Southern Survey Research Articles

Candidate Members of the VMP/EMP Disk System of the Galaxy from the SkyMapper and SAGES Surveys

Photometric stellar surveys now cover a large fraction of the sky, probe to fainter magnitudes than large-scale spectroscopic surveys, and are relatively free from the target selection biases often associated with such studies. Photometric-metallicity estimates that include narrow/medium-band filters can achieve comparable accuracy and precision to existing low-resolution spectroscopic surveys such as Sloan Digital Sky Survey/SEGUE and LAMOST. Here we report on an effort to identify likely members of the Galactic disk system among the very metal-poor (VMP; [Fe/H] ≤ −2) and extremely metal-poor (EMP; [Fe/H] ≤ −3) stars. Our analysis is based on an initial sample of ∼11.5 million stars with full space motions selected from the SkyMapper Southern Survey (SMSS) and Stellar Abundance and Galactic Evolution Survey (SAGES). After applying a number of quality cuts to obtain the best available metallicity and dynamical estimates, we analyze a total of ∼5.86 million stars in the combined SMSS/SAGES sample. We employ two techniques that, depending on the method, identify between 876 and 1476 VMP stars (6.9%−11.7% of all VMP stars) and between 40 and 59 EMP stars (12.4%−18.3% of all EMP stars) that appear to be members of the Galactic disk system on highly prograde orbits (v ϕ > 150 km s−1). The total number of candidate VMP/EMP disklike stars is 1496, the majority of which have low orbital eccentricities, ecc ≤ 0.4; many have ecc ≤ 0.2. The large fractions of VMP/EMP stars associated with the Milky Way disk system strongly suggest the presence of an early-forming “primordial” disk.

SkyMapper Southern Survey: Data release 4

Abstract We present the fourth data release (DR4) of the SkyMapper Southern Survey (SMSS), the last major step in our hemispheric survey with six optical filters: u, v, g, r, i, z. SMSS DR4 covers 26 000 deg $^{2}$ from over 400 000 images acquired by the 1.3 m SkyMapper telescope between 2014-03 and 2021-09. The 6-band sky coverage extends from the South Celestial Pole to $\delta=+16^{\circ}$ , with some images reaching $\delta\sim +28^{\circ}$ . In contrast to previous DRs, we include all good-quality images from the facility taken during that time span, not only those explicitly taken for the public Survey. From the image dataset, we produce a catalogue of over 15 billion detections made from $\sim$ 700 million unique astrophysical objects. The typical 10 $\sigma$ depths for each field range between 18.5 and 20.5 mag, depending on the filter, but certain sky regions include longer exposures that reach as deep as 22 mag in some filters. As with previous SMSS catalogues, we have cross-matched with a host of other imaging and spectroscopic datasets to facilitate additional science outcomes. SMSS DR4 is now available to the worldwide astronomical community.

Red Giants Search Method Based on Convolutional Neural Networks

Red giants play a crucial role in astronomical exploration. However, the current search for these stars heavily relies on spectrum analysis, making it a cumbersome process. In this paper, we propose a novel red giant search approach called CBAMResNets. CBAMResNets enhances feature extraction from images by incorporating the Convolutional Block Attention Module into the ResNets model. To train and validate our model, we utilize accurately labeled stellar image data obtained by combining the Sky Mapper Southern Survey (SMSS) and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope. Our experiments demonstrate that CBAMResNets outperforms other networks such as VGG16 and TPC across most performance metrics and remains competitive with traditional machine-learning methods. Specifically, for stars within the magnitude range of 11–19 in the u band, our model achieves a precision rate of 0.92 and a recall rate of 0.9194. Similarly, for stars within the magnitude range of 11–15 in the u band, the precision rate is 0.92, and the recall rate is 0.9813. Furthermore, we apply CBAMResNets to the SMSS subregion, resulting in the identification of 20,243 potential red giant candidates out of the 304,477 observed stars. We validate the authenticity of these candidates by analyzing their stellar absolute magnitudes and temperatures, estimating a contamination rate of approximately 6.4%. Additionally, we examine the approximate distribution of their metallicity. The catalog containing the identified red giant candidates can be accessed at Zenodo. 4 4 doi:10.5281/zenodo.8352420

Beyond Spectroscopy. II. Stellar Parameters for over 20 Million Stars in the Northern Sky from SAGES DR1 and Gaia DR3

We present precise photometric estimates of stellar parameters, including effective temperature, metallicity, luminosity classification, distance, and stellar age, for nearly 26 million stars using the methodology developed in the first paper of this series, based on the stellar colors from the Stellar Abundances and Galactic Evolution Survey (SAGES) Data Release 1 and Gaia Early Data Release 3. The optimal design of stellar-parameter sensitive uv filters by SAGES has enabled us to determine photometric-metallicity estimates down to −3.5, similar to our previous results with the SkyMapper Southern Survey (SMSS), yielding a large sample of over five million metal-poor ([Fe/H] ≤ −1.0) stars and nearly one million very metal-poor ([Fe/H] ≤ −2.0) stars. The typical precision is around 0.1 dex for both dwarf and giant stars with [Fe/H] > −1.0, and 0.15–0.25/0.3–0.4 dex for dwarf/giant stars with [Fe/H] < −1.0. Using the precise parallax measurements and stellar colors from Gaia, effective temperature, luminosity classification, distance, and stellar age are further derived for our sample stars. This huge data set in the Northern sky from SAGES, together with similar data in the Southern sky from SMSS, will greatly advance our understanding of the Milky Way, in particular its formation and evolution.

The first X-ray look at SMSS J114447.77-430859.3: the most luminous quasar in the last 9 Gyr

ABSTRACT SMSS J114447.77-430859.3 (z = 0.83) has been identified in the SkyMapper Southern Survey as the most luminous quasar in the last $\sim 9\, \rm Gyr$ . In this paper, we report on the eROSITA/Spectrum–Roentgen–Gamma (SRG) observations of the source from the eROSITA All Sky Survey, along with presenting results from recent monitoring performed using Swift, XMM-Newton, and NuSTAR. The source shows a clear variability by factors of ∼10 and ∼2.7 over time-scales of a year and of a few days, respectively. When fit with an absorbed power law plus high-energy cutoff, the X-ray spectra reveal a Γ = 2.2 ± 0.2 and $E_{\rm cut}=23^{+26}_{-5}\, \rm keV$ . Assuming Comptonization, we estimate a coronal optical depth and electron temperature of $\tau =2.5-5.3\, (5.2-8)$ and $kT=8-18\, (7.5-14)\, \rm keV$ , respectively, for a slab (spherical) geometry. The broadband SED is successfully modelled by assuming either a standard accretion disc illuminated by a central X-ray source, or a thin disc with a slim disc emissivity profile. The former model results in a black hole mass estimate of the order of $10^{10}\, \mathrm{ M}_\odot$ , slightly higher than prior optical estimates; meanwhile, the latter model suggests a lower mass. Both models suggest sub-Eddington accretion when assuming a spinning black hole, and a compact ($\sim 10\, r_{\rm g}$ ) X-ray corona. The measured intrinsic column density and the Eddington ratio strongly suggest the presence of an outflow driven by radiation pressure. This is also supported by variation of absorption by an order of magnitude over the period of $\sim 900 \ \rm d$ .

Outness, Discrimination, and Psychological Distress Among LGBTQ+ People Living in the Southern United States.

Purpose: Lesbian, gay, bisexual, transgender, queer, and other sexual and gender minority (LGBTQ+) people face mental health disparities. These disparities are amplified in the Southern regions of the United States. This study assessed the role of outness, discrimination, and other demographic variables on possible serious mental illness (SMI) among LGBTQ+ Southerners. Methods: This study used data from the 2017 LGBT Institute Southern Survey, a cross-sectional convenience sample of 6502 LGBTQ+ adults living in 14 Southern states. Multivariable logistic regression was performed to examine differences between those with and without possible SMI. Results: Outness was associated with a lower likelihood of possible SMI (odds ratio [OR]: 0.696, 95% confidence interval [CI]: 0.574-0.844, p = 0.001), especially when controlling for discrimination in the past 12 months (OR: 0.693, 95% CI: 0.576-0.834, p ≤ 0.001) and lifetime discrimination (OR: 0.678, 95% CI: 0.554-0.829, p = 0.001). Lifetime discrimination was associated with a higher likelihood of possible SMI (OR: 1.413, 95% CI: 1.034-1.932, p = 0.033), as was discrimination experienced in the past 12 months (OR: 1.626, 95% CI: 1.408-1.877, p ≤ 0.001). Black/African American respondents had the lowest percentage of possible SMI (21.0%) compared with other races, despite having lower or comparable rates of outness. Conclusion: These results indicate a possible promotive effect of outness against possible SMI among LGBTQ+ Southerners, as well as possible promotive group-level factors among Black/African American LGBTQ+ Southerners. Policies and interventions that address discrimination against LGBTQ+ Southerners should be expanded, and future research should address how the relationships between outness, discrimination, and mental health outcomes may vary by subgroup.

Spatially dependent photometric activity of M dwarfs in the solar cylinder

ABSTRACT We study the relationship between Galactic location (R, Z) and photometric activity for 3.6 million M dwarf stars within 1 kpc of the Sun. For this purpose, we identify 906 unique flare events as a proxy for magnetic activity from the SkyMapper Southern Survey Data Release 3. We adopt vertical distance |Z| from the Galactic disc as a proxy for age and confirm a strong trend of flaring fraction decreasing with growing stellar age. Among M dwarfs within 50 pc of the Sun, we find a flaring fraction of one in 1500, independent of spectral type from M2 to M7, suggesting that these stars are all in a flare-saturated young evolutionary stage. We find a hint of a kink in the slope of the overall flare fraction near 100 pc from the plane, where a steep decline begins; this slope change is visible for mid-type M dwarfs (M3–M5), suggesting it is not an artefact of mixing spectral type. Together with the Sloan Digital Sky Survey Hα emission, this trend is additional evidence that the activity fraction of M dwarfs depends on Galactic height and activity lifetime. While there is a hint of flattening of the overall activity fraction above |Z| ≈ 500 pc, our data do not constrain this further. Within ∼500 pc distance from the Sun, we find no sign of radial disc gradients in flare activity, which may only be revealed by samples covering a larger radial range.

Dynamically Tagged Groups of Metal-poor Stars. II. The Radial Velocity Experiment Data Release 6

Orbital characteristics based on Gaia Early Data Release 3 astrometric parameters are analyzed for ∼8000 metal-poor stars ([Fe/H] ≤ −0.8) compiled from the Radial Velocity Experiment (RAVE) Data Release 6. Selected as metal-poor candidates based on broadband photometry, RAVE collected moderate-resolution (R ∼ 7500) spectra in the region of the Ca triplet for these stars. About 20% of the stars in this sample also have medium-resolution (1200 ≲ R ≲ 2000) validation spectra obtained over a 4 yr campaign from 2014 to 2017 with a variety of telescopes. We match the candidate stars to photometric metallicity determinations from the Huang et al. recalibration of the SkyMapper Southern Survey Data Release 2. We obtain dynamical clusters of these stars from the orbital energy and cylindrical actions using the HDBSCAN unsupervised learning algorithm. We identify 179 dynamically tagged groups (DTGs) with between 5 and 35 members; 67 DTGs have at least 10 member stars. Milky Way (MW) substructures such as Gaia–Sausage–Enceladus, the Metal-weak Thick Disk, the Splashed Disk, Thamnos, the Helmi Stream, and LMS-1 (Wukong) are identified. Associations with MW globular clusters are determined for 10 DTGs; no recognized MW dwarf galaxies were associated with any of our DTGs. Previously identified dynamical groups are also associated with our DTGs, with emphasis placed on their structural determination and possible new identifications. We identify chemically peculiar stars as members of several DTGs; we find 22 DTGs that are associated with r-process-enhanced stars. Carbon-enhanced metal-poor (CEMP) stars are identified among the targets with available spectroscopy, and we assign these to morphological groups following the approach given by Yoon et al.

Multifilter photometry of Solar System objects from the SkyMapper Southern Survey

Context. The populations of small bodies of the Solar System (asteroids, comets, and Kuiper Belt objects) are used to constrain the origin and evolution of the Solar System. Their orbital distribution and composition distribution are both required to track the dynamical pathway from their formation regions to their current locations. Aims. We aim to increase the sample of Solar System objects (SSOs) that have multifilter photometry and compositional taxonomy. Methods. We searched for moving objects in the SkyMapper Southern Survey. We used the predicted SSO positions to extract photometry and astrometry from the SkyMapper frames. We then applied a suite of filters to clean the catalog from false-positive detections. We finally used the near-simultaneous photometry to assign a taxonomic class to objects. Results. We release a catalog of 880 528 individual observations, consisting of 205 515 known and unique SSOs. The catalog completeness is estimated to be about 97% down to V = 18 mag and the purity is higher than 95% for known SSOs. The near-simultaneous photometry provides either three, two, or a single color that we use to classify 117 356 SSOs with a scheme consistent with the widely used Bus-DeMeo taxonomy. Conclusions. The present catalog contributes significantly to the sample of asteroids with known surface properties (about 40% of main-belt asteroids down to an absolute magnitude of 16). We will release more observations of SSOs with future SkyMapper data releases.

Dynamically Tagged Groups of Metal-poor Stars from the Best and Brightest Survey

Abstract Orbital characteristics based on Gaia Early Data Release 3 astrometric parameters are analyzed for ∼4000 metal-poor stars ([Fe/H] ≤ −0.8) compiled from the Best and Brightest survey. Selected as metal-poor candidates based on broadband near- and far-IR photometry, 43% of these stars had medium-resolution (1200 ≲ R ≲ 2000) validation spectra obtained over a 7 yr campaign from 2014 to 2020 with a variety of telescopes. The remaining stars were chosen based on photometric metallicity determinations from the Huang et al. recalibration of the Sky Mapper Southern Survey. Dynamical clusters of these stars are obtained from the orbital energy and cylindrical actions using the HDBSCAN unsupervised learning algorithm. We identify 52 dynamically tagged groups (DTGs) with between five and 21 members; 18 DTGs have at least 10 member stars. Milky Way (MW) substructures such as Gaia-Sausage-Enceladus, the Metal-Weak Thick-Disk, Thamnos, the Splashed Disk, and the Helmi Stream are identified. Associations with MW globular clusters are determined for eight DTGs; no recognized MW dwarf galaxies were associated with any of our DTGs. Previously identified dynamical groups are also associated with our DTGs, with emphasis placed on their structural determination and possible new identifications. Chemically peculiar stars are identified as members of several DTGs, with six DTGs that are associated with r-process-enhanced stars. We demonstrate that the mean carbon and α-element abundances of our DTGs are correlated with their mean metallicity in an understandable manner. Similarly, we find that the mean metallicity, carbon, and α-element abundances are separable into different regions of the mean rotational-velocity space.

Dust and the intrinsic spectral index of quasar variations: hints of finite stress at the innermost stable circular orbit

ABSTRACT We present a study of 9 242 spectroscopically confirmed quasars with multiepoch ugriz photometry from the SDSS Southern Survey. By fitting a separable linear model to each quasar’s spectral variations, we decompose their five-band spectral energy distributions into variable (disc) and non-variable (host galaxy) components. In modelling the disc spectra, we include attenuation by dust on the line of sight through the host galaxy to its nucleus. We consider five commonly used attenuation laws, and find that the best description is by dust similar to that of the Small Magellanic Cloud, inferring a lack of carbonaceous grains from the relatively weak 2175-Å absorption feature. We go on to construct a composite spectrum for the quasar variations spanning 700–8000 Å. By varying the assumed power-law Lν ∝ να spectral slope, we find a best-fitting value α = 0.71 ± 0.02, excluding at high confidence the canonical Lν ∝ ν1/3 prediction for a steady-state accretion disc with a T ∝ r−3/4 temperature profile. The bluer spectral index of the observed quasar variations instead supports the model of Agol &amp; Krolik, and Mummery &amp; Balbus, in which a steeper temperature profile, T ∝ r−7/8, develops as a result of finite magnetically induced stress at the innermost stable circular orbit extracting energy and angular momentum from the black hole spin.

Dust distributions in the magellanic clouds

ABSTRACT We present high-resolution maps of the dust reddening in the Magellanic Clouds (MCs). The maps cover the Large and Small Magellanic Cloud (LMC and SMC) area and have a spatial angular resolution between ∼26 arcsec and 55 arcmin. Based on the data from the optical and near-infrared (IR) photometric surveys, including the Gaia Survey, the SkyMapper Southern Survey (SMSS), the Survey of the Magellanic Stellar History (SMASH), the Two Micron All Sky Survey (2MASS), and the near-IR YJKS VISTA survey of the Magellanic Clouds system (VMC), we have obtained multiband photometric stellar samples containing over 6 million stars in the LMC and SMC area. Based on the measurements of the proper motions and parallaxes of the individual stars from Gaia Early Data Release 3 (Gaia EDR3), we have built clean samples that contain stars from the LMC, SMC, and Milky Way (MW), respectively. We apply the spectral energy distribution (SED) fitting to the individual sample stars to estimate their reddening values. As a result, we have derived the best-fitting reddening values of ∼1.9 million stars in the LMC, 1.5 million stars in the SMC, and 0.6 million stars in the MW, which are used to construct dust reddening maps in the MCs. Our maps are consistent with those from the literature. The resultant high-resolution dust maps in the MCs are not only important tools for reddening correction of sources in the MCs, but also fundamental for the studies of the distribution and properties of dust in the two galaxies.

Ultraluminous high-redshift quasars from SkyMapper – II. New quasars and the bright end of the luminosity function

ABSTRACT We search for ultraluminous Quasi-Stellar Objects (QSOs) at high redshift using photometry from the SkyMapper Southern Survey Data Release 3 (DR3), in combination with 2MASS, VHS DR6, VIKING DR5, AllWISE, and CatWISE2020, as well as parallaxes and proper motions from Gaia DR2 and eDR3. We report 142 newly discovered Southern QSOs at 3.8 &amp;lt; z &amp;lt; 5.5, of which 126 have M145 &amp;lt; −27 AB mag and are found in a search area of 14 486 deg2. This Southern sample, utilizing the Gaia astrometry to offset wider photometric colour criteria, achieves unprecedented completeness for an ultraluminous QSO search at high redshift. In combination with already known QSOs, we construct a sample that is &amp;gt;80 per cent complete for M145 &amp;lt; −27.33 AB mag at z = 4.7 and for M145 &amp;lt; −27.73 AB mag at z = 5.4. We derive the bright end of the QSO luminosity function at rest frame 145 nm for z = 4.7–5.4 and measure its slope to be β = −3.60 ± 0.37 and β = −3.38 ± 0.32 for two different estimates of the faint-end QSO density adopted from the literature. We also present the first z ∼ 5 QSO luminosity function at rest frame 300 nm.

Discovery of the most luminous quasar of the last 9 Gyr

Abstract We report the discovery of a bright ( $g = 14.5$ mag (AB), $K = 11.9$ mag (Vega)) quasar at redshift $z=0.83$ — the optically brightest (unbeamed) quasar at $z&gt;0.4$ . SMSS J114447.77-430859.3, at a Galactic latitude of $b=+18.1^{\circ}$ , was identified by its optical colours from the SkyMapper Southern Survey (SMSS) during a search for symbiotic binary stars. Optical and near-infrared spectroscopy reveals broad Mg ii, H $\unicode{x03B2}$ , H $\unicode{x03B1}$ , and Pa $\unicode{x03B2}$ emission lines, from which we measure a black hole mass of $\log_{10}\! (M_{\mathrm{BH}}/\mathrm{M}_{\odot}) = 9.4 \pm 0.5$ . With its high luminosity, $L_{\mathrm{bol}} = (4.7\pm1.0)\times10^{47}\,\mathrm{erg\,s}^{-1}$ or $M_{i}(z=2) = -29.74$ mag (AB), we estimate an Eddington ratio of $\approx1.4$ . As the most luminous quasar known over the last ${\sim}$ 9 Gyr of cosmic history, having a luminosity $8\times$ greater than 3C 273, the source offers a range of potential follow-up opportunities.

Erratum “Milky Way Tomography with the SkyMapper Southern Survey. II. Photometric Recalibration of SMSS DR2” (2021, ApJ, 907, 68)

Erratum “Milky Way Tomography with the SkyMapper Southern Survey. II. Photometric Recalibration of SMSS DR2” (2021, ApJ, 907, 68)

SkyMapper colours of Seyfert galaxies and changing-look AGN – II. Newly discovered changing-look AGN

ABSTRACT Changing-look active galactic nuclei (CLAGN) are AGN that change type as their broad emission lines appear or disappear, which is usually accompanied by strong flux changes in their blue featureless continuum. We search for turn-on CLAGN by selecting type-2 AGN from the spectroscopic Six-degree Field Galaxy Survey (6dFGS), whose colours, observed ∼15 yr later by the SkyMapper Southern Survey, are suggestive of type-1 AGN. Starting from 1092 type-2 AGN, we select 20 candidates for follow-up and confirm that 14 of them have changed into type-1 and are thus turn-on CLAGN; further observations reveal 11 more turn-on CLAGN. While our search was not tailored to efficiently discover turn-off CLAGN, we discover two such cases as well. The result suggests a turn-on CLAGN rate of over 3 per cent over ∼15 yr and imply a total CLAGN rate of more than ∼6 per cent over this period. Finally, we present observations of AGN that are atypical for the CLAGN phenomenology, including J1109146 – a type-1 that did not appear as an AGN at all in 6dFGS; J1406507 – the second reported changing-look narrow-line Seyfert 1; and J1340153 – a CLAGN with a change time-scale of 3 months.

A search for distant, pulsating red giants in the southern halo

To investigate the asymptotic giant branch (AGB) population in the Galactic halo, we search for pulsating AGB stars at a heliocentric distance D &gt; 50 kpc. Our research is based on the Catalina Southern Survey (CSS) catalogue of variables, comprising 1286 long-period variables (LPVs) with δ &lt; −20°. We first focus on the 77 stars in the cap |b| &gt; 30° for which spectral M-type or C-type classification can be derived from Hamburg-ESO objective prism spectra. Most of these are oxygen-rich (M-type) and very few are carbon rich. The periods are in the range 100–500 days, and CSS amplitudes are up to 3 mag. In this small sample, no halo AGB star is fainter than Ks0 = 12.5. This may be due to the scarcity of AGBs in the outer halo, or insufficient instrumental depth. Leaving aside spectral information, we then searched for even fainter pulsators (Ks &gt; 12.5) in the entire CSS catalogue. Gaia astrometry makes it possible to identify some contaminants. Our final result is the identification of ten candidate distant LPVs. If these ten stars obey the fundamental mode K-band period–luminosity relation used for Miras and small-amplitude Miras, their distances are between 50 and 120 kpc from the Sun. In a diagram showing distance versus Gaia tangential velocity, these ten stars have positions consistent with that of other objects in the halo, such as globular clusters and dwarf galaxies. We detect some underluminous AGBs that deserve further study. Finally, the halo LPVs ressemble the slow redder variable of globular clusters when colour and periods are compared.

Stellar Metallicities from SkyMapper Photometry. II. Precise Photometric Metallicities of ∼280,000 Giant Stars with [Fe/H] &lt; −0.75 in the Milky Way

Abstract The Milky Way’s metal-poor stars are nearby ancient objects that are used to study early chemical evolution and the assembly and structure of the Milky Way. Here we present reliable metallicities of ∼280,000 stars with −3.75 ≲ [Fe/H] ≲ −0.75 down to g = 17 derived using metallicity-sensitive photometry from the second data release of the SkyMapper Southern Survey. We use the dependency of the flux through the SkyMapper v filter on the strength of the Ca ii K absorption features, in tandem with SkyMapper u, g, i photometry, to derive photometric metallicities for these stars. We find that metallicities derived in this way compare well to metallicities derived in large-scale spectroscopic surveys, and we use such comparisons to calibrate and quantify systematics as a function of location, reddening, and color. We find good agreement with metallicities from the APOGEE, LAMOST, and GALAH surveys, based on a standard deviation of σ ∼ 0.25 dex of the residuals of our photometric metallicities with respect to metallicities from those surveys. We also compare our derived photometric metallicities to metallicities presented in a number of high-resolution spectroscopic studies to validate the low-metallicity end ([Fe/H] &lt; −2.5) of our photometric metallicity determinations. In such comparisons, we find the metallicities of stars with photometric [Fe/H] &lt; −2.5 in our catalog show no significant offset and a scatter of σ ∼ 0.31 dex level relative to those in high-resolution work when considering the cooler stars (g − i &gt; 0.65) in our sample. We also present an expanded catalog containing photometric metallicities of ∼720,000 stars as a data table for further exploration of the metal-poor Milky Way.

Milky Way Tomography with the SkyMapper Southern Survey. II. Photometric Recalibration of SMSS DR2

Abstract We apply the spectroscopy-based stellar-color regression (SCR) method to perform an accurate photometric recalibration of the second data release from the SkyMapper Southern Survey (SMSS DR2). From comparison with a sample of over 200,000 dwarf stars with stellar atmospheric parameters taken from GALAH+ DR3 and with accurate, homogeneous photometry from Gaia DR2, zero-point offsets are detected in the original photometric catalog of SMSS DR2, in particular for the gravity- and metallicity-sensitive uv bands. For the uv bands, the zero-point offsets are close to zero at very low extinction, and then steadily increase with E(B − V), reaching as large as 0.174 and 0.134 mag respectively, at E(B − V) ∼ 0.5 mag. These offsets largely arise from the adopted dust term in the transformations used by SMSS DR2 to construct photometric calibrators from the ATLAS reference catalog. For the gr bands, the zero-point offsets exhibit negligible variations with the E(B − V) of Schlegel et al. due to their tiny coefficients on the dust term in the transformation. Our study also reveals small but significant spatial variations of the zero-point offsets in all uvgr bands. External checks using Strömgren photometry, WD loci, and the SDSS Stripe 82 standard-star catalog independently confirm the zero-points found by our revised SCR method.

Three-dimensional Distribution of the Interstellar Dust in the Milky Way

Abstract We present a three-dimensional (3D) extinction map of the southern sky. The map covers the SkyMapper Southern Survey (SMSS) area of ∼14,000 deg2 and has spatial resolutions between 6.′9 and 27′. Based on the multi-band photometry of SMSS, the Two Micron All Sky Survey, the Wide-Field Infrared Survey Explorer Survey, and the Gaia mission, we have estimated values of the r-band extinction for ∼19 million stars with the spectral energy distribution analysis. Together with the distances calculated from the Gaia data release 2 (DR2) parallaxes, we have constructed a 3D extinction map of the southern sky. By combining our 3D extinction map with those from the literature, we present an all-sky 3D extinction map, and use it to explore the 3D distribution of the Galactic dust grains. We use two different models, one consisting of a single disk and another of two disks, to fit the 3D distribution of the Galactic dust grains. The data is better fitted by a two-disk model, yielding smaller values of the Bayesian Information Criterion. The best-fit model has scale heights of 73 and 225 pc for the “thin” and “thick” dust disks, respectively.