1,476 research outputs found
Deep GeMS/GSAOI near-infrared observations of N159W in the Large Magellanic Cloud
Aims. The formation and properties of star clusters at the edge of H II
regions are poorly known, partly due to limitations in angular resolution and
sensitivity, which become particularly critical when dealing with extragalactic
clusters. In this paper we study the stellar content and star-formation
processes in the young N159W region in the Large Magellanic Cloud.
Methods. We investigate the star-forming sites in N159W at unprecedented
spatial resolution using JHKs-band images obtained with the GeMS/GSAOI
instrument on the Gemini South telescope. The typical angular resolution of the
images is of 100 mas, with a limiting magnitude in H of 22 mag (90 percent
completeness). Photometry from our images is used to identify candidate young
stellar objects (YSOs) in N159W. We also determine the H-band luminosity
function of the star cluster at the centre of the H II region and use this to
estimate its initial mass function (IMF).
Results. We estimate an age of 2 + or - 1 Myr for the central cluster, with
its IMF described by a power-law with an index of gamma = - 1.05 + or - 0.2 ,
and with a total estimated mass of 1300 solar mass. We also identify 104
candidate YSOs, which are concentrated in clumps and subclusters of stars,
principally at the edges of the H II region. These clusters display signs of
recent and active star-formation such as ultra-compact H II regions, and
molecular outflows. This suggests that the YSOs are typically younger than the
central cluster, pointing to sequential star-formation in N159W, which has
probably been influenced by interactions with the expanding H II bubble
GMOS-IFU Spectroscopy of 167-317 (LV2) Proplyd in Orion
We present high spatial resolution spectroscopic observations of the proplyd
167-317 (LV2) near the Trapezium cluster in the Orion nebula, obtained during
the System Verification run of the Gemini Multi Object Spectrograph (GMOS)
Integral Field Unit (IFU) at the Gemini South Observatory. We have detected 38
forbidden and permitted emission lines associated with the proplyd and its
redshifted jet. We have been able to detect three velocity components in the
profiles of some of these lines: a peak with a 28-33 km/s systemic velocity
that is associated with the photoevaporated proplyd flow, a highly redshifted
component associated with a previously reported jet (which has receding
velocities of about 80-120 km/s with respect to the systemic velocity and is
spatially distributed to the southeast of the proplyd) and a less obvious,
approaching structure, which may possibly be associated with a faint
counter-jet with systemic velocity of (-75 +/- 15) km/s. We find evidences that
the redshifted jet has a variable velocity, with slow fluctuations as a
function of the distance from the proplyd. We present several background
subtracted, spatially distributed emission line maps and we use this
information to obtain the dynamical characteristics over the observed field.
Using a simple model and with the extinction corrected Halpha fluxes, we
estimate the mass loss rate for both the proplyd photoevaporated flow and the
redshifted microjet, obtaining (6.2 +/- 0.6) x 10^{-7} M_sun/year and (2.0 +/-
0.7) x 10^{-8} M_sun/year, respectively.Comment: 26 pages, 10 figures (6 are in colors), accepted by A
Extented ionized gas emission and kinematics of the compact group galaxies in HCG 16: Signatures of mergers
We report on kinematic observations of Ha emission line from four late-type
galaxies of Hickson Compact Group 16 (H16a,b,c and d) obtained with a scanning
Fabry-Perot interferometer and samplings of 16 km/s and 1". The velocity fields
show kinematic peculiarities for three of the four galaxies: H16b, c and d.
Misalignments between the kinematic and photometric axes of gas and stellar
components (H16b,c,d), double gas systems (H16c) and severe warping of the
kinematic major axis (H16b and c) were some of the peculiarities detected. We
conclude that major merger events have taken place in at least two of the
galaxies group. H16c and d, based on their significant kinematic peculiarities,
their double nuclei and high infrared luminosities. Their Ha gas content is
strongly spatially concentred - H16d contains a peculiar bar-like structure
confined to the inner 1 h^-1 kpc region. These observations are in
agreement with predictions of simulations, namely that the gas flows towards
the galaxy nucleus during mergers, forms bars and fuel the central activity.
Galaxy H16b, and Sb galaxy, also presents some of the kinematic evidences for
past accretion events. Its gas content, however, is very spare, limiting our
ability to find other kinematic merging indicators, if they are present. We
find that isolated mergers, i.e., they show an anormorphous morphology and no
signs of tidal tails. Tidal arms and tails formed during the mergers may have
been stripped by the group potential (Barnes & Hernquist 1992) ar alternatively
they may have never been formed. Our observations suggest that HCG 16 may be a
young compact group in formation throught the merging of close-by objects in a
dense environment.Comment: Accepted for publication in ApJ. 35 pages, 13 figures. tar file
gzipped and uuencode
Round table on morbilliviruses in marine mammals.
Since 1988 morbilliviruses have been increasingly recognized and held responsible for mass mortality amongst harbour seals (Phoca vitulina) and other seal species. Virus isolations and characterization proved that morbilliviruses from seals in Northwest Europe were genetically distinct from other known members of this group including canine distemper virus (CDV), rinderpest virus, peste des petits ruminants virus and measles virus. An epidemic in Baikal seals in 1987 was apparently caused by a morbillivirus closely related to CDV so that two morbilliviruses have now been identified in two geographically distant seal populations, with only the group of isolates from Northwest Europe forming a new member of the genus morbillivirus: phocid distemper virus (PDV). Because of distemper-like disease, the Baikal seal morbillivirus was tentatively named PDV-2 in spite of its possible identity with CDV. The appearance of morbilliviruses in the Mediterranean Sea causing high mortality amongst dolphins should further increase the research activities on protection strategies for endangered species of marine mammals
The most recent burst of Star Formation in the Massive Elliptical Galaxy NGC 1052
High-spatial resolution near-infrared (NIR) images of the central 24 x 24
arcsec^2 (~ 2 x 2 kpc^2) of the elliptical galaxy NGC 1052 reveal a total of 25
compact sources randomly distributed in the region. Fifteen of them exhibit
Halpha luminosities an order of magnitude above the estimate for an evolved
population of extreme horizontal branch stars. Their Halpha equivalent widths
and optical-to-NIR spectral energy distributions are consistent with them being
young stellar clusters aged < 7 Myr. We consider this to be the first direct
observation of spatially resolved star-forming regions in the central
kiloparsecs of an elliptical galaxy. The sizes of these regions are ~< 11 pc
and their median reddening is E(B - V) ~ 1 mag. According to previous works,
NGC 1052 may have experienced a merger event about 1 Gyr ago. On the assumption
that these clusters are spreaded with similar density over the whole galaxy,
the fraction of galaxy mass (5 x 10^{-5}) and rate of star formation (0.01
Msun/yr) involved, suggest the merger event as the possible cause for the star
formation we see today.Comment: 5 pages, 3 figures. Accepted for publication in MNRAS Letter
Candidate tidal dwarf galaxies associated with the Stephan's Quintet
We present kinematic and photometric evidence for the presence of seven
candidate tidal dwarf galaxies in Stephan's quintet. The central regions of the
two most probable parent galaxies, N7319 and N7318B, contain little or no gas
whereas the intragroup medium, and particularly the optical tails that seem to
be associated with N7318B are rich in cold and ionized gas.
Two tidal-dwarf candidates may be located at the edge of a tidal tail, one
within a tail and for four others there is no obvious stellar/gaseous bridge
between them and the parent galaxy. Two of the candidates are associated with
HI clouds, one of which is, in addition, associated with a CO cloud. All seven
regions have low continuum fluxes and high H luminosity densities
(F(H) = 1 -- 60 10 erg s cm). Their
magnitudes (M --16.1 to --12.6), sizes ( 3.5 h kpc),
colors (typically ) and gas velocity gradients ( 8 -- 26
h km s kpc) are typical for tidal dwarf galaxies. In
addition the ratios between their star formation rates determined from
H and from the B band luminosity are typical of other tidal dwarf
galaxies. The masses of the tidal dwarf galaxies in Stephan's quintet range
from 2 10 to 10 M and the median value for
their inferred mass-to-light ratios is 7 M/L.Comment: Accepted for publication in Astronomical Journal (23p 11figures
The Shroud Around the Twin Radio Jets in NGC 1052
(Abridged) We discuss multiple VLBI continuum and spectral line observations
and WSRT spectroscopy of NGC 1052. Sub-parsec scale features move outward at
approximately 0.26c in bi-symmetric jets, most likely oriented near the plane
of the sky. Absorption and emission signatures reveal ionised, atomic, and
molecular components of the surrounding medium.
Seven-frequency (1.4 to 43 GHz) VLBA observations show free-free absorption
in the inner parsec, probably together with synchrotron self-absorption. There
is apparently a geometrically thick but patchy structure oriented roughly
orthogonal to the jets. The western jet is receding: it is covered more deeply
and extensively. HI spectral line VLBI reveals atomic gas in front of both
jets. There appear to be three velocity systems. The deepest, at "high
velocities" (receding by 125 to 200 km/s), seems restricted to a shell 1 to 2
pc away from the core, within which this gas might be largely ionised. WSRT
spectroscopy has revealed 1667 and 1665 MHz OH absorption with their line ratio
varying roughly from 1:1 to 2:1 between -35 and 200 km/s. In the high velocity
system the OH profiles are similar to HI, suggesting co-location of that atomic
and molecular gas, and leaving unclear the connection to the H2O masing gas
seen elsewhere. We have also detected both 18cm OH satellite lines in the high
velocity system. They have conjugate profiles: 1612 MHz is in absorption, and
1720 MHz in emission.Comment: 16 pages, 14 figures, LaTeX, includes aa.cls, accepted for
publication in Astronomy and Astrophysic
Extended HI disks in dust-lane elliptical galaxies
We present the results of HI observations of five dust-lane ellipticals with
the Australia Telescope Compact Array. Two galaxies (NGC 3108 and NGC 1947) are
detected, and sensitive upper limits are obtained for the other three. In the
two detected galaxies, the HI is distributed in a regular, extended and warped
disk-like structure of low surface brightness. Adding data from the literature,
we find that several more dust-lane ellipticals have regular HI structures.
This HI is likely to be a remnant of accretions/mergers which took place a
considerable time ago, and in which a significant fraction of the gas survived
to form a disk. The presence of regular HI structures suggests that some
mergers lead to galaxies with extended low surface brightness density gas
disks. These gas disk will evolve very slowly and these elliptical galaxies
will remain gas rich for a long period of time. (abridged)Comment: 21 pages, 12 separate jpeg figures, at
http://www.nfra.nl/~morganti/Papers/dust.ps.gz the full ps version is
available. Accepted for publication in A
Observation of an Excited Bc+ State
Using pp collision data corresponding to an integrated luminosity of 8.5 fb-1 recorded by the LHCb experiment at center-of-mass energies of s=7, 8, and 13 TeV, the observation of an excited Bc+ state in the Bc+Ï+Ï- invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(Bc+) MeV/c2, where the last uncertainty is due to the limited knowledge of the Bc+ mass. It is consistent with expectations of the Bcâ(2S31)+ state reconstructed without the low-energy photon from the Bcâ(1S31)+âBc+Îł decay following Bcâ(2S31)+âBcâ(1S31)+Ï+Ï-. A second state is seen with a global (local) statistical significance of 2.2Ï (3.2Ï) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(Bc+) MeV/c2, and is consistent with the Bc(2S10)+ state. These mass measurements are the most precise to date
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