- ID:
- ivo://CDS.VizieR/J/A+A/615/A158
- Title:
- Data cubes of observed species toward Messier 8
- Short Name:
- J/A+A/615/A158
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Messier 8 (M8) is one of the brightest HII regions in the sky. We collected an extensive dataset comprising multiple submillimeter spectral lines from neutral and ionized carbon and from CO. Based on this dataset, we aim to understand the morphology of M8 and that of its associated photodissociation region (PDR) and to carry out a quantitative analysis of the physical conditions of these regions such as kinetic temperatures and volume densities. We used the Stratospheric Observatory For Infrared Astronomy (SOFIA), the Atacama Pathfinder Experiment (APEX) 12m, and the Institut de Radioastronomie Millimetrique (IRAM) 30m telescopes to perform a comprehensive imaging survey of the emission from the fine structure lines of CII and CI and multiple rotational transitions of carbon monoxide (CO) isotopologs within 1.3x1.3pc around the dominant Herschel 36 (Her 36) system, which is composed of at least three massive stars. To further explore the morphology of the region, we compared archival infrared, optical, and radio images of the nebula with our newly obtained fine structure line and CO data, and in particular with the velocity information these data provide. We performed a quantitative analysis, using both LTE and non-LTE methods to determine the abundances of some of the observed species, kinetic temperatures, and volume densities. Bright CO, CII and CI emission have been found toward the HII region and the PDR in M8. Our analysis places the bulk of the molecular material in the background of the nebulosity illuminated by the bright stellar systems Her 36 and 9 Sagitarii. Since the emission from all observed atomic and molecular tracers peaks at or close to the position of Her 36, we conclude that the star is still physically close to its natal dense cloud core and heats it. A veil of warm gas moves away from Her 36 toward the Sun and its associated dust contributes to the foreground extinction in the region. One of the most prominent star forming regions in M8, the Hourglass Nebula, is particularly bright due to cracks in this veil close to Her 36. We obtain H_2_ densities ranging from ~10^4^-10^6^cm^-3^ and kinetic temperatures of 100-150K in the bright PDR caused by Her 36 using radiative transfer modeling of various transitions of CO isotopologs.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/463/1029
- Title:
- DCld303-14.8 & Thumbprint Nebula JHKs phot.
- Short Name:
- J/A+A/463/1029
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of radial density structure of the star forming globule, DCld303.8-14.2 (DC303), and a non-star forming globule, Thumbprint Nebula (TPN), using near-infrared data taken with the ISAAC instrument on the Very Large Telescope. We derive the extinction through the globules using the color excess technique and examine the radial density distribution using Bonnor-Ebert and power-law models.
- ID:
- ivo://CDS.VizieR/J/A+A/566/A120
- Title:
- 3D dust extinction in Milky Way bulge
- Short Name:
- J/A+A/566/A120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Three dimensional interstellar extinction maps provide a powerful tool for stellar population analysis. However, until now, these 3D maps were rather limited by sensitivity and spatial resolution. We use data from the VISTA Variables in the Via Lactea survey together with the Besancon stellar population synthesis model of the Galaxy to determine interstellar extinction as a function of distance in the Galactic bulge covering -10<l<10 and -10<b<5. We adopted a recently developed method to calculate the colour excess. First we constructed the H-Ks vs. Ks and J-Ks vs. Ks colour-magnitude diagrams based on the VVV catalogues that matched 2MASS. Then, based on the temperature-colour relation for M giants and the distance-colour relations, we derived the extinction as a function of distance. The observed colours were shifted to match the intrinsic colours in the Besancon model as a function of distance iteratively. This created an extinction map with three dimensions: two spatial and one distance dimension along each line of sight towards the bulge. We present a 3D extinction map that covers the whole VVV area with a resolution of 6'x6', for J-Ks and H-Ks using distance bins of 0.5-1.0kpc. The high resolution and depth of the photometry allows us to derive extinction maps for a range of distances up to 10kpc and up to 30 magnitudes of extinction in AV (3.0mag in AKs). Integrated maps show the same dust features and consistent values as other 2D maps. We discuss the spatial distribution of dust features in the line of sight, which suggests that there is much material in front of the Galactic bar, specifically between 5-7kpc. We compare our dust extinction map with the high-resolution ^12^CO maps (NANTEN2) towards the Galactic bulge, where we find a good correlation between ^12^CO and A_V_. We determine the X factor by combining the CO map and our dust extinction map. Our derived average value X=2.5+/-0.47x10^20^/(cm^2^.K.km/s) is consistent with the canonical value of the Milky Way. The X-factor decreases with increasing extinction.
- ID:
- ivo://CDS.VizieR/J/A+A/650/A100
- Title:
- Decomposition of Galactic sky with autoencoders
- Short Name:
- J/A+A/650/A100
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- All-sky observations show both Galactic and non-Galactic diffuse emission, for example from interstellar matter or the cosmic microwave background (CMB). The decomposition of the emission into different underlying radiative components is an important signal reconstruction problem. We aim to reconstruct radiative all-sky components using spectral data, without incorporating knowledge about physical or spatial correlations. We built a self-instructing algorithm based on variational autoencoders following three steps: (1) We stated a forward model describing how the data set is generated from a smaller set of features, (2) we used Bayes' theorem to derive a posterior probability distribution, and (3) used variational inference and statistical independence of the features to approximate the posterior. From this, we derived a loss function and optimized it with neural networks. The resulting algorithm contains a quadratic error norm with a self-adaptive variance estimate to minimize the number of hyperparameters. We trained our algorithm on independent pixel vectors, each vector representing the spectral information of the same pixel in 35 Galactic all-sky maps ranging from the radio to the gamma-ray regime. The algorithm calculates a compressed representation of the input data. We find the feature maps derived in the algorithm's latent space show spatial structures that can be associated with all-sky representations of known astrophysical components. Our resulting feature maps encode (1) the dense interstellar medium (ISM), (2) the hot and dilute regions of the ISM, and (3) the CMB, without being informed about these components a priori. We conclude that Bayesian signal reconstruction with independent Gaussian latent space statistics is sufficient to reconstruct the dense and the dilute ISM, as well as the CMB, from spectral correlations only. The approximation of the posterior can be performed computationally efficient using variational inference and neural networks, making them a suitable approach to probabilistic data analysis.
- ID:
- ivo://CDS.VizieR/J/MNRAS/452/2606
- Title:
- Deep echelle spectrophotometry of NGC3918
- Short Name:
- J/MNRAS/452/2606
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The chemical content of the planetary nebula NGC 3918 is investigated through deep, high-resolution (R~40000) UVES (Ultraviolet-Visual Echelle Spectrograph) at VLT (Very Large Telescope) spectrophotometric data. We identify and measure more than 750 emission lines, making ours one of the deepest spectra ever taken for a planetary nebula. Among these lines we detect very faint lines of several neutron-capture elements (Se, Kr, Rb, and Xe), which enable us to compute their chemical abundances with unprecedented accuracy, thus constraining the efficiency of the s-process and convective dredge-up in NGC 3918 progenitor star. We find that Kr is strongly enriched in NGC 3918 and that Se is less enriched than Kr, in agreement with the results of previous papers and with predicted s-process nucleosynthesis. We also find that Xe is not as enriched by the s-process in NGC 3918 as is Kr and, therefore, that neutron exposure is typical of modestly subsolar metallicity asymptotic giant branch (AGB) stars. A clear correlation is found when representing [Kr/O] versus log(C/O) for NGC 3918 and other objects with detection of multiple ions of Kr in optical data, confirming that carbon is brought to the surface of AGB stars along with s-processed material during third dredge-up episodes, as predicted by nucleosynthesis models. We also detect numerous refractory element lines (Ca, K, Cr, Mn, Fe, Co, Ni, and Cu) and a large number of metal recombination lines of C, N, O, and Ne. We compute physical conditions from a large number of diagnostics, which are highly consistent among themselves assuming a three-zone ionization scheme. Thanks to the high ionization of NGC 3918 we detect a large number of recombination lines of multiple ionization stages of C, N, O and Ne. The abundances obtained for these elements by using recently determined state-of-the-art ionization correction factor (ICF) schemes or simply adding ionic abundances are in very good agreement, demonstrating the quality of the recent ICF scheme for high-ionization planetary nebulae.
- ID:
- ivo://CDS.VizieR/J/ApJ/838/152
- Title:
- Deep NIR spectrum of the Orion Bar PDR
- Short Name:
- J/ApJ/838/152
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a deep near-infrared spectrum of the Orion Bar Photodissociation Region (PDR) taken with the Immersion Grating INfrared Spectrometer (IGRINS) on the 2.7m telescope at the McDonald Observatory. IGRINS has high spectral resolution (R~45000) and instantaneous broad wavelength coverage (1.45-2.45{mu}m), enabling us to detect 87 emission lines from rovibrationally excited molecular hydrogen (H_2_) that arise from transitions out of 69 upper rovibration levels of the electronic ground state. These levels cover a large range of rotational and vibrational quantum numbers and excitation energies, making them excellent probes of the excitation mechanisms of H_2_ and physical conditions within the PDR. The Orion Bar PDR is thought to consist of cooler high density clumps or filaments (T=50-250K, n_H_=10^5^-10^7^cm^-3^) embedded in a warmer lower density medium (T=250-1000K, n_H_=10^4^-10^5^cm^-3^). We fit a grid of constant temperature and density Cloudy models, which recreate the observed H_2_ level populations well, to constrain the temperature to a range of 600-650 K and the density to n_H_=2.5x10^3^-10^4^cm^-3^. The best-fit model gives T=625K and n_H_=5x10^3^cm^-3^. This well-constrained warm temperature is consistent with kinetic temperatures found by other studies for the Orion Bar's lower density medium. However, the range of densities well fit by the model grid is marginally lower than those reported by other studies. We could be observing lower density gas than the surrounding medium, or perhaps a density-sensitive parameter in our models is not properly estimated.
- ID:
- ivo://CDS.VizieR/J/ApJ/725/2232
- Title:
- Deep NIR survey of the Pipe Nebula. II.
- Short Name:
- J/ApJ/725/2232
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new set of high-resolution dust extinction maps of the nearby and essentially starless Pipe Nebula molecular cloud. The maps were constructed from a concerted deep near-infrared imaging survey with the ESO-VLT, ESO-NTT, CAHA 3.5m telescopes, and 2MASS data. The new maps have a resolution three times higher than the previous extinction map of this cloud by Lombardi et al. (2006A&A...454..781L) and are able to resolve structures down to 2600AU. We detect 244 significant extinction peaks across the cloud. These peaks have masses between 0.1 and 18.4M_{sun}_, diameters between 1.2 and 5.7x10^4^AU (0.06 and 0.28pc), and mean densities of about 10^4^cm^-3^, all in good agreement with previous results. From the analysis of the mean surface density of companions we find a well-defined scale near 1.4x10^4^AU below which we detect a significant decrease in structure of the cloud. This scale is smaller than the Jeans length calculated from the mean density of the peaks. The surface density of peaks is not uniform but instead it displays clustering. Extinction peaks in the Pipe Nebula appear to have a spatial distribution similar to the stars in Taurus, suggesting that the spatial distribution of stars evolves directly from the primordial spatial distribution of high-density material.
- ID:
- ivo://CDS.VizieR/J/ApJS/219/21
- Title:
- Deep NIR survey toward Aquila. I. MHOs
- Short Name:
- J/ApJS/219/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed an unbiased, deep near-infrared survey toward the Aquila molecular cloud with a sky coverage of ~1deg^2^. We identified 45 molecular hydrogen emission-line objects (MHOs), of which only 11 were previously known. Using the Spitzer archival data, we also identified 802 young stellar objects (YSOs) in this region. Based on the morphology and the location of MHOs and YSO candidates, we associate 43 MHOs with 40 YSO candidates. The distribution of jet length shows an exponential decrease in the number of outflows with increasing length, and the molecular hydrogen outflows seem to be oriented randomly. Moreover, there is no obvious correlation between jet lengths, jet opening angles, or jet H_2_ 1-0 S(1) luminosities and the spectral indices of the possible driving sources in this region. We also suggest that molecular hydrogen outflows in the Aquila molecular cloud are rather weak sources of turbulence, unlikely to generate the observed velocity dispersion in the region of survey.
- ID:
- ivo://CDS.VizieR/J/ApJ/891/81
- Title:
- Deep optical and infrared photometry of Sh2-305
- Short Name:
- J/ApJ/891/81
- Date:
- 17 Jan 2022 00:38:10
- Publisher:
- CDS
- Description:
- Using our deep optical and near-infrared photometry along with multiwavelength archival data, we here present a detailed study of the Galactic HII region Sh 2-305 to understand the star/star-cluster formation. On the basis of excess infrared emission, we have identified 116 young stellar objects (YSOs) within a field of view of ~18.5'x18.5' around Sh 2-305. The average age, mass, and extinction (AV) for this sample of YSOs are 1.8Myr, 2.9M_{sun}_, and 7.1mag, respectively. The density distribution of stellar sources along with minimal spanning tree calculations on the location of YSOs reveals at least three stellar subclusterings in Sh 2-305. One cluster is seen toward the center (i.e., Mayer 3), while the other two are distributed toward the north and south directions. Two massive O-type stars (VM2 and VM4; ages ~5Myr) are located at the center of the Sh 2-305 HII region. The analysis of the infrared and radio maps traces the photon-dominant regions (PDRs) in Sh 2-305. The association of the younger generation of stars with the PDRs is also investigated in Sh2-305. This result suggests that these two massive stars might have influenced the star formation history in Sh 2-305. This argument is also supported by the calculation of various pressures driven by massive stars, the slope of the mass function/K-band luminosity function, star formation efficiency, fraction of Class I sources, and mass of the dense gas toward the subclusterings in Sh 2-305.
- ID:
- ivo://CDS.VizieR/J/A+A/574/A104
- Title:
- Dense cores in L1495/B213 complex
- Short Name:
- J/A+A/574/A104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Cloud fragmentation into dense cores is a critical step in the process of star formation. A number of recent observations show that it is connected to the filamentary structure of the gas, but the processes responsible for core formation remain mysterious. We studied the kinematics and spatial distribution of the dense gas in the L1495/B213 filamentary region of the Taurus molecular cloud with the goal of understanding the mechanism of core formation. We mapped the densest regions of L1495/B213 in N_2_H^+^(1-0) and C_18_O(2-1) with the IRAM 30m telescope, and complemented these data with archival dust-continuum observations from the Herschel Space Observatory.
