Probing the Radio Loud/Quiet AGN dichotomy with quasar clustering

We investigate the clustering properties of 45441 radio-quiet quasars (RQQs) and 3493 radio-loud quasars (RLQs) drawn from a joint use of the Sloan Digital Sky Survey (SDSS) and Faint Images of the Radio Sky at 20 cm (FIRST) surveys in the range $0.3<z<2.3$. This large spectroscopic quasar sample allow us to investigate the clustering signal dependence on radio-loudness and black hole (BH) virial mass. We find that RLQs are clustered more strongly than RQQs in all the redshift bins considered. We find a real-space correlation length of $r_{0}=6.59_{-0.24}^{+0.33}\,h^{-1}\,\textrm{Mpc}$ and $r_{0}=10.95_{-1.58}^{+1.22}\,h^{-1}\,\textrm{Mpc}$ {\normalsize{}for} RQQs and RLQs, respectively, for the full redshift range. This implies that RLQs are found in more massive host haloes than RQQs in our samples, with mean host halo masses of $\sim4.9\times10^{13}\,h^{-1}\,M_{\odot}$ and $\sim1.9\times10^{12}\,h^{-1}\,M_{\odot}$, respectively. Comparison with clustering studies of different radio source samples indicates that this mass scale of $\gtrsim1\times10^{13}\,h^{-1}\,M_{\odot}$ is characteristic for the bright radio-population, which corresponds to the typical mass of galaxy groups and galaxy clusters. The similarity we find in correlation lengths and host halo masses for RLQs, radio galaxies and flat-spectrum radio quasars agrees with orientation-driven unification models. Additionally, the clustering signal shows a dependence on black hole (BH) mass, with the quasars powered by the most massive BHs clustering more strongly than quasars having less massive BHs. We suggest that the current virial BH mass estimates may be a valid BH proxies for studying quasar clustering. We compare our results to a previous theoretical model that assumes that quasar activityComment: 15 pages, 13 figures, A&A in pres

The role of competition by dominants and temperature in the foraging of subordinate species in Mediterranean ant communities

In this paper we test the influence of temperature and interference competition by dominant species on the foraging of subordinate species in Mediterranean ant communities. We have analyzed the changes in resource use by subordinate species in plots with different abundances of dominant ants, and in different periods of the day and the year, i.e., at different temperatures. The expected effects of competition by dominant species on foraging of subordinates were only detected for two species in the number of baits occupied per day, and for one species in the number of foragers at pitfall traps. In all three cases, subordinate species were less represented at baits or in traps in plots with a high density of dominants than in plots with a medium or low density of dominants. The number of workers per bait, and the foraging efficiency of subordinate species did not differ in plots differing in dominant abundance. Daily activity rhythms and curves of temperature versus foraging activity of subordinate species were also similar in plots with different abundance of dominant species, indicating no effect of dominants on the foraging times of subordinates. Instead, temperature had a considerable effect on the foraging of subordinate species. A significant relationship was found between maximum daily temperature and several variables related to foraging (the number of foragers at pitfall traps, the number of baits occupied per day, and the number of workers per bait) of a number subordinate species, both in summer and autumn. These results suggest that the foraging of subordinate ant species in open Mediterranean habitats is influenced more by temperature than by competition of dominants, although an effect of dominants on subordinates has been shown in a few cases. In ant communities living in these severe and variable environments, thermal tolerance reduces the importance of competition, and the mutual exclusion usually found between dominant and subordinate species appears to be the result of physiological specialization to different temperature ranges.Peer Reviewe

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

INFLUENCIA DE LOS FACTORES AMBIENTALES SOBRE LA ACTIVIDAD DIARIA DE RECOLECCIÓN DE LA HORMIGA CATAGLYPHIS IBERICA (EM.) (HYM.: FORMICIDAE)

Daily foraging activity of the desert ant Cataglyphis iberica and its relationship with some environmental factors (ground temperature at different levels, air temperature, relative humidity, light intensity) were studied in Bellaterra (Barcelona, NE Spain) during the summer of 1983. This is a strictly diurnal and highly thermophilic species: ground surface temperature is the environmental factor that is best correlated with foraging activity (R = 0.727), and greatest activity takes place at midday, when the temperature is maximum. This species, which nests in and zones, begins foraging activity when the outside temperature rises above 30 ºC, while the upper thermal limit has not been found at the study site (where the highest temperature registered was 51 ºC). Light intensity also influences C. iberica foraging activity, and its effect seems to be greatest in the hottest days. Rain stops the exits of foragers completely. Two multiple regression equations (the first one with al1 summer data and the other only with data of the hottest days) have been obtained in order to describe foraging activity of the species as a function of environmental factors. Ground surface temperature and light intensity are included in both equations, but their relative irnportance is different in each one of them.Se ha estudiado el ritmo diario de actividad de recolección de la hormiga Cataglyphis iberica en relación con los factores ambientales (temperaturas a diferentes niveles, humedad relativa e iluminación). Esta especie tiene una actividad exclusivamente diurna y es marcadamente termófila: la temperatura del suelo al sol es el factor ambiental mejor correlacionado con la actividad recolectora (R = 0.7273), la máxima actividad (y también el mayor aporte de presas) se da a mediodía, coincidiendo con las máximas temperaturas. Esta hormiga, que nidifica en zonas áridas, es activa a partir de los 30 "C de temperatura del suelo al sol, sin que en la zona de estudio (Bellaterra, Barcelona) se haya observado una temperatura superior que limite su actividad (se han alcanzado los 51 "C). La iluminación también influye en la actividad de C. iberica, siendo mayor la correlación entre actividad-iluminación los días de verano con las temperaturas más altas (R = 0.793). La lluvia detiene por completo las salidas recolectoras de las obreras de la especie. Se han elaborado dos ecuaciones de regresión múltiple de la actividad de C. iberica en función de los factores ambientales, una con todos los datos del verano y la otra sólo con los nueve días más calurosos. Temperatura del suelo al sol e iluminación son los dos parámetros que entran en ambas ecuaciones, aunque su importancia relativa varía en cada una de ellas