1,854 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
Steering chiral swimmers along noisy helical paths
Chemotaxis along helical paths towards a target releasing a chemoattractant
is found in sperm cells and many microorganisms. We discuss the stochastic
differential geometry of the noisy helical swimming path of a chiral swimmer. A
chiral swimmer equipped with a simple feedback system can navigate in a
concentration gradient of chemoattractant. We derive an effective equation for
the alignment of helical paths with a concentration gradient which is related
to the alignment of a dipole in an external field. We discuss the chemotaxis
index in the presence of fluctuations.Comment: 8 pages, 1 figur
Resolved Spectroscopy of the Narrow-Line Region in NGC 1068. I. The Nature of the Continuum Emission
We present the first long-slit spectra of the Seyfert 2 galaxy NGC 1068
obtained by the Space Telescope Imaging Spectrograph (STIS); the spectra cover
the wavelength range 1150 - 10,270 Angstroms at a spatial resolution of 0.05 -
0.1 arcsec and a spectral resolving power of 1000. In this first paper, we
concentrate on the far-UV to near-IR continuum emission from the continuum
``hot spot'' and surrounding regions extending out to +/- 6 arcsec (+/-432 pc)
at a position angle of 202 degrees In addition to the broad emission lines
detected by spectropolarimetry, the hot spot shows the ``little blue bump'' in
the 2000 - 4000 Ang. range, which is due to Fe II and Balmer continuum
emission. The continuum shape of the hot spot is indistinguishable from that of
NGC 4151 and other Seyfert 1 galaxies. Thus, the hot spot is reflected emission
from the hidden nucleus, due to electron scattering (as opposed to
wavelength-dependent dust scattering). The hot spot is ~0.3 arcsec in extent
and accounts for 20% of the scattered light in the inner 500 pc. We are able to
deconvolve the extended continuum emission in this region into two components:
electron-scattered light from the hidden nucleus (which dominates in the UV)
and stellar light (which dominates in the optical and near-IR). The scattered
light is heavily concentrated towards the hot spot, is stronger in the
northeast, and is enhanced in regions of strong narrow-line emission. The
stellar component is more extended, concentrated southwest of the hot spot,
dominated by an old (> 2 x 10 Gyr) stellar population, and includes a nuclear
stellar cluster which is ~200 pc in extent.Comment: 32 pages, Latex, includes 11 figures (postscript), to appear in the
Astrophysical Journa
Probing the Ionization Structure of the Narrow Line Region in the Seyfert 1 Galaxy NGC 4151
We present a study of the distribution of [O III] 5007 and [O II]
3727 emission in the Narrow Line Region (NLR) of the Seyfert 1 galaxy
NGC 4151. While the NLR of NGC 4151 exhibits an overall structure consistent
with the unified model of Seyfert galaxies, narrow-band [O III] and [O II]
images obtained with the Wide Field and Planetary Camera 2 aboard the Hubble
Space Telescope reveal significant emission from outside the the emission-line
bi-cone. The [O III]/[O II] ratios are lower in these regions, consistent with
a weaker ionizing flux. We performed a photoionization modeling analysis of the
emission-line gas within a series of annuli, centered on the the central
continuum source, with inner radii from 13 to 90 pc. The gas is ionized by
radiation that has been attenuated by a relatively highly-ionized absorber
(HABS), which completely covers the central source, and a lower-ionization
absorber (LABS), which has a covering factor ranging from 0 to 1. We found that
the [O III]/[O II] ratios are well fit by assuming that, within each segment of
an annulus, some fraction of the NLR gas is completely within the shadow of
LABS, while the rest is irradiated by the continuum filtered only by HABS. This
suggests that the structure of the NLR is due to filtering of the ionizing
radiation by ionized gas, consistent with disk-wind models. One possible
scenario is that the low-ionization absorbers are dense knots of gas swept up
by a wind.Comment: 43 pages, 18 figure Accepted for publication in the Astrophysical
Journa
Disentangling the near infrared continuum spectral components of the inner 500 pc of Mrk 573: two-dimensional maps
We present a near infrared study of the spectral components of the continuum
in the inner 500500 pc of the nearby Seyfert galaxy Mrk573 using
adaptive optics near-infrared integral field spectroscopy with the instrument
NIFS of the Gemini North Telescope at a spatial resolution of 50 pc. We
performed spectral synthesis using the {\sc starlight} code and constructed
maps for the contributions of different age components of the stellar
population: young ( Myr), young-intermediate (
Myr), intermediate-old ( Myr Gyr) to the
near-IR K-band continuum, as well as their contribution to the total stellar
mass. We found that the old stellar population is dominant within the inner 250
pc, while the intermediate age components dominate the continuum at larger
distances. A young stellar component contributes up to 20% within the
inner 70 pc, while hot dust emission and featureless continuum components
are also necessary to fit the nuclear spectrum, contributing up to 20% of the
K-band flux there. The radial distribution of the different age components in
the inner kiloparsec of Mrk573 is similar to those obtained by our group for
the Seyfert galaxies Mrk1066, Mrk1157 and NGC1068 in previous works using a
similar methodology. Young stellar populations (100 Myr) are seen in the
inner 200-300 pc for all galaxies contributing with 20% of the K-band
flux, while the near-IR continuum is dominated by the contribution of
intermediate-age stars (100 Myr-2 Gyr) at larger distances. Older stellar
populations dominate in the inner 250 pc
Outflows in the Narrow Line Region of Bright Seyfert Galaxies - I: GMOS-IFU Data
We present two-dimensional maps of emission-line fluxes and kinematics, as
well as of the stellar kinematics of the central few kpc of five bright nearby
Seyfert galaxies -- Mrk\,6, Mrk\,79, Mrk\,348, Mrk\,607 and Mrk\,1058 --
obtained from observations with the Gemini Multi-Object Spectrograph (GMOS)
Integral Field Unit (IFU) on the Gemini North Telescope. The data cover the
inner 3\farcs55\farcs0 -- corresponding to physical scales in the range
0.60.9 to 1.52.2\,kpc -- at a spatial resolution ranging
from 110 to 280 pc with a spectral coverage of 4300 -- 7100\,\AA\ and velocity
resolution of 90\,km\,s. The gas excitation is Seyfert like
everywhere but show excitation, but show excitation gradients that are
correlated with the gas kinematics, reddening and/or the gas density. The gas
kinematics show in all cases two components: a rotation one similar to that
observed in the stellar velocity field, and an outflow component. In the case
of Mrk607, the gas is counter-rotating relative to the stars. Enhanced gas
velocity dispersion is observed in association to the outflows according to two
patterns: at the locations of the highest outflow velocities along the
ionization axis or perpendicularly to it in a strip centered at the nucleus
that we attribute to an equatorial outflow. Bipolar outflows are observed in
Mrk\,348 and Mrk\,79, while in Mrk\,1058 only the blueshifted part is clearly
observed, while in the cases of Mrk\,6 and Mrk\,607 the geometry of the outflow
needs further constraints from modeling to be presented in a forthcoming study,
where the mass flow rate and powers will also be obtained.Comment: 20 pages, accepted by MNRA
- …