275 research outputs found
The emission line spectrum of the UV deficient quasar Ton 34: evidence of shock excitation?
Emission lines in quasars are believed to originate from a photoionized
plasma. There are, however, some emission features which appear to be
collisionally excited, such as the FeII multiplet bands. Shortward of Ly_alpha,
there also are a few permitted lines of species from low to intermediate
ionization. Ton 34 (z=1.928) exhibits the steepest far-UV continuum decline
known (Fnu propto nu^{-5.3}) shortward of 1050A. This object also emits
unusually strong low to intermediate excitation permitted lines shortward of
the Lyman limit. Using archive spectra of Ton 34 from HST, IUE and Palomar, we
measure the fluxes of all the lines present in the spectra and compare their
relative intensities with those observed in composite quasar spectra. Our
analysis reveals unusual strengths with respect to Ly_alpha of the following
low to intermediate excitation permitted lines: OII+OIII (835A), NIII+OIII
(686-703A) and NIII+NIV (765A). We compare the observed line spectrum with both
photoionization and shock models. Photoionization cannot reproduce the
strengths of these far-UV lines. Shocks with Vs ~ 100 km/s turn out to be
extremely efficient emitters of these lines and are favored as excitation
mechanism.Comment: 5 figures, accepted for publication in A&
Host Galaxies of low z Radio-loud Quasars: A search of HST archives
We searched the HST archives for unpublished WFPC2 images of low redshift
(z<0.5) radio loud quasars (RLQ). This led to the identification of 11 objects.
We present here the results of the analysis of these images from which we
derive the properties of their host galaxies. All objects are clearly resolved
and their surrounding nebulosity is consistent with an elliptical galaxy model.
These new data, together with previous published HST observations, form a
sample of 34 sources which significantly expands all previous studies of low
redshift RLQ based on HST data. For this full sample we derive the average
absolute magnitude of the host galaxies =-24.01+/-0.48, and the effective
radius =10.5+/-3.7kpc. No significant correlation is found between the
nucleus and the host galaxy luminosity. Using the relationship between black
hole mass (M_BH) and bulge luminosity we investigate the relation between M_BH
and total radio power for RLQ and compare with other classes of radio sources.
The overall distribution of AGN in the plane M_BH-P(radio) exhibits a trend for
increasing M_BH with increasing P(radio) but with a substantial spread. RLQ
occupy the region of most powerful sources and most massive BH. The quasars
appear to emit over a wide range of power with respect to their Eddington
luminosity as deduced by the estimated M_BH.Comment: 23 pages, 8 figures, ApJ in pres
Comment on "Correlation of the Highest-Energy Cosmic Rays with Nearby Extragalactic Objects"
We argue that the data published by the Pierre Auger Collaboration
(arXiv:0711.2256) disfavor at 99% confidence level their hypothesis that most
of the highest-energy cosmic rays are protons from nearby astrophysical
sources, either Active Galactic Nuclei or other objects with a similar spatial
distribution.Comment: 1000 words, 2 figures, scicite.st
The nature of the absorbing torus in compact Radio Galaxies
We present BeppoSAX observations of the two radio galaxies PKS 1934-63 and S5
1946+708. Strong Iron Kalpha lines are detected in both objects indicating that
the two sources are absorbed by column densities higher than 10^24 cm^(-2).
Combining radio continuum, HI absorption and X-ray data we can constrain the
physical state and the dimensions of the absorber. We find that the putative
obscuring torus is molecular and located at a distance higher than 20 pc from
the center in S5 1946+70. In PKS 1934-63 no radio nucleus has been observed. If
this is due to free-free absorption a radius of only a few pc is inferred.
Since the Kalpha lines have been detected only at 90% confidence, we also
discuss the implications if they would be not as strong as found from our data.
From our results it appears that the combination of hard X-ray data and
spatially resolved HI absorption measurements provides a powerful diagnostic
for conditions in the absorbing ``torus''.Comment: 8 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
Deep Chandra and multicolor HST observations of the jets of 3C 371 and PKS 2201+044
This paper presents multiwavelength imaging and broad-band spectroscopy of
the relativistic jets in the two nearby radio galaxies 3C 371 and PKS 2201+044,
acquired with Chandra, HST, VLA, and Merlin. Radio polarization images are also
available. The two sources stand out as "intermediate'' between FRIs and FRIIs;
their cores are classified as BL Lacs, although broad and narrow optical
emission lines were detected at times. The multiwavelength images show jet
morphologies with the X-ray emission peaking closer to the nucleus than the
longer wavelengths. The jets are resolved at all wavelengths in a direction
perpendicular to the jet axis. The jets SEDs are consistent with a single
spectral component from radio to X-rays, interpreted as synchrotron emission.
The SEDs show a progressive softening from the inner to the outer regions of
the jet, indicating that the electron break energy moves to lower energies with
distance from the core. Overall, the X-ray and multiwavelength properties of
the jets of 3C 371 and PKS 2201+044 appear intermediate between those of FRIs
and FRIIs.Comment: Accepted for publication in ApJ; 28 pages (emulateapj5), 17 figure
QSO's from Galaxy Collisions with Naked Black Holes
In the now well established conventional view (see Rees [1] and references
therein), quasi-stellar objects (QSOs) and related active galactic nuclei (AGN)
phenomena are explained as the result of accretion of plasma onto giant black
holes which are postulated to form via gravitational collapse of the high
density regions in the centers of massive host galaxies. This model is
supported by a wide variety of indirect evidence and seems quite likely to
apply at least to some observed AGN phenomena. However, one surprising set of
new Hubble Space Telescope (HST) observations [2-4] directly challenges the
conventional model, and the well known evolution of the QSO population raises
some additional, though not widely recognized, difficulties. We propose here an
alternative possibility: the Universe contains a substantial independent
population of super-massive black holes, and QSO's are a phenomenon that occurs
due to their collisions with galaxies or gas clouds in the intergalactic medium
(IGM). This hypothesis would naturally explain why the QSO population declines
very rapidly towards low redshift, as well as the new HST data.Comment: plain TeX file, no figures, submitted to Natur
Diagnostics of the structure of AGN's broad line regions with reverberation mapping data: confirmation of the two-component broad line region model
We re-examine the ten Reverberation Mapping (RM) sources with public data
based on the two-component model of the Broad Line Region (BLR). In fitting
their broad H-beta lines, six of them only need one Gaussian component, one of
them has a double-peak profile, one has an irregular profile, and only two of
them need two components, i.e., a Very Broad Gaussian Component (VBGC) and an
Inter-Mediate Gaussian Component (IMGC). The Gaussian components are assumed to
come from two distinct regions in the two-component model; they are Very Broad
Line Region (VBLR) and Inter-Mediate Line region (IMLR). The two sources with a
two-component profile are Mrk 509 and NGC 4051. The time lags of the two
components of both sources satisfy ,
where and are the lags of the two components while
and represent the mean gas velocities of the two regions,
supporting the two-component model of the BLR of Active Galactic Nuclei (AGN).
The fact that most of these ten sources only have the VBGC confirms the
assumption that RM mainly measures the radius of the VBLR; consequently, the
radius obtained from the R-L relationship mainly represent the radius of VBLR.
Moreover, NGC 4051, with a lag of about 5 days in the one component model, is
an outlier on the R-L relationship as shown in Kaspi et al. (2005); however
this problem disappears in our two-component model with lags of about 2 and 6
days for the VBGC and IMGC, respectively.Comment: 7 pages, 5 figures. Accepted for publication in the Special Issue of
Science in China (G) "Astrophysics of Black holes and Related Compact
Objects
Fabry Perot Halpha Observations of the Barred Spiral NGC 3367
We report the gross properties of the velocity field of the barred spiral
galaxy NGC 3367. The following values were found: inclination with respect to
the plane of the sky, i=30 deg; position angle (PA) of receding semi major axis
PA=51 and systemic velocity V(sys)=3032 km/s. Large velocity dispersion are
observed of upt o 120 km/s in the nuclear region, of up to 70 km/s near the
eastern bright sources just beyond the edge of the stellar bar where three
spiral arms seem to start and in the western bright sources at about 10 kpc.
Deviations from normal circular velocities are observed from all the disk but
mainly from the semi circle formed by the string of south western Halpha
sources. An estimate of the dynamical mass is M(dyn)=2x10^11 Msolar.Comment: Accepted to be published in May 2001 issue in the A.J. 19 pages, 7
figure
EUVE J0425.6-5714: A Newly Discovered AM Herculis Star
We detected a new AM Her star serendipitously in a 25 day observation with
the EUVE satellite. A coherent period of 85.82 min is present in the EUVE Deep
Survey imager light curve of this source. A spectroscopic identification is
made with a 19th magnitude blue star that has H and He emission lines, and
broad cyclotron humps typical of a magnetic cataclysmic variable. A lower limit
to the polar magnetic field of 46 MG is estimated from the spacing of the
cyclotron harmonics. EUVE J0425.6-5714 is also detected in archival ROSAT HRI
observations spanning two months, and its stable and highly structured light
curve permits us to fit a coherent ephemeris linking the ROSAT and EUVE data
over a 1.3 yr gap. The derived period is 85.82107 +/- 0.00020 min, and the
ephemeris should be accurate to 0.1 cycles until the year 2005. A narrow but
partial X-ray eclipse suggests that this object belongs to the group of Am Her
stars whose viewing geometry is such that the accretion stream periodically
occults the soft X-ray emitting accretion spot on the surface of the white
dwarf. A non-detection of hard X-rays from ASCA observations that are
contemporaneous with the ROSAT HRI shows that the soft X-rays must dominate by
at least an order of magnitude, which is consistent with a known trend among AM
Her stars with large magnetic field. This object should not be confused with
the Seyfert galaxy 1H 0419-577 (= LB 1727), another X-ray/EUV source which lies
only 4' away, and was the principal target of these monitoring observations.Comment: 13 pages, 5 figures, to appear in PASP, Dec. 1998 issu
Five new INTEGRAL unidentified hard X-Ray sources uncovered by Chandra
The IBIS imager on board INTEGRAL, with a sensitivity better than a mCrab in
deep observations and a point source location accuracy of the order of few
arcminutes, has localized so far 723 hard X-ray sources in the 17--100 keV
energy band, of which a fraction of about 1/3 are still unclassified. The aim
of this research is to provide sub-arcsecond localizations of the unidentified
sources, necessary to pinpoint the optical and/or infrared counterpart of those
objects whose nature is so far unknown. The cross-correlation between the new
IBIS sources published within the fourth INTEGRAL/IBIS Survey catalogue and the
CHANDRA/ACIS data archive resulted in a sample of 5 not yet identified objects.
We present here the results of CHANDRA X-ray Observatory observations of these
five hard X-ray sources discovered by the INTEGRAL satellite. We associated IGR
J10447-6027 with IR source 2MASSJ10445192-6025115, IGR J16377-6423 with the
cluster CIZA J1638.2-6420, IGR J14193-6048 with the pulsar with nebula PSR
J1420-6048 and IGR J12562+2554 with the Quasar SDSSJ125610.42+260103.5. We
suggest that the counterpart of IGR J12288+0052 may be an AGN/QSO type~2 at a
confidence level of 90%.Comment: ApJ accepte
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