arXiv subjects

I. Barlach Christensen

Publications and source records attributed to I. Barlach Christensen.

3 recordsLinked to original sources

arXiv2026

Exploring the interplay between molecular and ionized gas in HII regions

We aim to constrain the kinetic temperature and H$_2$ volume density of massive star-forming clumps associated with HII regions using multiple para-H$_2$CO transitions. In addition, we investigate the interplay between ionized gas, molecular gas, and dust to probe how massive stars influence their parental clumps. We observed the $J_{K_aK_c}$ transitions of para-H2CO (within its J = 3-2 and 4-3 states) with the Atacama Pathfinder EXperiment (APEX) 12 m submillimeter telescope using the nFLASH230 and SEPIA345 receivers towards a sample of 61 HII regions. Spectral line parameters are derived via multi-component Gaussian fitting, which was then used to constrain the physical conditions determined using PyRADEX, a non-local thermodynamic equilibrium (LTE) radiative transfer code in combination with Markov Chain Monte Carlo (MCMC) analysis. The non-LTE analysis yielded kinetic temperatures ($T_{kin}$) ranging from 33.7 K to 265 K and H2 densities (n(H$_2$)) between 0.8 X $10^4$ to 1.05 X $10^7$ cm$^{-3}$, providing a detailed characterization of the dense molecular gas contained in these clumps. In addition to the para-H$_2$CO emission arising from the targeted clump a large fraction (57%) of the sources exhibit multiple para-H$_2$CO components, with the secondary components being characterized by higher $T_{kin}$ and broader linewidths. Investigating the nature of the secondary component revealed its association with supersonic non-thermal motions and turbulent gas. When comparing the physical properties of the molecular gas and dust components with those of the ionizing gas, we find that parameters directly linked to the central high-mass star such as bolometric luminosity and Lyman continuum photon rate, show stronger and more systematic correlations. Emphasizing the role of the central star in governing the interplay between the molecular and ionized gas.(Abridged)

astro-ph.GA↗

arXiv2024

The Cygnus Allscale Survey of Chemistry and Dynamical Environments: CASCADE III. The large scale distribution of DCO+, DNC and DCN in the DR21 filament

Deuterated molecules and their molecular D/H-ratios (RD(D)) are important diagnostic tools to study the physical conditions of star-forming regions. The degree of deuteration, RD(D), can be significantly enhanced over the elemental D/H-ratio depending on physical parameters. Within the Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE), we aim to explore the large-scale distribution of deuterated molecules in the nearby Cygnus-X region. We focus on the analysis of large-scale structures of deuterated molecules in the filamentary region hosting the prominent Hii region DR21 and DR21(OH). Here we discuss the HCO+, HNC and HCN molecules and their deuterated isotopologues DCO+, DNC and DCN. The spatial distributions of integrated line emissions from DCO+, DNC, and DCN reveal morphological differences. DCO+ displays the most extended emission, characterized by several prominent peaks. Likewise, DNC exhibits multiple peaks, although its emission appears less extended compared to DCO+. In contrast to the extended emission of DCO+ and DNC, DCN appears the least extended, with distinct peaks. Focusing only on the regions where all three molecules are observed, the mean deuteration ratios for each species are 0.01 for both DNC and DCN, and = 0.005 for DCO+. Anti-correlations are found with deuterated molecules and dust temperature or N(H2). The strongest anti-correlation is found with RD(DCO+) and N(H2). The anti-correlation of RD(DCO+) and N(H2) is suggested to be a result of a combination of an increased photodissociation degree and shocks. A strong positive correlation between the ratio of integrated intensities of DCN and DNC with their 13C-isotopologues, are found in high column density regions. The positive relationship between the ratios implies that the D-isotopologue of the isomers could potentially serve as a tracer for the kinetic gas temperature.

astro-ph.GA↗

arXiv2023

High-resolution APEX/LAsMA $^{12}$CO and $^{13}$CO (3-2) observation of the G333 giant molecular cloud complex : II. Survival and gravitational collapse of dense gas structures under feedback

We investigate the physical properties of gas structures under feedback in the G333 complex using data of the 13CO (3-2) line in the LAsMA observation. We used the Dendrogram algorithm to identify molecular gas structures based on the integrated intensity map of the 13CO (3-2) emission, and extracted the average spectra of all structures to investigate their velocity components and gas kinematics. We derive the column density ratios between different transitions of the 13CO emission pixel-by-pixel, and find the peak values N(2-1)/N(1-0) ~ 0.5, N(3-2)/N(1-0) ~ 0.3, N(3-2)/N(2-1) ~ 0.5. These ratios can also be roughly predicted by RADEX for an average H$_2$ volume density of ~ 4.2 * 10$^3$ cm$^{-3}$. A classical virial analysis does not reflect the true physical state of the identified structures, and we find that external pressure from the ambient cloud plays an important role in confining the observed gas structures. For high column density structures, velocity dispersion and density show a clear correlation, while for low column density structures they do not, indicating the contribution of gravitational collapse to the velocity dispersion. For both leaf and branch structures, $σ-N*R$ always has a stronger correlation compared to $σ-N$ and $σ-R$. The scaling relations are stronger, and have steeper slopes when considering only self-gravitating structures, which are the structures most closely associated with the Heyer-relation. Although the feedback disrupting the molecular clouds will break up the original cloud complex, the substructures of the original complex can be reorganized into new gravitationally governed configurations around new gravitational centers. This process is accompanied by structural destruction and generation, and changes in gravitational centers, but gravitational collapse is always ongoing.

astro-ph.GA↗