851 research outputs found
High-resolution UKIRT observations of circumnuclear star formation in M100
We present high-resolution, near-infrared imaging of the circumnuclear region
of the barred spiral galaxy M100 (=NGC 4321), accompanied by near-infrared
spectroscopy. We identify a total of 43 distinct regions in the K-band image,
and determine magnitudes and colours for 41 of them. By comparison with other
near-infrared maps we also derive colour excesses and K-band extinctions for
the knots. Combining the imaging and spectroscopic results, we conclude that
the knots are the result of bursts of star formation within the last 15-25 Myr.
We discuss the implications of these new results for our dynamical and
evolutionary understanding of this galaxy.Comment: 10 pages, 4 figures, uses mn-1.4.sty. Accepted for publication in
Monthly Notices of the Royal Astronomical Societ
The central region of M83: Massive star formation, kinematics, and the location and origin of the nucleus
We report new near-IR integral field spectroscopy of the central starburst
region of the barred spiral galaxy M83 obtained with CIRPASS on Gemini-S, which
we analyse in conjunction with GHaFaS Fabry-Perot data, an AAT IRIS2 Ks-band
image, and near- and mid-IR imaging from the Hubble and Spitzer space
telescopes. The bulk of the current star formation activity is hidden from
optical view by dust extinction, but is seen in the near- and mid-IR to the
north of the nucleus. This region is being fed by inflow of gas through the bar
of M83, traced by the prominent dust lane entering into the circumnuclear
region from the north. An analysis of stellar ages confirms that the youngest
stars are indeed in the northwest. A gradual age gradient, with older stars
further to the south, characterises the well-known star-forming arc in the
central region of M83. Detailed analyses of the Pa beta ionised gas kinematics
and near-IR imaging confirm that the kinematic centre coincides with the
photometric centre of M83, and that these are offset significantly, by about 3
arcsec or 60 pc, from the visible nucleus of the galaxy. We discuss two
possible options, the first of which postulates that the kinematic and
photometric centre traces a galaxy nucleus hidden by a substantial amount of
dust extinction, in the range A_V=3-10 mag. By combining this information with
kinematic results and using arguments from the literature, we conclude that
such a scenario is, however, unlikely, as is the existence of other "hidden"
nuclei in M83. We thus concur with recent authors and favour a second option,
in which the nucleus of the galaxy is offset from its kinematic and photometric
centre. This is presumably a result of some past interaction, possibly related
to the event which lies at the origin of the disturbance of the outer disk of
the galaxy. (Abridged)Comment: MNRAS, in press; 16 pages latex, 15 figure
The puzzling interpretation of NIR indices: The case of NaI2.21
We present a detailed study of the Na I line strength index centered in the
-band at , {\AA} (NaI2.21 hereafter) relying on different samples of
early-type galaxies. Consistent with previous studies, we find that the
observed line strength indices cannot be fit by state-of-art scaled-solar
stellar population models, even using our newly developed models in the NIR.
The models clearly underestimate the large NaI2.21 values measured for most
early-type galaxies. However, we develop a Na-enhanced version of our newly
developed models in the NIR, which - together with the effect of a bottom-heavy
initial mass function - yield NaI2.21 indices in the range of the observations.
Therefore, we suggest a scenario in which the combined effect of [Na/Fe]
enhancement and a bottom-heavy initial mass function are mainly responsible for
the large NaI2.21 indices observed for most early-type galaxies. To a smaller
extent, also [C/Fe] enhancement might contribute to the large observed NaI2.21
values.Comment: 13 pages, 4 figures, accepted for publication in MNRA
Chandra X-Ray Point Sources, including Supernova 1979C, in the Spiral Galaxy M100
Six x-ray point sources, with luminosities of in the 0.4--7 keV band, were detected in Chandra
observations of the spiral galaxy M100. One source is identified with supernova
SN 1979C and appears to have roughly constant x-ray flux for the period 16--20
years after the outburst. The x-ray spectrum is soft, as would be expected if
the x-ray emission is due to the interaction of supernova ejecta with
circumstellar matter. Most of the other sources are variable either within the
Chandra observation or when compared to archival data. None are coincident with
the peak of the radio emission at the nucleus. These sources have harder
spectra than the supernova and are likely x-ray binaries. M100 has more bright
x-ray sources than typical for spiral galaxies of its size. This is likely
related to active star formation occurring in the galaxy.Comment: accepted by the Astrophysical Journal, 7 page
Constraints on Jupiters from Observations of Galactic bulge microlensing events during 2000
Peer reviewe
A SAURON study of stars and gas in Sa bulges
We present results from our ongoing effort to understand the morphological
and kinematical properties of early-type galaxies using the integral-field
spectrograph SAURON. We discuss the relation between the stellar and gas
morphology and kinematics in our sub-sample of 24 representative Sa spiral
bulges. We focus on the frequency of kinematically decoupled components and on
the presence of star formation in circumnuclear rings.Comment: 6 pages, 3 figures; To appear in the proceedings of the "Island
Universes: Structure and Evolution of Disk Galaxies" conference held in
Terschelling, Netherlands, July 2005, ed. R. de Jong. A high resolution
version is available at
http://www.strw.leidenuniv.nl/~jfalcon/JFB_terschelling.pdf.g
The JCMT Nearby Galaxies Legacy Survey -- XI. -- Environmental Variations in the Atomic and Molecular Gas Radial Profiles of Nearby Spiral Galaxies
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2017 The Author (s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We present an analysis of the radial profiles of a sample of 43 HI-flux selected spiral galaxies from the Nearby Galaxies Legacy Survey (NGLS) with resolved James Clerk Maxwell Telescope (JCMT) CO and/or Very Large Array (VLA) HI maps. Comparing the Virgo and non-Virgo populations, we confirm that the HI disks are truncated in the Virgo sample, even for these relatively HI-rich galaxies. On the other hand, the H distribution is enhanced for Virgo galaxies near their centres, resulting in higher H to HI ratios and steeper H and total gas radial profiles. This is likely due to the effects of moderate ram pressure stripping in the cluster environment, which would preferentially remove low density gas in the outskirts while enhancing higher density gas near the centre. Combined with H star formation rate data, we find that the star formation efficiency (SFR/H) is relatively constant with radius for both samples, but Virgo galaxies have a lower star formation efficiency than non-Virgo galaxies.Peer reviewedFinal Published versio
The stellar populations of spiral disks.II Measuring and modeling the radial distribution of absorption spectral indices
The radial distributions of the Mg2 and Fe5270 Lick spectral indices have
been measured to large radial distances on the disks of NGC 4303 and NGC 4535
using an imaging technique based on interference filters. These data, added to
those of NGC 4321 previously published in Paper I of this series are used to
constraint chemical (multiphase) evolutionary models for these galaxies.
Because the integrated light of a stellar disk is a time average over the
history of the galaxy weighted by the star formation rate, these constraints
complement the information on chemical gradients provided by the study of HII
regions which, by themselves, can only provide the alpha-elements abundance
accumulate over the life of the galaxy. The agreement between the observations
and the model predictions shown here lends confidence to the models which are
then used to describe the time evolution of galaxy parameters such as star
formation rates, chemical gradients, and gradients in the mean age of the
stellar population.Comment: to be published in Astrophysical Journa
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