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We present results of the detailed dust energy balance study for the seven large edge-on galaxies in the HEROES sample using 3D radiative transfer (RT) modelling. Based on available optical and near-infrared observations of the HEROES galaxies, we derive the 3D distribution of stars and dust in these galaxies. For the sake of uniformity, we apply the same technique to retrieve galaxy properties for the entire sample: we use a stellar model consisting of a S\'ersic bulge and three double-exponential discs (a superthin disc for a young stellar population and thin and thick discs for old populations). For the dust component, we adopt a double-exponential disc with the new THEMIS dust-grain model. We fit oligochromatic radiative transfer (RT) models to the optical and near-infrared images with the fitting algorithm FitSKIRT and do panchromatic simulations with the SKIRT code at wavelengths ranging from ultraviolet to submillimeter. We confirm the previously stated dust energy balance problem in galaxies: for the HEROES galaxies, the dust emission derived from our RT calculations underestimates the real observations by a factor 1.5-4 for all galaxies except NGC 973 and NGC 5907 (apparently, the latter galaxy has a more complex geometry than we used). The comparison between our RT simulations and the observations at mid-infrared-submillimeter wavelengths shows that most of our galaxies exhibit complex dust morphologies (possible spiral arms, star-forming regions, more extended dust structure in the radial and vertical directions). We suggest that, in agreement with the results from Saftly et al. (2015), the large- and small-scale structure is the most probable explanation for the dust energy balance problem., Comment: 53 pages, 31 figures, Accepted for publication in Astronomy & Astrophysics

A simple algorithm is employed to deproject the two-dimensional images of a pilot sample of 12 high-quality images of edge-on disc galaxies and to study their intrinsic three-dimensional (3D) stellar distribution. We examine the radial profiles of the stars as a function of height above the plane and report a general trend within our sample of an increasing radial scalelength with height outside of the dust lane. This could be explained by the widespread presence of a thick disc component in these galaxies. In addition, the 3D view allows the study of the vertical distribution of the outer disc, beyond the break region, where we detect a significant increase in scalelength with vertical distance from the major axis for the truncated discs. This could be regarded as a weakening of the ‘truncation’ with increasing distance from the plane. Furthermore, we conclude that the recently revised classification of the radial surface brightness profiles found for face-on galaxies is indeed independent of geometry. In particular, we find at least one example of each of the three main profile classes as defined in complete samples of intermediate to face-on galaxies: not-truncated, truncated and antitruncated. The position and surface brightness that mark the break location in the radial light distribution are found to be consistent with those of face-on galaxies.

We use linear perturbation theory to investigate how a groove in the phase space of a disc galaxy changes the stellar disc's stability properties. Such a groove is a narrow trough around a fixed angular momentum from which most stars have been removed, rendering part of the disc unresponsive to spiral waves. We find that a groove can dramatically alter a disc's eigenmode spectrum by giving rise to a set of vigorously growing eigenmodes. These eigenmodes are particular to the grooved disc and are absent from the original ungrooved disc's mode spectrum. We discuss the properties and possible origin of the different families of new modes. By the very nature of our technique, we prove that a narrow phase-space groove can be a source of rapidly growing spiral patterns that are true eigenmodes of the grooved disc and that no non-linear processes need to be invoked to explain their presence in N-body simulations of disc galaxies. Our results lend support to the idea that spiral structure can be a recurrent phenomenon, in which one generation of spiral modes alters a disc galaxy's phase space in such a way that a following generation of modes is destabilized., 18 pages, 17 figures, accepted for publication in MNRAS

[EN]We analyse N-body galaxy merger experiments involving disc galaxies. Mergers of disc–bulge–halo models are compared to those of bulgeless, disc–halo models to quantify the effects of the central bulge on merger dynamics and the structure of the remnant. Our models explore galaxy mass ratios 1:1 through 3:1, and use higher bulge mass fractions than previous studies. A full comparison of the structural and dynamical properties with our observations is carried out. The presence of central bulges results in longer tidal tails, oblate final intrinsic shapes, surface brightness profiles with a higher Sérsic index, steeper rotation curves and oblate-rotator internal dynamics. Mergers of bulgeless galaxies do not generate long-lasting tidal tails, and their strong triaxiality seems inconsistent with observations; these remnants show shells, which we do not find in models including central bulges. Giant ellipticals with boxy isophotes and anisotropic dynamics cannot be produced by the mergers modelled here; they could be the result of mergers between lower luminosity ellipticals, themselves plausibly formed in disc-disc mergers.

Asymmetries in the distribution of light and neutral hydrogen are often observed in spiral galaxies, Here, attention is drawn to the presence of large-scale asymmetries in their kinematics. Two examples of kinematically lopsided galaxies are presented and discussed. The shape of the rotation curve - rising more steeply on one side of the galaxy than on the other - is the signature of the kinematic lopsidedness. It is shown that kinematic lopsidedness may be related to lopsidedness in the potential, and that even a mild perturbation in the latter can produce significant kinematic effects. Probably at least half of all spiral galaxies are lopsided.

We have obtained high signal-to-noise spectra along the major axes of 28 S0 galaxies in order to search for the presence of disc stars on retrograde orbits. Full line-of-sight velocity distributions are extracted from the data, and the velocity distributions are modelled as arising from the superposition of populations of stars on prograde and retrograde orbits. We find no new cases in which a significant fraction of disc stars lie on retrograde orbits; an identical analysis of NGC 4550 does reveal the previously known counter-rotating stellar disc in this system. Upper limits determined for each object indicate that no more than similar to 5 per cent of the observed disc star light could arise from counter-rotating stellar components. These results suggest that previously discovered disc galaxies with counter-rotating stars are exceptional, and that (at 95 per cent confidence) less than 10 per cent of S0 galaxies contain significant counter-rotating populations. The most likely value for the fraction of such S0 galaxies lies closer to 1 per cent. This result contrasts with the prevalence of counter-rotating gas in these systems; combining our new observations with existing data, we find that 24+/-8 per cent (1 sigma error) of the gas discs in S0 galaxies counter-rotate relative to their stellar components.

I review observations of truncations of stellar disks and models for their origin, compare observations of truncations in moderately inclined galaxies to those in edge-on systems and discuss the relation between truncations and H I-warps and their systematics and origin. Truncations are a common feature in edge-on stellar disks, but the relation of truncations in face-on to those in edge-on galaxies needs further clarification. The origin of truncations is most likely related to a maximum in the specific angular momentum in the material that formed the stellar disks, but this model does probably require some redistribution of angular momentum. H I-warps start just beyond the truncation radius and disks and warps appear distinct components. This suggests that inner disks form initially and settle as rigid, very flat structures, while H I-warps result from later infall of gas with a different orientation of the angular momentum.

I review observations of truncations of stellar disks and models for their origin, compare observations of truncations in moderately inclined galaxies to those in edge-on systems and discuss the relation between truncations and H I-warps and their systematics and origin. Truncations are a common feature in edge-on stellar disks, but the relation of truncations in face-on to those in edge-on galaxies needs further clarification. The origin of truncations is most likely related to a maximum in the specific angular momentum in the material that formed the stellar disks, but this model does probably require some redistribution of angular momentum. H I-warps start just beyond the truncation radius and disks and warps appear distinct components. This suggests that inner disks form initially and settle as rigid, very flat structures, while H I-warps result from later infall of gas with a different orientation of the angular momentum.

Using imaging data from the SDSS survey, we present the g' and r' radial stellar light distribution of a complete sample of ~90 face-on to intermediate inclined, nearby, late-type (Sb-Sdm) spiral galaxies. The surface brightness profiles are reliable (1sigma uncertainty less than 0.2 mag) down to mu=~27magsqarcsec. Only ~10% of all galaxies have a normal/standard purely exponential disk down to our noise limit. The surface brightness distribution of the rest of the galaxies is better described as a broken exponential. About 60% of the galaxies have a break in the exponential profile between ~1.5-4.5 times the scalelength followed by a downbending, steeper outer region. Another ~30% shows also a clear break between ~4.0-6.0 times the scalelength but followed by an upbending, shallower outer region. A few galaxies have even a more complex surface brightness distribution. The shape of the profiles correlates with Hubble type. Downbending breaks are more frequent in later Hubble types while the fraction of upbending breaks rises towards earlier types. No clear relation is found between the environment, as characterised by the number of neighbours, and the shape of the profiles of the galaxies., LaTeX, 69 pages, 213 (very low resolution) figures, A&A accepted. Second version to match the accepted one including all referee's comments. Version with full resolution figures (highly recommended, but with 7.6MB) available at http://www.astro.rug.nl/~pohlen/pohlenSDSS.pdf

We study the HI Rotation Curve of the spiral galaxy NGC 3198 in terms of mass decomposition. We model the Rotation Curve in the framework of different models for the Dark Matter distribution: the Burkert profile and NFW profile. We show that Universal Rotation Curve (Burkert halo+stellar disk+gas disk) fits data accurately. Instead, the NFW (NFW halo+stellar disk+gas disk) model gives non-physical values of NFW halo parameters.

Lopsidedness is a common feature in galaxies, both in the distribution of light and in the kinematics. We investigate the kinematics of a model for lopsided galaxies that consists of a disc lying off-centre in a dark halo, and circling around the halo centre. We search for families of stable, closed, non-crossing orbits, and assume that gas in our galaxies moves on these orbits. Several of our models show strong lopsided gas kinematics, especially the ones in which the disc spins around its axis in a retrograde sense compared to its motion around the halo centre. We are able to reproduce the HI velocity map of the kinematically lopsided galaxy NGC 4395. The lopsidedness in our models is most pronounced in the models where the halo provides a relatively large fraction of the total mass at small radii. This may explain why the gas shows lopsidedness more frequently in late-type galaxies, which are dominated by dark matter. Surfaces of section show large regions of irregular orbits in the models where the halo density is low. This may indicate that these models are unstable., 19 pages, 12 figures. Accepted for publication in the Monthly Notices of the Royal Astronomical Society. For a version with high resolution figures, see http://www.astro.rug.nl/~edo/lopgal.ps

Morphological asymmetries between the approaching and receding sides in both the stellar and neutral hydrogen distribution are often observed in spiral galaxies. Here, attention is drawn to the presence of large-scale asymmetries in the kinematics of the neutral hydrogen gas. An example of such a kinematically lopsided galaxy is presented and discussed. The shape of the rotation curve - rising more steeply on one side of the galaxy than on the other - is the signature of the kinematic lopsidedness. It is shown that kinematic lopsidedness may be related to lopsidedness in the potential, and that even a mild perturbation in the latter can produce significant kinematical effects. Probably at least half of all spiral galaxies are lopsided.

Morphological asymmetries between the approaching and receding sides in both the stellar and neutral hydrogen distribution are often observed in spiral galaxies. Here, attention is drawn to the presence of large-scale asymmetries in the kinematics of the neutral hydrogen gas. An example of such a kinematically lopsided galaxy is presented and discussed. The shape of the rotation curve - rising more steeply on one side of the galaxy than on the other - is the signature of the kinematic lopsidedness. It is shown that kinematic lopsidedness may be related to lopsidedness in the potential, and that even a mild perturbation in the latter can produce significant kinematical effects. Probably at least half of all spiral galaxies are lopsided.

Morphological asymmetries between the approaching and receding sides in both the stellar and neutral hydrogen distribution are often observed in spiral galaxies. Here, attention is drawn to the presence of large-scale asymmetries in the kinematics of the neutral hydrogen gas. An example of such a kinematically lopsided galaxy is presented and discussed. The shape of the rotation curve - rising more steeply on one side of the galaxy than on the other - is the signature of the kinematic lopsidedness. It is shown that kinematic lopsidedness may be related to lopsidedness in the potential, and that even a mild perturbation in the latter can produce significant kinematical effects. Probably at least half of all spiral galaxies are lopsided.

We have obtained high signal-to-noise spectra along the major axes of 28 S0 galaxies in order to search for the presence of disc stars on retrograde orbits. Full line-of-sight velocity distributions are extracted from the data, and the velocity distributions are modelled as arising from the superposition of populations of stars on prograde and retrograde orbits. We find no new cases in which a significant fraction of disc stars lie on retrograde orbits; an identical analysis of NGC 4550 does reveal the previously known counter-rotating stellar disc in this system. Upper limits determined for each object indicate that no more than similar to 5 per cent of the observed disc star light could arise from counter-rotating stellar components. These results suggest that previously discovered disc galaxies with counter-rotating stars are exceptional, and that (at 95 per cent confidence) less than 10 per cent of S0 galaxies contain significant counter-rotating populations. The most likely value for the fraction of such S0 galaxies lies closer to 1 per cent. This result contrasts with the prevalence of counter-rotating gas in these systems; combining our new observations with existing data, we find that 24+/-8 per cent (1 sigma error) of the gas discs in S0 galaxies counter-rotate relative to their stellar components.