# Short talks abstracts

TUESDAY

Improving Hickson-like compact group finders in redshift surveys
Eugenia Díaz, Instituto de Astronomía Teórica y Experimental

In this work, we present an algorithm to identify compact groups of galaxies that closely follows Hickson’s original aim and that improves its implementation on redshift surveys to obtain complete samples of compact groups. The methodology is tested on a mock lightcone of galaxies built from the outputs of a seminanalytic model of galaxy formation run on top of the Millennium Simulation I after scaling to represent the first-year Planck cosmology. The new algorithm is able to identify twice the number of CGs than previous versions of it, without changing the percentage of groups that are contaminated by interlopers. A brand new catalogue of compact groups from the Sloan Digital Sky Survey is the natural corollary of this study. The publicly available sample of 461 observational groups fulfil all the ideal compact group requirements: compactness, isolation and velocity concordance of all of their members.

Local Group bar formation in the LCDM cosmology
Ornela Marioni

About two thirds of the galaxies in the local Universe have bars and about half of these are strong ones. We studied the formation and evolution of the bars in disk galaxies in a cosmological context. We analyze the CLUES (Constrained Local UniversE Simulations) project’s simulations which are high resolution cosmological hydrodynamical simulations designed to reproduce the main galaxies of the Local Group and its environment. We test the ability of the LCDM cosmology to reproduce the local neighborhood identifying the main members of the Local Group like Andromeda and the Milky Way. We compare intrinsic properties of the simulated galaxies with the observational data. We also study the mechanisms of bar formation
trough gravitational interactions between the main galaxy and its satellites. Previous works found that some intrinsic properties, like rotational speed, of the barred galaxies could present a problem for the LCDM cosmological model, nevertheless, we found that ours bars are
fast rotators in agreement with the observations.

Cluster Analysis of morphometric data from CALIFA
Vanessa de Oliveira Gil

To understand the processes of formation and evolution of galaxies, it is essential to identify properties that allow their classification. It is common to perform this type of classification through visual and individual inspection of each image, however this method is subjective and limited. It is necessary to seek an automatic method based on the quantification of its morphologies to find the classes of galaxies. We propose the automated separation through cluster analysis for objects in the space of morphometric parameters,
as measured by MORFOMETRYKA. This method proposes to find observations groups strongly correlated that indicate the same physical processes of formation and evolution. The study object corresponds to a subsample of the Calar Alto Legacy Integral Field Area Survey (CALIFA) survey composed by 314 galaxies with different morphological stages. Cluster analysis is an unsupervised technique, the morphological classes present in the data are results based on the characteristics of the survey. This technique demonstrates that it is possible to separate morphological types automatically using morphometric data from galaxies.

Cosmology with voids using the sky-plane and line-of -sight cross-correlation functions
Carlos Correa

We present a cosmological test using cosmic voids without assuming a fiducial cosmology. The test consists on measuring and modelling the sky-plane and line-of-sight cross-correlation functions only with angles and redshifts.  These functions are obtained integrating the usual correlation function along and perpendicular the line-of-sight. In this way, we can fit two fundamental cosmological parameters in an independent way: i) the omega-matter parameter,  related with the expansion and geometry of the Universe, and ii) the linear growth rate of density perturbations, related to the large scale structure of the Universe.

Marked correlation functions and modified gravity
Nelson Padilla

Models of modified gravity that do not require a cosmological constant show small differences with respect to LCDM in the low density regions. Therefore we devise marked correlation functions that highlight these differences, and propose ways to apply this measurement to observational data. We expect that an f(R) model with |f_{R0}|=1e-5 can be told apart from GR.

Resolved nuclear warm dust in a low luminosity AGN
Gaia Gaspar

Effects of the local and large-scale environments on nuclear activity and star formation
Maria Argudo-Fernández

Active galactic nuclei (AGN) are one of the main drivers for the transition from star-forming disk to passive spheroidal galaxies, however, the role of large-scale environment versus one-on-one interactions in triggering different types of AGN is still uncertain. The environment in which a galaxy resides plays an important role in its formation and evolution. Galaxies suffer intrinsic and secular evolution processes (i.e. nature processes), but they are also exposed to the influences of their local and large-scale environments (i.e. nurture processes). Are AGN triggered by mergers/interactions or by secular evolution of the host galaxies. I will present recent studies where we investigate the connections between AGN activity and stellar mass and environment. In particular, we focused on optical and radio
nuclear activity to study the prevalence of AGN and star-formation as a function of stellar-mass, the influence of the physically bound neighbour, and the influence of the large-scale environment around galaxies. The goal is to connect the environment with the possible source of gas fueling the central black holes.

WEDNESDAY

VVV Survey and Milky Way Globular Clusters
Tali Palma

The VVV NIR Survey had performed time-domain observations in the Ks-band for 6 years and provides an atlas of 562 sq. deg. of the sky in 5 wavebands (ZYJHKs). The VVV data products offer a unique dataset to map the stellar populations deeply embedded on highly obscured regions. The recent discoveries and characterization of a significant number of globular clusters (GCs) distributed in different regions of our Galaxy, using the VVV data, evidence the incompleteness of the known GC population. The new discoveries are important and impact statistically on the global known properties of these objects. In this talk I will discuss the different and indirect methods used to discover new and low luminosity globular clusters in the most obscured regions of our Galaxy, and the requirements or tests to take into account to confirm their real GC nature.

Spectral analysis of nearby Active Galactic Nuclei
Luis Vega

We present the results of a spectroscopic study of a sample of nearby Narrow Line Seyfert 1 (NLS1) galaxies, whose spectra were taken from the Sloan Digital Sky Survey (SDSS) DR7. By applying spectral synthesis techniques we characterize the non-stellar continuum for each NLS1. We also derive dynamical parameters such as black hole masses and acretion rates, and study the stellar and gaseous dynamics as well.

Globular cluster systems of massive elliptical galaxies in poor environments

Ana I. Ennis, Bruno J. de B\’ortoli, Lilia P. Bassino, Juan P. Caso

In this work, we aim to study the evolutionary history of massive elliptical galaxies in low density environments, through the characterization of their globular cluster systems (GCS). In particular, we focus on bright elliptical galaxies, typical of cluster environments rather than of the groups they inhabit, which might show signs of interaction with their neighbors. The two photometric studies correspond to the GCSs of NGC 6876 and NGC 3613, both of them observed with the GMOS camera in Gemini South. These two galaxies inhabit different poor groups and fall under the previous description.

Secondary Infall in the Seyfert’s Sextet: A Plausible Solution to the Compact Groups’ Short Crossing Time Problem.
Omar López-Cruz, INAOE

We combined CALIFA DR3 and multiwavelength data to revisit Seyfert’s Sextet (SS, HCG 79). We found that the galaxies H79a, H79b (NGC 6027), H79c, and H79f have low star-formation rates. Synthesis population modeling has allowed us to reconstruct the radial star formation histories (SFH) for each galaxy.  We found two episodes of strong star formation common to the four galaxies. We propose that a simple timing argument can be formed, using the episodes of star formation as markers of group crossings. We therefore, suggest that SS has collapsed at least twice in a Hubble time. After the first turn-around the originally gas-rich SS galaxies crossed, tidally induced starbursts or active galactic nuclei (AGN) consumed most of their gas. In addition, the resulting shocks and turbulence forced some gas and dust out of the galaxies.  On the second turn-around most mergers would likely be mixed or dry, except for gas-rich galaxies intruding for the first time. The proposed scenario provides a solution for the short crossing time problem in compact groups.  That is, compact groups are neither collapsing for the first time nor chance projections.

THURSDAY

Evection resonance in Saturn’s coorbital moons
Cristian Giuppone

In the Solar System is widely accepted that most distant region of stability for prograde and retrograde satellites is associated with the evection resonance, produced as a consequence of
the Sun as a perturber. At this region, the critical angle librates for moderate values of eccentricities, compatible with irregular satellites characteristics. It is important to note that the oblateness of a planet also produces a region of evection resonance at innermost regions of satellites of giant planets. The moons of Saturn exhibit a complex dynamical architecture, and coorbital configuration has a high occurrence in certain region near to the planet. Is our intention to study the location of evection resonance for Saturn and compare the dynamic for a single moon and a pair of coorbital moons. We study the location of evection resonance for single satellites with N-body integrations for single moon systems. Then we identify the regions of evection for coorbital moons. We develop an analytical model applied to the trojan case based on a classical averaged expansion of the disturbing function that considers a mix set of canonical coordinates. Finally we use numerical methods to test the validity of the models. In Saturn we find two important and unconnected regions where the evection rules the dynamics. The inner evection resonance is present near two Saturn radius and tidal evolution of satellites demonstrate that while evolve from inner to outer regions coorbital companions are exited and the more massive companion only survived. On the other hand, at the exterior evection resonance region the coorbital configurations present small diffusion that finally breaks the resonance.

Resonant Capture and Tidal Evolution in Circumbinary Systems: Testing the Case of Kepler-38
Federico Andr\’es Zoppetti

Circumbinary planets are thought to form far from the central binary and migrate inwards by interactions with the circumbinary disk, ultimately stopping near their present location either by a planetary trap near the disk inner edge or by resonance capture. Here, we analyze the second possibility, presenting a detailed numerical study on the capture process, resonant dynamics and tidal evolution of circumbinary planets in high-order mean-motion resonances (MMRs). Planetary migration was modeled as an external acceleration in an N-body code, while tidal effects were incorporated with a weak-friction equilibrium tide model. As a working example we chose Kepler-38, a highly evolved system with a planet in the vicinity of the 5/1 MMR. Our simulations show that resonance capture is a high-probability event under a large range of system parameters, although several different resonant configuration are possible. We identified three possible outcomes: aligned librations, anti-aligned librations and chaotic solutions. All were found to be dynamically stable, even after the dissipation of the disk, for time-spans of the order of the system’s age. We found that while tidal evolution decreases the binary’s separation, the semima- jor axis of the planet is driven outwards. Although the net effect is a secular increase in the mean-motion ratio, the system requires a planetary tidal parameter of the order of unity to reproduce the observed orbital configuration. The results presented here open an interesting outlook into the complex dynamics of high-order resonances in circumbinary systems.

Hall-MHD and trapping of dust in turbulent protoplanetary discs.
Leonardo Krapp

The evolution of the magnetic field in a plasma is subject to non-ideal effects when the gas is not fully ionized. In the presence of magneto-rotational-instability (MRI) the Hall effect may organize the vertical magnetic flux into strong axisymmetric zonal flows. This has an impact on protoplanetary discs dynamics, where regions of strong pressure gradient may act as a source of dust trapping. We have performed a series of 3D simulations with the code FARGO3D with the aim to investigate the conditions that induce the magnetic zonal flows and whether these regions may evolve as potential dust traps.

Stellar flybys in protoplanetary discs
Nicolás Cuello

Stellar flybys or encounters are expected to occur in stellar clusters. Presumably, such tidal encounters affect the surroundings of young stars, namely their protoplanetary discs. Here we present 3D hydrodynamical simulations of a circumprimary disc around a (single) star which is perturbed by a stellar flyby. We assume that the perturber is on an unbound parabolic orbit (e=1). By considering different orbital inclinations, pericentre distances, mass ratios and flyby times we study the disc response during and after the encounter. This is done for the gaseous phase and the dusty phase for grain sizes ranging from 1 $\mu$m to 1 cm. We observe a very rich structure in the disc during and after the flyby: warped rings, spirals with evolving pitch angles, increasing accretion rates and disc truncation. In addition, we compare these dynamical effects to the ones caused by an outer companion on an eccentric orbit. Finally, we discuss the implications for planet formation in such systems.

The influence of magnetic field on the CNM mass fraction and its alignment with density structures
Marco Villagran

To contribute to the understanding of the influence of magnetic fields on the segregation of CNM in the solar neighbourhood we analyse MHD simulations which include the main physical characteristics of the local neutral atomic ISM. The simulations have a continuous solenoidal Fourier forcing in a periodic box of 100 pc per side and an initial uniform magnetic field with intensities ranging between ? 0.4 ?G and ? 8 ?G. Our main results are: i) the CNM mass fraction diminishes with the increase in magnetic field intensity but when the mass fraction is measured considering individual “”lines of sight””, this behaviour is not recovered. ii) There is a preferred alignment between CNM structures and B in all our B0 range but the preference weakens with intensity of B0. It is worth noticing that this preference is also present in two-dimensional projections making an extreme angle (0 or ?/2) with respect to B0 and it is only lost for the strongest magnetic field. iii) The aforementioned results
are prevalent despite the inclusion of self-gravity in our continuously forced simulations.

FRIDAY

LLAMA telescope: instrumentation and science
Guillermo Gancio

The LLAMA telescope, which is being installed in the Puna Salte\~na in collaboration with Brasil, is a 12 m telescope to investigate the Universe in millimeter and submillimeter wavelengths. Here we present a status of the project and a summary of science and first light instrumentation.

Metallicity scaling relations of galaxies in cosmological simulations
Maria Emilia De Rossi

The study of the metallicity evolution of galaxies and its relation with other global properties of these systems, such as total stellar mass or gas fraction, might provide important constraints on galaxy formation models. In particular, over the last decades, different research projects have focused on the analysis of the mass-metallicity relation (MZR) and its evolution with redshift. In this work, we analyse metallicity scaling relations of galaxies since redshift z=3 by using the EAGLE (Evolution and Assembly of GaLaxies and their Environments) simulations. We investigate the evolution and scatter of the simulated MZR. We explore also possible dependences of this relation on secondary parameters. According to our results, the slope of the simulated MZR is mostly determined by stellar feedback at low stellar masses, and at high masses by the feedback from active galactic nuclei. In agreement with previous findings, the fundamental parameter that best correlates with the
metal content, in the simulations, is the gas fraction (De Rossi et al. 2017).

Unveiling the role of galactic rotation on star formation
Andres Escala

We study the star formation process at galactic scales and the role of galactic rotation through numerical simulations of spiral and starburst galaxies using the adaptive mesh refinement code Enzo. We focus on the study of three integrated star formation laws found in the literature: the Kennicutt-Schmidt (KS), Silk-Elmegreen (SE) and a modified KS law, corrected in order to be a dimensionally homogeneous equation $\Sigma_{SFR} \propto \sqrt{G/L} \Sigma_{gas}^{1.5}$ (where L the integration along the line of sight, Escala 2015). We find that the efficiencies displayed by our simulations are anti-correlated with the angular velocity of the disk ? for the three laws studied in this work. We show find that the dimensionless efficiency of star formation is well represented by an exponentially
decreasing function of $-1.9 \Omega t_{ff}^{ini}$, where $t_{ff}^{ini}$ is the initial free-fall time. This leads to a unique galactic star formation relation which reduces the scatter of the bi-modal KS, SE, and Escala (2015) relations by 43\%, 43\%, and 35\%, respectively. Reference: ApJ, 833, 13

Andrea Kulier

Hydrodynamical cosmological simulations can be used to investigate the accuracy of assumptions made in semi-analytic models of galaxy formation, which assign galaxies to dark matter halos from dark-matter-only simulations based on the properties and evolution of each halo. One assumption that is sometimes made is that galaxy and halo angular momentum are proportional. However, this leads to predictions for the size distribution of rotationally
supported galaxies that fail to match the observations. In the EAGLE simulation, which was calibrated to match the observed size distribution of galaxies, this proportionality between galaxy and halo angular momentum has been found to be broken. In this talk, I will discuss ongoing work on the evolution of the angular momentum of dark matter, hot and cold gas, and stars in EAGLE and their relation to one another.

Clustering dependence on halo angular momentum growth
Pablo López

Dark matter halos (DM) are the largest virialized structures in the Universe. Their internal dynamics are linked to the history of the galaxies, groups and clusters which form on their potential wells, but also to the large-scale structure of the Universe. Therefore, understanding the dynamical properties of halos becomes a keystone in any cosmological and galaxy formation model. The tidal torque theory (TTT) naturally relates the origin and evolution of angular momentum to the characteristics of the environment in which DM halos formed. Even though TTT is the most accepted model on the current paradigm, its validity range is limited to the early times of structure formation, and its predictions contrast in several aspects with measurements obtained from cosmological simulations on their non-linear stages. In this work, we study and characterize systematic deviations from the TTT model performing a statistical analysis of different DM halo populations in a cosmological simulation. We find that the classification according to their angular momentum growth results in samples with different levels of clustering and radically different distributions of spin parameters. Based on this classification, we find a strong correlation between the angular momentum history and the well known mass dependent alignment between the angular momentum direction and the large-scale structure. Our study suggests that a secondary tidal torque mechanism could be acting during the non-linear stages of halo formation.

Early-Type galaxies in cosmological context
Lucas Zenocratti

Early type galaxies constitute one of the largest populations inhabiting groups and clusters in the local Universe. Thus, their study might provide important clues to understand the process of formation and evolution of structures in the Universe. Results from a statistical analysis on this type of galaxies in numerical simulations within cosmological context will be presented. Integrated properties of such simulated systems will be analyzed at redshift $z=0$ in order to establish the main astrophysical processes which determine their evolution. The ability of models to reproduce observational results will be also tested.