Welcome to my Homepage.

Here you will find out about my scientific work on
Galactic & Stellar Dynamics.


(Photo: Cordillera de Los Andes)

Research Interests

◉ Barred galaxies ◉ Stellar dynamics
◉ Dwarf spheroidal galaxies ◉ N-body simulations
◉ Star clusters ◉ Made-to-measure modelling

Projects

The following research projects embrace several topics in Stellar Dynamics. The approach for the research is with N-body simulations, using tree codes, particle-mesh codes and Made-to-Measure models. I also like to experiment with gas-dynamic simulations.

The barred galaxy 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)

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 may see the fitting process for the 3.6μ image in the video on the side: here the orbits of the particles of an initial N-body model 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%.

The barred galaxy Andromeda (M31):
Part I

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

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"(1,2). The bar also presents a box/peanut bulge substructure, which is a vertical re-distribution of the bar mass, 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

Gas in barred galaxies

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 Spheroidal Galaxies:
Leo IV and Leo V

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

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 Spheroidal Galaxies:
Hercules

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

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).

Publications

An updated list of my publications and collaborations can be found in ADS (link)

First Author Publications

12. Sculpting Andromeda -- made-to-measure models for M31's bar and composite bulge: dynamics, stellar and dark matter mass. (Link Paper)
Blaña, M.; Gerhard, O.; Wegg, C.; Portail, M.; Opitsch, M.; Saglia, R.; Fabricius, M.; Erwin, P.; Bender R., 2018. MNRAS doi: 10.1093/mnras/sty2311 (Link)
11. Andromeda chained to the Box - Dynamical Models for M31: Bulge & Bar. (Link Paper)
Blaña, M.; Wegg, C.; Gerhard, O.; Erwin, P.; Portail, M.; Opitsch, M.; Saglia R.; Bender R., 2017. MNRAS.466.4279B
10. Life and death of a hero - lessons learned from modelling the dwarf spheroidal Hercules: an incorrect orbit? (Link Paper)
Blaña, M.; Fellhauer, M.; Smith, R.; Candlish, G. N.; Cohen, R.; Farias, J. P., 2015 MNRAS.446..144B
9. Leo IV and V - A possible dwarf galaxy pair? (Link Paper)
Blaña, M.; Fellhauer, M.; Smith, R., 2012 A&A...542A..61B
8. Leo IV and V - A possible dwarf galaxy pair? (Part II: a binary star clusters scenario). (Link Paper)
Blaña, M.; Fellhauer, M.; Smith, R., 2011 BAAA...54..397B

Collaborations

7. Stellar populations of the central region of M31 (Link Paper)
Saglia R.; Opitsch, M.; Fabricus, M.; Bender R.; Blaña, M.; Gerhard, O., 2018 A&A
6. Evidence for non-axisymmetry in M31 from wide-field kinematics of stars and gas (Link Paper)
Opitsch, M.; Fabricus, M.; Saglia R.; Bender R.; Blaña, M.; Gerhard, O., 2017 A&A.611A.38O
5. How fast is mass-segregation happening in hierarchical formed embedded star clusters? (Link Paper)
Domínguez, R.; Fellhauer, M.; Blaña, M.; Farias, J. P.; Dabringhausen, J., 2017 MNRAS.472..465D
4. Could Segue 1 be a destroyed star cluster? – a dynamical perspective (Link Paper)
Domínguez, R.; Fellhauer, M.; Blaña, M.; Farias, J. P.; Dabringhausen, J.; Candlish, G. N.; Smith, R.; Choque, N., 2016 MNRAS.461.3630D
3. The difficult early stages of embedded star clusters and the importance of the pre-gas expulsion virial ratio (Link Paper)
Farias, J. P.; Smith, R.; Fellhauer, M.; Goodwin, S.; Candlish, G. N.; Blaña, M.; Dominguez, R., 2015 MNRAS.450.2451
2. Ursa Major II - reproducing the observed properties through tidal disruption (Link Paper)
Smith, R.; Fellhauer, M.; Candlish, G. N.; Wojtak, R.; Farias, J. P.; Blaña, M., 2013 MNRAS.433.2529S
1. A possible formation scenario for dwarf spheroidal galaxies - II. A parameter study (Link Paper)
Assmann, P.; Fellhauer, M.; Wilkinson, M. I.; Smith, R.; Blaña, M., 2013 MNRAS.435.2391A

My Thesis

III. Dynamics of the bar and the bulge of the Andromeda galaxy (M31) (Doctoral Thesis) (Link PDF [English])
II. Effects of the Initial Mass Function on the Infant Mortality of Embedded Star Clusters (Master Thesis) (Link PDF [English])
I. Life of a Hero –Hercules, Stream or Dwarf Galaxy? (Thesis Professional Astronomer Degree) (Link PDF [English])

About Me

I was born in the wonderful country of Chile, growing up in Osorno, and studying Physics and Astronomy at the Universidad de Concepcion in the Astronomy Department in the Theory Group (Bachelor, Titulo and Master). I obtained my doctoral degree at the Ludwig-Maximilians-Universität (LMU) in München, Germany, working at the Max Planck Institute for Extraterrestrial Physics (MPE) in the Dynamics Group.
Currently I am a postdoctoral researcher in the Physics of Galactic Nuclei group (PGN) at MPE, and part of the Computational Astrophysics group (CAST) at the Observatory of the LMU (USM).

My research background consists on using N-body simulations to study diverse stellar dynamical systems, such as disc galaxies, dwarf galaxies and star clusters, using different codes written in Fortran 90 and 77, C for the simulation, and performing the data analysis with Python, Supermongo, IDL, Mathematica, MATLAB, among others.

You may download my CV here, and the extended version here.

Contact & Questions

Thanks for visiting my Homepage, and please feel free to contact me for any question, writing me to mblana@mpe.mpg.de or using the form below.

Also, if you want to apply to fellowships or grants in Chile or Germany, but do not know how, I am happy to help; I successfully applied to the DAAD (doctorate), CONICYT (Master), Becas Chile (postdoc), and participate in the IMPRS program, acquiring experience in the German and Chilean academic systems.
Also, write me if you want to study astronomy as a career and you have questions on the daily duties of astronomers (you can also check a presentation here).

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