9,927 research outputs found
Extended Gas in Seyfert Galaxies: Near Infrared Observations of NGC 2110 and Circinus
We present results of near--IR long-slit spectroscopy in the J and K bands of
the Seyfert 2 galaxies NGC 2110 and Circinus, investigating the gaseous
distribution, excitation, reddening and kinematics. In NGC 2110, the emission
line ratio [FeII]/Pa beta increases towards the nucleus (to ~ 7). The nuclear
[Fe II]1.257 (microns) and Pa beta lines are broader (FWHM ~ 500 km/s) than the
H2 (2.121) line (FWHM ~ 300 km/s). Both these results suggest that shocks,
driven by the radio jet, are an important source of excitation of [Fe II]. The
H2 excitation appears to be dominated by X-rays from the nucleus. In Circinus,
both [FeII]/Pa beta and H2/Br gamma decrease from ~ 2 at 4 arcsec from the
nucleus to nuclear values of ~ 0.6 and ~ 1, respectively, suggesting that the
starburst dominates the nuclear excitation, while the AGN dominates the
excitation further out (r > 2 arcsec). For both galaxies, the gaseous
kinematics are consistent with circular rotation in the plane of the disk. Our
rotation curves suggest that the nucleus (identified with the peak of the IR
continuum) is displaced from the kinematic centre of the galaxies. This effect
has been observed previously in NGC 2110 based on the kinematics of optical
emission lines, but the displacement is smaller in the infrared, suggesting the
effect is related to obscuration. The continuum J-K colours of the nuclear
region indicate a red stellar population in NGC 2110 and a reddened young
stellar population in Circinus. Right at the nucleus of both galaxies, the
colours are redder, apparently a result of hot dust emission from the inner
edge of a circumnuclear torus.Comment: 11 pages, 14 figures, accepted for publication in MNRA
Population synthesis of HII galaxies
We study the stellar population of galaxies with active star formation,
determining ages of the stellar components by means of spectral population
synthesis of their absorption spectra. The data consist of optical spectra of
185 nearby () emission line galaxies. They are mostly HII
galaxies, but we also include some Starbursts and Seyfert 2s, for comparison
purposes. They were grouped into 19 high signal-to-noise ratio template
spectra, according to their continuum distribution, absorption and emission
line characteristics. The templates were then synthesized with a star cluster
spectral base. The synthesis results indicate that HII galaxies are typically
age-composite stellar systems, presenting important contribution from
generations up to as old as 500 Myr. We detect a significant contribution of
populations with ages older than 1 Gyr in two groups of HII galaxies. The age
distributions of stellar populations among Starbursts can vary considerably
despite similarities in the emission line spectra. In the case of Seyfert 2
groups we obtain important contributions of old population, consistent with a
bulge. From the diversity of star formation histories, we conclude that typical
HII galaxies in the local universe are not systems presently forming their
first stellar generation.Comment: 12 pages, 4 figures, MNRAS in pres
Semi-automated image analysis for the assessment of megafaunal densities at the Arctic deep-sea observatory HAUSGARTEN
A New Superwind Wolf-Rayet Galaxy Mrk 1259
We report the discovery of a starburst-driven wind (superwind) from the
starburst nucleus galaxy Mrk 1259. The estimated number ratio of Wolf-Rayet
(WR) to O stars amounts to ~0.09. While the nuclear emission-line region is due
to usual photoionization by massive stars, the circumnuclear emission-line
regions show anomalous line ratios that can be due to cooling shocks. Since the
host galaxy seems to be a face-on disk galaxy and the excitation conditions of
the circumnuclear emission-line regions show the spatial symmetry, we consider
that we are seeing the superwind nearly from a pole-on view. Cooling shock
models may explain the observed emission line ratios of the circumnuclear
regions although a factor of 2 overabundance of nitrogen is necessary. All
these suggest that the high-mass enhanced starburst occurred ~5X10^6 years ago
in the nuclear region of Mrk 1259.Comment: To be published in the Astrophysical Journal Letters, 15 pages, 4
figure
The Ultraviolet Spectra of Active Galaxies With Double-Peaked Emission Lines
We present the results of UV spectroscopy of AGNs with double-peaked Balmer
emission lines. In 2/3 of the objects, the far-UV resonance lines are strong,
with single-peaked profiles resembling those of Seyfert galaxies. The Mg II
line is the only UV line with a double-peaked profile. In the remaining
objects, the far-UV resonance lines are relatively weak but still
single-peaked. The latter group also displays prominent UV absorption lines,
indicative of a low-ionization absorber. We interpret the difference in the
profiles of the emission lines as resulting from two different regions: a
dense, low-ionization accretion disk (the predominant source of the Balmer and
Mg II lines), and a lower density, higher-ionization wind (the predominant
source of the far-UV resonance lines). These results suggest a way of
connecting the double-peaked emitters with the greater AGN population: in
double-peaked emitters the accretion rate onto the black hole is low, making
the wind feeble and allowing the lines from the underlying disk to shine
through. This scenario also implies that in the majority of AGNs, the wind is
the source of the broad emission lines.Comment: To appear in "The Interplay among Black Holes, Stars and ISM in
Galactic Nuclei," IAU Coll. 222, eds. Storchi Bergmann, Ho, and Schmit
Evidence for a Physically Compact Narrow-Line Region in the Seyfert 1 Galaxy NGC 5548
We have combined HST/FOS and ground-based spectra of the Seyfert 1 galaxy NGC
5548 to study the narrow emission lines over the 1200 -- 10,000 angstrom
region. All of the spectra were obtained when the broad emission line and
continuum fluxes were at an historic low level, allowing us to accurately
determine the contribution of the narrow-line region (NLR) to the emission
lines. We have generated multicomponent photoionization models to investigate
the relative strength of the high ionization lines compared to those in Seyfert
2 galaxies, and the weakness of the narrow Mg II 2800 line. We present evidence
for a high ionization component of NLR gas that is very close to the nucleus
(~1 pc). This component must be optically thin to ionizing radiation at the
Lyman edge (tau = 2.5) to avoid producing [O I] and Mg II in a partially
ionized zone. The very high ionization lines (N V, [Ne V], [Fe VII], [Fe X])
are stronger than the predictions of our standard model, and we show that this
may be due to supersolar abundances and/or a ``blue bump'' in the extreme
ultraviolet (although recent observations do not support the latter). An outer
component of NLR gas (at only ~70 pc from the continuum source) is needed to
produce the low ionization lines. We show that the outer component may contain
dust, which further reduces the Mg II flux by depletion and by absorption of
the resonance photons after multiple scatterings. We show that the majority of
the emission in the NLR of NGC 5548 must arise within about ~70 pc from the
nucleus. Thus, the NLR in this Seyfert 1 galaxy is very physically compact,
compared to the typical NLR in Seyfert 2 galaxies.Comment: 38 pages, Latex, includes 2 figures (postscript), to appear in Ap
Composite fermions in periodic and random antidot lattices
The longitudinal and Hall magnetoresistance of random and periodic arrays of artificial scatterers, imposed on a high-mobility two-dimensional electron gas, were investigated in the vicinity of Landau level filling factor ν=1/2. In periodic arrays, commensurability effects between the period of the antidot array and the cyclotron radius of composite fermions are observed. In addition, the Hall resistance shows a deviation from the anticipated linear dependence, reminiscent of quenching around zero magnetic field. Both effects are absent for random antidot lattices. The relative amplitude of the geometric resonances for opposite signs of the effective magnetic field and its dependence on illumination illustrate enhanced soft wall effects for composite fermions
Passage of an integral membrane protein, the vesicular stomatitis virus glycoprotein, through the Golgi apparatus en route to the plasma membrane.
Oscillations of the magnetic polarization in a Kondo impurity at finite magnetic fields
The electronic properties of a Kondo impurity are investigated in a magnetic
field using linear response theory. The distribution of electrical charge and
magnetic polarization are calculated in real space. The (small) magnetic field
does not change the charge distribution. However, it unmasks the Kondo cloud.
The (equal) weight of the d-electron components with their magnetic moment up
and down is shifted and the compensating s-electron clouds don't cancel any
longer (a requirement for an experimental detection of the Kondo cloud). In
addition to the net magnetic polarization of the conduction electrons an
oscillating magnetic polarization with a period of half the Fermi wave length
is observed. However, this oscillating magnetic polarization does not show the
long range behavior of Rudermann-Kittel-Kasuya-Yosida oscillations because the
oscillations don't extend beyond the Kondo radius. They represent an internal
electronic structure of the Kondo impurity in a magnetic field. PACS: 75.20.Hr,
71.23.An, 71.27.+
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