- ID:
- ivo://CDS.VizieR/J/A+A/542/A98
- Title:
- Hydrocarbon solids. optEC(s) model. II.
- Short Name:
- J/A+A/542/A98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The properties of hydrogenated amorphous carbon (a-C:H) dust evolve in response to the local radiation field in the inter- stellar medium and the evolution of these properties is particularly dependent upon the particle size. A model for finite-sized, low-temperature amorphous hydrocarbon particles, based on the microphysical properties of random and defected networks of carbon and hydrogen atoms, with surfaces passivated by hydrogen atoms, has been developed. The eRCN/DG and the optEC(s) models have been combined, adapted and extended into a new optEC(s) (a) model that is used to calculate the optical properties of hydrocarbon grain materials down into the sub-nanometre size regime, where the particles contain only a few tens of carbon atoms.
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- ID:
- ivo://CDS.VizieR/J/A+A/600/A2
- Title:
- Hydrogen in diffuse molecular clouds
- Short Name:
- J/A+A/600/A2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent sub-millimeter and far-infrared wavelength observations of absorption in the rotational ground state lines of various simple molecules against distant Galactic continuum sources have opened the possibility to study the chemistry of diffuse molecular clouds Milky Way-wide. In order to calculate abundances the column densities of molecular and atomic hydrogen, HI, must be known. We aim at determining the atomic hydrogen column densities for diffuse clouds located on the sight lines toward a sample of prominent high mass star forming regions that were intensely studied with the HIFI instrument onboard Herschel. Based on Jansky Very Large Array data, we employ the 21-cm HI absorption-line technique to construct profiles of the HI opacity versus radial velocity toward our target sources. These profiles are combined with lower resolution archival data of extended HI emission to calculate the HI column densities of the individual clouds along the sight lines. We employ Bayesian inference to estimate the uncertainties of the derived quantities. Our study delivers reliable estimates of the atomic hydrogen column density for a large number of diffuse molecular clouds at various Galactocentric distances. Together with column densities of molecular hydrogen derived from its surrogates observed with HIFI, the measurements can be used to characterize the clouds and, e.g., investigate the dependence of their chemistry on the molecular fraction.
- 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.
404. IC 3476 Halpha image
- ID:
- ivo://CDS.VizieR/J/A+A/646/A139
- Title:
- IC 3476 Halpha image
- Short Name:
- J/A+A/646/A139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the IB(s)m galaxy IC 3476 observed in the context of the Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE), a blind narrow-band H{alpha}+[NII] imaging survey of the Virgo cluster carried out with MegaCam at the CFHT. The deep narrow-band image reveals a very pertubed ionised gas distribution that is characterised by a prominent banana-shaped structure in the front of the galaxy formed of giant HII regions crossing the stellar disc. Star-forming structures, at ~8kpc from the edges of the stellar disc, are also detected in a deep far-ultraviolet ASTROSAT/UVIT image. This particular morphology indicates that the galaxy is undergoing an almost edge-on ram pressure stripping event. The same H{alpha}+[NII] image also shows that the star formation activity is totally quenched in the leading edge of the disc, where the gas has been removed during the interaction with the surrounding medium. The spectral energy distribution fitting analysis of the multi-frequency data indicates that this quenching episode is very recent (~50Myr), and roughly corresponds to an increase of the star formation activity by a factor of ~161% in the inner regions with respect to that expected for secular evolution. The analysis of these data, whose angular resolution enables the study of the induced effects of the perturbation down to the scale of individual HII regions (r_eq_~=40pc), also suggests that the increase of star formation activity is due to the compression of the gas along the stellar disc of the galaxy, which is able to increase its mean electron density and boost the star formation process producing bright HII regions with luminosities up to L(H{alpha})~=10^38^erg/s. The combined analysis of the VESTIGE data with deep IFU spectroscopy gathered with MUSE and with high spectral resolution Fabry Perot data also indicates that the hydrodynamic interaction has deeply perturbed the velocity field of the ionised gas component while leaving that of the stellar disc unaffected. The comparison of the data with tuned high-resolution hydrodynamic simulations accounting for the different gas phases (atomic, molecular, ionised) consistently indicates that the perturbing event is very recent (50-150Myr), once again confirming that ram pressure stripping is a violent phenomenon that is able to perturb the evolution of galaxies in rich environments on short timescales.
- ID:
- ivo://CDS.VizieR/J/MNRAS/371/1744
- Title:
- Identification of nitride dust
- Short Name:
- J/MNRAS/371/1744
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Nitride dust is predicted to form in small amounts around carbon stars, but the most likely candidate species such as aluminium nitride (AlN) have not yet been detected. Recently, {alpha}-Si_3_N_4_ was inferred to be the main carrier of the 8.5-12.5um absorption band(s) of an extreme carbon star (AFGL 5625), based on comparison with laboratory KBr dispersion spectra. However, this absorption band has also been attributed to silicon carbide (SiC) and C_3_. To investigate whether or not nitride dust has truly been detected and if it is present in other extreme carbon stars, we (i) gathered new laboratory infrared (IR) absorbance spectra from a suite of nitride compounds, including Si_3_N_4_, using the thin film technique which provides correct relative intensities of weak and strong peaks, and (ii) compared these data to Infrared Space Observatory Short Wavelength Spectrometer (ISO SWS) spectra of seven different extreme carbon stars which also show broad absorption features around ~11m.
- ID:
- ivo://CDS.VizieR/J/MNRAS/404/1295
- Title:
- Impact of gas pressure on transverse structure
- Short Name:
- J/MNRAS/404/1295
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the impact of gas pressure on the transverse coherence of high-redshift (2>=z>=4) Lyman{alpha} (Lyalpha) forest absorption along neighbouring lines of sight that probe the gas Jeans scale (projected separation {Delta}rp<=500h^-1^kpc comoving, angular separation {Delta}{theta}<=30arcsec). We compare predictions from two smoothed particle hydrodynamics simulations that have different photoionization heating rates and thus different temperature-density relations in the intergalactic medium (IGM). We also compare spectra computed from the gas distributions to those computed from the pressureless dark matter.
- ID:
- ivo://CDS.VizieR/J/ApJ/743/131
- Title:
- Infrared absorbance of water H_2_O/H_2_O_2_ ice
- Short Name:
- J/ApJ/743/131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent surface chemistry experiments have shown that the hydrogenation of molecular oxygen on interstellar dust grains is a plausible formation mechanism, via hydrogen peroxide (H_2_O_2_), for the production of water (H_2_O) ice mantles in the dense interstellar medium. Theoretical chemistry models also predict the formation of a significant abundance of H_2_O_2_ ice in grain mantles by this route. At their upper limits, the predicted and experimental abundances are sufficiently high that H_2_O_2_ should be detectable in molecular cloud ice spectra. To investigate this further, laboratory spectra have been obtained for H_2_O_2_/H_2_O ice films between 2.5 and 200um, from 10 to 180K, containing 3%, 30%, and 97% H_2_O_2_ ice. Integrated absorbances for all the absorption features in low-temperature H_2_O_2_ ice have been derived from these spectra. For identifying H_2_O_2_ ice, the key results are the presence of unique features near 3.5, 7.0, and 11.3um. Comparing the laboratory spectra with the spectra of a group of 24 protostars and field stars, all of which have strong H_2_O ice absorption bands, no absorption features are found that can definitely be identified with H_2_O_2_ ice. In the absence of definite H_2_O_2_ features, the H_2_O_2_ abundance is constrained by its possible contribution to the weak absorption feature near 3.47um found on the long-wavelength wing of the 3um H_2_O ice band. This gives an average upper limit for H_2_O_2_, as a percentage of H_2_O, of 9%+/-4%. This is a strong constraint on parameters for surface chemistry experiments and dense cloud chemistry models.
- ID:
- ivo://CDS.VizieR/J/A+A/419/999
- Title:
- Infrared knots along protostellar jets
- Short Name:
- J/A+A/419/999
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the near infrared spectra (0.9-2.5 micron) of protostellar jets (HH 24-26, HH72, BHR71). The observations were carried out with Sofi at R~600 with the 1x290arcsec slit. The spectra are dominated by H2 rovibrational lines (v up 5). Faint emission from ionized material in form of [FeII] and [SII] lines is also recognizable. The tables contain the observed lines together with the measured flux. The reported error derives from the rms of the baseline, multiplied by the width of the instrumental profile (30 Angstrom).
- ID:
- ivo://CDS.VizieR/J/A+A/532/A127
- Title:
- Inner Galaxy HII regions
- Short Name:
- J/A+A/532/A127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report simultaneous H110{alpha} and H_2_CO line observations with the 25m radio telescope of Nanshan station toward 251 HII regions. We used the H110{alpha} line to establish the velocity of the HII regions and H_2_CO absorption lines to distinguish between near and far distances. We detected the H110{alpha} RRLs in 28 sources and H_2_CO absorption lines in 59 sources. In the latter case, 43 features had not previously been observed. H_2_CO and H110{alpha} lines were simultaneously detected toward 23 HII regions. We resolved the kinematic distance ambiguities for 14 HII regions and 20 intervening molecular clouds.
- ID:
- ivo://CDS.VizieR/J/ApJS/154/553
- Title:
- Inner galaxy massive star formation regions
- Short Name:
- J/ApJS/154/553
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report simultaneous H110{alpha} and H_2_CO line observations with the NRAO Green Bank Telescope toward 72HII regions in the Spitzer Space Telescope GLIMPSE survey area (|l|=10{deg}-65{deg} and |b|<=1{deg}). We used the H110{alpha} line to establish the velocity of the HII regions and H_2_CO absorption lines to distinguish between near and far distances. Accurate distances are crucial for the determination of physical properties of massive star formation regions.
