but about orders of magnitude less than that of luminous quasars. Further frequent photometric/spectroscopic monitoring is needed to support or refute the different alternatives discussed here on the nature of SDSS J153259.96-003944.1.Comment: 7 pages with 4 figures, uses mn2e.cls, Accepted for publication in MNRA

2QZJ215454.3-305654: a radio-quiet BL Lac object or lineless QSO?

High signal-to-noise spectroscopy has established a redshift of z=0.494 for the source 2QZJ215454.3-305654, originally selected from the 2dF/6dF QSO Redshift Surveys as one of 45 candidate BL Lac objects displaying a featureless continuum at optical wavelengths. Radio observations using the Australia Telescope Compact Array at 1.4 GHz place a 3\sigma upper limit on the object's radio flux density of approx 0.14mJy. The radio-to-optical flux ratio of this object is thus more than 7 times lower than the lowest such ratio observed in BL Lac objects. While the optical properties of 2QZJ215454.3-305654 are consistent with a BL Lac identification, the lack of radio and/or X-ray emission is not. It is uncertain whether this object is an AGN dominated by optical continuum emission from an accretion disk, or is similar to a BL Lac object with optical nonthermal emission from a relativistic jet.Comment: 7 pages, 6 figures, accepted by MNRA

Incidence of MgII absorbers towards Blazars and the GRB/QSO puzzle

In order to investigate the origin of the excess of strong MgII systems towards GRB afterglows as compared to QSO sightlines, we have measured the incidence of MgII absorbers towards a third class of objects: the Blazars. This class includes the BL Lac object population for which a tentative excess of MgII systems had already been reported. We observed with FORS1 at the ESO-VLT 42 Blazars with an emission redshift 0.8<z_em<1.9, to which we added the three high z northern objects belonging to the 1Jy BL Lac sample. We detect 32 MgII absorbers in the redshift range 0.35-1.45, leading to an excess in the incidence of MgII absorbers compared to that measured towards QSOs by a factor ~2, detected at 3 sigma. The amplitude of the effect is similar to that found along GRB sightlines. Our analysis provides a new piece of evidence that the observed incidence of MgII absorbers might depend on the type of background source. In front of Blazars, the excess is apparent for both 'strong' (w_ r(2796) > 1.0 A) and weaker (0.3 < w_r(2796) < 1.0 A) MgII systems. The dependence on velocity separation with respect to the background Blazars indicates, at the ~1.5 sigma level, a potential excess for beta = v/c ~0.1. We show that biases involving dust extinction or gravitational amplification are not likely to notably affect the incidence of MgII systems towards Blazars. Finally we discuss the physical conditions required for these absorbers to be gas entrained by the powerful Blazar jets. More realistic numerical modelling of jet-ambient gas interaction is required to reach any firm conclusions as well as repeat observations at high spectral resolution of strong MgII absorbers towards Blazars in both high and low states.Comment: 14 pages, 8 figures. Accepted for publication in A&

The Sedentary Survey of Extreme High Energy Peaked BL Lacs III. Results from Optical Spectroscopy

The multi-frequency Sedentary Survey is a flux limited, statistically well-defined sample of highly X-ray dominated BL Lacertae objects (HBLs) which includes 150 sources. In this paper, the third of the series, we report the results of a dedicated optical spectroscopy campaign that, together with results from other independent optical follow up programs, led to the spectroscopic identification of all sources in the sample. We carried out a systematic spectroscopic campaign for the observation of all unidentified objects of the sample using the ESO 3.6m, the KPNO 4m, and the TNG optical telescopes. We present new identifications and optical spectra for 76 sources, 50 of which are new BL Lac objects, 18 are sources previously referred as BL Lacs but for which no redshift information was available, and 8 are broad emission lines AGNs. We find that the multi-frequency selection technique used to build the survey is highly efficient (about 90%) in selecting BL Lacs objects. We present positional and spectroscopic information for all confirmed BL Lac objects. Our data allowed us to determined 36 redshifts out of the 50 new BL Lacs and 5 new redshifts for the previously known objects. The redshift distribution of the complete sample is presented and compared with that of other BL Lacs samples. For 26 sources without recognizable absorption features, we calculated lower limits to the redshift using a method based on simulated optical spectra with different ratios between jet and galaxy emission. For a subsample of 38 object with high-quality spectra, we find a correlation between the optical spectral slope, the 1.4 GHz radio luminosity, and the Ca H&K break value, indicating that for powerful/beamed sources the optical light is dominated by the non-thermal emission from the jet.Comment: 23 pages, accepted by A&

The Space Density of low redshift AGN

We present a new determination of the optical luminosity function (OLF) of active galactic nuclei (AGN) at low redshifts (z<0.15) based on Hubble Space Telescope (HST) observations of X-ray-selected AGN. The HST observations have allowed us to derive a true nuclear luminosity function for these AGN. The resulting OLF illustrates a two-power-law form similar to that derived for QSOs at higher redshifts. At bright magnitudes, M_B<-20, the OLF derived here exhibits good agreement with that derived from the Hamburg/ESO QSO survey. However, the single power law form for the OLF derived from the Hamburg/ESO survey is strongly ruled out by our data at M_B>-20. Although the estimate of the OLF is best-fit by a power law slope at M_B<-20.5 that is flatter than the slope of the OLF derived at z>0.35, the binned estimate of the low redshift OLF is still consistent with an extrapolation of the $z>0.35$ OLF based on pure luminosity evolution.Comment: MNRAS accepted (6 pages, 6 figures

Roma-BZCAT: A multifrequency catalogue of Blazars

We present a new catalogue of blazars based on multi-frequency surveys and on an extensive review of the literature. Blazars are classified as BL Lacertae objects, as flat spectrum radio quasars or as blazars of uncertain/transitional type. Each object is identified by a root name, coded as BZB, BZQ and BZU for these three subclasses respectively, and by its coordinates. This catalogue is being built as a tool useful for the identification of the extragalactic sources that will be detected by present and future experiments for X and gamma-ray astronomy, like Swift, AGILE, Fermi-GLAST and Simbol-X. An electronic version is available from the ASI Science Data Center web site at http://www.asdc.asi.it/bzcatComment: 7 pages, 3 figures; A&A, in pres

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.Comment: 18 pages, 10 figures, accepted for publication in A&

The Perceptions on Male Circumcision as a Preventive Measure Against HIV Infection and Considerations in Scaling up of the Services: A Qualitative Study Among Police Officers in Dar es Salaam, Tanzania.

\ud In recent randomized controlled trials, male circumcision has been proven to complement the available biomedical interventions in decreasing HIV transmission from infected women to uninfected men. Consequently, Tanzania is striving to scale-up safe medical male circumcision to reduce HIV transmission. However, there is a need to investigate the perceptions of male circumcision in Tanzania using specific populations. The purpose of the present study was to assess the perceptions of male circumcision in a cohort of police officers that also served as a source of volunteers for a phase I/II HIV vaccine (HIVIS-03) trial in Dar es Salaam, Tanzania. In-depth interviews with 24 men and 10 women were conducted. Content analysis informed by the socio-ecological model was used to analyze the data. Informants perceived male circumcision as a health-promoting practice that may prevent HIV transmission and other sexually transmitted infections. They reported male circumcision promotes sexual pleasure, confidence and hygiene or sexual cleanliness. They added that it is a religious ritual and a cultural practice that enhances the recognition of manhood in the community. However, informants were concerned about the cost involved in male circumcision and cleanliness of instruments used in medical and traditional male circumcision. They also expressed confusion about the shame of undergoing circumcision at an advanced age and pain that could emanate after circumcision. The participants advocated for health policies that promote medical male circumcision at childhood, specifically along with the vaccination program. The perceived benefit of male circumcision as a preventive strategy to HIV and other sexually transmitted infections is important. However, there is a need to ensure that male circumcision is conducted under hygienic conditions. Integrating male circumcision service in the routine childhood vaccination program may increase its coverage at early childhood. The findings from this investigation provide contextual understanding that may assist in scaling-up male circumcision in Tanzania.\u

Optical variability of radio-intermediate quasars

We report the results of our intensive intranight optical monitoring of 8 `radio-intermediate quasars' (RIQs) having flat or inverted radio spectra. The monitoring was carried out in {\it R-} band on 25 nights during 2005-09. An intranight optical variability (INOV) detection threshold of $\sim$ 1--2% was achieved for the densely sampled differential light curves (DLCs). These observations amount to a large increase over those reported hitherto for this rare and sparsely studied class of quasars which can, however, play an important role in understanding the link between the dominant varieties of powerful AGN, namely the radio-quiet quasars (RQQs), radio-loud quasars (RLQs) and blazars. Despite the probable presence of relativistically boosted nuclear jets, clear evidence for INOV in our extensive observations was detected only on one night. These results demonstrate that as a class, RIQs are much less extreme in nuclear activity compared to blazars. The availability in the literature of INOV data for another 2 RIQs conforming to our selection criteria allowed us to enlarge the sample to 10 RIQs (monitored on a total of 42 nights for a minimum duration of $\sim 4$ hours per night). The absence of large amplitude INOV $(\psi > 3$ persists in this enlarged sample. This extensive database has enabled us to arrive at the first estimate for the INOV Duty Cycle (DC) of RIQs. The DC is found to be small ($\sim$ 9%). The corresponding value is known to be $\sim 60$ for BL Lacs and $\approx 15$ for RLQs and RQQs. On longer-term, the RIQs are found to be fairly variable with typical amplitudes of $\approx$ 0.1-mag. The light curves of these RIQs are briefly discussed in the context of a theoretical framework proposed earlier for linking this rare kind of quasars to the much better studied dominant classes of quasars.Comment: 35 pages, 2 figures, 3 tables, accepted for publication in MNRA