- ID:
- ivo://CDS.VizieR/J/ApJS/155/123
- Title:
- JHKs photometry of ultracompact HII regions
- Short Name:
- J/ApJS/155/123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present adaptive optics (AO) assisted J, H, and K/K' images of eight ultracompact HII (UC HII) regions taken with the ALFA (Adaptive optics with a Laser For Astronomy) and ADONIS (ADaptive Optics Near-Infrared System) AO systems at Calar Alto and La Silla observatories. The images show details of the stellar population and the near-IR morphology of UC HII regions with unprecedented resolution.
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- ID:
- ivo://CDS.VizieR/J/A+A/453/517
- Title:
- JKs photometry of N159A
- Short Name:
- J/A+A/453/517
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present near-infrared imaging and spectroscopic observations of the HII region N159A (~10pc) in the giant star-forming region N159 (50pc) in the LMC. N159A was observed in the J and Ks bands at high spatial resolution ~0.2" using the ESO Very Large Telescope UT4 (VLT), equipped with the NAOS adaptative optics system. Our data reveal the morphology of this region in unprecedented detail. The protostar P2, one of the first YSOs of Class I identified in the LMC is now resolved in two YSO candidates. The ultracompact HII region LI-LMC 1501W is found to be a tight cluster embedded in a compact HII region ionised by a late O source. A new multiple system composed of a tight star cluster and an YSO candidate, all embedded in compact nebular region (0.4pc) is also detected at the north-east edge of N159A. The stellar population of the whole N159A region appears composed of two main stellar populations, one with an age <3Myr and the other one with a large range of age (300Myr-10Gyr). Using spectroscopy, one of the two exciting O stars in the HII region N159A is classified O5-O6.
293. JVLA images of W51A
- ID:
- ivo://CDS.VizieR/J/A+A/595/A27
- Title:
- JVLA images of W51A
- Short Name:
- J/A+A/595/A27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new JVLA observations of the high-mass cluster-forming region W51A from 2 to 16GHz with resolution {theta}_fwhm_~~0.3-0.5". The data reveal a wealth of observational results: (1) Currently-forming, very massive (proto-O) stars are traced by o-H_2_CO 2_1,1_-2_1,2_ emission, suggesting that this line can be used efficiently as a massive protostar tracer. (2) There is a spatially distributed population of <~mJy continuum sources, including hypercompact HII regions and candidate colliding wind binaries, in and around the W51 proto-clusters. (3) There are two clearly detected protoclusters, W51e and W51 IRS2, that are gas-rich but may have most of their mass in stars within their inner <~0.05pc. The majority of the bolometric luminosity in W51 most likely comes from a third population of OB stars between these clusters. The presence of a substantial population of exposed O-stars coincident with a population of still-forming massive stars, along with a direct measurement of the low mass loss rate via ionized gas outflow from W51 IRS2, together imply that feedback is ineffective at halting star formation in massive protoclusters. Instead, feedback may shut off the large-scale accretion of diffuse gas onto the W51 protoclusters, implying that they are evolving towards a state of gas exhaustion rather than gas expulsion. Recent theoretical models predict gas exhaustion to be a necessary step in the formation of gravitationally bound stellar clusters, and our results provide an observational validation of this process.
- ID:
- ivo://CDS.VizieR/J/ApJ/752/148
- Title:
- {kappa}-distributed electrons and OIII em. line
- Short Name:
- J/ApJ/752/148
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The measurement of electron temperatures and metallicities in H II regions and planetary nebulae (PNe) has--for several decades--presented a problem: results obtained using different techniques disagree. What is worse, they disagree consistently. There have been numerous attempts to explain these discrepancies, but none has provided a satisfactory solution to the problem. In this paper, we explore the possibility that electrons in H II regions and PNe depart from a Maxwell-Boltzmann equilibrium energy distribution. We adopt a "{kappa}-distribution" for the electron energies. Such distributions are widely found in solar system plasmas, where they can be directly measured. This simple assumption is able to explain the temperature and metallicity discrepancies in H II regions and PNe arising from the different measurement techniques. We find that the energy distribution does not need to depart dramatically from an equilibrium distribution. From an examination of data from H II regions and PNe, it appears that {kappa}>~10 is sufficient to encompass nearly all objects. We argue that the kappa-distribution offers an important new insight into the physics of gaseous nebulae, both in the Milky Way and elsewhere, and one that promises significantly more accurate estimates of temperature and metallicity in these regions.
- ID:
- ivo://CDS.VizieR/J/ApJ/700/654
- Title:
- Keck spectroscopy of extragalactic HII regions
- Short Name:
- J/ApJ/700/654
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present very deep spectrophotometry of 14 bright extragalactic HII regions belonging to spiral, irregular, and blue compact galaxies. The data for 13 objects were taken with the High Resolution Echelle Spectrometer on the Keck I telescope. We have measured CII recombination lines in 10 of the objects and OII recombination lines in eight of them. We have determined electron temperatures from line ratios of several ions, especially those of low ionization potential.
- ID:
- ivo://CDS.VizieR/J/A+A/426/81
- Title:
- Kinematic analysis of the Minispiral
- Short Name:
- J/A+A/426/81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained BEAR spectro-imaging data of the Galactic Center HII region "Sgr A West", also known as the "Minispiral", in the hydrogen Brackett {gamma} line (2.166 microns). Through multi-component line fitting, we have decomposed this HII region into nine overlapping velocity structures, for which we have extracted the line flux and radial velocity maps. We have then fitted a set of Keplerian orbits onto the radial velocity map of the most extended structure (the "Northern Arm"), assuming that it was orbiting the central black hole candidate Sgr A*. This fit allows us to propose a three-dimensional kinematic model for this structure, which is hereby given as a set of FITS files. In this model, the central mass, its location in the field, and the distance to the Galactic Center are fixed: we use a mass of 3e6 solar masses and a distance of 8kpc; the pixel scale is 0.353 arcsec/pix, Sgr A* is considered to be located at pixel (59.2538, 38.9849) (IDL notation: (0, 0) is the center of the lower-left pixel, add 1 for FITS convention).
- ID:
- ivo://CDS.VizieR/J/ApJ/753/62
- Title:
- Kinematic distance ambiguity in HII regions
- Short Name:
- J/ApJ/753/62
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using H I absorption spectra from the International Galactic Plane Survey, a new method is implemented to resolve the kinematic distance ambiguity for 75 H II regions with known systemic velocities from radio recombination lines. A further 40 kinematic distance determinations are made for H II region candidates without known systemic velocities through an investigation of the presence of H I absorption around the terminal velocity. New kinematic distance determinations can be used to further constrain spiral arm parameters and the location and extent of other structures in the Milky Way disk. H I absorption toward continuum sources beyond the solar circle is also investigated. Follow-up studies of H I at higher resolution than the 1' to 2' of existing Galactic Plane Surveys will provide kinematic distances to many more H II regions on the far side of the Galactic center. On the basis of the velocity channel summation technique developed in this paper, a much larger sample of H II regions will be analyzed in a future paper to remove the near-far distance ambiguity.
- ID:
- ivo://CDS.VizieR/J/A+A/327/1177
- Title:
- Kinematics and electron temperatures in Orion A
- Short Name:
- J/A+A/327/1177
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A map of the core of Orion A, with a 42" resolution in the 64{alpha} recombination line of hydrogen, covering ~5' by ~5', is presented. The V_lsr_ distribution shows a complex variation about the center of the ionized gas emission: From {DELTA}{alpha}=-200" to +300", the V_lsr_ varies from -5km/s to +2km/s then to -4km/s, finally rising to +3km/s. A search for cold (T_e_~3000K) ionized gas toward the KL nebula has revealed no measurable differences in T_e_ between this region and other parts of Orion A. The average T_e_ from our data is 8300+/-200K. We find no significant difference between T_e_ values determined from radio recombination lines and those determined from forbidden optical lines of [O III], although the T_e_ value from Balmer decrement data is markedly lower. The turbulent velocity varies by <5% over the region mapped. On the basis of our 2.45' resolution, high dynamic range 6cm continuum map, we find that the emission falls off faster in the East than in the West. We find support for the model in which Orion A is ionization bounded in the East but density bounded in the West. The ionized gas in the West is flowing in the direction of the Sun, while the more positive V_lsr_ values in the east may be caused by the flow of ionized gas off the foreground Dark Bay. This ionized region may have little fine scale structure, since there is little continuum emission in interferometer maps.
- ID:
- ivo://CDS.VizieR/J/ApJ/870/32
- Title:
- Kinematics in young star clusters & associations
- Short Name:
- J/ApJ/870/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Gaia mission has opened a new window into the internal kinematics of young star clusters at the sub-km/s level, with implications for our understanding of how star clusters form and evolve. We use a sample of 28 clusters and associations with ages from ~1-5Myr, where lists of members are available from previous X-ray, optical, and infrared studies. Proper motions from Gaia DR2 reveal that at least 75% of these systems are expanding; however, rotation is only detected in one system. Typical expansion velocities are on the order of ~0.5km/s, and in several systems, there is a positive radial gradient in expansion velocity. Systems that are still embedded in molecular clouds are less likely to be expanding than those that are partially or fully revealed. One-dimensional velocity dispersions, which range from {sigma}_1D_=1 to 3km/s, imply that most of the stellar systems in our sample are supervirial and that some are unbound. In star-forming regions that contain multiple clusters or subclusters, we find no evidence that these groups are coalescing, implying that hierarchical cluster assembly, if it occurs, must happen rapidly during the embedded stage.
- ID:
- ivo://CDS.VizieR/J/MNRAS/432/998
- Title:
- Kinematics of Arp 270 (NGC 3395)
- Short Name:
- J/MNRAS/432/998
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have observed the Arp 270 system (NGC 3395 and NGC 3396) in H{alpha} emission using the Galaxy H{alpha} Fabry-Perot spectrometer on the 4.2m William Herschel Telescope (La Palma). In NGC 3396, which is edge-on to us, we detect gas inflow towards the centre, and also axially confined opposed outflows, characteristic of galactic superwinds, and we go on to examine the possibility that there is a shrouded AGN in the nucleus. The combination of surface brightness, velocity and velocity dispersion information enabled us to measure the radii, FWHM, and the masses of 108 HII regions in both galaxies.
