Adrian Bittner

I am a Postdoctoral Researcher at the European Southern Observatory, working on the structure and evolution of galaxies

About Me

I recently completed my PhD with the grade 'Summa Cum Laude' at the European Southern Observatory in Garching, Germany. During my PhD, I studied the structure and evolution of galaxies, in particular bar-driven secular evolution processes in disc galaxies. To this end, I mainly used observations obtained with the MUSE spectrograph in the context of the TIMER and Fornax3D surveys.

In the coming months I will continue these studies as a Postdoctoral Researcher at ESO. I am specifically interested in exploring possible applications of machine learning algorithms in extragalactic astronomy, for instance to reduce the noise in spectroscopic observations of galaxies or even facilitate their scientific analysis.

I conducted my Bachelor and Master studies at the University of Munich. During this time, I already completed research projects at the Max-Planck Institute for Astrophysics (MPA) in Garching, at ESO in Santiago de Chile, the Instituto de Astrofisica de Canarias (IAC) in Tenerife, and the University Observatory Munich (USM).

In addition, I am passionate about public outreach. Before the pandemic, I delivered weekly planetarium shows at the ESO Supernova Planetarium & Visitor Centre and as well as an outreach talk during the European Researchers' Night.

Research

Galaxies within Galaxies: Inner bars are scaled replicas of main bars

Inner bars are frequent structures in the local Universe and thought to substantially influence the nuclear regions of disc galaxies. We explore the structure and dynamics of inner bars by deriving maps and radial profiles of their mean stellar population content and comparing them to previous findings in the context of main bars. Inner bars can be clearly distinguished based on their stellar population properties alone, in particular by their elevated metallicities and depleted [α/Fe] abundances. The ends of the inner bars are clearly younger compared to their inner parts, an effect known from main bars as orbital age separation. In particular, the youngest stars (i.e. those with the lowest radial velocity dispersion) seem to occupy the most elongated orbits along the (inner) bar major axis. Radial profiles of metallicity and [α/Fe] enhancements are flat along the inner bar major axis, but show significantly steeper slopes along the minor axis. This radial mixing in the inner bar is also known from main bars and indicates that inner bars significantly affect the radial distribution of stars. In summary, inner bars appear to be scaled down versions of the main bars seen in galaxies. This suggests the picture of a "galaxy within a galaxy", with inner bars in nuclear discs being dynamically equivalent to main bars in main galaxy discs.

Stellar Populations of Nuclear Discs: Bar-driven Inside-out Formation Scenario

We derived spatially resolved maps of the stellar population properties of the nuclear discs in the barred galaxies of the TIMER survey. We show that the nuclear discs in the sample are characterised by significantly younger, more metal-rich, and less alpha-enhanced stellar populations, as compared to the main discs of the galaxies. This result is fully consistent with the picture of bar-driven secular evolution. Moreover, nuclear discs exhibit well-defined radial gradients of the population properties with single slopes, suggesting that they are continuous components from their outer edge to the galaxy centre. We argue that these continuous (stellar) nuclear discs may form from a series of bar-built (initially gas-rich) nuclear rings that grow in radius, as the bar evolves. In this picture, nuclear rings are simply the (often) star-forming outer edge of nuclear discs. Finally, by combining results from the kinematic and stellar population analysis, we do not find evidence for the presence of large, dispersion-dominated components in the centres of these galaxies.

The TIMER survey: Time Inference with MUSE in Extragalactic Rings

The TIMER project is a survey of 24 barred galaxies with a large variety of presumably bar-built central structures, such as nuclear rings, inner discs, and inner bars. To date, 21 galaxies have been observed with MUSE on the Very Large Telescope. The main goal of the survey is to reconstruct the star formation histories of the inner discs in order to constrain the formation time of the bars and establish when the main discs of these galaxies became dynamically mature. The viability of this approach has been shown in a pilot study of NGC4371. In addition, we investigate the nature of inner discs and nuclear rings by combining information on their stellar kinematics as well as population properties. Other studies involve, for instance, the nature of bars, inner bars, and stellar feedback.

How do spiral arm contrasts relate to bars, disc breaks and other fundamental galaxy properties?

We investigate how the properties of spiral arms relate to other fundamental galaxy properties. To this end, we use previously published measurements of those properties, and our own measurements of arm-interarm luminosity contrasts for a large sample of galaxies, using 3.6μm images from the Spitzer Survey of Stellar Structure in Galaxies. Flocculent galaxies are clearly distinguished from other spiral arm classes, especially by their lower stellar mass and surface density. Multi-armed and grand-design galaxies are similar in most of their fundamental parameters, excluding some bar properties and the bulge-to-total luminosity ratio. Based on these results, we discuss dense, classical bulges as a necessary condition for standing spiral wave modes in grand-design galaxies. We further find a strong correlation between bulge-to-total ratio and bar contrast, and a weaker correlation between arm and bar contrasts.

Software

The GIST Framework: A Multi-Purpose Tool for the Analysis of Spectroscopic Data

The GIST Framework is a convenient, all-in-one framework for the analysis of spectroscopic data. It extracts stellar and gaseous kinematics, non-parametric star-formation-histories as well as line strength indices and stellar population properties from spectroscopic observations by exploiting the pPXF and GandALF routines. The software is not specific to any instrument or analysis technique, provides easy means of modification, and includes an elaborate parallelisation. It further features a dedicated visualization routine with a graphical user interface. This allows easy access of all measurements, spectra and fits in fully-interactive plots. The GIST pipeline is being used by various surveys (e.g. TIMER, Fornax3D and PHANGS) and has successfully been applied to both low and high-redshift data from MUSE, CALIFA, SINFONI, KWCI as well as to simulated data for HARMONI and WEAVE.

Bridson Poisson Disk Sampling with Variable Sampling Density

If a sample of points in a two-dimensional box is drawn from a uniform probability field, the resulting distribution of points will not necessarily appear smooth. As a result of the uniform probability field, in some areas the points will cluster while there will be voids in other parts of the sampling box. A truly uniform yet random distribution of points can be generated via so-called Poisson Disk Sampling algorithms. This Python package implements an adaptation of the original Poisson Disk Sampling algorithm of Bridson (2007). In summary, this algorithm achieves uniformity by creating new points in an annulus between radius R and 2R while checking that these newly created points are not closer than R to any other already existing point. My package not only provides an Python implementation of the Bridson algorithm, but also generalises it to facilitate variable sampling densities throughout the box.

printStatus: Print Progress Bars and Status Messages in the Console

This Python package contains a collection of functions to simplify the display of progress bars in the console. It further allows to print status messages of Python routines in a visually attractive way while distinguishing between routines that are currently running, finished successfully, returned a warning, or failed. The package is, for instance, used to produced the console outputs of the GIST Framework (see above).

Direct-sum Gravitational N-body Simulation in C++

This package contains a simple C++ implementation of a gravitational N-body simulation. The code employs the direct-sum approach for calculating the accelerations between particles, and offers an option to choose between the Kick-Drive-Kick (KDK) and Drive-Kick-Drive (DKD) Leap-Frog integration schemes. It further allows variable time steps, by defining a maximum spatial steps size.

Publications

You can find a complete list of my publications on ADS.

First and Second-Author Publications

“Galaxies within galaxies in the TIMER survey: stellar populations of inner bars are scaled replicas of main bars”
A. Bittner, A. de Lorenzo-Cáceres, D. A. Gadotti, P. Sánchez-Blázquez, et al.
A&A (2021), 646: A42

“Inside-out formation of nuclear discs and the absence of old central spheroids in barred galaxies of the TIMER survey”
A. Bittner, P. Sánchez-Blázquez, D. A. Gadotti, J. Neumann, et al.
A&A (2020), 643: A65

“Kinematic signatures of nuclear discs and bar-driven secular evolution in nearby galaxies of the MUSE TIMER project”
D. A. Gadotti, A. Bittner, J. Falcón-Barroso, J. Mendez-Abreu, et al.
A&A (2020), 643: A14

“The GIST pipeline: A multi-purpose tool for the analysis and visualisation of (integral-field) spectroscopic data”
A. Bittner, J. Falcón-Barroso, B. Nedelchev, A. Dorta, D. A. Gadotti, M. Sarzi, A. Molaeinezhad, et al.
A&A (2019), 628: A117

“How do spiral arm contrasts relate to bars, disc breaks and other fundamental galaxy properties?”
A. Bittner, D. Gadotti, B. Elmegreen, E. Athanassoula, D. Elmegreen, A. Bosma, J. Munoz-Mateos
MNRAS (2017), 471: 1070

Co-authored Publications

“Diversity of nuclear star cluster formation mechanisms revealed by their star formation histories”
K. Fahrion, M. Lyubenova, G. van de Ven, ..., and A. Bittner amongst others
accepted for publication in A&A

“The kinematics of young and old stellar populations in nuclear rings of MUSE TIMER galaxies”
D. Rosado-Belza, J. Falcón-Barroso, J. H. Knapen, A. Bittner, et al.
A&A (2020), 644: A116

“Stellar populations across galaxy bars in the MUSE TIMER project”
J. Neumann, F. Fragkoudi, I. Perez, ..., and A. Bittner amongst others
A&A (2020), 637: A56

“The Fornax 3D project: Non-linear colour-metallicity relation of globular clusters”
K. Fahrion, M. Lyubenova, M. Hilker, ..., and A. Bittner amongst others
A&A (2020), 637: A27

“The Fornax 3D project: Globular clusters tracing kinematics and metallicities”
K. Fahrion, M. Lyubenova, M. Hilker, ..., and A. Bittner amongst others
A&A (2020), 637: A26

“The Fornax3D project: Tracing the assembly history of the cluster from the kinematic and line-strength maps”
E. Iodice, M. Sarzi, A. Bittner, L. Coccato, L. Costantin, E. M. Corsini, G. van de Ven, et al.
A&A (2019), 627: A136

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