Sophie Penger, 21.2.25
Tidal disruption of the dwarf galaxy VCC 1249: Planetary Nebulae as tracers of galaxy interaction.
The fate of a satellite galaxy during a merger event primarily depends on the shape of its dark matter (DM) potential. Previous studies have shown that halos with a cored DM distribution are stripped more efficiently than those with cuspy potentials (e.g., Penarrubia et al., 2010). The dwarf irregular (dIrr) galaxy, VCC 1249, located within the extended halo of the early-type galaxy (ETG) M49, serves as an excellent observational template for theoretical studies of galaxy dynamics. Both galaxies are situated in the Virgo Subcluster B. VCC 1249 exhibits a tail of tidally stripped material, which is traced by H I gas (McNamara et al., 1994) and H II regions (Arrigoni Battaia et al., 2012). Hartke et al. (2018) identified a subset of planetary nebulae (PNe) in the southern halo of M49 that appear to be associated with the interaction between the two galaxies.
My work utilises data from the Multi-Unit Spectroscopic Explorer (MUSE) to further identify individual PNe in VCC 1249 using a detection method specifically designed for integral field unit (IFU) data. Additionally, I perform a kinematic analysis to describe the dynamic interactions between VCC 1249 and M49. I have found that approximately half of the detected PNe can be attributed to the extended halo of M49 based on their kinematics. In my talk, I will discuss the PNe detection method and the implications of the magnitude and velocity distributions of the sample, as well as the stellar kinematics inferred from the data.
Ivalu Barlach Christensen, 11.10.24
Title: Large scale physical and molecular conditions in structure and clumps within the giant molecular cloud Cygnus-X
The physical state of the interstellar medium (ISM) is essential for understanding the intricate processes involved in star formation within galaxies. 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 (d ∼ 1.5 kpc) Cygnus-X region, a giant molecular cloud complex that hosts multiple sites of high mass star formation.
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), a molecular hot core that is at an earlier evolutionary state. Deuterated molecules and their molecular D/H-ratios (RD) are important diagnostic tools to study the physical conditions of star-forming regions. The degree of deuteration, RD, can be significantly enhanced over the elemental D/H-ratio depending on physical parameters such as temperature, density, and ionization fraction. We find strong anti-correlations with dust temperature and H2 column density, with the strongest found with RD(DCO+) and N(H2). This strong correlation is suggested to be a result of a combination between an increased ionization degree and shocks.
Furthermore, utilizing the ubiquitous H2CO with CASCADE and follow-up observations with APEX, we analyze low-J transitions of H2CO to infer the physical properties of the molecular clumps. We obtain the kinetic gas temperature, H2 volume densities and H2CO column densities using radiative transfer modeling with pyradex+emcee in 102 sources. The kinetic gas temperatures obtained with the non-LTE pyradex+emcee agree well with the LTE kinetic gas temperature obtained with the ratio of H2CO (30,3−20,2) and H2CO (32,1−22,0) at densities n(H2) ≥ 105.5 cm−3. At higher densities, the LTE kinetic gas temperatures from this ratio are overestimated. The volume densities measured are probing lower densities compared to previous measurements of higher-lying H2CO lines, agreeing well with the volume densities obtained from dust continuum emission measurements.
Fengwei Xu (University of Cologne & Peking University), 24.5.24
From ASHES to ASSEMBLE: Dynamic Views of Massive Protocluster Formation and Evolution.
Massive stars form in massive protocluster, but the process of stellar mass assembly including fragmentation and accretion remains poorly understood. Thanks to the high resolution, sensitivity, and wide frequency coverage of the Atacama Large Millimeter/submillimeter Array (ALMA), we can now make surveys of massive protoclusters in great details. With the project ASSEMBLE, we resolved 11 massive protoclusters with 0.01 pc resolution. A total of 248 dense cores have been identified and physical properties including temperature, mass, and density have been derived. By comparing them with those at an early evolutionary stage, we found as a massive protocluster evolves, it becomes tighter and its members become more massive and denser. Besides, the mass correlation between the massive cores their parental clumps is built, possibly due to the continuous mass accretion. The systematically identified primordial mass segregation shed light on the long-term questions of origin of mass segregation in stellar clusters. Our results have been and will be supported by a much larger sample like QUARKS and ALMAGAL.
Veena Vadamattom (MPIfR), 15.3.24
Unveiling the Molecular Counterpart of Milky Way’s Nuclear Chimney
The Galactic Centre (GC) stands as the most dynamic and energetic region within the Milky Way, serving as an exceptional laboratory for probing gas dynamics and star formation processes down to sub-parsec scales. Recent studies reveal the existence of a multi-phase nuclear chimney extending hundreds of parsecs, which represent the channel connecting the quasi-continuous, intermittent activity at the GC. While previous studies have successfully identified ionised gas and warm dust components of this chimney through radio, X-ray, and infrared emissions, the existence of a molecular counterpart has remained elusive. We carried out a multiwavelength investigation to unveil a potential molecular counterpart of the multiphase chimney. Our study reveals a funnel-shaped molecular structure extending over a degree above the Galactic plane. We find a significant correlation between the molecular funnel and the northern lobe of the 430 parsec MeerKAT radio bubble. Millimeter observations also reveal the chemical complexity of the funnel. I will discuss key findings of our ongoing investigation and their implications for our understanding of feedback processes in Galactic nuclei.
Volker Ossenkopf-Okada (University of Cologne), 9.2.24
Is the concept of molecular clouds outdated?
In many models of the ISM giant molecular clouds (GMCs) are treated as well confined, static regions of high density providing the mass reservoir for star-formation. Focusing on the material visible in CO emission lines the discussion concentrates on the question whether GMCs form rather through cloud-cloud collisions or converging flows. However, this approach ignores that whatever we observe in molecular lines is just the “tip of the iceberg”. The mass reservoir for cloud and star-formation always includes the whole iceberg. Ubiquitous filamentary, turbulent structures and substructures on all scales create a configuration where most material is located close to surfaces in relatively dilute, translucent cloud structures, exposed to the interstellar radiation field and thereby forming photon-dominated regions (PDRs). They provide a significant mass reservoir of material not visible in CO emission.
[CII] observations allow us to trace cold material that is at the verge of turning molecular, so far invisible in CO. SOFIA/FEEDBACK observations show the interaction of velocity components with different molecular fractions, indicating a continuous transition from atomic to molecular material. Denser parts of a stream may be identified as individual clouds but SILCC simulations and HyGAL observations of light hydrides prove that the clouds are always embedded in surrounding transitional material. Some material can be traced in [CII] emission, but a large fraction of the CO-dark envelope of the clouds can only be traced through absorption. Absorption in hydrides can directly measure the molecular fraction but requires background sources. Alternatively, the combination of [CII] and [OI] foreground absorption and HI self-absorption (HISA) can be used to quantify the translucent accreting material. To really follow the process, a direct measurement of cold H2 through an heterodyne absorption measurements at 28µm would be needed. Currently, we therefore have no way of obtaining a reliable estimate of the mass reservoir for star-formation and thus the star-formation efficiency.
Josefa Grossschedl (University of Cologne), 8.12.23
Investigating the star formation history of nearby star-forming regions in 3D space and time with Gaia
In our quest to gain a deeper understanding of our Solar Neighborhood, Gaia has proven instrumental in elucidating the 3D spatial structure of the local interstellar medium (ISM) and the distribution of young stellar clusters. To unravel the origin and evolution of nearby young structures, a crucial dimension is the measurement of their 3D space motions. These motions allow us to trace back the orbits of stellar clusters and molecular clouds within our Galaxy, and investigate the relative space motions within single complexes.
To address these challenges, we have recently developed a machine learning-based clustering tool (SigMA) tailored for the selection of stellar clusters in the 5D phase space as provided by Gaia. This innovative approach was initially applied to the Scorpio-Centaurus complex, leading to the identification of previously unnoticed stellar substructures and richer stellar populations than earlier established. Combined with updated cluster ages, this framework enables a more comprehensive investigation of the history of this nearby region, including the evolution of velocity dispersion within a single complex and the propagation of star formation influenced by feedback from massive stars.
To achieve this we analyze the 6D phase-space of individual entities such as clusters and clouds, utilizing Gaia DR3 data in combination with ancillary radial velocity (RV) data. This approach allows us to reconstruct the formation history of star-forming complexes, also shedding light on past feedback processes. Consequently, we can study the interaction of stars with the ISM and the formation and evolution of feedback-driven bubbles, (e.g., Orion-Eridanus Superbubble, Local Bubble). Hence, our research provides a quantifiable assessment of the impact of feedback from massive stars on nearby regions, contributing to a more comprehensive understanding of star formation in the Milky Way.
Iason-Michail Skretas (MPIfR), 27.10.23
A kinematic analysis of the DR21 Main outflow
Molecular outflows are believed to be a key ingredient in the process of star formation. The molecular outflow associated with DR21 Main in Cygnus-X is one of the most extreme molecular outflows in the Milky Way in terms of mass and size. The outflow is suggested to belong to a rare class of explosive outflows formed by the disintegration of protostellar systems.
We aim to explore the morphology, kinematics, and energetics of the DR21 Main outflow, and to compare those properties to confirmed explosive outflows in order to unravel the underlying driving mechanism behind DR21. We studied line and continuum emission at a wavelength of 3.6 mm with IRAM 30 m and NOEMA telescopes as part of the Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE) program. The spectra include (J = 1 − 0) transitions of HCO+, HCN, HNC, N2H+, H2CO, and CCH, which trace different temperature and density regimes of the outflowing gas at high velocity resolution (∼ 0.8 km s−1). The map encompasses the entire DR21 Main outflow and covers all spatial scales down to a resolution of 3′′ (∼ 0.02 pc). Integrated intensity maps of the HCO+ emission reveal a strongly collimated bipolar outflow with significant overlap of the blueshifted and redshifted emission. The opening angles of both outflow lobes decrease with velocity, from ∼ 80 to 20◦ for the velocity range from 5 to 45 km s−1 relative to the source velocity. No evidence is found for the presence of elongated, “filament-like” structures expected in explosive outflows. N2H+ emission near the western outflow lobe reveals the presence of a dense molecular structure, which appears to be interacting with the DR21 Main outflow.The overall morphology as well as the detailed kinematics of the DR21 Main outflow are more consistent with a typical bipolar outflow than with an explosive counterpart.
Thanh Dat Hoang (MPIfR), 13.10.23
Velocity-resolved high-J CO emission from high-mass star-forming regions
High-mass stars are powerhouses of galaxies, and their formation involves energetic processes such as jets/outflows that provide mechanical feedback and regulate the local interstellar medium. In this talk, we present observations of highly-excited CO lines toward 13 massive star-forming regions using high spectral resolution spectroscopy from SOFIA/GREAT. Most of our targets show a strong CO 11-10 and CO 16-15 emission, characterised by broad line wings associated with outflows. Line wings’ contributions to velocity-integrated emission vary over a wide range from 28% to 76% but do not correlate with source evolutionary stages. Assuming local thermodynamics equilibrium (LTE), we determined excitation temperatures of 110-200 K for the full line profiles and 120-220 K for the line wings. Non-LTE RADEX modelling indicates gas densities of 1e5-1e7 cm-3, kinetic temperatures of 150-500K, and CO column densities of 1e17-1e18 cm2 in the line wings, comparable to the physical conditions of deeply embedded low-mass protostars. The correlation between velocity-integrated CO fluxes and bolometric luminosity spans 7 orders of magnitude, including low- and intermediate-mass protostars. Therefore, similar processes are likely responsible for the excitation of high-J CO lines over a wide range of physical scales.