Here you may find information on the fellows of the PhD::SPACE Program that have selected a topic on the thematic line on The assembly history of galaxies resolved in space and time.
2019/B004 Fellow: Abhishek Chougule (ongoing)
PhD Topic (2019/344): Reconstruction of the mass assembly history of Active Galactic Nuclei with FADO
Fitting Analysis using differential evolution Optimization (FADO) is a conceptually novel, publicly available spectral population synthesis (PS) code (www.spectralsynthesis.org), which employs for the first time genetic optimization and artificial intelligence to identify the star-formation and chemical evolution history (SFH and CEH, respectively) that self-consistently reproduce the main nebular characteristics of star-forming (SF) galaxies. This unique concept allows us to alleviate and even overcome, degeneracies in spectral synthesis studies, thereby opening new avenues to the investigation of galaxy formation and evolution.
However, a large fraction of emission-line galaxies hosts an Active Galactic Nucleus (AGN) powered by accretion of matter onto a central supermassive black hole of several million solar masses. Depending on our viewing angle to the galaxy nucleus and its surrounding obscuring torus, the strong non-stellar radiation from the AGN can provide an important fraction, or even outshine, the spectral continuum of the underlying galaxy host. Even a low-to-moderate (~20%) contribution of the AGN to the optical continuum emission of a galaxy can strongly bias conclusions drawn from state-of-the-art purely-stellar PS codes, as demonstrated in Cardoso, Gomes & Papaderos (2016,2017).
The work tasks and main objectives of this PhD thesis are to use FADO in order to:
1 - Quantify its accuracy with benchmark tests in retrieving the SFH & CEH in the presence of an AGN. Additionally, compare the results from FADO with those from purely stellar codes (e.g., STARLIGHT, STECKMAP, ULySS, FIREFLY). In this task, the student will make use of fictitious datasets created with the REBETIKO evolutionary synthesis code under the presence of an AGN;
2 - Disentangle the star-forming component from the non-thermal AGN component and estimate the AGN luminosity emission in various spectral bands;
3 - Test distinct recipes in modeling the spectral energy distribution of the AGN, like the inclusion of multi-component continuum (e.g., Ferland et al. 2017 - Big Blue Bump and distinct power-law slopes in the X-ray, UV and optical). The student will make use of the FADO AGN module;
4 - fit galaxy spectra data sets from SDSS & GAMA surveys as well as Integral Field Spectroscopy data from MUSE, MEGARA, MaNGA to investigate the SFH & CEH of galaxies hosting an AGN.
This project provides an excellent combination of astrophysical theory with observations, and it will lead to valuable expertise and several publications that will support the future career of the student. Preferable computing languages are Fortran, IDL and/or Python.
Starting date: 2019/10/01
2019/B021 Fellow: Rodrigo Carvajal (ongoing)
Advisors: José Afonso (IA-U.Lisboa), Israel Matute (IA-U.Lisboa), Hugo Messias (Joint ALMA Observatory)
PhD Topic (2019/341): The First radio galaxies in the Universe
Recent observations of the highest redshift quasars and radio galaxies pinpoint the early growth of supermassive black holes (SMBH) that trigger the formation of active galactic nuclei (AGNs) at redshifts greater than 7. It is anticipated that radio emission can be detected from such early AGN, although its characteristics are still quite indeterminate. The importance of such detection, however, is extremely high. It will: (a) provide us with a lighthouse that reveals the physics of the first accretion episodes to the first SMBHs in the Universe; (b) allow the direct study of the neutral gas throughout the Epoch of Reionisation itself with the next generation of radio telescopes, through the observation and study of the HI 21cm forest against such early AGN; (c) allow us to trace the early growth of Large Scale Structure in the Universe. After decades of laborious work, trying to understand the deepest radio observations, the conditions are now finally right to develop a project that can make us understand where are the “first radio galaxies” and how to find them with upcoming radio telescopes.
Starting date: 2019/12/18
2017/B019 Fellow: Sandy G. Morais (ongoing)
PhD Topic (2017/332c): Integral field observations and ionization modeling of extended emission line halos in high redshift galaxies
Using the MAPPINGS 1e photoionization code – the first to include kappa-distributed (KD) electron energies – an extensive exploration of photoionization model parameter space will be conducted, to ascertain the generalized impact of KD election energies on quasar / AGN line spectra, and how this impact depends on various model parameters (e.g., density, metallicity, kappa, ionization parameter, ionizing spectral energy distribution). Observational tests for the presence of KD in photoionized nebulae will be developed.
In addition, the student will study feedback activity in high-z radio-loud AGN using integral field spectroscopic observations from MUSE. At the time of writing there are MUSE IFU observations of more than 80 AGN at z>3 in the VLT data archive, many of which remain unpublished. This second component of the project aims to reach a global overview of the morphological, kinematic, ionization and feedback properties of extended Ly-alpha halos of powerful AGN at z>3, by pulling together all the archival MUSE IFU observations into a single, in-depth analysis. Making use of existing radio and infrared data, the student will also study the multi-wavelength properties of the sample, to study the co-evolution between the interstellar medium, star formation activity and the outputs of the active nucleus itself. The relatively large sample size will allow the student to look with greater precision for the existence of trends and correlations between observable properties, and to reach more representative conclusions.
Starting date: 2017/10/01
2015/B010 Fellow: (cancelled in 2017)
PhD Topic (2015/311): Exploring the Universe with the largest emission-line surveys: from the first galaxies to the peak and decline of the star formation history of the Universe
What are the physical drivers of galaxy formation and evolution? How much (and why) did galaxies like our own change across cosmic time? When, how and through which physical mechanisms are galaxies “quenched”? Why were galaxies in the distant Universe so efficient at producing new stars? What were the roles of “nature” (stellar mass) and “nurture” (environment) in the past, how did they change with cosmic time and is there a connection between those and the declining star formation activity? Is our current view of how galaxies form and evolve correct? When and how were the first galaxies and stars formed?
In order to make progress, the student will explore and conduct unique, large >10 deg^2 narrow- band surveys that have yielded 1000s of galaxies (similar to the Milky Way), selected in the same way across the last ~13 billion years (with WIRCam/CFHT and WFCAM/UKIRT) with Hα and Lyα, including a unique double blind survey which targets both lines (Hα and Lyα) simultaneously at z=2.23 over large areas. Currently almost all high redshift studies rely on the Lyα emission line to survey, study and understand the distant Universe (z>2-3), as it is often the only feature available to spectroscopically confirm/study such galaxies. However, the escape fraction of Lyα (fescape) is highly uncertain at z>2, and much is unknown about what Lyα actually traces. How much are we missing by relying on it? How biased is our current view of the very high redshift, almost completely based on Lyα? Can we finally calibrate and understand Lyα and Lyα emitters.
The samples will be ideal to study the metallicities, dust extinction, clustering, radio-loud fractions and evolution of “typical” star-forming galaxies all the way to z~7-9 (including the possibility to use J-PAS data), and to study the role of nature and nurture at z~1-2 (with PI VIMOS observations, but also by exploring the 128 night LEGA-C VIMOS observations on the VLT). By using observations that have already been conducted (e.g. MOSFIRE and DEIMOS/Keck, FMOS/Subaru, VIMOS/VLT and new data from radio surveys, e.g. EMU), the student will be able to gain unprecedentedly detailed information on a large sample of galaxies which will then be explored with MOONS (part of the data were already used to develop the MOONS science case). The results from the project will provide some of the strongest tests/constraints to the most sophisticated models of galaxy formation and evolution (e.g. EAGLE, Illustris), but the student will also be encouraged, towards the end of the PhD, to model and interpret the observations. The results will also be fully compared and contrasted to the best surveys at z~0 and to other very complimentary surveys. Several detailed follow-up studies are foreseen, particularly with X-SHOOTER, MOSFIRE and other instruments.
Starting date: 2015/10/01
2014/B004 Fellow: Íris P. Breda (completed)
PhD Topic (2014/307): The nature and formation history of pseudo-bulges in galaxies
The featureless appearance of bulges in Hubble-type galaxies has for decades sustained the view that these high-surface brightness spheroidal components are largely “simple” in terms of their assembly history, formed on a short timescale early on, and having experienced little evolution over the past several Gyr. However, our early understanding of bulges as essentially scaled ellipticals has undergone a substantial revision over the last years. It is now recognized that central luminosity components that closely resemble classical bulges can also form over much longer timescales through disk instabilities and ensuing star forming activity at the centers of galaxies. The nature and formation history of these “pseudo-bulges” is enigmatic and of considerable relevance to our understanding of the structural and spectrophotometric evolution of galaxies in general.
This PhD project aims at a spatially resolved investigation of the star formation- and chemical enrichment history of pseudo-bulges. A unique aspect of its methodology is the combined application of surface photometry and spectral population synthesis to a large sample of galaxies from the Calar Alto Legacy Integral Field spectroscopy Area survey (http://califa.caha.es) with the goal of conclusively addressing the star formation history (SFH) and the chemical abundance patterns of pseudo-bulges. One of the central questions to be investigated is whether pseudo-bulges form in a quasi-continuous manner over several Gyrs of galactic evolution and their SFH can be parametrized through a simple functional form involving integral or structural properties of their host galaxy (e.g., total stellar mass; central surface brightness and exponential scale length of the underlying disk). Additionally, this project will include a comparative study of pseudo-bulges and classical bulges with the goal of the identification of new empirical discriminators between them and yield robust observational constraints to theoretical models of pseudo-bulge formation and evolution.
Starting date: 2014/11/01
2014/B003 Fellow: Ana S. P. Afonso (completed)
PhD Topic (2014/302): The KMOS/VLT revolution: rotation curves, metallicities, dust extinction and galaxy formation and evolution with hundreds of galaxies at 0.8 < z < 2.23 vs z~0
What are the physical drivers of galaxy formation and evolution? How much (and why) did galaxies like our own change across cosmic time (e.g. metallicities, dynamics)? When, how and through which physical mechanisms are galaxies “quenched”? In order to make progress, the student will explore our unique, large ~10 deg2 narrow-band surveys that have yielded 1000s of galaxies (similar to the Milky Way), selected in the same way across the last 11 billion years (with WIRCam/CFHT and WFCAM/UKIRT). These are ideal samples to study the metallicities, dust extinction and rotation curves of “typical” star-forming galaxies and how these have evolved from the peak of the star-formation history (z~2.5) till today. By using KMOS (observations already started and thus all data is guaranteed both as PI and as part of GTO collaboration), the student will be able to gain unprecedentedly detailed information on a large sample of galaxies. KMOS, with its 24 Integral Field Units (IFUs) allows to target up to 24 galaxies at the same time, obtaining an image and a near-infrared spectrum for each pixel. This is a unique opportunity to map the distribution and intensity of star formation, dynamics and metallicity on ~4 kpc scales and address (and to fully interpret them): (i) What is the fraction of primitive disks, spheroids and mergers? (ii) Is the distribution of star formation at high-z more centrally concentrated than comparably luminous/turbulent galaxies at z~0? and iii) Are chemical abundance gradients weaker or stronger than local spiral galaxies and do those change with time? Answers to these questions using our well selected samples will provide some of the strongest tests/constraints to the most sophisticated models of galaxy formation and evolution. By selection, all of the targets have known Hα fluxes and all are sufficiently bright so their resolved properties can be recovered and the survey efficiency will be >95% (GTO observations already yielded samples of ~400 galaxies). The results will be fully compared and contrasted to the best local IFU surveys (including artificially redshifting a variety of local galaxies and fully addressing biases and systematics), and will be interpreted using our unique 3D modelling capabilities developed at CAUP. Another unique aspect of this project is that there are significant over-densities in the very large samples of Hα emitters, and thus, with KMOS, the student will be able to confirm and characterise the high redshift structures, derive accurate metallicities, measure the mass-metallicity relation, obtain Balmer decrement extinctions and identify AGN for a sample of hundreds of Hα-selected galaxies and investigate if the environment plays a role in setting these galaxy properties.
Notes: Mixed fellowship (up to one year in Lancanster).
Starting date: 2014/11/01