- ID:
- ivo://CDS.VizieR/J/A+A/632/A83
- Title:
- NGC 6334 filament with ALMA
- Short Name:
- J/A+A/632/A83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Herschel imaging surveys of galactic interstellar clouds support a paradigm for low-mass star formation in which dense molecular filaments play a crucial role. The detailed fragmentation properties of star-forming filaments remain poorly understood, however, and the validity of the filament paradigm in the intermediate- to high-mass regime is still unclear. Here, following up on an earlier 350um dust continuum study with the ArTeMiS camera on the APEX telescope, we investigate the detailed density and velocity structure of the main filament in the high-mass star-forming region NGC 6334. We conducted ALMA Band 3 observations in the 3.1mm continuum and of the N_2_H^+^(1-0), HC_5_N(36-35), HNC(1-0), HC_3_N(10-9), CH_3_CCH(6-5), and H_2_CS(3-2) lines at an angular resolution of 300, corresponding to 0.025 pc at a distance of 1.7kpc. The NGC 6334 filament was detected in both the 3.1mm continuum and the N_2_H^+^, HC_3_N, HC_5_N, CH_3_CCH, and H_2_CS lines with ALMA. We identified twenty-six compact (<0.03pc) dense cores at 3.1mm and five velocity-coherent fiber-like features in N_2_H^+^ within the main filament. The typical length (~0.5pc) of, and velocity difference (~0.8km/s) between, the fiber-like features of the NGC 6334 filament are reminiscent of the properties for the fibers of the low-mass star-forming filament B211/B213 in the Taurus cloud. Only two or three of the five velocity-coherent features are well aligned with the NGC 6334 filament and may represent genuine, fiber sub-structures; the other two features may trace accretion flows onto the main filament. The mass distribution of the ALMA 3.1mm continuum cores has a peak at 10 M, which is an order of magnitude higher than the peak of the prestellar core mass function in nearby, low-mass star-forming clouds. The cores can be divided into seven groups, closely associated with dense clumps seen in the ArTeMiS 350um data. The projected separation between ALMA dense cores (0.03-0.1pc) and the projected spacing between ArTeMiS clumps (0.2-0.3pc) are roughly consistent with the effective Jeans length (0.08+/-0.03pc) in the filament and a physical scale of about four times the filament width, respectively, if the inclination angle of the filament to line of sight is ~30{deg}. These two distinct separation scales are suggestive of a bimodal fragmentation process in the filament. Despite being one order of magnitude denser and more massive than the Taurus B211/B213 filament, the NGC 6334 filament has a density and velocity structure that is qualitatively very similar. The main difference is that the dense cores embedded in the NGC 6334 filament appear to be an order of magnitude denser and more massive than the cores in the Taurus filament. This suggests that dense molecular filaments may evolve and fragment in a similar manner in low- and high-mass star-forming regions, and that the filament paradigm may hold in the intermediate-mass (if not high-mass) star formation regime.
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- ID:
- ivo://CDS.VizieR/J/MNRAS/379/275
- Title:
- NGC 5033 1.4GHz radio emission
- Short Name:
- J/MNRAS/379/275
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new continuum VLA observations of the nearby Sy 1.5 galaxy NGC 5033, made at 4.9- and 8.4-GHz on 2003 April 8. Combined with VLA archival observations at 1.4- and 4.9-GHz made on 1993 August 7, 1999 August 29 and 1999 October 31, we sample the galaxy radio emission at scales ranging from the nuclear regions (<100pc) to the outer regions of the disc (~40kpc). The high-resolution VLA images show a corejet structure for the Sy 1.5 nucleus.
- ID:
- ivo://CDS.VizieR/J/A+A/600/A6
- Title:
- NGC628 3.1GHz total intensity & polarised images
- Short Name:
- J/A+A/600/A6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Magnetic fields are essential to fully understand the interstellar medium (ISM) and its role in the disk-halo interface of galaxies is still poorly understood. Star formation is known to expel hot gas vertically into the halo and these outflows have important consequences for mean-field dynamo theory in that they can be efficient in removing magnetic helicity. We perform new observations of the nearby face-on spiral galaxy NGC 628 with the Karl G. Jansky Very Large Array (JVLA) at S-band and the Effelsberg 100-m telescope at frequencies of 2.6GHz and 8.35GHz. We obtain some of the most sensitive radio continuum images in both total and linearly polarised intensity of any external galaxy observed so far in addition to high-quality images of Faraday depth and polarisation angle from which we obtained evidence for drivers of magnetic turbulence in the disk-halo connection. Such drivers include a superbubble detected via a significant Faraday depth gradient coinciding with a HI hole. We observe an azimuthal periodic pattern in Faraday depth with a pattern wavelength of 3.7+/-0.1kpc, indicating Parker instabilities. The lack of a significant anti-correlation between Faraday depth and magnetic pitch angle indicates that these loops are vertical in nature with little helical twisting, unlike in IC 342. We find that the magnetic pitch angle is systematically larger than the morphological pitch angle of the polarisation arms which gives evidence for the action of a large-scale dynamo where the regular magnetic field is not coupled to the gas flow and obtains a significant radial component. We additionally discover a lone region of ordered magnetic field to the north of the galaxy with a high degree of polarisation and a small pitch angle, a feature that has not been observed in any other galaxy so far and is possibly caused by an asymmetric HI hole.
- ID:
- ivo://CDS.VizieR/J/A+A/606/A121
- Title:
- NGC1333 IRAS 4A ALMA and PdBI maps
- Short Name:
- J/A+A/606/A121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Hot corinos are extremely rich in complex organic molecules (COMs). Accurate abundance measurements of COMs in such objects are crucial to constrain astrochemical models. In the particular case of close binary systems this can only be achieved through high angular resolution imaging. We aim to perform an interferometric study of multiple COMs in NGC1333 IRAS 4A, which is a protostellar binary hosting hot corino activity, at an angular resolution that is sufficient to distinguish easily the emission from the two cores separated by 1.8". We used the Atacama Large (sub-)Millimeter Array (ALMA) in its 1.2mm band and the IRAM Plateau de Bure Interferometer (PdBI) at 2.7mm to image, with an angular resolution of 0.5" (120au) and 1" (235au), respectively, the emission from 11 different organic molecules in IRAS 4A. This allowed us to clearly disentangle A1 and A2, the two protostellar cores. For the first time, we were able to derive the column densities and fractional abundances simultaneously for the two objects, allowing us to analyse the chemical differences between them. Molecular emission from organic molecules is concentrated exclusively in A2, while A1 appears completely devoid of COMs or even simpler organic molecules, such as HNCO, even though A1 is the strongest continuum emitter. The protostellar core A2 displays typical hot corino abundances and its deconvolved size is 70au. In contrast, the upper limits we placed on COM abundances for A1 are extremely low, lying about one order of magnitude below prestellar values. The difference in the amount of COMs present in A1 and A2 ranges between one and two orders of magnitude. Our results suggest that the optical depth of dust emission at these wavelengths is unlikely to be sufficiently high to completely hide a hot corino in A1 similar in size to that in A2. Thus, the significant contrast in molecular richness found between the two sources is most probably real. We estimate that the size of a hypothetical hot corino in A1 should be less than 12 au. Our results favour a scenario in which the protostar in A2 is either more massive and/or subject to a higher accretion rate than A1, as a result of inhomogeneous fragmentation of the parental molecular clump. This naturally explains the smaller current envelope mass in A2 with respect to A1 along with its molecular richness. The extremely low abundances of organic molecules in A1 with respect to those in A2 demonstrate that the dense inner regions of a young protostellar core lacking hot corino activity may be poorer in COMs than the outer protostellar envelope.
- ID:
- ivo://CDS.VizieR/J/A+A/606/A52
- Title:
- NGC7538-IRS1 THz water maser
- Short Name:
- J/A+A/606/A52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The formation of massive stars (M>10M_{sun}_, L>10^3^L_{sun}_) is still not well understood. Accumulating a large amount of mass infalling within a single entity in spite of radiation pressure is possible if, among several other conditions, enough thermal energy is released. Despite numerous water line observations, over a broad range of energies, with the Herschel Space Observatory, in most of the sources observations were not able to trace the emission from the hot core around the newly forming protostellar object. We want to probe the physical conditions and water abundance in the inner layers of the host protostellar object NGC7538-IRS1 using a highly excited H_2_O line. Water maser models predict that several THz water masers should be detectable in these objects. We therefore aim to detect for the first time the o-H_2_O 8_2,7_-7_3,4_ line in a star forming region, which model calculations predict to show maser action. We present SOFIA observations of the o-H_2_O 8_2,7_-7_3,4_ line at 1296.41106GHz and a 6_16_-5_23_ 22GHz e-MERLIN map of the region (first-ever 22GHz images made after the e-MERLIN upgrade). In order to be able to constrain the nature of the emission - thermal or maser - we use near-simultaneous observations of the 22GHz water maser performed with the Elsberg radiotelescope and e-MERLIN. A thermal water model using the RATRAN radiative transfer code is presented based on HIFI pointed observations. Molecular water abundances are derived for the hot core. The of the o-H_2_O 8_2,7_-7_3,4_ line is detected toward NGC7538-IRS1 with one feature at the source velocity (-57.7km/s) and another one at -48.4km/s. We propose that the emission at the source velocity is consistent with thermal excitation and is excited in the innermost part of the IRS1a massive protostellar object's closest circumstellar environment. The other emission is very likely the first detection of a water THz maser line, pumped by shocks due to IRS1b outflow, in a star-forming region. Assuming thermal excitation of the THz line, the water abundance in NGC7538-IRS1's hot core is estimated to be 5.2x10^-5^ with respect to H_2_.
- ID:
- ivo://CDS.VizieR/J/A+A/615/A98
- Title:
- NGC 891 LOFAR and AMI maps
- Short Name:
- J/A+A/615/A98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Cosmic rays and magnetic fields play an important role for the formation and dynamics of gaseous halos of galaxies. Low-frequency radio continuum observations of edge-on galaxies are ideal to study cosmic-ray electrons (CREs) in halos via radio synchrotron emission and to measure magnetic field strengths. Spectral information can be used to test models of CRE propagation. Free-free absorption by ionized gas at low frequencies allows us to investigate the properties of the warm ionized medium in the disk. We obtained new observations of the edge-on spiral galaxy NGC 891 at 129-163MHz with the LOw Frequency ARray (LOFAR) and at 13-18GHz with the Arcminute Microkelvin Imager (AMI) and combine them with recent high-resolution Very Large Array (VLA) observations at 1-2GHz, enabling us to study the radio continuum emission over two orders of magnitude in frequency. The spectrum of the integrated nonthermal flux density can be fitted by a power law with a spectral steepening towards higher frequencies or by a curved polynomial. Spectral flattening at low frequencies due to free-free absorption is detected in star-forming regions of the disk. The mean magnetic field strength in the halo is 7+/-2{mu}G. The scale heights of the nonthermal halo emission at 146MHz are larger than those at 1.5GHz everywhere, with a mean ratio of 1.7+/-0.3, indicating that spectral ageing of CREs is important and that diffusive propagation dominates. The halo scale heights at 146MHz decrease with increasing magnetic field strengths which is a signature of dominating synchrotron losses of CREs. On the other hand, the spectral index between 146MHz and 1.5GHz linearly steepens from the disk to the halo, indicating that advection rather than diffusion is the dominating CRE transport process. This issue calls for refined modelling of CRE propagation. Free-free absorption is probably important at and below about 150MHz in the disks of edge-on galaxies. To reliably separate the thermal and nonthermal emission components, to investigate spectral steepening due to CRE energy losses, and to measure magnetic field strengths in the disk and halo, wide frequency coverage and high spatial resolution are indispensable.
- ID:
- ivo://CDS.VizieR/J/A+A/372/L41
- Title:
- NGC 2068/2071 protoclusters
- Short Name:
- J/A+A/372/L41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on a wide-field submillimeter continuum survey of the NGC 2068/2071 protoclusters in the Orion B cloud complex. We used the SCUBA bolometer array on JCMT to map a 32'x18' region in size (~4pcx2pc) at 850 and 450 microns. Our survey shows that the dense cores mapped in CS(2-1) by Lada et al. (1991ApJ...368..432L) and labelled with LBS numbers break up into 82 small-scale (~5000AU) fragments. The latter include 70 starless condensations, believed to be the immediate progenitors of accreting protostars, and 5 circumstellar envelopes/disks around protostars. The nature of the 7 remaining cloud fragments is unclear because their dust continuum emission is largely contaminated by line emission.
- ID:
- ivo://CDS.VizieR/J/A+A/632/A13
- Title:
- NGC 4013 radio and polarization maps
- Short Name:
- J/A+A/632/A13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From the Continuum HAloes in Nearby Galaxies - an EVLA Survey (CHANG-ES) radio continuum data from the Karl G. Jansky Very Large Array (VLA), observed in two frequency bands, 6GHz (C-band) and 1.5GHz (L-band), we present the radio maps, including polarization of the edge-on spiral galaxy NGC 4013. Supplemantary X-ray data are also presented here. The central point source of NGC 4013 dominates the radio continuum emission in both CHANG-ES bands. Complementary X-ray data from Chandra show one dominant point source in the central part. The XMM-Newton spectrum shows hard X-rays, but no clear AGN classification is possible at this time. The radio continuum halo of NGC 4013 in C-band is rather small, while the low-frequency LOFAR data reveal a large halo. The scale height analysis shows that Gaussian fits better represent the intensity profiles than do exponential fits. The frequency dependence gives clear preference to diffusive CRE transport. The radio halo of NGC 4013 is relatively faint. Diffusion is the dominating transport process up to heights of 1-2kpc. The polarization data reveal plane-parallel, regular magnetic fields within the entire disk and vertical halo components indicating the presence of an axisymmetric field having a radial component pointing outwards. The mean magnetic field strength of the disk of NGC 4013 of 6.6{mu}G is rather small. Large-scale vertical fields are observed in the halo out to heights of about 6kpc. The interaction and the low star formation rate (SFR) across the disk of NGC 4013 probably influence the appearance of its radio continuum halo and are correlated with the low total magnetic field strength. Several observable quantities give consistent evidence that the CR transport in the halo of NGC 4013 is diffusive: the frequency dependence of the synchrotron scale height, the disk/halo flux density ratio, the vertical profile of the synchrotron spectral index, the small propagation speed measured modeled with spinnaker, and the low temperature of the X-ray emitting hot gas.
- ID:
- ivo://CDS.VizieR/J/A+A/639/A111
- Title:
- NGC 4217 radio and polarization maps
- Short Name:
- J/A+A/639/A111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the radio continuum halo, the magnetic field, and the transport processes of the CRs of the edge-on spiral galaxy NGC 4217 using Continuum HAlos in Nearby Galaxies - an Evla Survey (CHANG-ES) radio data at two frequencies, 6GHz (C-band) and 1.5GHz (L-band), and supplemental LOFAR data of this galaxy at 150MHz. With additional X-ray Chandra data, we study the connection of radio features to the diffuse hot gas around NGC 4217. NGC 4217 shows a large-scale X-shaped magnetic field structure, covering a major part of the galaxy with a mean total magnetic field strength in the disk of 9G. From the analysis of the rotation measure map at C-band, we found that the direction of the disk magnetic field is pointing inward. A helical outflow structure is furthermore present in the northwestern part of the galaxy, which is extended nearly 7 kpc into the halo. More polarized emission is observed on the approaching side of the galaxy, indicating that Faraday depolarization has to be considered at C-band. With a simplified galaxy disk model, we are able to explain the finding of higher polarized intensity on the approaching side. We generalize the model to predict that roughly 75% of edge-on spiral galaxies will show higher polarized intensity on the approaching side. Many loop and shell structures are found throughout the galaxy in total intensity at C-band. One structure, a symmetric off-center (to the southwest of the disk) superbubble-like structure is prominent in total and polarized intensity, as well as in Halpha and optical dust filaments. This is at a location where a second peak of total intensity (to the southwest of the disk) is observed, making this superbubble-like structure a possible result of a concentrated star formation region in the disk. The X-ray diffuse emission shows similarities to the polarized diffuse emission of NGC 4217. The flux density extension of the radio continuum halo increases toward lower frequencies. While the total flux density of the disk and halo are comparable at C-band, the contribution of the disk flux density decreases toward LOFAR to 18% of the total flux density. Dumbbell-shaped structures are present at C-band and at the LOFAR frequency. Total intensity profiles at the two CHANG-ES bands and the LOFAR frequency show a clear two-component behavior and were fit best with a two-component exponential fit. The halo scale heights are 1.10+/-0.04kpc, 1.43+/-0.09kpc, and 1.55+/-0.04kpc in C-band, L-band, and 150MHz, respectively. The frequency dependence of these scale heights between C-band and L-band suggests advection to be the main transport process. The 1D CRE transport modeling shows that advection appears to be more important than diffusion.
- ID:
- ivo://CDS.VizieR/J/A+A/632/A10
- Title:
- NGC 4631 total intensity images
- Short Name:
- J/A+A/632/A10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 4631 is an interacting galaxy that exhibits one of the largest, gaseous halos observed among edge-on galaxies. We aim to examine the synchrotron and cosmic-ray propagation properties of its disk and halo emission with new radio continuum data. Radio continuum observations of NGC 4631 were performed with the Karl G. Jansky Very Large Array at C-band (5.99GHz) in the C and D array configurations, and at L-band (1.57GHz) in the B, C, and D array configurations. Complementary observations of NGC 4631 with the Effelsberg telescope were performed at 1.42 and 4.85 GHz. The interferometric total intensity data were combined with the single-dish Effelsberg data in order to recover the missing large-scale total power emission. The thermal and nonthermal components of the total radio emission were separated by estimating the thermal contribution through the extinction-corrected H{alpha} emission. The H{alpha} radiation was corrected for extinction using a linear combination of the observed H{alpha} and 24{mu}m data. NGC 4631 has a global thermal fraction at 5.99(1.57)GHz of 14+/-3% (5.4+/-1.1%). The mean scale heights of the total emission in the radio halo (thick disk) at 5.99(1.57)GHz are 1.79+/-0.54kpc (1.75+/-0.27kpc) and have about the same values for the synchrotron emission. The total magnetic field of NGC 4631 has a mean strength of <Beq>~=9{mu}G in the disk, and a mean strength of <Beq>~=7{mu}G in the halo. We also studied a double-lobed background radio galaxy southwest of NGC 4631, which is an FR II radio galaxy according to the distribution of spectral index across the lobes. From the halo scale heights we estimated that the radio halo is escape-dominated with convective cosmic ray propagation, and conclude that there is a galactic wind in the halo of NGC 4631.