580 research outputs found
The Fluctuating Intergalactic Radiation Field at Redshifts z = 2.3-2.9 from He II and H I Absorption towards HE 2347-4342
We provide an in-depth analysis of the He II and H I absorption in the
intergalactic medium (IGM) at redshifts z = 2.3-2.9 toward HE 2347-4342, using
spectra from the Far Ultraviolet Spectroscopic Explorer (FUSE) and the
Ultraviolet-Visual Echelle Spectrograph (UVES) on the VLT telescope. Following
up on our earlier study (Kriss et al. 2001, Science, 293, 1112), we focus here
on two major topics: (1) small-scale variability (Delta z = 10^-3) in the ratio
eta = N(He II)/N(H I); and (2) an observed correlation of high-eta absorbers
(soft radiation fields) with voids in the (H I) Ly-alpha distribution. These
effects may reflect fluctuations in the ionizing sources on scales of 1 Mpc,
together with radiative transfer through a filamentary IGM whose opacity
variations control the penetration of 1-5 ryd radiation over 30-40 Mpc
distances. Owing to photon statistics and backgrounds, we can measure optical
depths over the ranges 0.1 < tau(HeII) < 2.3 and 0.02 < tau(HI) < 3.9, and
reliably determine values of eta = 4 tau(HeII)/tau(HI) over the range 0.1 to
460. Values of eta = 20-200 are consistent with models of photoionization by
quasars with observed spectral indices alpha_s = 0-3. Values of eta > 200 may
require additional contributions from starburst galaxies, heavily filtered
quasar radiation, or density variations. Regions with eta < 30 may indicate the
presence of local hard sources. We find that eta is higher in "void" regions,
where H I is weak or undetected and 80% of the path length has eta > 100. These
voids may be ionized by soft sources (dwarf starbursts) or by QSO radiation
softened by escape from the AGN cores or transfer through the "cosmic web". The
apparent differences in ionizing spectra may help to explain the 1.45 Gyr lag
between the reionization epochs, z(HI) = 6.2 +/-0.2 and z(HeII) = 2.8 +/-0.2.Comment: 27 pages, 7 figures, to appear in Ap
Multiwavelength campaign on Mrk 509 XII. Broad band spectral analysis
(Abridged) The simultaneous UV to X-rays/gamma rays data obtained during the
multi-wavelength XMM/INTEGRAL campaign on the Seyfert 1 Mrk 509 are used in
this paper and tested against physically motivated broad band models. Each
observation has been fitted with a realistic thermal comptonisation model for
the continuum emission. Prompted by the correlation between the UV and soft
X-ray flux, we use a thermal comptonisation component for the soft X-ray
excess. The UV to X-rays/gamma-rays emission of Mrk 509 can be well fitted by
these components. The presence of a relatively hard high-energy spectrum points
to the existence of a hot (kT~100 keV), optically-thin (tau~0.5) corona
producing the primary continuum. On the contrary, the soft X-ray component
requires a warm (kT~1 keV), optically-thick (tau~15) plasma. Estimates of the
amplification ratio for this warm plasma support a configuration close to the
"theoretical" configuration of a slab corona above a passive disk. An
interesting consequence is the weak luminosity-dependence of its emission, a
possible explanation of the roughly constant spectral shape of the soft X-ray
excess seen in AGNs. The temperature (~ 3 eV) and flux of the soft-photon field
entering and cooling the warm plasma suggests that it covers the accretion disk
down to a transition radius of 10-20 . This plasma could be the
warm upper layer of the accretion disk. On the contrary the hot corona has a
more photon-starved geometry. The high temperature ( 100 eV) of the
soft-photon field entering and cooling it favors a localization of the hot
corona in the inner flow. This soft-photon field could be part of the
comptonised emission produced by the warm plasma. In this framework, the change
in the geometry (i.e. ) could explain most of the observed flux and
spectral variability.Comment: 19 pages, 14 figures. Accepted for publication in A&
Ultraviolet Broad Absorption Features and the Spectral Energy Distribution of the QSO PG 1351+64
We present a moderate-resolution (~20 km/s) spectrum of the mini
broad-absorption-line QSO PG1351+64 between 915-1180 A, obtained with the Far
Ultraviolet Spectroscopic Explorer (FUSE). Additional spectra at longer
wavelengths were also obtained with the HST and ground-based telescopes. Broad
absorption is present on the blue wings of CIII 977, Ly-beta, OVI 1032,1038,
Ly-alpha, NV 1238,1242, SiIV 1393,1402, and CIV 1548,1450. The absorption
profile can be fitted with five components at velocities of ~ -780, -1049,
-1629, -1833, and -3054 km/s with respect to the emission-line redshift of z =
0.088. All the absorption components cover a large fraction of the continuum
source as well as the broad-line region. The OVI emission feature is very weak,
and the OVI/Lyalpha flux ratio is 0.08, one of the lowest among low-redshift
active galaxies and QSOs. The UV continuum shows a significant change in slope
near 1050 A in the restframe. The steeper continuum shortward of the Lyman
limit extrapolates well to the observed weak X-ray flux level. The absorbers'
properties are similar to those of high-redshift broad absorption-line QSOs.
The derived total column density of the UV absorbers is on the order of 10^21
cm^-2, unlikely to produce significant opacity above 1 keV in the X-ray. Unless
there is a separate, high-ionization X-ray absorber, the QSO's weak X-ray flux
may be intrinsic. The ionization level of the absorbing components is
comparable to that anticipated in the broad-line region, therefore the
absorbers may be related to broad-line clouds along the line of sight.Comment: 23 pages, Latex, 5 figure
Multiwavelength campaign on Mrk 509: testing realistic comptonization models
Mrk 509 was observed by XMM-Newton and INTEGRAL in October/November 2009, with one observation every four days for a total of ten observations. Each observation has been fitted with a realistic thermal Comptonization model for the continuum emission. Prompted by the correlation between the UV and soft X-ray flux, we used a thermal Comptonization component for the soft X-ray excess. The UV to X-ray/gamma-ray emission of Mrk 509 can be well fitted by these components, pointing to the existence of a hot (kT ⌠100 keV), optically-thin (Ï âŒ 0.5) corona producing the primary continuum. In contrast, the soft X-ray component requires a warm (kT ⌠1 keV), optically-thick (Ï âŒ 10-20) plasma. Estimates of the amplification ratio for this warm plasma support a configuration relatively close to the âtheoreticalâ configuration of a slab corona above a passive disk. This plasma could be the warm upper layer of the accretion disk. In contrast, the hot corona has a more photon-starved geometry. The high temperature (⌠100 eV) of the soft-photon field entering and cooling it favors a localization of the hot corona in the inner flow. This soft-photon field could be part of the comptonized emission produced by the warm plasma
Understanding AGN-Host Connection in Partially Obscured Active Galactic Nuclei. Part I: The Nature of AGN+HII Composites
The goal of our serial papers is to examine the evolutionary connection
between AGN and star formation in its host galaxy in the partially obscured
AGNs (i.e., Seyfert 1.8 and 1.9 galaxies). Taking advantage of these galaxies,
the properties of both components can be studied together by direct
measurements. In this paper, we focus on the broad-line composite galaxies
(composite AGNs) which are located between the theoretical and empirical
separation lines in the [NII]/Ha vs. [OIII]/Hb diagram. These galaxies are
searched for from the composite galaxies provided by the SDSS DR4 MPA/JHU
catalogs. After re-analyze the spectra, we perform a fine classification for
the 85 composite AGNs in terms of the BPT diagrams. All the objects located
below the three theoretical separation lines are associated with a young
stellar population (<1Gyrs), while either a young or old stellar population is
identified in the individual multiply-classified object. The
multiply-classified objects with a very old stellar population are located in
the LINER region in the [OI]/Ha vs. [OIII]/Hb diagram. We then consider the
connection between AGN and star formation to derive the key results. The
Eddington ratio inferred from the broad Ha emission, the age of the stellar
population of AGN's host as assessed by D_n(4000), and the line ratio [OI]/Ha
are found to be related with each other. These relations strongly support the
evolutionary scenario in which AGNs evolve from high L/L_Edd state with soft
spectrum to low L/L_Edd state with hard spectrum as young stellar population
ages and fades. The significant correlation between the line ratio [OI]/Ha and
D_n(4000) leads us to suggest that the line ratio could be used to trace the
age of stellar population in type I AGNs.Comment: 39 pages, 11 figures, 1 table, accepted by Ap
HUT observations of carbon monoxide in the coma of Comet Levy (1990c)
Observations of comet Levy (1990c) were made with the Hopkins Ultraviolet Telescope during the Astro-1 Space Shuttle mission on 10 Dec. 1990. The spectrum, covering the wavelength range 415 to 1850 A at a spectral emission of 3 A (in first order), shows the presence of carbon monoxide and atomic hydrogen, carbon, and sulfur in the coma. Aside from H I Lyman-beta, no cometary features are detected below 1200 A, although cometary O I and O II would be masked by the same emissions present in the day airglow spectrum. The 9.4 x 116 arcsec aperture corresponds to 12,000 x 148,000 km at the comet. The derived production rate of CO relative to water, 0.13 + or - 0.02, compared with the same ratio derived from IUE observations (made in Sep. 1990) which sample a much smaller region of the coma, 0.04 + or - 0.01, suggests the presence of an extended source of CO, as was found in comet Halley. Upper limits on Ne and Ar abundance are within an order of magnitude or solar abundances
Multiwavelength campaign on Mrk 509 XV. A global modeling of the broad emission lines in the Optical, UV and X-ray bands
We model the broad emission lines present in the optical, UV and X-ray
spectra of Mrk 509, a bright type 1 Seyfert galaxy. The broad lines were
simultaneously observed during a large multiwavelength campaign, using the
XMM-Newton-OM for the optical lines, HST-COS for the UV lines and
XMM-Newton-RGS and Epic for the X-ray lines respectively. We also used FUSE
archival data for the broad lines observed in the far-ultra-violet. The goal is
to find a physical connection among the lines measured at different wavelengths
and determine the size and the distance from the central source of the emitting
gas components. We used the "Locally optimally emission Cloud" (LOC) model
which interprets the emissivity of the broad line region (BLR) as regulated by
powerlaw distributions of both gas density and distances from the central
source. We find that one LOC component cannot model all the lines
simultaneously. In particular, we find that the X-ray and UV lines likely may
originate in the more internal part of the AGN, at radii in the range
~5x10^{14}-3x10^{17} cm, while the optical lines and part of the UV lines may
likely be originating further out, at radii ~3x10^{17}-3x^{18} cm. These two
gas components are parametrized by a radial distribution of the luminosities
with a slope gamma of ~1.15 and ~1.10, respectively, both of them covering at
least 60% of the source. This simple parameterization points to a structured
broad line region, with the higher ionized emission coming from closer in,
while the emission of the low-ionization lines is more concentrated in the
outskirts of the broad line region.Comment: 10 pages, 5 figures, accepted for publication in Astronomy and
Astrophysic
Multiwavelength campaign on Mrk 509. V. Chandra-LETGS observation of the ionized absorber
We present here the results of a 180 ks Chandra-LETGS observation as part of
a large multi-wavelength campaign on Mrk 509. We study the warm absorber in Mrk
509 and use the data from a simultaneous HST-COS observation in order to assess
whether the gas responsible for the UV and X-ray absorption are the same. We
analyzed the LETGS X-ray spectrum of Mrk 509 using the SPEX fitting package. We
detect several absorption features originating in the ionized absorber of the
source, along with resolved emission lines and radiative recombination
continua. The absorption features belong to ions with, at least, three distinct
ionization degrees. The lowest ionized component is slightly redshifted (v =
+73 km/s) and is not in pressure equilibrium with the others, and therefore it
is not likely part of the outflow, possibly belonging to the interstellar
medium of the host galaxy. The other components are outflowing at velocities of
-196 and -455 km/s, respectively. The source was observed simultaneously with
HST-COS, finding 13 UV kinematic components. At least three of them can be
kinematically associated with the observed X-ray components. Based on the
HST-COS results and a previous FUSE observation, we find evidence that the UV
absorbing gas might be co-located with the X-ray absorbing gas and belong to
the same structure.Comment: 12 pages, 7 figures, 9 tables. Accepted for publication in Astronomy
& Astrophysic
A Composite HST Spectrum of Quasars
We construct a composite quasar spectrum from 284 HST FOS spectra of 101
quasars with redshifts z > 0.33. The spectrum covers the wavelengths between
350 and 3000 A in the rest frame. There is a significant steepening of the
continuum slope around 1050 A. The continuum between 1050 and 2200 A can be
modeled as a power law with alpha = -0.99. For the full sample the power-law
index in the extreme ultraviolet (EUV) between 350 and 1050 A is alpha = -1.96.
The continuum flux in the wavelengths near the Lyman limit shows a depression
of about 10 percent. The break in the power-law index and the slight depression
of the continuum near the Lyman limit are features expected in Comptonized
accretion-disk spectra.Comment: 10 figures To appear in the February 1, 1997, issue of the Ap.
- âŠ