Effects of Massive Star Formation on the ISM of Dwarf Galaxies

We are studying star formation effects on the properties of the ISM in low metallicity environments using mid-infrared (MIR) and far-infrared (FIR) observations of starbursting dwarf galaxies taken with the Infrared Space Observatory (ISO) and the Kuiper Airborne Observatory (KAO). Effects of the hard pervasive radiation field on the gas and dust, due to the dust-poor environments are apparent in both the dust and gas components. From a 158 micron [CII] survey we find enhanced I[CII]/FIR ratios in dwarf galaxies and I[CII]/I(CO) ratios up to 10 times higher than those for normal metallicity starburst galaxies. We consider MIR observations in understanding the star formation properties of dwarf galaxies and constraints on the stellar SED. Notably, the strong MIR [NeIII]/[NeII] ratios reveal the presence of current massive stellar populations < 5 My old in NGC1569, NGC1140 and IIZw40. The MIR unidentified infrared bands (UIBs) are weak, if present at all, as a general characteristic in low metallicity environments, revealing the destruction of the smallest carbon particles (e.g. PAHs) over large spatial scales. This is confirmed with our dust modeling: mass fractions of PAHs are almost negligible compared to the larger silicate grains emitting in the FIR as well as the small carbon grains emitting in the MIR, which appear to be the source of the photoelectric gas heating in these galaxies, in view of the [CII] cooling.Comment: To appear in New Astronomy Reviews, Eds. D. Schaerer & R. Delgado-Gonzalez. Proceedings for JENAM99: "The Interplay between Massive Stars and the ISM" 13 pages including 5 color figure

Modeling the Dust Spectral Energy Distributions of Dwarf Galaxies

Recent efforts on the modeling of the infrared spectral energy distributions (SEDs) of dwarf galaxies are summarised here. The characterisation of the dust properties in these low metallicity environments is just unfolding, as a result of recently available mid-infrared to millimetre observations. From the limited cases we know to date, it appears that the hard radiation fields that are present in these star-bursting dwarf galaxies, as well as the rampent energetics of supernovae shocks and winds have modified the dust properties, in comparison with those in the Galaxy, or other gas and dust rich galaxies. The sophistication of the SED models is limited by the availability of detailed data in the mid infrared and particularly in the submillimetre to millimetre regime, which will open up in the near future with space-based missions, such as Herschel.Comment: 8 pages presented at "The Spectral Energy Distribution of Gas-Rich Galaxies: Confronting Models with Data" Heidelberg (Germany), October 2004. To be published in The Spectral Energy Distribution of Gas-Rich Galaxies, ed. C. Popescu & R. Tuffs (Melville:AIP) in pres

Interstellar Gas in Low Mass Virgo Cluster Spiral Galaxies

We have measured the strengths of the [C II] 158 micron, [N II] 122 micron, and CO (1 - 0) lines from five low blue luminosity spiral galaxies in the Virgo Cluster, using the Infrared Space Observatory and the NRAO 12m millimeter telescope. Two of the five galaxies have high L([C II)]/L(CO) and L(FIR)/L(CO) ratios compared to higher mass spirals. These two galaxies, NGC 4294 and NGC 4299, have L([C II])/L(CO) ratios of >14,300 and 15,600, respectively, which are similar to values found in dwarf irregular galaxies. This is the first time that such enhanced L([C II])/L(CO) ratios have been found in spiral galaxies. This result may be due to low abundances of dust and heavy elements, which can cause the CO (1 - 0) measurements to underestimate the molecular gas content. Another possibility is that radiation from diffuse HI clouds may dominate the [C II] emission from these galaxies. Less than a third of the observed [C II] emission arises from HII regions.Comment: 24 pages, Latex, 2 Figures, 6 Tables To appear in the Astronomical Journal, July 199

A multi-transition study of the cyclic molecule cyclopropenylidene (C2H2) in the galaxy.

We report results of multi-transition observations and modeling of the hydrocarbon ring molecule cyclopropenylidene (C\sb3H\sb2). From a survey of the 1\sb{10}-1\sb{01} (18 GHz) and 2\sb{12}-1\sb{01} (85 GHz) transitions in the Galaxy, we have found C\sb3H\sb2 present in a variety of sources including cold, dark clouds, giant molecular clouds, the envelope of a carbon star, and diffuse clouds. Up to 10 transitions of C\sb3H\sb2 ranging in wavelength from 1.3 cm to 1.3 mm were observed in the dark clouds L1498, L134N, B335 and toward several positions in TMC-1. The Large Velocity Gradient (LVG) approximation was used to model the observations. Optical depth values of C\sb3H\sb2, estimated from C\sp{13}C\sb2H\sb2 observations, are necessary to constrain the results since the range in excitation energies of the observed C\sb3H\sb2 transitions does not contrast sufficiently. The molecular hydrogen density in TMC-1 is estimated to be 3.7 $\times$ 10\sp4 cm\sp{-3}, while the fractional abundance of C{\sb3}H\sb2 relative to H\sb2 is 5.7 $\times$ 10\sp{-9}. Previous estimates assuming LTE conditions overestimate the abundance of C\sb3H\sb2. The abundance in the ridge component in Orion is estimated to be approximately 8 $\times$ 10\sp{-10} cm \sp{-2}. Gas phase chemical models can reproduce the high C\sb3H\sb2 abundance found in dark clouds under assumptions such as steady state conditions with (C) / (O) / $\u3e$ 1.0, conditions of earlier evolutionary time, or \u27optimistic\u27 rate coefficients. However, large deuteration ratios (0.05 to 0.15) create difficulties for gas phase models

Exploring The Factors Associated With Social Media Use In Local Health Departments

Background: The health system in the United States is rapidly advancing, including newer technologies, newer ways of delivering essential public health services and population health. Approximately 70% of the public uses social media as a communication tool, which makes it an ideal platform for dissemination of information. Local health departments (LHDs) are accountable for assuring ten essential public health services, including informing, educating, and empowering people about health issues. Previous research showed less than 70% of LHDs are adequately performing this essential service. The purpose of this study was to examine what factors impact the use of social media by LHDs to communicate with the public. Methods: This study utilized a cross-sectional study design, using data from the 2016 NACCHO profile of local health departments. The data assessed for this study was derived from a set of questions in a module containing the questions of interest for this study related to social media utilization. Results: Results varied across platforms but showed significant associations between social media use and: youngest executives, larger populations, higher expenditures, locally governed LHDs, greater informatics use, greater communication channel use, LHDs employing Public Information Professionals, change in annual budget, PHAB accreditation status, top executive degree, top executive length of service, and top executive race. Conclusion: LHDs can utilize these results as a starting point for training and education for employees and leaders. As more people utilize social media platforms for communicating, understanding the LHD characteristics that influence social media use can be vital for designing an effective system to reach audiences in the community for public health education. The strategic addition of new policies and procedures related to social media use at the executive level are needed in order to ensure public health essential service #3 is being sufficiently reached

Discovery of PAHs in the Halo of NGC 5907

We have used sensitive archival data from the Infrared Space Observatory (ISO) to make maps of the edge-on low SFR galaxy, NGC 5907, in 6 different MIR bands: LW2, LW5, LW6, LW7, LW8, and LW10, covering the spectrum from 6.5 to 15.0 microns and including several narrow bands that isolate the infrared aromatic spectral features commonly referred to as PAHs. Most of the MIR emission is dominated by PAHs and it is likely that emission from VSGs contribute only negligibly except in the broad IRAS-equivalent band. The flux ratios are typical of galaxies with low SFRs or quiesent regions within galaxies (e.g M~83) and a very high PAH/continuum ratio is observed. The PAH emission follows the CO distribution and also shows some correlation within the disk with the lambda 850 micron distribution. However, the PAH emission also reaches larger galactocentric radii than the CO and other correlations suggest that the PAHs are also more widespread. A significant new discovery is the presence of PAHs in the halo of the galaxy. In the narrow bands that isolate single PAH features, the emission shows structure similar to high latitude features seen in other galaxies in other tracers. The features extend as far as 6.5 kpc from the plane but scale heights of 3.5 kpc are more typical. The (lambda 11.3/lambda7.7) ratio also appears to increase with distance from the major axis. To our knowledge, this is the first time PAHs have been seen in the halo of an external galaxy. Just as significantly, they are seen in a low SFR galaxy, suggesting that strong SNe and winds are not necessary for these large molecules to reach high latitudes.Comment: A&A accept. 8 Sept. 05, 15 pages, 14 fig., pdf at www.astro.queensu.ca/~irwin/pub/ngc590

The LMC+ SOFIA Legacy Program

With the goal of elucidating the effects of low metallicity on the star formation activity, feedback and interstellar medium of low metallicity environments, SOFIA has observed a 40' x 20' (60 pc x 30 pc) area of our neighboring metal-poor Large Magellanic Cloud in 158 micron [CII] and 88 micron [OIII], targeting the southern molecular ridge just south of 30Doradus. We find extensive [CII] emission over the region, which encompasses a wide variety of local physical conditions, from bright compact star forming regions to lower density environments beyond, much of which does not correspond to CO structures. Preliminary analyses indicates that most of the molecular hydrogen is in a CO-dark gas component.Comment: Proceedings of the 7th Chile-Cologne-Bonn-Symposium "Physics and Chemistry of Star Formation, The Dynamical ISM Across Time and Spatial Scales", Puerto-Varas Chile, September 26-30, 2022 V. Ossenkopf-Okada, R. Schaaf, I. Breloy (eds.