arXiv subjects

V. S. Veena

Publications and source records attributed to V. S. Veena.

At least 19 recordsLinked to original sources

arXiv2026

Spectroscopic surveys with the SKA probing the ionized and molecular Milky Way

Radio spectroscopic surveys provide us with a comprehensive picture of the Milky Way across many physical and chemical regimes. Spectral lines primarily probe the multi-phase gaseous interstellar medium (ISM) from its ionized to atomic and molecular phases, and constrain both local and galaxy-scale kinematics and structure through Doppler shifts. By investigating the physical and chemical properties and distribution of the ISM, the processes driving star formation and galaxy evolution can be studied in detail. This motivates line surveys of our Galaxy that allow us to use the range of physical conditions found in the Milky Way as a template for understanding star formation in extragalactic environments. In this chapter, we describe the science enabled by the spectroscopy of small molecules and radio recombination lines of atoms toward a range of Galactic environments with the SKA. We address questions concerning the processes that dictate the formation of molecular clouds (OH, CH), the properties of warm, ionized gas and the potential of HII regions in understanding the structure of the Galaxy (radio recombination lines), and the impact of CO-dark molecular gas across various density regimes on star formation and galaxy evolution (OH, H2CO). We propose a survey that includes the inner and outer Galaxy disk, characterized by a broad range of densities, temperatures, and metallicities. Deep, wide-field observations of small molecules will be uniquely accessible with SKA, providing key insights on the condition of interstellar medium in galaxies and its impact on star formation.

astro-ph.GA↗

arXiv2026

Class I CH3OH Maser Emission from Bar-Driven Inflow Colliding with the Central Molecular Zone

The Central Molecular Zone of the Milky Way is shaped by the interplay of bar-driven inflows, shocks, and star formation. At Galactic longitude l=1.3, gas inflowing along the near-side dust lane has been proposed to interact with the CMZ boundary and overshoot above the Galactic plane, making this a key site to investigate how large-scale gas dynamics regulates star formation. We aim to investigate the presence of Class I methanol maser emission in this transitional region, testing whether large-scale gas interactions in the CMZ can trigger widespread maser activity via star formation or shocks. We conducted a dedicated search for the 36.2 and 44.1 GHz Class I CH3OH maser lines, along with the 48.4 GHz thermal transition, using the Yebes 40m telescope. We complemented these data with archival data from the Herschel-HiGAL survey and the CHIMPS2 survey to explore links between masers, shocks, and star formation. We detect widespread 36.2 GHz maser emission and two candidate 44.1 GHz masers in a region extending several parsecs. The brightest maser has an isotropic luminosity 0.9x10^-3 L_Sun, placing it among the most luminous Galactic Class I masers. Thermal CH3OH and SiO emission extend over mapped area of 24 pc, with both species showing enhanced fractional abundances. CO position-velocity analysis further shows that the masers are associated with an extended velocity feature at VLSR~100 km/s. We conclude that the observed masers are primarily associated with shock-processed gas in a kinematically complex bar-CMZ interface region. Large-scale gas interactions are likely to play an important role in producing the maser emission, although a subset of the masers may also be linked to shocks driven by local star-formation activity. This region therefore provides a promising Galactic analogue of shock-dominated Class I CH3OH maser environments observed in nuclear regions of barred galaxies.

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arXiv2026

Massive star formation at the Galactic crossroads: Insights from G358.69+0.03 in the Galactic center

We investigated the high-mass star formation activity in a subregion of the Sagittarius E star-forming complex, centered at (l,b) = (358.69 deg, 0.03 deg), where infrared and radio sources trace a prominent U-shaped structure that has not been identified in previous studies. We used radio continuum data from the Global View on Star Formation (GLOSTAR) survey, which is a wide-band radio (4-8 GHz) survey of the Milky Way that combines data from the Karl G. Jansky Very Large Array and the Effelsberg 100 m telescope. Using BLOBCAT source extraction software, we identified 49 compact radio sources. Based on multiwavelength associations and spectral index estimates, we identified GLOSTAR counterparts to 27 previously confirmed HII regions, detected radio emission from 3 WISE "radio-quiet" candidates, and report 5 new HII region candidates. The derived physical properties indicate that most are relatively evolved HII regions. We find around 50 cold dust clumps, predominantly toward the south and southeast. Mid-infrared flux-ratio maps ([4.5]/[3.6]) show localized shock enhancements along the arc and adjacent clumps, and 15 clumps exhibit SiO emission with broad components indicative of shocks. Together with CO data, the SiO velocity components delineate a continuous (>100 km/s) velocity bridge that links the far dust-lane inflow to the central molecular zone (CMZ) stream. The largest concentration of clumps and compact HII regions lies at this interface. These combined diagnostics favor a scenario in which bar-driven cloud-cloud collision at the far dust-lane-CMZ interface compressed the gas and triggered the observed high-mass star formation.

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arXiv2026

G183: An outer galaxy filament feeding a massive protostar

We present the first detailed multi-tracer observation of a 5-pc long outer Galaxy filament, G183, and the massive young stellar object (YSO) IRAS 05480+2545 associated with it. Using the IRAM 30-m telescope at lambda = 1.4 and 3 mm, we probed the molecular gas distribution at angular resolutions of ~12"-28" (0.1-0.3 pc at d = 2.1 kpc). The velocity-resolved C18O(1-0) observations conclusively show a main filament with a skeleton of ridges. The main filament is a 5 pc long velocity-coherent structure with a continuous and quiescent velocity field along its length up to the star-forming hub that accretes mass from the filament. The internal gas kinematics of most of the G183 filament is dominated by thermal motions (sigma_NT/cs~1) and large-scale velocity gradients arising due to outflows and accretion of matter in the massive YSO. The dispersion-size relation almost up to 1 pc is consistent with Larson's law, suggesting that the origin of the filament is a turbulence cascade. The massive YSO, S1, with no corresponding radio continuum detection is characterized as a high-mass protostellar object with a mass of 156 Msun and an M/L ratio of 0.04. We identify a kinematic signature of the accretion of material from the filament onto the YSO, S1. The rates of molecular gas accretion and entrainment in S1 are estimated to be 8.6 and 2.6 (in units of 10^-4 Msun/yr), respectively. In comparison to the inner Galaxy high-mass star-forming filaments forming massive stars, G183 has a lower column density; however, the accretion and outflow rates in S1 are similar. The detection of hydrocarbons such as CH3CN and HC3N indicates the presence of hot-core chemistry in S1. These results highlight the universality of physical processes involved in massive star formation across a range of Galactic environments.

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arXiv2025

A global view on star formation: The GLOSTAR Galactic plane survey XII. Effelsberg's continuum view and data release

Extended radio continuum emission and its linear polarization play a key role in probing large-scale structures of synchrotron and free-free emission in the Milky Way. Despite the existence of many radio continuum surveys, sensitive and high-angular-resolution single-dish surveys of extended radio continuum emission remain scarce. As part of the GLObal view of STAR formation (GLOSTAR) survey, we will also crucially complement the existing data from the Karl G. Jansky Very Large Array (VLA) by addressing the missing zero-spacing gap. Within the framework of the GLOSTAR Galactic plane survey, we performed large-scale radio continuum imaging observations toward the Galactic plane in the range $-2^{\circ}< \ell <60^{\circ}$ and $|b|<1.1^{\circ}$, as well as the Cygnus X region with the Effelsberg 100-m radio telescope. We present the Effelsberg continuum survey at 4.89GHz and 6.82GHz including linear polarization with angular resolutions of 145$^{\prime\prime}$ and 106$^{\prime\prime}$, respectively. The survey has been corrected for missing large-scale emission using available low-angular-resolution surveys. Comparison with previous single-dish surveys indicates that our continuum survey represents the highest-quality single-dish data collected to date at this frequency. More than 90\% of the flux density missed by the VLA D-array data is effectively recovered by the Effelsberg continuum survey. The improved sensitivity and angular resolution of our survey enable reliable mapping of Galactic magnetic field structures, with polarization data that are less affected by depolarization than in previous surveys. The GLOSTAR single-dish continuum data will be released publicly, offering a valuable resource for studying extended objects including HII regions, supernova remnants, diffuse interstellar medium, and Galactic structure. (Abridged)

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arXiv2025

ALMAGAL I. The ALMA evolutionary study of high-mass protocluster formation in the Galaxy. Presentation of the survey and early results

Fundamental questions about the physics responsible for fragmenting molecular parsec-scale clumps into cores of ~1000 au are still open, that only a statistically significant investigation with ALMA is able to address: what are the dominant agents that determine the core demographics, mass, and spatial distribution as a function of the physical properties of the hosting clumps, their evolutionary stage and the different Galactic environments in which they reside? To what extent extent is fragmentation driven by clumps dynamics or mass transport in filaments? With ALMAGAL we observed the 1.38 mm continuum and lines toward more than 1000 dense clumps in our Galaxy, with M>500M_sun, surface density > 0.1 g/cm2 and d<7.5 kpc. The ACA and two 12-m array setups were used to deliver a minimum resolution of ~1000 au over the entire sample distance range. The sample covers all evolutionary stages from infrared dark clouds (IRDCs) to HII regions from the tip of the Galactic bar to the outskirts of the Galaxy. The spectral setup includes several molecular lines to trace the multiscale physics and dynamics of gas, notably CH3CN, H2CO, SiO, CH3OH, DCN, HC3N, SO etc. We present an initial overview of the observations and the early science product and results, with a first characterization of the morphological properties of the continuum emission. We use "perimeter-versus-area" and convex hull-versus-area metrics to classify the different morphologies. More extended and morphologically complex shapes are found toward clumps that are relatively more evolved and have higher surface densities.

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arXiv2025

The Cygnus Allscale Survey of Chemistry and Dynamical Environments: CASCADE. IV. Unveiling the hidden structures in DR18

The Cygnus-X complex is a massive, nearby (1.4 kpc) star-forming region with several OB associations. As part of the Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE) program, we carried out 3.6 millimeter (mm) continuum and spectral line high-resolution observations ($\sim$ 3 - 4$''$) toward DR18, covering several molecular species with the Northern Extended Millimeter Array (NOEMA) and the Institut de Radioastronomie Millimétrique (IRAM) 30m telescope. In addition, multi-wavelength archival datasets were used to provide a comprehensive analysis of the region. A comparison of the 3.6mm and 6 cm continuum emission confirms that a B2 star (DR18-05) shapes the cometary HII region in the DR18 cavity, with ionized gas escaping toward the OB2 association. On the other hand, the extended 3.6mm and 6 cm continuum emission are likely to trace photoevaporating ionized gas from ultraviolet radiation from the Cyg OB2 association, not from DR18-05. The shell structure around DR18-05 indicates photodissociation regions (PDRs) formed by the expanding HII region and photo-erosion from DR18-05 and OB2 stars. We also identified 18 compact cores with N$_2$H$^+$ emission, half of which are gravitationally bound and mostly located in colder regions behind the PDRs. The SiO emission is found only in PDRs, with narrow-line widths ( 0.8 - 2.0 km s$^{-1}$) and lower abundances (X(SiO) $\sim$ 5$\times$10$^{-11}$ - 1$\times$10$^{-10}$). Comparing with the UV irradiated shock models, we suggest that the SiO emission partially encompassing the HII region arises from the molecular gas region, marginally compressed by low-velocity shocks with $\sim$ 5 km s$^{-1}$, irradiated by external UV radiation (G$_{\rm 0} \sim 10^{2} - 10^{3}$), as they traverse through a medium with $n_{\rm H} \sim 10^{4}$ to 10$^5$ cm$^{-3}$.

astro-ph.GA↗

arXiv2024

A global view on star formation: The GLOSTAR Galactic plane survey. XI. Radio source catalog IV: $2^\circ < \ell < 28^\circ$, $36^\circ < \ell < 60^\circ$ and $|b| < 1^\circ$

The GLOSTAR survey studies star formation with the VLA and the Effelsberg 100m telescope in the Galactic plane (-2d<l<60d; |b|<1d) and the Cygnus X region with unprecedented sensitivity in both flux density (~50uJy/beam) and the capability of detecting emission with angular scales in the range from 1" to the largest radio structures in the Galaxy. We provide a complete GLOSTAR-VLA D-configuration radio source catalog for the covered part of the Galactic disk. A catalog for the pilot region (28d<l<36d) has been published in a previous paper and here we present the complementary catalog for the area within 2d<l<28d, 36d<l<60d and |b|<1d. Observations were taken with the VLA in a 4-8GHz band to image 100 degrees$^2$ of the inner Galactic disk at a reference frequency of 5.8GHz, using 260h of telescope time. We determined spectral indices inside the observed band and in the frequency range 1.4-5.8GHz by complementing our results with those from the THOR survey (1-2GHz). The final images have an angular resolution of 18" and an average sensitivity of 123uJy/beam. The sensitivity is better (~60uJy/beam) in areas free of extended emission. The Galactic disk catalog presented in this work, consists of 11211 radio sources. Of these, 1965 are known large-scale structure sources such as star-forming region complexes, well-known SNRs, SNR candidates or parts thereof. The remaining 9227 are discrete individual sources. Source parameters, namely flux densities, sizes, spectral indices, and classifications are reported. We identify 769 HII region candidates, 359 are newly classified as such. The mean value of spectral indices of 225 HII regions is 0.14$\pm$0.02, consistent with most of them emitting optically thin thermal radio emission. Combining our results with the previously published catalog of the pilot region, the final GLOSTAR-VLA D-configuration catalog contains 12981 radio sources.

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arXiv2024

Star Formation in Extreme Environments: A 200 pc High Velocity Gas Stream in the Galactic Centre

The expanding molecular ring (EMR) manifests itself as a parallelogram in the position-velocity diagram of spectral line emission from the Central Molecular Zone (CMZ) surrounding the Galacic centre (GC). Using multiwavelength data, we investigate the gas kinematics, star formation activity, and the presence of shocked gas in a 200 pc long high velocity gas stream (V~ +150 km/s) with a double helix morphology named the helix stream, that is located 15-55 pc above the CMZ and is kinematically associated with the EMR/parallelogram. We carried out molecular line observations using the IRAM 30m, Yebes 40m, and APEX 12m telescopes. The detection of four rotational transitions of the SiO molecule indicate the presence of shocks. We derived the SiO column densities and abundances in different regions of the helix stream. The presence of protostellar clumps and a candidate HII region signify the ongoing star formation activity within the helix stream. The cloud is massive (2.5x10^6 M_sun) and highly turbulent. We find evidence of cloud-cloud collisions towards the eastern edge (l~1.3°), suggesting a dynamic interaction with the CMZ. An expanding shell is detected within the cloud with radius of 6.7 pc and an expansion velocity of 35 km/s. The shell might be powered by several supernovae or a single hypernova. The SiO abundance within the helix stream implies extensive shock processes occurring on large scales. The helical or cork-screw velocity structure of the helix stream indicates twisting and turning motions within the cloud. We propose that the helix stream is the continuation of the near side bar lane, that is overshooting after brushing the CMZ. Our findings carry profound implications for understanding star formation in extreme conditions and elucidate the intricate properties of gas and dust associated with nuclear inflows in barred spiral galaxies.

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arXiv2024

A global view on star formation: The GLOSTAR Galactic plane survey X. Galactic HII region catalog using radio recombination lines

Studies of Galactic HII regions are of crucial importance for studying star formation and the evolution of the interstellar medium. Gaining an insight into their physical characteristics contributes to a more comprehensive understanding of these phenomena. The GLOSTAR project aims to provide a GLObal view on STAR formation in the Milky Way by performing an unbiased and sensitive survey. This is achieved by using the extremely wideband (4{-}8 GHz) C-band receiver of the Karl G. Jansky Very Large Array and the Effelsberg 100 m telescope. Using radio recombination lines observed in the GLOSTAR survey with the VLA in D-configuration with a typical line sensitivity of 1σ {\sim} 3.0 mJy beam{^-1} at {\sim} 5 km s{^-1} and an angular resolution of 25", we cataloged 244 individual Galactic HII regions and derived their physical properties. We examined the mid-infrared (MIR) morphology of these HII regions and find that a significant portion of them exhibit a bubble-like morphology in the GLIMPSE 8 μm emission. We also searched for associations with the dust continuum and sources of methanol maser emission, other tracers of young stellar objects, and find that 48\% and 14\% of our HII regions, respectively, are coextensive with those. We measured the electron temperature for a large sample of HII regions within Galactocentric distances spanning from 1.6 to 13.1 kpc and derived the Galactic electron temperature gradient as {\sim} 372 {\pm} 28 K kpc{^-1} with an intercept of 4248 {\pm} 161 K, which is consistent with previous studies.

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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.

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arXiv2024

High-mass star formation across the Large Magellanic Cloud I. Chemical properties and hot molecular cores observed with ALMA at 1.2 mm

To study the impact of the initial effects of metallicity (i.e., the abundance of elements heavier than helium) on star formation and the formation of different molecular species, we searched for hot molecular cores in the sub-solar metallicity environment of the Large Magellanic Cloud (LMC). We conducted an ALMA Band 6 observations of 20 fields centered on young stellar objects (YSOs) distributed over the LMC in order to search for hot molecular cores in this galaxy. We detected a total of 65 compact 1.2 mm continuum cores in the 20 ALMA fields and analyzed their spectra with XCLASS software. The main temperature tracers are CH3OH and SO2, with more than two transitions detected in the observed frequency ranges. Other molecular lines with high detection rates in our sample are CS , SO, H13CO+, H13CN, HC15 N, and SiO. More complex molecules, such as HNCO, HDCO, HC3N, CH3CN, and NH2CHO, and multiple transitions of SO and SO2 isotopologues showed tentative or definite detection toward a small subset of the cores. According to the chemical richness of the cores and high temperatures from the XCLASS fitting, we report the detection of four hot cores and one hot core candidate. With one new hot core detection in this study, the number of detected hot cores in the LMC increases to seven. Six out of seven hot cores detected in the LMC to date are located in the stellar bar region of this galaxy. These six hot cores show emission from complex organic molecules (COMs), such as CH3OH, CH3CN, CH3OCHO, and CH3OCH3. The only known hot core in the LMC with no detection of COMs is located outside the bar region. The metallicity in the LMC presents a shallow gradient increasing from outer regions toward the bar. We suggest that the formation of hot molecular cores containing COMs ensues from the new generation of stars forming in the more metal-rich environment of the LMC bar.

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arXiv2023

A global view on star formation: The GLOSTAR Galactic plane survey. IX. Radio Source Catalog III: 2<l<28, 36<l<40, 56<l<60 and |b|<1, VLA B-configuration

As part of the GLOSTAR (GLObal view of STAR formation in the Milky Way) survey, we present the high-resolution continuum source catalog for the regions (l = 2-28, 36-40, 56-60, &|b|<1.0), observed with the Karl G. Jansky Very Large Array (VLA) in its B-configuration. The continuum images are optimized to detect compact sources on angular scales up to 4", and have a typical noise level of 1sigma ~ 0.08mJy/beam for an angular resolution of 1", which makes GLOSTAR currently the highest resolution as well as the most sensitive radio survey of the northern Galactic plane at 4-8GHz. We extracted 13354 sources above a threshold of 5sigma and 5437 sources above 7sigma that represent the high-reliability catalog. We determined the in-band spectral index (alpha) for the sources in the 7sigma-threshold catalog. The mean value is alpha=-0.6, which indicates that the catalog is dominated by sources emitting non-thermal radio emission. We identified the most common source types detected in radio surveys: 251 HII region candidates (113 new), 282 planetary nebulae (PNe) candidates (127 new), 784 radio star candidates (581 new), and 4080 extragalactic radio source candidates (2175 new). A significant fraction of HII regions and PNe candidates have alpha<-0.1 indicating that these candidates could contain radio jets, winds or outflows from high-mass and low-mass stellar objects. We identified 245 variable radio sources by comparing the flux densities of compact sources from the GLOSTAR survey and the Co-Ordinated Radio `N' Infrared Survey for High-mass star formation (CORNISH), and find that most of them are infrared quiet. The catalog is typically 95% complete for point sources at a flux density of 0.6 mJy (i.e. typical 7sigma level) and the systematic positional uncertainty is <= 0.1". The GLOSTAR data and catalogs are available online at https://glostar.mpifr-bonn.mpg.de.

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arXiv2023

A survey of SiO $J=$ 1 -- 0 emission toward massive star-forming regions

The application of silicon monoxide (SiO) as a shock tracer arises from its propensity to occur in the gas phase as a result of shock-induced phenomena, including outflow activity and interactions between molecular clouds and expanding HII regions or supernova remnants. We searched for indications of shocks toward 366 massive star-forming regions by observing the ground rotational transition of SiO ($v=0$, $J=1-0$) at 43 GHz with the Korean VLBI Network (KVN) 21 m telescopes to extend our understanding on the origins of SiO in star-forming regions. We detected SiO emission toward 104 regions that consist of 57 IRDCs, 21 HMPOs, and 26 UCHIIs. The determined median SiO column density, $N$(SiO), and abundance, $X$(SiO), relative to $N$(H$_2$) are $8.12\times10^{12}$ cm$^{-2}$ and $1.28\times10^{-10}$, respectively. These values are similar to those obtained toward other star-forming regions and also consistent with predicted values from shock models with low-velocity shocks ($\lesssim$10 - 15 km s$^{-1}$). While the $X$(SiO) does not exhibit any strong correlation with the evolutionary stages of their host clumps, $L_{\rm SiO}$ is highly correlated with dust clump mass, and $L_{\rm SiO}/L_{\rm bol}$ also has a strong negative correlation with $T_{\rm dust}$. This shows that colder and younger clumps have high $L_{\rm SiO}/L_{\rm bol}$ suggestive of an evolutionary trend. This trend is not due to excess emission at higher velocities, such as SiO wing features, as the colder sources with high $L_{\rm SiO}/L_{\rm bol}$ ratios lack wing features. Comparing SiO emission with H$_2$O and Class I CH$_3$OH masers, we find a significant correlation between $L_{\rm SiO}$/$L_{\rm bol}$ and $L_{\rm CH_3OH}/L_{\rm bol}$ ratios, whereas no similar correlation is seen for the H$_2$O maser emission. This suggests a similar origin for the SiO and Class I CH$_3$OH emission in these sources.

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arXiv2023

A global view on star formation: The GLOSTAR Galactic plane survey VIII. Formaldehyde absorption in Cygnus~X

Cygnus X is one of the closest and most active high-mass star-forming regions in our Galaxy, making it one of the best laboratories for studying massive star formation. As part of the GLOSTAR Galactic plane survey, we performed large scale simultaneous H$_{2}$CO (1$_{1,0}$-1$_{1,1}$) spectral line and radio continuum imaging observations toward Cygnus X at $λ\sim$6 cm with the Karl G. Jansky Very Large Array and the Effelsberg-100 m radio telescope. Our Effelsberg observations reveal widespread H$_{2}$CO (1$_{1,0}$-1$_{1,1}$) absorption with a spatial extent of $\gtrsim$50 pc in Cygnus~X for the first time. On large scales of 4.4 pc, the relative orientation between local velocity gradient and magnetic field tends to be more parallel at H$_{2}$ column densities of $\gtrsim$1.8$\times 10^{22}$~cm$^{-2}$. On the smaller scale of 0.17 pc, our VLA+Effelsberg combined data reveal H$_{2}$CO absorption only toward three bright H{\scriptsize II} regions. Our observations demonstrate that H$_{2}$CO (1$_{1,0}$-1$_{1,1}$) is commonly optically thin. Kinematic analysis supports the assertion that molecular clouds generally exhibit supersonic motions on scales of 0.17-4.4 pc. We show a non-negligible contribution of the cosmic microwave background radiation in producing extended absorption features in Cygnus X. Our observations suggest that H$_{2}$CO ($1_{1,0}-1_{1,1}$) can trace molecular gas with H$_{2}$ column densities of $\gtrsim 5 \times 10^{21}$ cm$^{-2}$. The ortho-H$_{2}$CO fractional abundance with respect to H$_{2}$ has a mean value of 7.0$\times 10^{-10}$. A comparison of velocity dispersions on different linear scales suggests that the dominant $-3$ km s$^{-1}$ velocity component in the prominent DR21 region has nearly identical velocity dispersions on scales of 0.17-4.4 pc, which deviates from the expected behavior of classic turbulence.

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arXiv2023

A CO Funnel in the Galactic Centre: Molecular Counterpart of the Northern Galactic Chimney?

We report the discovery of a velocity coherent, funnel shaped ^13CO emission feature in the Galactic centre (GC) using data from the SEDIGISM survey. The molecular cloud appears as a low velocity structure (V_LSR=[-3.5, +3.5] km/s) with an angular extent of 0.95° x 1°, extending toward positive Galactic latitudes. The structure is offset from Sgr A* toward negative Galactic longitudes and spatially and morphologically correlates well with the northern lobe of the 430 pc radio bubble, believed to be the radio counterpart of the multiwavelength GC chimney. Spectral line observations in the frequency range of 85-116 GHz have been carried out using the IRAM 30 metre telescope toward 12 positions along the funnel-shaped emission. We examine the ^12C/^13C isotopic ratios using various molecules and their isotopologues. The mean ^12C/^13C isotope ratio (30.6+-2.9) is consistent with the structure located within inner 3 kpc of the Galaxy and possibly in the GC. The velocity of the molecular funnel is consistent with previous radio recombination line measurements of the northern lobe of radio bubble. Our multiwavelength analysis suggests that the funnel shaped structure extending over 100 pc above the Galactic plane is the molecular counterpart of the northern GC chimney.

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arXiv2023

Spiral Structure and Massive Star formation in the Hub-Filament-System G326.27-0.49

Hub-filament systems (HFSs) are potential sites of formation of star clusters and high mass stars. To understand the HFSs and to provide observational constraints on current theories that attempt to explainstar formation globally, we report a study of the region associated with G326.27-0.49 using infrared data of dust continuum and newly obtained observations on molecular tracers using the APEX telescope. We use the spectroscopic observations to identify velocity-coherent structures (filaments and clumps) and study their properties at a resolution of 0.4 pc. The region contains two main velocity components: first component shows four filaments between -63 and -55 km/s forming a spiral structure converging in a hub, the second filamentary component at -72 km/s harbors a massive young stellar object and possibly interacts with the hub. The clumps harbouring the three main YSOs in the region are massive (187-535 Msun), have luminosities consistent with B-type stars, have central densities of ~10^6 cm^-3 and drive large outflows. Majority of the velocity-coherent clumps in the region show virial parameters between 2-7, which considering the detection of protostars implies collapse to be gradual. We conclude that the region consists of a network of filaments through which mass accretes (~10^-4 Msun/yr) onto the hub. The hub and some of the ends of filaments appear to be undergoing collapse to form new stars. This study identifies a target region for future high resolution observations that could probe the link between the core and filament evolution.

astro-ph.GA↗

arXiv2022

HyGAL: Characterizing the Galactic ISM with observations of hydrides and other small molecules II. The absorption line survey with the IRAM 30 m telescope

As a complement to the HyGAL Stratospheric Observatory for Infrared Astronomy Legacy Program, we report the results of a ground-based absorption line survey of simple molecules in diffuse and translucent Galactic clouds. Using the Institut de Radioastronomie Millimétrique (IRAM) 30 m telescope, we surveyed molecular lines in the 2 mm and 3 mm wavelength ranges toward 15 millimeter continuum sources. These sources, which are all massive star-forming regions located mainly in the first and second quadrants of the Milky Way, form the subset of the HyGAL sample that can be observed by the IRAM 30 m telescope. We detected HCO$^+$ absorption lines toward 14 sightlines, toward which we identified 78 foreground cloud components, as well as lines from HCN, HNC, C$_2$H, and c-C$_3$H$_2$ toward most sightlines. In addition, CS and H$_2$S absorption lines are found toward at least half of the continuum sources. Static Meudon photodissociation region (PDR) isobaric models that consider ultraviolet-dominated chemistry were unable to reproduce the column densities of all seven molecular species by just a factor of a few, except for H$_2$S. The inclusion of other formation routes driven by turbulent dissipation could possibly explain the observed high column densities of these species in diffuse clouds. There is a tentative trend for H$_2$S and CS abundances relative to H$_2$ to be larger in diffuse clouds ($X$(H$_2$S) and $X$(CS) $\sim 10^{-8} - 10^{-7}$) than in translucent clouds ($X$(H$_2$S) and $X$(CS) $\sim 10^{-9} - 10^{-8}$) toward a small sample; however, a larger sample is required in order to confirm this trend. The derived H$_2$S column densities are higher than the values predicted from the isobaric PDR models, suggesting that chemical desorption of H$_2$S from sulfur-containing ice mantles may play a role in increasing the H$_2$S abundance.

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