Project examples – University of Copenhagen

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Dark Cosmology Centre > Students - bachelor's, master's and PhD > Project examples

PROJECT EXAMPLES

The following are project examples that can be customized at the bachelor's or master's levels. We encourage students to discuss and suggest projects to supervising faculty (faculty, senior research staff and postdocs here >>).

Stellar magnetic activity and its effect on exoplanets and their detection

The magnetic activity of cool stars in the form of flares, winds and coronal mass ejections have a direct impact on surrounding planets. This activity varies with the mass, age and rotation rate of the star and can be hazardous for the creation and development of life and is therefore of potential importance for habitability. If you are interested in the effects stars have on planets, and also on the detection of exoplanets, here are few topics that might be for you:

 1) Hunting for stellar coronal mass ejections



Coronal mass ejections (CMEs) are explosive events that occur basically daily on the Sun. It is thought that these events play a crucial role in the angular momentum loss of late-type stars, and also shape the environment in which planets form and live. So, far only a handful of CMEs have been detected in other stars than the Sun. In this project you will hunt for CMEs in data sets, which have not previously been analysed for CMEs. This project can be fine-tuned to fit either Bachelor or Master thesis time frame. Project requires some programming skills and basic knowledge of IRAF.



 2) Stellar Superflares



Kepler satellite discovered thousands of superflares on hundreds of solar-like stars. These flares, which are 10-100 times more powerful than the largest solar flares, mainly occur on stars that are more magnetically active than the Sun. Surprisingly, they can also occur at Sun-like activity levels, implying that the Sun could be capable of producing them too. In this project you will analyse high-resolution spectra of a Kepler superflare star investigating its detailed properties and studying how solar-like the star really is. This project can be used for Bachelor and Master thesis topic. Project requires some programming skills, mainly for plotting.



3) Detection of small exoplanets



The detection of exoplanets using any method is prone to confusion due to the intrinsic variability of the host star. In this project you will apply recently developed methods to study the detectability of small planets, and especially the case of alpha Centauri B planet, which could be a spurious detection due to stellar activity. Mainly a Bachelor thesis topic, but other related projects can be also given for Master thesis. Project requires some programming skills.




Supervisors: Heidi Korhonen & Anja C. Andersen

Galaxies, Quasars and Transients at high redshifts

I am overall interested in exploring the distant Universe (lookback times of 8-13 Gyr) through a range of methods such as quasar absorption line systems, emission line galaxies or cosmic explosions like gamma-ray bursts. Of particular interest to me is the chemical evolution of the interstellar matter in galaxies, i.e. the gradual increase in the amount of heavy elements formed by previous generations of starts. If you are interested in similar questions you are welcome to come by and discuss possible master thesis projects.

Supervisor: Johan Fynbo

Galaxy halos in emission and absorption 

Absorption lines seen in Quasar or Gamma-ray burst afterglow spectra can be used to explore the high-redshift universe through metal-absorption lines that arise in randomly intersected intervening galaxies. By combining absorption-line studies with the characteristics of the galaxies that give rise to them, we can examine galaxy outskirts and halos. The gas comes from out-flowing galactic winds, filamentary accretion, or in tidal debris, and cannot be detected in emission. Various projects are offered to explore the connection between metal-enriched galaxy halos with the host galaxies in order to get a coherent picture of galaxy formation in emission and absorption.

Supervisor: Lise Christensen

Extreme starbursts in young galaxies

Finding star-forming galaxies in the distant universe has primarily relied on deep images and colour selection to identify the galaxies. Recent observations have found a population of galaxies that have more unusual characteristics in the form of extremely strong emission lines. Such lines may arise in the first star-burst event in the galaxies. This project will use data from the Very Large Telescope to locate these types of galaxies and explore their nature and their role in building up galaxies with cosmic time.

Supervisor: Lise Christensen

Origin of cosmic dust

Cosmic dust is the dominant form of solid matter in the universe and radiates half of the non-primordial radiation in the universe, is vital for forming virtually all molecules, stars and planets. But we don't know where it comes from or what its detailed properties are. It should not exist in the early universe, but it does.




1) We investigate the origin of cosmic dust by:
- Looking at the dust masses in very metal-poor galaxies in the local universe to determine how dust forms in environments like the early universe.
- The effects of formation and destruction of dust in nearby supernova remnants
- The existing project on dust extinction curves is still valid.

2) X-rays from Gamma-ray burst explosions (more or less the same project as before), involving:
- X-raying the gas surrounding the burst to determine what it is and the binarity and mass of the progenitor star. Includes computational modelling of the dynamic ionisation of the gas surrounding the burst
- Looking for signatures of rotation or line emission from the massive star explosions in the X-ray afterglows of GRBs

3) Intensity Interferometry (II) is a method to achieve extremely high resolution imaging through the earth's atmosphere using quantum optics:
- Look at the practicality of II using large, mass-produced optics

4) Spectral variability in quasars and other AGN provides information on the structure of the regions around AGN, this is called reverberation mapping. Currently, the code used to extract specific information is sub-optimal:
- Code better reverberation mapping software to maximise information extraction from variability information.

Supervisor: Darach Watson

Impossibly Early Galaxies: Are they Real?

A key disconnect between theory and observation of evolving galaxies at high redshift is that we observe luminous things (a fraction of the baryons) in a galaxy, yet the theory of galactic assembly makes predictions nearly exclusively about the dark matter which dominates the mass in the galactic halo.  At low redshift, there are scaling relations between the halo mass and observable quantities such as stellar mass.  Using these relations produces a consistent result out to z~4-5, but at z>5 yields a shocking result: it appears that massive galaxies assemble so early that they exist even before gravity has brought their components together!  This, of course, is impossible...  
So, what's gone wrong?  Discovering that some exotic new force that assembles galaxies more quickly is required would be a tantalizing conclusion, but is hardly the only possible answer.  A few different projects would be possible looking at different explanations that would be less exotic, with the goal of either finding a good solution or ruling out everything more mundane.  Given the effort necessary to examine one of these carefully, each would be a different possible project.

1) High-redshift galaxies are studied nearly exclusively by fitting a small number of measurements encompassing broad spectral bands with templates derived from lower-redshift galaxies.  Thus, we make the strong assumption that high-redshift galaxies look very similar to low-redshift galaxies.  So far, this assumption has proven valid when later observations have been able to measure high-resolution spectra, but at some point this assumption must break down.  We would investigate how different the physics of galactic dynamics and star formation would need to be at high-redshift in order for their masses to be overestimated enough via this process of photometric template fititng that correcting them resolves the problem.

2) If we have indeed overestimated the masses, a likely candidate would be that the stellar initial mass function (when a batch of stars is made, its distribution of masses) has changed at high redshift.  There would need to be a greater fraction of high-mass stars at z~6-10 than at z<4.  Several long period, high-redshift surveys offer the possibility of testing this possibility directly by searching for superluminous superovae at very high redshift.  This is one of the few problems in astronomy that is slightly helped by the high redshift, as despite these supernovae being fainter, relativistic time dilation means that the variability takes place over about a year.

3) Another approach to this seeming disconnect between observation and theory would be that of "abundance matching", in which we simply assert that both theoretical halo mass distributions and all observed galaxy properties are correct, and then use that to match galaxies with halos.  For impossibly early galaxies, this would mean that at redshift 0-4 the stellar mass is approximately a constant fraction of the halo mass, and at higher redshifts a greater and greater fraction of the mass of a halo ends up in stars.  Our goal would be to detail the parameters of this model and to determine whether we can naturally turn it into a more complete theory or whether such a theory would require its own set of exotic astrophysics.

4) A completely independent possibly approach comes from using the thermal Sunyaev-Zel'dovich effect to look more directly for galaxy halos in observations of the cosmic microwave background.  This is sensitive to the entire number of electrons in a galaxy rather than just to those in stars, and gives us a nearly direct measurement of the halo mass.  It is also one of the few problems in astronomy that gets easier at high redshift.  If theoretical models of galaxy assembly are correct, high-redshift galaxies will not be massive enough for us to find a signal.  However, if these "impossibly early galaxies" are indeed as massive as we have inferred from template fitting, targeted followup observations of ~10 high-redshift, high-mass galaxies should produce a composite signal.  A small overlap between high-resolution CMB observations and ultradeep galaxy surveys already exists and might be enough to perform this test.  If not, we would then propose for targeted high-resolution CMB observations in order to find out the answer.

 Supervisor: Charles Steinhardt

Why are Galaxies All So Similar?

Many different ways of observing galaxies at a variety of stages in their evolution reach the same surprising conclusion: evolving galaxies all look remarkably similar.  For example, almost all star-forming galaxies lie on a tight relation between redshift, the existing stellar mass, and their new star-formation rate.  Thus, we can predict the star-formation rate quite well from time and mass alone, without having to know anything about the age of the galaxy, its environment, its morphology, or any of the other things that might seem like they should be important.  Two projects that could arise from research in this area might be:

1) This similarly should prompt us to try and build a model in which galaxies share a common evolutionary history, and the various stages that we observe (star formation, quasar accretion, eventual turnoff, etc.) are all included.  In this case, the problem suffers from a wealth of data -- there is so much information out there about so many different states of galaxy evolution that it's difficult to make sense of it all.  Thus, the initial stages of this investigation will likely involve taking some time to become familiar with the enormous literature on what we've learned in the past few decades about how galaxies grow.

2) Even if we cannot figure out exactly what that common history is, we might be able to use pieces of it to build indicators of galactic maturity.  If we can do so successfully, it would allow new insights into several of the most important questions in galaxy evolution.  For example, we know that today there are tight relationships between properties of central supermassive black holes and of their host galaxies.  We would like to see how these relationships evolve over time, but of course we only ever get to see any one galaxy at one time in its history.  Studies often try and investigate this using observations of galaxies at different redshifts, but often at the same stage of their evolution.  If we had a good maturity indicator, it would provide a much better way of determining whether supermassive black holes and their host galaxies truly co-evolve or whether a more complex behavior has been masked by observational selection.

Supervisor: Charles Steinhardt

Spectroscopy of the most distant galaxy clusters in the Universe

Galaxy clusters are the largest bound structures in the Universe, and are believed to form in its highest density peaks, which is also where the first galaxies form. In the local Universe, galaxies in clusters are observed to be older and more evolved than galaxies in lower density regions.
Old evolved galaxies in clusters have been spectroscopically confirmed out to a redshift of 1.3. Beyond that redshift, spectroscopic confirmation of evolved galaxies have to be done in the Near Infrared, as the spectral features are redshifted out of the optical.
Several examples of "proto-cluster" candidates are known out to redshifts of z~5, but spectroscopic confirmation old evolved galaxies in these have yet to been achieved. Finding such galaxies is essential to testing our hypothesis that galaxies form first in dense environment.
Using recently obtained Near Infrared spectroscopic observations from the Hubble Space Telescope and the Japanese 8m Subaru telescope, the project aims at, for the first time, spectroscopically confirm old evolved galaxies in proto clusters at a record redshift of z~2, and investigate if these have different properties, than galaxies in lower density environments at similar redshifts.

Supervisor: Sune Toft

The build up of galaxies over the last 12 billion years

CANDLES: the largest deep survey of the structure and morphology of galaxies over the last 12 Billion years, is currently being undertaken with the Hubble Space Telescope. Large amounts of exquisite data is publicly available, which allows us to study the evolution of the structure of galaxies from their formation in the early universe to the present. The project goal is to retrieve this data, and fit the surface brightness distributions of galaxies, to build a catalog of galaxy shapes and sizes as a function of cosmic time. This catalog will be a treasure trove for studying how galaxies build up their mass and shape from their formation to today.  

Supervisor: Sune Toft

Estimating metallicity build-up in quasars

Quasars are powered by supermassive black holes and reside in centers of distant galaxies. The quasar phenomenon is thought to be an early evolutionary phase of galaxies during which stars are forming and the black hole becomes active as it accretes matter.
The aim of this project is to trace the chemical evolution in quasars using the FeII and MgII (alpha-element) abundances. FeII is thought to be produced in stars that take about 1 Gyr to mature to the point where significant iron is produced, while MgII is thought to be produced by supernovae with shortlived progenitors. As a result we can use the FeII/MgII line ratio as a cosmic clock to trace the build-up of chemical elements in these interesting, early evolutionary stages of galaxies. We will look at how this ratio changes with age of the universe by measuring these line ratios in spectra of quasars from the Sloan Digital Sky Survey. We will discuss the implications for our understanding of galaxy evolution.
Light to moderate programming is involved.
(15 - 60 ETCS)

Supervisor: Marianne Vestergaard

How well does the FeII/MgII ratio reflect the metallicities in quasars?

Quasars are powered by supermassive black holes and reside in centers of distant galaxies. The quasar phenomenon is thought to be an early evolutionary phase of galaxies during which stars are forming and the black hole becomes active as it accretes matter.
FeII is thought to be produced in stars that take about 1 Gyr to mature to the point where significant iron is produced, while MgII is thought to be produced by supernovae with shortlived progenitors. As a result we can use the FeII/MgII line ratio as a cosmic clock to trace the build-up of chemical elements in these interesting, early evolutionary stages of galaxies.
The aim of this project is to trace the chemical evolution in quasars using the FeII and MgII (alpha-element) abundances and compare this ratio with other metallicity indicators, especially various ratios of the Nitrogen, Carbon, and Helium lines, in order to test how good a metallicity measure the FeII/MgII ratio really is. We will look at how the FeII/MgII ratio changes with age of the universe by measuring these line ratios in spectra of quasars from the Sloan Digital Sky Survey. In addition, we will measure the Nitrogen, Carbon, and Helium lines in order to perform the above-mentioned test of the FeII/MgII line ratio. We will also compare and calibrate this line ratio measure to the alternative metallicity measures.  The results will be discussed in the light of current galaxy evolutionary scenarios and the implications for cosmology and our understanding of galaxy evolution will also be addressed.
This project will involve some programming  in order to allow a timely conclusion of the project. (15 - 60 ETCS)

Supervisor: Marianne Vestergaard
Determining black hole masses of high redshift quasars

Astronomers are rutinely using spectral measurements to estimate the mass of the central supermassive black hole in order to study black hole growth across cosmic history. Specifically, measures of the gas velocities and the distances of the gas from the black hole are estimated and the virial theorem is applied. However, for some type sources and lower quality data the line width measure FWHM is more uncertain. We will take a closer look at this method by expanding the ways in which the gas velocities are measured in order to investigate if there are more robust gas velocity measures that can be used.
In addition, we will investigate the implications of taking into account the effects of radiation pressure on the gas clouds that are used for the black hole mass estimates using published relationships.
This project involves some programming. (15 - 60 ETCS)

Supervisor: Marianne Vestergaard
Host galaxies of quasars and active galactic nuclei and relationship to the active black hole

We will use archival images in the optical and infrared of nearby active galactic nuclei and more distant quasars to detect and study their host galaxies. The aim is first to characterize best possible the stellar populations. Thereafter the project can engage in analysis of whether the stellar ages relate to morphological signatures of a potential recent merger or galaxy interaction. Other options are to relate the stellar properties extracted from the imaging with information extracted from spectroscopy so to test how well those two methods trace one another. One option is also to compare the galaxy and stellar properties with estimates of the black hole mass using our own measurements based on spectral analysis. The length of the project determines the amount of data that we'll look at and the depth and scope of the discussion. (15 - 60 ETCS)

Supervisor: Marianne Vestergaard
Estimating the mass of actively accreting black holes in nearby and distant active galactic nuclei and quasars and studing the black hole mass relationship with quasar properties

Quasars are powered by supermassive black holes and reside in centers of distant galaxies. We will use spectroscopic data from the Sloan Digital Sky Survey to estimate the mass of the central supermassive black hole that powers active galactic nuclei and quasars. We will extract spectral parameters that characterize the quasar properties (governed by the black hole accretion physics and physics of the central gaseous region) and study how these properties vary with black hole mass. One option is to investigate ways to improve on the black hole mass estimates. We can complement our spectroscopic study with SDSS and HST imaging and also study how quasar properties or black hole mass relates to the host galaxy properties.
The length of the project determines the amount and type of data that we'll look at and the depth and scope of the discussion (15 - 60 ETCS).

Supervisor: Marianne Vestergaard

Measure a fundamental property of dark matter

We don’t know which particle is the dark matter, but we want to try to measure its scattering cross section. By looking at X-ray emitting gas in galaxy clusters, we can extract a property of the dark matter particles called the “velocity anisotropy”. If this turns out to be different from zero, then the scattering cross section of the dark matter particle cannot be big.

Requirements, computational and analytical skills.


Supervisor:
Steen H. Hansen

A new way to measure the accelerated expansion?

Dark Energy is believed to accelerate the expansion of the Universe. However, the acceleration is almost always measured using supernovae. We want to invent a new method, which does not use “luminosity”, but instead uses “a yard-stick on the sky”. The technique is being developed at DARK these years, and includes finding huge pancakes on the sky.

Requirements, computational and analytical skills.

Supervisor: Steen H. Hansen

Physical parametrization of cosmic dust extinction laws

Cosmic dust is ubiquitous in the Universe and distorts our view of distant objects. For example, the interpretation of the light curves of high-redshift supernovae used to infer the existence of dark energy critically depends on correction for dimming by dust. The standard 'extinction law' is based on observations of stars in the Milky Way and is purely empirical. This project aims to derive a new parametrization of the extinction law based on (1) devising a new physical parametrization of the Milky Way extinction law and (2) extending the law to other galaxies and higher redshift. The new law will be used to address the nature of the famous 2175 Å feature and the consequences for what we can infer from dark energy based on distant supernovae.

Selection bias in academic positions (and other areas)

There are very few female lecturers and professors at NBI and in the natural or technical sciences in general. This is despite a recruiting pool of about 30 % women at the PhD level. The dramatic decrease in female scientists as a function of seniority is known as the 'leaking pipeline'. The effect is sometimes attributed to a combination of women's lack of competitiveness and personal choice as they get kids and prioritize differently. However, a recent study (Watson, Andersen & Hjorth, Nature 436, 174, 2005) shows exactly the same effect occurring over just a few months resulting from small biases in a series of selections of applicants for the European Young Investigator Awards. The purpose of this project is to create a physical model capturing the main effects of a multidimensional set of skills required for selection, a suitable dispersion in these, small selection biases leading to a leaking pipeline. Armed with this model one can address the causes of gender bias in academia, business, and government.

Physical properties of galaxies hosting gamma-ray bursts

Gamma-ray bursts occur in violently star-forming galaxies, generally at high redshift. Such galaxies can be used to map the star formation in the universe and the fundamental routes to galaxy formation and build-up. This project aims to exploit a huge data set of GRB host galaxies gathered in Copenhagen, the most comprehensive and statistically available worldwide. Scientific questions that can be addressed are: What is the redshift distribution of GRBs and how does this relate to the star formation history of the universe? What is the fraction of obscured star formation in the universe? What is the relation between GRB host galaxies and other populations of high-redshift galaxies such as Lyman-alpha emitters and Lyman break galaxies? What are the ages and dust content of individual galaxies?

Supervisors: Jens Hjorth, Johan Fynbo, Darach Watson & Daniele Malesani

Dark energy equation of state, dark matter distribution, and galaxies at the end of the dark ages as probed by massive clusters of galaxies

Massive clusters of galaxies at intermediate redshifts act as gravitational lenses of background galaxies. The locations of the multiply imaged arcs depend on the dark-matter distribution in the cluster and the cosmological parameters, notably the matter and dark-energy density parameters. Ideally, an extremely deep Hubble Space Telescope image of the most spectacular cluster lens can constrain both at unprecedented accuracy. The project will involve modeling of HST and Chandra X-ray observatory, and VLT/X-shooter data on massive clusters.

Supervisors: Jens Hjorth & Darach Watson

Bibliometrics and other quantitative measures of scientific quality: caveats and new ideas

Quantifying scientific productivity (quality, quantity, impact, etc.) is becoming more and more important. A relatively new academic discipline "scienometrics" is gaining momentum while politicians and science administrators are implementing various measures supposed to be 'simple' and operation, e.g., for distributing funding. This project aims to study current ideas in the field and will address the issue from both the scienometrics point of view and the administrator point of view. The purpose of the project is to help define useful criteria and measures and at the same time help scientists define their 'bottom line'.

Supervisors:
Jens Hjorth & Darach Watson

 

X-raying massive stars

Gamma-ray bursts are the explosive deaths of very massive stars. Because they are so incredibly bright, they are an important tool in understanding the history of star-formation, especially in the very early universe and to probe the dust, gas and dynamics in the galaxies in which they occur. But apart from knowing that GRBs come from stripped massive stars, we don't know much else about them: why and where do they form, what makes a star explode so violently? X-rays are highly penetrating, which makes them the only way we have to see into the extreme conditions close to the burst. The high-resolution data now exist to try to analyse the medium surrounding GRBs, which should allow us to understand their circumstellar environments, potentially constraining the progenitor star's age, mass, binarity and environment.

Supervisor: Darach Watson