Matías Blaña Díaz

Dwarfs Galaxies:
Leo T internal dynamics
and interaction with the Milky Way Corona

Title: Dwarfs in the Milky Way Halo Outer Rim: interaction with the Milky Way


Preface: We study the secular evolution of gas rich dwarfs that interact with the Milky Way hot halo through ram pressure and KH stripping. For this we implemented wind tunnel models, setting up multicomponent models in equillibrium with DICE for a dwarf galaxy, containing a stellar component (Plummer), a gas component (also Plummer), and a dark matter component (Burkert halo). Then we run the hydrosimulations with the grid code Ramses, which is well suited for modelling the discontinouities like shocks. The wind is injected with a gas density and temperature according to observational models of the MW corona. For now we assume here that the hot halo is static (some observations might indicate some coronal flow) and the galactic wind is given by the relative motion of the dwarf in the medium. Here we explore a velocity wind of 200km/s (many more values to be tested).

More Simulation Videos? (Link Here)

Dwarf Galaxies:
Backsplash vs first infall Milky Way Satellites

Preface: cosmological galaxy simulations predict that beyond the virial radius of the Milky Way there are two types of populations of dwarf galaxies: field galaxies that currently are on their first in-fall into the Milky Way, and therefore they evolved mostly in isolation; and the population of backsplash satellites, which have already passed through the Milky Way halo in the past. Tidal and ram pressure stripping by the host (MW) strongly influenced the evolution of latter type, resulting in substansial differences of their main properties between these two populations.

The gas rich dwarf LeoT (M_gas=5.4x10⁵M_⊙) is an ideal laboratory to study the formation and evolution of dSph galaxies in the Local Group. Given its location at 409kpc (1.4R_vir) from the MW, its large gas-to-stellar mass fraction (~2) and its negative GSR LOS velocity (-65km/s), it is assumed to be a field dwarf on its first in fall. Here, we present proper motion space solutions using dynamical and hydrodynamical constraints, finding backsplash satellite solutions when the tangential GSR velocity is lower than 60km/s, while for larger values we find first infall solutions. Furthermore, we apply our method to other distant Milky Way dwarfs, finding a range of backsplash solutions for Eridanus II and Cetus, while for Phoenix we find only first infall solutions. In the video you may watch our Nbody simulation of particle models for Leo T and the Milky Way following a backsplash orbit for 12Gyr. We note here that, despite the dark matter stripping, the stellar component of the satellite remains protected in the inner part of the subhalo, results effectivly almost un-affected.

Galaxy Clusters:
Tidal effects on Fornax Cluster Satellites

Preface: The evolution of galaxies at high redshift (z>1) is dominated by fast processes such as galaxy mergers, active galactic nuclei (AGN), strong accretion and a high star formation that peaked at z=2.5 (Madau & Dickinson 2014, Conselice 2014). At lower redshifts the evolution of observed galaxies in the local Universe is dominated mostly by environmental or external secular processes such as galaxy harassment, tidal distruption and ram pressure stripping (RPS) (Kormendy 2012), as well as by internal secular processes driven by stellar evolution, gas accretion, starvation and the internal dynamics of galaxy substructures such as bars, spiral arms and rings that can drive resonances and mass redistribution (Kormendy 2013). Kormendy & Bender (2012, see also Côté 2007, Ferrarese 2006) suggest that there is a continuous transition of the morphological properties of galaxies of types Spiral (S) with lenticulars (S0), and Irregular (Im) with Spheroidals (Sph). Cosmological galaxy simulations have revolutionized the study of galaxy formation and evolution, not only reproducing the large scale structures in the observed Universe, but also the different types of galaxies and the mechanisms that could form them. For example they predict that there is a population of satellites beyond the virial radius (Rvir) of their host system (galaxy groups or clusters), which are called backsplash systems, and they would have different properties compared to other infalling satellites found at similar distances due to environmental processes (Gill 2005, Lotz 2019, Haggar 2020, Diemer 2020). Similarly, within the host it is possible to find satellites on their first infall, and probably still containing gas and in the process of being tidal and ram pressure stripped.

Galaxy Clusters:
Orbits of Satellites in the Fornax Cluster

Preface: We want to understand the evolution of galaxies in denser environments, we will analyse galaxy clusters. The Fornax cluster is an ideal laboratory to study environmental evolution at larger scales than in the Local Group. It is located at a distance of 20.3Mpc and is visible from the southern hemisphere, and therefore it is accessible to all radio and optical telescopes in Chile. There are several observations, with for example The Next Generation Fornax Survey (NGFS) taken with the Dark Energy Camera (DECam; Flaugher et al. 2015) mounted on the 4 m Blanco telescope at Cerro Tololo Interamerican Observatory (CTIO) in Chile which is led by the research group of Prof. Puzia at PUC (Muñoz 2015, Eigenthaler 2018, Ordenes-Briceño 2018, Johnston 2019, Rong 2019). These observations resulted in a high number of newly discovered dwarfs and satellites. In addition, Fornax has a total cluster virial mass of ~7xE13M☉ which makes it an interesting probe for being near the transition regime (1014M☉) below which the quenching for satellites with masses below ~1.5xE10M☉ is weaker (Lotz 2019). In these projects our goal is to identify possible candidates of backsplash systems in the outskirts of the cluster that could lay beyond Rvir in deprojection, as well as first infalling satellites, such as Irregulars like NGC 1427A (right figure) located at Rvir/10 in projection from the cluster center. Furthermore, we will also explore orbits of distant satellites using new observations of Fornax that extend out to Rvir in projection.

Barred galaxies:
Andromeda (M31) Part II

Title: Sculpting Andromeda -- made-to-measure models for M31's bar and composite bulge: dynamics, stellar and dark matter mass (Link Paper)

Preface: What is the amount of dark matter in the center of Andromeda? In this article we want to quantify the main dynamical properties of the centre of M31. Andromeda is a barred galaxy that buckled generating a box/peanut bulge substructure wich is entangled with a classical bulge building a composite bulge. Therefore, we require a triaxial dynamical modelling to measure the central stellar and dark matter mass, and the pattern of rotation of the bar.

For this we use the made-to-measure (M2M) technique to directly fit the 3.6μm image from the Spitzer Space Telescope, and the IFU stellar kinematic observations from the VIRUS-W spectrometer at the McDonald observatory. You can watch the fitting process for the 3.6μ image in the video on the side: here the orbits of the particles of the best N-body model found in Blana et al 2017 are integrated in time in the potential from the particles. Model observables are built to measure the same quantities as the observational data. Then the masses of the particles that are passing by the model observables are changed in order to better match the observations (e.g. minimising a χ²), while the potential is frequently re-computed, obtaining a self-gravitating system in equilibrium. At the end of the parameter exploration, we find a central dynamical mass within 3kpc of 4.25^+0.10_-0.29•10¹⁰M_⊙ where the dark matter mass contributes with 27%.

Barred galaxies:
Andromeda (M31) Part I

Title: Andromeda chained to the box -- dynamical models for M31: bulge and bar (Link Paper)

Preface: The Andromeda galaxy is a barred galaxy; this has been revealed already by Lindblad in 1956 in his publication titled "On a Barred Spiral Structure in the Andromeda Nebula (Link Paper) "^(1,2). The bar also presents a box/peanut bulge substructure, which is a vertical re-distribution of the bar stellar material, generating a triaxial structure. Historically, the bulge of M31 has been considered and modeled only as a classical bulge, while in fact it is a composite bulge built with a box/peanut bulge and a classical bulge.

In this article we use barred galaxy N-body simulations built with classical bulges of different masses and scales to construct composite bulges that reproduce M31's triaxial bulge by comparing with the Spitzer Space Telescope 3.6μm image. We find that the stellar mass of the composite bulge within 3kpc is composed by ~1/3 of a compact classical bulge and ~2/3 of box/peanut bulge. In the vido aside you may see the bar formation and buckling process, where we set an N-body model with an initial stellar disc, classical bulge and dark matter halo. Initial perturbations grow producing spiral arms which then form a bar. The bar grows capturing material from the disc, and slows down its rotation as it transfers angular momentum to the classical bulge and the dark matter halo. Finally, the bar becomes vertically unstable to the buckling, fire-hose, or pipe-hose vertical instability, forming the box/peanut bulge.
(1) Stockholms Observatoriums Annaler 1956 volume 19 Nr 2; (2) Lindblad & Ramberg 1951

Barred galaxies:
Gas dynamics

Preface: the triaxial potential of bars in galaxies can change the dynamics of the gaseous disk, perturbing its circular motion. In the centre the bar can produce shocks and streams of the gas that precipitate the gas to the centre. And in the outer regions the outer resonances can perturbe the circular motion of the gas, generating substructures such as rings and spiral arms. We explore the dynamical evolution of the gas in a barred potential (Ferrers) using PHANTOM (Price 2017).

Dwarf Galaxies:
Leo IV and Leo V

Title: Leo IV and V - A possible dwarf galaxy pair? (Link Paper)

Preface: Dwarf spheroidal galaxies are among the faintest, most metal-poor and most dark matter dominated systems in the Universe. Cosmological galaxy simulations predict that these galaxies were the building blocks of the hierarchical merging process that built the present day large galaxies. It is also predicted that a significant fraction of these primordial dwarf galaxy satellites should have survived hierarchical merging, leaving hundreds of fossil satellites as relics.

However, in the Milky Way (MW) galaxy there have been detected only a few dozen satellite low mass dwarf galaxies, similar to our neighbouring galaxy Andromeda (M31) with its satellites. The over-prediction of satellites is named "The Missing Satellite Problem", while the over-prediction of massive satellites (Vmax≥25km/s) is named the "Too-Big-To-Fail" problem; Boylan-Kolchin et al. 2011, 2012). Besides the MW's gas-rich irregular dwarfs, the Magellanic Clouds, most of the detected satellites are ultra-faint (UFD) and dwarf spheroidal galaxies (dSph) that show very little or no gas. At the beginning, only a few gas-rich exceptions were discovered (Blitz et al 2000). However, with the new and more sensitive telescopes like the SDSS telescope (band limit r〜22.5[mag]), and the new upcoming Large Synoptic Survey Telescope (LSST) survey in Chile even more sensitive, with a r〜27.5[mag] limit, will detect these new systems much more easily, solving the problem of the missing satellites.

In this article we explore the scenario where the dwarf spheroidal galaxies Leo V and Leo IV are a gravitationally bound system, and we constrain the minimum total dark matter mass required for the system to remain bound using for this a restricted N-body code and also full N-body simulations. We discover that each satellite would require a dynamical mass between 7•10⁹ M_⊙ and 1.3•10¹⁰M_⊙, which agrees with many simulated satellites in new cosmological simulations (Simpson et al 2017).

Furthermore, we also explore a scenario where Leo IV and Leo V are star clusters orbiting a common dark matter halo, finding slightly lower dynamical masses (Link Paper).

Dwarf Galaxies:
Hercules

Title: Life and death of a hero - lessons learned from modeling the dwarf spheroidal Hercules: an incorrect orbit? (Link Paper)

Preface: Galactic cannibalism is an important mechanism where the dwarf galaxy satellites are tidally destroyed by the host galaxy. In this article we use N-body simulations to study this mechanism to reproduce the observed photometric and kinematic properties of the dwarf spheroidal galaxy Hercules, which is orbiting the Milky Way. The position and radial velocity of this galaxy are known however, the tangential velocity is not. We study an orbit estimated from the assumption that this galaxy's elongation is aligned with the tangential velocity proposed by Martin & Jin 2010. For this we developed a systematic parameter exploration method (see also Domínguez et al. 2016) to find the properties and initial conditions of the progenitor of Hercules, calculating the orbit backwards 10Gyr and then evolving the N-body system in time through the orbit around the Milky Way for 10 Gyr until its present position. We find that the proposed orbit can tidally disrupt this dwarf; however, the ellipticity is not large enough to reproduce the observed elongation. Furthermore, we find a flip in the orientation of the elongation of 90 degree respect to the orbit trajectory. Further analysis by Küpper et al 2016 find the same process and attribute it to the stream fanning of Hercules as it orbits the Milky Way, proposing a new orbit perpendicular to the previous orbit.

Star Clusters":
"Infant Mortality

Title: Effects of the Initial Mass Function on the Infant Mortality of Star Clusters Link Master Thesis

Preface: stars are formed in clusters; however, most of the stars in galaxies are distributed homogeneously in the field, as star clusters are destroyed during the evolution: a problem called Infant Mortality. In this project we expand the parameter space of the research made by Farias et al 2015 that used equal mass stars, by including the effects of the Kroupa IMF in the evolution of embedded star clusters when the gas is expelled. We use the direct N-body code Nbody6 (Aarseth 2003) to evolve the orbits of stars with an initial fractal distribution to mimic the clumpy distribution, with different initial virial equilibriums in an analytical potential for the gas cloud distribution that is deactivated motivated by the expulsion of the gas due to stellar evolution (see video). We measure the stellar mass of the final gravitationally bound cluster after the expulsion, finding a strong and quick effect of mass segregation of the stars during the early evolution, that increases the final bound mass of the cluster. The results are part of the master thesis found in the links below, and are part of the analysis in Dominguez et al 2017).