V. Zitelli

Line and continuum variability of two intermediate-redshift, high-luminosity quasars

Context. It has been shown that the luminosity of active galactic nuclei and the size of their broad line region obey a simple relation of the type R-BLR = aL(gamma), from faint Seyfert nuclei to bright quasars, allowing single-epoch determination of the central black hole mass M-BH = bL(gamma) Delta(2) H-beta from their luminosity L and width of H-beta emission line. Adopting this mass determination for cosmological studies requires the extrapolation to high redshift and luminosity of a relation whose calibration relies so far on reverberation mapping measurements performed for L less than or similar to 1046 erg s(-1) and redshift z less than or similar to 0.4. Aims. We initiated a campaign for the spectrophotometric monitoring of a few luminous, intermediate redshift quasars whose apparent magnitude, V < 15.7, allows observations with a 1.8 m telescope, aimed at proving that emission lines vary and respond to continuum variations even for luminosities less than or similar to 1047 erg s(-1), and determining eventually their MBH from reverberation mapping. Methods. We have repeatedly performed simultaneous spectrophotometric observations of quasars and reference stars to determine relative variability of continuum and emission lines. We describe the observations and methods of analysis. Results. For the quasars PG 1634+ 706 and PG 1247+ 268 we obtain light-curves respectively for CIII](lambda lambda 1909 angstrom), MgII(lambda lambda 2798 angstrom) and for CIV(lambda lambda 1549 angstrom), CIII](lambda lambda 1909 angstrom) emission lines with the relevant continua. During 3.2 years of observation, in the former case no continuum variability was detected and the evidence for line variability is marginal, while in the latter case both continuum and line variability are detected with high significance and the line variations appear correlated with continuum variations. Conclusions. The detection of the emission line variability in a quasar with L similar to 10(47) erg s(-1) encourages the continuation of the monitoring campaign which should provide a black hole mass estimate in another 5-6 years, constraining the mass-luminosity relation in a poorly explored range of luminosity.

A new sample of bright galaxy pairs in UZC

Aims. We present a new sample of bright galaxy pairs extracted applying an objective selection code to the UZC catalog. The sample is volume-limited to Mzw = −18.9 + 5l ogh and contains 89 galaxy pairs. Methods. We analyze the kinematical, morphological, and photometrical properties of galaxies belonging to this sample. Results. We show that velocity separation, |∆vr|, between pair members is significantly lower in spiral type (S+S) pairs than in earlytype (E+E) and mixed (E+S) pairs. This indicates that truly isolated galaxy pairs are more likely to be found among S+ Sp airs. We show that ellipticals are rare and underluminous in B and that late spirals (T ≥ 4) are overluminous. Conclusions. We confirm that the formation of bright ellipticals is a phenomenon linked to group/cluster environment. while galaxy– galaxy interaction may enhance the blue luminosity of disk galaxies through SF phenomena. This last statement is supported by the presence of strong FIR emission from early spirals in this sample and by the high frequency of the AGN/SB phenomenon, revealed mainly in pairs of low relative radial velocity separation showing signs of interaction.

Seyfert galaxies in UZC-Compact Groups

We present results concerning the occurrence of Seyfert galaxies in a new automatically selected sample of nearby Compact Groups of galaxies (UZC-CGs). Seventeen Seyferts are found, constituting ∼3% of the UZC-CG galaxy population. CGs hosting and non-hosting a Seyfert member exhibit no significant differences, except that a relevant number of Sy2 is found in unusual CGs, all presenting large velocity dispersion ( σ> 400 km s −1 ), many neighbours and a high number of ellipticals. We also find that the fraction of Seyferts in CGs is 3 times as large as that among UZC-single-galaxies, and results from an excess of Sy2s. CG-Seyferts are not more likely than other CG galaxies to present major interaction patterns, nor to display a bar. Our results indirectly support the minor-merging fueling mechanism.

El Roque de Los Muchachos site characteristics III. Analysis of atmospheric dust and aerosol extinction

Context. It is known that the Canary Islands are normally affected by dominant winds flowing from north-northeast, that in some meteorological conditions, can transport sand from the Sahara desert at high altitude. The dust may affect the efficiency of the telescopes and decrease the transparency of the sky. Aims. To maximize the scientific return of the telescopes located at the Observatorio del Roque de Los Muchachos (ORM), we present an analysis of the atmospheric dust content and its effects on astronomical observations. Than B, V and I dust aerosol astronomical extinction are derived. Methods. Using a 5-year series database of data taken from a dust monitor located inside the Telescopio Nazionale Galileo (TNG) dome, we computed mean hourly and daily values of the dust content as measured with a four-channel dust monitor. Results. We detected particles of 0.3, 0.5, 1.0, and 5.0 µm. Furthermore, using a power law we derived the content of 10.0 µm particles. We found a typical local dust concentration ranging from 3 × 10 6 particles per cubic metre at 0.3 µm, to 10 3 at 5.0 µm and 10 at 10.0µm, increasing up to 3 orders of magnitudes during the dust storms, with a relatively higher increase of 1.0, 5.0, and 10.0 µm particles. The number of local dust storm events is the same in the local winter and summer, but the average background and storm-related increases in the dust concentration in summer are significantly higher than in winter. In a uniform approximation, during the dust storms, an average height of the dust layer of 2.5 km above the telescope is inferred. Conclusions. During the sand storms, La Palma Island is affected by an almost uniform layer extending up to 5 km above the sea level. The visible extinction is dominated by particles at 1.0, 5.0 and 10.0 µm. In agreement with the results from Carlsberg Automatic Meridian Circle (CAMC), we find a typical extinction of about 0.2 mag airmass −1 during dust storms.

Optical Spectroscopy of Active Galactic Nuclei in SA57

Context. The cosmological evolution of X-ray-selected and optically selected active galactic nuclei (AGNs) show different behaviours interpreted in terms of two different populations. The difference is evident mainly for low luminosity AGNs (LLAGNs), many of which are lost by optical photometric surveys. Aims. We are conducting a spectroscopical study of a composite sample of AGN candidates selected in SA57 following different searching techniques, to identify low luminosity AGNs and break down the sample into different classes of objects. Methods. AGN candidates were obtained through optical variability and/or X-ray emission. Of special interest are the extended variable objects, which are expected to be galaxies hosting LLAGNs. Results. Among the 26 classified objects a fair number (9) show typical AGN spectra. Ten objects show Narrow Emission Line Galaxy spectra, and in most of them (8/10) optical variability suggests the presence of LLAGNs.

Dust pollution monitoring at the TNG telescope

The Italian Galileo telescope (TNG) is part of the Roque de Los Muchachos astronomical complex, also referred as ENO, European Northern Observatory. Astronomical sites must be carefully selected in order to maximize the scientific return from the fairly large investment they require, both in terms of money as well as of human resources. This also means to maximize (and/or optimize) the amount of time available for observations, so that the requirements of the telescope to have good performance in both optical and NIR wavelengths strongly depends on meteorological conditions (e.g. differential air temperature between inside and outside telescope dome, presence of atmospheric dust, etc.). TNG site is monitored on a continuous basis by an automatic weather station, which provides on line measurements of a few local meteorological parameters, e.g. temperature and relative humidity. Since a few month we added a multichannel dust monitor to the set of meteorological sensors. This four channel facility provides the size distribution of atmospheric dust particles, being able to detect and discriminate among four different particles sizes: 0.3, 0.5, 1 and 5 micron. This contribution will present the first preliminary data which have collected at the Roque site close to the TNG dome, in order to analyze the (possible) relationship between dust data and meteorological parameters trend.

A study of the aerosol extinction from ground-based dust measurements at ORM

We present an analysis of the atmospheric dust content and its effects on astronomical observations at Observatorio del Roque de Los Muchachos (ORM), in La Palma Island (Canaries). We have detected atmospheric particles having size 0.3, 0.5, 1.0 and 5.0 μm, closer to Telescopio Nazionale Galileo (TNG) dome and using a power law we have derived the content of 10.0 µm particles. Using a model we have calculated the contribute of aerosols to astronomical extinction in B, V and I from a 5 years series database in two typical conditions: clear and dusty days. A correlation is also analysed comparing the aerosol extinction and total astronomical extinction using the Carlsberg Automatic Meridian Circle (CAMC) extinction database in V. We have estimated that the dust reach an altitude of about 5 km above the sea level during the sand storms. Finally we have concluded that in the visible band extension is dominated by particles at 1.0, 5.0, and 10.0 μm.

New dust measurements at ORM, and comparison with Paranal Observatory

The performances of a modern telescope and its safety are dependent on the presence of atmospheric dust. The TNG telescope at ORM (Canary Islands) was one of the first sites monitored on a continuous basis by an automatic dust monitor. This paper presents the analysis of about 10 years of atmospheric dust content collected at the ORM using the TNG facilities. We have detected particles of 0.3, 0.5, 1.0, 3.0, 5.0 and 10.0 μm size. In this study particles of 0.5 and 5.0 μm measured at Paranal Observatory (Chile) are also compared to those similar at TNG. The seasonal behavior of the particles content in the atmosphere is compared between the two sites. The contribution of the dust emissivity to the sky brightness in the NIR is computed for the first time. To complete this study we defined the aerosol mass critical limit to be used as a safety limit for the observations. We found a limit of 12 μg m-3 as total mass of (0.5 + 5.0) μm particles.

Three years of dust monitoring at the Galileo telescope

Since summer 2001, dust pollution of the air is regularly measured through a particle counter at the Telescopio Nazionale Galileo (TNG) located at the Roque de los Muchachos Observatory (La Palma - Canary Islands). Canary Islands are normally interested by a dominant atmospheric circulation with NE winds. Depending on their strenght, and their exact direction, winds may bring with themselves small to large amount of dust from the Sahara desert, with important consequences on the transparency of the sky. Meteorological satellites gave us some impressive examples of such these phenomenon. We show here the results of trying a correlation between dust-pollution data and the nightly atmospheric extinction measured at other telescopes. While the transparency is mostly affecting the astronomical work, other effects like changes of air temperature and humidity are clearly visible; for this reason dust-pollution data are also compared with the weather data recorded at the TNG meteo tower.

Nuclear activity in galaxy pairs: a spectroscopic analysis of 48 UZC-BGPs

Context. The role played by interaction on galaxy formation and evolution continues to be debated. Several questions remain open, among them whether, and to what extent, galaxy interaction induce nuclear activity, as theoretical predictions, so far, have not been adequately supported by observations. Part of the uncertainty affecting the observational results is likely to be due to the limited sizes and the inhomogeneity of the samples. Aims. Galaxy pairs are ideal sites in which to investigate the role of interaction on nuclear activity, since the proximity, in redshift and in projected separation, between members make interaction and encounters highly probable. For this reason we have undertaken a spectroscopic survey of a large homogeneous sample of galaxy pairs (UZC-BGP) selected applying an objective neighbour search algorithm to a 3D galaxy catalog (UZC). Methods. We present the results of the nuclear spectral classification, performed using standard diagnostic diagrams, of 48 UZC-BGPs, which represents more than half of the whole sample and has an excellent morphological match with it. Results. The fraction of emission line galaxies in our pair sample is large, especially among spirals where it reaches 84% and 95%, for early and late spirals. Star Burst (SB) is the most frequent type of nuclear activity encountered (30% of galaxies), while AGNs (Active Galactic Nuclei) make only 19%. The fractions increase to 45% and 22% when considering only spirals. Late spirals are characterized by both an unusual increase (35%) of AGN activity and high luminosity (44% have MB < −20.0 + 5l ogh). LLAGNs (Low Luminosity AGNs) are only 8% of the total number of galaxies, but this kind of activity could be present in another 10% of the galaxies (LLAGN candidates). If confirmed, these candidates would make LLAGNs constitute a significant fraction of the whole AGN (LLAGN + AGN) population, and raise the AGN population as a whole to 37%. Absorption line galaxies reside mostly (61%) in S0 galaxies and display the lowest B luminosity in the sample; only 18% of them have MB < −20 + 5l ogh, but together with LLAGNs (candidates included) they are the most massive galaxies in the sample. Intense-SB nuclei are found in galaxy pairs with galaxy-galaxy projected separation of up to 160 h −1 kpc suggesting that in bright isolated galaxy pairs interaction may be at work and effective up to that distance. Conclusions. AGNs are characterized by an advanced morphological type while the SB phenomenon occurs with the same frequency in early and late spirals. Whether and how these unusual characteristics relate to the pair environment needs to be further investigated. LLAGNs and LLAGN candidates do not always show similar properties; the former are more luminous in B, richer in early-type (E-S0s) galaxies, and half of them are hosted in galaxies showing visible signs of interaction with fainter companions. This last finding suggests that minor interactions might be a driving mechanism for a fraction of LLAGNs. The differences between LLAGNs and LLAGN candidates might confirm the heterogeneous nature of this class of objects.