2019 projects


Proposed by : Elodie Savary & Aymeric Galan (PhD students) and Frédéric Courbin (faculty)

Type of Project: TP4b

Project flavour: observations, data science

The Sauverny Observatory hosts a new 60cm telescope that needs to be characterized. The goal of this practical work is to design a full reduction pipeline to go from the raw data to aligned and combined frames and to carry out photometric measurements of all objects in the images. Eventually, the (python) pipeline should be automated and documented and also feature a function to produce a mosaic of images in order to cover a very large field of view.

Data is already acquired but, with spring time coming, new data should be taken as part of this practical work.

URL/References: https://actu.epfl.ch/news/inauguration-of-astrodome-and-new-telesto-telesc-2/




Proposed by: James Chan (Postdoc) and Frédéric Courbin (Faculty)

Type of Project: TP4b or Master/CSE project

Project flavour: Observation/Data Science

Strong gravitationally lensed quasars provide powerful means to study galaxy evolution and cosmology. We can study galaxy mass structures and substructures through the use of the positions, shapes, and fluxes of lensed images. We can also measure time delays between multiple images and determine the time-delay distance, which is sensitive to the Hubble constant.

Though they are rare but powerful, there have been several undertakings to look for them in various surveys. To find such lens systems, we apply an existing algorithm, CHITAH, in imaging surveys. The philosophy of CHITAH is to model the predicted image configuration using the singular isothermal ellipsoid (SIE) model. Identifying image positions correctly is the key to enhancing the performance of CHITAH.

This project will aim at improving CHITAH’s performance in terms of point source detection.






Proposed by : Loic Hausammann (PhD students) and Yves Revaz (faculty)

Type of Project: TP4b

Project flavour: simulations, high performance computing

Since ten years, researchers at LASTRO have studied the formation and evolution of galaxies from a numerical point of view, by simulating isolated galaxies or portions of the Universe.

Those simulations rely on complex astrophysics codes that include the dominant astrophysical processes: gravity, gas hydrodynamics
and cooling as well as recipes mimicking the formation of stars.

We are now in a process where we aim to migrate our hydro-dynamical code GEAR towards the new emerging code, SWIFT.
Among different ingredients, there is an urgent need to implement and test our recipe for the formation of stars.

The aim of this work will be to implement it in SWIFT and perform a series of tests to check its validity in different contexts, like isolated spiral or dwarf galaxies as well as in a cosmological context, by reproducing observed relations, like the Kennicutt-Schmidt law.

URL/References: http://swift.dur.ac.uk/


Proposed by : Gianluca Castignani (postdoc) and Pascale Jablonka (faculty)

Type of Project: TP4b

Project flavour: Modelisation, data science

Clusters of galaxies are the most massive gravitationally bound structures in the Universe. Hence they are optimal laboratories to study the coeval evolution of the galaxies and the cosmic web.

The aim of this project is to select and study a pilot sample of distant (z>0.7) galaxy clusters from  COSMOS, the largest extragalactic survey observed at nearly all wavelengths, from the radio to the X-rays.

To that purpose, existing catalogs of groups/clusters of galaxies will be used in combination with spectroscopic/photometric redshift catalogs of galaxies to select the clusters with the best spectroscopic coverage, up to several virial radii (i.e, ~10 Mpc). The cosmic filaments around these clusters will  be then characterized. The selected clusters will be followed up with milimeter facilities such as NOEMA and ALMA, to probe the impact of the large scale environments on processing galaxies’ molecular gas and understand how galaxies either fuel or quench their star formation activity.

This project requires coding, interest in data-mining and in multiwavelength analyses.


-Knobel et al. 2009 – http://adsabs.harvard.edu/abs/2009ApJ…697.1842K

-Knobel et al. 2012 – http://adsabs.harvard.edu/abs/2012ApJ…753..121K

-Diener et al. 2013 – http://adsabs.harvard.edu/abs/2013ApJ…765..109D

-Laigle et al. 2016 – http://adsabs.harvard.edu/abs/2016ApJS..224…24L

-COSMOS survey webpage: http://cosmos.astro.caltech.edu/



Proposed by:  Martin Millon (PhD) and James Chan (Postdoc) and Frédéric Courbin (Faculty)

Type of Project: TP4b or Master/CSE project

Project flavour: Observation/Data Science

Quasars accretion disks are known to be the most luminous objects in the Universe. They are powered by matter falling on a central black hole, releasing the gravitational energy in the form of radiations. As the high-energy photons emitted at the center travel across the disk, they trigger delayed emission at longer wavelength. Reverberation mapping consists of measuring the time-delays between different spectral bands, which correlate to the physical size of the accretion disks.

This project will imply to reduce the high-cadence data currently taken at the Euler 1.2m Swiss Telescope, and measure the time-delays between the different filters. This will involve applying the existing techniques and to develop new methods to measure time-delays between distorted light-curves.






Proposed by : Gianluca Castignani (postdoc) and Pascale Jablonka (faculty)

Type of project: TP4b

Project flavour : Modelisation, data science

Galaxies are distributed in a network called the cosmic web, which has a complex filamentary structure. The intersections of the cosmic filaments host cluster of galaxies, which are the most massive gravitationally bound structures in the Universe.

The ultimate goal of the project is to investigate the effect of filaments in processing molecular gas of galaxies as they fall into the Virgo cluster, which is the nearest cluster of galaxies and therefore an optimal laboratory for a detailed study.

Molecular gas is indeed associated with star forming regions in galaxies and is a powerful tool to study the star formation history of cluster galaxies. To achieve our final goal a mass-complete sample of galaxies is needed to estimate environmental properties such as local densities around Virgo. The project consists of estimating stellar masses for ~10,000 galaxies around Virgo, up to ~5 virial radii. Spectral energy distribution modelling will be performed using available multi-wavelength archival data and basic parallel programming techniques.


Kourkchi &  Tully (2017)  : http://adsabs.harvard.edu/abs/2017ApJ…843…16K

Kim et al. (2016) : http://adsabs.harvard.edu/abs/2016ApJ…833..207K





Proposed by:  Pascale Jablonka. (Faculty) and Frédéric Courbin. (Faculty)

Type of Project: TP4b and/or Master/CSE project

Project flavour: Image analysis technique – Computing techniques

We enter an era of extragalactic research which benefit from an unprecedented wealth of  multi-wavelength sky surveys. Even of good quality, the images that are gathered will never have a spatial resolution of comparable quality as those generated by the Hubble Space Telescope. However, these are mandatory to address some of the most crucial questions related to galaxy evolution.

Hence,  one solution is to apply deconvolution techniques to these ground-based images. This allows to reach an HST-like spatial resolution.  The Laboratory of Astrophysics has worked on an efficient code, FireDec, which has been tested already on ground based images of distant galaxy clusters. The image quality is improved by a factor 10. The goal of this project is to further improve the treatment of the noise in the images, make it run efficient sets of large images, and to make the code “user-friendly »






Proposed by:  Martin Millon (PhD), Vivien Bonvin (Postdoc) and Frédéric Courbin (Faculty)

Type of Project: TP4b

Project flavour: Data Science/Simulation

Time-delay cosmology with multiply imaged quasars is a promising probe to achieve a precise measurement of the Hubble constant. This technique is based on the measurement of time-delays between the different images created by a strong gravitational lens.

This state of the art method consists of monitoring lensed quasars during several years in order to produce long light curves. It is then possible to find the optimal time-shift between the different images. A precise and accurate measurement of the time-delays is critical as the errors propagate directly to final estimate of the Hubble constant.

This project aims to assess the reliability of the current curve-shifting technique, namely PyCS, on a simulated set of light curves. It will involve the use of parallel programming to rapidly optimise  a large data set.



– Liao et al. (2014) : https://arxiv.org/abs/1409.1254

– Bonvin et al. (2015) : https://arxiv.org/abs/1506.07524

– Suyu et al. (2016) : https://arxiv.org/abs/1607.00017

– Bonvin et al. (2017) : https://arxiv.org/abs/1607.01790



Proposed by:  Cheng Zhao (Postdoc) and Jean-Paul Kneib (Faculty)

Type of Project: TP4b and Master/CSE project

Project flavour: Modelisation/Data Science/Simulation

Baryon Acoustic Oscillation (BAO) is known as a standard ruler for measuring distances in the Universe, and is thus a probe for the cosmic evolution history, including the structure formation process dominated by dark matter, and the expansion of the Universe due to dark energy.

As a complementary type of tracers to galaxies, under-densities, represented by cosmic voids, also encode the BAO signature. In particular, the BAO scale constraint from a combined sample of LRGs and voids is tighter than that from LRGs alone. Therefore, we expect a better understanding of dark matter density and dark energy equation of state, with a complete 3D map of structures consisting of galaxies and voids.

To this end, we shall resolve voids from the eBOSS LRG/ELG/QSO samples, and study the auto- and cross-correlations. We aim at a joint constraint on BAO and cosmological parameters with multi-tracers.

Project-1: apply the combined void+galaxy BAO constraint to eBOSS data

Project-2: investigate the response of void BAO to systematic effects using mocks

Project-3: improve the method by including a void radius dependent weighting scheme






Proposed by:  Karina Rojas (Postdoc) and Frederic Courbin (Faculty)

Type of Project: TP4b project

Project flavour: Observation

Galaxy groups are important cosmological probes because they cover the intermediate mass spectrum between large elliptical galaxies and galaxy clusters providing information about the formation and evolution processes, the galactic content of dark matter haloes, and galaxy clustering.

The Strong Lensing Legacy Survey (SL2S) classified groups of galaxies by their strong lensing features. From this sample we observed galaxy candidates to be part of ~8 groups using the Very Large Telescope (VLT).

The goal of this project is contribute to the first step of the dynamical analysis which consists of estimating the redshift of each galaxy candidate, identifying features in the spectra like emission and/or absorptions lines. This contribution will help us to perform a combined dynamical + strong lensing analysis to probe the dark matter density profiles of the groups.






Proposed by:  A. Raichoor (Postdoc) and Jean-Paul Kneib (Faculty)

Type of Project: TP4b / Master/CSE project

Project flavour: Instrumentation/Observation/Data Science

One of the main cosmological probes is galaxy clustering (where both the Baryon Acoustic Oscillation (BAO) and the Redshift Space Distorsion (RSD) can be measured). The on-going SDSS/eBOSS program – currently the largest redshift survey program for cosmology – uses several tracers to measure the galaxy cluster, one of which are the Emission Line Galaxies (ELGs): ~250k star-forming galaxies at redshift ~0.85.

The goal of this project is to improve the sky subtraction in the pipeline estimating the redshift from the galaxy spectra. This step is critical for the ELG in SDSS/eBOSS project – and future projects such as DESI and 4MOST.

ELGs are star-forming galaxies whose redshift is mainly estimated thanks to the OII emission line. The sky emission lines are numerous and close to the OII line for the ELGs at redshift ~1. An incorrect subtraction of the sky introduces spurious features which confuses the redshift measurement. Furthermore, a clean sky subtraction would enable many science projects, as the search for supernovae in the galaxy spectra.

The goal is to use wavelet filtering or other advanced signal processing techniques.


eBOSS: http://adsabs.harvard.edu/abs/2016AJ….151…44D ; eBOSS/ELG: http://adsabs.harvard.edu/abs/2017MNRAS.471.3955R



Proposed by:  A. Raichoor (Postdoc) and Jean-Paul Kneib (Faculty)

Type of Project: TP4b / Master/CSE project

Project flavour: Instrumentation/Observation/Data Science

One of the main cosmological probes is galaxy clustering (where both the Baryon Acoustic Oscillation (BAO) and the Redshift Space Distorsion (RSD) can be measured). The SDSS is the leader in this type of experiment, with the BOSS (2008-2014, 1.5M spectra) and eBOSS (2014-2019, 1M spectra) programs.

The goal of this project is to look for high-redshift, faint objects, serendipitously observed with sky fibers. SDSS observations are done per plate, where 1,000 spectra are observed at the same time. On each observation, 80 fibers are allocated to sky measurement. Those sky regions are chosen where there is no object detection in the (rather shallow) SDSS imaging.

Current BOSS+eBOSS observations gather ~290k sky spectra. We thus expect that a non-negligible number of interesting faint objects being observed by those sky fibers. Such a detection algorithm will promise fruitful results on the DESI experiment (2021-2026, 35M spectra), which will be one order of magnitude larger.


BOSS: http://adsabs.harvard.edu/abs/2013AJ….145…10D 

eBOSS: http://adsabs.harvard.edu/abs/2016AJ….151…44D

BOSS/eBOSS spectral pipeline: http://adsabs.harvard.edu/abs/2012AJ….144..144B



Proposed by:  A. Raichoor (Postdoc) and Jean-Paul Kneib (Faculty)

Type of Project: TP4b / Master/CSE project

Project flavour: Instrumentation/Observation/Data Science

One of the main cosmological probes is galaxy clustering (where both the Baryon Acoustic Oscillation (BAO) and the Redshift Space Distorsion (RSD) can be measured). The SDSS is the leader in this type of experiment, with the BOSS (2008-2014, 1.5M spectra) and eBOSS (2014-2019, 1M spectra) programs.

The goal of this project is to look for superposed spectra observed with the BOSS/eBOSS programs. When an object is observed with a fiber, it can happen that a second object is in the same line of sight: the observed spectrum will thus be the addition of the two individual spectra.

If the second object is a star-forming galaxy, we can identify its redshift thanks to its emission lines, once the first object spectrum has been subtracted. We will conduct a systematic search for such emission lines in both galaxy and quasar samples and will use machine learning to obtain an automated classification of the lens candidates. That approach has various applications, as for instance looking for strong lensing events.


eBOSS: http://adsabs.harvard.edu/abs/2016AJ….151…44D BOSS/eBOSS spectral pipeline: http://adsabs.harvard.edu/abs/2012AJ….144..144B

strong lenses detection with double-spectra: http://adsabs.harvard.edu/abs/2012ApJ…744…41B



Proposed by:  J. Blazek (Postdoc) and J.-P. Kneib (Faculty)

Type of Project: Master/CSE project

Project flavour: Observation and connections to modeling

Understanding the properties of galaxies in their broader environment of large-scale structure is critical for the success of future cosmological analyses.

Combining the imaging data from the Dark Energy Survey (DES) and the spectroscopic information from the extended Baryon Oscillation Spectroscopic Survey (eBOSS) provides a unique opportunity to measure these properties.

There are several possible measurements that can be made with this combined data set. For example, we can examine correlations between the intrinsic shapes, luminosities, or colors of galaxies with the large-scale environment.

This project will involve assembling a combined galaxy catalog with information on distance (redshift) and other galaxy properties, adapting existing code to estimate the relevant correlations, and comparing the results to different theoretical predictions.