4,405 research outputs found
Identification of a high-velocity compact nebular filament 2.2 arcsec south of the Galactic Centre
The central parsec of the Milky Way is a very special region of our Galaxy;
it contains the supermassive black hole associated with Sgr A* as well as a
significant number of early-type stars and a complex structure of streamers of
neutral and ionized gas, within two parsecs from the centre, representing a
unique laboratory. We report the identification of a high velocity compact
nebular filament 2.2 arcsec south of Sgr A*. The structure extends over ~1
arcsec and presents a strong velocity gradient of ~200 km s^{-1} arcsec^{-1}.
The peak of maximum emission, seen in [Fe III] and He I lines, is located at
d{\alpha} = +0.20 +/- 0.06 arcsec and d{\delta} = -2.20 +/- 0.06 arcsec with
respect to Sgr A*. This position is near the star IRS 33N. The velocity at the
emission peak is Vr = -267 km s^{-1}. The filament has a position angle of PA =
115{\degr} +/- 10{\degr}, similar to that of the Bar and of the Eastern Arm at
that position. The peak position is located 0.7 arcsec north of the binary
X-ray and radio transient CXOGX J174540.0-290031, a low-mass X-ray binary with
an orbital period of 7.9 hr. The [Fe III] line emission is strong in the
filament and its vicinity. These lines are probably produced by shock heating
but we cannot exclude some X-ray photoionization from the low-mass X-ray
binary. Although we cannot rule out the idea of a compact nebular jet, we
interpret this filament as a possible shock between the Northern and the
Eastern Arm or between the Northern Arm and the mini-spiral "Bar".Comment: 7 pages, 4 figures, published online in MNRA
NGC 7097: the AGN and its mirror, revealed by PCA Tomography
Three-dimensional (3D) spectroscopy techniques are becoming more and more
popular, producing an increasing number of large data cubes. The challenge of
extracting information from these cubes requires the development of new
techniques for data processing and analysis. We apply the recently developed
technique of Principal Component Analysis (PCA) Tomography to a data cube from
the center of the elliptical galaxy NGC 7097 and show that this technique is
effective in decomposing the data into physically interpretable information. We
find that the first five principal components of our data are associated with
distinct physical characteristics. In particular, we detect a LINER with a weak
broad component in the Balmer lines. Two images of the LINER are present in our
data, one seen through a disk of gas and dust, and the other after scattering
by free electrons and/or dust particles in the ionization cone. Furthermore, we
extract the spectrum of the LINER, decontaminated from stellar and extended
nebular emission, using only the technique of PCA Tomography. We anticipate
that the scattered image has polarized light, due to its scattered nature.Comment: 12 pages, 5 figures, accepted for publication in ApJ Letter
IFU spectroscopy of 10 early type galactic nuclei: II - Nuclear emission line properties
Although it is well known that massive galaxies have central black holes,
most of them accreting at low Eddington ratios, many important questions still
remain open. Among them, are the nature of the ionizing source, the
characteristics and frequencies of the broad line region and of the dusty
torus. We report observations of 10 early-type galactic nuclei, observed with
the IFU/GMOS spectrograph on the Gemini South telescope, analysed with standard
techniques for spectral treatment and compared with results obtained with
principal component analysis Tomography (Paper I). We performed spectral
synthesis of each spaxel of the data cubes and subtracted the stellar component
from the original cube, leaving a data cube with emission lines only. The
emission lines were decomposed in multi-Gaussian components. We show here that,
for eight galaxies previously known to have emission lines, the narrow line
region can be decomposed in two components with distinct line widths. In
addition to this, broad H emission was detected in six galaxies. The
two galaxies not previously known to have emission lines show weak H+[N
II] lines. All 10 galaxies may be classified as low-ionization nuclear emission
regions in diagnostic diagrams and seven of them have bona fide active galactic
nuclei with luminosities between 10 and 10 erg s.
Eddington ratios are always < 10.Comment: 16 pages, 9 figures, accepted for publication in MNRA
Integral field unit spectroscopy of 10 early type galactic nuclei: I - Principal component analysis Tomography and nuclear activity
Most massive galaxies show emission lines that can be characterized as
LINERs. To what extent this emission is related to AGNs or to stellar processes
is still an open question. In this paper, we analysed a sample of such galaxies
to study the central region in terms of nuclear and circumnuclear emission
lines, as well as the stellar component properties. For this reason, we
selected 10 massive ( > 200 km/s) nearby (d < 31 Mpc) galaxies and
observed them with the IFU/GMOS (integral field unit/Gemini Multi-Object
Spectrograph) spectrograph on the Gemini South Telescope. The data were
analysed with principal component analysis (PCA) Tomography to assess the main
properties of the objects. Two spectral regions were analysed: a yellow region
(5100-5800 A), adequate to show the properties of the stellar component, and a
red region (6250-6800 A), adequate to analyse the gaseous component. We found
that all objects previously known to present emission lines have a central
AGN-type emitting source. They also show gaseous and stellar kinematics typical
of discs. Such discs may be co-aligned (NGC 1380 and ESO 208 G-21), in
counter-rotation (IC 1459 and NGC 7097) or misaligned (IC 5181 and NGC 4546).
We also found one object with a gaseous disc but no stellar disc (NGC 2663),
one with a stellar disc but no gaseous disc (NGC 1404), one with neither
stellar nor gaseous disc (NGC 1399) and one with probably ionization cones (NGC
3136). PCA Tomography is an efficient method for detecting both the central AGN
and gaseous and stellar discs. In the two cases (NGC 1399 and NGC 1404) in
which no lines were previously reported, we found no evidence of either nuclear
or circumnuclear emission, using PCA Tomography only.Comment: 26 pages, 17 figures, accepted for publication in MNRA
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