Polar-ring galaxies in the Illustris TNG50 simulation

Polar-ring galaxies (PRGs) are an outstanding example of galaxies with misaligned kinematics where a typically red central galaxy is surrounded by a large-scale ring or disk of stars, gas and dust oriented almost perpendicular to the main body. It is believed that polar structures are formed in a secondary event after the assembly of a central galaxy, but due to their scarcity, their formation paths are not well constrained yet. We present a study of PRGs from TNG50 cosmological simulations, focusing on the origin of their polar structures. Based on the synthetic images and baryonic mass distribution, we found 6 galaxies with stellar polar rings. Using Supplementary Data Catalogues and available particle data, we confirm that the selected galaxies are direct analogs of real PRGs. In our sample, the polar structures are a result of the close interaction between the host galaxy and its companion. We track two formation paths for the stellar polar rings in our sample: (i) star formation in the accreted gas, (ii) tidal disruption of the satellite's stellar component. Rings formed during the first scenario are, on average, bluer and younger than ones formed due to the satellite disruption. We report a steady increase of the ring's inclination around the two most massive galaxies across a few billion years with a rate of $\approx8^{\circ}$/Gyr. The formation of a polar structure in some cases can increase the nuclear activity of the central galaxy and/or turn the active nucleus off completely.Comment: 19 pages, 18 figures, accepted for publication in MNRA

A new, purely photometric method for determination of resonance locations in spiral galaxies

The knowledge of the positions of the corotation resonance in spiral arms is a key way to estimate their pattern speed, which is a fundamental parameter determining the galaxy dynamics. Various methods for its estimation have been developed, but they all demonstrate certain limitations and a lack of agreement with each other. Here, we present a new method for estimating the corotation radius. This method takes into account the shape of the profile across the arm and its width and, thus, only photometric data is needed. The significance of the method is that it can potentially be used for the farthest galaxies with measurable spiral arms. We apply it to a sample of local galaxies from Savchenko et al. and compare the obtained corotation radii with those previously measured in the literature by other methods. Our results are in good agreement with the literature. We also apply the new method to distant galaxies from the COSMOS field. For the first time, corotation locations for galaxies with photometric redshifts up to $z\sim0.9$ are measured.Comment: accepted in MNRAS Letter

The haloes and environments of nearby galaxies (HERON) -- III. A 45 kpc spiral structure in the GLSB galaxy UGC 4599

We use a 0.7-m telescope in the framework of the Halos and Environments of Nearby Galaxies (HERON) survey to probe low surface brightness structures in nearby galaxies. One of our targets, UGC 4599, is usually classified as an early-type galaxy surrounded by a blue ring making it a potential Hoag's Object analog. Prior photometric studies of UGC 4599 were focused on its bright core and the blue ring. However, the HERON survey allows us to study its faint extended regions. With an eight hour integration, we detect an extremely faint outer disk with an extrapolated central surface brightness of $\mu_\mathrm{0,d}(r)=25.5$ mag arcsec$^{-2}$ down to 31 mag arcsec$^{-2}$ and a scale length of 15 kpc. We identify two distinct spiral arms of pitch angle ~6{\deg} surrounding the ring. The spiral arms are detected out to ~45 kpc in radius and the faint disk continues to ~70 kpc. These features are also seen in the GALEX FUV and NUV bands, in a deep u-band image from the 4.3m Lowell Discovery Telescope (which reveals inner spiral structure emerging from the core), and in HI. We compare this galaxy to ordinary spiral and elliptical galaxies, giant low surface brightness (GLSB) galaxies, and Hoag's Object itself using several standard galaxy scaling relations. We conclude that the pseudobulge and disk properties of UGC 4599 significantly differ from those of Hoag's Object and of normal galaxies, pointing toward a GLSB galaxy nature and filamentary accretion of gas to generate its outer disk.Comment: 17 pages, 14 figures, accepted for publication in MNRA

Probing the spectral shape of dust emission with the DustPedia galaxy sample

The objective of this paper is to understand the variance of the far-infrared (FIR) spectral energy distribution (SED) of the DustPedia galaxies, and its link with the stellar and dust properties. An interesting aspect of the dust emission is the inferred FIR colours which could inform us about the dust content of galaxies, and how it varies with the physical conditions within galaxies. However, the inherent complexity of dust grains as well as the variety of physical properties depending on dust, hinder our ability to utilise their maximum potential. We use principal component analysis (PCA) to explore new hidden correlations with many relevant physical properties such as the dust luminosity, dust temperature, dust mass, bolometric luminosity, star-formation rate (SFR), stellar mass, specific SFR, dust-to-stellar mass ratio, the fraction of absorbed stellar luminosity by dust (f_abs), and metallicity. We find that 95% of the variance in our sample can be described by two principal components (PCs). The first component controls the wavelength of the peak of the SED, while the second characterises the width. The physical quantities that correlate better with the coefficients of the first two PCs, and thus control the shape of the FIR SED are: the dust temperature, the dust luminosity, the SFR, and f_abs. Finally, we find a weak tendency for low-metallicity galaxies to have warmer and broader SEDs, while on the other hand high-metallicity galaxies have FIR SEDs that are colder and narrower

High-resolution, 3D radiative transfer modelling : V. A detailed model of the M 51 interacting pair

Context. Investigating the dust heating mechanisms in galaxies provides a deeper understanding of how the internal energy balance drives their evolution. Over the last decade radiative transfer simulations based on the Monte Carlo method have emphasised the role of the various stellar populations heating the diffuse dust. Beyond the expected heating through ongoing star formation, older stellar populations (>= 8 Gyr) and even active galactic nuclei can both contribute energy to the infrared emission of diffuse dust.Aims. In this particular study we examine how the radiation of an external heating source, such as the less massive galaxy NGC 5195 in the M 51 interacting system, could affect the heating of the diffuse dust of its parent galaxy NGC 5194, and vice versa. Our goal is to quantify the exchange of energy between the two galaxies by mapping the 3D distribution of their radiation field.Methods. We used SKIRT, a state-of-the-art 3D Monte Carlo radiative transfer code, to construct the 3D model of the radiation field of M 51, following the methodology defined in the DustPedia framework. In the interest of modelling, the assumed centre-to-centre distance separation between the two galaxies is similar to 10 kpc.Results. Our model is able to reproduce the global spectral energy distribution of the system, and it matches the resolved optical and infrared images fairly well. In total, 40.7% of the intrinsic stellar radiation of the combined system is absorbed by dust. Furthermore, we quantify the contribution of the various dust heating sources in the system, and find that the young stellar population of NGC 5194 is the predominant dust-heating agent, with a global heating fraction of 71.2%. Another 23% is provided by the older stellar population of the same galaxy, while the remaining 5.8% has its origin in NGC 5195. Locally, we find that the regions of NGC 5194 closer to NGC 5195 are significantly affected by the radiation field of the latter, with the absorbed energy fraction rising up to 38%. The contribution of NGC 5195 remains under the percentage level in the outskirts of the disc of NGC 5194. This is the first time that the heating of the diffuse dust by a companion galaxy is quantified in a nearby interacting system