arXiv subjects

Lise Ramambason

Publications and source records attributed to Lise Ramambason.

23 records · Page 2Linked to original sources

arXiv2023

Infrared view of the multiphase ISM in NGC 253 II. Modelling the ionised and neutral atomic gas

Context. Multi-wavelength studies of galaxies and galactic nuclei allow us to build a relatively more complete picture of the interstellar medium (ISM), especially in the dusty regions of starburst galaxies. An understanding of the physical processes in nearby galaxies can assist in the study of more distant sources at higher redshifts, which cannot be resolved. Aims. We aimed to use observations presented in the first part of this series of papers to model the physical conditions of the ISM in the nuclear region of NGC 253, in order to obtain primary parameters such as gas densities and metallicities. From the created model we further calculated secondary parameters such as gas masses of the different phases, and estimated the fraction of [C II] 158 um from the different phases, which allowed us to probe the nuclear star-formation rate. Methods. To compare theory with our observations we used MULTIGRIS, a probabilistic tool that determines probabilities for certain ISM parameters from a grid of Cloudy models together with a set of spectroscopic lines. Results. We find that the hypothetical active galactic nucleus within NGC 253 has only a minor impact compared to the starburst on the heating of the ISM as probed by the observed lines. We characterise the ISM and obtain parameters such as a solar metallicity, a mean density of ~230cm-3 , an ionisation parameter of log U = -3, and an age of the nuclear cluster of ~2 Myr. Furthermore, we estimate the masses of the ionised (3.8 x 10^6 M_sol ), neutral atomic (9.1 x 10^6 M_sol ), and molecular (2.0 x 10^8 M_sol ) gas phases as well as the dust mass (1.8 x 10^6 M_sol ) in the nucleus of NGC 253.

astro-ph.GA↗

arXiv2023

Dissecting the Mid-Infrared Heart of M83 with JWST

We present a first look at the MRS observations of the nucleus of the nearby galaxy M83, taken with MIRI onboard JWST. The observations show a rich set of emission features from the ionized gas, warm molecular gas, and dust. To begin dissecting the complex processes in this part of the galaxy, we divide the observations into four different regions. We find that the strength of the emission features varies strongly from region to region, with the south-east region displaying the weakest features tracing the dust continuum and ISM properties. Comparison between the cold molecular gas traced by the $^{12}$CO (1-0) transition with ALMA and the H$_2$ S(1) transition shows a similar spatial distribution. This is in contrast to the distribution of the much warmer H$_2$ emission from the S(7) transition found to be concentrated around the optical nucleus. We use the rotational emission lines and model the H$_2$ excitation to estimate a total molecular gas mass accounting for the warm H$_2$ component of M($>$50 K)$_{\rm H_{2}}$ = 67.90 ($\pm 5.43$)$\times$10$^{6}$ M$_{\odot}$. We compare this value to the total gas mass inferred by probing the cold H$_2$ gas through the $^{12}$CO (1-0) emission, M(CO)$_{\rm H_{2}}$ = 17.15$\times$10$^{6}$ M$_{\odot}$. We estimate that $\sim$75\% of the total molecular gas mass is contained in the warm H$_2$ component. We also identify [\ion{O}{4}] 25.89 $μ$m and [\ion{Fe}{2}] 25.99 $μ$m emission. We propose that the diffuse [\ion{Fe}{2}] 25.99 $μ$m emission might be tracing shocks created during the interactions between the hot wind produced by the starburst and the much cooler ISM above the galactic plane. More detailed studies are needed to confirm such a scenario.

astro-ph.GA↗

arXiv2022

Topological models to infer multiphase interstellar medium properties

(abridged) Spectroscopic observations of high-redshift galaxies slowly reveal the same complexity of the interstellar medium (ISM) as expected from resolved observations in nearby galaxies. While providing a wealth of diagnostics, such high-z spectra are often unresolved, and inferring reliable diagnostics represents a major obstacle. Bright, nearby, unresolved galaxies provide many constraints to design methods to infer ISM properties, but they have so far been limited to deterministic methods and/or with simple topological assumptions. Multicomponent ISM models associate a complex enough distribution of matter and phases with a simple enough topological description to be constrained with probabilistic frameworks. Our goal is to provide a flexible statistical framework that is agnostic to the model grid and that considers either a few discrete components defined by their parameter values and/or statistical distributions of parameters. In this study we present a the MULTIGRIS framework and use it to model a suite of spectral lines in the star-forming regions of the metal-poor dwarf galaxy IZw18. We are able to calculate accurate values for the metallicity, number of ionizing photons, masses of ionized and neutral hydrogen, as well as the dust mass and the dust-to-gas mass ratio. We find a relatively modest amount of H$_2$ which is predominantly CO-dark and traced by C$^+$ rather than C$^0$. Nevertheless, more than $90$% of the [CII] emission is associated with the neutral atomic gas. Our models confirm the necessity to consider an X-ray source. Finally, we investigate the escape fraction of ionizing photons for different energy ranges. While the escape fraction for the main HII region lies around $50-65$%, we show that most of the soft X-ray photons are able to escape and may play a role in the ionization and heating of the circumgalactic or intergalactic medium.

astro-ph.GA↗

arXiv2022

Disentangling emission from star-forming regions in the Magellanic Clouds: Linking [OIII]88 micron and 24 micron

This study explores the link between the [OIII]88mu emission, a well-known tracer of HII regions, and 24mu continuum, often used to trace warm dust in the ionized phases of galaxies. We investigate the local conditions driving the relation between those tracers in the Magellanic Clouds, comparing observations with Cloudy models consisting of an HII region plus a photodissociation region (PDR) component, varying the stellar age, the initial density (at the illuminated edge of the cloud), and the ionization parameter. We introduce a new parameter, cPDR, to quantify the proportion of emission arising from PDRs and that with an origin in HII regions along each line of sight. We use the ratio ([CII]+[OI])/[OIII] as a proxy for the ratio of PDR versus HII region emission, and compare it to [OIII]/24mu. The use of [OIII]/24mu and [OIII]/70mu together allows us to constrain the models most efficiently. We find a correlation over at least 3 orders of magnitude in [OIII]88mu and 24mu continuum in spatially resolved maps of the Magellanic Cloud regions as well as unresolved galaxy-wide low metallicity galaxies of the Dwarf Galaxy Survey. Most of the regions have low proportions of PDRs along the lines of sight (< 12%), while a limited area of some of the mapped regions can reach 30 to 50%. For most lines of sight within the star-forming regions we have studied in the Magellanic Clouds, HII regions are the dominant phase. We propose the use of the correlation between the [OIII]88mu and 24mu continuum as a new predictive tool to estimate, for example, the [OIII]88mu emission when the 24mu continuum is available or inversely. This can be useful to prepare for ALMA observations of [OIII]88mu in high-z galaxies. This simple and novel method may also provide a way to disentangle different phases along the line of sight, when other 3D information is not available.

astro-ph.GA↗

arXiv2022

Infrared view of the multiphase ISM in NGC 253 I. Observations and fundamental parameters of the ionised gas

Context. Massive star-formation leads to enrichment with heavy elements of the interstellar medium. On the other hand, the abundance of heavy elements is a key parameter to study the star-formation history of galaxies. Furthermore, the total molecular hydrogen mass, usually determined by converting CO or [C ii] 158 $μ$m luminosities, depends on the metallicity as well. The excitation of metallicity-sensitive emission lines, however, depends on the gas density of H ii regions, where they arise. Aims. We used spectroscopic observations from SOFIA, Herschel, and Spitzer of the nuclear region of the starburst galaxy NGC 253, as well as photometric observations from GALEX, 2MASS, Spitzer, and Herschel in order to derive physical properties such as the optical depth to correct for extinction, as well as the gas density and metallicity of the central region. Methods. Ratios of the integrated line fluxes of several species were utilised to derive the gas density and metallicity. The [O iii] along with the [S iii] and [N ii] line flux ratios for example, are sensitive to the gas density but nearly independent of the local temperature. As these line ratios trace different gas densities and ionisation states, we examined if these lines may originate from different regions within the observing beam. The ([Ne ii] 13 $μ$m + [Ne iii] 16 $μ$m)/Hu $α$ line flux ratio on the other hand, is independent of the depletion onto dust grains but sensitive to the Ne/H abundance ratio and will be used as a tracer for metallicity of the gas. Results. We derived values for gas phase abundances of the most important species, as well as estimates for the optical depth and the gas density of the ionised gas in the nuclear region of NGC 253. We obtained densities of at least two different ionised components $(< 84$ cm$^{-3}$ and $\sim 170 - 212$ cm$^{-3})$ and a metallicity of solar value.

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