We present the SEDs of a hard X-ray selected sample containing 136 sources with FSUB2-10keV/SUB>10SUP-14/SUP erg cmSUP-2/SUP sSUP-1/SUP 132 are AGNs. The sources are detected in a 1 degSUP2/SUP area ...of the XMM-Newton Medium Deep Survey where optical data from the VVDS and CFHTLS and infrared data from the SWIRE survey are available. Based on a SED fitting technique we derive photometric redshifts with sigma(1+z)=0.11 and 6% of outliers and identify AGN signatures in 83% of the objects. This fraction is higher than derived when a spectroscopic classification is available. The remaining 17SUP+9/SUPSUB-6/SUB% of AGNs show star-forming galaxy SEDs (SF class). The sources with AGN signatures are divided in two classes, AGN1 (33SUP+6/SUPSUB-1/SUB%) and AGN2 (50SUP+6/SUPSUB-11/SUB%). The AGN1 and AGN2 classes include sources whose SEDs are fitted by type 1 and type 2 AGN templates, respectively. On average, AGN1s show soft X-ray spectra, consistent with being unabsorbed, while AGN2s and SFs show hard X-ray spectra, consistent with being absorbed. The analysis of the average SEDs as a function of X-ray luminosity shows a reddening of the infrared SEDs, consistent with a decreasing contribution from the host galaxy at higher luminosities. The AGNs in the SF classes are likely obscured in the mid-infrared, as suggested by their low LSUB3-20mum/SUB/LSUPcorr/SUPSUB0.5-10keV/SUB ratios. We confirm the previously found correlation for AGNs between the radio luminosity and the X-ray and the mid-infrared luminosities. The X-ray-radio correlation can be used to identify heavily absorbed AGNs. However, the estimated radio fluxes for the missing AGN population responsible for the bulk of the background at E>10 keV are too faint to be detected even in the deepest current radio surveys.
Context. Accurate star formation histories (SFHs) of galaxies are fundamental for understanding the build-up of their stellar content. However, the most accurate SFHs – those obtained from ...colour-magnitude diagrams (CMDs) of resolved stars reaching the oldest main-sequence turnoffs (oMSTO) – are presently limited to a few systems in the Local Group. It is therefore crucial to determine the reliability and range of applicability of SFHs derived from integrated light spectroscopy, as this affects our understanding of unresolved galaxies from low to high redshift. Aims. We evaluate the reliability of current full spectral fitting techniques in deriving SFHs from integrated light spectroscopy by comparing SFHs from integrated spectra to those obtained from deep CMDs of resolved stars. Methods. We have obtained a high signal-to-noise (S/N ~ 36.3 per Å) integrated spectrum of a field in the bar of the Large Magellanic Cloud (LMC) using EFOSC2 at the 3.6-metre telescope at La Silla Observatory. For this same field, resolved stellar data reaching the oMSTO are available. We have compared the star formation rate (SFR) as a function of time and the age-metallicity relation (AMR) obtained from the integrated spectrum using STECKMAP, and the CMD using the IAC-star/MinnIAC/IAC-pop set of routines. For the sake of completeness we also use and discuss other synthesis codes (STARLIGHT and ULySS) to derive the SFR and AMR from the integrated LMC spectrum. Results. We find very good agreement (average differences ~4.1%) between the SFR (t) and the AMR obtained using STECKMAP on the integrated light spectrum, and the CMD analysis. STECKMAP minimizes the impact of the age-metallicity degeneracy and has the advantage of preferring smooth solutions to recover complex SFHs by means of a penalized χ2. We find that the use of single stellar populations (SSPs) to recover the stellar content, using for instance STARLIGHT or ULySS codes, hampers the reconstruction of the SFR (t) and AMR shapes, yielding larger discrepancies with respect to the CMD results. These discrepancies can be reduced if spectral templates based on known and complex SFHs are employed rather than SSPs.
This paper presents and examines new near-infrared integral field observations of the three so-called “embedded star clusters” located in the nuclear region of NGC 1365. Adaptive-optics-corrected ...K-band data cubes were obtained with the ESO/VLT instrument SINFONI. The continuum in the K-band and emission lines such as He I, Brγ, and several H2 lines were mapped at an achieved angular resolution of 0.2′′ over a field of 3 × 3′′2 around each source. We find that the continuum emission of the sources is spatially resolved. This means that they are indeed cluster complexes confined to regions of about 50 pc extension. We performed robust measurements of the equivalent width of the CO absorption band at 2.3 μm and of Brγ. For the main mid-infrared bright sources, the data only allow us to determine an upper limit to the equivalent width of the CO bands. Under the assumption of an instantaneously formed standard initial mass function Starburst99 model, the new measurements are found to be incompatible with previously published mid-infrared line ratios. We show that an upper mass limit of 25 to 30 M⊙, lower than the typically assumed 100 M⊙, allows one to simply remove this inconsistency. For such a model, the measurements are consistent with ages in the range of 5.5 Myr to 6.5 Myr, implying masses in the range from 3 to 10 × 106 M⊙. We detect extended gas emission both in H ii and H2. We argue that the central cluster complexes are the sources of excitation for the whole nebulae, through ionisation and shock heating. We detect a blue wing on the Brγ emission profile, suggesting the existence of gas outflows centred on the cluster complexes. We do not find any evidence for the presence of a lower mass cluster population, which would fill up a “traditional” power law cluster mass function.
Context. In the course of a mid-infrared imaging campaign of close-by active galaxies, we discovered the mid-infrared counterparts of bright compact radio sources in the central star-forming region ...of NGC 1808. Aims. We aim at confirming that these sources are deeply embedded, young star clusters and at deriving some of their intrinsic properties. Methods. To complement the mid-infrared images, we have collected a set of near-infrared data with ISAAC at the VLT: J, K s, and L ' images, as well as low-resolution, long-slit spectra for three of the sources. Results. Surprisingly, the new images unveil a near-infrared counterpart for only one of the mid-infrared/radio sources, namely M 8 in the L ' band. All the other sources are so deeply embedded that their emission does not pop out above the extended diffuse near-infrared emission. The near-infrared spectra of the sources look alike, with intense, ionised hydrogen lines. This supports the interpretation of these sources in terms of embedded young clusters. We derive extinctions and ionising photon production rates for two of the clusters.
Context. Nearly 100 new strong-lens candidates have been discovered in the COSMOS field. Among these, 20 lens candidates with 0.34 ≲ zlens ≲ 1.13 feature multiple images of background sources. Aims. ...Using the multi-wavelength coverage of the field and its spectroscopic follow-up, we characterize the evolution with redshift of the environment and of the dark-matter (DM) fraction of the lens galaxies. Methods. We present spectroscopic and new photometric redshifts of the strong-lens candidates. The lens environment is characterized in the following way: we account for the projected 10 closest galaxies around each lens and for galaxies with a projected distance less than 1 Mpc at the lens galaxy redshift. In both cases, we perform similar measurements on a control sample of “twin” non-lens early-type galaxies (ETGs). In addition, we identify group members and field galaxies in the X-ray and optical catalogs of galaxy groups and clusters. From those catalogs, we measure the external shear contribution of the groups/clusters surrounding the lens galaxies. The systems are then modeled using a singular isothermal ellipsoid for the lens galaxies plus the external shear produced by the groups/clusters. Results. We observe that the average stellar mass of lens galaxies increases with redshift. In addition, we measure that the environment of lens galaxies is compatible with that of the twins over the whole redshift range tested here. During the lens modeling, we notice that when let free, the external shear points in a direction which is the mean direction of the external shear produced by the groups/clusters and of the closest galaxy to the lens. We also notice that the DM fraction of the lens galaxies measured within the Einstein radius significantly decreases as the redshift increases. Conclusions. Given these observations, we conclude that while the environment of lens galaxies is compatible with that of non-lens ETGS over a wide range of redshifts, their mass properties evolves significantly with redshift: it is still not clear whether this advocates in favor of a stronger lensing bias toward massive objects at high redshift or if it is simply representative of the high proportion of massive and high stellar density galaxies at high redshift.
Context. The luminosity-metallicity relation is one of the fundamental constraints in the study of galaxy evolution; yet none of the relations available today has been universally accepted by the ...community. Aims. The present work is a first step to collect homogeneous abundances and near-infrared (NIR) luminosities for a sample of dwarf irregular (dIrr) galaxies, located in nearby groups. The use of NIR luminosities is intended to provide a better proxy to mass than the blue luminosities commonly used in the literature; in addition, selecting group members reduces the impact of uncertain distances. Accurate abundances are derived to assess the galaxy metallicity. Methods. Optical spectra are collected for $\ion{H}{ii}$ regions in the dIrrs, allowing the determination of oxygen abundances by means of the temperature-sensitive method. For each dIrr galaxy H-band imaging is performed and the total magnitudes are measured via surface photometry. Results. This high-quality database allows us to build a well-defined luminosity-metallicity relation in the range $-13\geq M_{H}\geq-20$. The scatter around its linear fit is reduced to 0.11 dex, the lowest of all relations currently available. There might exist a difference between the relation for dIrrs and the relation for giant galaxies, although a firm conclusion should await direct abundance determinations for a significant sample of massive galaxies. Conclusions. This new dataset provides an improved luminosity-metallicity relation, based on a standard NIR band, for dwarf star-forming galaxies. The relation can now be compared with some confidence to the predictions of models of galaxy evolution. Exciting follow-ups of this work are (a) exploring groups with higher densities, (b) exploring nearby galaxy clusters to probe environmental effects on the luminosity-metallicity relation, and (c) deriving direct oxygen abundances in the central regions of star-forming giant galaxies, to settle the question of a possible dichotomy between the chemical evolution of dwarfs and that of massive galaxies.
High resolution, mid-infrared (MIR) images of nine nearby active galaxies are presented. The data were obtained with the TIMMI 2 instrument mounted at the ESO 3.6 m telescope using a set of N-band ...narrow filters. The resulting images have an angular resolution of 0.6"-1". The MIR emission has been resolved in four galaxies: NGC 253, NGC 1365, NGC 1808 and NGC 7469. The images show a circumnuclear population of unknown MIR sources in NGC 1365 and NGC 1808, coincident with radio sources. These MIR/radio sources are interpreted in terms of embedded young star clusters. A high-resolution MIR map of NGC 253 is also presented, and enables the identification of a previously unknown MIR counterpart to the radio nucleus. Extended MIR emission is detected in NGC 7469, and concurs with previous observations in the NIR and radio. For this source, an interesting morphological difference between the 10.4 km and the 11.9 km emission is observed, suggesting the presence of a dust-rich micro-bar. Our MIR images of Circinus do not show resolved emission from the nucleus down to an angular scale of 0.5". In the case of NGC 2992, an upper limit to the extended MIR emission can be set. We provide new MIR flux measurements for the unresolved AGN in NGC 5995, IZw1 and IIZw136.
We revisit in this paper the location of the various components observed in the AGN of NGC 1068. Discrepancies between previously published studies are explained, and a new measurement for the ...absolute location of the K-band emission peak is provided. It is found to be consistent with the position of the central engine as derived by Gallimore et al. (1997), Capetti et al. (1997) and Kishimoto (1999). A series of map overlays is then presented and discussed. Model predictions of dusty tori show that the nuclear unresolved NIR-MIR emission is compatible with a broad range of models: the nuclear SED alone does not strongly constrain the torus geometry, while placing reasonable constraints on its size and thickness. The extended MIR emission observed within the ionizing cone is shown to be well explained by the presence of optically thick dust clouds exposed to the central engine radiation and having a small covering factor. Conversely, a distribution of diffuse dust particles within the ionizing cone is discarded. A simple model for the H2 and CO emission observed perpendicularly to the axis of the ionizing cone is proposed. We show that a slight tilt between the molecular disc and the Compton thick central absorber naturally reproduces the observed distribution of H2 of CO emission.
Context. Gravitationally lensed quasars constitute an independent tool to derive the Hubble constant through the time-delays of their different images; they offer as well the opportunity to study the ...mass distribution and interstellar medium of their lensing galaxies and, through microlensing due to stars in their lensing galaxy, they also allow one to study details of the emitting source. Aims. For such studies, one needs to have an excellent knowledge of the close environment of the lensed images in order to model the lensing potential: this means, ideally, observational data over a large field-of-view and spectroscopy at high spatial resolution. Methods. We present VIMOS integral field observations of 27´´ $\times$ 27´´ fields of view around four lensed quasars: HE 0230-2130, RX J0911.4 + 0551, H 1413 + 117 and B 1359 + 154. Using the low, medium and high resolution modes, we study the quasar images and the quasar environments. Because of the complexity of the reduction of integral field datasets, we provide a detailed report of the data reduction. Results. Comparison between the quasar spectra of the different images reveals differences for HE 0230–2130, RX J0911.4 + 0551 and H 1413+117: flux ratios between the images of the same quasar are different when measured in the emission lines and in the continuum. We have also measured the redshifts of galaxies in the neighborhood of HE 0230–2130 and RX J0911.4 + 0551 which possibly contribute to the total lensing potential, given their close proximity to the line-of-sight toward the quasars. Conclusions. A careful analysis reveals that microlensing is the most natural explanation for the (de)magnification of the continuum emitting region of the background sources. In HE 0230-2130, image D is likely to be affected by microlensing magnification; in RX J0911.4+0551, images A1 and A3 are likely to be modified by microlensing de-magnification and in H 1413+117, at least image D is affected by microlensing. We have not been able to recover any microlensing information or galaxies close to the line-of-sight in the neighborhood of B 1359+154.
Following the presentation of the XMM-Large Scale Structure (XMM-LSS) survey X-ray source detection package by Pacaud et al., we provide the source lists for the first surveyed 5.5 deg2. The ...catalogues pertain to the 0.5–2 and 2–10 keV bands and contain in total 3385 point-like or extended sources above a detection likelihood of 15 in either band. The agreement with deep log N– log S is excellent. The main parameters considered are position, count rate, source extent with associated likelihood values. A set of additional quantities such as astrometric corrections and fluxes are further calculated while errors on the position and count rate are deduced from simulations. We describe the construction of the band-merged catalogue allowing rapid subsample selection and easy cross-correlation with external multiwavelength catalogues. A small optical Canada–France–Hawaii Telescope Legacy Survey multiband subset of objects are associated with each source along with an X-ray/optical overlay. We make the full X-ray images available in FITS format. The data are available at the Centre de Données de Strasbourg and, in a more extended form, at the Milan XMM-LSS survey data base.
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