The Physical Conditions and Dynamics of the Interstellar Medium in the Nucleus of M83: Observations of CO and CI

This paper presents CI, CO J=4-3, and CO J=3-2 maps of the barred spiral galaxy M83 taken at the James Clerk Maxwell Telescope. Observations indicate a double peaked structure which is consistent with gas inflow along the bar collecting at the inner Lindblad resonance. This structure suggests that nuclear starbursts can occur even in galaxies where this inflow/collection occurs, in contrast to previous studies of barred spiral galaxies. However, the observations also suggest that the double peaked emission may be the result of a rotating molecular ring oriented nearly perpendicular to the main disk of the galaxy. The CO J=4-3 data indicate the presence of warm gas in the nucleus that is not apparent in the lower-J CO observations, which suggests that CO J=1-0 emission may not be a reliable tracer of molecular gas in starburst galaxies. The twelve CI/CO J=4-3 line ratios in the inner 24'' x 24'' are uniform at the 2 sigma level, which indicates that the CO J=4-3 emission is originating in the same hot photon-dominated regions as the CI emission. The CO J=4-3/J=3-2 line ratios vary significantly within the nucleus with the higher line ratios occurring away from peaks of emission along an arc of active star forming regions. These high line ratios (>1) likely indicate optically thin gas created by the high temperatures caused by star forming regions in the nucleus of this starburst galaxy.Comment: 15 pages with 10 figures. To appear in the August 10 1998 issue of The Astrophysical Journa

Conformational modulation of sequence recognition in synthetic macromolecules

The different triplet sequences in high molecular weight aromatic copolyimides comprising pyromellitimide units ("I") flanked by either ether-ketone ("K") or ether-sulfone residues ("S") show different binding strengths for pyrene-based tweezer-molecules. Such molecules bind primarily to the diimide unit through complementary π-π-stacking and hydrogen bonding. However, as shown by the magnitudes of 1H NMR complexation shifts and tweezer-polymer binding constants, the triplet "SIS" binds tweezer-molecules more strongly than "KIS" which in turn bind such molecules more strongly than "KIK". Computational models for tweezer-polymer binding, together with single-crystal X-ray analyses of tweezer-complexes with macrocyclic ether-imides, reveal that the variations in binding strength between the different triplet sequences arise from the different conformational preferences of aromatic rings at diarylketone and diarylsulfone linkages. These preferences determine whether or not chain-folding and secondary π−π-stacking occurs between the arms of the tweezermolecule and the 4,4'-biphenylene units which flank the central diimide residue

A First Look at the Nuclear Region of M31 with Chandra

We report on the first observation of the nuclear region of M31 with the Chandra X-ray Observatory. The nuclear source seen with the Einstein and ROSAT HRIs is resolved into five point sources. One of these sources is within 1'' of the M31 central super-massive black hole. As compared to the other point sources in M31, this nuclear source has an unusual x-ray spectrum. Based on the spatial coincidence we identify this source with the central black hole, and note that the unusual spectrum is a challenge to current theories. A bright transient is detected ~26'' to the west of the nucleus, which may be associated with a stellar mass black hole.Comment: Submitted to ApJ Letters, 4 pages, 4 figures. email: garcia,ssm,fap,wrf,jem,cjf, @head-cfa.harvard.ed

ROSAT PSPC Observations of the Richest (R≥2R \geq 2) ACO Clusters

We have compiled an X-ray catalog of optically selected rich clusters of galaxies observed by the PSPC during the pointed GO phase of the ROSAT mission. This paper contains a systematic X-ray analysis of 150 clusters with an optical richness classification of $R \geq 2$ from the ACO catalog (Abell, Corwin, and Olowin 1989). All clusters were observed within 45' of the optical axis of the telescope during pointed PSPC observations. For each cluster, we calculate: the net 0.5-2.0 keV PSPC count rate (or $4 \sigma$ upper limit) in a 1 Mpc radius aperture, 0.5-2.0 keV flux and luminosity, bolometric luminosity, and X-ray centroid. The cluster sample is then used to examine correlations between the X-ray and optical properties of clusters, derive the X-ray luminosity function of clusters with different optical classifications, and obtain a quantitative estimate of contamination (i.e, the fraction of clusters with an optical richness significantly overestimated due to interloping galaxies) in the ACO catalog

Childhood and Adolescent Pesticide Exposure and Breast Cancer Risk

To date, epidemiological studies have not strongly supported an association between pesticide exposure and breast cancer. However, few previous studies had the ability to assess specific time periods of exposure. Studies that relied on adult serum levels of metabolites of organochlorine pesticides may not accurately reflect exposure during developmental periods. Further, exposure assessment often occurred after diagnosis and key tumor characteristics, such as hormone receptor status, have rarely been available to evaluate tumor-subtype specific associations. We examine the association between pesticide exposure during childhood and adolescence and breast cancer risk in the prospective Sister Study cohort (N=50,844 women) to assess this relation by tumor subtype

Genomics reveals historic and contemporary transmission dynamics of a bacterial disease among wildlife and livestock

Whole-genome sequencing has provided fundamental insights into infectious disease epidemiology, but has rarely been used for examining transmission dynamics of a bacterial pathogen in wildlife. In the Greater Yellowstone Ecosystem (GYE), outbreaks of brucellosis have increased in cattle along with rising seroprevalence in elk. Here we use a genomic approach to examine Brucella abortus evolution, cross-species transmission and spatial spread in the GYE. We find that brucellosis was introduced into wildlife in this region at least five times. The diffusion rate varies among Brucella lineages (∼3 to 8 km per year) and over time. We also estimate 12 host transitions from bison to elk, and 5 from elk to bison. Our results support the notion that free-ranging elk are currently a self-sustaining brucellosis reservoir and the source of livestock infections, and that control measures in bison are unlikely to affect the dynamics of unrelated strains circulating in nearby elk populations

Modeling the dynamics of Plasmodium vivax infection and hypnozoite reactivation in vivo

The dynamics of Plasmodium vivax infection is characterized by reactivation of hypnozoites at varying time intervals. The relative contribution of new P. vivax infection and reactivation of dormant liver stage hypnozoites to initiation of blood stage infection is unclear. In this study, we investigate the contribution of new inoculations of P. vivax sporozoites to primary infection versus reactivation of hypnozoites by modeling the dynamics of P. vivax infection in Thailand in patients receiving treatment for either blood stage infection alone (chloroquine), or the blood and liver stages of infection (chloroquine + primaquine). In addition, we also analysed rates of infection in a study in Papua New Guinea (PNG) where patients were treated with either artesunate, or artesunate + primaquine. Our results show that up to 96% of the P. vivax infection is due to hypnozoite reactivation in individuals living in endemic areas in Thailand. Similar analysis revealed the around 70% of infections in the PNG cohort were due to hypnozoite reactivation. We show how the age of the cohort, primaquine drug failure, and seasonality may affect estimates of the ratio of primary P. vivax infection to hypnozoite reactivation. Modeling of P. vivax primary infection and hypnozoite reactivation provides important insights into infection dynamics, and suggests that 90–96% of blood stage infections arise from hypnozoite reactivation. Major differences in infection kinetics between Thailand and PNG suggest the likelihood of drug failure in PNG

HST/NICMOS observations of the GLIMPSE9 stellar cluster

We present HST/NICMOS photometry, and low-resolution K-band spectra of the GLIMPSE9 stellar cluster. The newly obtained color-magnitude diagram shows a cluster sequence with H-Ks =1 mag, indicating an interstellar extinction Aks=1.6\pm0.2 mag. The spectra of the three brightest stars show deep CO band-heads, which indicate red supergiants with spectral type M1-M2. Two 09-B2 supergiants are also identified, which yield a spectrophotometric distance of 4.2\pm0.4 kpc. Presuming that the population is coeval, we derive an age between 15 and 27 Myr, and a total cluster mass of 1600\pm400 Msun, integrated down to 1 Msun. In the vicinity of GLIMPSE9 are several HII regions and SNRs, all of which (including GLIMPSE 9) are probably associated with a giant molecular cloud (GMC) in the inner galaxy. GLIMPSE9 probably represents one episode of massive star formation in this GMC. We have identified several other candidate stellar clusters of the same complex.Comment: 13 pages, 14 figures. accepted for publication in ApJ. A version with high-resolution figures can be found at the following location ftp://ftp.rssd.esa.int/pub/mmessine/ms.pdf New version with updated reference

Are Luminous cD Haloes Formed by the Disruption of Dwarf Galaxies?

From a total sample of 45 Abell clusters observed by the Einstein X-ray observatory, we present the results on the galaxy luminosity function (LF) for a group of seven clusters that were identified by the morphology of their LFs. The LFs were derived using photometric data to a completeness limit ~5.5 magnitudes below M*. We found that a single Schechter function with an average $\alpha \approx -1.0$ gives a good fit to these individual LFs within the magnitude range. These seven clusters have common properties, which indicate they form a homogeneous class of dynamically evolved clusters that can be characterized by the presence of a dominant cD galaxy, high richness, symmetrical single-peaked X-ray emission, and high gas mass. On the other hand, steep faint-end slopes (-2.0 < \alpha < -1.4) are usually detected in poorer clusters. Our result gives a direct indication that the faint-end slope of the galaxy LF is subject to environmental effects. We propose that the flatness of the faint-end slope in these clusters results from the disruption of a large fraction of dwarf galaxies during the early stages of cluster evolution. The stars and gas from the disrupted galaxies are redistributed throughout the cluster potential during violent relaxation. This heuristic scenario can explain the origin of the luminous haloes of cD galaxies and a large fraction of the gas content in the intracluster medium as a by-product. The correlation between the cluster gas mass determined from the modeling of the X-ray emission and the cD halo optical luminosity is presented to support the proposed model.Comment: 11 pages,Latex,2 Postscript figures, 2 Postscript tables, accepted for publication in Apj

Massive stars in the Cl 1813-178 Cluster. An episode of massive star formation in the W33 complex

Young massive (M >10^4 Msun) stellar clusters are a good laboratory to study the evolution of massive stars. Only a dozen of such clusters are known in the Galaxy. Here we report about a new young massive stellar cluster in the Milky Way. Near-infrared medium-resolution spectroscopy with UIST on the UKIRT telescope and NIRSPEC on the Keck telescope, and X-ray observations with the Chandra and XMM satellites, of the Cl 1813-178 cluster confirm a large number of massive stars. We detected 1 red supergiant, 2 Wolf-Rayet stars, 1 candidate luminous blue variable, 2 OIf, and 19 OB stars. Among the latter, twelve are likely supergiants, four giants, and the faintest three dwarf stars. We detected post-main sequence stars with masses between 25 and 100 Msun. A population with age of 4-4.5 Myr and a mass of ~10000 Msun can reproduce such a mixture of massive evolved stars. This massive stellar cluster is the first detection of a cluster in the W33 complex. Six supernova remnants and several other candidate clusters are found in the direction of the same complex.Comment: 11 Figures. Accepted for publication in Ap