Spectroscopic Survey Data Research Articles

The mass profiles of dwarf galaxies from Dark Energy Survey lensing

ABSTRACT We present a novel approach to extracting dwarf galaxies from photometric data to measure their average halo mass profile with weak lensing. We characterize their stellar mass and redshift distributions with a spectroscopic calibration sample. By combining the ${\sim} 5000\,\mathrm{deg}^2$ multiband photometry from the Dark Energy Survey and redshifts from the Satellites Around Galactic Analogs Survey with an unsupervised machine learning method, we select a low-mass galaxy sample spanning redshifts $z\lt 0.3$ and divide it into three mass bins. From low to high median mass, the bins contain [146 420, 330 146, 275 028] galaxies and have median stellar masses of $\log _{10}(M_*/\text{M}_\odot)=\left[8.52\substack{+0.57 -0.76},\, 9.02\substack{+0.50 -0.64},\, 9.49\substack{+0.50 -0.58}\right]$ . We measure the stacked excess surface mass density profiles, $\Delta \Sigma (R)$, of these galaxies using galaxy–galaxy lensing with a signal-to-noise ratio of [14, 23, 28]. Through a simulation-based forward-modelling approach, we fit the measurements to constrain the stellar-to-halo mass relation and find the median halo mass of these samples to be $\log _{10}(M_{\rm halo}/\text{M}_\odot)$ = [$10.67\substack{+0.2 -0.4}$, $11.01\substack{+0.14 -0.27}$, $11.40\substack{+0.08 -0.15}$]. The cold dark matter profiles are consistent with NFW (Navarro, Frenk, and White) profiles over scales ${\lesssim} 0.15 \, {h}^{-1}$ Mpc. We find that ${\sim} 20$ per cent of the dwarf galaxy sample are satellites. This is the first measurement of the halo profiles and masses of such a comprehensive, low-mass galaxy sample. The techniques presented here pave the way for extracting and analysing even lower mass dwarf galaxies and for more finely splitting galaxies by their properties with future photometric and spectroscopic survey data.

The 3D Lyman-α forest power spectrum from eBOSS DR16

Abstract We measure the three-dimensional power spectrum (P3D) of the transmitted flux in the Lyman-α (Ly-α) forest using the complete extended Baryon Oscillation Spectroscopic Survey data release 16 (eBOSS DR16). This sample consists of ∼ 205,000 quasar spectra in the redshift range 2 ≤ z ≤ 4 at an effective redshift z = 2.334. We propose a pair-count spectral estimator in configuration space, weighting each pair by exp (ik · r), for wave vector k and pixel pair separation r, effectively measuring the anisotropic power spectrum without the need for fast Fourier transforms. This accounts for the window matrix in a tractable way, avoiding artifacts found in Fourier-transform based power spectrum estimators due to the sparse sampling transverse to the line-of-sight of Ly-α skewers. We extensively test our pipeline on two sets of mocks: (i) idealized Gaussian random fields with a sparse sampling of Ly-α skewers, and (ii) log-normal LyaCoLoRe mocks including realistic noise levels, the eBOSS survey geometry and contaminants. On eBOSS DR16 data, the Kaiser formula with a non-linear correction term obtained from hydrodynamic simulations yields a good fit to the power spectrum data in the range (0.02 ≤ k ≤ 0.35) h Mpc−1 at the 1 − 2σ level with a covariance matrix derived from LyaCoLoRe mocks. We demonstrate a promising new approach for full-shape cosmological analyses of Ly-α forest data from cosmological surveys such as eBOSS, the currently observing Dark Energy Spectroscopic Instrument and future surveys such as the Prime Focus Spectrograph, WEAVE-QSO and 4MOST.

Optimal constraints on Primordial non-Gaussianity with the eBOSS DR16 quasars in Fourier space

We present constraints on the amplitude of local Primordial Non-Gaussianities (PNG), f NL, using the quasar sample in the Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic Survey (eBOSS) Data Release 16 (DR16). We analyze the power spectrum monopole, testing for the presence of scale-dependent galaxy bias induced by local PNG. Our analysis makes use of optimal redshift weights that maximize the response of the quasar sample to the possible presence of non-zero PNG. We find -4 < f NL < 27 at 68% confidence level, which is among the strongest bounds with Large Scale Structure data. The optimal analysis reduces the error bar by ~10% compared to the standard one, but this improvement is lower than the one expected from previous forecasts. In addition, the larger volume of this dataset, when compared to previous releases of the eBOSS quasar catalog, does not always correspond to a reduction of the final uncertainty on local PNG. This could suggest the presence of still unknown systematic effects in the data.If the quasars have a lower response to local PNG, our optimal constraint becomes -23 < f NL < 21 at 68%, with an improvement of 30% over standardanalyses. We alsoshow how to use the optimal weights to put data-driven priors on the sample's response tolocal PNG.

High-accuracy emulators for observables in ΛCDM, Neff, Σmν, and w cosmologies

ABSTRACT We use the emulation framework CosmoPower to construct and publicly release neural network emulators of cosmological observables, including the cosmic microwave background (CMB) temperature and polarization power spectra, matter power spectrum, distance-redshift relation, baryon acoustic oscillation (BAO) and redshift-space distortion (RSD) observables, and derived parameters. We train our emulators on Einstein–Boltzmann calculations obtained with high-precision numerical convergence settings, for a wide range of cosmological models including ΛCDM, wCDM, ΛCDM + Neff, and ΛCDM + Σmν. Our CMB emulators are accurate to better than 0.5 per cent out to ℓ = 104, which is sufficient for Stage-IV data analysis, and our P(k) emulators reach the same accuracy level out to $k=50 \, \, \mathrm{Mpc}^{-1}$, which is sufficient for Stage-III data analysis. We release the emulators via an online repository (CosmoPower Organisation), which will be continually updated with additional extended cosmological models. Our emulators accelerate cosmological data analysis by orders of magnitude, enabling cosmological parameter extraction analyses, using current survey data, to be performed on a laptop. We validate our emulators by comparing them to class and camb and by reproducing cosmological parameter constraints derived from Planck TT, TE, EE, and CMB lensing data, as well as from the Atacama Cosmology Telescope Data Release 4 CMB data, Dark Energy Survey Year-1 galaxy lensing and clustering data, and Baryon Oscillation Spectroscopic Survey Data Release 12 BAO and RSD data.

The Near-infrared Ca ii Triplet as a Stellar Activity Indicator: A Library and Comparative Study

We have established and released a new stellar index library of the Ca ii triplet, which serves as an indicator for characterizing the chromospheric activity of stars. The library is based on data from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Low-Resolution Spectroscopic Survey (LRS) Data Release 9. To better reflect the chromospheric activity of stars, we have defined new indices R and R +. The library includes measurements of R and R + for each Ca ii infrared triplet (IRT) from 699,348 spectra of 562,863 F, G, and K-type solar-like stars with a signal-to-noise ratio higher than 100, as well as the stellar atmospheric parameters and basic information inherited from the LAMOST LRS catalog. We compared the differences between the three individual indices of the Ca ii triplet and also conducted a comparative analysis of Rλ8542+ to the Ca ii H and K S and RHK+ index databases. We observe the fraction of less active stars decreases with T eff and the fraction of more active stars first decreases with decreasing temperature and turns to increase with decreasing temperature at 5800 K. We also find that a significant fraction of stars that show a high activity index in both Ca ii H and K and IRT are binaries with low activity; some of them could be discriminated in the Ca ii H and K S index and Rλ8542+ space. This new stellar library serves as a valuable resource for studying chromospheric activity in stars and can be used to improve our comprehension of stellar magnetic activity and other astrophysical phenomena.

High-dimensional Statistical Analysis and Its Application to an ALMA Map of NGC 253

In astronomy, if we denote the dimension of data as d and the number of samples as n, we often find a case with n ≪ d. Traditionally, such a situation is regarded as ill-posed, and there was no choice but to discard most of the information in data dimensions to let d < n. The data with n ≪ d is referred to as the high-dimensional low sample size (HDLSS). To deal with HDLSS problems, a method called high-dimensional statistics has rapidly developed in the last decade. In this work, we first introduce high-dimensional statistical analysis to the astronomical community. We apply two representative methods in the high-dimensional statistical analysis methods, noise-reduction principal component analysis (NRPCA) and automatic sparse principal component analysis (A-SPCA), to a spectroscopic map of a nearby archetype starburst galaxy NGC 253 taken by the Atacama Large Millimeter/submillimeter Array (ALMA). The ALMA map is an example of a typical HDLSS data set. First, we analyzed the original data, including the Doppler shift due to the systemic rotation. High-dimensional PCA can precisely describe the spatial structure of the rotation. We then applied to the Doppler-shift corrected data to analyze more subtle spectral features. NRPCA and R-SPCA were able to quantify the very complicated characteristics of the ALMA spectra. Particularly, we were able to extract information on the global outflow from the center of NGC 253. This method can also be applied not only to spectroscopic survey data, but also to any type of data with a small sample size and large dimension.

Classifying Emission-line Galaxies Using a Dense Neural Network and Support Vector Machine

In this study we present an innovative approach to classifying emission-line galaxies, specifically categorizing them as Star-forming, Seyfert, Low Ionization Nuclear Emission Line Regions, or Composites. Leveraging both a Dense Neural Network and Support Vector Machine, we use key emission-line flux ratios as input features extracted from the Baryon Oscillation Spectroscopic Survey data within the Sloan Digital Sky Survey. The high accuracy in classification for both Machine Learning models showcases their effectiveness and viability in accurately classifying emission-line galaxies with slightly different inputs and target classifications compared to past Machine Learning models.

Observational properties of active galactic nucleus obscuration during the peak of accretion growth

ABSTRACT We investigated the gas obscuration and host galaxy properties of active galactic nuclei (AGNs) during the peak of cosmic accretion growth of supermassive black holes at redshift 0.8–1.8 using X-ray-detected AGNs with mid-infrared and far-infrared detection. The sample was classified as type-1 and type-2 AGNs using optical spectral and morphological classification while the host galaxy properties were estimated with multiwavelength spectral energy distribution fitting. For type-1 AGNs, the black hole mass was determined from MgII emission lines while the black hole mass of type-2 AGNs was inferred from the host galaxy’s stellar mass. Based on the derived parameters, the distribution of the sample in the absorption hydrogen column density (NH) versus Eddington ratio diagram is examined. Among the type-2 AGNs, 28 ± 5 per cent are in the forbidden zone, where the obscuration by dust torus cannot be maintained due to radiation pressure on dusty material. The fraction is higher than that observed in the local universe from the Burst Alert Telescope AGN Spectroscopic Survey data release 2 (BASS DR2) (11 ± 3 per cent). The higher fraction implies that the obscuration of the majority of AGNs is consistent with the radiation pressure regulated unified model but with an increased incidence of interstellar matter (ISM)-obscured AGNs. We discuss the possibility of dust-free absorption in type-1 AGNs and heavy ISM absorption in type-2 AGNs. We also find no statistical difference in the star-formation activity between type-1 and type-2 AGNs which may suggest that obscuration triggered by a gas-rich merging is not common among X-ray detected AGNs in this epoch.

Reconstructing the baryonic acoustic oscillations in the presence of photo-z uncertainties

ABSTRACT The reconstruction method has been widely employed to improve the baryon acoustic oscillations (BAO) measurement in spectroscopic survey data analysis. In this study, we explore the reconstruction of the BAO signals in the realm of photometric data. By adapting the Zel’dovich reconstruction technique, we develop a formalism to reconstruct the transverse BAO in the presence of photo-z uncertainties under the plane-parallel approximation. We access the performance of the BAO reconstruction through comoving N-body simulations. The transverse reconstruction potential can be derived by solving a 2D potential equation, with the surface density and the radial potential contribution acting as the source terms. The solution is predominantly determined by the surface density. As is evident in dense samples, such as the matter field, the transverse BAO reconstruction can enhance both the strength of the BAO signals and their cross correlation with the initial conditions. At z = 0, the cross-correlation is increased by a factor of 1.2 at $k_\perp = 0.2 \, \mathrm{Mpc}^{-1}h$ and 1.4 at $k_\perp = 0.3 \, \mathrm{Mpc}^{-1}h$, respectively. We contrast the 2D potential results with the 3D Poisson equation solution, wherein we directly solve the potential equation using the position in photo-z space, and find good agreement. Additionally, we examine the impact of various conditions, such as the smoothing scales and the level of photo-z uncertainties, on the reconstruction results. We envision the straightforward application of this method to survey data.

On the Migration Origin of the Hercules Moving Group with GAIA, LAMOST, APOGEE, and GALAH Surveys

Using Gaia DR3 data and the wavelet transformation technique, we study the substructures of the Hercules moving group (HMG): Hercules 1 (H1) and Hercules 2 (H2). Spectroscopic survey data from LAMOST, APOGEE, and GALAH are used to obtain metallicities and ages of stars belonging to the HMG. Our analysis leads to several key findings as follows: (a) the HMG is on average richer in metallicity than the Galactic disk, with H2 being metal richer than H1; (b) the HMG likely has a radial metallicity gradient distinct from that of the disk; (c) the HMG is on average older than the disk, with H2 being older than H1; (d) the HMG likely has a radial age gradient distinct from that of the disk; and (e) the metallicity and age distributions of the HMG depend mainly on the Galactic radius but show no dependence on the azimuthal velocity. Taken all together, we conclude that the HMG is composed primarily of stars undergoing radial migration. We suggest that the HMG is associated with a higher-order dynamical resonance of the bar of the Galaxy.

Void BAO measurements on quasars from eBOSS

Abstract We present the clustering of voids based on the quasar (QSO) sample of the extended Baryon Oscillation Spectroscopic Survey Data Release 16 in configuration space. We define voids as overlapping empty circumspheres computed by Delaunay tetrahedra spanned by quartets of quasars, allowing for an estimate of the depth of underdense regions. To maximise the BAO signal-to-noise ratio, we consider only voids with radii larger than 36h−1Mpc. Our analysis shows a negative BAO peak in the cross-correlation of QSOs and voids. The joint BAO measurement of the QSO auto-correlation and the corresponding cross-correlation with voids shows an improvement in 70% of the QSO mocks with an average improvement of $\sim 5\%$. However, on the SDSS data, we find no improvement compatible with cosmic variance. For both mocks and data, adding voids does not introduce any bias. We find under the flat ΛCDM assumption, a distance joint measurement on data at the effective redshift zeff = 1.51 of DV(zeff) = 26.558 ± 0.553. A forecast of a DESI-like survey with 1000 boxes with a similar effective volume recovers the same results as for light-cone mocks with an average of 4.8% improvement in 68% of the boxes.

A Dynamically Distinct Stellar Population in the Leading Arm of the Sagittarius Stream

We present a chemical and dynamical analysis of the leading arm (LA) and trailing arm (TA) of the Sagittarius (Sgr) stream, as well as for the Sgr dwarf galaxy core (SC), using red giant branch, main-sequence, and RR Lyrae stars from large spectroscopic survey data. The different chemical properties among the LA, TA, and SC generally agree with recent studies and can be understood by a radial metallicity gradient established in the progenitor of the Sgr dwarf, followed by preferential stellar stripping from the outer part of the Sgr progenitor. One striking finding is a relatively larger fraction of low-eccentricity stars (e < 0.4) in the LA than in the TA and SC. The TA and SC exhibit very similar distributions. Considering that a tidal tail stripped off from a dwarf galaxy maintains the orbital properties of its progenitor, we expect that the e-distribution of the LA should be similar to that of the TA and SC. Thus, the disparate behavior of the e-distribution of the LA is of particular interest. Following the analysis of Vasiliev et al., we attempt to explain the different e-distribution by introducing a time-dependent perturbation of the Milky Way by the Large Magellanic Cloud's (LMC) gravitational pull, resulting in substantial evolution of the angular momentum of the LA stars to produce the low-e stars. In addition, we confirm from RR Lyrae stars with high eccentricity (e > 0.6) that the TA stars farther away from the SC are also affected by disturbances from the LMC.

Cosmological Constraints from the BOSS DR12 Void Size Function

We present the first cosmological constraints derived from the analysis of the void size function. This work relies on the final Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 12 (DR12) data set, a large spectroscopic galaxy catalog, ideal for the identification of cosmic voids. We extract a sample of voids from the distribution of galaxies, and we apply a cleaning procedure aimed at reaching high levels of purity and completeness. We model the void size function by means of an extension of the popular volume-conserving model, based on two additional nuisance parameters. Relying on mock catalogs specifically designed to reproduce the BOSS DR12 galaxy sample, we calibrate the extended size function model parameters and validate the methodology. We then apply a Bayesian analysis to constrain the Lambda cold dark matter (ΛCDM) model and one of its simplest extensions, featuring a constant dark energy equation of state parameter, w. Following a conservative approach, we put constraints on the total matter density parameter and the amplitude of density fluctuations, finding Ωm = 0.29 ± 0.06 and . Testing the alternative scenario, we derive w = −1.1 ± 0.2, in agreement with the ΛCDM model. These results are independent and complementary to those derived from standard cosmological probes, opening up new ways to identify the origin of potential tensions in the current cosmological paradigm.

Multi-site evaluation of stratified and balanced sampling of soil organic carbon stocks in agricultural fields

Estimating soil organic carbon (SOC) stocks in agricultural fields is essential for environmental and agronomic research, management, and policy. Stratified sampling is a classic strategy for estimating mean soil properties, and has recently been codified in SOC monitoring protocols. However, for the specific task of estimating the SOC stock of an agricultural field, concrete guidance is needed for which covariates to stratify on and how much stratification can improve estimation efficiency. It is also unknown how stratified sampling of SOC stocks compares to modern alternatives, notably doubly balanced sampling. To address these gaps, we collected high-density (average of 7 samples ha−1) and deep (average of 75 cm) measurements of SOC stocks at eight commercial fields under maize-soybean production in two US Midwestern states. We combined these measurements with a Bayesian geostatistical model to evaluate stratified and balanced sampling strategies that use a set of readily-available geographic, topographic, spectroscopic, and soil survey data. We examined the number of samples needed to achieve a given level of SOC stock estimation accuracy. While stratified sampling using these variables enables an average sample size reduction of 17% (95% CI, 11% to 23%) compared to simple random sampling, doubly balanced sampling is consistently more efficient, reducing sample sizes by 32% (95% CI, 25% to 37%). The data most important to these efficiency gains are a remotely-sensed SOC index, SSURGO estimates of SOC stocks, and the topographic wetness index. We conclude that in order to meet the urgent challenge of climate change, SOC stocks in agricultural fields could be more efficiently estimated by taking advantage of this readily-available data, especially with doubly balanced sampling.

First test of the consistency relation for the large-scale structure using the anisotropic three-point correlation function of BOSS DR12 galaxies

ABSTRACT We present, for the first time, an observational test of the consistency relation for the large-scale structure (LSS) of the Universe through a joint analysis of the anisotropic two- and three-point correlation functions (2PCF and 3PCF) of galaxies. We parameterize the breakdown of the LSS consistency relation in the squeezed limit by Es, which represents the ratio of the coefficients of the shift terms in the second-order density and velocity fluctuations. Es ≠ 1 is a sufficient condition under which the LSS consistency relation is violated. A novel aspect of this work is that we constrain Es by obtaining information about the non-linear velocity field from the quadrupole component of the 3PCF without taking the squeezed limit. Using the galaxy catalogues in the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 12, we obtain $E_{\rm s} = -0.92_{-3.26}^{+3.13}$, indicating that there is no violation of the LSS consistency relation in our analysis within the statistical errors. Our parameterization is general enough that our constraint can be applied to a wide range of theories, such as multicomponent fluids, modified gravity theories, and their associated galaxy bias effects. Our analysis opens a new observational window to test the fundamental physics using the anisotropic higher-order correlation functions of galaxy clustering.

New constraints on cosmological modified gravity theories from anisotropic three-point correlation functions of BOSS DR12 galaxies

ABSTRACT We report a new test of modified gravity theories using the large-scale structure of the Universe. This paper is the first attempt to (1) apply a joint analysis of the anisotropic components of galaxy two- and three-point correlation functions (2 and 3PCFs) to actual galaxy data and (2) constrain the non-linear effects of degenerate higher-order scalar-tensor (DHOST) theories on cosmological scales. Applying this analysis to the Baryon Oscillation Spectroscopic Survey (BOSS) data release 12, we obtain the lower bounds of −1.655 &amp;lt; ξt and −0.504 &amp;lt; ξs at the $95{{\ \rm per\ cent}}$ confidence level on the parameters characterizing the time evolution of the tidal and shift terms of the second-order velocity field. These constraints are consistent with GR predictions of ξt = 15/1144 and ξs = 0. Moreover, they represent a 35-fold and 20-fold improvement, respectively, over the joint analysis with only the isotropic 3PCF. We ensure the validity of our results by investigating various quantities, including theoretical models of the 3PCF, window function corrections, cumulative S/N, Fisher matrices, and statistical scattering effects of mock simulation data. We also find statistically significant discrepancies between the BOSS data and the Patchy mocks for the 3PCF measurement. Finally, we package all of our 3PCF analysis codes under the name hitomi and make them publicly available so that readers can reproduce all the results of this paper and easily apply them to ongoing future galaxy surveys.

Baryon acoustic oscillations from a joint analysis of the large-scale clustering in Fourier and configuration space

Baryon acoustic oscillations (BAOs) are a powerful probe of the expansion history of our Universe and are typically measured in the two-point statistics of a galaxy survey, either in Fourier space or in configuration space. In this work, we report a first measurement of BAOs from a joint fit of power spectrum and correlation function multipoles. We tested our new framework with a set of 1000 mock catalogs and showed that our method yields smaller biases on BAO parameters than individually fitting power spectra or correlation functions, or when combining them with the Gaussian approximation method. Our estimated uncertainties are slightly larger than those from the Gaussian approximation, likely due to noise in our sample covariance matrix, the larger number of nuisance parameters, or the fact that our new framework does not rely on the assumption of Gaussian likelihoods for the BAO parameters. However, we argue that our uncertainties are more reliable since they rely on fewer assumptions, and because our method takes correlations between Fourier and configuration space at the level of the two-point statistics. We performed a joint analysis of the luminous red galaxy sample of the extended baryon oscillation spectroscopic survey (eBOSS) data release 16, obtaining DH/rd = 19.27 ± 0.48 and DM/rd = 17.77 ± 0.37, in excellent agreement with the official eBOSS consensus BAO-only results DH/rd = 19.33 ± 0.53 and DM/rd = 17.86 ± 0.33.

Model-independent Test for the Cosmic Distance–Duality Relation with Pantheon and eBOSS DR16 Quasar Sample

In this Paper, we carry out a new model-independent cosmological test for the cosmic distance–duality relation (CDDR) by combining the latest five baryon acoustic oscillation (BAO) measurements and the Pantheon type Ia supernova (SNIa) sample. Particularly, the BAO measurement from the extended Baryon Oscillation Spectroscopic Survey data release 16 quasar sample at effective redshift z = 1.48 is used, and two methods, i.e., a compressed form of the Pantheon sample and the artificial neural network combined with the binning SNIa method, are applied to overcome the redshift-matching problem. Our results suggest that the CDDR is compatible with the observations, and the high-redshift BAO and SNIa data can effectively strengthen the constraints on the violation parameters of CDDR with the confidence interval decreasing by more than 20%. In addition, we find that the compressed form of observational data can provide a more rigorous constraint on the CDDR, and thus can be generalized to the applications of other actual observational data with limited sample size in the test for CDDR.

Three-dimensional extinction maps: Inverting inter-calibrated extinction catalogues

Context. Three-dimensional (3D) maps of the extinction density in the Milky Way can be built through the inversion of large catalogues of distance-extinction pairs for individual target stars. Considerable progress is currently achieved in this field through the Gaia mission. Available catalogues are based on various types of photometric or spectrophotometric information and on different techniques of extinction estimations. Aims. The spatial resolution of the maps that can be achieved increases with the spatial density of the target stars, and, consequently, with the combination of input catalogues containing different target lists. However, this requires careful inter-calibration of the catalogues. Our aim is to develop methods of inter-comparison and inter-calibration of two different extinction catalogues. Methods. The catalogue we used as reference for inter-calibration is a spectrophotometric catalogue. It provides a more accurate extinction than a purely photometric catalogue. In order to reduce the dimension of the problem, a principal component analysis was performed in (G, GB, GR, J, H, K) multi-colour space. The subspace constituted by the two first components was split into cells in which we estimated the deviations from the reference. The deviations were computed using all targets from the reference catalogue that were located at a short spatial distance of each secondary target. Corrections and filtering were deduced for each cell in the multi-colour space. Results. We applied the inter-calibration to two very different extinction datasets: on the one hand, extinctions based on both spectroscopy and photometry, representing 6 million objects and serving as a reference, and, on the other hand, a catalogue of 35 million extinctions based on photometry of Gaia eDR3 and 2MASS. After calibration, the dispersion of the extinction among neighbouring points in the second catalogue is reduced, regardless of whether reference targets are present locally. Weak structures are then more apparent. The extinction of high Galactic latitude targets is significantly more tightly correlated with the dust emission measured by Planck, a property acquired from the first catalogue. A hierarchical inversion technique was applied to the two merged inter-calibrated catalogues to produce 3D extinction density maps corresponding to different volumes and maximum spatial resolution. The maximum resolution is 10 pc for a 3000 pc × 3000 pc × 800 pc volume around the Sun, and the maximum size of the maps is 10 kpc × 10 kpc × 800 pc for a resolution of 50 pc. The inclusion of the spectroscopic survey data increases the dynamic range of the extinction density, improves the accuracy of the maps, and allows the mapping to be extended to greater distances to better constrain the remarkable ≃ 2.5 kpc wide dust-free region in the second quadrant in particular, which now appears as a giant oval superbubble. Maps can be downloaded or used by means of on-line tools.

Infrared Excess of a Large OB Star Sample

The infrared (IR) excess from OB stars is commonly considered to be a contribution from ionized stellar wind or circumstellar dust. With the newly published Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST)-OB catalog and Galactic O-Star Spectroscopic Survey data, this work steps further on understanding the IR excess of OB stars. Based on a forward-modeling approach comparing the spectral slope of observational spectral energy distributions and photospheric models, 1147 stars are found to have IR excess out of 7818 stars with good-quality photometric data. After removing the objects in the sightline of dark clouds, 532 (∼7%) B-type stars and 118 (∼23%) O-type stars are identified to be true OB stars with circumstellar IR excess emission. The ionized stellar wind model and the circumstellar dust model are adopted to explain the IR excess, and Bayes factors are computed to quantitatively compare the two. It is shown that the IR excess can be accounted for by the stellar wind for about 65% cases, of which 33% by free–free emission and 32% by synchrotron radiation. Other 30% sources could have and 4% should have a dust component or other mechanisms to explain the sharp increase in flux at λ > 10 μm. The parameters of the dust model indicate a large-scale circumstellar halo structure, which implies the origin of the dust from the birthplace of the OB stars. A statistical study suggests that the proportion with IR excess in OB stars increases with the stellar effective temperature and luminosity, and that there is no systematic change in the mechanism for IR emission with stellar parameters.