1,493 research outputs found
Seyfert Activity and Nuclear Star Formation in the Circinus Galaxy
We present high angular resolution (0".15-0".5) near infrared images and
spectroscopy of the Circinus galaxy, the closest Seyfert 2 galaxy known. The
data reveal a non-stellar nuclear source at 2.2 microns. The coronal line
region and the hot molecular gas emission extend for 20-50 pc in the ionization
cone. The data do not show evidence for a point-like concentration of dark
mass; we set an upper limit of 4*10^6 Mo to the mass of a putative black hole.
We find evidence for a young nuclear stellar population, with typical ages
between 4*10^7 and 1.5*10^8 yrs. The luminosity of the starburst inside a few
hundred pc is comparable to the intrinsic luminosity of the Seyfert nucleus,
and the two of them together account for most of the observed bolometric
luminosity of the galaxy. Within the central 12 pc the starburst has an age of
about 7*10^7 yrs and radiates about 2% of the luminosity of the active nucleus.
We discuss the implications of these results for models that have been proposed
for the starburst-AGN connection.Comment: 44 pages, Latex (including 11 Figures), Color Figures 1, 2 and 4 are
available at http://www.arcetri.astro.it/~maiolino/ , ApJ in pres
Photometry and dynamics of the minor mergers AM\,1228-260 and AM\,2058-381
We investigate interaction effects on the dynamics and morphology of the
galaxy pairs AM\,2058-381 and AM\,1228-260. This work is based on images
and long-slit spectra obtained with the Gemini Multi-Object Spectrograph at the
Gemini South Telescope. The luminosity ratio between the main (AM\,2058A) and
secondary (AM\,2058B) components of the first pair is a factor of 5,
while for the other pair, the main (AM\,1228A) component is 20 times more
luminous than the secondary (AM\,1228B). The four galaxies have pseudo-bulges,
with a S\'ersic index . Their observed radial velocities profiles (RVPs)
present several irregularities. The receding side of the RVP of AM\,2058A is
displaced with respect to the velocity field model, while there is a strong
evidence that AM\,2058B is a tumbling body, rotating along its major axis. The
RVPs for AM\,1228A indicate a misalignment between the kinematic and
photometric major axes. The RVP for AM\,1228B is quite perturbed, very likely
due to the interaction with AM\,1228A. NFW halo parameters for AM\,2058A are
similar to those of the Milky Way and M\,31. The halo mass of AM\,1228A is
roughly 10\% that of AM\,2058A. The mass-to-light (M/L) of AM\,2058 agrees with
the mean value derived for late-type spirals, while the low M/L for AM\,1228A
may be due to the intense star formation ongoing in this galaxy.Comment: 20 pages, 10 figures, accepted for publication in MNRA
A first study of the galaxy HRG 2304 and its companion AM 1646-795 (NED01)
Aims. We report the first study of the peculiar ring-like galaxy HRG 2304
(NED02),which was previously classified as a ring galaxy with an elliptical
smooth ring. This object was selected to prove that it is a candidate for the
Solitaire-type ring galaxies in an early stage of ring formation. The main goal
of this work is to provide the spectral characteristics of the current object
and its companion AM 1646-795 (NED01). Methods. The study is based on
spectroscopic observations in the optical band to highlight the characteristics
of this interacting galaxy. To investigate the star formation history of HRG
2304 we used the stellar population synthesis code STARLIGHT. The direct V and
B broad band images were used to enhance some fine structures. Results. Along
the entire long-slit signal, the spectra of HRG 2304 and its companion resemble
that of an early-type galaxy. We estimated a heliocentric systemic redshift of
z = 0.0415, corresponding to heliocentric velocities of 12449 km s-1 for HRG
2304 (NED02) and 12430 km s-1 for AM1646-795 (NED01). The spatial variation in
the contribution of the stellar population components for both objects are
dominated by an old stellar population 2x10^9 < t < 13x10^9 yr. The observed
radial-velocity distribution and the fine structures around HRG 2304 suggest an
ongoing tidal interaction of both galaxies. Conclusions.The spectroscopic
results and the morphological peculiarities of HRG 2304 can be adequately
interpreted as an ongoing interaction with the companion galaxy. Both galaxies
are early-type, the companion is elliptical, and the smooth distribution of the
material around HRG 2304 and its off-center nucleus in the direction of
AM1646-795 (NED01) characterize HRG 2304 as a Solitaire-type galaxy candidate
in an early stage of ring formation.Comment: Accepted for publication in Astronomy and Astrophysics, 9 pages, 10
figures and 3 table
LIINUS/SERPIL: a design study for interferometric imaging spectroscopy at the LBT
LIINUS/SERPIL is a design study to augment LBTs interferometric beam combiner
camera LINC-NIRVANA with imaging spectroscopy. The FWHM of the interferometric
main beam at 1.5 micron will be about 10 mas, offering unique imaging and
spectroscopic capabilities well beyond the angular resolution of current 8-10m
telescopes. At 10 mas angular scale, e.g., one resolution element at the
distance of the Galactic Center corresponds to the average diameter of the
Pluto orbit (79 AU), hence the size of the solar system. Taking advantage of
the LBT interferometric beam with an equivalent maximum diameter of 23 m,
LIINUS/SERPIL is an ideal precursor instrument for (imaging) spectrographs at
extremely large full aperture telescopes. LIINUS/SERPIL will be built upon the
LINC-NIRVANA hardware and LIINUS/SERPIL could potentially be developed on a
rather short timescale. The study investigates several concepts for the optical
as well as for the mechanical design. We present the scientific promises of
such an instrument together with the current status of the design study.Comment: 12 pages, SPIE conference proceeding, Orlando, 200
Electron temperature fluctuations in NGC 346
The existence and origin of large spatial temperature fluctuations in HII
regions and planetary nebulae are assumed to explain the differences between
the heavy element abundances inferred from collisionally excited and
recombination lines, although this interpretation remains significantly
controversial. We investigate the spatial variation in electron temperature
inside NGC 346, the brightest HII region in the Small Magellanic Cloud. Long
slit spectrophotometric data of high signal-to-noise were employed to derive
the electron temperature from measurements derived from localized observations
of the [OIII]( ratio in three
directions across the nebula. The electron temperature was estimated in 179
areas of 5 of size distributed along
three different declinations. A largely homogeneous temperature distribution
was found with a mean temperature of 12 269 K and a dispersion of 6.1%. After
correcting for pure measurements errors, a temperature fluctuation on the plane
of the sky of (corresponding to a dispersion of 4.5%)
was obtained, which indicates a 3D temperature fluctuation parameter of . A large scale gradient in temperature of the order of
K arcsec was found. The magnitude of the temperature
fluctuations observed agrees with the large scale variations in temperature
predicted by standard photoionization models, but is too small to explain the
abundance discrepancy problem. However, the possible existence of small spatial
scale temperature variations is not excluded.Comment: 6 pages, 5 figures, 2 table
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