Young Super Star Clusters in the Starburst of M82: The Catalogue

Recent results from Hubble Space Telescope (HST) have resolved starbursts as collections of compact young stellar clusters. Here we present a photometric catalogue of the young stellar clusters in the nuclear starburst of M82, observed with the HST WFPC2 in Halpha (F656N) and in four optical broad-band filters. We identify 197 young super stellar clusters. The compactness and high density of the sources led us to develop specific techniques to measure their sizes. Strong extinction lanes divide the starburst into five different zones and we provide a catalogue of young super star clusters for each of these. In the catalogue we include relative coordinates, radii, fluxes, luminosities, masses, equivalent widths, extinctions, and other parameters. Extinction values have been derived from the broad-band images. The radii range between 3 and 9 pc, with a mean value of 5.7 +/- 1.4pc, and a stellar mass between 10e4 and 10e6 Mo. The inferred masses and mean separation, comparable to the size of super star clusters, together with their high volume density, provides strong evidence for the key ingredients postulated by Tenorio et al. (2003) as required for the development of a supergalactic wind.Comment: 45 pages, 5 figures, 12 tables. Accepted for publication in ApJ. Added Erratu

On the feedback from super stellar clusters. I. The structure of giant HII regions and HII galaxies

We review the structural properties of giant extragalactic HII regions and HII galaxies based on 2D hydrodynamic calculations, and propose an evolutionary sequence that accounts for their observed detailed structure. The model assumes a massive and young stellar cluster surrounded by a large collection of clouds. These are thus exposed to the most important star-formation feedback mechanisms: photoionization and the cluster wind. The models show how the two feedback mechanisms compete in the disruption of clouds and lead to two different hydrodynamic solutions: The storage of clouds into a long lasting ragged shell that inhibits the expansion of the thermalized wind, and the steady filtering of the shocked wind gas through channels carved within the cloud stratum. Both solutions are claimed to be concurrently at work in giant HII regions and HII galaxies, causing their detailed inner structure. This includes multiple large-scale shells, filled with an X-ray emitting gas, that evolve to finally merge with each other, giving the appearance of shells within shells. The models also show how the inner filamentary structure of the giant superbubbles is largely enhanced with matter ablated from clouds and how cloud ablation proceeds within the original cloud stratum. The calculations point at the initial contrast density between the cloud and the intercloud media as the factor that defines which of the two feedback mechanisms becomes dominant throughout the evolution. Animated version of the models can be found at http://www.iaa.csic.es/\~{}eperez/ssc/ssc.html.Comment: 28 pages, 10 figures, accepted for publication in the ApJ. Animated version of the models can be found at http://www.iaa.csic.es/\~{}eperez/ssc/ssc.htm

The Interaction between the ISM and Star Formation in the Dwarf Starburst Galaxy NGC 4214

We present the first interferometric study of the molecular gas in the metal-poor dwarf starburst galaxy NGC 4214. Our map of the 12CO(1-0) emission, obtained at the OVRO millimeter array, reveals an unexpected structural wealth. We detected three regions of molecular emission in the north-west (NW), south-east (SE) and centre of NGC 4214 which are in very different and distinct evolutionary stages (total molecular mass: 5.1 x 10^6 M_sun). These differences are apparent most dramatically when the CO morphologies are compared to optical ground based and HST imaging: massive star formation has not started yet in the NW region; the well-known starburst in the centre is the most evolved and star formation in the SE complex started more recently. We derive a star formation efficiency of 8% for the SE complex. Using high--resolution VLA observations of neutral hydrogen HI and our CO data we generated a total gas column density map for NGC 4214 (HI + H_2). No clear correlation is seen between the peaks of HI, CO and the sites of ongoing star formation. This emphasizes the irregular nature of dwarf galaxies. The HI and CO velocities agree well, so do the H-alpha velocities. In total, we cataloged 14 molecular clumps in NGC 4214. Our results from a virial mass analysis are compatible with a Galactic CO-to-H_2 conversion factor for NGC 4214 (lower than what is usually found in metal-poor dwarf galaxies).Comment: accepted for publication in the AJ (February 2001), full ps file at: ftp://ftp.astro.caltech.edu/users/fw/ngc4214/walter_prep.p

Competition between nucleation and confinement in the crystallization of poly(ethylene glycol)/ large aspect ratio hectorite nanocomposites

Unformatted preprint version of the submitted articleThe overall crystallization kinetics of polymer nanocomposites is determined by nucleation and crystal growth, which are both greatly affected by confinement. Heterogeneous nucleation is influenced by the interphase area between filler and polymer matrix. Starting with a homogeneous nematic aqueous dispersion of a mixture containing polyethylene glycol (PEG) and varying amounts of a high aspect ratio layered silicate (hectorite, Hec), nanocomposite films were casted displaying a systematic variation of the degree of PEG confinement. This is achieved by a partial phase segregation upon drying, where independently of filler content a thermodynamically stable, 1 dimensional crystalline hybrid with constant volume of intercalated PEG (0.81 nm corresponding to a fraction 75 wt% and 55 vol%, respectively) is formed. This intercalated hybrid phase is incorporated into segregated PEG domains. The segregation is a kinetically controlled process and the length scale of segregation increases with PEG available in surplus of the hybrid. Due to the very large lateral extension of the Hec, the segregated domains are increasingly two dimensional. As evidenced by transmission electron micrographs and powder X-ray diffraction, the segregation produces composite structures where, in dependency of filler content, PEG slabs of different thickness are separated by domains of the intercalated hybrid material. The crystallization behavior of these bi-phasic materials was investigated by Differential Scanning Calorimetry (DSC) and Polarized Light Optical Microscopy (PLOM). DSC results reveal a competition between the nucleating effect of Hec, which was particularly important at low amounts, and the PEG confinement effect at higher filler loadings. Applying a self-nucleation protocol, the nucleation efficiency of the hectorite was shown to be up to 67%. The isothermal crystallization kinetics accelerated at low Hec contents (nucleation), went through a maximum and then decreased (confinement) as Hec content increased. Additionaly, a clear correlation between filler content and the Avrami index was obtained supporting the increase in confinement as filler loading increased.The authors thank Florian Puchtler for producing the synthetic sodium hectorite, Marco Schwarzmann for the SEM and TEM measurements and sample preparation via cryo ion slicing, and Dr. Sabine Rosenfeldt for the SAXS measurements. We appreciate the support of the Keylab for Optical and Electron Microscopy and the Keylab for Small Scale Polymer Processing of the Bavarian Polymer Institute (BPI). This work was supported by the German Science Foundation (DFG) within the collaborative research project SFB 1357. J.M. acknowledges support from the Provincial Council of Gipuzkoa under the program Fellow Gipuzkoa and partial financial support to the IBERDROLA Foundation. J.L.O.M. wish to thank the National Council of Science and Technology (CONACYT) in México for his grant 471837. We acknowledge funding by Mineco MAT2017-83014-C2-1-P project and by the Basque Government through grant IT1309-19. This work has also received funding from the European Union´s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 778092

New Wolf-Rayet Galaxies with Detection of WC Stars

We report the discovery of two new Wolf-Rayet (WR) galaxies: Mrk~1039, and F08208$+$2816. Two broad WR bumps at 5808\AA~ and 4650\AA~ indicate the presence of WCE and WNL star population in all two sources. We also confirm the presenceof WR features in Mrk~35, previously detected in a different position. The observed equivalent width of the WR bump at 4650\AA~ and the derived number ratios of WR/(WR$+$O) imply that star formation in these sources takes place inshort burst duration. Comparisons with the recent models of WR populations in young starbursts with the observed EW(\HeII)/EW(\CIV)/EW(WRbump) and their relative intensitie provide an indication that the stellar initial mass function in some WR galaxies might not be Salpeter-like. It is interesting to find that the luminous IRAS source, F08208$+$2816, has little dust reddening, probably because of the existence of a powerful superwind. By comparisons with other starbursts observed with the Hopkins Ultraviolet Telescope, F08208$+$2816 as a merging system renders a chance to study the contribution from young starbursts to the UV background radiation in universe.Comment: 22 pages, 6 figures, 4 tables, accepted by The Astrophysical Journa

Atypical presentation of acute pancreatitis in a man with pancreatic insufficiency and cystic fibrosis: a case report

<p>Abstract</p> <p>Introduction</p> <p>Whether acute pancreatitis can occur in pancreatically insufficient individuals with cystic fibrosis remains a matter of debate.</p> <p>Case presentation</p> <p>We describe a case of acute pancreatitis occurring in a 52-year-old Caucasian Australian man with moderately severe cystic fibrosis lung disease and pancreatic insufficiency. An inflammatory mass within the head of his pancreas was confirmed using computed tomography, magnetic resonance imaging and pancreatic biopsy, but serum amylase and lipase remained normal throughout the acute phase of his illness. His symptoms and the pancreatic mass resolved following the insertion of a biliary stent and the introduction of ursodeoxycholic acid.</p> <p>Conclusion</p> <p>Our case report highlights the potential for acute pancreatitis to occur in patients with pancreatic insufficiency and cystic fibrosis. We further demonstrate that conventional biochemical markers that are normally assessed to confirm the diagnosis may not be of particular use. As patients with cystic fibrosis survive into their fourth and fifth decades of life, atypical presentations of acute pancreatitis may become more common.</p

Metal enrichment in near-IR luminous galaxies at z~2: signatures of proto-ellipticals?

We present the analysis of the coadded rest-frame UV spectrum (1200<z<2000 A) of five K-luminous galaxies at z~2 from the K20 survey. The composite spectrum is characterized by strong absorption lines over the UV continuum from C, N, O, Al, Si, and Fe in various ionization stages. While some of these lines are interstellar, several among the strongest absorptions are identified with stellar photospheric lines. Most of the photospheric and interstellar features are stronger in the K-luminous composite spectrum than in LBGs at z~3. This suggests higher metallicity and possibly also larger interstellar velocity dispersion caused by macroscopic motions. The absorption lines and the slope of the UV continuum is well matched by the spectrum of the nearby luminous infrared galaxy NGC 6090, which is in the process of merging. A metallicity higher than solar is suggested by comparing the pure photospheric lines (SiIII, CIII, FeV) with starburst models. The evidence of high metallicity, together with the high masses, high star-formation rates, and possibly strong clustering, well qualify these galaxies as progenitors of local massive ellipticals.Comment: 4 pages, 3 figures, Accepted ApJ Letter

Nuclear activity and massive star formation in the low luminosity AGN NGC4303: Chandra X-ray observations

We present evidence of the co-existence of either an AGN or an ultraluminous X-ray source (ULX), together with a young super stellar cluster in the 3 central parsecs of NGC4303. The galaxy contains a low luminosity AGN and hosts a number of starburst regions in a circumnuclear spiral, as well as in the nucleus itself. A high spatial resolution Chandra image of this source reveals that the soft X-ray emission traces the ultraviolet nuclear spiral down to a core, which is unresolved both in soft and hard X-rays. The astrometry of the X-ray core coincides with the UV core within the Chandra positioning accuracy. The total X-ray luminosity of the core, 1.5*10^{39} erg/s, is similar to that from some LINERs or from the weakest Seyferts detected so far. The soft X-rays in both the core and the extended structure surrounding it can be well reproduced by evolutionary synthesis models (which include the emission expected from single stars, the hot diffuse gas, supernova remnants and binary systems), consistent with the properties of the young stellar clusters identified in the UV. The hard X-ray tail detected in the core spectrum, however, most likely requires the presence of an additional source. This additional source could either be a weak active nucleus black hole or an ultraluminous X-ray object. The implications of these results are discussed.Comment: 37 pages, 7 figures, ApJ accepte

The Dwarf Irregular/Wolf-Rayet Galaxy NGC4214: I. A New Distance, Stellar Content, and Global Parameters

We present the results of a detailed optical and near-IR study of the nearby star-forming dwarf galaxy NGC4214. We discuss the stellar content, drawing particular attention to the intermediate-age and/or old field stars, which are used as a distance indicator. On images obtained with the Hubble Space Telescope WFPC2 and NICMOS instruments in the equivalents of the V, R, I, J and H bands, the galaxy is well resolved into stars. We achieve limiting magnitudes of F814W ~27 in the WF chips and F110W ~25 in the NIC2. The optical and near-infrared color-magnitude diagrams confirm a core-halo galaxy morphology: an inner high surface-brightness young population within ~1.5' (~1 kpc) from the center of the galaxy, where the stars are concentrated in bright complexes along a bar-like structure; and a relatively low-surface-brightness, field-star population extending out to at least 8' (7 kpc). The color-magnitude diagrams of the core region show evidence of blue and red supergiants, main-sequence stars, asymptotic giant branch stars and blue loop stars. We identify some candidate carbon stars from their extreme near-IR color. The field-star population is dominated by the "red tangle", which contains the red giant branch. We use the I-band luminosity function to determine the distance based on the tip-of-the-red-giant-branch method: 2.7\pm0.3 Mpc. This is much closer than the values usually assumed in the literature, and we provide revised distance dependent parameters such as physical size, luminosity, HI mass and star-formation rate.Comment: 24 pages, 19 figures, accepted for publication in the July 2002 issue of AJ. Version with high resolution figures is available at http://www.astro.spbu.ru/staff/dio/preprints.htm