Resumen:

Dwarf barred galaxies are the perfect candidates for hosting slowly-rotating bars. They are common in dense environments and they have a shallow potential well, making them prone to be heated by interactions. They are expected to reside in massive and centrally-concentrated dark matter halos, which should slow down the bar rotation through dynamical friction. When an interaction induces bar formation and when dynamical friction is efficient, the bar should rotate slowly. Despite being predicted within the cold dark matter cosmology, measurements of bar pattern speed, using the Tremaine-Weinberg method, find that slow bars seem to be rare in the local Universe. We present a photometric and kinematic characterisation of bars hosted by two dwarf galaxies NGC 4483 and NGC 4516 members of the Virgo Cluster. We derive the bar length and strength using the Next Generation Virgo Survey deep imaging and the circular velocity, bar pattern speed, and bar rotation rate using dedicated spectroscopy from the Multi Unit Spectroscopic Explorer at the Very Large Telescope. By considering the previously studied IC 3167, we compare the bar properties of the three dwarf galaxies with those of their massive counterparts from literature. Bars in dwarf galaxies are shorter and relatively weaker, and rotate slightly slower with respect to those in massive galaxies, in agreement with theoretical studies and simulations. This could be due to a different bar formation mechanism and/or to the presence of a large dark matter fraction in the centre of dwarf galaxies. We show that it is possible to push the application of the Tremaine-Weinberg method to the galaxy low mass regime, when the targets are carefully selected and dedicated high quality data are available. However, it is necessary to increase the sample of characterised bars in dwarf galaxies to give stronger constraints on their formation and evolution.

Resumen:

In this study, we have investigated the morphological properties of the galaxy NGC 2619 and its spiral structure through image analysis and the application of the Fourier method. Our goal is to identify and characterize the distribution of spiral patterns present in the disk of this galaxy, as it is known for its multiple spiral structure. By processing the images, we have identified the presence of multiple spiral arms in NGC 2619, each with distinctive features such as internal symmetries and fragmentations. Additionally, we have detected a nuclear bar and a central ring in the galactic structure. These evidence are highly relevant as they provide valuable information about the structure and dynamics of the galaxy, as well as the evolution and formation of spiral components in galaxies with multiple arms. Our work highlights the importance of the Fourier method as a tool for analyzing spiral galaxies and its potential to uncover hidden features in their structure. These results contribute to the general knowledge of galaxy formation and evolution, enriching our understanding of the cosmos.

Resumen:

In this study, we investigated the presence of bifurcations in the galaxy NGC 2756, a phenomenon in which a spiral arm separates from the main structure and divides into two or more additional arms. Our goal is to understand the origin of these bifurcations and their relationship with internal processes associated with the dynamics of the disk and star formation. To achieve this, we employed the two-dimensional Fourier transform algorithm, which allowed us to identify with precision and efficiency the bifurcation present in this Seyfert-type spiral galaxy. Additionally, we carefully analyzed images taken in the g and i bands to identify morphological properties. This preliminary study constitutes a significant advancement in the understanding of the complex characteristics of NGC 2756 and its spiral structure, as well as in the study of galactic bifurcations in general.

Resumen:

Dwarf ellipticals (dEs) galaxies are at the low luminosity end of the elliptical sequence, having smaller sizes and lower luminosities than normal elliptical galaxies. Below the masses of dwarf ellipticals we find the Ultra compact dwarf galaxies (UCDs). UCDs are compact objects with a lower mass limit of $2\times 10^{6}$ solar masses. Their luminosities are above the brightest known Star Clusters (SCs) and their effective radii are between 10 and 100 pc. We need to understand if dE galaxies can lose their stellar component by the tidal stripping scenario leaving their dense central cores on the type of orbits on which UCDs are found. I.e, a Nucleated dE galaxy with a dense core gets partly destroyed by the gravitational forces of one or many bigger galaxies. Only the compact central part survives as UCD. Is this scenario enough to explain all UCDs? Are the current orbits of UCDs consistent with the orbits which allow sufficient tidal destruction to have only the former core surviving?

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In this study, we present the implementation of a Nuclear Star Cluster (NSC) model within Galacticus, a semi-analytic code designed for simulating galaxy formation and evolution. Our focus is on understanding the role of NSCs during the formation of Supermassive Black Holes (SMBHs). We assume here that the dominant channel for NSC formation is the transfer of gas from the galactic bulge into a dedicated NSC gas reservoir. This gas transfer process occurs as a result of the expulsion of gas from young stars, leading to the formation of NSCs through in-situ star formation at the galactic center. Moreover, we introduce a collapse model for NSCs, where they ultimately collapse into a Black Hole (BH) seed upon reaching a critical mass. This critical mass is derived based on the relaxation time being longer than the collision time within the NSC. By exploring this collapse scenario, we aim to shed light on its potential implications for the population of SMBHs, as well as the relationships between NSCs and galaxies, SMBHs and galaxies, and NSCs and SMBHs. Our investigation delves into how this collapse scenario can influence the overall SMBH population, as well as the intricate connections between NSCs, galaxies, and SMBHs. This research helps to gain insights into the formation and evolution of NSCs and their impact on the galactic and black hole environments.

Resumen:

Defining the main features of the arms of a spiral galaxy remains an unsolved problem for modern astronomy. In previous studies, some authors have used different tracers to identify and measure the characteristics of the arms of different spiral galaxies, such as star clusters, Maseres, H$_{\alpha}$, among others. It was only until recently that individual stars were used as a tracer of the spiral structure in the Milky Way. One of the characteristics studied in the spiral arms is their width, whose norm is estimated from 1$\sigma$ around the means of the distribution of the data of the spiral structure given by the tracer. In this work, we used the individual stars of the galaxies M83, M101 and M33 (NGC5236, NGC5457 and NGC598) as a tracer of spiral arms and we measured their width using two methods: the traditional method of 1$\sigma$ of the distribution, and from the study of the stellar density of the medium ; this last method was not use before to measured the arms width of a external galaxies). In this work we obtained the following results: it was found that the field of individual stars can trace the spiral arms of the galaxies, we found a connection between the width of the arms and the galactocentric radius, and it was found that the growth slope of the width of the arms could be correlated with the morphological type of the spiral galaxies (this last result was published only for the galaxy M83 in in MNRAS doi:10.1093/mnrasl/slac047). From the information of the arms of the galaxies we are going to study the stellar populations in the arms looking for evidences to the density wave theory.

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For decades, various models have been proposed to explain the mechanism of formation of spiral arms in disk galaxies (density waves, swing amplification, tidal perturbations, etc.), however, to this day it is not fully understood under which conditions each of these mechanisms operates. In this work we study the correlation between the morphological features of the spiral arms in disc galaxies and the extragalactic environment in which they reside with the aim to analyze how this relationship can be interpreted in terms of the formation models. To achieve this goal, a sample of 2323 images of spiral galaxy was selected from the NASA-Sloan-Atlas catalog. Using GALFIT (Peng et al. 2010), the surface brightness distribution of each object is studied in order to highlight the spiral structures in each image and P2FFT (Davis et al. 2012, Hewitt \\& Treuthardt 2020) is used to determine the geometric properties of the spiral arms. To quantify the characteristics of the extragalactic environment, we use the mass density field reconstruction methods presented in Muñoz-Cuartas et al. (2011). Then, the environment of each galaxy is identified and classified following different criteria: zones of high and low density, galaxies with close neighbors in a distance range, galaxies with neighboring pairs, galaxies in filaments, etc. When the properties of the spiral arms are correlated with the environment in which the galaxy is located, it is found that there is no strong correlation between the intensity of the spiral arms and the density of the environment. On the other hand, a weak bias is found indicating that galaxies with symmetrical spiral arms have neighboring pairs, suggesting an interaction as the origin for the formation of the arms. The results of this work suggest that different arm formation mechanisms may be activated under different environmental conditions of the host galaxy.

Resumen:

Spiral galaxies show qualities in their morphology, and their evolutionary processes are of great interest to the astronomical community. The conditions that allow the formation of discoidal galaxies with spiral structure remain unclear. Additionally, each spiral galaxy is unique in the universe, but they can be classified based on distinct morphological characteristics, including grand-design galaxies and galaxies with multiple arms, While grand-design galaxies has its own theories of evolution and origin, the formation theories specifically addressing the spiral structure in multiple-armed galaxies have not been extensively explored, and the existing theories for grand-design galaxies are typically applied in such cases. To expand the studies on spiral galaxies with multiple arms, this work aims to identify morphological and dynamis characteristics in this type of galaxy. To achieve this, we employ the Fourier transform method and propose a technique to quantify the importance of modes in the radial distribution of the disk and detect the presence of symmetric or fragmented spiral structures. Using radial density functions, we generate synthetic images of galaxies to confirm the effectiveness of the method for analyzing spiral structures in discoidal galaxies. Through this technique, it becomes evident that it is not possible to consider a galaxy as having multiple arms or grand design throughout its entire disk. The multiple-arm structures detected in this study are found only in certain regions of the radius. For a set of galaxies, it is observed that multiple-arm structures are located in the inner regions of the disk, near the nucleus, while in another group, the spiral structure is present in the intermediate or outer regions of the disk.

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We study a sample of disturbed spiral galaxies in the nearby, relaxed cluster A496 (z = 0.033). This work is based on multifrequency data including HI (21cm), optical, NIR and FUV imaging. We analyze the orbital histories of the brightest spirals, both detected and non-detected in HI, based on the projected phase-space (PPS) distribution, separating infalling from virialized objects, and detecting possible backsplash galaxies too. The study of the orbits plus the disruptions seen in HI and in other bands, help to better understand the role played by different physical mechanisms accounting for the strong transformation of galaxies observed in this cluster.

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Interacting galaxies offer a fascinating laboratory to study the gravitational forces at play in systems governed by potentials. These interactions can lead to morphological changes in the structures of the involved galaxies. In the specific case of spiral galaxies, the interaction disturbs the galactic potentials, resulting in morphological alterations in the spiral arms. In this study, we analyze images of a pair of interacting spiral galaxies, NGC 2207-IC 2163, obtained from the OSUBSGS catalog, using the Fourier Transform. This technique allows us to identify significant morphological parameters, such as the dominant mode of the galaxy, the mass distribution in the disk, the pitch angle, among other relevant physical parameters. Our goal is to identify morphological changes that provide a clearer insight into the interaction process between this pair of galaxies. By gaining a better understanding of these interactions, we can enrich our comprehension of the gravitational phenomena shaping galactic structures and shed light on the evolution of interacting galaxies.

Resumen:

Under the Lambda CDM paradigm, Milky Way sized haloes were formed via the merger of smaller Dark Matter (DM) Halos. Some of these haloes have survived until today, where we see them as dwarf spheroidal galaxies. As the gas inside the DM halo starts to collapse, conservation of angular momentum will produce a rotationally supported structure, whose orbital speed will depend on the mass distribution of the halo. Under the dissolving cluster scenario, dwarf galaxies form their field stars via the dissolution of star clusters inside the DM halo, modifying the velocity distribution of the rotating component. We aim to determine if there is a region in halo parameter space where the internal dispersion of the dissolving clusters is able to erase the rotation signature of the initial distribution of clusters. To achieve this, we use a DM halo with a Navarro-Frenk-White mass density, and a disk of clusters moving with circular velocity. Our simulations show that, for a completely rotationally supported stellar component, the DM halos require a mass under 1e7 solar masses to be able to hide the original rotation signature.

Resumen:

Galaxy groups play an important role in galactic evolution, where galaxies may strongly interact with one another and with the intra-group medium. These groups may later fall into clusters, participating in the development and growth of the large-scale structure. In this study, we examine in detail the group dominated by a pair of elliptical galaxies, NGC 5098, which exhibits a sizable substructure to the south. Using deep $r$ and $g$ imaging from MegaCam/CFHT, we modeled the stellar distribution of the main galaxies and detected a significant component of diffuse intragroup light. By analyzing the velocity distribution of galaxy members, we propose a dynamical scenario for the evolution of this group, taking into account the sloshing phenomenon detected in the X-ray surface brightness observations made with the Chandra space telescope.

Resumen:

Spiral galaxies form a significant portion of Local Universe galaxies, hosting predominant star formation within their spiral arms. To comprehend arm genesis, identifying key parameters like pitch angle (winding degree) and arm width is crucial. Yet, arm width remains less explored. Our research focuses on unraveling spiral arm width, enhancing insights into galaxy structure. Our research utilizes CALIFA survey data containing approximately 1000 elliptical and spiral galaxies. Employing the Integral Field Unit (IFU) technique, the survey offers comprehensive spatial insight through analysis of spectroscopic elements. Pertinent to CALIFA galaxies are data on both gas and stellar components. Our selection process focuses on galaxies meeting specific criteria: inclination angles $\leq 40^o$, absence of interactions, and distinct spiral formations. Our investigation will employ multiple indicators to identify arms, encompassing the widely referenced $H_\alpha$ emission, derived from ionized gas in star-forming zones. Other indicators consist of emissions from young stellar constituents (O and B stars) in the blue spectrum and from aged stellar elements in the red and infrared spectrum, revealing recognizable spiral structures. After tracing the arms using some of the aforementioned tracers, we measured their width by making cuts across them with an approximate width of $3.5$ kpc, which is the average width of arms in grand design galaxies according to Savchenko et al. (2020). Subsequently, arm width was determined using two methods: (1) conventionally via the $1\sigma$ distribution width; and (2) by pinpointing the flux equilibrium where arm and non-arm regions meet. We have selected five spiral galaxies for investigation: NGC234, NGC309, NGC776, NGC7653, and UGC12224. For each galaxy, we traced the arms using the stellar population (as shown in the pseudo-V-mag map, see Figure) and gas ($H_\alpha$ emission). Our observations have revealed distinctions that present challenges in terms of explanation within the context of current models.