48 research outputs found
Stellar Absorption Lines in the Spectra of Seyfert Galaxies
We have measured the strengths of Ca II Triplet and Mgb stellar absorption
lines in the nuclear and off-nuclear spectra of Seyfert galaxies. These
features are diluted to varying degrees by continuum emission from the active
nucleus and from young stars. Ca II Triplet strengths can be enhanced if
late-type supergiant stars dominate the near-IR light. Thus, objects with
strong Ca II Triplet and weak Mgb lines may be objects with strong bursts of
star formation. We find that for most of our sample the line strengths are at
least consistent with dilution of a normal galaxy spectrum by a power law
continuum, in accord with the standard model for AGN. However, for several
Seyferts in our sample, it appears that dilution by a power law continuum
cannot simultaneously explain strong Ca II Triplet and relatively weak Mgb.
Also, these objects occupy the region of the IRAS color-color diagram
characteristic of starburst galaxies. In these objects it appears that the
optical to near-IR emission is dominated by late-type supergiants produced in a
circumnuclear burst of star formation.Comment: 4 pages, 3 figures, to appear in Advances in Space Research,
presented at "The AGN/Host Galaxy Connection" as part of the Scientific
Assembly of COSPAR, July 12-18 Nagoya, Japa
The Eastern Filament of W50
We present new spectral (FPI and long-slit) data on the Eastern optical
filament of the well known radionebula W50 associated with SS433. We find that
on sub-parsec scales different emission lines are emitted by different regions
with evidently different physical conditions. Kinematical properties of the
ionized gas show evidence for moderately high (V ~ 100 km/s) supersonic
motions. [OIII]5007 emission is found to be multi-component and differs from
lower-excitation [SII]6717 line both in spatial and kinematical properties.
Indirect evidence for very low characteristic densities of the gas (n ~
0.1cm^{-3}) is found. We propose radiative (possibly incomplete) shock waves in
low-density, moderately high metallicity gas as the most probable candidate for
the power source of the optical filament. Apparent nitrogen over-abundance is
better understood if the location of W50 in the Galaxy is taken into account.Comment: accepted to Astronomische Nachrichten; 9 pages, 4 figures, 2 table
A spectroscopic study of NGC 6251 and its companion galaxies
Measurements of the velocities of galaxies thought to be associated with the
giant radio galaxy NGC 6251 confirm the presence of a poor cluster with a
systemic redshift of z= 0.0244 +/- 0.0004 and a line-of-sight velocity
dispersion of sigma_{z}= 283 (+109, -52) km/s. This suggests a cluster
atmosphere temperature of T = 0.7 (+0.6, -0.2) keV, which is not enough to
confine the radio jet by gas pressure. The core of NGC 6251 shows strong
emission lines of [O III] and H alpha + [N II], but there is no evidence for
line emission from the jet (detected in optical continuum by Keel (1988)).Comment: 7 pages, 2 figures, to be published in MNRA
The contribution of Narrow-Line Seyfert 1 galaxies to the soft X-ray background
The ROSAT Ultradeep HRI survey in the Lockman Hole contains a complete sample
of 91 X-ray sources with fluxes in the 0.5-2 keV band larger than 1.2 times
10e-15 erg cm-2 s-1, where over about 75 per cent of the sources are quasars or
Seyfert galaxies. During the course of our optical identification work, we have
obtained optical spectra of 67 narrow emission line galaxies (NELG), which are
physically not associated with the X-ray sources. We have derived the
equivalent width (EW) and the full width at half maximum (FWHM) for the most
prominent emission lines of 41 quasars and Seyfert galaxies taken from the
ROSAT Deep Survey (RDS), which has a flux limit of 5.5 times 10e-15 erg cm-2
s-1 in the 0.5-2.0 keV band. Furthermore we have obtained the EW and FWHM
values of the field NELGs. Here we present the spectroscopic discrimination
between RDS Seyfert galaxies and field galaxies (NELG). The analysis of the
emission lines has revealed that a single object out of 69 spectroscopically
identified AGN fits the optical criteria of Narrow-Line Seyfert 1 galaxies
(NLS1). This may indicate that NLS1 contribute only marginally to the soft
X-ray background, but we can not exclude a possible larger contribution.Comment: Invited talk presented at the Joint MPE,AIP,ESO workshop on NLS1s,
Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also available at
http://wave.xray.mpe.mpg.de/conferences/nls1-worksho
The host galaxy/AGN connection. Brightness profiles of early-type galaxies hosting Seyfert nuclei
[ABRIDGED] We recently presented evidence of a connection between the
brightness profiles of nearby early-type galaxies and the properties of the AGN
they host. The radio loudness of the AGN appears to be univocally related to
the host's brightness profile: radio-loud nuclei are only hosted by ``core''
galaxies while radio-quiet AGN are only found in ``power-law'' galaxies. We
extend our analysis here to a sample of 42 nearby (V < 7000 km/s) Seyfert
galaxies hosted by early-type galaxies. We used the available HST images to
study their brightness profiles. Having excluded complex and highly nucleated
galaxies, in the remaining 16 objects the brightness profiles can be
successfully modeled with a Nuker law with a steep nuclear cusp characteristic
of ``power-law'' galaxies (with logarithmic slope 0.51 - 1.07). This result is
what is expected for these radio-quiet AGN based on our previous findings, thus
extending the validity of the connection between brightness profile and radio
loudness to AGN of a far higher luminosity. We explored the robustness of this
result against a different choice of the analytic form for the brightness
profiles, using a Sersic law. In no object could we find evidence of a central
light deficit with respect to a pure Sersic model, the defining feature of
``core'' galaxies in this modeling framework. We conclude that, regardless of
the modeling strategy, the dichotomy of AGN radio loudness can be univocally
related to the host's brightness profile. Our general results can be re-phrased
as ``radio-loud nuclei are hosted by core galaxies, while radio-quiet AGN are
found in non-core galaxies''.Comment: Accepted for publication in A&
Automated optical identification of a large complete northern hemisphere sample of flat spectrum radio sources with S_6cm > 200 mJy
This paper describes the automated optical APM identification of radio
sources from the Jodrell Bank - VLA Astrometric Survey (JVAS), as used for the
search for distant radio-loud quasars. The sample has been used to investigate
possible relations between optical and radio properties of flat spectrum radio
sources. From the 915 sources in the sample, 756 have an optical APM
identification at a red (e) and/or blue (o) plate,resulting in an
identification fraction of 83% with a completeness and reliability of 98% and
99% respectively. About 20% are optically identified with extended APM objects
on the red plates, e.g. galaxies. However the distinction between galaxies and
quasars can not be done properly near the magnitude limit of the POSS-I plates.
The identification fraction appears to decrease from >90% for sources with a 5
GHz flux density of >1 Jy, to <80% for sources at 0.2 Jy. The identification
fraction, in particular that for unresolved quasars, is found to be lower for
sources with steeper radio spectra. In agreement with previous studies, we find
that the quasars at low radio flux density levels also tend to have fainter
optical magnitudes, although there is a large spread. In addition, objects with
a steep radio-to-optical spectral index are found to be mainly highly polarised
quasars, supporting the idea that in these objects the polarised synchrotron
component is more prominent. It is shown that the large spread in
radio-to-optical spectral index is possibly caused by source to source
variations in the Doppler boosting of the synchrotron component [Abridged].Comment: LaTex, 17 pages, 5 gif figures, 4 tables. Accepted for publication in
MNRAS. High resolution figures can be found at http://www.roe.ac.uk/~ignas
A Look at What Is (and Isn't) Known About Quasar Broad Line Regions and How Narrow-Line Seyfert 1 Galaxies Fit In
The evidence is reviewed that the Broad Line Region (BLR) probably has two
distinct components located at about the same distance from the central black
hole. One component, BLR II, is optically-thick, low-ionization emission at
least some of which arises from a disc and the other, BLR I, is probably
optically-thin emission from a more spherically symmetric halo or atmosphere.
The high Fe II/H-beta ratios seen in Narrow-Line Seyfert 1 galaxies (NLS1s) are
not due to strong Fe II emission, as is commonly thought, but to unusually weak
Balmer emission, probably caused by higher densities. NLS1s probably differ
from non-NLS1s because of the higher density of gas near the black hole. This
produces a higher accretion rate, a denser BLR, and a view of the central
regions that is more face-on.Comment: Contributed talk presented at the Joint MPE,AIP,ESO workshop on
NLS1s, Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also
available at http://wave.xray.mpe.mpg.de/conferences/nls1-worksho
Chandra unveils a binary Active Galactic Nucleus in Mrk463
We analyse Chandra, XMM-Newton and HST data of the double-nucleus
Ultraluminous Infrared Galaxy (ULIRG), Mrk463. The Chandra detection of two
luminous ( and
erg cm s), unresolved nuclei in Mrk~463
indicates that this galaxy hosts a binary AGN, with a projected separation of
kpc ( arcsec). While the East nucleus was already
known to be a Seyfert 2 (and this is further confirmed by our Chandra detection
of a neutral iron line), this is the first unambiguous evidence in favour of
the AGN nature of the West nucleus. Mrk463 is therefore the clearest case so
far for a binary AGN, after NGC6240.Comment: 7 pages, 7 figures, accepted for publication in MNRA
Deep optical observations of the interaction of the SS 433 microquasar jet with the W 50 radio continuum shell
Four mosaics of deep, continuum-subtracted, CCD images have been obtained
over the extensive galactic radio continuum shell, W 50, which surrounds the
remarkable stellar system SS 433. Two of these mosaics in the Halpha+[N II] and
[O III] 5007 A emission lines respectively cover a field of ~2.3 x 2.5 degr^2
which contains all of W 50 but at a low angular resolution of 5 arcsec. The
third and fourth mosaics cover the eastern (in [O III] 5007 A) and western (in
Halpha+[N II]) filamentary nebulosity respectively but at an angular resolution
of 1 arcsec. These observations are supplemented by new low dispersion spectra
and longslit, spatially resolved echelle spectra. The [O III] 5007 A images
show for the first time the distribution of this emission in both the eastern
and western filaments while new Halpha+[N II] emission features are also found
in both of these regions. Approaching flows of faintly emitting material from
the bright eastern filaments of up 100 km/s in radial velocity are detected.
The present observations also suggest that the heliocentric systemic radial
velocity of the whole system is 56+-2 km/s. Furthermore, very deep imagery and
high resolution spectroscopy of a small part of the northern radio ridge of W
50 has revealed for the first time the very faint optical nebulosity associated
with this edge. It is suggested that patchy foreground dust along the ~5 kpc
sightline is inhibiting the detection of all of the optical nebulosity
associated with W 50. The interaction of the microquasar jets of SS 433 with
the W 50 shell is discussed.Comment: 19 pages, 13 figures, 2 tables. Accepted for pubication in MNRA
Stellar population analysis on local infrared-selected galaxies
To study the stellar population of local infrared galaxies, which contain
star-forming galaxies, composite galaxies, LINERs, and Seyfert 2s. We also want
to find whether infrared luminosity and spectral class have any effects on
their stellar populations. The sample galaxies are selected from the main
galaxy sample of SDSS-DR4 and then cross-correlated with the IRAS-PSCz catalog.
We fit our spectra (stellar absorption lines and continua) using the spectral
synthesis code STARLIGHT on the base of the templates of Simple Stellar
Population and the spectra of star clusters.Among the 4 spectral classes,
LINERs present the oldest stellar populations, and the other 3 sub-samples all
present substantial young and intermediate age populations and very few old
populations. The importance of young populations decreases from star-forming,
composite, Seyfert 2 to LINER. As to different infrared luminosity bins, ULIGs
& LIGs (log(11) present younger populations than
starbursts and normal galaxies. However, the dominant contributors to mass are
old populations in all sample galaxies. The fittings by using the spectra of
star clusters with different ages and metallicities as templates also give
consistent results. The dominated populations in star-forming and composite
galaxies are those with metallicity , while LINERs and Seyfert 2s
are more metal-rich. The normal galaxies are more metal-rich than the ULIGs &
LIGs and starbursts for the star-forming galaxies within different infrared
luminosity bins. Additionally, we also compare some synthesis results with
other parameters obtained from the MPA/JHU catalog.Comment: 13 pages, 11 figures, accepted for publication by A&