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 ($\sim$ 3 Mpc$^2$) 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 $B \sim 21$). 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 ``$\beta$-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 $\times$ 10$^7$ $M_{\odot}$ 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 $M_{\odot}$ yr$^{-1}$.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