16 research outputs found
HST Observations of the Double-Peaked Emission Lines in the Seyfert Galaxy Markarian 78: Mass Outflows from a Single AGN
Previous ground based observations of the Seyfert 2 galaxy Mrk 78 revealed a
double set of emission lines, similar to those seen in several AGN from recent
surveys. Are the double lines due to two AGN with different radial velocities
in the same galaxy, or are they due to mass outflows from a single AGN?We
present a study of the outflowing ionized gas in the resolved narrow-line
region (NLR) of Mrk 78 using observations from Space Telescope Imaging
Spectrograph (STIS) and Faint Object Camera (FOC) aboard the Hubble Space
Telescope(HST) as part of an ongoing project to determine the kinematics and
geometries of active galactic nuclei (AGN) outflows. From the spectroscopic
information, we deter- mined the fundamental geometry of the outflow via our
kinematics modeling program by recreating radial velocities to fit those seen
in four different STIS slit positions. We determined that the double emission
lines seen in ground-based spectra are due to an asymmetric distribution of
outflowing gas in the NLR. By successfully fitting a model for a single AGN to
Mrk 78, we show that it is possible to explain double emission lines with
radial velocity offsets seen in AGN similar to Mrk 78 without requiring dual
supermassive black holes.Comment: 22 pages, 7 figures (2 color), accepted for publication in The
Astrophysical Journa
Weak lensing analysis of MS 1008-1224 with the VLT
We present a gravitational lensing analysis of the cluster of galaxies MS
1008-1224 (z=0.30), based on very deep observations obtained using the VLT with
FORS and ISAAC during the science verification phase. We reconstructed the
projected mass distribution from B,V,R,I bands using two different methods
independently. The mass maps are remarkably similar, which confirm that the PSF
correction worked well. The ISAAC and FORS data were combined to measure the
photometric redshifts and constrain the redshift distribution of the lensed
sources. The total mass inferred from weak shear is 2.3 10^{14} h^{-1} Mo on
large scales, in agreement with the X-ray mass. The measured mass profile is
well fit by both Navarro, Frenk and White and isothermal sphere with core
radius models although the NFW is slightly better. In the inner regions, the
lensing mass is about 2 times higher than the X-ray mass, which supports the
view that complex physical processes in the innermost parts of clusters are
responsible for the X-ray/lensing mass discrepancy. The central part of the
cluster is composed of two mass peaks whose the center of mass is 15 arcsecond
north of the cD galaxy. This provides an explanation for the 15 arcsecond
offset between the cD and the center of the X-ray map reported elsewhere. The
optical, X-ray and the mass distributions show that MS 1008-1224 is composed of
many subsystems which are probably undergoing a merger. MS 1008-1224 shows a
remarkable case of cluster-cluster lensing. The photometric redshifts show an
excess of galaxies located 30 arcseconds south-west of the cD galaxy at a
redshift of about 0.9 which is lensed by MS 1008-1224. These results show the
importance of getting BVRIJK images silmultenously. The VLT is a unique tool to
provide such datasets.Comment: 22 pages, submitted to A&A, paper with `big' figures available at
ftp://ftp.cita.utoronto.ca/pub/waerbeke/ms1008paper
Implications of Cosmological Gamma-Ray Absorption - I.Evolution of the Metagalactic Radiation Field
Gamma-ray absorption due to gamma-gamma-pair creation on cosmological scales
depends on the line-of-sight integral of the evolving density of low-energy
photons in the Universe, i.e. on the history of the diffuse, isotropic
radiation field. Here we present and discuss a semi-empirical model for this
metagalactic radiation field based on stellar light produced and reprocessed in
evolving galaxies. With a minimum of parameters and assumptions, the
present-day background intensity is obtained from the far-IR to the ultraviolet
band. Predicted model intensities are independent of cosmological parameters,
since we require that the comoving emissivity, as a function of redshift,
agrees with observed values obtained from deep galaxy surveys. The far-infrared
background at present day prediced from optical galaxy surveys falls short in
explaining the observed one, and we show that this deficit can be removed by
taking into account (ultra)luminous infrared galaxies (ULIGs/LIGs) with a
seperate star formation rate. The accuracy and reliability of the model, out to
redshifts of 5, allow a realistic estimate of the attenuation length of
GeV-to-TeV gamma-rays and its uncertainty, which is the focus of a subsequent
paper.Comment: 12 pages, 6 figures; accepted for publication in Astronomy and
Astrophysic
Predictions of Quasar Clustering: Redshift, Luminosity and Selection Dependence
We show that current clustering observations of quasars and luminous AGN can
be explained by a merger model augmented by feedback from outflows. Using
numerical simulations large enough to study clustering out to 25 comoving
h^{-1} Mpc, we calculate correlation functions, biases, and correlation lengths
as a function of AGN redshift and optical and X-ray luminosity. At optical
wavelengths, our results match a wide range of current observations and
generate predictions for future data sets. We reproduce the weak luminosity
dependence of clustering over the currently well-measured range, and predict a
much stronger dependence at higher luminosities. The increase in the amplitude
of binary quasar clustering observed in the Sloan Digital Sky Survey (SDSS) is
also reproduced and is predicted to occur at higher redshift, an effect that is
due to the one halo term in the correlation function. On the other hand, our
results do not match the rapid evolution of the correlation length observed in
the SDSS at z\simeq 3, a discrepancy that is at least partially due to
differences in the scales probed by our simulation versus this survey. In fact,
we show that changing the distances sampled from our simulations can produce
changes as large as 40% in the fitted correlation lengths. Finally, in the
X-ray, our simulations produce correlation lengths similar to that observed in
the Chandra Deep Field (CDF) North, but not the significantly larger
correlation length observed in the CDF South.Comment: 13 page, 7 figures. Accepted for publication in Ap
An ISOCAM survey through gravitationally lensing galaxy clusters
ISOCAM was used to perform a deep survey through three gravitationally
lensing clusters of galaxies. Nearly seventy sq. arcmin were covered over the
clusters A370, A2218 and A2390. We present maps and photometry at 6.7 & 14.3
microns, showing a total of 145 mid-IR sources and the associated source
counts. The 15 micron counts reach the faintest level yet recorded. All sources
have counterparts in the optical or near-IR. Models of the clusters were used
to correct for the effects of lensing, which increases the sensitivity of the
survey. Seven of fifteen SCUBA sources were detected at 15 microns. Five have
redshift between 0.23 & 2.8, with a median of 0.9. The field sources were
counted to a lensing-corrected sensitivity of 30 microJy at 15 microns, and 14
microJy at 7 microns. The counts, corrected for completeness, contamination by
cluster sources and lensing, confirm and extend findings of an excess by a
factor of ten in the 15 micron population with respect to source models with no
evolution. Source redshifts are mostly between 0.4 and 1.5. For the counts at 7
microns, integrating from 14 microJy to 460 microJy, we resolve 0.49+/-0.2
nW.m^(-2).sr^(-1) of the infrared background light (IBL) into discrete sources.
At 15 microns we include the counts from other ISOCAM surveys to integrate from
30 microJy to 50 mJy, two to three times deeper than unlensed surveys, to
resolve 2.7+/-0.62 nW.m^(-2).sr^(-1) of the IBL. These values are 10% and 55%,
respectively, of the upper limit to the IBL, derived from photon-photon pair
production of the TeV gamma rays from BL-Lac sources on the IBL photons.
However, recent detections of TeV gamma rays from the z=0.129 BL Lac H1426+428
suggest that the 15 micron background reported implies substantial absorption
of TeV photons from that source.Comment: 35 pages, 17 figures, to appear in Astronomy and Astrophysics, full
paper with high-resolution figures available at
http://www.iso.vilspa.esa.es/science/pub/2003
Radio Sources in Low-Luminosity Active Galactic Nuclei. III. "AGNs" in a Distance-Limited Sample of "LLAGNs"
(abbreviated): This paper presents the results of a high resolution radio
imaging survey of all known (96) low-luminosity active galactic nuclei (LLAGNs)
at D<19Mpc. We find that almost half of all LINERs and low-luminosity Seyferts
have flat-spectrum radio cores when observed at 150mas resolution. Higher
(2mas) resolution observations of a flux-limited subsample have provided a 100%
(16 of 16) detection rate of pc-scale radio cores, with implied brightness
temperatures > 10^8 K. The five LLAGNs with the highest core radio fluxes also
have pc-scale `jets.' Compact radio cores are almost exclusively found in
massive ellipticals and in type1 nuclei. The core radio power is correlated
with the nuclear optical `broad' Halpha luminosity, the nuclear optical
`narrow' emission line luminosity and width, and with the galaxy luminosity. In
these correlations LLAGNs fall close to the low-luminosity extrapolations of
more powerful AGNs. About half of all LLAGNs with multiple epoch data show
significant inter-year radio variability.
Investigation of a sample of ~150 nearby bright galaxies, most of them
LLAGNs, shows that the nuclear (<150mas size) radio power is strongly
correlated with both the black hole mass and the galaxy bulge luminosity;
linear regression fits to all ~150 galaxies give: log P(2cm) = 1.31 log
M_blackhole + 8.77 and log P(2cm) = 1.89 log L_B(bulge) - 0.17. Low accretion
rates are implied in both advection- and jet-type models. In brief, all
evidence points towards the presence of accreting massive black holes in a
large fraction, perhaps all, of LLAGNs.Comment: to appear in A&
Galaxy Collisions - Dawn of a New Era
The study of colliding galaxies has progressed rapidly in the last few years,
driven by observations with powerful new ground and space-based instruments.
These instruments have used for detailed studies of specific nearby systems,
statistical studies of large samples of relatively nearby systems, and
increasingly large samples of high redshift systems. Following a brief summary
of the historical context, this review attempts to integrate these studies to
address the following key issues. What role do collisions play in galaxy
evolution, and how can recently discovered processes like downsizing resolve
some apparently contradictory results of high redshift studies? What is the
role of environment in galaxy collisions? How is star formation and nuclear
activity orchestrated by the large scale dynamics, before and during merger?
Are novel modes of star formation involved? What are we to make of the
association of ultraluminous X-ray sources with colliding galaxies? To what do
degree do mergers and feedback trigger long-term secular effects? How far can
we push the archaeology of individual systems to determine the nature of
precursor systems and the precise effect of the interaction? Tentative answers
to many of these questions have been suggested, and the prospects for answering
most of them in the next few decades are good.Comment: 44 pages, 9 figures, review article in press for Astrophysics Update
Vol.
The X-Ray Weakness of GPS Radio Galaxies: A Volume-Limited Complete Sample
The XMM-Newton observations of the GPS sample was completed last summer. We are in process of finalizing the paper describing the data and the results. The main goal of the project was to determine the X-ray spectra of the GPS galaxies in comparison to regular radio galaxies. Our XMM observations show evidence that the GPS galaxies are heavily obscured with the large absorbing columns exceeding N(H)greater than le22 cm^-2. Taking into account the obscuration we determined that the intrinsic X-ray luminosities of GPS galaxies are of order le43-le44 erg/s, comparable to low luminosity radio loud quasars. The large GPS samples can confirm the result, as at this moment our evidence is based only on 7 GPS galaxies observed with good S/N/ in X-rays. The first paper summarizing the results of the XMM observation of Mkn 668 has been published Astronomy & Astrophysics. We found soft X-ray signatures of a hot plasma (kT approximately 10^7~K) and a hard X-ray emission from the nucleus. The X-ray spectrum above 2.5-keV is characterized by a very flat (observed photon index, Gamma-0.5) power-law continuum, alongside with a strong Fe-K-alpha neutral iron fluorescent line (EW~600-eV). The best explanation for the origin of this high energy X-ray emission is in terms of the Compton-reflection of the nuclear emission. The primary X-ray emission is obscured by a Compton-thick (N_H ~ to 10^24 ~cm-2) matter which becomes transparent at higher energies. The observed above 2.5-keV X-rays are mostly due to reflection which is indicated by a strong Fe-K-alpha line. This source represented the second hard X-ray detection of the GPS galaxy ever (the first one being 1345+125; O'Dea et al. 2000). The observations of the other GPS galaxies in our sample confirmed the trend of the large obscuration present in the spectra. However, we do not have a compelling evidence for a hot gas in the nucleus. The two other GPS galaxies observed with Chandra were added to the total of 7 GPS galaxies. This GPS sample was compared against the sample of radio loud galaxies and quasar. The paper is about to be submitted. Our preliminarily results based on the XMM-Newton data for the entire sample were presented at the meeting in July 2004