Search

We present KRATOS, a comprehensive suite of 28 open access pure N-body simulations of isolated and interacting LMC-like galaxies, to study the formation of substructures in their disc after the interaction with an SMC-mass galaxy. The primary objective of this paper is to provide theoretical models that help interpreting the formation of general structures of an LMC-like galaxy under various tidal interaction scenarios. This is the first paper of a series that will be dedicated to the analysis of this complex interaction. Simulations are grouped in 11 sets of at most three configurations each containing: (1) a control model of an isolated LMC-like galaxy; (2) a model that contains the interaction with an SMC-mass galaxy, and; (3) the most realistic configuration where both an SMC-mass and MW-mass galaxies may interact with the LMC-like galaxy. In each simulation, we analyse the orbital history between the three galaxies and examine the morphological and kinematic features of the LMC-like disc galaxy throughout the interaction. This includes investigating the disc scale height and velocity maps. When a bar develops, our analysis involves characterising its strength, length, off-centeredness and pattern speed. The diverse outcomes found in the KRATOS simulations, including the presence of bars, warped discs, or various spiral arm shapes (along with the high spatial, temporal, and mass resolution used), demonstrate their capability to explore a range of LMC-like galaxy morphologies. Those directly correspond to distinct disc kinematic maps, making them well-suited for a first-order interpretation of the LMC's kinematic maps. From the simulations we note that tidal interactions can: boost the disc scale height; both destroy and create bars, and; naturally explain the off-center stellar bars. The bar length and pattern speed of long-lived bars are not appreciably altered by the interaction., Comment: Visit https://www.oscarjimenezarranz.com/visualizations for additional figures and animations of the KRATOS suite

Context: The Large Magellanic Cloud (LMC) internal kinematics have been studied in unprecedented depth thanks to the excellent quality of the Gaia mission data, revealing the disc's non-axisymmetric structure. Aims: We want to constrain the LMC bar pattern speed using the astrometric and spectroscopic data from the Gaia mission. Methods: We apply three methods to evaluate the bar pattern speed: it is measured through the Tremaine-Weinberg (TW) method, the Dehnen method and a bisymmetric velocity (BV) model. The methods provide additional information on the bar properties such as the corotation radius and the bar length and strength. The validity of the methods is tested with numerical simulations. Results: A wide range of pattern speeds are inferred by the TW method, owing to a strong dependency on the orientation of the galaxy frame and the viewing angle of the bar perturbation. The simulated bar pattern speeds (corotation radii, respectively) are well recovered by the Dehnen method (BV model). Applied to the LMC data, the Dehnen method finds a pattern speed Omega_p = -1.0 +/- 0.5 km s-1 kpc-1, thus corresponding to a bar which barely rotates, slightly counter-rotating with respect to the LMC disc. The BV method finds a LMC bar corotation radius of Rc = 4.20 +/- 0.25 kpc, corresponding to a pattern speed Omega_p = 18.5^{+1.2}_{-1.1} km s-1 kpc-1. Conclusions: It is not possible to decide which global value best represents an LMC bar pattern speed with the TW method, due to the strong variation with the orientation of the reference frame. The non-rotating bar from the Dehnen method would be at odds with the structure and kinematics of the LMC disc. The BV method result is consistent with previous estimates and gives a bar corotation-to-length ratio of 1.8 +/- 0.1, which makes the LMC hosting a slow bar., Comment: 20 pages, 16 figures

Only recently, complex models that include the global dynamics from dwarf satellite galaxies, dark matter halo structure, gas infalls, and stellar disk in a cosmological context became available to study the dynamics of disk galaxies such as the Milky Way (MW). We use a MW model from a high-resolution hydrodynamical cosmological simulation named GARROTXA to establish the relationship between the vertical disturbances seen in its galactic disk and multiple perturbations, from the dark matter halo, satellites and gas. We calculate the bending modes in the galactic disk in the last 6 Gyr of evolution. To quantify the impact of dark matter and gas we compute the vertical acceleration exerted by these components onto the disk and compare them with the bending behavior with Fourier analysis. We find complex bending patterns at different radii and times, such as an inner retrograde mode with high frequency, as well as an outer slower retrograde mode excited at different times. The amplitudes of these bending modes are highest during the early stages of the thin disk formation and reach up to 8.5 km s-1 in the late disk evolution. We find that the infall of satellite galaxies leads to a tilt of the disk, and produces anisotropic gas accretion with subsequent star formation events, and supernovae, creating significant vertical accelerations onto the disk plane. The misalignment between the disk and the inner stellar/dark matter triaxial structure, formed during the ancient assembly of the galaxy, creates a strong vertical acceleration on the stars. We conclude that several agents trigger the bending of the stellar disk and its phase spirals in this simulation, including satellite galaxies, dark sub-halos, misaligned gaseous structures, and the inner dark matter profile, which coexist and influence each other, making it challenging to establish direct causality.

Galaxies are expected to accrete pristine gas from their surroundings to sustain their star formation over cosmic timescales. Its lower abundance affects the metallicity of the ISM in which stars are born, leaving chemical imprints in the stellar populations. We measure the amount of pristine gas that galaxies accrete during their lifetime, using information on the ages and abundances of their stellar populations and a chemical evolution model. We also aim to determine the efficiency of star formation over time. We derived star formation histories and metallicity histories for a sample of 8523 galaxies from the MaNGA survey. We use the former to predict the evolution of the metallicity in a closed-box scenario, and estimate for each epoch the gas accretion rate required to match these predictions with the measured stellar metallicity. Using only chemical parameters, we find that the history of gas accretion depends on the mass of galaxies. More massive galaxies accrete more gas and at higher redshifts than less massive galaxies, which accrete their gas over longer periods. We also find that galaxies with a higher star formation rate at z = 0 have a more persistent accretion history for a given mass. The star formation efficiency shows similar correlations: early-type galaxies and higher-mass galaxies had a higher efficiency in the past, and it declined such that they are less efficient in the present. Our analysis of individual galaxies shows that compactness affects the peak star formation efficiency that galaxies reach, and that the slope of the efficiency history of galaxies with current star formation is flat. Our results support the hypothesis that a steady and substantial supply of pristine gas is required for persistent star formation in galaxies. Once they lose access to this gas supply, star formation comes to a halt., Comment: 17 pages, 11 figures. Accepted at A&A

The nature of the few known solar-mass stars simultaneously containing debris disks and planets remains an open question. A number of works have shown that this property appears to be independent of planetary masses as well as of stellar age, but possible correlations with stellar kinematics and metallicity have not been investigated. In this paper, we show that the majority of known stars containing both debris disks and planets belong to the metal-enriched Galactic thin disk. The few exceptions are stars that seem to be born in the star formation peak occurring in times of thick disk formation (i.e., HD 10700, HD 20794, and HD 40307), that is, between 11 and 8 Gyr. The mass of the dusty disk of these three old stars measured at 70 $\mu$m is very small - in fact, it is lower than that of the Kuiper belt of our Solar system by several orders of magnitude. These results are not surprising, as they remain within the values expected for the stellar disk evolution of such primitive stars. In parallel, we found another six thick-disk stars containing only debris disks or planets. These results enable us to establish a correlation between stellar metallicity and the mass of the dust disk modulated by the different formation epochs of the thick and thin Galactic disks., Comment: 13 pages, 5 figures

Context: The high quality of the Gaia mission data is allowing to study the internal kinematics of the Large Magellanic Cloud (LMC) in unprecedented detail, providing insights on the non-axisymmetric structure of its disc. Aims: To define and validate an improved selection strategy to distinguish the LMC stars from the Milky Way foreground. To check the possible biases that assumed parameters or sample contamination from the Milky Way can introduce in the analysis of the internal kinematics of the LMC using Gaia data. Methods: Our selection is based on a supervised Neural Network classifier using as much as of the Gaia DR3 data as possible. We select three samples of candidate LMC stars with different degrees of completeness and purity; we validate them using different test samples and we compare them with the Gaia Collaboration paper sample. We analyse the resulting velocity profiles and maps, and we check how these results change when using also the line-of-sight velocities, available for a subset of stars. Results: The contamination in the samples from Milky Way stars affects basically the results for the outskirts of the LMC, and the absence of line-of-sight velocities does not bias the results for the kinematics in the inner disc. For the first time, we perform a kinematic analysis of the LMC using samples with the full three dimensional velocity information from Gaia DR3. Conclusions: The dynamics in the inner disc is mainly bar dominated; the kinematics on the spiral arm over-density seem to be dominated by an inward motion and a rotation faster than that of the disc in the piece of the arm attached to the bar; contamination of MW stars seem to dominate the outer parts of the disc and mainly affects old evolutionary phases; uncertainties in the assumed disc morphological parameters and line-of-sight velocity of the LMC can in some cases have significant effects. [ABRIDGED]

A variety of new physical processes have proven to play an important role in orbital decay of a satellite galaxy embedded inside a dark matter halo but this is not fully understood. Our goal is to assess if the orbital history of a satellite remains unchanged during a concurrent sinking. For this purpose we analyze the impact that the internal structure of the satellites and their spatial distribution inside the host halo may have on the concurrent sinking process due to both mass loss and the combined effect of self-friction, which have not been studied before for concurrent sinking. We set up a set of N-body simulations that include multiple satellites, sinking simultaneously in a host halo and we compare them with models including a single satellite. The main result of our work is that the satellite's accretion history differs from the classical isolated view when we consider the collective effects. The accretion history of each satellite strongly depends on the initial configuration, the number of satellites in the halo at the time of infall and the internal properties of each satellite. We observe that compact satellites in a flat configuration fall slower than extended satellites that have lost mass, showing a non-reported behavior of self-friction. We find that such effects are maximized when satellites are located in a flat configuration. We show that in a flat configuration similar to the Vast Polar Structure, deviations in the apocenters can be of about 30% with respect to the isolated case, and up to 50% on the eccentricities. We conclude that ignoring the collective effects produced by the concurrent sinking of satellite galaxies may lead to large errors in the determination of the merger progenitors properties, making it considerably more challenging to trace back the accretion event. Timing constrains on host density profile may be modified by the effects discussed here., Comment: A&A, Forthcoming article Received: 29 March 2022 / Accepted: 26 September 2022 6 pages, 6 figures

We investigate two topics regarding solar mass FGK-type stars, the lithium rotation connection (LRC) and the existence of the "lithium desert". We determine the minimum critical rotation velocity ($v \sin i$) related with the LRC separating slow from rapid stellar rotators, as being 5 km s$^{-1}$. This value also split different stellar properties. For the first time we explore the behaviour of the LRC for some stellar associations with ages between 45 Myr and 120 Myr. This allows us to study the LRC age dependence at the beginning of the general spin down stage for low mass stars, which starts at $\sim$ 30-40 Myr. We find that each stellar group presents a characteristic minimum lithium (Li) depletion connected to a specific large rotation velocity and that this minimum changes with age. For instance, this minimum changes from $\sim$ 50 km s$^{-1}$ to less than 20 km s$^{-1}$ in 200 Myr. Regarding the lithium desert, it was described as a limited region in the A(Li)-$T_{\rm eff}$ map containing no stars. Using $T_{\rm eff}$ from {\em Gaia} DR2 we detect 30 stars inside and/or near the same box defined originally as the Li desert. Due to their intrinsic $T_{\rm eff}$ errors some of these stars may be inside or outside the box, implying a large probability that the box contains several stars. Considering this last fact the "lithium desert" appears to be more a statistical distribution fluctuation than a real problem., Comment: Accepted for publication in Astronomy & Astrophysics All data is available in electronic format at the CDS

We use Gaia DR2 magnitudes, colours and parallaxes for stars with G<12 to explore a 15-dimensional space that includes simultaneously the initial mass function (IMF) and a non-parametric star formation history (SFH) for the Galactic disc. This inference is performed by combining the Besancon Galaxy Model fast approximate simulations (BGM FASt) and an approximate Bayesian computation algorithm. We find in Gaia DR2 data an imprint of a star formation burst 2-3 Gyr ago, in the Galactic thin disc domain, and a present star formation rate (SFR) of about 1 Msun. Our results show a decreasing trend of the SFR from 9-10 Gyr to 6-7 Gyr ago. This is consistent with the cosmological star formation quenching observed at redshifts z<1.8. This decreasing trend is followed by a SFR enhancement starting at about 5 Gyr ago and continuing until about 1 Gyr ago which is detected with high statistical significance by discarding the null hypothesis of an exponential SFH with a p-value=0.002. We estimate, from our best fit model, that about the 50% of the mass used to generate stars, along the thin disc life, was expended in the period from 5 to 1 Gyr ago. The timescale and the amount of stellar mass generated during the SFR enhancement event lead us to hypothesise that its origin, currently under investigation, is not intrinsic to the disc. Thus, an external perturbation is needed for its explanation. Additionally we find, for the thin disc, a slope of the IMF of $\alpha_3 \approx 2$ for masses M>1.53 Msun and $\alpha_2 \approx 1.3$ for the mass range between 0,5 and 1,53 Msun. This is the first time that we consider a non-parametric SFH for the thin disc in the Besancon Galaxy Model. This new step, together with the capabilities of the Gaia DR2 parallaxes to break degeneracies between different stellar populations, allow us to better constrain the SFH and the IMF., Comment: 6 pages, 3 figures. Accepted for publication to A&A letters

We study the components of cool and warm/hot gas in the circumgalactic medium (CGM) of simulated galaxies and address the relative production of OVI by photoionization versus collisional ionization, as a function of halo mass, redshift, and distance from the galaxy halo center. This is done utilizing two different suites of zoom-in hydro-cosmological simulations, VELA (6 halos; $z>1$) and NIHAO (18 halos; to $z=0$), which provide a broad theoretical basis because they use different codes and physical recipes for star formation and feedback. In all halos studied in this work, we find that collisional ionization by thermal electrons dominates at high redshift, while photoionization of cool or warm gas by the metagalactic radiation takes over near $z\sim2$. In halos of $\sim 10^{12}M_{\odot}$ and above, collisions become important again at $z<0.5$, while photoionization remains significant down to $z=0$ for less massive halos. In halos with $M_{\textrm v}>3\times10^{11}~M_{\odot}$, at $z\sim 0$ most of the photoionized OVI is in a warm, not cool, gas phase ($T\lesssim 3\times 10^5$~K). We also find that collisions are dominant in the central regions of halos, while photoionization is more significant at the outskirts, around $R_{\textrm v}$, even in massive halos. This too may be explained by the presence of warm gas or, in lower mass halos, by cool gas inflows.

We use the Gaia-TGAS data to compare the transverse velocities in Galactic longitude (coming from proper motions and parallaxes) in the Milky Way disk for negative and positive longitudes as a function of distance. The transverse velocities are strongly asymmetric and deviate significantly from the expectations for an axisymmetric Galaxy. The value and sign of the asymmetry changes at spatial scales of several tens of degrees in Galactic longitude and about 0.5 kpc in distance. The asymmetry is statistically significant at 95% confidence level for 57% of the region probed, which extends up to ~1.2 kpc. A percentage of 24% of the region studied shows absolute differences at this confidence level larger than 5 km/s and 7% larger than 10 km/s. The asymmetry pattern shows mild variations in the vertical direction and with stellar type. A first qualitative comparison with spiral arm models indicates that the arms are unlikely to be the main source of the asymmetry. We briefly discuss alternative origins. This is the first time that global all-sky asymmetries are detected in the Milky Way kinematics, beyond the local neighbourhood, and with a purely astrometric sample., Comment: Accepted for publication in A&A Letters

We model the effects of the spiral arms of the Milky Way on the disk stellar kinematics in the Gaia observable space. We also estimate the Gaia capabilities of detecting the predicted signatures. We use both controlled orbital integrations in analytic potentials and self-consistent simulations. We introduce a new strategy, which consists of comparing the stellar kinematics of symmetric Galactic longitudes (+l and -l), in particular the median transverse velocity (from parallaxes and proper motions). This approach does not require the assumption of an axisymmetric model. The typical differences between the transverse velocity in symmetric longitudes in the models are of ~2 km/s, but can be larger than 10 km/s for certain longitudes and distances. The kinematic differences for +l and -l show trends that depend on the properties of spiral arms. Thus, this method can be used to quantify the importance of the effects of spiral arms on the orbits of stars in the different disk regions, and to constrain the location of the arms, main resonances and, thus, pattern speed. Moreover, the method allows us to test the dynamical nature of the spiral structure (e.g. grand design versus transient multiple arms). We estimate the number of stars of each spectral type that Gaia will observe in representative Galactic longitudes, their errors in distance and transverse velocity, and the error in computing the median velocity as a function of distance. We will be able to measure the median transverse velocity with Gaia data, with precision smaller than ~1 km/s up to distances of ~4-6 kpc for certain giant stars, and up to ~2-4 kpc and better kinematic precision (<= 0.5 km\s) for certain sub-giants and dwarfs. These are enough to measure the typical signatures seen in the models. We also show that a similar strategy can be used with line-of-sight velocities from other upcoming spectroscopic surveys.(Abridged), Comment: Accepted for publication in A&A; new version with minor updates to meet the published version