374 research outputs found
A CO Survey of Gravitationally Lensed Quasars with the IRAM Interferometer
We present the results of a CO survey of gravitationally lensed quasars,
conducted with the Plateau de Bure Interferometer over the last three years.
Among the 18 objects surveyed, one was detected in CO line emission, while six
were detected in the continuum at 3mm and three in the continuum at 1mm. The
low CO detection rate may at least in part be due to uncertainties in the
redshifts derived from quasar broad emission lines. The detected CO source, the
z=3.2 radio quiet quasar MG0751+2716, is quite strong in the CO(4-3) line and
in the millimeter/submillimeter continuum, the latter being emission from cool
dust. The integrated CO line flux is 5.96 +- 0.45 Jy.km/s, and the total
molecular gas mass is estimated to be in the range M(H_2) = 1.6-3.1 X 10^9
solar masses.Comment: 5 pages, 2 figures, uses aa.cls and psfig.st
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.Comment: 7 pages, 2 figures To appear in Astronomy and Astrophysic
A search for clusters and groups of galaxies on the line of sight towards 8 lensed quasars
In this paper we present new ESO/VLT FORS1 and ISAAC images of the fields
around eight gravitationally lensed quasars: CTQ414, HE0230-2130,
LBQS1009-0252, B1030+074, HE1104-1805, B1359+154, H1413+117 and HE2149-2745.
When available and deep enough, HST/WFPC2 data were also used to infer the
photometric redshifts of the galaxies around the quasars. The search of galaxy
overdensities in space and redshift, as well as a weak-shear analysis and a
mass reconstruction are presented in this paper. We find that there are most
probably galaxy groups towards CTQ414, HE0230-2130, B1359+154, H1413+117 and
HE2149-2745, with a mass ~ 4x10^14 M_sol h^-1. Considering its photometric
redshift, the galaxy group discovered in the field around HE1104-1805 is
associated with the quasar rather than with the lensing potential.Comment: 14 pages, 11 figures(.jpg
Revisiting the location and environment of the central engine in NGC1068
We revisit in this paper the location of the various components observed in
the AGN of NGC1068. 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 (1997), Capetti (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.Comment: 17 pages, 11 figures, revised version for A&
Embedded clusters in NGC1808 central starburst - Near-infrared imaging and spectroscopy
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 NGC1808. We aim at confirming that these
sources are deeply embedded, young star clusters and at deriving some of their
intrinsic properties. To complement the mid-infrared data, we have collected a
set of near-infrared data with ISAAC at the VLT: J, Ks, and L' images, as well
as low-resolution, long-slit spectra for three of the sources. Surprisingly,
the new images unveil a near-infrared counterpart for only one of the
mid-infrared/radio sources, namely M8 in the L' band. All the other sources are
so deeply embedded that their emission does not pop out above an 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.Comment: accepted A&A research note, 7 pages, 4 figures and 1 tabl
Dense Molecular Gas and the Role of Star Formation in the Host Galaxies of Quasi-Stellar Objects
New millimeter-wave CO and HCN observations of the host galaxies of
infrared-excess Palomar Green quasi-stellar objects (PG QSOs) previously
detected in CO are presented. These observations are designed to assess the
validity of using the infrared luminosity to estimate star formation rates of
luminous AGN by determining the relative significance of dust-heating by young,
massive stars and active galactic nuclei (AGN) in QSO hosts and IRAS galaxies
with warm, AGN-like infrared colors. The HCN data show the PG QSO host IZw1 and
most of the warm IRAS galaxies to have high L_IR / L'_HCN (>1600) relative to
the cool IRAS galaxy population for which the median L_IR / L'_HCN ~
890(+440,-470). If the assumption is made that the infrared emission from cool
IRAS galaxies is reprocessed light from embedded star-forming regions, then
high values of L_IR / L'_HCN are likely the result of dust heating by the AGN.
Further, if the median ratio of L'_HCN / L'_CO ~ 0.06 observed for Seyfert
galaxies and IZw1 is applied to the PG QSOs not detected in HCN, then the
derived L_IR / L'_HCN correspond to a stellar contribution to the production of
L_IR of ~ 7-39%, and star formation rates ~ 2-37 M_sun/yr are derived for the
QSO hosts. Alternatively, if the far-infrared is adopted as the star formation
component of the total infrared in cool galaxies, the stellar contributions in
QSO hosts to their L_FIR are up to 35% higher than the percentages derived for
L_IR. This raises the possibility that the L_FIR in several of the PG QSO
hosts, including IZw1, could be due entirely to dust heated by young, massive
stars. Finally, there is no evidence that the global HCN emission is enhanced
relative to CO in galaxies hosting luminous AGN.Comment: LaTex, 31 pages, including 9 postscript figures, AJ, in press
(December 2006
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