References of "Letawe, Géraldine"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailGalaxy counterparts of intervening high-z sub-DLAs/DLAs and Mg ii absorbers towards gamma-ray bursts
Schulze, steve; Letawe, Géraldine ULg

in Astronomy and Astrophysics (2012), 546(A20),

We present the first search for galaxy counterparts of intervening high-z (2 < z < 3.6) sub-damped Lyα absorbers (sub-DLAs) and DLAs towards gamma-ray bursts (GRBs). Our final sample comprises five ... [more ▼]

We present the first search for galaxy counterparts of intervening high-z (2 < z < 3.6) sub-damped Lyα absorbers (sub-DLAs) and DLAs towards gamma-ray bursts (GRBs). Our final sample comprises five intervening sub-DLAs and DLAs in four GRB fields. To identify candidate galaxy counterparts of the absorbers we used deep optical- and near-infrared imaging, and low-, mid- and high-resolution spectroscopy acquired with 6-m to 10-m class telescopes, the Hubble and the Spitzer Space Telescopes. Furthermore, we used the spectroscopic information and spectral-energy-distribution fitting techniques to study them in detail. Our main result is the detection and spectroscopic confirmation of the galaxy counterpart of the intervening DLA at z = 3.096 in the field of GRB 070721B (zGRB = 3.6298) as proposed by other authors. We also identify good candidates for the galaxy counterparts of the two strong Mg ii absorbers at z = 0.6915 and 1.4288 towards GRB 050820A (zGRB = 2.615). The properties of the detected DLA galaxy are typical for Lyman-break galaxies (LBGs) at similar redshifts; a young, highly star-forming galaxy that shows evidence for a galactic outflow. This supports thehypothesis that a DLA can be the gaseous halo of an LBG. In addition, we report a redshift coincidence of different objects associated with metal lines in the same field, separated by 130–161 kpc. The high detection rate of three correlated structures on a length scale as short as ~150 kpc in two pairs of lines of sight is intriguing. The absorbers in each of these are most likely not part of the same gravitationally bound structure. They more likely represent groups of galaxies. [less ▲]

Detailed reference viewed: 15 (1 ULg)
Full Text
Peer Reviewed
See detailModelling the huge, Herschel-resolved debris ring around HD 207129
Löhne, T.; Augereau, J.-C.; Ertel, S. et al

in Astronomy and Astrophysics (2012), 537

Debris disks, which are inferred from the observed infrared excess to be ensembles of dust, rocks, and probably planetesimals, are common features of stellar systems. As the mechanisms of their formation ... [more ▼]

Debris disks, which are inferred from the observed infrared excess to be ensembles of dust, rocks, and probably planetesimals, are common features of stellar systems. As the mechanisms of their formation and evolution are linked to those of planetary bodies, they provide valuable information. The few well-resolved debris disks are even more valuable because they can serve as modelling benchmarks and help resolve degeneracies in modelling aspects such as typical grain sizes and distances. Here, we present an analysis of the HD 207129 debris disk, based on its well-covered spectral energy distribution and Herschel/PACS images obtained in the framework of the DUNES (DUst around NEarby Stars) programme. We use an empirical power-law approach to the distribution of dust and we then model the production and removal of dust by means of collisions, direct radiation pressure, and drag forces. The resulting best-fit model contains a total of nearly 10[SUP]-2[/SUP] Earth masses in dust, with typical grain sizes in the planetesimal belt ranging from 4 to 7 μm. We constrain the dynamical excitation to be low, which results in very long collisional lifetimes and a drag that notably fills the inner gap, especially at 70 μm. The radial distribution stretches from well within 100 AU in an unusual, outward-rising slope towards a rather sharp outer edge at about 170-190 AU. The inner edge is therefore smoother than that reported for Fomalhaut, but the contribution from the extended halo of barely bound grains is similarly small. Both slowly self-stirring and planetary perturbations could potentially have formed and shaped this disk. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. [less ▲]

Detailed reference viewed: 30 (3 ULg)
Full Text
See detailNew Insights into the Quasar Type 1/Type 2 Dichotomy from Correlations between Quasar Host Orientation and Polarization
Borguet, Benoît ULg; Hutsemekers, Damien ULg; Letawe, Géraldine ULg et al

in Bastien, Pierre (Ed.) Astronomical Polarimetry 2008: Science from Small to Large Telescopes. ASPC 449 (2011, November 01)

We investigate correlations between the direction of the optical linear polarization and the orientation of the host galaxy/extended emission for type 1 and type 2 radio-loud and radio-quiet quasars. We ... [more ▼]

We investigate correlations between the direction of the optical linear polarization and the orientation of the host galaxy/extended emission for type 1 and type 2 radio-loud and radio-quiet quasars. We have used high resolution Hubble Space Telescope data and a deconvolution process to obtain a good determination of the host galaxy/extended emission (EE) position angle. With these new measurements and a compilation of data from the literature, we find a significant correlation, different for type 1 and type 2 objects, between the linear polarization position angle and the orientation of the EE, suggesting scattering by an extended UV/blue region in both types of objects. Our observations support the extension of the Unification Model to the higher luminosity AGNs like the quasars, assuming a two component scattering model. [less ▲]

Detailed reference viewed: 50 (23 ULg)
Full Text
Peer Reviewed
See detailDeep near-infrared imaging of the HE0450-2958 system
Letawe, Géraldine ULg; Magain, Pierre ULg

in Astronomy and Astrophysics (2010), 515

The QSO HE0450-2958 and the companion galaxy with which it is interacting, both ultra luminous in the infrared, have been the subject of much attention in recent years, as the quasar host galaxy remained ... [more ▼]

The QSO HE0450-2958 and the companion galaxy with which it is interacting, both ultra luminous in the infrared, have been the subject of much attention in recent years, as the quasar host galaxy remained undetected. This led to various interpretations on QSO and galaxy formation and co-evolution, such as black hole ejection, jet induced star formation, dust obscured galaxy, or normal host below the detection limit. We carried out deep observations in the near-IR in order to solve the puzzle concerning the existence of any host. The object was observed with the ESO VLT and HAWK-I in the near-IR J-band for 8 hours. The images have been processed with the MCS deconvolution method (Magain, Courbin & Sohy, 1998), permitting accurate subtraction of the QSO light from the observations. The compact emission region situated close to the QSO, called the blob, which previously showed only gas emission lines in the optical spectra, is now detected in our near-IR images. Its high brightness implies that stars likely contribute to the near-IR emission. The blob might thus be interpreted as an off-centre, bright and very compact host galaxy, involved in a violent collision with its companion. [less ▲]

Detailed reference viewed: 28 (17 ULg)
Full Text
See detailThe Power of Deconvolution for Study of QSO Host Galaxies
Letawe, Géraldine ULg; Letawe, Yannick; Magain, Pierre ULg

in Proceedings of the International Astronomical Union, IAU Symposium (2010, May 01), Vol 267

The major challenge in studying QSO host galaxies is to remove the QSO contribution, which often outshines the whole system. Our group has acquired the technical ability to handle such data, for images ... [more ▼]

The major challenge in studying QSO host galaxies is to remove the QSO contribution, which often outshines the whole system. Our group has acquired the technical ability to handle such data, for images and slit spectroscopy, as well as integral field spectroscopy. We review here the major techniques developed by our team, and their latest applications. We are open for collaboration with other teams to spread the use of these powerful techniques. [less ▲]

Detailed reference viewed: 11 (4 ULg)
Full Text
See detailStudy of quasar host galaxies combining HST/ACS images and VLT Spectroscopy
Letawe, Yannick; Letawe, Géraldine ULg; Magain, Pierre ULg

in Macchetto, F. D. (Ed.) The Impact of HST on European Astronomy (2010, March 22)

We present the results of a study of the host galaxies of a few bright low redshift quasars, based on a combination of high resolution HST/ACS images with deep VLT spectra. Using a version of the MCS ... [more ▼]

We present the results of a study of the host galaxies of a few bright low redshift quasars, based on a combination of high resolution HST/ACS images with deep VLT spectra. Using a version of the MCS deconvolution algorithm specially adapted to HST images, the light from the central point source can be efficiently removed, which allows to study the environment of the quasar down to a few hundreds of parsecs from the center. In a similar way, the spectra can be separated into a quasar contribution and a spatialy resolved slit spectrum of the host galaxy. Combinig the images and spectra allows to carry out a detailed analysis of the immediate environment of the quasar: excitation and ionisation state of the gas, dynamics... Up to now, this method has been applied to six quasars, including the peculiar HE0450-2958 for which no host galaxy could be detected. [less ▲]

Detailed reference viewed: 29 (5 ULg)
Full Text
Peer Reviewed
See detailStudy of a homogeneous QSO sample: relations between the QSO and its host galaxy
Letawe, Yannick; Letawe, Géraldine ULg; Magain, Pierre ULg

in Monthly Notices of the Royal Astronomical Society (2010), 403(4), 2088-2104

ABSTRACT We analyse a sample of 69 quasi-stellar objects (QSOs) which have been randomly selected in a complete sample of 104 QSOs (R < 18,0.142 < z < 0.198, d< 10°). 60 have been observed with the NTT ... [more ▼]

ABSTRACT We analyse a sample of 69 quasi-stellar objects (QSOs) which have been randomly selected in a complete sample of 104 QSOs (R < 18,0.142 < z < 0.198, d< 10°). 60 have been observed with the NTT/SUSI2 at La Silla, through two filters in the optical band (WB 655 and V 812), and the remaining nine are taken from archive data bases. The filter V 812 contains the redshifted Hβ and forbidden [OIII] emission lines, while WB 655 covers a spectral region devoid of emission lines, thus measuring the QSO and stellar continua. The contributions of the QSO and the host are separated thanks to the MCS deconvolution algorithm, allowing a morphological classification of the host, and the computation of several parameters such as the host and nucleus absolute V magnitude, distance between the luminosity centre of the host and the QSO and colour of the host and nucleus. We define a new asymmetry coefficient, independent of any galaxy models and well suited for QSO host studies. The main results from this study are (i) 25 per cent of the total number of QSO hosts are spirals, 51 per cent are ellipticals and 60 per cent show signs of interaction, (ii) highly asymmetric systems tend to have a higher gas ionization level and (iii) elliptical hosts contain a substantial amount of ionized gas and some show off-nuclear activity. These results agree with hierarchical models merger driven evolution. [less ▲]

Detailed reference viewed: 24 (7 ULg)
Full Text
Peer Reviewed
See detailQuasar induced galaxy formation: a new paradigm?
Elbaz, David; Jahnke, Knud; Pantin, eric et al

in Astronomy and Astrophysics (2009), 507

Aims: We discuss observational evidence that quasars play a key role in the formation of galaxies, starting from the detailed study of the quasar HE0450-2958 and extending the discussion to a series of ... [more ▼]

Aims: We discuss observational evidence that quasars play a key role in the formation of galaxies, starting from the detailed study of the quasar HE0450-2958 and extending the discussion to a series of converging evidence that radio jets may trigger galaxy formation. Methods: We use mid infrared imaging with VISIR at the ESO-VLT to model the mid to far infrared energy distribution of the system and the stellar population of the companion galaxy using optical VLT-FORS spectroscopy. The results are combined with optical, CO, radio continuum imaging from ancillary data. Results: The direct detection with VISIR of the 7 kpc distant companion galaxy of HE0450-2958 allows us to spatially separate the sites of quasar and star formation activity in this composite system made of two ultra-luminous infrared galaxies (ULIRGs), where the quasar generates the bulk of the mid infrared light and the companion galaxy powered by star formation dominates in the far infrared. No host galaxy has yet been detected for this quasar, but the companion galaxy stellar mass would bring HE0450-2958 in the local MBH - Mstar-bulge relation if it were to merge with the QSO. This is bound to happen because of their close distance (7 kpc) and low relative velocity ( 60-200 km s-1). We conclude that we may be witnessing the building of the MBH - Mstar-bulge relation, or at least of a major event in that process. The star formation rate ( 340 Mȯ yr-1), age (40-200 Myr) and stellar mass ( [5-6]×10^10 Mȯ) are consistent with jet-induced formation of the companion galaxy. We suggest that HE0450-2958 may be fueled by fresh material from cold gas accretion from intergalactic filaments. We map the projected galaxy density surrounding the QSO as a potential tracer of intergalactic filaments and discuss a putative detection. Comparison to other systems suggest that an inside-out formation of quasar host galaxies and jet-induced galaxy formation may be a common process. Two tests are proposed for this new paradigm: (1) the detection of offset molecular gas or dust emission with respect to the position of distant QSOs; (2) the delayed formation of host galaxies as a result of QSO activity, hence the two step building of the M_BH/Mstar-bulge ratio. [less ▲]

Detailed reference viewed: 28 (3 ULg)
Full Text
Peer Reviewed
See detailThe QSO HE0450-2958: Scantily dressed or heavily robed? A normal quasar as part of an unusual ULIRG
Jahnke, Knud; Elbaz, David; Pantin, Eric et al

in Astrophysical Journal (2009), 700(2), 1820-1830

(Abridged) The luminous z=0.286 quasar HE0450-2958 is interacting with a companion galaxy at 6.5 kpc distance and the whole system is a ULIRG. A so far undetected host galaxy triggered the hypothesis of a ... [more ▼]

(Abridged) The luminous z=0.286 quasar HE0450-2958 is interacting with a companion galaxy at 6.5 kpc distance and the whole system is a ULIRG. A so far undetected host galaxy triggered the hypothesis of a mostly "naked" black hole (BH) ejected from the companion by three-body interaction. We present new HST/NICMOS 1.6micron imaging data at 0.1" resolution and VLT/VISIR 11.3micron images at 0.35" resolution that for the first time resolve the system in the near- and mid-infrared. We combine these with existing optical HST and CO maps. (i) At 1.6micron we find an extension N-E of the quasar nucleus that is likely a part of the host galaxy, though not its main body. If true, this places HE0450-2958 directly onto the M_BH-M_bulge-relation for nearby galaxies. (ii) HE0450-2958 is consistent with lying at the high-luminosity end of Narrow-Line Seyfert 1 Galaxies, and more exotic explanations like a "naked quasar" are unlikely. (iii) All 11.3micron radiation in the system is emitted by the quasar nucleus, which is radiating at super-Eddington rate, L/L_Edd=6.2+3.8-1.8, or 12 M_sun/yr. (iv) The companion galaxy is covered in optically thick dust and is not a collisional ring galaxy. It emits in the far infrared at ULIRG strength, powered by Arp220-like star formation (strong starburst-like). An M82-like SED is ruled out. (v) With its black hole accretion rate HE0450-2958 produces not enough new stars to maintain its position on the M_BH-M_bulge-relation, and star formation and black hole accretion are spatially disjoint; the bulge has to grow by redistribution of preexisting stars. (vi) Systems similar to HE0450-2958 with spatially disjoint ULIRG-strength star formation and quasar activity are rare. At z<0.43 we only find <4% (3/77) candidates for a similar configuration. [less ▲]

Detailed reference viewed: 28 (7 ULg)
Full Text
Peer Reviewed
See detailNear-intrared observations of the HE 0450-2958 system: discovery of a second active galactic nucleus?
Letawe, Géraldine ULg; Magain, Pierre ULg; Chantry, Virginie ULg et al

in Monthly Notices of the Royal Astronomical Society (2009), 396(1), 78-84

The quasi-stellar object (QSO) HE 0450−2958 was brought to the front scene by the non-detection of its host galaxy and strong upper limits on the latter's luminosity. The QSO is also a powerful infrared ... [more ▼]

The quasi-stellar object (QSO) HE 0450−2958 was brought to the front scene by the non-detection of its host galaxy and strong upper limits on the latter's luminosity. The QSO is also a powerful infrared emitter, in gravitational interaction with a strongly distorted ultraluminous infrared companion galaxy. We investigate the properties of the companion galaxy, through new near- and mid-infrared observations of the system obtained with Near Infrared Camera and Multi-Object Spectrometer (NICMOS) onboard Hubble Space Telescope, Infrared Spectrometer and Array Camera (ISAAC) and Very Large Telescope Imager and Spectrometer in the Infrared (VISIR) on the European Southern Observatory Very Large Telescope. The companion galaxy is found to harbour a point source revealed only in the infrared, in what appears as a hole or dark patch in the optical images. Various hypotheses on the nature of this point source are analysed and it is found that the only plausible one is that it is a strongly reddened active galactic nucleus hidden behind a thick dust cloud. The hypothesis that the QSO supermassive black hole might have been ejected from the companion galaxy in the course of a galactic collision involving three-body black holes interaction is also reviewed, on the basis of this new insight on a definitely complex system. [less ▲]

Detailed reference viewed: 44 (14 ULg)
Full Text
See detailQuasar Host Orientation and Polarization: Insights into the Type 1/Type 2 Dichotomy
Borguet, Benoît ULg; Hutsemekers, Damien ULg; Letawe, Géraldine ULg et al

in Revista Mexicana de Astronomía y Astrofísica (2008), 32

We investigate correlations between the optical linear polarization position angle and the orientation of the host galaxy/extended emission of Type 1 and Type 2 Radio-Loud (RL) and Radio-Quiet (RQ ... [more ▼]

We investigate correlations between the optical linear polarization position angle and the orientation of the host galaxy/extended emission of Type 1 and Type 2 Radio-Loud (RL) and Radio-Quiet (RQ) quasars. We have used high resolution Hubble Space Telescope (HST) data and deconvolution process to obtain a good determination of the host galaxy orientation. With these new measurements and a compilation of data from the literature, we find a significant correlation between the polarization position angle and the position angle of the major axis of the host galaxy/extended emission. The correlation appears different for Type 1 and Type 2 objects and depends on the redshift of the source. Interpretations in the framework of the unification model are discussed. [less ▲]

Detailed reference viewed: 27 (6 ULg)
Full Text
Peer Reviewed
See detailEvidence of a type 1/type 2 dichotomy in the correlation between quasar optical polarization and host-galaxy/extended emission position angles
Borguet, Benoît ULg; Hutsemekers, Damien ULg; Letawe, Géraldine ULg et al

in Astronomy and Astrophysics (2008), 478

Aims.For Seyfert galaxies, the AGN unification model provides a simple and well-established explanation of the type 1/type 2 dichotomy through orientation-based effects. The generalization of this ... [more ▼]

Aims.For Seyfert galaxies, the AGN unification model provides a simple and well-established explanation of the type 1/type 2 dichotomy through orientation-based effects. The generalization of this unification model to the higher luminosity AGNs that quasars are remains a key question. The recent detection of type 2 radio-quiet quasars seems to support such an extension. We propose a further test of this scenario. Methods: On the basis of a compilation of quasar host-galaxy position angles consisting of previously published data and of new measurements performed using HST Archive images, we investigate the possible existence of a correlation between the linear polarization position angle and the host-galaxy/extended emission position angle of quasars. Results: We find that the orientation of the rest-frame UV/blue extended emission is correlated to the direction of the quasar polarization. For type 1 quasars, the polarization is aligned with the extended UV/blue emission, while these two quantities are perpendicular in type 2 objects. This result is independent of the quasar radio loudness. We interpret this (anti-)alignment effect in terms of scattering in a two-component polar+equatorial model that applies to both type 1 and type 2 objects. Moreover, the orientation of the polarization -and then of the UV/blue scattered light- does not appear correlated to the major axis of the stellar component of the host-galaxy measured from near-IR images. [less ▲]

Detailed reference viewed: 31 (13 ULg)
Full Text
See detailStudy of the QSO HE0354-5500 with combined HST imaging and VLT spectroscopy . An example of a deconvolution-based method for probing the QSOs host galaxies characteristics
Letawe, Yannick ULg; Magain, Pierre ULg; Letawe, Géraldine ULg et al

in Memorie della Società Astronomica Italiana : Journal of the Italian Astronomical Society (2008), 79

The host galaxy of the QSO HE0354-5500 (M_B=-24.7, z=0.2674) is studied on the basis of high resolution HST optical images and spatially resolved VLT slit spectra. The morphology and dynamics of the host ... [more ▼]

The host galaxy of the QSO HE0354-5500 (M_B=-24.7, z=0.2674) is studied on the basis of high resolution HST optical images and spatially resolved VLT slit spectra. The morphology and dynamics of the host are described. The gas ionization and velocity are mapped as a function of the distance to the central QSO. Reflection or scattering of the QSO Halpha line from remote regions of the galaxy is detected. The line shifts show that the matter responsible for the light reflection moves away from the QSO, likely accelerated by its radiation pressure. Moreover, different resolved emission regions are found in the central kpc, both in the images and the spectra. [less ▲]

Detailed reference viewed: 19 (2 ULg)
Full Text
Peer Reviewed
See detailSlit and integral-field optical spectroscopy of the enigmatic quasar HE 0450-2958
Letawe, Géraldine ULg; Magain, Pierre ULg; Courbin

in Astronomy and Astrophysics (2008), 480

Detailed reference viewed: 21 (6 ULg)
Full Text
Peer Reviewed
See detailUnderstanding the relations between QSOs and their host galaxies from combined HST imaging and VLT spectroscopy
Letawe, Yannick ULg; Magain, Pierre ULg; Letawe, Géraldine ULg et al

in Astrophysical Journal (2008), 679(2), 967-983

The host galaxies of six nearby QSOs are studied on the basis of high-resolution HST optical images and spatially resolved VLT slit spectra. The gas ionization and velocity are mapped as a function of the ... [more ▼]

The host galaxies of six nearby QSOs are studied on the basis of high-resolution HST optical images and spatially resolved VLT slit spectra. The gas ionization and velocity are mapped as a function of the distance to the central QSO. In the majority of the cases, the QSO significantly contributes to the gas ionization in its whole host galaxy, and sometimes even outside. Reflection or scattering of the QSO H alpha line from remote regions of the galaxy is detected in several instances. The line shifts show that, in all cases, the matter responsible for the light reflection moves away from the QSO, likely accelerated by its radiation pressure. The two faintest QSOs reside in spirals, with some signs of a past gravitational perturbation. One of the intermediate-luminosity QSOs resides in a massive elliptical containing gas ionized (and probably pushed away) by the QSO radiation. The other medium-power object is found in a spiral galaxy displaying complex velocity structure, with the central QSO moving with respect to the bulge, probably as a result of a galactic collision. The two most powerful objects are involved in violent gravitational interactions, and one of them has no detected host. These results suggest that (1) large-scale phenomena, such as galactic collisions, are closely related to the triggering and the feeding of the QSO and (2) once ignited, the QSO has significant influence on its large-scale neighborhood ( often the whole host and sometimes further away). [less ▲]

Detailed reference viewed: 24 (7 ULg)
See detailQSO Type1/Type2 dichotomy (Borguet+, 2008)
Borguet, Benoît ULg; Hutsemekers, Damien ULg; Letawe, Géraldine ULg et al

Textual, factual or bibliographical database (2007)

This table contains the measurements/compilation of host galaxy/ extended emission position angle in the visible and near-IR domain, polarimetric data, and radio axis orientation for the 135 quasars of ... [more ▼]

This table contains the measurements/compilation of host galaxy/ extended emission position angle in the visible and near-IR domain, polarimetric data, and radio axis orientation for the 135 quasars of our sample. The angles are given in degrees east of north. The table gives the spectral and the radio-loud/radio-quiet classification of each object according to the references. (2 data files). [less ▲]

Detailed reference viewed: 26 (2 ULg)
Full Text
See detailDECPHOT: An Optimal Deconvolution-based Photometric Reduction Method
Gillon, Michaël ULg; Magain, Pierre ULg; Chantry, Virginie ULg et al

in Transiting Extrapolar Planets Workshop (2007, July 01)

A high accuracy photometric reduction method is needed to take full advantage of the potential of the transit method for the detection and characterization of exoplanets, especially in deep crowded fields ... [more ▼]

A high accuracy photometric reduction method is needed to take full advantage of the potential of the transit method for the detection and characterization of exoplanets, especially in deep crowded fields. In this context, we present DECPHOT, a new deconvolution-based photometry algorithm able to deal with a very high level of crowding and large variations of seeing. It also increases the resolution of astronomical images, an important advantage for the discrimination of false positives in transit photometry. [less ▲]

Detailed reference viewed: 68 (18 ULg)
Full Text
Peer Reviewed
See detailSpatial decomposition of on-nucleus spectra of quasar host galaxies
Jahnke, K.; Wisotzki, L.; Courbin, F. et al

in Monthly Notices of the Royal Astronomical Society (2007), 378(1), 23-40

In order to study the host galaxies of type 1 (broad-line) quasars, we present a semi-analytic modelling method to decompose the on-nucleus spectra of quasars into nuclear and host galaxy channels. The ... [more ▼]

In order to study the host galaxies of type 1 (broad-line) quasars, we present a semi-analytic modelling method to decompose the on-nucleus spectra of quasars into nuclear and host galaxy channels. The method uses the spatial information contained in long-slit or slitlet spectra. A routine determines the best-fitting combination of the spatial distribution of the point like nucleus and extended host galaxy. This is fully complementary to a numerical spatial deconvolution technique that we applied to the same data in a previous analysis, which allows a cross-calibration of the two methods. Inputs are a simultaneously observed point spread function, and external constraints on galaxy morphology from imaging. We demonstrate the capabilities of the method to two samples of a total of 18 quasars observed with EFOSC at the ESO 3.6-m telescope and FORS1 at the ESO VLT. similar to 50 per cent of the host galaxies with successful decomposition show distortions in their rotation curves or peculiar gas velocities above normal maximum velocities for discs. This is consistent with the fraction from optical imaging. All host galaxies have quite young stellar populations, typically 1-2 Gyr. For the disc dominated hosts these are consistent with their inactive counterparts, the luminosity-weighted stellar ages are much younger for the bulge dominated hosts, compared to inactive early-type galaxies. While this presents further evidence for a connection of galaxy interaction and active galactic nucleus (AGN) activity for half of the sample, this is not clear for the other half. These are often undistorted disc dominated host galaxies, and interaction on a smaller level might be detected in deeper high-resolution images or deeper spectroscopic data. The velocity information does not show obvious signs for large scale outflows triggered by AGN feedback - the data are consistent with velocity fields created by galaxy interaction. [less ▲]

Detailed reference viewed: 23 (1 ULg)
Full Text
Peer Reviewed
See detailOn-axis spectroscopy of the host galaxies of 20 optically luminous quasars at z similar to 0.3
Letawe, Géraldine ULg; Magain, Pierre ULg; Courbin, F. et al

in Monthly Notices of the Royal Astronomical Society (2007), 378(1), 83-108

We present the analysis of a sample of 20 bright low-redshift quasars (M-B < -23 and z < 0.35) observed spectroscopically with the Very Large Telescope (VLT). The Focal Reducer/low dispersion Spectrograph ... [more ▼]

We present the analysis of a sample of 20 bright low-redshift quasars (M-B < -23 and z < 0.35) observed spectroscopically with the Very Large Telescope (VLT). The Focal Reducer/low dispersion Spectrograph (FORS1) spectra, obtained in Multi-Object Spectroscopy (MOS) mode, allow to observe simultaneously the quasars and several reference stars used to spatially deconvolve the data. Applying the Magain, Courbin, & Sohy (MCS) deconvolution method, we are able to separate the individual spectra of the quasar and of the underlying host galaxy. Contrary to some previous claims, we find that luminous quasars are not exclusively hosted by massive ellipticals. Most quasar host galaxies harbour large amounts of gas, irrespective of their morphological type. Moreover, the stellar content of half of the hosts is a young Sc-like population, associated with a rather low-metallicity interstellar medium. A significant fraction of the galaxies contain gas ionized at large distances by the quasar radiation. This large distance ionization is always associated with signs of gravitational interactions (as detected from images or disturbed rotation curves). The spectra of the quasars themselves provide evidence that gravitational interactions bring dust and gas in the immediate surrounding of the super massive black hole, allowing to feed it. The quasar activity might thus be triggered (1) in young gas-rich spiral galaxies by local events and (2) in more evolved galaxies by gravitational interactions or collisions. The latter mechanism gives rises to the most powerful quasars. Finally, we derive mass models for the isolated spiral host galaxies and we show that the most reliable estimators of the systemic redshift in the quasar spectrum are the tips of the Hα and Hβ lines. [less ▲]

Detailed reference viewed: 19 (4 ULg)
Full Text
Peer Reviewed
See detailA deconvolution-based algorithm for crowded field photometry with unknown point spread function
Magain, Pierre ULg; Courbin, F.; Gillon, Michaël ULg et al

in Astronomy and Astrophysics (2007), 461

A new method is presented for determining the point spread function (PSF) of images that lack bright and isolated stars. It is based on the same principles as the MCS image deconvolution algorithm. It ... [more ▼]

A new method is presented for determining the point spread function (PSF) of images that lack bright and isolated stars. It is based on the same principles as the MCS image deconvolution algorithm. It uses the information contained in all stellar images to achieve the double task of reconstructing the PSFs for single or multiple exposures of the same field and to extract the photometry of all point sources in the field of view. The use of the full information available allows us to construct an accurate PSF. The possibility to simultaneously consider several exposures makes it well suited to the measurement of the light curves of blended point sources from data that would be very difficult or even impossible to analyse with traditional PSF fitting techniques. The potential of the method for the analysis of ground-based and space-based data is tested on artificial images and illustrated by several examples, including HST/NICMOS images of a lensed quasar and VLT/ISAAC images of a faint blended Mira star in the halo of the giant elliptical galaxy NGC 5128 (Cen A). [less ▲]

Detailed reference viewed: 25 (4 ULg)