5,752 research outputs found
Expansive components in H II regions
We study the presence of low intensity high velocity components, which we
have termed wing features in the integrated Halpha emission line profiles of
the HII region populations of the spiral barred galaxies NGC 1530, NGC 3359 and
NGC 6951. We find that more than a third of the HII region line profiles in
each galaxy show these components. The highest fraction is obtained in the
galaxy whose line profiles show the best S:N, which suggests that wing features
of this type may well exist in most, if not all, HII region line profiles.
Applying selection criteria to the wing features, we obtain a sample of HII
regions with clearly defined high velocity components in their profiles.
Deconvolution of a representative sample of the line profiles eliminates any
doubt that the wing features could possibly be due to instrumental effects. We
present an analysis of the high velocity low intensity features fitting them
with Gaussian functions; the emission measures, central velocities and velocity
dispersions for the red and blue features take similar values. We interpret the
features as signatures of expanding shells inside the HII regions. Up to a
shell radius of R(shell)~0.2R(reg), the stellar winds from the central ionizing
stars appear to satisfy the energy and momentum requirements for the formation
and driving the shell. Several examples of the most luminous HII regions show
that the shells appear to have larger radii; in these cases additional
mechanisms may well be needed to explain the kinetic energies and momenta of
the shells.Comment: 16 pages, 9 figures, accepted for publication in A&
The internal dynamical equilibrium of HII regions: a statistical study
We present an analysis of the integrated Halpha emission line profiles for
the HII region population of the spiral galaxies NGC 1530, NGC 6951 and NGC
3359. We show that 70% of the line profiles show two or three Gaussian
components. The relations between the Halpha luminosity and non-thermal line
width for the HII regions of the three galaxies are studied and compared with
the relation found taken all the HII regions of the three galaxies as a single
distribution. A clearer envelope in non-thermal line width is found when only
those HII regions with non-thermal line width bigger than 13kms are considered.
The linear fit for the envelope is logL=36.8+2.0*log(sigma). The masses of the
HII regions on the envelope using the virial theorem and the mass estimates
from the Halpha luminosity are comparable, which offers evidence that the HII
regions on the envelope are virialized systems, while the remaining regions,
the majority, are not in virial equilibrium.Comment: 19 pages, 10 figures,accepted for publication in A&
Locally projective monoidal model structure for complexes of quasi-coherent sheaves on P^1(k)
We will generalize the projective model structure in the category of
unbounded complexes of modules over a commutative ring to the category of
unbounded complexes of quasi-coherent sheaves over the projective line.
Concretely we will define a locally projective model structure in the category
of complexes of quasi-coherent sheaves on the projective line. In this model
structure the cofibrant objects are the dg-locally projective complexes. We
also describe the fibrations of this model structure and show that the model
structure is monoidal. We point out that this model structure is necessarily
different from other known model structures such as the injective model
structure and the locally free model structure
HIIphot: Automated Photometry of HII Regions Applied to M51
We have developed a robust, automated method, hereafter designated HIIphot,
which enables accurate photometric characterization of HII regions while
permitting genuine adaptivity to irregular source morphology. HIIphot utilizes
object-recognition techniques to make a first guess at the shapes of all
sources then allows for departure from such idealized ``seeds'' through an
iterative growing procedure. Photometric corrections for spatially coincident
diffuse emission are derived from a low-order surface fit to the background
after exclusion of all detected sources. We present results for the
well-studied, nearby spiral M51 in which 1229 HII regions are detected above
the 5-sigma level. A simple, weighted power-law fit to the measured H-alpha
luminosity function (HII LF) above log L_H-alpha = 37.6 gives alpha =
-1.75+/-0.06, despite a conspicuous break in the HII LF observed near L_H-alpha
= 10^38.9. Our best- fit slope is marginally steeper than measured by Rand
(1992), perhaps reflecting our increased sensitivity at low luminosities and to
notably diffuse objects. HII regions located in interarm gaps are
preferentially less luminous than counterparts which constitute M51's
grand-design spiral arms and are best fit with a power-law slope of alpha =
-1.96+/-0.15. We assign arm/interarm status for HII regions based upon the
varying surface brightness of diffuse emission as a function of position
throughout the image. Using our measurement of the integrated flux contributed
by resolved HII regions in M51, we estimate the diffuse fraction to be
approximately 0.45 -- in agreement with the determination of Greenawalt et al.
(1998). Automated processing of degraded datasets is undertaken to gauge
systematic effects associated with limiting spatial resolution and sensitivity.Comment: 41 pages, 14 figures, Postscript version with high-resolution figures
at ftp://ftp.aoc.nrao.edu/staff/dthilker/preprint
An improved method for statistical studies of the internal kinematics of HII regions: the case of M 83
We present the integrated Halpha emission line profile for 157 HII regions in
the central 3.4' x 3.4' of the galaxy M 83 (NGC 5236). Using the Fabry-Perot
interferometer GHaFaS, on the 4.2 m William Herschel on La Palma, we show the
importance of a good characterization of the instrumental response function for
the study of line profile shapes. The luminosity-velocity dispersion relation
is also studied, and in the log(L)-log(sigma) plane we do not find a linear
relation, but an upper envelope with equation log(L)=0.9 *log(sigma)+38.1. For
the adopted distance of 4.5 Mpc, the upper envelope appears at the luminosity
L=10^38.5 ergs, in full agreement with previous studies of other galaxies,
reinforcing the idea of using HII regions as standard candles.Comment: 13 pages, 9 figures, accepted for publication in MNRA
Star Forming Objects in the Tidal Tails of Compact Groups
A search for star forming objects belonging to tidal tails has been carried
out in a sample of deep Halpha images of 16 compact groups of galaxies. A total
of 36 objects with Halpha luminosity larger than 10^38 erg s-1 have been
detected in five groups. The fraction of the total Halpha luminosity of their
respective parent galaxies shown by the tidal objects is always below 5% except
for the tidal features of HCG95, whose Halpha luminosity amounts to 65% of the
total luminosity. Out of this 36 objects, 9 star forming tidal dwarf galaxy
candidates have been finally identified on the basis of their projected
distances to the nuclei of the parent galaxies and their total Halpha
luminosities. Overall, the observed properties of the candidates resemble those
previously reported for the so-called tidal dwarf galaxies.Comment: 5 gif figures. Accepted for publication in Astrophysical Journa
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