We present new three-dimensional (3D) interstellar extinction maps in the V and Gaia G filters within 2 kpc of the Sun, a 3D differential extinction (dust spatial distribution density) map along the lines of sight in the same space, a 3D map of variations in the ratio of the extinctions in the V and Gaia G filters within 800 pc of the Sun, and a 2D map of total Galactic extinction through the entire dust half-layer from the Sun to extragalactic space for Galactic latitudes |b|>13 degrees. The 3D maps have a transverse resolution from 3.6 to 11.6 pc and a radial resolution of 50 pc. The 2D map has an angular resolution of 6.1 arcmin. We have produced these maps based on the Gaia DR3 parallaxes and Gaia, Pan-STARRS1, SkyMapper, 2MASS, and WISE photometry for nearly 100 million stars. We have paid special attention to the space within 200 pc of the Sun and high Galactic latitudes as regions where the extinction estimates have had a large relative uncertainty so far. Our maps estimate the extinction within the Galactic dust layer from the Sun to an extended object or through the entire dust half-layer from the Sun to extragalactic space with a precision sigma(A(V))=0.06 mag. This gives a high relative precision of extinction estimates even at high Galactic latitudes, where, according to our estimates, the median total Galactic extinction through the entire dust half-layer from the Sun to extragalactic objects is AV=0.12 +/- 0.06 mag. We have shown that the presented maps are among the best ones in data amount, space size, resolution, precision, and other properties.

The structural parameters of a galaxy can be used to gain insight into its formation and evolution history. In this paper, we strive to compare the Milky Way's structural parameters to other, primarily edge-on, spiral galaxies in order to determine how our Galaxy measures up to the Local Universe. For our comparison, we use the galaxy structural parameters gathered from a variety of literature sources in the optical and near-infrared wave bands. We compare the scale length, scale height, and disk flatness for both the thin and thick disks, the thick-to-thin disk mass ratio, the bulge-to-total luminosity ratio, and the mean pitch angle of the Milky Way's spiral arms to those in other galaxies. We conclude that many of the Milky Way's structural parameters are largely ordinary and typical of spiral galaxies in the Local Universe, though the Galaxy's thick disk appears to be appreciably thinner and less extended than expected from zoom-in cosmological simulations of Milky Way-mass galaxies with a significant contribution of galaxy mergers involving satellite galaxies.

In this paper, we look to analyse the spiral features of grand-design, multiarmed, and flocculent spiral galaxies using deep optical imaging from DESI Legacy Imaging Surveys. We explore the resulting distributions of various characteristics of spiral structure beyond the optical radius, such as the distributions of azimuthal angle, the extent of spiral arms, and of the spiral arm widths for the aforementioned galaxy classes. We also compare the measured properties for isolated galaxies and galaxies in groups and clusters. We find that, on average, compared to multiarmed and flocculent spiral galaxies, the spiral arms of grand-design galaxies exhibit slightly larger azimuthal angles, greater extent, and larger widths in the periphery of the galaxy. Furthermore, on average, isolated galaxies tend to have slightly smaller widths of outer spiral arms compared to galaxies in tight environments, which is likely related to the tidally induced mechanism for generating wider outer spiral arms. We also report that breaks of the disc surface brightness profiles are often related to the truncation of spiral arms in galaxies.

Polar-ring galaxies are photometrically and kinematically decoupled systems that are highly inclined to the major axis of the host. These galaxies have been explored since the 1970s, but the rarity of these systems has made such systematic studies difficult. However, over 250 good candidates have been identified. In this work, we examine a sample of over 18 000 galaxies from the Sloan Digital Sky Survey (SDSS) Stripe 82 for the presence of galaxies with polar structures. Using deep SDSS Stripe 82, DESI Legacy Imaging Surveys, and Hyper Suprime-Cam Subaru Strategic Program, we selected 53 good candidate galaxies with photometrically decoupled polar rings, 9 galaxies with polar halos, 6 galaxies with polar bulges, and 34 possibly forming polar-ring galaxies, versus 13 polar-ring candidates previously selected in Stripe 82. Our results suggest that the occurrence rate of galaxies with polar structures may be significantly underestimated, as revealed by the deep observations, and may amount to 1-3% of non-dwarf galaxies.

Spiral structure can contribute significantly to a galaxy’s luminosity. However, only rarely are proper photometric models of spiral arms used in decompositions. As we show in the previous work, including the spirals as a separate component in a photometric model of a galaxy would both allow to obtain their structural parameters, and reduce the systematic errors in estimating the parameters of other components. Doing so in different wavebands, one can explore how their properties vary with the wavelength. In this paper, second in this series, we perform decomposition of M 51 in 17 bands, from the far UV to far IR, using imaging from the DustPedia project. We use the same 2D photometric model of spiral structure where each arm is modelled independently. The complex and asymmetric spiral structure in M 51 is reproduced relatively well with our model. We analyze the differences between models with and without spiral arms, and investigate how the fit parameters change with wavelength. In particular, we find that the spiral arms demonstrate the largest width in the optical, whereas their contribution to the galaxy luminosity is most significant in the UV. The disk central intensity drops by a factor of 1.25–3 and its exponential scale changes by 5–10\\% when spiral arms are included, depending on wavelength. Taking into account the full light distribution across the arms, we do not observe the signs of a long-lived density wave in the spiral pattern of M 51 as a whole.

Spiral structure can occupy a significant part of the galaxy, but properly accounting for it in photometric decomposition is rarely done. This may lead to significant errors in the parameters determined. To estimate how exactly neglecting the presence of spiral arms affects the estimation of galaxy decomposition parameters, we perform fitting of 29 galaxies considering spiral arms as a separate component. In this study, we utilize 3.6 μm-band images from the S4G survey and use a new 2D photometric model where each spiral arm is modelled independently. In our model, the light distribution both along and across the arm and its overall shape can be varied significantly. We analyse the differences between models with and without spiral arms, and show that neglecting spiral arms in decomposition causes errors in estimating the parameters of the disc, the bulge, and the bar. We retrieve different parameters of the spiral arms themselves, including their pitch angles, widths, and spiral-to-total luminosity ratio, and examine various relations between them and other galaxy parameters. In particular, we find that the spiral-to-total ratio is higher for galaxies with more luminous discs and with higher bulge-to-total ratios. We report that the pitch angle of spiral arms decreases with increasing bulge or bar fraction. We measure the width of the spiral arms to be 53 per cent of the disc scale length, on average. We examine the contribution of the spiral arms to the azimuthally averaged brightness profile and find that spiral arms produce a ‘bump’ on this profile with a typical height of 0.3–0.7 mag.