5,235 research outputs found
High resolution spectroscopy of H II Galaxies: Structure and Supersonic line widths
We present high resolution echelle spectroscopy of a sample of H II galaxies.
In all galaxies we identify different H(alpha) emitting knots along the slit
crossing the nucleus. All of these have been isolated and separately analyzed
through luminosity and size vs diagnosis plots. We find that in all cases, for
a particular galaxy, the bulk of emission comes from their main knot and
therefore, at least for the compact class galaxies we are dealing with,
luminosity and sigma values measured using single aperture observations would
provide similar results to what is obtained with spatially resolved
spectroscopy. In the size vs plots as expected there is a shift in the
correlations depending on whether we are including all emission in a single
point or we split it in its different emitting knots. The problem of a proper
determination of the size of the emitting region so that it can be used to
determine the mass of the system remains open. From the data set gathered,
using the highest surface brightness points as recently proposed by
Fuentes-Masip et al. (2000), the best luminosity vs correlation turns out to be
consistent with a Virial model.Comment: 14 pages, 4 figures, ApJ accepted. Also available from
http://www.daf.on.br/~etelles/papers/wht.ps.g
Radiation from carbon in a rocket plume mixing region with coupled convective and radiative energy fluxes and general optical thickness
Carbon radiant heat transfer from plume mixing region to base of rocket vehicl
Evidence of Substructure in the Cluster of Galaxies A3558
We investigate the dynamical properties of the cluster of galaxies A3558
(Shapley 8). Studying a region of one square degree ( 3 Mpc) centered
on the cluster cD galaxy, we have obtained a statistically complete photometric
catalog with positions and magnitudes of 1421 galaxies (down to a limiting
magnitude of ). This catalog has been matched to the recent velocity
data obtained by Mazure et al. (1997) and from the literature, yielding a
radial velocity catalog containing 322 galaxies. Our analysis shows that the
position/velocity space distribution of galaxies shows significant
substructure. A central bimodal core detected previously in preliminary studies
is confirmed by using the Adaptive Kernel Technique and Wavelet Analysis. We
show that this central bimodal subtructure is nevertheless composed of a
projected feature, kinematically unrelated to the cluster, plus a group of
galaxies probably in its initial merging phase into a relaxed core. The cD
velocity offset with respect to the average cluster redshift, reported earlier
by several authors, is completely eliminated as a result of our dynamical
analysis. The untangling of the relaxed core component also allows a better,
more reliable determination of the central velocity dispersion, which in turn
eliminates the ``-problem'' for A3558. The cluster also shows a
``preferential'' distribution of subclumps coinciding with the direction of the
major axis position angle of the cD galaxy and of the central X-ray emission
ellipsoidal distribution, in agreement with an anisotropic merger scenario.Comment: 35 pages in latex, 17 figures in Postscript, accepted for publication
in the Astrophysical Journa
Reconstruction of the HII Galaxy Hubble Diagram using Gaussian Processes
The Hubble diagram constructed using HII galaxies (HIIGx) and Giant
extragalactic HII regions (GEHR) as standard candles already extends beyond the
current reach of Type Ia SNe. A sample of 156 HIIGx and GEHR sources has been
used previously to compare the predictions of LCDM and R_h=ct, the results of
which suggested that the HIIGx and GEHR sources strongly favour the latter over
the former. But this analysis was based on the application of parametric fits
to the data and the use of information criteria, which disfavour the less
parsimonious models. In this paper, we advance the use of HII sources as
standard candles by utilizing Gaussian processes (GP) to reconstruct the
distance modulus representing these data without the need to pre-assume any
particular model, none of which may in the end actually be the correct
cosmology. In addition, this approach tightly constrains the 1 sigma confidence
region of the reconstructed function, thus providing a better tool with which
to differentiate between competing cosmologies. With this approach, we show
that the Planck concordance model is in tension with the HII data at more than
2.5 sigma, while R_h=ct agrees with the GP reconstruction very well,
particularly at redshifts > 10^{-3}.Comment: 11 pages, 4 figures. Accepted for publication in JCA
A Two-point Diagnostic for the HII Galaxy Hubble Diagram
A previous analysis of starburst-dominated HII Galaxies and HII regions has
demonstrated a statistically significant preference for the
Friedmann-Robertson-Walker cosmology with zero active mass, known as the R_h=ct
universe, over LCDM and its related dark-matter parametrizations. In this
paper, we employ a 2-point diagnostic with these data to present a
complementary statistical comparison of R_h=ct with Planck LCDM. Our 2-point
diagnostic compares---in a pairwise fashion---the difference between the
distance modulus measured at two redshifts with that predicted by each
cosmology. Our results support the conclusion drawn by a previous comparative
analysis demonstrating that R_h=ct is statistically preferred over Planck LCDM.
But we also find that the reported errors in the HII measurements may not be
purely Gaussian, perhaps due to a partial contamination by non-Gaussian
systematic effects. The use of HII Galaxies and HII regions as standard candles
may be improved even further with a better handling of the systematics in these
sources.Comment: 7 pages, 6 figures, 2 tables. Accepted for publication in MNRA
Detection and Mapping of Decoupled Stellar and Ionized Gas Structures in the Ultraluminous Infrared Galaxy IRAS 12112+0305
Integral field optical spectroscopy with the INTEGRAL fiber-fed system and
HST optical imaging are used to map the complex stellar and warm ionized gas
structure in the ultraluminous infrared galaxy IRAS 12112+0305. Images
reconstructed from wavelength-delimited extractions of the integral field
spectra reveal that the observed ionized gas distribution is decoupled from the
stellar main body of the galaxy, with the dominant continuum and emission-line
regions separated by projected distances of up to 7.5 kpc. The two optical
nuclei are detected as apparently faint emission-line regions, and their
optical properties are consistent with being dust-enshrouded weak-[OI] LINERs.
The brightest emission-line region is associated with a faint (m_{I}= 20.4),
giant HII region of 600 pc diameter, where a young (about 5 Myr) massive
cluster of about 2 10 dominates the ionization.
Internal reddening towards the line-emitting regions and the optical nuclei
ranges from 1 to 8 magnitudes, in the visual. Taken the reddening into aacount,
the overall star formation in IRAS 12112+0305 is dominated by starbursts
associated with the two nuclei and corresponding to a star formation rate of 80
yr.Comment: 2 figures, accepted to Ap.J. Letter
Hubble Space Telescope Photometry of Hodge 301: An "Old" Star Cluster in 30 Doradus
We present Hubble Space Telescope Planetary Camera UVI data for the
little-studied cluster Hodge 301 3' northwest of 30 Doradus' central ionizing
cluster R136. The average reddening of Hodge 301 is found to be =
(0.28+-0.05) mag from published infrared and ultraviolet photometry. Using two
different sets of evolutionary models, we derive an age of ~ 20-25 Myr for
Hodge 301, which makes it roughly 10 times as old as R136. Hodge 301 is the
most prominent representative of the oldest population in the 30 Dor starburst
region; a region that has undergone multiple star formation events. This range
of ages is an important consideration for the modelling of starburst regions.
Hodge 301 shows a widened upper main sequence largely caused by Be stars. We
present a list of Be star candidates. The slope of the initial mass function
for intermediate-mass main sequence stars ranging from 10 to 1.3 solar masses
is found to be -1.4+-0.1 in good agreement with a Salpeter law. There is no
indication for a truncation or change of slope of the IMF within this mass
range. In accordance with the age of Hodge 301 no obvious pre-main-sequence
stars are seen down to 1 solar mass. We estimate that up to 41+-7 stars with
more than 12 solar masses may have turned into supernovae since the formation
of the cluster. Multiple supernova explosions are the most likely origin of the
extremely violent gas motions and the diffuse X-ray emission observed in the
cluster surroundings.Comment: To appear in the Astronomical Journal (Feb 2000 issue). 16 pages in
two-column style. 9 separate figures, in part in significantly reduced
resolution for space reasons (bitmapped postscript or jpg
The Massive Star Content of NGC 3603
We investigate the massive star content of NGC 3603, the closest known giant
H II region. We have obtained spectra of 26 stars in the central cluster using
the Baade 6.5-m telescope (Magellan I). Of these 26 stars, 16 had no previous
spectroscopy. We also obtained photometry of all of the stars with previous or
new spectroscopy, primarily using archival HST ACS/HRC images. We use these
data to derive an improved distance to the cluster, and to construct an H-R
diagram for discussing the masses and ages of the massive star content of this
cluster.Comment: Accepted by the Astronomical Journal. This revision updates the
coordinates in Table 1 by (-0.18sec, +0.2") to place them on the UCAC2 syste
Radiative Transfer Effects in He I Emission Lines
We consider the effect of optical depth of the 2 ^{3}S level on the nebular
recombination spectrum of He I for a spherically symmetric nebula with no
systematic velocity gradients. These calculations, using many improvements in
atomic data, can be used in place of the earlier calculations of Robbins. We
give representative Case B line fluxes for UV, optical, and IR emission lines
over a range of physical conditions: T=5000-20000 K, n_{e}=1-10^{8} cm^{-3},
and tau_{3889}=0-100. A FORTRAN program for calculating emissivities for all
lines arising from quantum levels with n < 11 is also available from the
authors.
We present a special set of fitting formulae for the physical conditions
relevant to low metallicity extragalactic H II regions: T=12,000-20,000 K,
n_{e}=1-300 cm^{-3}, and tau_{3889} < 2.0. For this range of physical
conditions, the Case B line fluxes of the bright optical lines 4471 A, 5876 A,
and 6678 A, are changed less than 1%, in agreement with previous studies.
However, the 7065 A corrections are much smaller than those calculated by
Izotov & Thuan based on the earlier calculations by Robbins. This means that
the 7065 A line is a better density diagnostic than previously thought. Two
corrections to the fitting functions calculated in our previous work are also
given.Comment: To be published in 10 April 2002 ApJ; relevant code available at
ftp://wisp.physics.wisc.edu/pub/benjamin/Heliu
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