228 research outputs found
Miscellaneous observations of active galactic nuclei. II
We observed 37 AGN candidates and classified them on the basis of their
spectroscopic properties; three are confirmed QSOs, one is a BL Lac object,
nine are Seyfert 1 galaxies, four Seyfert 2s, while twenty are HII regions.Comment: LaTeX 2e, 15 pages (4 tables and 9 .eps figures included in text).
Uses L-AA 3.0, epsf.tex and psfig.sty (not included). Accepted to appear in
A&
The "red shelf" of the Hb line in the Seyfert 1 galaxies RXS J01177+3637 and HS 0328+05
A few Seyfert 1s have a Hb profile with a red wing usually called the "red
shelf". The most popular interpretation of this feature is that it is due to
broad redshifted lines of Hb and [OIII]4959,5007; we have observed two Seyfert
1s displaying a "red shelf" and showed that in these two objects the main
contributor is most probably the HeI 4922,5016 lines having the velocity and
width of the broad Hb component. There is no evidence for the presence of a
broad redshifted component of Hb or [OIII] in any of these two objects.Comment: LaTeX file (uses AA vers. 5.1 class, enclosed), 8 pages, 9 figures.
Accepted for publication in Astronomy & Astrophysics. Also available at
http://www.obs-hp.fr/www/preprints.htm
A spectrophotometric atlas of Narrow-Line Seyfert 1 galaxies
We have compiled a list of 83 objects classified as Narrow-Line Seyfert 1
galaxies (NLS1s) or known to have a broad Balmer component narrower than 2000
km/s. Out of these, 19 turned out to have been spectroscopically misidentified
in previous studies; only 64 of the selected objects are genuine NLS1s. We have
spectroscopically observed 59 of them and tried to characterize their Narrow
and Broad-Line Regions (NLR and BLR) by fitting the emission-lines with
Gaussian and/or Lorentzian profiles. In most cases, the broad Balmer components
are well fitted by a single Lorentzian profile. This has consequences
concerning their FWHMs and line ratios: when the broad Balmer components are
fitted with a Lorentzian, most narrow line regions have line ratios typical of
Seyfert 2s while, when a Gaussian profile isused for fitting the broad Balmer
components, the line ratios are widely scattered in the usual diagnostic
diagrams (Veilleux & Osterbrock 1987). We find that, in general, the [O III]
lines have a relatively narrow Gaussian profile (~ 200-500 km/s FWHM) with
often, in addition, a second broad (~ 500-1800 km/s FWHM), blueshifted Gaussian
component. We do not confirm that the [O III] lines are weak in NLS1s. As
previously suggested, there is a continuous transition of all properties
between NLS1s and classical Broad-Line Seyfert 1 Galaxies (BLS1s) and the limit
of 2000 km/s used to separate the two species is arbitrary; R_4570, the ratio
of the Fe II to the H_beta fluxes, could be a physically more meaningful
parameter to distinguish them. (abridged abstract)Comment: LaTeX file, 24 pages, 15 figures, uses the new A&A macro (enclosed:
aa5.cls). Figs. 1-5 and 7 are bitmapped; non-bitmapped, high quality figures
are included in the .ps and .pdf versions of the paper, available at
http://www.obs-hp.fr/www/preprints.html. Accepted for publication in
Astronomy & Astrophysic
Empirical Uncertainty Estimators for Astrometry from Digital Databases
In order to understand the positional uncertainties of arbitrary objects in
several of the current major databases containing astrometric information, a
sample of extragalactic radio sources with precise positions in the
International Celestial Reference Frame (ICRF) is compared with the available
positions of their optical counterparts. The discrepancies between the radio
and various optical positions are used to derive empirical uncertainty
estimators for the USNO-A2.0, USNO-A1.0, Guide Star Selection System (GSSS)
images, and the first and second Digitized Sky Surveys (DSS-I and DSS-II). In
addition, an estimate of the uncertainty when the USNO-A2.0 catalog is
transferred to different image data is provided. These optical astrometric
frame uncertainties can in some cases be the dominant error term when
cross-identifying sources at different wavelengths.Comment: 12 pages including 2 figures and 1 table. Accepted for publication in
The Astronomical Journal, October 1999. Values in Table 1 for DSS I corrected
99-07-1
Spectral energy distributions of a large sample of BL Lacertae objects
We have collected a large amount of multifrequency data for the objects in
the Metsahovi Radio Observatory BL Lacertae sample and computed their spectral
energy distributions (SED). This is the first time the SEDs of BL Lacs have
been studied with a sample of over 300 objects. The synchrotron components of
the SEDs were fitted with a parabolic function to determine the synchrotron
peak frequency. We checked the dependence between luminosities at several
frequency bands and synchrotron peak frequency to test the blazar sequence
scenario, which states that the source luminosity depends on the location of
the synchrotron peak. We also calculated broad band spectral indices and
plotted them against each other and the peak frequency. The range of peak
frequencies in our study was considerably extended compared to previous
studies. There were 22 objects for which log\nu_{peak}>19. The data shows that
at 5 GHz, 37 GHz and 5500 A there is negative correlation between luminosity
and nu_{peak}. There is no significant correlation between source luminosity at
synchrotron peak and peak frequency. Several low radio luminosity-low energy
peaked BL Lacs were found. The negative correlation between broad band spectral
indices and nu_{peak} is also significant, although there is substantial
scatter. Therefore we find that neither alpha_{rx} nor alpha_{ro} can be used
to determine the synchrotron peak of BL Lacs. On the grounds of our results we
conclude that the blazar sequence scenario is not valid. In all our results the
BL Lac population is continuous with no hint of the bimodality of the first BL
Lac samples.Comment: 10 + 27 pages, 13 figures, accepted to 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
Quasars in the 2MASS Second Incremental Data Release
Using the 2MASS Second Incremental Data Release, we have searched for near
infrared counterparts to 13214 quasars from the Veron-Cetty & Veron(2000)
catalog. We have detected counterparts within 4 arcsec for 2277 of the
approximately 6320 quasars within the area covered by the 2MASS Second
Incremental Data Release. Only 1.6% of these are expected to be chance
coincidences. Though this sample is heterogeneous, we find that known
radio-loud quasars are more likely to have large near-infrared-to-optical
luminosity ratios than radio-quiet quasars are, at a statistically significant
level. This is consistent with dust-reddened quasars being more common in
radio-selected samples than in optically-selected samples, due to stronger
selection effects against dust-reddened quasars in the latter. We also find a
statistically significant dearth of optically luminous quasars with large
near-infrared-to-optical luminosity ratios. This can be explained in a dust
obscuration model but not in a model where synchrotron emission extends from
the radio into the near-infrared and creates such large ratios. We also find
that selection of quasar candidates from the B-J/J-K color-color diagram,
modelled on the V-J/J-K selection method of Warren, Hewett & Foltz (2000), is
likely to be more sensitive to dust-obscured quasars than selection using only
infrared-infrared colors.Comment: To be published in May issue of Astronomical Journal (26 pages, 8
figures, 2 tables) Replaced Figure 6 and
Spectroscopy and 3D imaging of the Crab nebula
Spectroscopy of the Crab nebula along different slit directions reveals the 3
dimensional structure of the optical nebula. On the basis of the linear radial
expansion result first discovered by Trimble (1968), we make a 3D model of the
optical emission. Results from a limited number of slit directions suggest that
optical lines originate from a complicated array of wisps that are located in a
rather thin shell, pierced by a jet. The jet is certainly not prominent in
optical emission lines, but the direction of the piercing is consistent with
the direction of the X-ray and radio jet. The shell's effective radius is ~ 79
seconds of arc, its thickness about a third of the radius and it is moving out
with an average velocity 1160 km/s.Comment: 21 pages, 14 figures, submitted to ApJ, 3D movie of the Crab nebula
available at http://www.fiz.uni-lj.si/~vidrih
- …