No Arabic abstract
We used the large binocular camera (LBC) mounted on the large binocular telescope (LBT) to observe the Lockman Hole in the U, B, and V bands. Our observations cover an area of 925 sq.arcmin. We reached depths of 26.7, 26.3, and 26.3 mag(AB) in the three bands, respectively, in terms of 50% source detection efficiency, making this survey the deepest U-band survey and one of the deepest B and V band surveys with respect to its covered area. We extracted a large number of sources (~89000), detected in all three bands and examined their surface density, comparing it with models of galaxy evolution. We find good agreement with previous claims of a steep faint-end slope of the luminosity functions, caused by late-type and irregular galaxies at z>1.5. A population of dwarf star-forming galaxies at 1.5<z<2.5 is needed to explain the U-band number counts. We also find evidence of strong supernova feedback at high redshift. This survey is complementary to the r, i, and z Lockman Hole survey conducted with the Subaru telescope and provides the essential wavelength coverage to derive photometric redshifts and select different types of sources from the Lockman Hole for further study.
We present a study of the 1173 sources brighter than $S_{1.4,rm GHz}= 120,mu$Jy detected over an area of $simeq 1.4,hbox{deg}^{2}$ in the Lockman Hole field. Exploiting the multi-band information available in this field for $sim$79% of the sample, sources have been classified into radio loud (RL) active galactic nuclei (AGNs), star forming galaxies (SFGs) and radio quiet (RQ) AGNs, using a variety of diagnostics available in the literature. Exploiting the observed tight anti-correlations between IRAC band 1 or band 2 and the source redshift we could assign a redshift to 177 sources missing a spectroscopic measurement or a reliable photometric estimate. A Monte Carlo approach was used to take into account the spread around the mean relation. The derived differential number counts and luminosity functions at several redshifts of each population show a good consistency with models and with earlier estimates made using data from different surveys and applying different approaches. Our results confirm that below $sim300,mu$Jy SFGs$+$RQ AGNs overtake RL AGNs that dominate at brighter flux densities. We also confirm earlier indications of a similar evolution of RQ AGNs and SFGs. Finally, we discuss the angular correlation function of our sources and highlight its sensitivity to the criteria used for the classification.
Active Galactic Nuclei (AGN) play a decisive role in galaxy evolution, particularly so when operating in a radiatively inefficient mode, where they launch powerful jets that reshape their surroundings. However, identifying them is difficult, since radio observations commonly have resolutions of between 1 arcsec and 10 arcsec, which is equally sensitive to radio emission from star-forming activity and from AGN. Very Long Baseline Interferometry (VLBI) observations allow one to filter out all but the most compact non-thermal emission from radio survey data. The observational and computational demands to do this in large surveys have been, until recently, too high to make such undertakings feasible. Only the recent advent of wide-field observing techniques have facilitated such observations, and we here present the results from a survey of 217 radio sources in the Lockman Hole/XMM field. We describe in detail some new aspects of the calibration, including primary beam correction, multi-source self-calibration, and mosaicing. As a result, we detected 65 out of the 217 radio sources and were able to construct, for the first time, the source counts of VLBI-detected AGN. They indicate that at least 15%-25% of the sub-mJy radio sources are AGN-driven, consistent with recent findings using other AGN selection techniques. We have used ancillary data to investigate the AGN hosts. We find that among the sources nearby enough to be resolved in the optical images, 88% (23/26) could be classified as early-type or bulge-dominated galaxies. While 50% of these sources are correctly represented by the SED of an early-type galaxy, for the rest the best fit was obtained with a heavily extinct starburst template, an effect we ascribe to a degeneracy in the fit. Overall, the typical hosts of VLBI-detected sources are in good agreement with being early-type or bulge-dominated galaxies.
Deep Swift UV/Optical Telescope (UVOT) imaging of the Chandra Deep Field South is used to measure galaxy number counts in three near ultraviolet (NUV) filters (uvw2: 1928 A, uvm2: 2246 A, uvw1: 2600 A) and the u band (3645 A). UVOT observations cover the break in the slope of the NUV number counts with greater precision than the number counts by the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) and the Galaxy Evolution Explorer (GALEX), spanning a range from 21 < m_AB < 25. Number counts models confirm earlier investigations in favoring models with an evolving galaxy luminosity function.
This paper presents the results of a study of X-ray spectral and flux variability on time scales from months to years, of the 123 brightest objects (including 46 type-1 AGN and 28 type-2 AGN) detected with XMM-Newton in the Lockman Hole field. We detected flux variability with a significance >3sigma in ~50% of the objects, including 68+-11% and 48+-15% among our samples of type-1 and type-2 AGN. However we found that the fraction of sources with best quality light curves that exhibit flux variability on the time scales sampled by our data is >80%, i.e the great majority of the AGN population may actually vary in flux on long time scales. The mean relative intrinsic amplitude of flux variability was found to be ~0.15 although with a large dispersion in measured values, from ~0.1 to ~0.65. The flux variability properties of our samples of AGN do not significantly depend on the redshift or X-ray luminosity of the objects and seem to be similar for the two AGN types. Using a broad band X-ray colour we found that the fraction of sources showing spectral variability with a significance >3sigma is ~40% i.e. less common than flux variability. Spectral variability was found to be more common in type-2 AGN than in type-1 AGN with a significance >99%. This result is consistent with the fact that part of the soft emission in type-2 AGN comes from scattered radiation, and this component is expected to be much less variable than the hard component. The observed flux and spectral variability properties of our objects cannot be explained as being produced by variability of one spectral component alone, for example changes in the continuum shape associated with changes in the mass accretion rate, or variability in the amount of X-ray absorption. At least two spectral components must vary in order to explain the X-ray variability of our objects.
We report initial results of far-infrared observations of the Lockman hole with Far-Infrared Surveyor (FIS) onboard the AKARI infrared satellite. On the basis of slow scan observations of a 0.6 deg x 1.2 deg contiguous area, we obtained source number counts at 65, 90 and 140 um down to 77, 26 and 194 mJy (3 sigma), respectively. The counts at 65 and 140 um show good agreement with the Spitzer results. However, our 90 um counts are clearly lower than the predicted counts by recent evolutionary models that fit the Spitzer counts in all the MIPS bands. Our 90 um counts above 26 mJy account for about 7% of the cosmic background. These results provide strong constraints on the evolutionary scenario and suggest that the current models may require modifications.