- ID:
- ivo://CDS.VizieR/J/A+A/550/A12
- Title:
- NGC253 near-infrared H_2_ emission
- Short Name:
- J/A+A/550/A12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Because of its large angular size and proximity to the Milky Way, NGC 253, an archetypal starburst galaxy, provides an excellent laboratory to study the intricacies of this intense episode of star formation. We aim to characterize the excitation mechanisms driving the emission in NGC 253. Specifically we aim to distinguish between shock excitation and ultraviolet (UV) excitation as the dominant driving mechanism, using Br{gamma}, H_2_ and [FeII] as diagnostic emission line tracers.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/515/A55
- Title:
- NGC 6334-NGC 6357 complex
- Short Name:
- J/A+A/515/A55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our knowledge of high-mass star formation has been mainly based on follow-up studies of bright sources found by IRAS, and has thus been incomplete for its earliest phases, which are inconspicuous at infrared wavelengths. With a new generation of powerful bolometer arrays, unbiased large-scale surveys of nearby high-mass star-forming complexes now search for the high-mass analog of low-mass cores and class 0 protostars. Following the pioneering study of Cygnus X, we investigate the star-forming region NGC 6334-NGC 6357 (~1.7kpc)
- 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/MNRAS/453/2006
- Title:
- NGC 2264 SCUBA-2 observations
- Short Name:
- J/MNRAS/453/2006
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present wide-field observations of the NGC 2264 molecular cloud in the dust continuum at 850 and 450{mu}m using SCUBA-2 on the James Clerk Maxwell Telescope. Using ^12^CO 3->2 molecular line data, we determine that emission from CO contaminates the 850{mu}m emission at levels ~30 per cent in localized regions associated with high-velocity molecular outflows. Much higher contamination levels of 60 per cent are seen in shocked regions near the massive star S Mon. If not removed, the levels of CO contamination would contribute an extra 13 per cent to the dust mass in NGC 2264. We use the fellwalker routine to decompose the dust into clumpy structures, and a Hessian-based routine to decompose the dust into filamentary structures. The filaments can be described as a hub-filament structure, with lower column density filaments radiating from the NGC 2264 C protocluster hub. Above mean filament column densities of 2.4x10^22^cm^-2^, star formation proceeds with the formation of two or more protostars. Below these column densities, filaments are starless, or contain only a single protostar.
- ID:
- ivo://CDS.VizieR/J/ApJ/806/74
- Title:
- NH3 line profiles in star-forming regions
- Short Name:
- J/ApJ/806/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Anomalous ammonia (NH_3_) spectra, exhibiting asymmetric hyperfine satellite intensity profiles in the (J,K)=(1,1) inversion transition, have been observed in star-forming regions for over 35 years. We present a systematic study of this "hyperfine intensity anomaly" (HIA) toward a sample of 334 high-mass star forming regions: 310 high-mass (>~100M_{sun}_) clumps and 24 infrared dark clouds. The HIA is ubiquitous in high-mass star forming regions. Although LTE excitation predicts that the intensity ratios of the outer satellites and inner satellites are exactly unity, for this sample the ensemble average ratios are 0.812+/-0.004 and 1.125+/-0.005, respectively. We have quantified the HIA and find no significant relationships between the HIA and temperature, line width, optical depth, and the stage of stellar evolution. The fact that HIAs are common in high-mass star-forming regions suggests that the conditions that lead to HIAs are ubiquitous in these regions. A possible link between HIAs and the predictions of the competitive accretion model of high-mass star formation is suggested; however, the expected trends of HIA strength with clump evolutionary stage, rotational temperature, and line width for evolving cores in competitive accretion models are not found. Thus, the exact gas structures that produce HIAs remain unknown. Turbulent gas structures are a possible explanation, but the details need to be explored.
- ID:
- ivo://CDS.VizieR/J/A+A/472/519
- Title:
- N2H+(1-0) maps of Ophiuchus main cloud
- Short Name:
- J/A+A/472/519
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The earliest phases of clustered star formation and the origin of the stellar initial mass function (IMF) are currently much debated. In order to constrain the origin of the IMF, we investigated the internal and relative motions of starless condensations and protostars previously detected by us in the dust continuum at 1.2mm in the L1688 protocluster of the Ophiuchus molecular cloud complex. The starless condensations have a mass spectrum resembling the IMF and are therefore likely representative of the initial stages of star formation in the protocluster. We carried out detailed molecular line observations, including some N2H+(1-0) mapping, of the Ophiuchus protocluster condensations using the IRAM 30m telescope. We measured subsonic or at most transonic levels of internal turbulence within the condensations, implying virial masses which generally agree within a factor of ~2 with the masses derived from the 1.2mm dust continuum. This supports the notion that most of the L1688 starless condensations are gravitationally bound and prestellar in nature. We measured a global one-dimensional velocity dispersion of less than 0.4km/s between condensations. This small relative velocity dispersion implies that, in general, the condensations do not have time to interact with one another before evolving into pre-main-sequence objects. Our observations support the view that the IMF is partly determined by cloud fragmentation at the prestellar stage. Competitive accretion is unlikely to be the dominant mechanism at the protostellar stage in the Ophiuchus protocluster, but it may possibly govern the growth of starless, self-gravitating condensations initially produced by gravoturbulent fragmentation toward an IMF, Salpeter-like mass spectrum.
- ID:
- ivo://CDS.VizieR/J/A+A/587/A118
- Title:
- N2H+, N2D+ and C17O spectra in Ophiuchus
- Short Name:
- J/A+A/587/A118
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In cold (T<25K) and dense (n_H_>10^4^cm^-3^) interstellar clouds, molecules such as CO are significantly frozen onto dust grain surfaces. Deuterium fractionation is known to be very efficient in these conditions as CO limits the abundance of H_3_^+^, which is the starting point of deuterium chemistry. In particular, N_2_D^+^ is an excellent tracer of dense and cold gas in star- forming regions. We measure the deuterium fraction, RD, and the CO depletion factor, fd, towards a number of starless and protostellar cores in the L1688 region of the Ophiuchus molecular cloud and search for variations based upon environmental differences across L1688. The kinematic properties of the dense gas traced by the N_2_H^+^ and N_2_D^+^ (1-0) lines are also discussed. Deuterium fraction has been measured via observations of the J=1-0 transition of N2H+ and N2D+ towards 33 dense cores in different regions of L1688. We estimated the CO depletion factor using C^17^O(1-0) and 850 micron dust continuum emission from the SCUBA survey. We carried out all line observations with the IRAM 30 meter antenna.
- ID:
- ivo://CDS.VizieR/J/A+A/599/A135
- Title:
- NH_3_ Odin observations towards Sgr A
- Short Name:
- J/A+A/599/A135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Odin satellite is now into its sixteenth year of operation, much surpassing its design life of two years. One of the sources which Odin has observed in great detail is the Sgr A Complex in the centre of the Milky Way. The aim is to study the presence of NH_3_ in the Galactic Centre and spiral arms. Recently, Odin has made complementary observations of the 572GHz NH_3_ line towards the Sgr A +50km/s cloud and Circumnuclear Disk (CND). Significant NH_3_ emission has been observed in both the +50km/s cloud and the CND. Clear NH_3_ absorption has also been detected in many of the spiral arm features along the line of sight from the Sun to the core of our Galaxy. The very large velocity width (80km/s) of the NH_3_ emission associated with the shock region in the southwestern part of the CND may suggest a formation/desorption scenario similar to that of gas-phase H_2_O in shocks/outflows.
- ID:
- ivo://CDS.VizieR/J/ApJ/739/100
- Title:
- [NII] observations of the Carina Nebula (NGC 3372)
- Short Name:
- J/ApJ/739/100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a ~250arcmin^2^ mapping of the 205um [NII] fine-structure emission over the northern Carina Nebula, including the Car I and Car II HII regions. Spectra were obtained using the South Pole Imaging Fabry-Perot Interferometer (SPIFI) at the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) at the South Pole. We supplement the 205um data with new reductions of far-IR fine-structure spectra from the Infrared Space Observatory (ISO) Long Wavelength Spectrometer (LWS) in 63um [OI], 122um [NII], 146um [OI], and 158um [CII]; the 146um [OI] data include 90 raster positions which have not been previously published. Morphological comparisons are made with optical, radio continuum, and CO maps. The 122/205 line ratio is used to probe the density of the low-ionization gas, and the 158/205 line ratio is used to probe the fraction of C^+^ arising from photodissociation regions (PDRs). The [OI] and [CII] lines are used to construct a PDR model of Carina. When the PDR properties are compared with other sources, Carina is found to be more akin to 30 Doradus than galactic star-forming regions such as Orion, M17, or W49; this is consistent with the view of Carina as a more evolved region, where much of the parent molecular cloud has been ionized or swept away. These data constitute the first ground-based detection of the 205um [NII] line, and the third detection overall since those of COBE FIRAS and the Kuiper Airborne Observatory in the early 1990s.
- 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.
