arXiv subjects

K. M. Menten

Publications and source records attributed to K. M. Menten.

At least 163 records · Page 9Linked to original sources

arXiv2019

The complex chemistry of hot cores in Sagittarius B2(N): Influence of cosmic-ray ionization and thermal history

As the number of complex organic molecules (COMs) detected in the interstellar medium increases, it becomes important to place meaningful constraints on the formation pathways of these species. The molecular cloud SgrB2(N) is host to several hot molecular cores in the early stage of star formation, where a great variety of COMs are detected in the gas phase. Because of its exposure to the extreme conditions of the the Galactic center region, SgrB2(N) is one of the best targets to study the impact of environmental conditions on the production of COMs. Our main goal is to characterize the physico-chemical evolution of SgrB2(N)'s sources in order to explain their chemical differences and constrain their environmental conditions. The chemical composition of SgrB2(N)'s hot cores, N2, N3, N4, and N5 is derived by modeling their 3mm emission spectra extracted from the EMoCA imaging spectral line survey performed with ALMA. We derive the density distribution in the envelope of the sources based on the masses computed from the ALMA dust continuum emission maps. We use the radiative transfer code RADMC-3D to compute temperature profiles based on the COM rotational temperatures derived from population diagrams. We use published results of 3D RMHD simulations of high-mass star formation to estimate the time evolution of the sources properties. We employ the chemical code MAGICKAL to compute time-dependent chemical abundances in the sources and investigate how physical properties and environmental conditions influence the production of COMs. We find that chemical models with a cosmic-ray ionization rate of 7e-16s-1 best reproduce the abundances with respect to methanol of ten COMs observed toward SgrB2(N2-N5). We also show that COMs still form efficiently on dust grains with minimum dust temperatures in the prestellar phase as high as 15K, but that minimum temperatures higher than 25K are excluded.

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arXiv2019

Warm gas in protostellar outflows. II. EHV jet and outflows from OMC-2/3

OMC-2/3 is one of the nearest embedded cluster-forming region that includes intermediate-mass protostars at early stages of evolution. A previous CO (3--2) mapping survey towards this region revealed outflow activity related to sources at different evolutionary phases. The present work aims to study the warm gas in the high-velocity emission from several outflows found in CO (3--2) emission by previous observations, determine their physical conditions, and make comparison with previous results in low-mass star-forming regions. We use the CHAMP+ heterodyne array on the APEX telescope to map the CO (6--5) and CO (7--6) emission in the OMC-2 FIR 6 and OMC-3 MMS 1-6 regions, and to observe $^{13}$CO (6--5) at selected positions. We analyze these data together with previous CO (3--2) observations. In addition, we mapped the SiO (5--4) emission in OMC-2 FIR 6. The CO (6--5) emission was detected in most of the outflow lobes in the mapped regions, while the CO (7--6) was found mostly from the OMC-3 outflows. In the OMC-3 MMS 5 outflow, a previously undetected extremely high velocity gas was found in CO (6--5). This extremely high velocity emission arises from the regions close to the central object MMS 5. Radiative transfer models revealed that the high-velocity gas from MMS 5 outflow consists of gas with $n_{\rm H_2}=$10$^4$--10$^{5}$ cm$^{-3}$ and $T>$ 200 K, similar to what is observed in young Class 0 low-mass protostars. For the other outflows, values of $n_{\rm H_2}>$10$^{4}$ cm$^{-3}$ were found. The physical conditions and kinematic properties of the young intermediate-mass outflows presented here are similar to those found in outflows from Class 0 low-mass objects. Due to their excitation requirements, mid$-J$ CO lines are good tracers of extremely high velocity gas in young outflows likely related to jets.

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arXiv2019

Weak and Compact Radio Emission in Early High-Mass Star Forming Regions: II. The Nature of the Radio Sources

In this study we analyze 70 radio continuum sources associated with dust clumps and considered to be candidates for the earliest stages of high-mass star formation. The detection of these sources was reported by Rosero et al. (2016), who found most of them to show weak (${\scriptstyle <}$1 mJy) and compact (${\scriptstyle <}\,$0.6$^{\prime \prime}$) radio emission. Herein, we used the observed parameters of these sources to investigate the origin of the radio continuum emission. We found that at least $\sim 30\%$ of these radio detections are most likely ionized jets associated with high-mass protostars, but for the most compact sources we cannot discard the scenario that they represent pressure-confined HII regions. This result is highly relevant for recent theoretical models based on core accretion that predict the first stages of ionization from high-mass stars to be in the form of jets. Additionally, we found that properties such as the radio luminosity as a function of the bolometric luminosity of ionized jets from low and high-mass stars are extremely well-correlated. Our data improve upon previous studies by providing further evidence of a common origin for jets independently of luminosity.

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arXiv2019

GLOSTAR -- Radio Source Catalog I: $28^{\circ}< \textit{l} < 36^{\circ}$ and $|b| < 1^{\circ}$

The GLOSTAR survey will study the star formation in the Galactic plane between $-2^{\circ}< \textit{l}< 85^{\circ}$ and $|b| < 1^{\circ}$ with unprecedented sensitivity in both, flux density ($\sim$ 40 $μJy$ beam$^{-1}$) and range of angular scales ($\sim$ 1."5 to the largest radio structures in the Galaxy). In this paper we present the first results obtained from a radio continuum map of a 16 square degree sized region of the Galactic plane centered on $\textit{l} = 32^{\circ}$ and $b = 0^{\circ}$ ($28^{\circ} < \textit{l} < 36^{\circ}$ and $|b| < 1^{\circ}$). This map has a resolution of 18" and sensitivity of $\sim$ 60-150 $μJy$ beam$^{-1}$. We present data acquired with the VLA in D-configuration. Two 1 GHz wide sub-bands were observed simultaneously and centred at 4.7 and 6.9 GHz. These data were calibrated and imaged using the $\textit{Obit}$ software package. The source extraction has been performed using the BLOBCAT software package and verified through a combination of visual inspection and cross-matching with other radio and mid-infrared surveys. The final catalog consists of 1575 discrete radio sources and 27 large scale structures (including W43 and W44). By cross-matching with other catalogs and calculating the spectral indices ($S(ν) \propto ν^α$), we have classified 231 continuum sources as HII regions, 37 as ionization fronts, and 46 as planetary nebulae. The longitude and latitude distribution and negative spectral indices are all consistent with the vast majority of the unclassified sources being extragalactic background sources. We present a catalog of 1575 radio continuum sources and discuss their physical properties, emission nature and relation with previously reported. These first GLOSTAR results have increased the number of reliable HII regions in this part of the Galaxy by a factor of four.

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arXiv2019

ALMA reveals potential evidence for spiral arms, bars, and rings in high-redshift submillimeter galaxies

We present sub-kpc-scale mapping of the 870 $μ$m ALMA continuum emission in six luminous ($L_{\rm IR}~\sim~5~\times10^{12}$ L$_{\odot}$) submillimeter galaxies (SMGs) from the ALESS survey of the Extended Chandra Deep Field South. Our high-fidelity 0.07$''$-resolution imaging ($\sim$500 pc) reveals robust evidence for structures with deconvolved sizes of $\lesssim$0.5-1 kpc embedded within (dominant) exponential dust disks. The large-scale morphologies of the structures within some of the galaxies show clear curvature and/or clump-like structures bracketing elongated nuclear emission, suggestive of bars, star-forming rings, and spiral arms. In this interpretation, the ratio of the `ring' and `bar' radii (1.9$\pm$0.3) agrees with that measured for such features in local galaxies. These potential spiral/ring/bar structures would be consistent with the idea of tidal disturbances, with their detailed properties implying flat inner rotation curves and Toomre-unstable disks (Q<1). The inferred one-dimensional velocity dispersions ($σ_{\rm r}\lesssim$ 70-160 km s$^{-1}$) are marginally consistent with the limits implied if the sizes of the largest structures are comparable to the Jeans length. We create maps of the star formation rate density ($Σ_{\rm SFR}$) on $\sim$500 pc scales and show that the SMGs are able to sustain a given (galaxy-averaged) $Σ_{\rm SFR}$ over much larger physical scales than local (ultra-)luminous infrared galaxies. However, on 500 pc scales, they do not exceed the Eddington limit set by radiation pressure on dust. If confirmed by kinematics, the potential presence of non-axisymmetric structures would provide a means for net angular momentum loss and efficient star formation, helping to explain the very high star formation rates measured in SMGs.

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arXiv2019

Observational study of hydrocarbons in the bright photodissociation region of Messier 8

Hydrocarbons are ubiquitous in the interstellar medium, but their formation is still not well understood, depending on the physical environment they are found in. M8 is host to one of the brightest HII regions and PDRs in our galaxy. Using the APEX, and the IRAM 30 m telescopes, we performed a line survey toward Herschel 36 (Her 36), which is the main ionizing stellar system in M8, and an imaging survey within 1.3 $\times$ 1.3 pc around Her 36 of various transitions of C$_{2}$H and c-C$_{3}$H$_{2}$. We used both LTE and non-LTE methods to determine the physical conditions of the emitting gas along with the column densities and abundances of the observed species, which we compared with (updated) gas phase photochemical PDR models. In order to examine the role of PAHs in the formation of small hydrocarbons and to investigate their association with M8, we compared archival GLIMPSE 8 $μ$m and the SPIRE 250 $μ$m continuum images with the C$_{2}$H emission maps. We observed a total of three rotational transitions of C$_{2}$H with their hyperfine structure components and four rotational transitions of c-C$_{3}$H$_{2}$ with ortho and para symmetries toward M8. Fragmentation of PAHs seems less likely to contribute to the formation of small hydrocarbons as the 8 $μ$m emission does not follow the distribution of C$_{2}$H emission, which is more associated with the molecular cloud. From the quantitative analysis, we obtained abundances of $\sim$ 10$^{-8}$ and 10$^{-9}$ for C$_{2}$H and c-C$_{3}$H$_{2}$ respectively, and volume densities of the hydrocarbon emitting gas in the range $n(\rm H_2)$ $\sim$ 5 $\times$ 10$^{4}$--5 $\times$ 10$^{6}$ cm$^{-3}$. The observed column densities of C$_{2}$H and c-C$_3$H$_{2}$ are reproduced reasonably well by our PDR models. This supports the idea that in high-UV flux PDRs, gas phase chemistry is sufficient to explain hydrocarbon abundances.

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arXiv2019

Accretion disk versus jet orientation in H$_{2}$O megamaser galaxies

An essential part of the paradigm describing active galactic nuclei is the alignment between the radio jet and the associated rotation axis of the sub-pc sized accretion disks. Because of the small linear and angular scales involved, this alignment has not yet been checked in a sufficient number of Low Luminosity Active Galactic Nuclei (LLAGNs). The project intends to examine the validity of this paradigm by measuring the radio continuum on the same physical scale as the accretion disks, to investigate any possible connection between these disks and the radio continuum. We observed a sample of 18 LLAGNs in the 4.8 GHz (6 cm) radio continuum using the Very Long Baseline Array (VLBA) with 3.3 to 6.5 milliarcseconds resolution. The sources were selected to show both an edge-on accretion disk revealed by 22 GHz H$_{2}$O megamaser emission and signatures of a radio jet. Furthermore, the sources were previously detected in 33GHz radio continuum observations made with the Very Large Array. Five out of 18 galaxies observed were detected at 8 sigma or higher levels (Mrk0001, Mrk1210, Mrk1419, NGC2273 and UGC3193). While all these sources are known to have maser disks, four of these five sources exhibit a maser disk with known orientation. For all four sources, the radio continuum is misaligned relative to the rotation axis of the maser disk, but with a 99.1% confidence level, the orientations are not random and are confined to a cone within 32 degree of the maser disk's normal. Among the four sources the misalignment of the radio continuum with respect to the normal vector to the maser disk is smaller when the inner radius of the maser disk is larger. Furthermore, a correlation is observed between the 5 GHz VLBA radio continuum and the [OIII] luminosity and also with the H$_{2}$O maser disk's inner radius.

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arXiv2019

Discovery of 14NH3 (2,2) maser emission in Sgr B2-Main

We report the discovery of the first 14NH3 (2,2) maser, seen in the Sgr B2 Main star forming region near the center of the Milky Way, using data from the Very Large Array radio telescope. The maser is seen in both lower resolution (3" or ~0.1 pc) data from 2012 and higher resolution (0''.1 or ~1000 AU) data from 2018. In the higher resolution data ammonia (2,2) maser emission is detected toward 5 independent spots. The maser spots are not spatially or kinematically coincident with any other masers in this region, or with the peaks of the radio continuum emission from the numerous ultracompact and hypercompact \hii\, regions in this area. While the (2,2) maser spots are spatially unresolved in our highest resolution observations, they have unusually broad linewidths of several kilometers per second, which suggests that each of these spots consists of multiple masers tracing unresolved velocity structure. No other ammonia lines observed in Sgr B2 Main are seen to be masers, which continues to challenge theories of ammonia, maser emission that predict simultaneous maser emission in multiple ammonia transitions.

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arXiv2019

Trigonometric Parallaxes of Star Forming Regions Beyond the Tangent Point of the Sagittarius Spiral Arm

As part of the BeSSeL Survey, we report trigonometric parallaxes and proper motions of molecular maser sources associated with 13 distant high mass star forming regions in the Sagittarius spiral arm of the Milky Way. In particular, we obtain improved parallax distance estimates for three well studied regions: 1.9 +0.1/-0.1 kpc for M17, 5.3 +1.3/-0.9 kpc for W51, and 7.9 +0.9/-0.7 kpc for GAL 045.5+00.0. Peculiar motions for all but one source are less than 20 km/s. We fit a log-periodic spiral to the locations and estimate an average pitch angle of 7.2+-1.9 deg. We find that the section of the arm beyond the tangent point in the first quadrant of the Milky Way appears 15 pc below the IAU-defined Galactic plane.

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arXiv2019

Discovery of a sub-Keplerian disk with jet around a 20Msun young star. ALMA observations of G023.01-00.41

It is well established that Solar-mass stars gain mass via disk accretion, until the mass reservoir of the disk is exhausted and dispersed, or condenses into planetesimals. Accretion disks are intimately coupled with mass ejection via polar cavities, in the form of jets and less collimated winds, which allow mass accretion through the disk by removing a substantial fraction of its angular momentum. Whether disk accretion is the mechanism leading to the formation of stars with much higher masses is still unclear. Here, we are able to build a comprehensive picture for the formation of an O-type star, by directly imaging a molecular disk which rotates and undergoes infall around the central star, and drives a molecular jet which arises from the inner disk regions. The accretion disk is truncated between 2000-3000au, it has a mass of about a tenth of the central star mass, and is infalling towards the central star at a high rate (6x10^-4 Msun/yr), as to build up a very massive object. These findings, obtained with the Atacama Large Millimeter/submillimeter Array at 700au resolution, provide observational proof that young massive stars can form via disk accretion much like Solar-mass stars.

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arXiv2019

Small-scale physical and chemical structure of diffuse and translucent molecular clouds along the line of sight to Sgr B2

The diffuse and translucent molecular clouds traced in absorption along the line of sight to strong background sources have so far been investigated mainly in the spectral domain because of limited angular resolution or small sizes of the background sources. We aim to resolve and investigate the spatial structure of molecular clouds traced by several molecules detected in absorption along the line of sight to SgrB2(N). We have used spectral line data from the EMoCA survey performed with ALMA, taking advantage of the high sensitivity and angular resolution. We identify, on the basis of the spectral analysis of c-C3H2 across the field of view, 15 main velocity components along the line of sight to SgrB2(N) and several components in the envelope of SgrB2. The c-C3H2 column densities reveal two categories of clouds. Clouds in Category I (3 kpc arm, 4 kpc arm, and some GC clouds) have smaller c-C3H2 column densities, smaller linewidths, and smaller widths of their column density PDFs than clouds in Category II (Scutum arm, Sgr arm, and other GC clouds). To investigate the spatial structure we derive opacity maps for the following molecules: c-C3H2, H13CO+, 13CO, HNC, HN13C, HC15N, CS, C34S, 13CS, SiO, SO, and CH3OH. These maps reveal that most molecules trace relatively homogeneous structures that are more extended than the field of view defined by the background continuum emission (about 15", that is 0.08-0.6pc depending on the distance). SO and SiO show more complex structures with smaller clumps of size ~5-8". Our analysis suggests that the driving of the turbulence is mainly solenoidal in the investigated clouds. On the basis of HCO+, we conclude that most line-of-sight clouds towards SgrB2 are translucent, including all clouds where complex organic molecules were recently detected. We also conclude that CCH and CH are good probes of H2 in both diffuse and translucent clouds.

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arXiv2019

A timeline for massive star-forming regions via combined observation of o-H$_2$D$^+$ and N$_2$D$^+$

Context: In cold and dense gas prior to the formation of young stellar objects, heavy molecular species (including CO) are accreted onto dust grains. Under these conditions H$_3^+$ and its deuterated isotopologues become more abundant, enhancing the deuterium fraction of molecules such as N$_2$H$^+$ that are formed via ion-neutral reactions. Because this process is extremely temperature sensitive, the abundance of these species is likely linked to the evolutionary stage of the source. Aims: We investigate how the abundances of o-H$_2$D$^+$ and N$_2$D$^+$ vary with evolution in high-mass clumps. Methods: We observed with APEX the ground-state transitions of o-H$_2$D$^+$ near 372 GHz, and N$_2$D$^+$(3-2) near 231 GHz for three massive clumps in different evolutionary stages. The sources were selected within the G351.77-0.51 complex to minimise the variation of initial chemical conditions, and to remove distance effects. We modelled their dust continuum emission to estimate their physical properties, and also modelled their spectra under the assumption of local thermodynamic equilibrium to calculate beam-averaged abundances. Results: We find an anticorrelation between the abundance of o-H$_2$D$^+$ and that of N$_2$D$^+$, with the former decreasing and the latter increasing with evolution. With the new observations we are also able to provide a qualitative upper limit to the age of the youngest clump of about 10$^5$ yr, comparable to its current free-fall time. Conclusions: We can explain the evolution of the two tracers with simple considerations on the chemical formation paths, depletion of heavy elements, and evaporation from the grains. We therefore propose that the joint observation and the relative abundance of o-H$_2$D$^+$ and N$_2$D$^+$ can act as an efficient tracer of the evolutionary stages of the star-formation process.

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arXiv2019

Histogram of oriented gradients: a technique for the study of molecular cloud formation

We introduce the histogram of oriented gradients (HOG), a tool developed for machine vision that we propose as a new metric for the systematic characterization of observations of atomic and molecular gas and the study of molecular cloud formation models. In essence, the HOG technique takes as input extended spectral-line observations from two tracers and provides an estimate of their spatial correlation across velocity channels. We characterize HOG using synthetic observations of HI and $^{13}$CO(J=1-0) emission from numerical simulations of MHD turbulence leading to the formation of molecular gas after the collision of two atomic clouds. We find a significant spatial correlation between the two tracers in velocity channels where $v_{HI}\approx v_{^{13}CO}$, independent of the orientation of the collision with respect to the line of sight. We use HOG to investigate the spatial correlation of the HI, from the THOR survey, and the $^{13}$CO(J=1-0) emission, from the GRS, toward the portion of the Galactic plane 33.75$\lt l\lt$35.25$^{o}$ and $|b|\lt$1.25$^{o}$. We find a significant spatial correlation between the tracers in extended portions of the studied region. Although some of the regions with high spatial correlation are associated with HI self-absorption features, suggesting that it is produced by the cold atomic gas, the correlation is not exclusive to this kind of region. The HOG results also indicate significant differences between individual regions: some show spatial correlation in channels around $v_{HI}\approx v_{^{13}CO}$ while others present this correlation in velocity channels separated by a few km/s. We associate these velocity offsets to the effect of feedback and to the presence of physical conditions that are not included in the atomic-cloud-collision simulations, such as more general magnetic field configurations, shear, and global gas infall.

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arXiv2018

Characterising the high-mass star forming filament G351.776--0.527 with Herschel and APEX dust continuum and gas observations

G351.776-0.527 is among the most massive, closest, and youngest filaments in the inner Galactic plane and therefore it is an ideal laboratory to study the kinematics of dense gas and mass replenishment on a large scale. In this paper, we present far-infrared (FIR) and submillimetre wavelength continuum observations combined with spectroscopic C$^{18}$O (2-1) data of the entire region to study its temperature, mass distribution, and kinematics. The structure is composed of a main elongated region with an aspect ratio of $\sim 23$, which is associated with a network of filamentary structures. The main filament has a remarkably constant width of 0.2 pc. The total mass of the network (including the main filament) is $\geq 2600$ M$_\odot$, while we estimate a mass of $\sim 2000$ M$_\odot$ for the main structure. Therefore, the network harbours a large reservoir of gas and dust that could still be accreted onto the main structure. From the analysis of the gas kinematics, we detect two velocity components in the northern part of the main filament. The data also reveal velocity oscillations in C$^{18}$O along the spine in the main filament and in at least one of the branches. Considering the region as a single structure, we find that it is globally close to virial equilibrium indicating that the entire structure is approximately in a stable state.

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arXiv2018

OH absorption in the first quadrant of the Milky Way as seen by THOR

The hydroxyl radical (OH) is present in the diffuse molecular and partially atomic phases of the interstellar medium (ISM), but its abundance relative to hydrogen is not clear. We aim to evaluate the abundance of OH with respect to molecular hydrogen using OH absorption against cm-continuum sources over the first Galactic quadrant. This OH study is part of the HI/OH/Recombination line survey (THOR). THOR is a Karl G. Jansky Very Large Array large program of atomic, molecular and ionized gas in the range 15°$\leq$l$\leq$67° and |b|$\leq$1°. It is the highest-resolution unbiased OH absorption survey to date towards this region. We combine the derived optical depths with literature 13CO(1-0) and HI observations to determine the OH abundance. We detect absorption in the 1665 and 1667 MHz transitions for continuum sources stronger than $F_{\rm cont}\geq$0.1 Jy/beam. OH absorption is found against $\sim$15% of these continuum sources with increasing fractions for stronger sources. Most of the absorption is associated with Galactic HII regions. We find OH and 13CO gas to have similar kinematic properties. The OH abundance decreases with increasing hydrogen column density. The OH abundance with respect to the total hydrogen nuclei column density (atomic and molecular phase) is in agreement with a constant abundance for $A_V$ < 10-20. Towards the lowest column densities, we find sources that exhibit OH absorption but no 13CO emission, indicating that OH is a well suited tracer of the low column density molecular gas. We present spatially resolved OH absorption towards W43. The unbiased nature of the THOR survey opens a new window onto the gas properties of the ISM. The characterization of the OH abundance over a large range of hydrogen gas column densities contributes to the understanding of OH as a molecular gas tracer and provides a starting point for future investigations.

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arXiv2018

SEDIGISM: The kinematics of ATLASGAL filaments

Analysing the kinematics of filamentary molecular clouds is a crucial step towards understanding their role in the star formation process. Therefore, we study the kinematics of 283 filament candidates in the inner Galaxy, that were previously identified in the ATLASGAL dust continuum data. The $^{13}$CO(2 - 1) and C$^{18}$O(2 - 1) data of the SEDIGISM survey (Structure, Excitation, and Dynamics of the Inner Galactic Inter Stellar Medium) allows us to analyse the kinematics of these targets and to determine their physical properties at a resolution of 30 arcsec and 0.25 km/s. To do so, we developed an automated algorithm to identify all velocity components along the line-of-sight correlated with the ATLASGAL dust emission, and derive size, mass, and kinematic properties for all velocity components. We find two-third of the filament candidates are coherent structures in position-position-velocity space. The remaining candidates appear to be the result of a superposition of two or three filamentary structures along the line-of-sight. At the resolution of the data, on average the filaments are in agreement with Plummer-like radial density profiles with a power-law exponent of p = 1.5 +- 0.5, indicating that they are typically embedded in a molecular cloud and do not have a well-defined outer radius. Also, we find a correlation between the observed mass per unit length and the velocity dispersion of the filament of $m \sim σ_v^2$. We show that this relation can be explained by a virial balance between self-gravity and pressure. Another possible explanation could be radial collapse of the filament, where we can exclude infall motions close to the free-fall velocity.

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arXiv2018

Radio continuum emission in the northern Galactic plane: Sources and spectral indices from the THOR survey

Radio continuum surveys of the Galactic plane can find and characterize HII regions, supernova remnants (SNRs), planetary nebulae (PNe), and extragalactic sources. A number of surveys at high angular resolution (<25") at different wavelengths exist to study the interstellar medium (ISM), but no comparable high-resolution and high-sensitivity survey exists at long radio wavelengths around 21cm. We observed a large fraction of the Galactic plane in the first quadrant of the Milky Way (l=14.0-67.4deg and |b| < 1.25deg) with the Karl G. Jansky Very Large Array (VLA) in the C-configuration covering six continuum spectral windows. These data provide a detailed view on the compact as well as extended radio emission of our Galaxy and thousands of extragalactic background sources. We used the BLOBCAT software and extracted 10916 sources. After removing spurious source detections caused by the sidelobes of the synthesised beam, we classified 10387 sources as reliable detections. We smoothed the images to a common resolution of 25" and extracted the peak flux density of each source in each spectral window (SPW) to determine the spectral indices $α$ (assuming $I(ν)\proptoν^α$). By cross-matching with catalogs of HII regions, SNRs, PNe, and pulsars, we found radio counterparts for 840 HII regions, 52 SNRs, 164 PNe, and 38 pulsars. We found 79 continuum sources that are associated with X-ray sources. We identified 699 ultra-steep spectral sources ($α< -1.3$) that could be high-redshift galaxies. Around 9000 of the sources we extracted are not classified specifically, but based on their spatial and spectral distribution, a large fraction of them is likely to be extragalactic background sources. More than 7750 sources do not have counterparts in the SIMBAD database, and more than 3760 sources do not have counterparts in the NED database.

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arXiv2018

Core fragmentation and Toomre stability analysis of W3(H2O): A case study of the IRAM NOEMA large program CORE

The fragmentation mode of high-mass molecular clumps and the properties of the central rotating structures surrounding the most luminous objects have yet to be comprehensively characterised. Using the IRAM NOrthern Extended Millimeter Array (NOEMA) and the IRAM 30-m telescope, the CORE survey has obtained high-resolution observations of 20 well-known highly luminous star-forming regions in the 1.37 mm wavelength regime in both line and dust continuum emission. We present the spectral line setup of the CORE survey and a case study for W3(H2O). At ~0.35" (700 AU at 2 kpc) resolution, the W3(H2O) clump fragments into two cores (West and East), separated by ~2300 AU. Velocity shifts of a few km/s are observed in the dense-gas tracer, CH3CN, across both cores, consistent with rotation and perpendicular to the directions of two bipolar outflows, one emanating from each core. The kinematics of the rotating structure about W3(H2O) W shows signs of differential rotation of material, possibly in a disk-like object. The observed rotational signature around W3(H2O) E may be due to a disk-like object, an unresolved binary (or multiple) system, or a combination of both. We fit the emission of CH3CN (12-11) K = 4-6 and derive a gas temperature map with a median temperature of ~165 K across W3(H2O). We create a Toomre Q map to study the stability of the rotating structures against gravitational instability. The rotating structures appear to be Toomre unstable close to their outer boundaries, with a possibility of further fragmentation in the differentially-rotating core W3(H2O) W. Rapid cooling in the Toomre-unstable regions supports the fragmentation scenario. Combining millimeter dust continuum and spectral line data toward the famous high-mass star-forming region W3(H2O), we identify core fragmentation on large scales, and indications for possible disk fragmentation on smaller spatial scales.

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