Context. Dark galaxies are small, dark matter-dominated haloes whose gas remains in hydrostatic and thermal equilibrium and has never formed stars. These systems are of particular interest because they represent a strong prediction of the Lambda cold dark matter (ΛCDM) model. As of today, only a few dark galaxy candidates have been detected so far, the most intriguing of which being Cloud-9. Aims. Using several state-of-the-art hydrodynamical simulations, we aim to predict the abundance of dark galaxies within our Local Group, characterise their physical properties, and provide guidance for their potential observational detection. Methods. We analyse Local Group simulations with constrained initial conditions, each run with different codes, implementing different baryonic physics, feedback prescriptions, and employing two distinct values of star-formation density threshold, nth = 0.13 and 10 cm−3, to select samples of dark and bright galaxies harboured in haloes of similar mass. Results. We demonstrate that dark galaxies exist in all such simulations, though their number is larger in simulations that use a higher, more realistic nth. These galaxies, whose gas remains diffuse and never forms stars, predominantly inhabit less-concentrated, higher-spin dark matter haloes than their luminous counterparts. Dark galaxies are typically found in low-density regions at the outskirts of the Local Group. Their formation and evolution across redshift indicate that both the dark matter and gas densities in the surroundings of dark galaxies were consistently lower than those found around bright galaxies, making them less susceptible to interactions, mergers, or gas inflows. We estimate that up to eight dark galaxies should be detectable in H I emission within 2.5 Mpc of the Milky Way, with the FAST radio telescope, accounting for its sky coverage and minimum H I mass and column density. Conclusions. Current hydrodynamical simulations of galaxies, combined with upcoming H I surveys, will offer a direct and powerful test of ΛCDM through their ability to predict and measure properties of dark galaxies within and beyond the Local Group.

Aims. We trace the evolution of eight edge-on star-forming disk galaxies by analyzing stellar population properties of their thin and thick disks. These galaxies have relatively low stellar masses (4 x 109-6 x 1010 M circle dot). Methods. We used Multi-Unit Spectroscopic Explorer (MUSE) observations and a full-spectrum fitting to produce spatially resolved maps of the ages, metallicities, and [Mg/Fe] abundances, and we extracted the star formation histories of the stellar disks. Results. Our maps show thick disks that are older, more metal-poor, and more [Mg/Fe]-enhanced than thin disks on average. The age differences between thin and thick disks are small (about 2 Gyr), however, and the thick disks are younger than previously observed in more massive and more quiescent galaxies. The thin and thick disks both show mostly sub-solar metallicities, and the vertical metallicity gradient is milder than previously observed in similar studies. The [Mg/Fe] differences between thick and thin disks are not sharp. The star formation histories of thick disks extend to recent times, although most of the mass in young stars was formed in thin disks. Conclusions. Our findings show thick disks that are different from the old quiescent thick disks that were previously observed in galaxies with different morphologies and/or masses. We propose that the thick disks in these galaxies did not form quickly at high redshift, but formed slowly over an extended time. The thin disks also formed slowly, but a larger mass fraction was created at very recent times.

Star formation estimates based on the counting of YSOs is commonly applied to nearby star-forming regions in the Galaxy. With this method, the SFRs are measured using the counts of YSOs in a particular protostellar Class, a typical protostellar mass, and the lifetime associated with this Class. However, the assumptions underlying the validity of the method such as that of a constant star formation history (SFH) and whether the method is valid for all protostellar Classes has never been fully tested. In this work, we use Monte Carlo models to test the validity of the method. We build synthetic clusters in which stars form at times that are randomly drawn from a specified SFH. The latter is either constant or time-dependent with a burst like behavior. The masses of the protostars are randomly drawn from an IMF which can be either similar to that of the Milky Way field or be variable . For each star in every cluster, the lifetimes associated with the different protostellar classes are also randomly drawn from Gaussian distribution functions centered around their most likely value as suggested by the observations. We find that only the SFR derived using the Class 0 population can reproduce the true SFR at all epochs, and this is true irrespective of the shape of the SFH. For a constant SFH, the SFR derived using the more evolved populations of protostars (Classes I, F, II, and III) reproduce the real SFR only at later epochs which correspond to epochs at which their numbers have reached a steady state. For a time-dependent burst-like SFH, all SFR estimates based on the number counts of the evolved populations fail to reproduce the true SFR. We also show how the offsets between Class I and Class II based SFRs and the true SFR plotted as a function of the number ratios of Class I and Class II versus Class III YSOs can be used in order to constrain the SFH of observed molecular clouds.

Near-infrared imaging is a powerful technique in observational astronomy, but the bright background - primarily from the Earth's atmosphere - makes the detection of faint features particularly challenging. To recover low surface brightness (LSB) structures in such data, we present NASIM (Near-infrared Automated low Surface brightness reduction In Maneage), a fully automated and reproducible data reduction pipeline optimised for VISTA/VIRCAM observations. NASIM builds on advanced techniques from the GNU Astronomy Utilities (Gnuastro) to effectively remove large-scale instrumental artefacts and detector patterns while preserving faint, diffuse emission crucial for LSB science. As a key science application, we focus on the deep K-s-band observations of the Euclid Deep Field South (KEDFS), one of the deepest VISTA/VIRCAM datasets and a high-priority field for synergy with current and future facilities, including Euclid, JWST, LSST, Roman, Spitzer, and ALMA. Situated near the South Ecliptic Pole, KEDFS offers favourable conditions for deep extragalactic observations due to minimal Galactic foreground contamination. With VIRCAM no longer operational, it now stands as a unique and irreplaceable legacy dataset for near-infrared astronomy. We release selected tiles from the KEDFS survey and highlight representative science cases - including galaxy outskirts, LSB galaxies, and intracluster light - that demonstrate NASIM's ability to recover diffuse structures. Our reduction reaches a surface brightness limit of similar to 27.7 mag arcsec(-2) (3 sigma over 100 arcsec(2)) in the K-s band, approximately 67 times deeper than 2MASS and 11 times deeper than VISTA Hemisphere Survey (VHS). A direct comparison with conventional VISTA data reduction pipelines demonstrates the advantages of NASIM in preserving diffuse emission without compromising compact source detection. All quantitative results presented in this paper are fully reproducible with Maneage (commit a02b40dd).

Nuclear star clusters (NSCs) are dense, compact stellar systems only a few parsecs across, located at galaxy centers. Their small sizes make them difficult to resolve spatially. NSCs often coexist with massive black holes, and both trace the dynamical state and evolution of their host galaxies. Dense stellar environments such as NSCs are also ideal sites for forming intermediate-mass black holes (IMBHs). To date, spatially resolved NSC properties, crucial for reconstructing dynamical and star-formation histories, have only been obtained for galaxies within 5 Mpc, using the highest-resolution instruments on the current class of very large telescopes. This severely limits spectroscopic studies, and a systematic, unbiased survey has never been accomplished. Because the vast majority of known NSCs are located in the Northern Hemisphere, only a 30-m-class telescope in the North can provide the statistical power needed to study their physical properties and measure the mass of coexisting central black holes. We propose leveraging the capabilities of a 30-m-class Northern telescope to obtain the first comprehensive, spatially resolved survey of NSCs, finally allowing us to unveil their formation pathways and their yet unknown connection with central massive black holes.

Highly inclined (edge-on) disk galaxies offer the unique perspective to constrain their intrinsic flattening, c/a, where c and a are, respectively, the vertical and long radial axes of the disk measured at suitable stellar densities. The ratio c/a is a necessary quantity in the assessment of galaxy inclinations, three-dimensional structural reconstructions, and total masses, as well as a constraint to galaxy formation models. The 3.6 mu m maps of 133 edge-on spiral galaxies from the Spitzer Survey of Stellar Structure in Galaxies (S4G) and its early-type galaxy extension are used to revisit the assessment of c/a free from dust extinction and away from the influence of a stellar bulge. We present a simple definition of c/a and explore trends with other galactic physical parameters: total stellar mass, concentration index, total H i mass, mass of the central mass concentration, circular velocity, model-dependent scales, and Hubble type. Other than a dependence on early/late Hubble types and a related trend with light concentration, no other parameters were found to correlate with the intrinsic flattening of spiral galaxies. The latter is mostly constant with < c/a > = 0.124 +/- 0.001 (stat) +/- 0.033 (intrinsic/systematic) and greater for earlier types.

Understanding how gas flows into galactic centres, fuels the active galactic nucleus (AGN), and is in turn expelled back through feedback processes is of great importance to appreciate the role AGN play in the growth and evolution of galaxies. We use Multi Unit Spectroscopic Explorer-adaptive optics (MUSE-AO) optical spectra of the inner $7 1.3\,kpc 1.3\,kpc $) of the nearby Seyfert 1 galaxy NGC\,4593 to characterise its ionised gas kinematics. We fitted single-Gaussian components to the O\ iii \,lambda 5007 and N\ ii \,lambda 6583 emission lines, and double-Gaussian components to Halpha and Hbeta to determine the main ionisation mechanism of the gas. To determine the kinematics of the ionised gas, we fit double-Gaussian components to the O\ iii \,lambda 5007 line. The high angular resolution MUSE data ($ pc $) capture structures of the circumnuclear region including the innermost spiral that feeds the nucleus. Based on the stellar kinematic maps, we confirm the presence of a rotating disc, whilst for the ionised gas, we find high-velocity dispersion values of up to $ $ that show that part of the gas is highly perturbed. The dominant ionisation mechanism of the gas is AGN photoionisation, which reaches the highest values within the innermost 4 (680\,pc) diameter of the galaxy. At larger radii, the emission line ratios correspond to values in the composite region of the Baldwin, Phillips and Terlevich (BPT) diagram. The broad-component of O\ iii \,lambda 5007 shows blue-shifted velocities on the east side of the central 2 (340\,pc), which spatially coincide with a region of high velocity-dispersion. This confirms the presence of outflowing gas. We estimate a mass outflow rate and kinetic power of M 0.048 \,M_ yr $ and $ E kin erg s $. The derived mass outflow rate is consistent with that expected from empirical relations between mass outflow rate and AGN luminosity for a low-luminosity AGN such as NGC 4593. High angular resolution integral field observations can enable multi-component analysis of the innermost regions of galaxies, allowing a detailed view of ionised gas flows.

The ionization of diffuse gas located far above the energetic midplane OB stars poses a challenge to the commonly accepted notion that radiation from OB stars is the primary ionization source for gas in galaxies. We investigated the sources of ionizing radiation, specifically leaking midplane HII regions and/or in situ hot low-mass evolved stars (HOLMES), in extraplanar diffuse ionized gas (eDIG) in a sample of eight nearby (17-52 Mpc) edge-on disk galaxies observed with the Multi Unit Spectroscopic Explorer (MUSE). We constructed a model for the photoionization of eDIG clouds and the propagation of ionizing radiation through the eDIG using subsequent runs of Cloudy photoionization code. Our model includes radiation originating both from midplane OB stars and in situ evolved stars and its dilution and processing as it propagates in the eDIG. We fit the model to the data using the vertical line ratio profiles of our sample galaxies, and find that while the ionization by in situ evolved stars is insignificant for most of the galaxies in our sample, it may be able to explain the enhanced high-ionization lines in the eDIG of the green valley galaxy ESO 544-27. Our results show that while leaking radiation from midplane HII regions is the primary ionization source for eDIG, in situ evolved stars can play a significant part in ionizing extraplanar gas in galaxies with low star forming rates.

Metallicity measurements in galaxies can provide valuable clues about galaxy evolution. One of the mechanisms postulated for metallicity redistribution in galaxies is gas flows induced by active galactic nuclei (AGNs), but the details of this process remain elusive. We report the discovery of a positive radial gradient in the gas-phase metallicity of the narrow-line region of the Seyfert 2 galaxy NGC 7130, which is not found when considering the star-forming (SF) components in the galaxy disc. To determine gas-phase metallicities for each kinematic component, we used both AGN and SF strong-line abundance relations, as well as Baldwin-Phillips-Terlevich diagnostic diagrams. These relations involve sensitive strong emission lines, namely [O III]lambda 5007, [N II]lambda 6584, H alpha, H beta, [S II]lambda 6716, and [S II]lambda 6731, observed with the adaptive-optics-assisted mode of the Multi Unit Spectroscopic Explorer at the Very Large Telescope. The presence of a positive radial metallicity gradient in only the ionised AGN component suggests that metals may be transported from central areas of a galaxy to its purlieus by AGN activity.

Context. The universality or non-universality of the initial mass function (IMF) has significant implications for determining star formation rates and star formation histories from photometric properties of stellar populations. Aims. We reexamine whether the IMF is deficient in high-mass stars (top-light) in the low-density environment of the outer disk of M 83 and constrain the shape of the IMF therein. Methods. Using archival Galaxy Evolution Explorer (GALEX) far ultraviolet (FUV) and near ultraviolet (NUV) data and new deep OmegaCAM narrowband H α imaging, we constructed a catalog of FUV-selected objects in the outer disk of M 83. We counted H α -bright clusters and clusters that are blue in FUV−NUV in the catalog, measured the maximum flux ratio F H α / f λ FUV among the clusters, and measured the total flux ratio Σ F H α /Σ f λ FUV over the catalog. We then compared these measurements to predictions from stellar population synthesis models made with a standard Salpeter IMF, truncated IMFs, and steep IMFs. We also investigated the effect of varying the assumed internal extinction on our results. Results. We are not able to reproduce our observations with models using the standard Salpeter IMF or the truncated IMFs. It is only when assuming an average internal extinction of 0.10 < A V < 0.15 in the outer disk stellar clusters that models with steep IMFs ( α > 3.1) simultaneously reproduce the observed cluster counts, the maximum observed F H α / f λ FUV , and the observed Σ F H α /Σ f λ FUV . Conclusions. Our results support a non-universal IMF that is deficient in high-mass stars in low-density environments.

According to the Λ cold dark matter (ΛCDM) cosmology, present-day galaxies with stellar massesM⋆ > 1011 M⊙should contain a sizable fraction of dark matter within their stellar body. Models indicate that in massive early-type galaxies (ETGs) withM⋆ ≈ 1.5 × 1011 M⊙, dark matter should account for ∼15% of the dynamical mass within one effective radius (1 Re) and for ∼60% within 5 Re. Most massive ETGs have been shaped through a two-phase process: the rapid growth of a compact core was followed by the accretion of an extended envelope through mergers. The exceedingly rare galaxies that have avoided the second phase, the so-called relic galaxies, are thought to be the frozen remains of the massive ETG population atz ≳ 2. The best relic galaxy candidate discovered to date is NGC 1277, in the Perseus cluster. We used deep integral fieldGeorgeandCynthia MitchelSpectrograph (GCMS) data to revisit NGC 1277 out to an unprecedented radius of 6 kpc (corresponding to 5 Re). By using Jeans anisotropic modelling, we find a negligible dark matter fraction within 5 Re(fDM(5 Re) < 0.05; two-sigma confidence level), which is in tension with the ΛCDM expectation. Since the lack of an extended envelope would reduce dynamical friction and prevent the accretion of an envelope, we propose that NGC 1277 lost its dark matter very early or that it was dark matter deficient ab initio. We discuss our discovery in the framework of recent proposals, suggesting that some relic galaxies may result from dark matter stripping as they fell in and interacted within galaxy clusters. Alternatively, NGC 1277 might have been born in a high-velocity collision of gas-rich proto-galactic fragments, where dark matter left behind a disc of dissipative baryons. We speculate that the relative velocities of ≈2000 km s−1required for the latter process to happen were possible in the progenitors of the present-day rich galaxy clusters.

Context. The hierarchical model of galaxy formation suggests that galaxies are continuously growing. However, our position inside the Milky Way prevents us from studying the disk edge. Truncations are low surface brightness features located in the disk outskirts of external galaxies. They indicate where the disk brightness abruptly drops, and their location is thought to change dynamically. In previous analyses of Milky Way-like galaxies, truncations were detected up to 3 kpc above the mid-plane, but whether they remain present beyond that height remains unclear. Aims. Our goal is to determine whether truncations can be detected above 3 kpc in height in the Milky Way-like galaxy NGC 4565 and thus establish the actual disk thickness. We also aim to study how the truncation relates to disk properties such as star formation activity or the warp. Methods. We performed a vertical study of the disk of the NGC 4565 edge in unprecedented detail. We explored the truncation radius at different heights above and below the disk mid-plane (0 < z < 8 kpc) and at different wavelengths. We used new ultra-deep optical data ( μ g,lim = 30.5 mag arcsec −2 ; 3 σ within 10 × 10 arcsec 2 boxes) in the g , r , and i broadbands, along with near-ultraviolet, far-ultraviolet, H α , and H I observations. Results. We detect the truncation up to 4 kpc in the g , r , and i ultra-deep bands, which is 1 kpc higher than in any previous study for any galaxy. The radial position of the truncation remains constant up to 3 kpc, while higher up it is located at a smaller radius. This result is independent of the wavelength but is affected by the presence of the warp. Conclusions. We propose an inside-out growth scenario for the formation of the disk of NGC 4565. Our results point towards the truncation feature being linked to a star-forming threshold and to the onset of the disk warp.

Context. In the standard cosmological model of galaxy evolution, mergers and interactions play a fundamental role in shaping galaxies. Galaxies that are currently isolated are thus interesting because they allow us to distinguish between internal and external processes that affect the galactic structure. However, current observational limits may obscure crucial information in the low-mass or low-brightness regime. Aims. We use optical imaging of a subsample of the AMIGA catalogue of isolated galaxies to explore the impact of different factors on the structure of these galaxies. In particular, we study the type of disc break as a function of the degree of isolation and the presence of interaction indicators such as tidal streams or plumes, which are only detectable in the ultra-low surface brightness regime. Methods. We present ultra-deep optical imaging in the r band of a sample of 25 low-redshift ( z < 0.035) isolated galaxies. Through careful data processing and analysis techniques, the nominal surface brightness limits achieved are comparable to those to be obtained on the ten-year LSST coadds ( μ r ,lim ≳ 29.5 mag arcsec −2 [3 σ ; 10″ × 10″]). We place special emphasis on preserving the low surface brightness features throughout the processing. Results. The extreme depth of our imaging allows us to study the interaction signatures of 20 galaxies since Galactic cirrus is a strong limiting factor in the characterisation of interactions for the remaining 5 of them. We detect previously unreported interaction features in 8 (40% ± 14%) galaxies in our sample. We identify 9 galaxies (36% ± 10%) with an exponential disc (Type I), 14 galaxies (56% ± 10%) with a down-bending (Type II) profile, and only 2 galaxies (8% ± 5%) with up-bending (Type III) profiles. Isolated galaxies have considerably more purely exponential discs and fewer up-bending surface brightness profiles than field or cluster galaxies. We find clear minor merger activity in some of the galaxies with single exponential or down-bending profiles, and both of the galaxies with up-bending profiles show signatures of a past interaction. Conclusions. We show the importance of ultra-deep optical imaging in revealing faint external features in galaxies that indicate a probable history of interaction. We confirm that up-bending profiles are likely produced by major mergers, while down-bending profiles are probably formed by a threshold in star formation. Unperturbed galaxies that slowly evolve with a low star formation rate could induce the high rate of Type I discs in isolated galaxies.

Context: The hierarchical model of galaxy formation suggests that galaxies are continuously growing. However, our position inside the Milky Way prevents us from studying the disk edge. Truncations are low surface brightness features located in the disk outskirts of external galaxies. They indicate where the disk brightness abruptly drops and their location is thought to change dynamically. In previous analyses of Milky Way-like galaxies, truncations were detected up to 3 kpc above the mid-plane but whether they remain present beyond that height remains unclear. Aims: Our goal is to determine whether truncations can be detected above 3 kpc height in the Milky Way-like galaxy NGC 4565, thus establishing the actual disk thickness. We also aim to study how the truncation relates to disk properties such as star formation activity or the warp. Methods: We perform a vertical study of the disk of NGC 4565 edge in unprecedented detail. We explore the truncation radius at different heights above/below the disk mid-plane (0<z<8 kpc) and at different wavelengths. We use new ultra-deep optical data (μ_g,lim=30.5 mag arcsec^-2; 3 σ within 10 × 10 arcsec^2 boxes) in the g, r and i broad bands, along with near- and far-ultraviolet, Hα, and Hi observations. Results: We detect the truncation up to 4 kpc in the g, r and i ultra-deep bands which is 1 kpc higher than in any previous study for any galaxy. The radial position of the truncation remains constant up to 3 kpc while higher up it is located at a smaller radius. This result is independent of the wavelength but is affected by the presence of the warp. Conclusions: We propose an inside-out growth scenario for the formation of the disk of NGC 4565. Our results point towards the truncation feature being linked to a star-forming threshold and to the onset of the disk warp.

According to the Lambda cold dark matter (Lambda CDM) cosmology, present-day galaxies with stellar masses M-star > 10(11) M-circle dot should contain a sizable fraction of dark matter within their stellar body. Models indicate that in massive early-type galaxies (ETGs) with M-star approximate to 1.5 x 10(11) M-circle dot, dark matter should account for similar to 15% of the dynamical mass within one effective radius (1 R-e) and for similar to 60% within 5 Re. Most massive ETGs have been shaped through a two-phase process: the rapid growth of a compact core was followed by the accretion of an extended envelope through mergers. The exceedingly rare galaxies that have avoided the second phase, the so-called relic galaxies, are thought to be the frozen remains of the massive ETG population at z greater than or similar to 2. The best relic galaxy candidate discovered to date is NGC1277, in the Perseus cluster. We used deep integral field George and Cynthia Mitchel Spectrograph (GCMS) data to revisit NGC1277 out to an unprecedented radius of 6 kpc (corresponding to 5 R-e). By using Jeans anisotropic modelling, we find a negligible dark matter fraction within 5 R-e (f(DM)(5 R-e) < 0.05; two-sigma confidence level), which is in tension with the Lambda CDM expectation. Since the lack of an extended envelope would reduce dynamical friction and prevent the accretion of an envelope, we propose that NGC1277 lost its dark matter very early or that it was dark matter deficient ab initio. We discuss our discovery in the framework of recent proposals, suggesting that some relic galaxies may result from dark matter stripping as they fell in and interacted within galaxy clusters. Alternatively, NGC1277 might have been born in a high-velocity collision of gas-rich proto-galactic fragments, where dark matter left behind a disc of dissipative baryons. We speculate that the relative velocities of approximate to 2000 km s(-1) required for the latter process to happen were possible in the progenitors of the present-day rich galaxy clusters.

We show that the rotation curves of 16 nearby disc galaxies in the THINGS sample and the Milky Way can be described by the NFW halo model and by the Bosma effect at approximately the same level of accuracy. The latter effect suggests that the behavior of the rotation curve at large radii is determined by the rescaled gas component and thus that dark matter and gas distributions are tightly correlated. By focusing on galaxies with exponential decay in their gas surface density, we can normalize their rotation curves to match the exponential thin disc model at large enough radii. This normalization assumes that the galaxy mass is estimated consistently within this model, assuming a thin disc structure. We show that this rescaling allows us to derive a new version of the Tully-Fisher (TF) relation, the Bosma TF relation that nicely fit the data. In the framework of this model, the connection between the Bosma Tully-Fisher (TF) relation and the baryonic TF relation can be established by considering an additional empirical relation between the baryonic mass and the total mass of the disc, as measured in the data.

In the standard cosmological model of galaxy evolution, mergers and interactions play a fundamental role in shaping galaxies. Galaxies that are currently isolated are thus interesting, allowing us to distinguish between internal and external processes affecting the galactic structure. However, current observational limits may obscure crucial information in the low-mass or low-brightness regime. We use optical imaging of a subsample of the AMIGA catalogue of isolated galaxies to explore the impact of different factors on the structure of these galaxies. We study the type of disc break as a function of the degree of isolation and the presence of interaction indicators like tidal streams or plumes only detectable in the low surface brightness regime. We present deep optical imaging of a sample of 25 isolated galaxies. Through careful data processing and analysis techniques, the surface brightness limits achieved are comparable to those to be obtained on the 10-year LSST coadds. The extreme depth of our imaging allows us to study the interaction signatures of 20 galaxies, given that the presence of Galactic cirrus is a strong limiting factor in the characterisation of interactions for the remaining 5 of them. We detect previously unreported interaction features in 8 (40%) galaxies in our sample. We identify 9 galaxies (36%) showing an exponential disc (Type I), 14 galaxies (56%) with down-bending (Type II) profile and only 2 galaxies (8%) with up-bending (Type III) profiles. Isolated galaxies have considerably more purely exponential discs and fewer up-bending surface brightness profiles than field or cluster galaxies. We suggest that major mergers produce up-bending profiles while a threshold in star formation probably forms down-bending profiles. Unperturbed galaxies, evolving slowly with a low star formation rate could cause the high rate of Type I discs in isolated galaxies observed.

Disk galaxies are typically in a stable configuration where matter moves in almost closed circular orbits. However, non-circular motions caused by distortions, warps, lopsidedness, or satellite interactions are common and leave distinct signatures on galaxy velocity maps. We develop an algorithm that uses an ordinary least square method for fitting a non-axisymmetric model to the observed two-dimensional line-of-sight velocity map of an external galaxy, which allows for anisotropic non-circular motions. The method approximates a galaxy as a flat disk, which is an appropriate assumption for spiral galaxies within the optical radius where warps are rare. In the outer parts of HI distributions, which may extend well into the warp region, we use this method in combination with a standard rotating tilted ring model to constrain the range of radii where the flat disk assumption can be conservatively considered valid. Within this range, the transversal and radial velocity profiles, averaged in rings, can be directly reconstructed from the velocity map. The novelty of the algorithm consists in using arc segments in addition to rings: in this way spatial velocity anisotropies can be measured in both components, allowing for the reconstruction of angularly resolved coarse-grained two-dimensional velocity maps. We applied this algorithm to 25 disk galaxies from the THINGS sample for which we can provide 2D maps of both velocity components.

The Vanishing & Appearing Sources during a Century of Observations (VASCO) project investigates astronomical surveys spanning a time interval of 70 years, searching for unusual and exotic transients. We present herein the VASCO Citizen Science Project, which can identify unusual candidates driven by three different approaches: hypothesis, exploratory, and machine learning, which is particularly useful for SETI searches. To address the big data challenge, VASCO combines three methods: the Virtual Observatory, user-aided machine learning, and visual inspection through citizen science. Here we demonstrate the citizen science project and its improved candidate selection process, and we give a progress report. We also present the VASCO citizen science network led by amateur astronomy associations mainly located in Algeria, Cameroon, and Nigeria. At the moment of writing, the citizen science project has carefully examined 15,593 candidate image pairs in the data (ca. 10% of the candidates), and has so far identified 798 objects classified as "vanished". The most interesting candidates will be followed up with optical and infrared imaging, together with the observations by the most potent radio telescopes.

Thin and thick disks are found in most spiral galaxies, yet their formation scenarios remain uncertain. Whether thick disks form through slow or fast, internal or environmental, processes is unclear. The physical origin of outer truncations in thin and thick disks, observed as a drop in optical and near-infrared (NIR) surface brightness profiles, is also a much debated topic. These truncations have been linked to star formation (SF) thresholds in Milky-Way type galaxies, but no such connection has been made for their low-mass counterparts or in thick disks. Our photometric analysis of the edge-on galaxy UGC 7321 offers a possible breakthrough. This well-studied diffuse, isolated, bulgeless, ultra-thin galaxy is thought to be under-evolved both dynamically and in SF. It is an ideal target to disentangle internal effects in the formation of thick disks and truncations. Our axial light profiles from deep far- and near-ultraviolet (UV; GALEX) images, tracing recent SF, and optical (DESI grz) and NIR (Spitzer 3.6 microns) images, tracing old stellar populations, enable a detailed identification of an outer truncation in all probed wavelengths in both the thin and thick disks. After deprojecting to a face-on view, a sharp truncation signature is found at a stellar density of roughly 1.5 solar masses per square parsec, in agreement with theoretical expectations of gas density SF thresholds. The redder colours beyond the truncation radius are indicative of stellar migration towards the outer regions. We thus show that thick disks and truncations can form via internal mechanisms alone, given the pristine nature of UGC 7321. We report the discovery of a truncation at and above the mid-plane of a diffuse galaxy that is linked to a SF threshold; this poses a constraint on physically-motivated disk size measurements among low-mass galaxies.