Practical works (TP4)

Les TPIVb 2019-20 d’astrophysique commenceront le 18 février 2019 (Cubotron 6ieme étage, BSP607 à  9:30).

Pour participer à ce travaux, merci de contacter Frédéric Courbinet de s’inscrire sur IS-academia.

Les deux semestres de TP4 (travaux pratiques — practical works) prépare au travail de master. Durant le semestre d’automne, les TP se déroulent sur le site de l’EPFL (BSP = Cubotron), tandis que pendant le semestre de printemps, les TP sont donnés sur les sites de l’EPFL et de l’Observatoire de Sauverny (qui est le site principal du LASTRO).

TP4a: Semestre d’automne

Le but du premier semestre est d’introduire les outils informatiques utilisés en astrophysique (avec un très fort accent sur le Python, mais aussi SExtractor et bien sûr UNIX). Plusieurs exercices intéressants sont à faire sur des sujets variés qui proposent des sujets relativement complexes, mais dont les données sont rapides à traiter. Les sujets couvrent la préparation un diagramme Hertzsprung-Russell depuis les données bruts du CCD, peser un amas de galaxies, régresser une courbe de rotation d’une galaxie spirale et mesurer un signal de lentille gravitationnel faible à partir d’images profondes du VLT.

TP4b: Semestre d’été

Le travail du second semestre constiste à effectuer des projets individuels liés aux recherches du moment au LASTRO. Les projets ci-dessous ont été effectués lors de l’année académique 2017-2018 et seront remplacés par de nouveaux projets pour l’année 2019-2020. Ils donnent cependant un aperçu des de la gamme de sujets possibles au laboratoire d’astrophysique de l’EPFL.

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Projects for the 2019 Spring semester:

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Title: An imaging and photometric pipeline for the 60cm Telesto observatory in Sauverny.

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

Type of Project: TP4b

The observatory of Sauverny 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 fonction to produce mosaic of image in order to cover a very large field of view. Data are already acquired but, with spring time coming, new ones should be taken as part of this practical work.

Project flavour:: observations, data science

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

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TITLE: Improving Point Source Detection for Imaging Searches for Lensed Quasars

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

URL/References:

https://arxiv.org/abs/1411.5398

https://arxiv.org/abs/1602.02167

https://arxiv.org/abs/astro-ph/9704059

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Title: Simulating the star formation in galaxies with the code SWIFT

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

Type of Project: TP4b

Since ten years, the LASTRO study the formation and evolution of galaxies from a numerical point of
view, by simulating isolated galaxies or portion of the Universe. Those simulations relie 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.

Project flavour:: simulations, high performance computing

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

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Title: Distant galaxy clusters in the COSMOS survey an their >~1-10 Mpc scale environment.

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 millimeter 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.

URL/References:

-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/

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TITLE: Measuring the size of black holes’ accretion disks from Reverberation Mapping

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

Abstract: 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 in 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 to apply the existing techniques and to develop new methods to measure time-delays between distorted light-curves.

URL/References:

https://cosmograil.epfl.ch/

https://arxiv.org/abs/1711.11588

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TITLE: Stellar mass estimates for a volume limited sample of galaxies around the Virgo cluster

PROPOSED BY : Gianluca Castignani (postdoc) and Pascale Jablonka (faculty)

TYPE OF THE PROJECT: TP4b

PROJECT FLAVOR : modelisation, data science

ABSTRACT: 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 final 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 in estimating stellar masses for ~10,000 galaxies around Virgo, up to ~5 virial radii. Spectral energy distribution modeling will be performed using available multi-wavelength archival data and basic parallel programming techniques.

URL/REFERENCES:

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

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

http://www.iap.fr/magphys/

http://www.cfht.hawaii.edu/~arnouts/LEPHARE/lephare.html

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TITLE: Deconvolution of images for the next generation of cosmological imaging surveys

Proposed by:  PJablonka. (Faculty) and F. Courbin. (Faculty)

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

Project flavour: Image analysis technique – Computing techniques

Abstract: We enter an era of extragalactic research with 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 the Hubble Space Telescope ones. 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 improve further the treatment of the noise in the images, make it run efficient of sets of large images, and to make the code “user-friendly »

URL/References:

https://arxiv.org/abs/1601.05192

https://arxiv.org/abs/1602.02167

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TITLE: Assessing the reliability of current curve-shifting techniques for time-delay cosmology

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

Type of Project: TP4b

Project flavour: Data Science/Simulation

Abstract:

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. The state of the art method consists in 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 optimise rapidly a large data set.

URL/References:

https://cosmograil.epfl.ch/

– 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

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TITLE: BAO measurement and cosmological parameter constraints using eBOSS galaxies and voids

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

Type of Project: TP4b and Master/CSE project

Project flavour: Modelisation/Data Science/Simulation

Abstract:

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 consist 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

URL/References:

* http://www.sdss.org/surveys/eboss/

* https://arxiv.org/abs/1802.03990

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TITLE: Redshift estimation for SL2S groups of galaxies.

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

Type of Project: TP4b project

Project flavour: Observation

Abstract: 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 galaxies candidates to be part of ~8 groups using the Very Large Telescope (VLT). The goal of this project is contribute in the first step of the dynamical analysis which consist in estimate the redshift of each galaxy candidate identifying features in the spectra like emission and/or absorptions lines. This contribution will help us to performed a combined dynamical + strong lensing analysis to probe the dark matter density profiles of the groups.

URL/References:

https://arxiv.org/abs/1212.2624

https://arxiv.org/abs/1608.03687

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TITLE: Advanced data analysis of massive spectroscopic surveys of galaxies with eBOSS and DESI

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

Type of Project: TP4b / Master/CSE project

Project flavour: Instrumentation/Observation/Data Science

Abstract: 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 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.

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

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TITLE: Data mining of massive spectroscopic surveys of galaxies with SDSS BOSS and eBOSS: sky fibers

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

Type of Project: TP4b / Master/CSE project

Project flavour: Instrumentation/Observation/Data Science

Abstract: 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 on 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.

URL/References: 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

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TITLE: Data mining of massive spectroscopic surveys of galaxies with SDSS BOSS and eBOSS: double-spectra

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

Type of Project: TP4b / Master/CSE project

Project flavour: Instrumentation/Observation/Data Science

Abstract: 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 on 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.

URL/References: 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

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TITLE: Galaxy physics with combined eBOSS and DES data

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

Type of Project: Master/CSE project

Project flavour: Observation and connections to modeling

Abstract: 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.

URL/References: Here is one example of an earlier analysis with similar goals: https://arxiv.org/abs/0911.5347

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Projects for the 2018 Spring semester:

  • Homegeneity measurement with Emission Line Galaxies in the eBOSS survey (with Gorgoni, Raichoor & Kneib)

A fundamental assumption in cosmology, known as the Cosmological Principle, is that the Universe is isotropic and homogeneous on large scales. The validity of this assumption can now be tested with current data, especially the massive spectroscopic surveys, which map the 3D map distribution of galaxies. The SDSS/eBOSS/ELG (2016-2018) survey is the current largest spectroscopic survey at a redshift z~0.85, i.e. when the Universe was ~6.5 Gyrs old. This project proposes to test the assumption that the Universe is homogeneous at z~0.85 with the eBOSS/ELG data. It will use the same methodology as Laurent et al. (2016, https://arxiv.org/abs/1602.09010) and Ntelis et al. (2017, https://arxiv.org/abs/1702.02159), which demonstrated with the SDSS data that the Universe was indeed homogeneous at higher and lower redshifts, respectively.

  • http://www.sdss.org/surveys/eboss/
  • New model-free measurement of  the universe expansion (with Gorgoni, Raichoor & Kneib)Baryon Acoustic Oscillations (BAOs) provide a cosmological standard ruler with which to measure the expansion history of the Universe and probe the nature of dark energy. BAOs were produced in the early Universe by sound waves propagating in the primordial plasma, and have imprinted a characteristic scale in the clustering of matter. The result is an excess number of galaxies separated by a distance of about 150Mpc. This work proposes to study a new way of investigating the BAO feature, by looking at a new scale in the correlation function of galaxies called the “linear-point” (https://arxiv.org/abs/1703.01275). This “linear point” method is promising as it is insensitive to many assumptions made in the standard BAO scale measurement (non-linear gravity, redshift space distorsions and scale-dependent bias). It is also independent of the power spectrum of the primordial density fluctuations parameters. These properties make the “linear point” a very interesting and attractive tool for cosmology.
  • http://www.sdss.org/surveys/eboss/
  • Sloan data mining: searching for strong lensing systems in BOSS and eBOSS (with Schaefer, Raichoor & Kneib) –   Strong lensing happens when the path of the light coming from a background galaxy or quasar is distorted by a foreground massive and compact object. The project is to search for strong lensing systems in the ~2 millions galaxy and quasar spectra of the BOSS and eBOSS catalogs. Spectra are provided with PCA templates of galaxy or quasar automatically fitted by the BOSS pipeline. Strong lensing candidates are identified by looking for emission lines in the spectra not associated with the template, indicating the presence of an additional galaxy along the line of sight of the object. The goal is to 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.
  • http://www.sdss.org/surveys/eboss/

     

  • Morphologies et populations stellaires de galaxies d’amas (with Joseph, Jablonka & Courbin) 

Il s’agit d’analyser des images de galaxies autour d’amas à z~0.5 et de séparer les différentes  composantes stellaires: étoiles vieilles ou nouvellement formées. La méthode utilise les notions de sparsité des données astrophysique et décompose les distributions spectrales d’énergie des galaxies sur des bibliothèques choisies. Pour la première fois, la PSF des images sera prise en compte dans les calculs. Les résultats serviront à comprendre l’influence des environnements denses sur l’évolution des galaxies et en particulier comment la formation s’éteint.

Référence: https://arxiv.org/abs/1603.00473

  • Galaxy Simulation with a new HPC code (with Hausammann, Revaz & Jablonka)  Simulations have largely increased in accuracy during this last decade through some better subgrid models and numerical methods but are not optimized enough to deal with high resolution and large volume. The code SWIFT is emerging as the future of cosmological simulations due to its task based approach and deep optimization. While the code has been proved to be faster than its concurrents, it still miss some physical comparison. Therefore this project consists in simulating an isolated disk (with a mass comparable to the Milky Way) and comparing to the most famous cosmological code (such as GADGET and RAMSES). See https://arxiv.org/abs/1308.2669 for more informations.

Projects completed in 2017:

  • Using a Machine Learning tool for denoising galaxy images while preserving their shapes (with M. Gentile) – Amélie Tamone.

Future space cosmological surveys will measure the weak gravitational lensing effect of large scale structures on the image of distant galaxies, providing new clues on the nature of dark matter, dark energy, and on the content of the Universe. In practice, this requires to measure precisely the shape of billions of faint and small galaxies and will requires “image denoising”.  The work will consist in applying a denoising autoencoder (DA) to galaxy images with the objective of removing noise without altering the shapes of galaxies e.g. size  and ellipticity. An autoencoder is a specific type of Artificial Neural Network where the input and output layers are identical. The objective is to have the autoencoder learn how to build a new representation of the input data (the galaxy image) that has less noise while preserving the galaxy shape attributes. The DA will be applied to simulated galaxy images with noise of different levels and types (Gaussian, Poisson). The alteration of shapes before and after applying the DA will be assessed using a galaxy shape measurement tool.

  • Premières étoiles : optimisation de la détermination des paramètres stellaires (with  Jablonka & North) – Tobias Meier.

Il s’agit de mettre au point une méthode rapide (C + python) pour la détermination automatique des paramètres atmosphériques d’étoiles: température effective, gravité, vitesse de micro-turbulence, et métallicité. Cette méthode s’appuyera sur des méthodes de minimisation robustes, inclura des prises de décision automatiques et des accès web à des bases de données extérieures.

Le code sera testé sur des données réelles et servira au plus grand survey actuellement en cours d’étoiles extrêmement déficientes en métaux dans le halo de notre galaxie pour comprendre les premières étapes dans la formation des galaxies.

Exemple de code existant: http://www.aanda.org/articles/aa/pdf/2014/04/aa22430-13.pdf

  • The influence of collisions and merger on the stellar properties of dwarf galaxies(Revaz/Jablonka) – Elisabeth Wybo.

Accurately reproducing the observed stellar properties of dwarf spheroidal galaxies (dSphs),

the smallest and faintest galaxies in our universe, represents a challenging task for the standard cosmological model. The work proposed here will consist in understanding the impact on the stellar properties of dSphs (star formation history, metallicity distribution, metallicity gradient, stellar populations, rotation) of the interactions and collisions that dSphs may suffer during a Hubble time.

The study will consist in extracting dwarf galaxies formed in cosmological numerical simulations and make them collide, running idealised N-body simulations based on the chemo-dynamical-C/MPI-code GEAR (Revaz & Jablonka 2012, Revaz et al. 2016) which includes

a complete treatment of the baryonic physics (gas cooling, star formation, chemical enrichment, supernova feedback). The aim will be to explore the effect of parameters like the mass of the progenitors, the impact parameter and the relative velocity on the final properties of the dwarf galaxies. In this purpose, a set of python routines will be developed to allow for a comparison between the model predictions and the observations. The final goal will be to try to reproduce peculiar features observed in local group dwarf galaxies, like distinct stellar populations and metallicity gradients.

  • Sloan data mining: searching for strong lensing systems in BOSS and eBOSS (with Delubac & Kneib) – Elodie Savary.

Strong lensing happens when the path of the light coming from a background galaxy or quasar is distorted by a foreground massive and compact object. The project is to search for strong lensing systems in the ~2 millions galaxy and quasar spectra of the BOSS and eBOSS catalogs. Spectra are provided with PCA templates of galaxy or quasar automatically fitted by the BOSS pipeline. Strong lensing candidates are identified by looking for emission lines in the spectra not associated with the template, indicating the presence of an additional galaxy along the line of sight of the object. The goal is to 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.
http://www.sdss.org/surveys/eboss/
http://www.sdss.org/surveys/boss/

  • An automated inteligent detection of atypical quasar spectra for DESI (with Delubac & Kneib) – Romain Buchs.

Quasars are supermassive black holes living at the centre of galaxies. The Dark Energy Spectroscopic Instrument (DESI) will obtain 700’000 quasar spectra to map the Universe at redshift z>2.1 using a recent technique called the Lyman-alpha forest. The detection of atypical spectra including broad absorption line and damped lyman-alpha systems will be essential for cosmological analyses. The project is to exploit the large quasar spectra database from BOSS and eBOSS (~100’000 object using machine learning algorithm to setup an automatic finder for atypical quasars to be used for DESI.
http://desi.lbl.gov/
http://www.sdss.org/surveys/eboss/
http://www.sdss.org/surveys/boss/

  • Toile cosmique: Identification des filaments de galaxies (Ricciardelli, Jablonka & Revaz) – Clément Camus.

Il s’agit de tester et d’améliorer un algorithme d’identification de filaments, c’est à dire de galaxies corrélées spatialement en 3 dimensions, dans des champs dans lesquels nous avons les redshifts des systèmes. La méthode proposée s’appuie sur une technique de tesselation. Elle sera testée sur des simulations numériques et des données observées.

Code: http://www2.iap.fr/users/sousbie/web/html/indexd41d.html

Références:

http://adsabs.harvard.edu/abs/2011MNRAS.414..350S

http://adsabs.harvard.edu/abs/2011MNRAS.414..384S

https://arxiv.org/abs/1611.07045

  • H2 formation in galaxies (Revaz, Jablonka) – Aymeric Galan 
  • Documents et liens

Présentation de travaux pratiques par Prof. Meylan (pdf)

TP4 documents en ligne