189 research outputs found
Imagery and long-slit spectroscopy of the Polar-Ring Galaxy AM2020-504
Interactions between galaxies are very common. There are special kinds of
interactions that produce systems called Polar Ring Galaxies (PRGs), composed
by a lenticular, elliptical, or spiral host galaxy, surrounded by a ring of
stars and gas, orbiting in an approximately polar plane. The present work aims
to study AM2020-504, a PRG with an elliptical host galaxy, and a narrow and
well defined ring, probably formed by accretion of material from a donor
galaxy, collected by the host galaxy. Our observational study was based on BVRI
broad band imagery as well as longslit spectroscopy in the wavelenght range
4100--8600\AA, performed at the 1.6m telescope at the Observat\'orio do Pico
dos Dias (OPD), Brazil. We estimated a redshift of z= 0.01683, corresponding a
heliocentric radial velocity of 5045 +/-23 km/s. The (B-R) color map shows that
the ring is bluer than the host galaxy, indicating that the ring is a younger
structure. Standard diagnostic diagrams were used to classify the main ionizing
source of selected emission-line regions (nucleus, host galaxy and ring). It
turns out that the ring regions are mainly ionized by massive stars while the
nucleus presents AGN characteristics. Using two empirical methods, we found
oxygen abundances for the HII regions located in the ring in the range
12+log(O/H)=8.3-8.8 dex, the presence of an oxygen gradient across the ring,
and that AM2020-504 follows the metallicity-luminosity relation of spiral
galaxies. These results support the accretion scenario for this object and
rules out cold accretion as source for the HI gas in the polar ring
Galaxy transmutations: The double ringed galaxy ESO 474-G26
Surface photometry and a 21cm HI line spectrum of the giant double-ringed
galaxy ESO 474-G26 are presented. The morphology of this system is unique among
the 30,000 galaxies with >B15. Two almost orthogonal optical rings with
diameters of 60 and 40 kpc surround the central body (assuming H0=70 km/s/Mpc).
The outer one is an equatorial ring, while the inner ring lies in a nearly
polar plane. The rings have blue optical colors typical of late-type spirals.
Both appear to be rotating around the central galaxy, so that this system can
be considered as a kinematically confirmed polar ring galaxy. Its observational
characteristics are typical of galaxy merger remnants. Although the central
object has a surface brightness distribution typical of elliptical galaxies, it
has a higher surface brightness for its effective radius than ordinary
ellipticals. Possible origins of this galaxy are discussed and numerical
simulations are presented that illustrate the formation of the two rings in the
merging process of two spiral galaxies, in which the observed appearance of ESO
474-G26 appears to be a transient stage.Comment: Accepted for publication in A&
A study of the remarkable galaxy system AM 546-324 (the core of Abell S0546)
We report first results of an investigation of the tidally disturbed galaxy
system AM\,546-324, whose two principal galaxies 2MFGC 04711 and AM\,0546-324
(NED02) were previously classified as interacting doubles. This system was
selected to study the interaction of ellipticals in a moderately dense
environment. We provide spectral characteristics of the system and present an
observational study of the interaction effects on the morphology, kinematics,
and stellar population of these galaxies. The study is based on long-slit
spectrophotometric data in the range of 4500-8000 obtained with
the Gemini Multi-Object Spetrograph at Gemini South (GMOS-S). We have used the
stellar population synthesis code STARLIGHT to investigate the star formation
history of these galaxies. The Gemini/GMOS-S direct r-G0303 broad band pointing
image was used to enhance and study fine morphological structures. The main
absorption lines in the spectra were used to determine the radial velocity.
Along the whole long-slit signal, the spectra of the Shadowy galaxy (discovered
by us), 2MFGC 04711, and AM\,0546-324 (NED02) resemble that of an early-type
galaxy. We estimated redshifts of z= 0.0696, z= 0.0693 and z= 0.0718,
corresponding to heliocentric velocities of 20\,141 km s, 20\,057 km
s, and 20\,754 km s for the Shadowy galaxy, 2MFGC 04711 and
AM\,0546-324 (NED02), respectively. ..
A New Kind of Quinonic-Antibiotic Useful Against Multidrug-Resistant S. aureus and E. faecium Infections
Indexación: Scopus.A rapid emergence of resistant bacteria is occurring worldwide, endangering the efficacy of antibiotics and reducing the therapeutic arsenal available for treatment of infectious diseases. In the present study, we developed a new class of compounds with antibacterial activity obtained by a simple, two step synthesis and screened the products for in vitro antibacterial activity against ATCC® strains using the broth microdilution method. The compounds exhibited minimum inhibitory concentrations (MIC) of 1⁻32 μg/mL against Gram-positive ATCC® strains. The structure⁻activity relationship indicated that the thiophenol ring is essential for antibacterial activity and the substituents on the thiophenol ring module, for antibacterial activity. The most promising compounds detected by screening were tested against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecium (VREF) clinical isolates. We found remarkable activity against VREF for compounds 7 and 16, were the MIC50/90 were 2/4 µg/mL and 4/4 µg/mL, respectively, while for vancomycin the MIC50/90 was 256/512 µg/mL. Neither compound affected cell viability in any of the mammalian cell lines at any of the concentrations tested. These in vitro data show that compounds 7 and 16 have an interesting potential to be developed as new antibacterial drugs against infections caused by VREF.https://www.mdpi.com/1420-3049/23/7/177
Spitzer-IRAC GLIMPSE of high mass protostellar objects. I Infrared point sources and nebulae
The GLIMPSE archive was used to obtain 3.6--8.0micron, point source
photometry and images for 381 massive protostellar candidates lying in the
Galactic mid-plane. The colours, magnitudes and spectral indicies of sources in
each of the 381 target fields were analysed and compared with the predictions
of 2D radiative transfer model simulations. Although no discernable embedded
clusters were found in any targets, multiple sources or associations of
redenned young stellar objects were found in many sources indicating
multiplicity at birth. The spectral index () of these point sources in
3.6--8.0mum bands display large values of =2--5. A color-magnitude
analog plot was used to identify 79 infrared counterparts to the HMPOs. Compact
nebulae are found in 75% of the detected sources with morphologies that can be
well described by core-halo, cometary, shell-like and bipolar geometries
similar to those observed in ultra-compact HII regions. The IRAC band SEDs of
the IR counterparts of HMPOs are best described to represent YSOs with a mass
range of 8--20\msun in their Class I stages when compared with 2D radiative
transfer models. They also suggest that the high values represent
reprocessed star/star+disk emission that is arising in the dense envelopes.
Thus we are witnessing the luminous envelopes around the protostars rather than
their photospheres or disks. We argue that the compact infrared nebulae likely
reflect the underlying physical structure of the dense cores and are found to
imitate the morphologies of known UCHII regions. Our results favour models of
continuuing accretion involving both molecular and ionised accretion components
to build the most massive stars rather than purely molecular rapid accretion
flows.Comment: 13 pages, 7 figures, accepted by A&
AM 1934-563: A giant spiral polar-ring galaxy in a triplet
We have observed the emission-line kinematics and photometry of a southern
triplet of galaxies. The triplet contains a giant spiral galaxy AM 1934-563
which optical structure resembles a polar-ring galaxy: distorted spiral disk,
seen almost edge-on, and a faint large-scale (45 kpc in diameter) warped
structure, inclined by 60^o-70^o with respect to the disk major axis. The
triplet shows relatively small velocity dispersion (69 km/s) and a large
crossing time (0.17 in units of the Hubble time). The disk of AM 1934-563
demonstrates optical colors typical for an early-type spirals, strong radial
color gradient, and almost exponential surface brightness distribution with an
exponential scale-length value of 3.1 kpc (R passband). The galaxy shows a
maximum rotation velocity of about 200 km/s and it lies close to the
Tully-Fisher relation for spiral galaxies. The suspected polar ring is faint
(\mu(B) > 24) and strongly warped. Its total luminosity comprises (10-15)% of
the total luminosity of AM 1934-563. We then try to model this system using
numerical simulations, and study its possible formation mechanisms. We find
that the most robust model, that reproduces the observed characteristics of the
ring and the host galaxy, is the tidal transfer of mass from a massive gas-rich
donor galaxy to the polar ring. The physical properties of the triplet of
galaxies are in agreement with this scenario.Comment: Accepted for publication in A&
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