- ID:
- ivo://CDS.VizieR/J/A+A/645/A110
- Title:
- Hypercompact HII regions
- Short Name:
- J/A+A/645/A110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The derived physical parameters for young HII regions are normally determined assuming the emission region to be optically-thin. However, this is unlikely to hold for young HII regions such as Hyper-compact HII(HCHII) and Ultra-compact HII(UCHII) regions and leads to the underestimation of their properties. This can be overcome by fitting the SEDs over a wide range of radio frequencies. Two primary goals are (1) determining physical properties from radio SEDs and finding potential HCHII regions; (2) using these physical properties to investigate their evolution. We used Karl G. Jansky Very Large Array (VLA) to make observations of X-band and K-band with angular-resolutions of ~1.7" and ~0.7", respectively, toward 114 HII regions with rising-spectra between 1-5GHz. We complement our observations with VLA archival data and construct SEDs between 1-26GHz and model them assuming an ionisation-bounded HII region with uniform density. The sample has a mean electron density of ne=1.6*10^4^cm^-3^, diameter diam=0.14pc, and emission measure EM=1.9*10^7^pc/cm^6^. We identify 16 HCHII region candidates and 8 intermediate objects between the classes of HCHII and UCHII regions. The ne, diam, and EM change as expected, however, the Lyman continuum flux is relatively constant over time. We find that about 67% of Lyman continuum photons are absorbed by dust within these HII regions and the dust absorption fraction tends to be more significant for more compact and younger HII regions. Young HII regions are commonly located in dusty clumps; HCHII regions and intermediate objects are often associated with various masers, outflows, broad radio recombination lines, and extended green objects, and the accretion at the two stages tends to be quickly reduced or halted.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/559
- Title:
- IC 63 and IC 59 magnetic field structure
- Short Name:
- J/MNRAS/465/559
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Bright-rimmed clouds (BRCs) are formed at the periphery of HII regions as the radiation from the central star interacts with dense gas. The ionization and resulting compression of the clouds may lead to cloud disruption causing secondary star formation depending on the stellar and gas parameters. Here we use R-band polarimetry to probe the plane-of-the sky magnetic field for two nearby BRCs, IC 59 and IC 63. Both nebulae are illuminated by {gamma} Cas with the direction of the ionizing radiation being orientated parallel or perpendicular to the local magnetic field, allowing us to probe the importance of magnetic field pressure in the evolution of BRCs. Because of the proximity of the system (~200pc), we have acquired a substantial sample of over 500 polarization measurements for stars that form the background to the nebulae. On large scales, the magnetic field geometries of both clouds are anchored to the ambient magnetic field. For IC 63, the magnetic field is aligned parallel to the head-tail morphology of the main condensation, with a convex morphology relative to the direction of the ionizing radiation. We estimate the plane-of-the-sky magnetic field strength in IC 63 to be ~90{mu}G. In IC 59, the projected magnetic field follows the M-shape morphology of the cloud. Here, field lines present a concave shape with respect to the direction of the ionizing radiation from {gamma} Cas. Comparing our observations to published theoretical models, we find good general agreement, supporting the importance of magnetic fields in BRC evolution.
243. IC1805 YSOs
- ID:
- ivo://CDS.VizieR/J/MNRAS/468/2684
- Title:
- IC1805 YSOs
- Short Name:
- J/MNRAS/468/2684
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- W4 is a giant HII region ionized by the OB stars of the cluster IC 1805. The HII region/cluster complex has been a subject of numerous investigations as it is an excellent laboratory for studying the feedback effect of massive stars on the surrounding region. However, the low-mass stellar content of the cluster IC 1805 remains poorly studied till now. With the aim to unravel the low-mass stellar population of the cluster, we present the results of a multiwavelength study based on deep optical data obtained with the Canada-France-Hawaii Telescope, infrared data from Two Micron All Sky Survey and SpitzerSpace Telescope and X-ray data from ChandraSpace Telescope. The present optical data set is complete enough to detect stars down to 0.2M_{sun}_, which is the deepest optical observation so far for the cluster. We identified 384 candidate young stellar objects (YSOs; 101 Class I/II and 283 Class III) within the cluster using various colour-colour and colour-magnitude diagrams. We inferred the mean age of the identified YSOs to be ~2.5Myr and mass in the range 0.3-2.5M_{sun}_. The mass function of our YSO sample has a power-law index of -1.23+/-0.23, close to the Salpeter value (-1.35), and consistent with those of other star-forming complexes. We explored the disc evolution of the cluster members and found that the disc-less sources are relatively older compared to the disc bearing YSO candidates. We examined the effect of high-mass stars on the circumstellar discs and within uncertainties, the influence of massive stars on the disc fraction seems to be insignificant. We also studied the spatial correlation of the YSOs with the distribution of gas and dust of the complex to conclude that IC 1805 would have formed in a large filamentary cloud.
- ID:
- ivo://CDS.VizieR/J/AJ/121/169
- Title:
- Imaging and spectroscopy of Tol 1214-277
- Short Name:
- J/AJ/121/169
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectrophotometric study based on VLT/FORS I observations of one of the most metal-deficient blue compact dwarf (BCD) galaxies known, Tol 1214-277 (Z~Zsolar/25). The data show that roughly half of the total luminosity of the BCD originates from a bright and compact starburst region located at the northeastern tip of a faint dwarf galaxy with cometary appearance. The starburst has ignited less than 4 Myr ago and its emission is powered by several thousand O7V stars and ~170 late-type nitrogen Wolf-Rayet stars located within a compact region with <~500pc in diameter. For the first time in a BCD, a relatively strong [Fe V] {lambda}4227 emission line is seen which together with intense He II {lambda}4686 emission indicates the presence of a very hard radiation field in Tol 1214-277. We argue that this extraordinarily hard radiation originates from both Wolf-Rayet stars and radiative shocks in the starburst region. The structural properties of the low surface brightness (LSB) component underlying the starburst have been investigated by means of surface photometry down to 28 B mag.arcsec^-2^. We find that, for a surface brightness level fainter than ~24.5 B mag.arcsec^-2^, an exponential fitting law provides an adequate approximation to its radial intensity distribution. The broadband colors in the outskirts of the LSB component of Tol 1214-277 are nearly constant and are consistent with an age below one Gyr. This conclusion is supported by the comparison of the observed spectral energy distribution (SED) of the LSB host with theoretical SEDs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/394/900
- Title:
- Infrared colors in HII region Sh2-173
- Short Name:
- J/MNRAS/394/900
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on a multiwavelength study, the interstellar medium around the HII region Sh2-173 has been analysed. The ionized region is clearly detected in the optical and the radio continuum images. The analysis of the H i data shows a region of low emissivity that has an excellent morphological correlation with the radio continuum emission. The HII region is partially bordered by a photodissociation region, which, in turn, is encircled by a molecular structure. The HI and CO structures related to Sh2-173 are observed in the velocity ranges from -25 to -31km/s and from -27 to -39km/s, respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/579/A71
- Title:
- Infrared emission of young HII regions
- Short Name:
- J/A+A/579/A71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Investigating the relationship between radio and infrared emission of HII regions may help shed light on the nature of the ionizing stars and the formation mechanism of early-type stars in general. We have taken advantage of recent unbiased surveys of the Galactic plane such as Herschel/Hi-GAL and VLA/CORNISH to study a bona fide sample of young HII regions located in the Galactic longitude range 10{deg}-65{deg} by comparing the mid- and far-IR continuum emission to the radio free-free emission at 5GHz. We have identified the Hi-GAL counterparts of 230 CORNISH HII regions and reconstructed the spectral energy distributions of 204 of these by complementing the Hi-GAL fluxes with ancillary data at longer and shorter wavelengths. Using literature data, we obtained a kinematical distance estimate for 200 HII regions with Hi-GAL counterparts and determined their luminosities by integrating the emission of the corresponding spectral energy distributions. We have also estimated the mass of the associated molecular clumps from the (sub)millimeter flux densities. Our main finding is that for ~1/3 of the HII regions the Lyman continuum luminosity appears to be greater than the value expected for a zero-age main-sequence star with the same bolometric luminosity. This result indicates that a considerable fraction of young, embedded early-type stars presents a "Lyman excess" possibly due to UV photons emitted from shocked material infalling onto the star itself and/or a circumstellar disk. Finally, by comparing the bolometric and Lyman continuum luminosities with the mass of the associated clump, we derive a star formation efficiency of 5%. The results obtained suggest that accretion may still be present during the early stages of the evolution of HII regions, with important effects on the production of ionizing photons and thus on the circumstellar environment. More reliable numerical models describing the accretion process onto massive stars are required to shed light on the origin of the observed Lyman excess.
- ID:
- ivo://CDS.VizieR/J/A+A/537/A1
- Title:
- Infrared fluxes of HII regions and PNe
- Short Name:
- J/A+A/537/A1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We determine infrared color criteria for distinguishing between HII regions and planetary nebulae.
- ID:
- ivo://CDS.VizieR/J/AZh/94/1003
- Title:
- Infrared morphology of HII regions
- Short Name:
- J/AZh/94/1003
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A search for infrared ring nebulae associated with regions of ionized hydrogen has been carried out. The New GPS Very Large Array survey at 20 cm forms the basis of the search, together with observations obtained with the Spitzer Space Telescope at 8 and 24um and the Herschel Space Telescope at 70um. Objects having ring-like morphologies at 8um and displaying extended emission at 20cm were selected visually. Emission at 24um having the form of an inner ring or central peak is also observed in the selected objects. A catalog of 99 ring nebulae whose shapes at 8 and 70um are well approximated by ellipses has been compiled. The catalog contains 32 objects whose shapes are close to circular (eccentricities of the fitted ellipses at 8um no greater than 0.6, angular radius exceeding 20"). These objects are promising for comparisons with the results of one-dimensional hydrodynamical simulations of expanding regions of ionized hydrogen.
- ID:
- ivo://CDS.VizieR/J/ApJ/675/1319
- Title:
- Infrared photometry of NGC 3603
- Short Name:
- J/ApJ/675/1319
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the initial mass function (IMF) of one of the most massive Galactic star-forming regions NGC 3603 to answer a fundamental question in current astrophysics: is the IMF universal, or does it vary? Using our very deep, high angular resolution JHKSL' images obtained with NAOS-CONICA at the VLT at ESO, we have successfully revealed the stellar population down to the subsolar mass range in the core of the starburst cluster.
- ID:
- ivo://CDS.VizieR/J/AJ/157/112
- Title:
- Infrared photometry of YSOs in the W4 cloud complex
- Short Name:
- J/AJ/157/112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is well known that most of the stars form in rich clusters. However, recent Spitzer observations have shown that a significant number of stars also form in the distributed mode; their origin is not well understood. In this work, we aim to investigate clustered and distributed modes of star formation in the W4 complex. To do so, we identified and characterized the young stellar population associated with the region using homogeneous infrared data sets obtained from the Two Micron All Sky Survey, GLIMPSE, MIPS, and Wide-field Infrared Survey Explorer surveys. We make stellar surface density and minimum spanning tree maps to identify young clusters, and use Spitzer images to identify irradiated structures, such as elephant-trunk-like structures (ETLSs) and pillars in the region. The surface density distribution of the young stellar objects (YSOs) reveals three new clusterings and ~50% distributed protostars in the H II region. The clusters are of low-mass nature but significantly younger than the central cluster IC 1805. We identified ~38 ETLSs in the region, a majority of which consist of one or a few stars at their tips. We find that these stars are low-mass (<2 M_{sun}_) YSOs, located at the outskirts (>17 pc) of the cluster IC 1805 and are part of the scattered distributed population. We argued that the star formation in the ETLSs of W4 is going on possibly due to the triggering effect of the expanding W4 bubble. Although high-resolution photometric and spectroscopic data would be required to confirm the scenario, nonetheless, we discuss the implications of this scenario for our understanding of distributed low-mass star formation in cloud complexes as opposed to other mechanisms such as turbulent fragmentation and dynamical ejection.
