The Role of Pressure in GMC Formation II: The H_2 - Pressure Relation

We show that the ratio of molecular to atomic gas in galaxies is determined by hydrostatic pressure and that the relation between the two is nearly linear. The pressure relation is shown to be good over three orders of magnitude for 14 galaxies including dwarfs, HI-rich, and H_2-rich galaxies as well as the Milky Way. The sample spans a factor of five in mean metallicity. The rms scatter of individual points of the relation is only about a factor of two for all the galaxies, though some show much more scatter than others. Using these results, we propose a modified star formation prescription based on pressure determining the degree to which the ISM is molecular. The formulation is different in high and low pressure regimes defined by whether the gas is primarily atomic or primarily molecular. This formulation can be implemented in simulations and provides a more appropriate treatment of the outer regions of spiral galaxies and molecule-poor systems such as dwarf irregulars and damped Lyman-alpha systems.Comment: 14 pages, 7 figures, Accepted to the Astrophysical Journa

Time-dependent variation: A new defect-based prediction methodology

For the first time, different impacts of as-grown and generated defects on nm-sized devices are demonstrated. As-grown hole traps are responsible for WDF, which increases with Vg_op and tw. The generated defects are substantial, but do not contribute to WDF and consequently are not detected by RTN. The non-discharging component follows the same model as that for large devices: the `AG' model. Based on this defect framework, a new methodology is proposed for test engineers to predict the long term TDV and yield and its prediction-capability is verified

Evidence for an outflow from the Seyfert galaxy NGC 4051

New observations using narrow band imaging, long-slit spectroscopy and MERLIN observations of the nuclear region of the Seyfert galaxy NGC~4051 have been made. An edge brightened, triangular region of ionized gas extending 420 pc from the centre of the galaxy has been detected. Long-slit spectra of this ionised gas, taken at 1.5\arcsec\ from the core, show the \oiii\ emission line to consist of two velocity components, both blue-shifted from the systemic radial velocity, with velocity widths of 140\kms\ and separated by 120\kms. This region is co-spatial with weak extended radio emission and is suggestive of a centrally driven outflow. The \oiii\ line spectrum and image of this region have been modelled as an outflowing conical structure at 50\degr\ to the line of sight with a half opening angle of 23\degr . In addition to the extended structure, high resolution MERLIN observations of the 18-cm nuclear radio emission reveal a compact (1\arcsec) radio triple source in PA 73$^{\circ}$. This source is coincident with the HST-imaged emission line structure. These high resolution observations are consistent with a more compact origin of activity (i.e. a Seyfert nucleus) than a starburst region.Comment: latex, epsf.sty, 8 pages, 8 figures. Also available at http://axp2.ast.man.ac.uk:8000/Preprints.htm

Far infrared and Radio emission in dusty starburst galaxies

We revisit the nature of the FIR/Radio correlation by means of the most recent models for star forming galaxies. We model the IR emission with our population synthesis code, GRASIL (Silva et al. 1998). As for the radio emission, we revisit the simple model of Condon & Yin (1990). We find that a tightFIR/Radio correlation is natural when the synchrotron mechanism dominates over the inverse Compton, and the electrons cooling time is shorter than the fading time of the supernova rate. Observations indicate that both these conditions are met in star forming galaxies. However since the radio non thermal emission is delayed, deviations are expected both in the early phases of a starburst, when the radio thermal component dominates, and in the post-starburst phase, when the bulk of the NT component originates from less massive stars. This delay allows the analysis of obscured starbursts with a time resolution of a few tens of Myrs, unreachable with other star formation indicators. We suggest to complement the analysis of the deviations from the FIR/Radio correlation with the radio slope to obtain characteristic parameters of the burst. The analysis of a sample of compact ULIRGs shows that they are intense but transient starbursts, to which one should not apply usual SF indicators devised for constant SF rates. We also discuss the possibility of using the q- radio slope diagram to asses the presence of obscured AGN. A firm prediction of the models is an apparent radio excess during the post-starburst phase, which seems to be typical of a class of star forming galaxies in rich cluster cores. We discuss how deviations from the correlation, due to the evolutionary status of the starburst, affect the technique of photometric redshift determination widely used for high-z sources.Comment: accepted by A&A, 16 page

H-alpha Kinematics of the SINGS Nearby Galaxies Survey. II

This is the second part of an H-alpha kinematics follow-up survey of the Spitzer Infrared Nearby Galaxies Survey (SINGS) sample. The aim of this program is to shed new light on the role of baryons and their kinematics and on the dark/luminous matter relation in the star forming regions of galaxies, in relation with studies at other wavelengths. The data for 37 galaxies are presented. The observations were made using Fabry-Perot interferometry with the photon-counting camera FaNTOmM on 4 different telescopes, namely the Canada-France-Hawaii 3.6m, the ESO La Silla 3.6m, the William Herschel 4.2m, and the Observatoire du mont Megantic 1.6m telescopes. The velocity fields are computed using custom IDL routines designed for an optimal use of the data. The kinematical parameters and rotation curves are derived using the GIPSY software. It is shown that non-circular motions associated with galactic bars affect the kinematical parameters fitting and the velocity gradient of the rotation curves. This leads to incorrect determinations of the baryonic and dark matter distributions in the mass models derived from those rotation curves.Comment: 18 pages, 5 figures, 4 tables. Accepted for publication in MNRAS. All high-res. figures are available at http://www.astro.umontreal.ca/fantomm/singsII

The infrared supernova rate in starburst galaxies

We report the results of our ongoing search for extincted supernovae (SNe) at near-infrared wavelengths. We have monitored at 2.2 micron a sample of 46 Luminous Infrared Galaxies and detected 4 SNe. The number of detections is still small but sufficient to provide the first estimate of supernova rate at near-infrared wavelengths. We measure a SN rate ofv 7.6+/-3.8 SNu which is an order of magnitude larger than observed in quiescent galaxies. On the other hand, the observed near-infrared rate is still a factor 3-10 smaller than that estimated from the far-infrared luminosity of the galaxies. Among various possibilities, the most likely scenario is that dust extinction is so high (Av>30) to obscure most SNe even in the near-IR. The role of type Ia SNe is also discussed within this context. We derive the type Ia SN rate as a function of the stellar mass of the galaxy and find a sharp increase toward galaxies with higher activity of star formation. This suggests that a significant fraction of type Ia SNe are associated with young stellar populations. Finally, as a by-product, we give the average K-band light curve of core-collapse SNe based on all the existing data, and review the relation between SN rate and far-infrared luminosity.Comment: A&A, in press, 13 page

Evolutionary dynamics of methicillin-resistant Staphylococcus aureus within a healthcare system

Background: In the past decade, several countries have seen gradual replacement of endemic multi-resistant healthcare-associated methicillin-resistant Staphylococcus aureus (MRSA) with clones that are more susceptible to antibiotic treatment. One example is Singapore, where MRSA ST239, the dominant clone since molecular profiling of MRSA began in the mid-1980s, has been replaced by ST22 isolates belonging to EMRSA-15, a recently emerged pandemic lineage originating from Europe.Results: We investigated the population structure of MRSA in Singaporean hospitals spanning three decades, using whole genome sequencing. Applying Bayesian phylogenetic methods we report that prior to the introduction of ST22, the ST239 MRSA population in Singapore originated from multiple introductions from the surrounding region; it was frequently transferred within the healthcare system resulting in a heterogeneous hospital population. Following the introduction of ST22 around the beginning of the millennium, this clone spread rapidly through Singaporean hospitals, supplanting the endemic ST239 population. Coalescent analysis revealed that although the genetic diversity of ST239 initially decreased as ST22 became more dominant, from 2007 onwards the genetic diversity of ST239 began to increase once more, which was not associated with the emergence of a sub-clone of ST239. Comparative genomic analysis of the accessory genome of the extant ST239 population identified that the Arginine Catabolic Mobile Element arose multiple times, thereby introducing genes associated with enhanced skin colonization into this population.Conclusions: Our results clearly demonstrate that, alongside clinical practice and antibiotic usage, competition between clones also has an important role in driving the evolution of nosocomial pathogen populations.</p

A 0.8-2.4 microns spectral atlas of Active Galactic Nuclei

Aims: We present a near-infrared spectral atlas of 47 active galactic nuclei (AGN), of all degrees of activity, in the wavelength interval of 0.8-2.4 microns, including the fluxes of the observed emission lines. We analyze the spectroscopic properties of the continuum and emission line spectra of the sources Methods: In order to exclude aperture and seeing effects we use near-infrared spectroscopy in the short cross-dispersed mode (SXD, 0.8-2.4 microns), taking the JHK-bands spectra simultaneously. Results: We present the most extensive NIR spectral atlas of AGN to date. This atlas offers a suitable database for studying the continuum and line emission properties of these objects in a region full of interesting features. The shape of the continuum of QSOs and Seyfert 1's are similar, being essentially flat in H and K band, in the J band, a strong variation is found. In Seyfert 2 galaxies, the continuum in the F_lambda X lambda space smoothly decreases from 1.2 microns redwards in almost all sources. In J, it smoothly rises bluewards in some sources while in others a small decreased in flux is observed. The spectra are dominated by strong emission features of H I, He I, He II, [S III] and conspicuous forbidden lines of low and high ionization species. Molecular lines of H2 are common features to most objects. The absence of O I and Fe II lines in Seyfert 2 galaxies give observational support to the fact that these lines are formated in the outermost portion of the broad line region. [P II] and coronal lines are detected in all degrees of activity. The [Fe II] 12570A/16436A line ratio becomes a reliable reddening indicator for the narrow-line region of Seyfert galaxies.Comment: 39 pages, 17 figures, accepted for publication in Astronomy and Astrophysics (15/05/2006