Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userIonization of the diffuse gas in galaxies: Hot low-mass evolved stars at work
158
0
0.0
(
0
)
Added by
Christophe Morisset
Publication date
2011
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
We revisit the question of the ionization of the diffuse medium in late type galaxies, by studying NGC 891, the prototype of edge-on spiral galaxies. The most important challenge for the models considered so far was the observed increase of [OIII]/Hbeta, [OII]/Hbeta, and [NII]/Halpha with increasing distance to the galactic plane. We propose a scenario based on the expected population of massive OB stars and hot low-mass evolved stars (HOLMES) in this galaxy to explain this observational fact. In the framework of this scenario we construct a finely meshed grid of photoionization models. For each value of the galactic latitude z we look for the models which simultaneously fit the observed values of the [OIII]/Hbeta, [OII]/Hbeta, and [NII]/Halpha ratios. For each value of z we find a range of solutions which depends on the value of the oxygen abundance. The models which fit the observations indicate a systematic decrease of the electron density with increasing z. They become dominated by the HOLMES with increasing z only when restricting to solar oxygen abundance models, which argues that the metallicity above the galactic plane should be close to solar. They also indicate that N/O increases with increasing z.
rate research
Read More
In this Letter we demonstrate that the two claims of $zsimeq 0.03$ OVII K$alpha$ absorption lines from Warm Hot Intergalactic Medium (WHIM) along the lines of sight to the blazars H~2356-309 (Buote et al., 2009; Fang et al., 2010) and Mkn~501 (Ren, Fang & Buote, 2014) are likely misidentifications of the $z=0$ OII K$beta$ line produced by a diffuse Low-Ionization Metal Medium in the Galaxys Interstellar and Circum-Galactic mediums. We perform detailed modeling of all the available high signal-to-noise Chandra LETG and XMM-Newton RGS spectra of H 2356-309 and Mkn 501 and demonstrate that the $zsimeq 0.03$ WHIM absorption along these two sightlines is statistically not required. Our results, however, do not rule out a small contribution from the $zsimeq 0.03$ OVII K$alpha$ absorber along the line of sight to H~2356-309. In our model the temperature of the putative $z = 0.031$ WHIM filament is T$= 3times 10^5$ K and the OVII column density is N$_{OV II} le 4times 10^{15}$ cm$^{-2}$, twenty times smaller than the OVII column density previously reported, and now more consistent with the expectations from cosmological hydrodynamical simulations.
We present measurements of the singly ionized helium to hydrogen ratio ($n_{He^+}/n_{H^+}$) toward diffuse gas surrounding three Ultra-Compact HII (UCHII ) regions: G10.15-0.34, G23.46-0.20 & G29.96-0.02. We observe radio recombination lines (RRLs) of hydrogen and helium near 5 GHz using the GBT to measure the $n_{He^+}/n_{H^+}$ ratio. The measurements are motivated by the low helium ionization observed in the warm ionized medium (WIM) and in the inner Galaxy diffuse ionized regions (DIR). Our data indicate that the helium is not uniformly ionized in the three observed sources. Helium lines are not detected toward a few observed positions in sources G10.15-0.34 & G23.46-0.20 and the upper limits of the $n_{He^+}/n_{H^+}$ ratio obtained are 0.03 and 0.05 respectively. The selected sources harbor stars of type O6 or hotter as indicated by helium line detection toward the bright radio continuum emission from the sources with mean $n_{He^+}/n_{H^+}$ value 0.06$pm$0.02. Our data thus show that helium in diffuse gas located a few pc away from the young massive stars embedded in the observed regions is not fully ionized.We investigate the origin of the non-uniform helium ionization and rule out the possibilities : (a) that the helium is doubly ionized in the observed regions and (b) that the low $n_{He^+}/n_{H^+}$ values are due to additional hydrogen ionizing radiation produced by accreting low-mass stars (Smith 2014). We find that selective absorption of ionizing photons by dust can result in low helium ionization but needs further investigation to develop a self-consistent model for dust in HII regions.
During his too short career, Olivier Chesneau pioneered the study of the circumstellar environments of low mass evolved stars using very high angular resolution techniques. He applied state of the art high angular resolution techniques, such as optical interferometry and adaptive optics imaging, to the the study of a variety of objects, from AGB stars to Planetary Nebulae, via e.g. Born Again stars, RCB stars and Novae. I present here an overview of this work and most important results by focusing on the paths he followed and key encounters he made to reach these results. Olivier liked to work in teams and was very strong at linking people with complementary expertises to whom he would communicate his enthusiasm and sharp ideas. His legacy will live on through the many people he inspired.
Dwarf galaxies provide a special environment due to their low mass, small size and generally low metal content. These attributes make them perfect laboratories for the interaction of massive stars with the interstellar medium on small and especially large spatial scales. The natural result of the spatially concentrated energy output from stellar winds and supernovae of an OB association is an expanding bubble. These bubbles can grow to kpc-size and become the dominant driver of the chemical and dynamical evolution of dwarf galaxies. In such low mass systems, bubbles have an enhanced probability of breaking out of the gaseous disk into the halo of the host galaxy. This may lead to venting metal enriched hot gas to large distances from the sites of creation. In this work I review the current observational material on hot gas inside bubbles, blow-outs, and hot halos of dwarf galaxies and discuss several conclusions which can be drawn from the observations. I will also present an analysis of the dwarf galaxy NGC 1705 as a case study, highlighting observational methods and problems with the current data. Finally I will comment on some areas where large progress should be possible in the near future.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
