arXiv subjects

D. Alloin

Publications and source records attributed to D. Alloin.

31 records · Page 2Linked to original sources

arXiv2002

On-axis spatially resolved spectroscopy of low redshift quasar host galaxies: HE 1503+0228 at z=0.135

We present the first result of a comprehensive spectroscopic study of quasar host galaxies. On-axis, spatially resolved spectra of low redshift quasars have been obtained with FORS1, mounted on the 8.2m ESO Very Large Telescope, Antu. The spectra are spatially deconvolved using a spectroscopic version of the ``MCS deconvolution algorithm''. The algorithm decomposes two dimensional spectra into the individual spectra of the central point-like nucleus and of its host galaxy. Applied to HE1503+0228, at z=0.135 (M_B=-23.0), it provides us with the spectrum of the host galaxy between 3600A, and 8500A, (rest-frame), at a mean resolving power of 700. The data allow us to measure several of the important Lick indices. The stellar populations and gas ionization state of the host galaxy of HE1503+0228, are very similar to the ones measured for normal non-AGN galaxies. Dynamical information is also available for the gas and stellar components of the galaxy. Using deconvolution and a deprojection algorithm, velocity curves are derived for emission lines, from the center up to 4arcsec, away from the nucleus of the galaxy. Fitting a simple three-components mass model (point mass, spherical halo of dark matter, disk) to the position-velocity diagram, we infer a mass of M(r<1kpc) = (2.0 +- 0.3) 10^{10} solar mass within the central kiloparsec of the galaxy, and a mass integrated over 10 kpc of M(r<10kpc) = (1.9 +- 0.3) 10^{11} solar mass, with an additional 10% error due to the uncertainty on the inclination of the galaxy. This, in combination with the analysis of the stellar populations indicates that the host galaxy of HE1503+0228, is a normal spiral galaxy.

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arXiv2002

The lensing system towards the doubly imaged quasar SBS 1520+530

The gravitational potential responsible for the lensing effect in SBS 1520+530 is studied over length scales from a few arc-seconds to a few arc-minutes. For this purpose, we use sharply deconvolved Hubble Space Telescope images in the optical and near-IR, in combination with ground based optical data obtained over a wider field-of-view. In particular, we have carried out a multi-color analysis in order to identify groups or clusters of galaxies along the line of sight. Photometric redshifts are measured for 139 galaxies unveiling significant excesses of galaxies 1.0 arcmin, NW and 1.7 arcmin, SW of the main lensing galaxy. The photometric redshift inferred both for the main lensing galaxy and for the galaxy concentrations is z=0.9^{+0.10}_{-0.25}. This is in rough agreement with the measured spectroscopic redshift of the main lensing galaxy, z=0.71 (Burud et al. 2002), suggesting that it is part of a larger group or cluster. We investigate the impact of including the galaxy cluster, first on the modelling of the lensing system, and second on the expected time--delay between the two quasar images.

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arXiv2001

The Spectral Energy Distribution of the Seyfert galaxy Ton S180

We present spectral results from a multi-satellite, broad-band campaign on the Narrow-line Seyfert 1 galaxy Ton S180 performed at the end of 1999. We discuss the spectral-energy distribution of the source, combining simultaneous Chandra, ASCA and EUVE data with contemporaneous FUSE, HST, and ground-based optical and infra-red data. The resulting SED shows that most of the energy is emitted in the 10 -- 100 eV regime, which must be dominated by the primary energy source. No spectral turnover is evident in the UV regime. This, the strong soft X-ray emission, and the overall shape of the SED indicate that emission from the accretion disk peaks between 15 and 100 eV. High resolution FUSE spectra showing UV absorption due to O VI and the lack of detectable X-ray absorption in the Chandra spectrum demonstrate the presence of a low column density of highly ionized gas along our line-of-sight. The highly-ionized state of the circumnuclear gas is most likely linked to the high luminosity and steep spectrum of the active nucleus. Given the strong ionizing flux in Ton S180, it is possible that the clouds within a few tens of light days of the central source are too highly ionized to produce much line emission. Thus the narrow width of the emission lines in Ton S180 is due to the emission arising from large radii.

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arXiv2001

The first ISO ERO: a dusty quasar at z = 1.5

We report the discovery of an extremely red object (ERO) in a medium-deep ISOCAM extragalactic survey. The object is also a radio source. Subsequent VLT NIR spectroscopy revealed a prominent Halpha line giving a redshift of 1.5. We present the spectrum and photometric data points and discuss evidence that ISO J1324-2016 is a quasar harbouring a significant amount of very hot dust.

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arXiv2001

Kinematics of Molecular Gas in the Nucleus of NGC1068, from H2 line emission observed with VLT

We present results about the distribution and kinematics of the molecular environment of the AGN in NGC1068, over a 1.5'' x 3.5'' region around the central engine in NGC1068, derived from H2 line emission detected with ISAAC at VLT/ANTU on ESO/Paranal. The H2 emitting molecular gas is found to be distributed along the East-West direction and with two main peak emission (knots) located at a distance of about 70 pc from the central engine. The eastern H2 knot is more intense than the western one. The line profiles mapped across the entire 1.5'' x 3.5'' region, at a spatial resolution of 0.3'' x 0.45'', appear to be quite complex with either a blue or red wing. At first order, we find a velocity difference of 140 km/s between the two knots; if interpreted as quasi-keplerian velocity, this implies a central enclosed mass of 10^8 solar masses.

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arXiv2001

Monitoring of the optical and 2.5-11.7 micron spectrum and mid-IR imaging of the Seyfert 1 galaxy Mrk279 with ISO

Mid-infrared images of the Seyfert 1 galaxy Mrk 279 obtained with the ISO satellite are presented together with the results of a one-year monitoring campaign of the 2.5-11.7 micron spectrum. Contemporaneous optical photometric and spectrophotometric observations are also presented. The galaxy appears as a point-like source at the resolution of the ISOCAM instrument, 4-5". The 2.5-11.7 micron average spectrum of the nucleus in Mrk 279 shows a strong power law continuum with a spectral index alpha = -0.80+/-0.05 and weak PAH emission features. The Mrk 279 spectral energy distribution shows a mid-IR bump, which extends from 2 to 15-20 micron . The mid-IR bump is consistent with thermal emission from dust grains at a distance of >= 100 light-days. No significant variations of the mid-IR flux have been detected during our observing campaign, consistent with the relatively low amplitude (~10 % rms) of the optical variability during the campaign. The time delay for the Hbeta line emission in response to the optical continuum variations is 16.7 +5.3/5.6 days, consistent with previous measurements.

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arXiv2000

High resolution images at 11 and 20 microns of the Active Galactic Nucleus in NGC 1068

We present diffraction-limited IR images at 11.2 and 20.5 microns of the central 6''x6'' region in NGC 1068, collected with the CAMIRAS instrument mounted at the f/36 IR focus of the CFHT/Hawaii 3.6m telescope and at the f/35 IR focus of the ESO/La Silla 3.6m telescope, respectively. After deconvolution, the achieved resolution (0.6'') reveals a prominent central core emitting about 95 % of the total flux at these wavelengths, as well as extended emission, to the South-West and to the North-East, broken into patchy components which are particularly conspicuous at 20.5 microns and can be isolated as individual clouds. The central core shows an East-West FWHM of 0.6'' (hence unresolved) and a North-South FWHM of 0.9'' corresponding to a resolved full size extension of abound 100 pc. Such an elongated shape is in agreement with model predictions of a dusty/molecular torus surrounding the central engine in NGC 1068, observed under an inclination angle around 65 degrees.

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arXiv1999

Adaptive Optics Images at 3.5 and 4.8 microns of the Core Arcsec of NGC1068, More Evidence for a Dusty/Molecular Torus

This paper presents unique adaptive optics images at 3.5 and 4.8 microns of the central arcsec in the AGN of NGC1068. They enlight the presence of hot to warm dust close to the central engine of the AGN. At a radius around 40 pc, the dust is clearly contained within a disc-like structure perpendicular to the ionizing cone axis. These observations support AGN dusty/molecular torus modeling.

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arXiv1998

Near-IR Images of the Torus and Micro-Spiral Structure in NGC 1068 using Adaptive Optics

We present diffraction-limited near-IR images in J, H and K of the nucleus of NGC 1068, obtained with the Adaptive Optics system {Pueo} at CFHT. The achieved resolution (0.12") reveals several components, particularly prominent on the [J-K] image: a) an unresolved, conspicuous core (size < 9 pc); b) an elongated structure at P.A. ~102 deg, beginning to show up at radius ~ 15 pc; c) a S-shaped structure with radial extent ~ 20 pc, including a bar-like central elongation at P.A. ~ 15 deg and two short spiral arms. The K core is at the location of the putative central engine (radio source S1) : the core is likely the emission from the hot inner walls of the dust/molecular torus. The extremely red colors of the central 0.2", [J-K]=7.0, [H-K]=3.8, lead to an extinction Av > 25. The elongated structure at P.A.~ 102 deg may trace the presence of cooler dust within and around the torus. This interpretation is supported by two facts : a) the elongated structure is perpendicular to the local radio jet originating at S1; b) its direction follows exactly that of the disk of ionized gas recently found with the VLBA. The S-shaped feature suggests an extremely compact barred spiral structure, that would be the innermost of a series of nested spiral structures, as predicted by simulations. This is supported by the inner stellar distribution - deduced from the J image - which clearly follows an exponential disk with a 19 pc scale-length, precisely that expected from the rotation of a bar.

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arXiv1998

Steps towards determination of the size and structure of the Broad-Line Region in Active Galactic Nuclei. XIII. Ultraviolet observations of the Broad-Line Radio Galaxy 3C 390.3

As part of an extensive multi-wavelength monitoring campaign, the International Ultraviolet Explorer satellite was used to observe the broad-line radio galaxy 3C 390.3 during the period 1994 December 31 to 1996 March 5. Spectra were obtained every 6-10 days. The UV continuum varied by a factor of 7 through the campaign, while the broad emission-lines varied by factors of 2-5. Unlike previously monitored Seyfert 1 galaxies, in which the X-ray continuum generally varies with a larger amplitude than the UV, in 3C 390.3 the UV continuum light-curve is similar in both amplitude and shape to the X-ray light-curve observed by ROSAT. The UV broad emission-line variability lags that of the UV continuum by 35-70 days for Ly-alpha and CIV 1549; values larger than those found for Seyfert 1 galaxies of comparable UV luminosity. These lags are also larger than those found for the Balmer lines in 3C 390.3 over the same period. The red and blue wings of CIV and Ly-alpha vary in phase, suggesting that radial motion does not dominate the kinematics of the UV line-emitting gas. Comparison with archival data provides evidence for velocity-dependent changes in the Ly-alpha and CIV line profiles, indicating evolution in the detailed properties and/or distribution of the broad-line emitting gas.

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arXiv1998

Unveiling the nature of the Cloverleaf lens-system: HST/NICMOS-2 observations

We present new elements in the identification of the lens-system producing the 4 images of the BAL quasar H1413+117, based on the recent HST/NICMOS-2/F160W observations. After a careful PSF subtraction of the 4 images of the quasar, the residual H image reveals the presence of a faint object (H~20.5) within the region enclosed by the 4 quasar images. This object corresponds to a single galaxy: the primary lens of the lens-system. We also identify the galaxies around the Cloverleaf which had been proposed to belong to a galaxy cluster/group at high redshift (Kneib et al 1998): the other component in the lens-system that provides the additional "external" shear. For these galaxies, we have derived a likely redshift based upon their R, I and H magnitudes. We find that most of them are consistent with belonging to a galaxy cluster/group with mean redshift =0.9 +/- 0.1. Furthermore we detect 2 very red objects (I-H~4): the faintest one has no observed optical (R and I) counterpart, while the brightest has a predicted redshift around z~2, and may be identified with one of the Cloverleaf absorbers. This gravitational-lens system constitutes an excellent target for IR imaging/spectroscopy with the new generation of 8m ground-based telescopes.

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arXiv1998

High Resolution Data on the Cloverleaf in the UV and in CO(7-6)

We present a new investigation of the Cloverleaf (z$=$2.56) based on the HST/WFPC2, IRAM and CFHT/FOCAM images data. The WFPC2 data shows a significant overdensity of galaxies around the Cloverleaf that we interpret as the presence of a distant cluster of galaxies along the line of sight. The Cloverleaf is probably the result of the lensing effects which include, in addition to a single galaxy, a distant clusters of galaxies. We have modelled the lens accordingly. The high-resolution IRAM/CO map provides the orientation and the ellipticity of the CO spots induced by the shear component. Velocity-positional effects are detected at the 8$σ$ level in the CO map. A strong limit can then be put on the size, shape and location of the CO source around the quasar. The CO source is found to form a disk- or ring- structure orbiting the central engine at $\sim$ 100km/s at a radial distance of $\sim$ 100pc, leading to a central mass of $\sim$ 10$^{9}$ M$_\odot$ possibly in the form of a black hole.

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arXiv1997

Modelling the Cloverleaf: Contribution of a Galaxy Cluster at z~1.7

We present a new investigation of the Cloverleaf (z=2.558) based on the combination of archival HST/WFPC2 data, recent IRAM CO(7-6) maps and wide field CFHT/FOCAM images. The deepest WFPC2 observation shows a significant overdensity of I ~ 23--25 galaxies around the Cloverleaf that we interpret as the presence of a cluster of galaxies along the line of sight. The typical magnitude, red color (R-I ~ 0.9) and small angular size of these galaxies suggest that the cluster is very distant and could be associated with the absorption systems observed in the spectra of the quasar spots. The Cloverleaf is probably the result of the lensing effects of a system which includes a single-galaxy and one of the most distant cluster of galaxies. We have modelled the lens using altogether the WFPC2 data and the IRAM/CO(7-6) map, considereing two cases: one in which the mass model is a galaxy and a dark halo at z=1.7, and a second one in which the mass model is the combination of a cluster and an individual galaxy located amid the Cloverleaf, both at z=1.7. The CO source is found to form a ring-like structure orbiting the central engine at ~ 100km/s at a radial distance of ~ 100pc, leading to a black-hole mass of ~ 10^9 M_solar. The cluster component increases significantly the convergence of the lens and this pulls down the requirement on the mass of the lensing galaxy by a factor 2. This may explain the mystery of the lensing galaxy not detected yet.

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