Search

Through an optical campaign performed at 5 telescopes located in the northern and the southern hemispheres, plus archival data from two on line sky surveys, we have obtained optical spectroscopy for 17 counterparts of suspected or poorly studied hard X-ray emitting active galactic nuclei (AGNs) detected with Swift/BAT in order to determine or better classify their nature. We find that 7 sources of our sample are type 1 AGNs, 9 are type 2 AGNs, and 1 object is an X-ray bright optically normal galaxy; the redshifts of these objects lie in a range between 0.012 and 0.286. For all these sources, X-ray data analysis was also performed to estimate their absorption column and to search for possible Compton thick candidates. Among our type 2 objects, we did not find any clear Compton thick AGN, but at least 6 out of 9 of them are highly absorbed (NH> 1023cm-2), while one does not require intrinsic absorption; i.e., it appears to be a naked Seyfert 2 galaxy.

Within the framework of our program of assessment of the nature of unidentified or poorly known INTEGRALsources, we present here spectroscopy of optical objects, selected through positional cross-correlation with soft X-ray detections (afforded with satellites such as Swift, ROSAT, Chandraand/or XMM-Newton) as putative counterparts of hard X-ray sources detected with the IBIS instrument onboard INTEGRAL. Using 6 telescopes of various sizes and archival data from two on-line spectroscopic surveys we are able to identify, either for the first time or independent of other groups, the nature of 20 INTEGRALhard X-ray sources. Our results indicate that: 11 of these objects are active galactic nuclei (AGNs) at redshifts between 0.014 and 0.978, 7 of which display broad emission lines, 2 show narrow emission lines only, and 2 have unremarkable or no emission lines (thus are likely Compton thick AGNs); 5 are cataclysmic variables (CVs), 4 of which are (possibly magnetic) dwarf novae and one is a symbiotic star; and 4 are Galactic X-ray binaries (3 with high-mass companions and one with a low-mass secondary). It is thus again found that the majority of these sources are AGNs or magnetic CVs, confirming our previous findings. When possible, the main physical parameters for these hard X-ray sources are also computed using the multiwavelength information available in the literature. These identifications support the importance of INTEGRALin the study of the hard X-ray spectrum of all classes of X-ray emitting objects, and the effectiveness of a strategy of multi-catalogue cross-correlation plus optical spectroscopy to securely pinpoint the actual nature of unidentified hard X-ray sources.

Aims. We present a sample of candidate quasars selected using the KX-technique. The data cover 0.68 deg2of the X-ray Multi-Mirror (XMM) Large-Scale Structure (LSS) survey area where overlapping multi-wavelength imaging data permits an investigation of the physical nature of selected sources.

Optical spectroscopic identification of the nature of 21 unidentified southern hard X-ray objects is reported here in the framework of our campaign aimed at determining the nature of newly-discovered and/or unidentified sources detected by INTEGRAL. Our results show that 5 of these objects are magnetic Cataclysmic Variables (CVs), 4 are High-Mass X-ray Binaries (HMXBs; one of which is in the Large Magellanic Cloud) and 12 are Active Galactic Nuclei (AGNs). When feasible, the main physical parameters for these hard X-ray sources are also computed using the multiwavelength information available in the literature. These identifications further underscore the importance of INTEGRALin the study of the hard X-ray spectrum of AGNs, HMXBs and CVs, and the usefulness of a strategy of catalogues cross-correlation plus optical spectroscopy to securely pinpoint the actual nature of the X-ray sources detected with INTEGRAL.

Using the Gaussian+Schechter composite luminosity functions measured from the ESO-Sculptor Survey ([CITE], A&A, 404, 831) and assuming that these functions do not evolve with redshift out to $z\sim1$, we obtain evidence for evolution in the late spectral class containing late-type Spiral (Sc+Sd) and dwarf Irregular (dI) galaxies. There are indications that the Sc+Sd galaxies are the evolving population, but we cannot exclude that the dI galaxies also undergo some evolution. This evolution is detected as an increase of the Sc+Sd+dI galaxy density which can be modeled as either $n(z)\propto1+3(z-0.15)$or $n(z)\propto(1+z)^2$using the currently favored cosmological parameters $\Omega_{\rm m}=0.3$and $\Omega_\Lambda=0.7$; the uncertainty in the linear and power-law evolution rates is of the order of unity. For $\Omega_{\rm m}=1.0$and $\Omega_\Lambda=0.0$, the linear and power-law evolution rates are ~$4\pm1$and ~$2.5\pm1$respectively. Both models yield a good match to the ESS ${\it BVR}_{\rm c}$redshift distributions to $21{-}22$magand to the number-counts to $23{-}23.5$mag, which probe the galaxy distribution to redshifts $z\sim0.5$and $z\sim1.0$respectively.
The present analysis shows the usefulness of the joint use of the magnitude and redshift distributions for studying galaxy evolution. It also illustrates how Gaussian+Schechter composite luminosity functions provide more robust constraints on the evolution rate than pure Schechter luminosity functions, thus emphasizing the importance of performing realistic parameterizations of the luminosity functions for studying galaxy evolution.
The detected density evolution indicates that mergers could play a significant role in the evolution of late-type Spiral and dwarf Irregular galaxies. However, the ESO-Sculptor density increase with redshift could also be caused by a ~1magbrightening of the Sc+Sd+dI galaxies at $z\sim0.5$and $a \sim 1.5{-}2.0$magbrightening at $z\sim1$, which is compatible with the expected passive brightening of Sc galaxies at these redshifts. Distinguishing between luminosity and density evolution is a major difficulty as these produce the same effect on the redshift and magnitude distributions. The detected evolution rate of the ESO-Sculptor Sc+Sd+dI galaxies is nevertheless within the range of measured values from the other existing analyses, whether they provide evidence for density or luminosity evolution.

We present the first statistical analysis of the completeESO-Sculptor Survey (ESS) of faint galaxies. The flux-calibrated sample of 617 galaxies with $R_{\rm c}\le20.5$is separated into 3 spectral classes, based on a principal component analysis which provides a continuous and template-independent spectral classification. We use an original method to estimate accurate K-corrections: comparison of the ESS spectra with a spectral library using the principal component analysis allows us to extrapolate the missing parts of the observed spectra at blue wavelengths, then providing a polynomial parameterization of K-corrections as a function of spectral type and redshift. We also report on all sources of random and systematic errors which affect the spectral classification, the K-corrections, and the resulting absolute magnitudes.
We use the absolute magnitudes to measure the Johnson-Cousins B, V, Rcluminosity functions of the ESS as a function of spectral class. The shape of the derived luminosity functions show marked differences among the 3 spectral classes, which are common to the B, V, Rcbands, and therefore reflect a physical phenomenon: for galaxies of later spectral type, the characteristic magnitude is fainter and the faint-end is steeper. The ESS also provides the firstestimates of luminosity functions per spectral type in the Vband.
The salient results are obtained by fitting the ESS luminosity functions with composite functions based on the intrinsic luminosity functions per morphological type measured locally by (1985) and (1997). The Gaussian luminosity functions for the nearby Spiral galaxies can be reconciled with the ESS intermediate and late-type luminosity functions if the corresponding classes contain an additional Schechter contribution from Spheroidal and Irregular dwarf galaxies, respectively. The present analysis of the ESS luminosity functions offers a renewed interpretation of the galaxy luminosity function from redshift surveys. It also illustrates how luminosity functions per spectral type may be affected by morphological type mixing, and emphasizes the need for a quantitative morphological classification at $z\ga0.1$which separates the giant and dwarf galaxy populations.

Trough photometric methods we have constructed the luminosity function for the southern open cluster NGC 2477 down to Mv≈12. We present $R-I$color-magnitude diagrams and near-infrared color-color diagrams, which allow us to separate statistically the cluster stars from the field ones, numerous because of the galactic latitude of the cluster. Our luminosity function (LF) reproduces some features obtained by other authors, namely, a dip at Mv≈7, and a probable maximum at Mv≈12. The method developed to separate cluster stars from field stars could be of interest to other astronomical problems.

Using 8 telescopes in the northern and southern hemispheres, plus archival data from two on-line sky surveys, we performed a systematic optical spectroscopic study of 39 putative counterparts of unidentified or poorly studied INTEGRAL sources in order to determine or at least better assess their nature. This was implemented within the framework of our campaign to reveal the nature of newly-discovered and/or unidentified sources detected by INTEGRAL. Our results show that 29 of these objects are active galactic nuclei (13 of which are of Seyfert 1 type, 15 are Seyfert 2?galaxies and one is possibly a BL Lac object) with redshifts between 0.011 and 0.316, 7 are X-ray binaries (5 with high-mass companions and 2 with low-mass secondaries), one is a magnetic cataclysmic variable, one is a symbiotic star and one is possibly an active star. Thus, the large majority (74%) of the identifications in this sample belongs to the AGN class. When possible, the main physical parameters for these hard X-ray sources were also computed using the multiwavelength information available in the literature. These identifications further underscore the importance of INTEGRAL in studying the hard X-ray spectra of all classes of X-ray emitting objects, and the effectiveness of a strategy of multi-catalogue cross-correlation plus optical spectroscopy to securely pinpoint the actual nature of still unidentified hard X-ray sources.

The major purpose of the investigation presented in this paper was to prove or disprove the nature of planetary nebula (PN) candidates in the southern hemisphere, selected from the third volume of the Atlas of Galactic Nebulae by Neckel & Vehrenberg. We present imaging and spectroscopic observations of seven PNe, five of them identified for the first time. An additional object probably is an H iiregion. All observed PNe represent evolved stages, their angular diameter ranging from 15?to 170?, and exhibit low surface brightnesses.

Context.XMM and Chandra opened a new area for the study of clusters of galaxies not only for cluster physics, but also for the detection of faint and distant clusters that were inaccessible with previous missions.

Hard X-ray surveys performed by the INTEGRALsatellite have discovered a conspicuous fraction (up to 30%) of unidentified objects among the detected sources. Here we continue our program of identification of these objects by (i) selecting probable optical candidates by means of positional cross-correlation of the INTEGRALdetections with soft X-ray, radio, and/or optical archives and (ii) performing optical spectroscopy on them. As a result, we pinpointed and identified, or more accurately characterized, 44 definite or likely counterparts of INTEGRALsources. Among them, 32 are active galactic nuclei (AGNs; 18 with broad emission lines, 13 with narrow emission lines only, and one X-ray bright, optically normal galaxy) with redshift 0.019 

Hard X-ray surveys performed by the INTEGRALsatellite have discovered a conspicuous fraction (up to 30%) of unidentified objects among the detected sources. Here we continue our program of identification of these objects by (i) selecting probable optical candidates by means of positional cross-correlation of the INTEGRALdetections with soft X-ray, radio, and/or optical archives and (ii) performing optical spectroscopy on them. As a result, we pinpointed and identified, or more accurately characterized, 44 definite or likely counterparts of INTEGRALsources. Among them, 32 are active galactic nuclei (AGNs; 18 with broad emission lines, 13 with narrow emission lines only, and one X-ray bright, optically normal galaxy) with redshift 0.019