Research :: PhD Topics for 2016 :: Galaxies

Topics under the thematic line The assembly history of galaxies resolved in space and timeavailable for the 2016 Call (12 PhD Topics):

  • 2016/317 - Probing Galaxy Evolution and Feedback Using Giant Gaseous Structures Associated with Powerful Radio-Loud Galaxies at High Redshift
  • 2016/318 -Testing the impact of kappa-distributed electron energies in quasar nebulae
  • 2016/319 - The dust and molecular content of normal primeval galaxies
  • 2016/320 - Investigating Structure Formation around Massive Galaxies through a Radio- Infrared Synergy
  • 2016/321 - The First Radio Galaxies in the Universe
  • 2016/322 - Objective criteria for the selection of the most distant radio galaxies
  • 2016/323 - The quest for the origins of Early-Type Galaxies
  • 2016/324 - Diffuse ionized gas and Lyman continuum photon escape in spiral galaxies
  • 2016/325 - Chasing Gaia Galaxy Clusters
  • 2016/326 - Spatial distribution of α-elements in CALIFA galaxies
  • 2016/327 - The importance of star-formation, black-hole accretion and other physical mechanisms into the Far-IR – radio correlation
  • 2016/328 - Unveiling the early Universe with the James Webb Space Telescope

For further details, please see the listing below for abstracts and advisors. Prospective candidates are welcome to contact directly the proposers of the topics for inquiries and further details.

2016/317 - Probing Galaxy Evolution and Feedback Using Giant Gaseous Structures Associated with Powerful Radio-Loud Galaxies at High Redshift

Advisors: Andrew Humphrey (IA U.Porto)

Powerful radio-loud active galaxies at high redshifts (z>2) are often associated with ~100 kpc scale nebulae that emit strongly in the line of Lyman-alpha. Moreover, many also show associated extended Lyman-alpha absorbers that are at least as large. The global properties of these gaseous structures are, at present, poorly understood. This project aims for a substantially improved characterisation of the Lyman-alpha emitting and absorbing gases, making use of new observations from state of the art observing facilities.

University: Porto

2016/318 - Testing the impact of kappa-distributed electron energies in quasar nebulae

Advisors: Andrew Humphrey (IA U.Porto)

A long-held assumption is that the electron energies in extrasolar warm ionized nebulae (HII regions, quasar-ionized nebulae, etc.) follow the Maxwell-Boltzmann (MB) distribution. However, direct measurements from a number of plasmas within our Solar system have revealed the presence non-equilibrium electron energy distributions, which have been characterised by the ‘kappa-distribution’ (KD). Armed with the MAPPINGS 1e photoionization code – the first to include kappa-distributed 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. Moreover, diagnostics of gas physical conditions with the least (or no) dependence on the value of kappa, or on the choice of KD of MB cases, will be developed. The possible impact on BPT diagrams (and similar), and on the spectral classification of emission line galaxies, will also be elucidated.

University: Porto

2016/319 - The dust and molecular content of normal primeval galaxies

Advisors: Hugo Messias (IA U.Lisboa), José M. Afonso (IA U.Lisboa & DF/FCUL)

In these recent years, we have witnessed a significant increase in the numbers of galaxies observed at an epoch when the Universe was extremely young, less than one tenth of its current age. This was possible due to the advent of deep space- and ground-based near-infrared (nIR) surveys. However, the characterisation of these galaxies faces large uncertainties given the fact that, at those distances, the nIR analysis targets the rest-frame UV alone, where only the hottest stars emit and dust obscuration is critical. In order to finally understand the true nature of these primeval sources, long-wavelength (mm-to-cm) observations are required. State-of-the-art facilities working in this spectral range now provide continuum and spectral information all at once, enabling the study of dust and gas contents, and dynamics in galaxies. This project focuses on thousands of normal galaxies found in the early Universe, addressing dust particle formation and growth, and chemical enrichment.

University: Lisboa

2016/320 - Investigating Structure Formation around Massive Galaxies through a Radio- Infrared Synergy

Advisors: José M. Afonso (IA U.Lisboa & DF/FCUL), Hugo Messias (IA U.Lisboa)

One of the greatest challenges facing observational cosmology is understanding the formation of large scale structure in the Universe. Hierarchical models for structure formation developed over the last few years, achieving the high degree of predictive success that they do, are however still unconstrained, in particular in helping to understand how the light (galaxies) traces the underlying (dark) matter and how this relation evolves over time. We will address this problem by performing a systematic study of the evolution of the densest regions of the Universe, as traced by the most massive galaxies and their environments, improving our understanding of how the most massive regions of the Universe form and evolve. This will only be possible by using data from a deep mid- infrared wide-field survey, the Spitzer Extragalactic Representative Volume Survey (SERVS), which has recently finished the data processing for a 1400 hour-long observational programme capable of finally overcoming long-standing observational limitations.

University: Lisboa

2016/321 - The First Radio Galaxies in the Universe

Advisors: José M. Afonso (IA U.Lisboa & DF/FCUL), Hugo Messias (IA U.Lisboa), Israel Matute (IA U.Lisboa)

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 undeterminated. 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.

University: Lisboa

2016/322 - Objective criteria for the selection of the most distant radio galaxies

Advisors: José M. Afonso (IA U.Lisboa & DF/FCUL), Hugo Messias (IA U.Lisboa), Israel Matute (IA U.Lisboa)

Studies of the high redshift Universe have relied on a number of methods to identify increasingly distant and, consequently, younger galaxies. Radio selection has been reborn as one of the most promising methods, as powerful radio AGN can currently be detected at radio frequencies at essentially any redshift. Using the next generation of deep radio surveys, these searches are now being pushed to new sensitivity levels, to find radio AGN at the highest distances and at the earliest formation stages, presumably well within the Epoch of Reionization. Using multiwavelength data (x- rays, optical, infrared and millimetre, besides the radio itself), the faint radio population has started to be characterized, contributing not only to a better understanding of the radio sky, but, even more interestingly, selecting elusive, more extreme sources that can only be understood with the upcoming full capabilities of the Atacama Large Millimetre Array. These studies are exciting, but can only currently be performed over very small areas. Extending such studies to virtually the whole sky is a prime objective of the next generation of radio surveys, and this project aims to play a pivotal role in such expansion.

The host institution for this project is involved (with co-Is and co-PIs) in two of the most ambitious projects in the pre-Square Kilometre Array era, surveys that will map the entire sky at 1.4GHz at microJansky levels. The Evolutionary Map of the Universe (EMU), to be performed with the Australia Square Kilometre Array Pathfinder, will cover the sky at declinations below 30deg, while the Westerbork Observations of the Deep APERTIF Northern-Sky (WODAN) will cover the northern regions. Both surveys should start producing data by 2017. Together, the EMU and WODAN surveys will produce a unique dataset that, together with other multiwavelength data being obtained or soon to be obtained, will be able to find the most extreme and unique radio galaxies, including the first-generation of powerful AGN in the Universe, in the Epoch of Reionization. This project proposes to (a) establish a set of objective criteria for the selection of very high redshift radio galaxies; (b) find and analyse candidates for very high redshift radio galaxies, including the preparation of follow-up observations of particularly interesting candidates with ALMA; (c) play an active role in the optimization of the next generation of ultra-deep whole-sky radio surveys, the EMU and WODAN projects, in order to explore more efficiently the highest redshift Universe.

University: Lisboa

2016/323 - The quest for the origins of Early-Type Galaxies

Advisors: Fernando Buitrago (IA U.Lisboa), José Afonso (IA U.Lisboa & DF/FCUL), Polychronis Papaderos (IA U.Porto)

Massive Early-Type Galaxies (ETGs) have changed dramatically their structural and spectrophotometric properties (star formation rates, sizes, morphologies, kinematics, etc.) from the high redshift Universe (z=2-3) to the present day. According to our current paradigm of galaxy formation and evolution, and given the ubiquity of galaxy merging near and far, the formation of present-day massive ETGs must be associated with continuous bombardment of low-mass satellites, which results in the gradual build-up of the outskirts of massive ETGs. This project will quantitatively investigate this process, both by using deep photometry and spectroscopy. The student will take advantage of the expertise hosted by IA’s Thematic Line “The assembly history of galaxies resolved in space and time” both in Lisbon and Porto to thoroughly explore for the first time how the structural, spectrophotometric and kinematic evolution of massive ETGs over the past few Gyr. It will also explore the crucial link between ETG evolution and the number density/colors/star formation rates of low-mass companions in their vicinity.

University: Lisboa

2016/324 - Diffuse ionized gas and Lyman continuum photon escape in spiral galaxies

Advisors: Polychronis Papaderos (IA U.Porto), Jean Michel Gomes (IA U.Porto)

Diffuse ionized gas (DIG) is an ubiquitous component in the disk and halo of spiral galaxies. The excitation mechanisms and ionization conditions of the DIG pose a long-standing enigma. The prevailing picture though is that the DIG originates from Lyman continuum (LyC) photons escaping from sites of ongoing star formation and their reprocessing into nebular emission on scales of ~1 kpc away from HII regions. The mechanisms facilitating escape and transport of LyC radiation are unclear, it is yet likely that a key role is played by injection of energy and momentum by stellar winds and SNe into a porous multi- phase interstellar medium. Various lines of evidence indicate that the diffuse, low-surface brightness DIG contributes ~20-50% of the total Hα emission in late-type galaxies, a fact that may introduce a substantial observational bias on estimates of star formation rates in high-redshift galaxies where DIG emission is barely detectable. This project aims at a detailed investigation of the physical properties of the DIG in a representative sample of nearby face-on spiral galaxies using narrow/broad-band imaging, spatially resolved integral field spectroscopy from the CALIFA survey (http://califa.caha.es) and advanced spectral synthesis models. A central question to be addressed concerns the relation between the fractional contribution of the DIG to the total Hα luminosity and the star formation history and structural properties of spiral galaxies.

University: Porto

2016/325 - Chasing Gaia Galaxy Clusters

Advisors: Sónia Antón (IA U.Lisboa), Catarina Lobo (IA U.Porto)

Galaxy clusters are the largest gravitationally bound structures of the Universe and are undoubtedly among the best astrophysical laboratories one can think of. Up to now, the only all-sky optical catalogue of clusters is the Abell catalogue, that mainly assembles the richest systems. Gaia (ESA cornerstone satellite) is the first optical photometric and spectro-photometric all-sky survey mission from space. Even if this astrometric mission has been designed to make the most accurate 3-D map of our Galaxy, the detection and discovery of many new objects besides stars is foreseen, as every object down to magnitude V~20 will be observed about 70 times over the 5-year mission period. In particular, it will detect well above 106 extragalactic objects, mainly unresolved galaxies and AGNs, with elliptical/bulge morphology. Gaia offers an unique opportunity in a long time to search for nearby clusters in the optical all over the sky and perform studies on their dominant galaxy population, namely the brightest cluster galaxy (BCG). The mission is operating routinely since mid-2014, and the first catalogue will be released by mid-2016, whereas the following one ~6 months later, a perfect timing to get the most of the new data. The final catalogue will be published one year after the end of the mission (2019), and intermediate catalogues in-between. A main objective of this project is to adapt current algorithms to detect galaxy clusters in Gaia data. The sample will then be cross-correlated with known all-sky multi-wavelength catalogs (NVSS, 2MASS, ROSAT, etc) in order to thoroughly investigate brightest central galaxies (BCGs) with an unprecedentedly large sample, and address key issues on their evolution. This work will certainly contribute to pave the way for several finer applications using EUCLID data (launch expected in 2020), a mission in which the IA also participates.

University: Porto

2016/326 - Spatial distribution of α-elements in CALIFA galaxies

Advisors: Jean Michel Gomes (IA U.Porto), Polychronis Papaderos (IA U.Porto)

A long-standing puzzle in extragalactic research concerns the anomalous abundances of so-called α-elements (e.g., C, N, O, Ne, Si, S, Mg and Na) relative to iron (Fe) in early-type galaxies (ETGs). These elements are generally enhanced relative to Fe by an “enhancement-ratio” [E/Fe] correlating with the stellar velocity dispersion (hence, the total stellar mass) of an ETG. The dominant physical mechanism responsible for this trend is still unknown yet fundamental to the understanding of the chemo-dynamical evolution of ETGs across their entire mass spectrum.

Three main scenarios have been proposed for these discrepancies: a) a varying star-formation rate efficiency in massive ETGs, b) a non-universality of the stellar initial mass function (IMF) in the sense of a “top-heavy” IMF and c) selective loss of elements due to galactic winds. All these scenarios attempt reproducing the observed [E/Fe] ratios as essentially the result of chemical enrichment by Type II and Type Ia Supernovae, each acting on different timescales, and with a relative frequency closely linked to the galaxy star formation history.

Studies of stellar populations in galaxies have dramatically advanced in the last decade. Instead of using a few hand-picked Lick indices, fluxes and integral colours to constrain the star formation- and chemical enrichment history of galaxies, modern spectral synthesis codes and computing facilities now permit a detailed modelling of the full optical spectrum of a galaxy in a pixel-by-pixel approach. These modelling tools and the availability of high-quality data sets (e.g., 2dF, 6dF, SDSS and GAMA surveys) offer a promising avenue for a better understanding on how galaxies form and evolve through time. However, all spectral synthesis studies carried out over the past decade on the basis of these single-fibre spectroscopic surveys lack the necessary spatial coverage and resolution to study the radial trends in galaxies (cf. Gomes et al. 2016b&c).

Only recently spatially-resolved data from Integral Field Spectroscopy (IFS) has become available, permitting the study of radial abundance patterns of α-elements in galaxies with unprecedented detail. An innovative aspect of this PhD research project is the use of IFS data for ~600 local Hubble-type galaxies from The Calar Alto Legacy Integral Field spectroscopy Area survey (CALIFA – http://califa.caha.es) to determine the 2D α-element distribution in a spatially resolved pattern. This observational input will be combined with the derived Star-Formation Histories and structural properties of ETGs from CALIFA with the goal of developing new evolutionary diagnostics for ETGs and shedding light into the origin of the α-element enhancement in these systems.

University: Porto

2016/327 - The importance of star-formation, black-hole accretion and other physical mechanisms into the Far-IR – radio correlation

Advisors: Cirino Pappalardo (IA U.Lisboa), Israel Matute (IA U.Lisboa), José Afonso (IA U.Lisboa)

One of the most challenging astrophysical questions is to determine the star-formation history of the Universe. In this context, one of the most interesting and intriguing correlations is the one found between the radio and the far infrared (FIR) emission in galaxies. Although both emissions can be related to the current star formation, the apparent direct connection between them is far from obvious. The main problem arises from the fact that the radio emission can be produced in different ways (e.g. radio emission from an AGN) and the FIR is not always strictly related to star formation processes (e.g. also stars in their late evolutionary stages can produce a radiation field able to heat the dust). Despite all these different emission mechanisms, the relation is surprisingly tight and universal for galaxies over several orders or magnitude in mass and luminosity. Nowadays, a complete theoretical understanding for the tightness of this correlation is still missing. An invaluable insight into the physics of this correlation could be gain by considering a statistical large sample of galaxies were we can precisely measure both the radio continuum and FIR properties. With modern radio continuum surveys and with the large FIR database produced by the Herschel Space Observatory during its lifetime, such samples can be built and explored. The goal of this project is to investigate the influence of the average dust mass and dust temperature into the FIR-radio correlation as well as the significance of the emission of the central super massive black-hole (SMBH) in Active Galactic Nuclei (AGN). With this objective in mind, the student will build a large sample of galaxies with high quality data both in the radio and at FIR wavelengths. With such sample we will investigate the scatter in the FIR-radio correlation as a function of different dust mass bins, and as a function of redshift. Taking advantage of the multi-wavelength coverage that will be available for a large fraction of the sample, we will be able to investigate the physical differences between different dust heating sources and provide an indication on the reliability of the FIR-radio correlation when the available data doe snot properly sample the peak of dust emission. The data sample and results to be obtained during the thesis time frame will be crucial for future studies of star-forming galaxies. In particular the analysis to be conducted will be very important to understand the faint radio population that will be uncovered by the future radio continuum survey, such as the Square Kilometer Array pathfinder and precursor radio continuum surveys from ASKAP (Norris et al. 2011), LOFAR (Rottgering et al. 2011), MeerKAT (Jarvis 2012), and the Jansky Very Large Array (JVLA).

University: Lisboa

2016/328 - Unveiling the early Universe with the James Webb Space Telescope

Advisors: Silvio Lorenzoni (IA U.Lisboa), José Afonso (IA U.Lisboa)

In recent years, our knowledge of the high redshift Universe (z>6) has greatly improved, allowing the discovery of hundreds of galaxies up to z∼10, about half a billion years after the Big Bang. However, many questions are still unanswered, or only partially answered: what reionized the Universe? How were the first galaxies different from today’s? Did the star formation rate increased steadily up to its peak, and if not, why? Are the theoretical models of early formation and assembly of galaxies in agreement with the observations? Is the drop in observed Lyman-α emission beyond z∼6 intrinsic to galaxies, or is it caused by a largely neutral IGM? Is reionization a smooth or a patchy process?

The James Webb Space Telescope (JWST), due to be launched in October 2018, will provide invaluable information to address these questions, unveiling an even more distant part of the Universe (up to z∼15), but also allowing for a more complete view of the full population of galaxies at 6<z<10 and the detection of very faint galaxies at 3<z<6 which will be crucial to improve our knowledge in mass assembly and galaxy clustering in the early stages of the Universe.

The goal of this project is to train a PhD student in the methods of observation of the high redshift Universe and its main scientific topics, using both ground- and space-based data (already available), in order to be ready to take full advantage of JWST’s outstanding capabilities from the very beginning.

The main scientific topics will be:

- discovery of the first galaxies ever formed (z∼15).

- determination of the UV luminosity function and its evolution through cosmic time, both extending the ones we already have (for z<8) to fainter magnitudes (fundamental to determine star forming galaxies’ role in reionization) and obtaining new ones at even higher redshifts, understanding the star formation history of the Universe.

- spectroscopic confirmation, characterisation and analysis of high redshift galaxies.

- identification and characterization of close physical pairs or groups of galaxies at z>3 to determine the contribution of merging processes to the early mass assembly of galaxies.

University: Lisboa