- ID:
- ivo://CDS.VizieR/J/A+A/643/A36
- Title:
- HI-to-H2 transition in local diffuse ISM dataset
- Short Name:
- J/A+A/643/A36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The amount of data collected by spectrometers from radio to ultraviolet (UV) wavelengths opens a new era where the statistical and chemical information contained in the observations can be used concomitantly to investigate the thermodynamical state and the evolution of the interstellar medium (ISM). In this paper, we study the statistical properties of the HI-to-H_2_ transition observed in absorption in the local diffuse and multiphase ISM. Our goal is to identify the physical processes that control the probability of occurrence of any line of sight and the origins of the variations of the integrated molecular fraction from one line of sight to another. The turbulent diffuse ISM is modeled using the RAMSES code, which includes detailed treatments of the magnetohydrodynamics, the thermal evolution of the gas, and the chemistry of H_2_. The impacts of the UV radiation field, the mean density, the turbulent forcing, the integral scale, the magnetic field, and the gravity on the molecular content of the gas are explored through a parametric study that covers a wide range of physical conditions. The statistics of the HI-to-H_2_ transition are interpreted through analytical prescriptions and compared with the observations using a modified and robust version of the Kolmogorov-Smirnov test. The analysis of the observed background sources shows that the lengths of the lines of sight follow a flat distribution in logarithmic scale from ~100pc to ~3kpc. Without taking into account any variation of the parameters along a line of sight or from one line of sight to another, the results of one simulation, convolved with the distribution of distances of the observational sample, are able to simultaneously explain the position, the width, the dispersion, and most of the statistical properties of the HI-to-H_2_ transition observed in the local ISM. The tightest agreement is obtained for a neutral diffuse gas modeled over ~200pc, with a mean density n_H_=1-2cm^-3^, illuminated by the standard interstellar UV radiation field, and stirred up by a large-scale compressive turbulent forcing. Within this configuration, the 2D probability histogram of the column densities of H and H_2_, poetically called the kingfisher diagram, is remarkably stable and is almost unaltered by gravity, the strength of the turbulent forcing, the resolution of the simulation, or the strength of the magnetic field B_x_, as long as B_x_<4{mu}G. The weak effect of the resolution and our analytical prescription suggest that the column densities of HI are likely built up in large-scale warm neutral medium and cold neutral medium (CNM) structures correlated in density over ~20pc and ~10pc, respectively, while those of H_2_ are built up in CNM structures between ~3 and ~10pc. Combining the chemical and statistical information contained in the observations of HI and H_2_ sheds new light on the study of the diffuse matter. Applying this new tool to several atomic and molecular species is a promising perspective to understanding the effects of turbulence, magnetic field, thermal instability, and gravity on the formation and evolution of molecular clouds.
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- ID:
- ivo://CDS.VizieR/J/A+A/637/A40
- Title:
- HMSCs classification and physical parameters
- Short Name:
- J/A+A/637/A40
- Date:
- 07 Dec 2021 10:47:33
- Publisher:
- CDS
- Description:
- The role of ionization feedback on high-mass (>8M_{sun}_) star formation is still highly debated. Questions remain concerning the presence of nearby HII regions changes the properties of early high-mass star formation and whether H ii regions promote or inhibit the formation of high-mass stars. To characterize the role of HII regions on the formation of high-mass stars, we study the properties of a sample of candidates high-mass starless clumps (HMSCs), of which about 90% have masses larger than 100 Msun. These high-mass objects probably represent the earliest stages of high-mass star formation; we search if (and how) their properties are modified by the presence of an HII region. We took advantage of the recently published catalog of HMSC candidates. By cross matching the HMSCs and HII regions, we classified HMSCs into three categories: 1) The HMSCs associated with HII regions both in the position in the projected plane of the sky and in velocity; 2) HMSCs associated in the plane of the sky, but not in velocity; and 3) HMSCs far away from any HII regions in the projected sky plane. We carried out comparisons between associated and non-associated HMSCs based on statistical analyses of multiwavelength data from infrared to radio. We show that there are systematic differences of the properties of HMSCs in different environments. Statistical analyses suggest that HMSCs associated with HII regions are warmer, more luminous, more centrally-peaked and turbulent. We also clearly show, for the first time, that the ratio of bolometric luminosity to envelope mass of HMSCs (L/M) could not be a reliable evolutionary probe for early massive star formation due to the external heating effects of the HII regions. We show HMSCs associated with HII regions present statistically significant differences from HMSCs far away from HII regions, especially for dust temperature and L/M. More centrally peaked and turbulent properties of HMSCs associated with HII regions may promote the formation of high-mass stars by limiting fragmentation. High-resolution interferometric surveys toward HMSCs are crucial to reveal how HII regions impact the star formation process inside HMSCs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/454/2292
- Title:
- H_3_O^+^ and D_3_O^+^ rotational transitions
- Short Name:
- J/MNRAS/454/2292
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mass sensitivity of the vibration-rotation-inversion transitions of H_3_^16^O^+^, H_3_^18^O^+^, and D_3_^16^O^+^ is investigated variationally using the nuclear motion program trove (Yurchenko, Thiel & Jensen 2007JMoSp.245..126Y). The calculations utilize new high-level ab initio potential energy and dipole moment surfaces. Along with the mass dependence, frequency data and Einstein A coefficients are computed for all transitions probed. Particular attention is paid to the {Delta}|k|=3 and {Delta}|k-l|=3 transitions comprising the accidentally coinciding |J, K=0, v_2_=0^+^> and |J, K=3, v_2_=0^-^> rotation-inversion energy levels. The newly computed probes exhibit sensitivities comparable to their ammonia and methanol counterparts, thus demonstrating their potential for testing the cosmological stability of the proton-to-electron mass ratio. The theoretical trove results are in close agreement with sensitivities obtained using the non-rigid and rigid inverter approximate models, confirming that the ab initio theory used in the present study is adequate.
- ID:
- ivo://CDS.VizieR/J/MNRAS/406/1745
- Title:
- H2O in interstellar shock waves
- Short Name:
- J/MNRAS/406/1745
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The dissipation of kinetic energy that occurs in interstellar shock waves is accompanied by the emission of radiation. In the case of shocks that are propagating into mainly molecular gas, the emission occurs principally in lines of the species H_2_, H, O, CO and H_2_O. The relative intensities of these emission lines are indicative of the type and speed of the shock wave and of the physical conditions in the ambient gas. We present the results of computations of the intensities of these lines, for small grids of models of C- and J-type shock waves, and compare with the results of previous calculations. Our results should serve to aid the interpretation of observations made with the Herschel and other satellites.
- ID:
- ivo://CDS.VizieR/J/A+A/595/A80
- Title:
- H_2_O lines reduced spectra in 11 ULIRGs or HyLIRGs
- Short Name:
- J/A+A/595/A80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report rest-frame submillimeter H_2_O emission line observations of 11 ultra- or hyper-luminous infrared galaxies (ULIRGs or HyLIRGs) at z~2-4 selected among the brightest lensed galaxies discovered in the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS). Using the IRAM NOrthern Extended Millimeter Array (NOEMA), we have detected 14 new H_2_O emission lines. These include five 3_21_-3_12_ ortho-H_2_O lines (Eup/k=305K) and nine J=2 para-H_2_O lines, either 2_02_-1_11_ (E_up/k=101K) or 2_11_-2_02_ (E_up/k = 137K). The apparent luminosities of the H_2_O emission lines are {mu}L_H2O_~6-21x10^8^L_{sun}_ (3<{mu}<15, where {mu} is the lens magnification factor), with velocity-integrated line fluxes ranging from 4-15Jy.km/s. We have also observed CO emission lines using EMIR on the IRAM 30m telescope in seven sources (most of those have not yet had their CO emission lines observed). The velocity widths for CO and H_2_O lines are found to be similar, generally within 1{sigma} errors in the same source. With almost comparable integrated flux densities to those of the high-J CO line (ratios range from 0.4 to 1.1), H_2_O is found to be among the strongest molecular emitters in high-redshift Hy/ULIRGs. We also confirm our previously found correlation between luminosity of H_2_O (LH_2_O) and infrared (LIR) that LH_2_O~LIR^(1.1-1.2)^, with our new detections. This correlation could be explained by a dominant role of far-infrared pumping in the H_2_O excitation. Modelling reveals that the far-infrared radiation fields have warm dust temperature T_warm_~45-75K, H_2_O column density per unit velocity interval N_H2O_/{DELTA}V>~0.3x10^15^km/s/cm^2^ and 100{mu}m continuum opacity {tau}_100_>1 (optically thick), indicating that H_2_O is likely to trace highly obscured warm dense gas. However, further observations of J>=4 H_2_O lines are needed to better constrain the continuum optical depth and other physical conditions of the molecular gas and dust. We have also detected H_2_O^+^ emission in three sources. A tight correlation between L_H_2_O and L_H_2_O^+^ has been found in galaxies from low to high redshift. The velocity-integrated flux density ratio between H_2_O^+^ and H_2_O suggests that cosmic rays generated by strong star formation are possibly driving the H_2_O^+^ formation.
- ID:
- ivo://CDS.VizieR/J/ApJ/764/34
- Title:
- HRDS IV. H, He and C radio recombination lines
- Short Name:
- J/ApJ/764/34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Green Bank Telescope H II Region Discovery Survey (GBT HRDS) found hundreds of previously unknown Galactic regions of massive star formation by detecting hydrogen radio recombination line (RRL) emission from candidate H II region targets. Since the HRDS nebulae lie at large distances from the Sun, they are located in previously unprobed zones of the Galactic disk. Here, we derive the properties of helium and carbon RRL emission from HRDS nebulae. Our target sample is the subset of the HRDS that has visible helium or carbon RRLs. This criterion gives a total of 84 velocity components (14% of the HRDS) with helium emission and 52 (9%) with carbon emission. For our highest quality sources, the average ^4^He^+^/H^+^ abundance ratio by number, <y^+^>, is 0.068+/-0.023(1{sigma}). This is the same ratio as that measured for the sample of previously known Galactic H II regions. Nebulae without detected helium emission give robust y^+^ upper limits. There are 5 RRL emission components with y^+^ less than 0.04 and another 12 with upper limits below this value. These H II regions must have either a very low ^4^He abundance or contain a significant amount of neutral helium. The HRDS has 20 nebulae with carbon RRL emission but no helium emission at its sensitivity level. There is no correlation between the carbon RRL parameters and the 8um mid-infrared morphology of these nebulae.
- ID:
- ivo://CDS.VizieR/J/ApJ/886/99
- Title:
- HST obs. in the region of 3 young LMC SNIa remnants
- Short Name:
- J/ApJ/886/99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used two methods to search for surviving companions of Type Ia supernova progenitors in three Balmer-dominated supernova remnants in the Large Magellanic Cloud: 0519-69.0, 0505-67.9 (DEM L71), and 0548-70.4. In the first method, we use the Hubble Space Telescope photometric measurements of stars to construct color-magnitude diagrams (CMDs) and compare positions of stars in the CMDs with those expected from theoretical post-impact evolution of surviving main-sequence or helium star companions. No obvious candidates of surviving companions are identified in this photometric search. Future models for surviving red giant companions or with different explosion mechanisms are needed for thorough comparisons with these observations in order to make more definitive conclusions. In the second method, we use Multi Unit Spectroscopic Explorer observations of 0519-69.0 and DEM L71 to carry out spectroscopic analyses of stars in order to use large peculiar radial velocities as diagnostics of surviving companions. We find a star in 0519-69.0 and a star in DEM L71 moving at radial velocities of 182+/-0km/s and 213+/-0km/s, respectively, more than 2.5{sigma} from the mean radial velocity of the underlying stellar population, 264 and 270km/s, respectively. These stars need higher-quality spectra to investigate their abundances and rotation velocities to determine whether they are indeed surviving companions of the supernova progenitors.
- ID:
- ivo://CDS.VizieR/J/ApJ/831/18
- Title:
- H through Ni intensities in LISM from Voyager 1
- Short Name:
- J/ApJ/831/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Since 2012 August Voyager 1 has been observing the local interstellar energy spectra of Galactic cosmic-ray nuclei down to 3MeV/nuc and electrons down to 2.7MeV. The H and He spectra have the same energy dependence between 3 and 346MeV/nuc, with a broad maximum in the 10-50MeV/nuc range and a H/He ratio of 12.2+/-0.9. The peak H intensity is ~15 times that observed at 1AU, and the observed local interstellar gradient of 3-346MeV H is -0.009+/-0.055%/AU, consistent with models having no local interstellar gradient. The energy spectrum of electrons (e^-^+e^+^) with 2.7-74MeV is consistent with E^-1.30+/-0.05^ and exceeds the H intensity at energies below ~50MeV. Propagation model fits to the observed spectra indicate that the energy density of cosmic-ray nuclei with >3MeV/nuc and electrons with >3MeV is 0.83-1.02eV/cm^3^ and the ionization rate of atomic H is in the range of 1.51-1.64x10^-17^s^-1^. This rate is a factor >10 lower than the ionization rate in diffuse interstellar clouds, suggesting significant spatial inhomogeneity in low-energy cosmic rays or the presence of a suprathermal tail on the energy spectrum at much lower energies. The propagation model fits also provide improved estimates of the elemental abundances in the source of Galactic cosmic rays.
- ID:
- ivo://CDS.VizieR/J/A+AS/141/297
- Title:
- H_2_ total transition probability
- Short Name:
- J/A+AS/141/297
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The tables display the total emission probabilities, the total dissociation probabilities and the mean kinetic energies released in the dissociation for the rovibronic levels of B, C, B' and D states. As these states are mixed together, we have labeled and ordered them according to the Born Oppenheimer state of greatest weight. For each rovibrational state they display also the term value and the weight of Born Oppenheimer states B, C, B', D defined in eq (6) of the paper.
- ID:
- ivo://CDS.VizieR/J/A+A/642/A87
- Title:
- Hub-filament candidates
- Short Name:
- J/A+A/642/A87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Star formation takes place in giant molecular clouds, resulting in mass-segregated young stellar clusters composed of Sun-like stars, brown dwarves and massive O-type (50-100M_{sun}_) stars. To identify candidate hub-filament systems (HFS) in the Milky-Way and examine their role in the formation of the highest mass stars and star clusters. Filaments around ~35000 HiGAL clumps that are detected using the DisPerSE algorithm. Hub is defined as a junction of three or more filaments. Column density maps were masked by the filament skeletons and averaged for HFS and non-HFS samples to compute the radial profile along the filaments into the clumps. ~3700~(11%) are candidate HFS of which, ~2150~(60%) are pre-stellar, ~1400~(40%) are proto-stellar. All clumps with L>10^4^L_{sun}_ and L>10^5^L_{sun}_ at distances respectively within 2kpc and 5kpc are located in the hubs of HFS. The column-densities of hubs are found to be enhanced by a factor of ~2 (pre-stellar sources) up to ~10 (proto-stellar sources). All high-mass stars preferentially form in the density enhanced hubs of HFS. This amplification can drive the observed longitudinal flows along filaments providing further mass accretion. Radiation pressure and feedback can escape into the inter-filamentary voids. We propose a 'filaments to clusters' unified paradigm for star formation, with the following salient features: a) low-intermediate mass stars form in the filaments slowly (10^6^yr) and massive stars quickly (10^5^yr) in the hub, b) the initial mass function is the sum of stars continuously created in the HFS with all massive stars formed in the hub, c) Feedback dissipation and mass segregation arise naturally due to HFS properties, and c) explain age spreads within bound clusters and formation of isolated OB associations.
