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Start Over Subject interstellar medium Publisher CDS
621. NIKA view of two star-forming IRDCs
ID:
ivo://CDS.VizieR/J/A+A/615/A18
Title:
NIKA view of two star-forming IRDCs
Short Name:
J/A+A/615/A18
Date:
21 Oct 2021
Publisher:
CDS
Description:
The thermal emission of dust grains is a powerful tool for probing cold, dense regions of molecular gas in the interstellar medium, and so constraining dust properties is key to obtaining accurate measurements of dust mass and temperature. By placing constraints on the dust emissivity spectral index, {beta}, towards two star-forming infrared dark clouds - SDC18.888-0.476 and SDC24.489-0.689 - we aim to evaluate the role of mass concentration in the associated star-formation activity. We exploited the simultaneous 1.2mm and 2.0mm imaging capability of the NIKA camera on the IRAM 30m telescope to construct maps of {beta} for both clouds, and by incorporating Herschel observations, we created H_2_ column density maps with 13" angular resolution. While we find no significant systematic radial variations around the most massive clumps in either cloud on 0.1 pc scales, their mean {beta} values are significantly different, with {bar}{beta}=2.07+/-0.09(random)+/-0.25(systematic) for SDC18.888-0.476 and {bar}{beta}=1.71+/-0.09(random)+/-0.25(systematic) for SDC24.489-0.689. These differences could be a consequence of the very different environments in which both clouds lie, and we suggest that the proximity of SDC18.888-0.476 to the W39 HII region may raise {beta} on scales of ~1pc. We also find that the mass in SDC24.489-0.689 is more centrally concentrated and circularly symmetric than in SDC18.888-0.476, and is consistent with a scenario in which spherical globally-collapsing clouds concentrate a higher fraction of their mass into a single core than elongated clouds that will more easily fragment, distributing their mass into many cores. We demonstrate that {beta} variations towards interstellar clouds can be robustly constrained with high signal-to-noise ratio (S/N) NIKA observations, providing more accurate estimates of their masses. The methods presented here will be applied to the Galactic Star Formation with NIKA2 (GASTON) guaranteed time large programme, extending our analysis to a statistically significant sample of star-forming clouds.
622. N in Galactic high-mass star-forming cores
ID:
ivo://CDS.VizieR/J/MNRAS/478/3693
Title:
N in Galactic high-mass star-forming cores
Short Name:
J/MNRAS/478/3693
Date:
10 Dec 2021 00:14:43
Publisher:
CDS
Description:
The fractionation of nitrogen (N) in star-forming regions is a poorly understood process. To put more stringent observational constraints on the N-fractionation, we have observed with the IRAM-30-m telescope a large sample of 66 cores in massive star-forming regions. We targeted the (1-0) rotational transition of HN^13^C, HC^15^N, H^13^CN and HC^15^N, and derived the ^14^N/^15^N ratio for both HCN and HNC. We have completed this sample with that already observed by Colzi et al., and thus analysed a total sample of 87 sources. The ^14^N/^15^N ratios are distributed around the Proto-Solar Nebula value with a lower limit near the TA value (~272). We have also derived the ^14^N/^15^N ratio as a function of the Galactocentric distance and deduced a linear trend based on unprecedented statistics. The Galactocentric dependences that we have found are consistent, in the slope, with past works but we have found a new local ^14^N/^15^N value of ~400, i.e. closer to the Prosolar Nebula value. A second analysis was done, and a parabolic Galactocentric trend was found. Comparison with Galactic chemical evolution models shows that the slope until 8 kpc is consistent with the linear analysis, while the flattening trend above 8 kpc is well reproduced by the parabolic analysis.
623. NIR imaging of HH 223
ID:
ivo://CDS.VizieR/J/A+A/523/A16
Title:
NIR imaging of HH 223
Short Name:
J/A+A/523/A16
Date:
21 Oct 2021
Publisher:
CDS
Description:
The dark cloud Lynds 723 (L723) is a low-mass star-forming region where one of the few known cases of a quadrupolar CO outflow has been reported. Two recent works have found that the radio continuum source VLA 2, towards the centre of the CO outflow, is actually a multiple system of young stellar objects (YSOs). We imaged a field of 5'x 5' centred on HH 223, which includes the whole region of the quadrupolar CO outflow with narrow-band filters centred on the [FeII] 1.644mum and H_2_ 2.122mum lines, together with off-line H_c_ and K_c_ filters. Our aim is to study L723 in the near-infrared and look for line-emission nebulae associated with the optical and CO outflows.
624. NIR knots in the Cas A supernova remnant
ID:
ivo://CDS.VizieR/J/ApJ/837/118
Title:
NIR knots in the Cas A supernova remnant
Short Name:
J/ApJ/837/118
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the results of broadband (0.95-2.46{mu}m) near-infrared spectroscopic observations of the Cassiopeia A supernova remnant. Using a clump-finding algorithm in two-dimensional dispersed images, we identify 63 "knots" from eight slit positions and derive their spectroscopic properties. All of the knots emit [FeII] lines together with other ionic forbidden lines of heavy elements, and some of them also emit H and He lines. We identify 46 emission line features in total from the 63 knots and measure their fluxes and radial velocities. The results of our analyses of the emission line features based on principal component analysis show that the knots can be classified into three groups: (1) He-rich, (2) S-rich, and (3) Fe-rich knots. The He-rich knots have relatively small, <~200km/s, line-of-sight speeds and radiate strong He I and [FeII] lines resembling closely optical quasi-stationary flocculi of circumstellar medium, while the S-rich knots show strong lines from O-burning material with large radial velocities up to ~2000km/s indicating that they are supernova ejecta material known as fast-moving knots. The Fe-rich knots also have large radial velocities but show no lines from O-burning material. We discuss the origin of the Fe-rich knots and conclude that they are most likely "pure" Fe ejecta synthesized in the innermost region during the supernova explosion. The comparison of [FeII] images with other waveband images shows that these dense Fe ejecta are mainly distributed along the southwestern shell just outside the unshocked ^44^Ti in the interior, supporting the presence of unshocked Fe associated with ^44^Ti.
625. NIR observations of LDN1512
ID:
ivo://CDS.VizieR/J/A+A/647/A109
Title:
NIR observations of LDN1512
Short Name:
J/A+A/647/A109
Date:
21 Oct 2021
Publisher:
CDS
Description:
Light scattering at near-infrared wavelengths has been used to study the optical properties of the interstellar dust grains, but these studies are limited by the assumptions on the strength of the radiation field. On the other hand, thermal dust emission can be used to constrain the properties of the radiation field, although this is hampered by uncertainty about the dust emissivity. Combining light scattering and emission studies allows us to probe the properties of the dust grains in detail. We wish to study if current dust models allow us to model a molecular cloud simultaneously in the near infrared (NIR) and far infrared (FIR) wavelengths and compare the results with observations. Our aim is to place constraints on the properties of the dust grains and the strength of the radiation field. We present computations of dust emission and scattered light of a quiescent molecular cloud LDN1512. We use NIR observations covering the J, H, and Ks bands, and FIR observations between 250 and 500 micron from Herschel space telescope. We construct radiative transfer models for LDN1512 that include an anisotropic radiation field and a three-dimensional cloud model. We are able to reproduce the observed FIR observations, with a radiation field derived from the DIRBE observations, with all of the tested dust models. However, with the same density distribution and the assumed radiation field, the models fail to reproduce the observed NIR scattering in all cases except for models that take into account dust evolution via coagulation and mantle formation. The intensity from the diffuse interstellar medium (ISM) like, dust models can be increased to match the observed one by reducing the derived density, increasing the intensity of the background sky and the strength of the radiation field between factors from 2 to 3. We find that the column densities derived from our radiative transfer modelling can differ by a factor of up to two, compared to the column densities derived from the observations with modified blackbody fits. The discrepancy in the column densities is likely caused because of temperature difference between a modified blackbody fit and the real spectra.The difference between the fitted temperature and the true temperature could be as high as {Delta}T=+/-1.5K. We show that the observed dust emission can be reproduced with several different assumptions about the properties of the dust grains. However, in order to reproduce the observed scattered surface brightness dust evolution must be taken into account.
626. NIR photometry and polarization in NGC 2264
ID:
ivo://CDS.VizieR/J/ApJ/741/35
Title:
NIR photometry and polarization in NGC 2264
Short Name:
J/ApJ/741/35
Date:
21 Oct 2021
Publisher:
CDS
Description:
Near-infrared imaging polarimetry in the J, H, and Ks bands has been carried out for the protostellar cluster region around NGC 2264 IRS 2 in the Monoceros OB1 molecular cloud. Various infrared reflection nebula clusters (IRNCs) associated with NGC 2264 IRS 2 and the IRAS 12 S1 core, as well as local infrared reflection nebulae (IRNe), were detected. The illuminating sources of the IRNe were identified with known or new near- and mid-infrared sources. In addition, 314 point-like sources were detected in all three bands and their aperture polarimetry was studied. Using a color-color diagram, reddened field stars and diskless pre-main-sequence stars were selected to trace the magnetic field (MF) structure of the molecular cloud. The mean polarization position angle of the point-like sources is 81+/-29{deg} in the cluster core, and 58+/-24{deg} in the perimeter of the cluster core, which is interpreted as the projected direction on the sky of the MF in the observed region of the cloud. The Chandrasekhar-Fermi method gives a rough estimate of the MF strength to be about 100uG. A comparison with recent numerical simulations of the cluster formation implies that the cloud dynamics is controlled by the relatively strong MF. The local MF direction is well associated with that of CO outflow for IRAS 12 S1 and consistent with that inferred from submillimeter polarimetry. In contrast, the local MF direction runs roughly perpendicular to the Galactic MF direction.
627. N66, N88 & N25+N26 emission line maps
ID:
ivo://CDS.VizieR/J/A+A/589/A28
Title:
N66, N88 & N25+N26 emission line maps
Short Name:
J/A+A/589/A28
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper presents [CII], [CI] and CO emission line maps of the star-forming regions N66, N25+N26, and N88 in the metal-poor Local Group dwarf galaxy SMC. The spatial and velocity structure of the large HII region N66 reveals an expanding ring of shocked molecular gas centered on the exciting star cluster NGC346, whereas a more distant dense molecular cloud is being eroded by UV radiation from the same cluster. In the N25+N26 and N88 maps, diffuse [CII] emission at a relatively low surface brightness extends well beyond the compact boundaries of the bright emission associated with the HII regions. In all regions, the distribution of this bright [CII] emission and the less prominent [CI] emission closely follows the outline of the CO complexes, but the intensity of the [CII] and [CI] emission is generally anticorrelated, which can be understood by the action of photodissociation and photoionization processes. Notwithstanding the overall similarity of CO and [CII] maps, the intensity ratio of these lines varies significantly, mostly due to changes in CO brightness. [CII] emission line profiles are up to 50% wider in velocity than corresponding CO profiles. A radiative transfer analysis shows that the [CII] line is the dominant tracer of (CO-dark) molecular hydrogen in the SMC. CO emission traces only a minor fraction of the total amount of gas. The similarity of the spatial distribution and line profile shape, and the dominance of molecular gas associated with CII rather than CO emission imply that in the low-metallicity environment of the SMC the small amount of dense molecular gas traced by CO is embedded in the much more extended molecular gas traced only by [CII] emission. The contribution from neutral atomic and ionized hydrogen zones is negligible in the star-forming regions observed
628. Nobeyama 45m Cygnus-X CO. II. C180 clumps
ID:
ivo://CDS.VizieR/J/ApJ/883/156
Title:
Nobeyama 45m Cygnus-X CO. II. C180 clumps
Short Name:
J/ApJ/883/156
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the statistical physical properties of the C^18^O(J=1-0) clumps present in a prominent cluster-forming region, Cygnus X, using the data set obtained by the Nobeyama 45m radio telescope. This survey covers 9deg^2^ of the northern and southern regions of Cygnus X, and, in total, 174 C^18^O clumps are identified using the dendrogram method. Assuming a distance of 1.4kpc, these clumps have radii of 0.2-1pc, velocity dispersions of <2.2km/s, gas masses of 30-3000M_{sun}_, and H_2_ densities of (0.2-5.5)x10^4^cm^-3^. We confirm that the C^18^O clumps in the northern region have a higher H_2_ density than those in the southern region, supporting the existence of a difference in the evolutionary stages, consistent with the star-formation activity of these regions. The difference in the clump properties of the star-forming and starless clumps is also confirmed by the radius, velocity dispersion, gas mass, and H_2_ density. The average virial ratio of 0.3 supports that these clumps are gravitationally bound. The C^18^O clump mass function shows two spectral index components, {alpha}=-1.4 in 55-140M_{sun}_ and {alpha}=-2.1 in >140M_{sun}_, which are consistent with the low- and intermediate-mass parts of the Kroupa's initial mass function. The spectral index of the star-forming clumps >140M_{sun}_ is consistent with that of the starless clumps ranging from 55-140M_{sun}_, suggesting that the latter will evolve into star-forming clumps while retaining the gas accretion. Assuming a typical star-formation efficiency of molecular clumps (10%), about 10 C^18^O clumps having a gas mass of >10^3^M_{sun}_ will evolve into open clusters containing one or more OB stars.
629. Northern disk of M31 XMM-Newton images
ID:
ivo://CDS.VizieR/J/A+A/637/A12
Title:
Northern disk of M31 XMM-Newton images
Short Name:
J/A+A/637/A12
Date:
21 Oct 2021
Publisher:
CDS
Description:
We use new deep XMM-Newton observations of the northern disk of M31 to trace the hot interstellar medium (ISM) in unprecedented detail and to characterise the physical properties of the X-ray emitting plasmas. We used all XMM-Newton data up to and including our new observations to produce the most detailed image yet of the hot ISM plasma in a grand design spiral galaxy such as our own. We compared the X-ray morphology to multi-wavelength studies in the literature to set it in the context of the multi-phase ISM. We performed spectral analyses on the extended emission using our new observations as they offer sufficient depth and count statistics to constrain the plasma properties. Data from the Panchromatic Hubble Andromeda Treasury were used to estimate the energy injected by massive stars and their supernovae. We compared these results to the hot gas properties. The brightest emission regions were found to be correlated with populations of massive stars, notably in the 10kpc star-forming ring. The plasma temperatures in the ring regions are ~0.2keV up to ~0.6keV. We suggest this emission is hot ISM heated in massive stellar clusters and superbubbles. We derived X-ray luminosities, densities, and pressures for the gas in each region. We also found large extended emission filling low density gaps in the dust morphology of the northern disk, notably between the 5kpc and 10kpc star-forming rings. We propose that the hot gas was heated and expelled into the gaps by the populations of massive stars in the rings. It is clear that the massive stellar populations are responsible for heating the ISM to X-ray emitting temperatures, filling their surroundings, and possibly driving the hot gas into the low density regions. Overall, the morphology and spectra of the hot gas in the northern disk of M 31 is similar to other galaxy disks.
630. Nulling of 20 pulsars
ID:
ivo://CDS.VizieR/J/A+A/644/A73
Title:
Nulling of 20 pulsars
Short Name:
J/A+A/644/A73
Date:
21 Oct 2021
Publisher:
CDS
Description:
Most of pulsar nulling observations were conducted at frequencies lower than 1400MHz. We aim to understand the nulling behaviors of pulsars at relatively high frequency, and to check if nulling is caused by a global change of pulsar magnetosphere. 20 bright pulsars are observed at 2250MHz with unprecedented lengths of time by using Jiamusi 66m telescope. Nulling fractions of these pulsars are estimated, and the null and emission states of pulses are identified. Nulling degrees and scales of the emission-null pairs are calculated to describe the distributions of emission and null lengths. Three pulsars, PSRs J0248+6021, J0543+2329 and J1844+00, are found to null for the first time. The details of null-to-emission and emission-to-null transitions within pulse window are first observed for PSR J1509+5531, which is a small probability event. A complete cycle of long nulls for hours is observed for PSR J1709-1640. For most of these pulsars, the K-S tests of nulling degrees and nulling scales reject the hypothesis that null and emission are of random processes at high significance levels. Emission-null sequences of some pulsars exhibit quasi-periodic, low-frequency or featureless modulations, which might be related to different origins. During transitions between emission and null states, pulse intensities have diverse tendencies for variations. Significant correlations are found for nulling fraction, nulling cadence and nulling scales with the energy loss rate of the pulsars. Combined with the nulling fractions reported in literatures for 146 nulling pulsars, we found that statistically large nulling fractions are more tightly related to pulsar period than to characteristic age or energy loss rate.

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