- 2019/336 - The build-up of metals within galaxies with cosmic time
- 2019/337 – Self-consistent spectral modeling of quasars and its implication to the mass assembly history galaxies
- 2019/338 – Spatial distribution of α-elements in galaxies
- 2019/339 - Dark matter and metal poor stars in Ultra Faint Dwarfs
- 2019/340 - Investigating Structure Formation around Massive Galaxies through a Radio-Infrared Synergy
- 2019/341 - The First Radio Galaxies in the Universe
- 2019/342 - Fitting galaxies with MANGA
- 2019/343 - Spectro Photometric Analysis of MOONS Galaxy Evolution Legacy
- 2019/344 – Reconstruction of the mass assembly history of Active Galactic Nuclei with FADO
- 2019/345 - Studying extended gas associated with distant AGN using MUSE observations of extended Lyman-alpha emission
- 2019/346 – Diffuse ionized gas and Lyman continuum photon escape in spiral galaxies
- 2019/347 – Uncovering the mass assembly history of late-type galaxies in different environments with IFS data
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.
2019/336 - The build-up of metals within galaxies with cosmic time
Advisors: Jarle Brinchamnn (IA U.Porto)
Abstract: With the MUSE instrument on the VLT we are producing the deepest spectroscopic observations of the Universe with an unprecedented sensitivity and spatial resolution. In this project the student will develop a method to combine the data from MUSE with spectra from HST and in the future the Euclid satellite. With this in hand he/she will carry out the largest survey of how metals are distributed in galaxies as a function of cosmic time – constraining the physics of galaxy formation.
2019/337 – Self-consistent spectral modeling of quasars and its implication to the mass assembly history galaxies
Advisors: Jean Michel Gomes (IA U.Porto), Luis Vega Neme (IATE – OAC, Córdoba)
Abstract: Quasars are thought to be hosted by a supermassive black hole (SMBH) capable of producing an energy release due to matter accretion that easily outshines the whole host galaxy, leading to this featureless quasi-stellar object appearance the most massive and luminous galaxies in the early Universe. Over the past few years, it was discovered several quasars even at early times (redshift ~7). We propose a new spectral fitting code for fitting the UV-optical range in a self- consistent manner to be applied to quasars. This code will include a standard accretion disk model (Shakura & Sunyaev 1973) and a more realistic UV-optical model from, e.g., Kubota & Done (2018). We will tie these prescriptions together in order to energetically reproduce both the observed continuum plus emission- lines in quasars considering internal attenuation. This new fitting code will be publicly available and additionally applied to ~500 000 quasars from the SDSS DR15. We will produce a full database catalog for the astronomical community. This is a preparatory work for the MOONS spectrograph in which IA co- leads also it will add value when the modules for fitting quasars are incorporated in the population synthesis code FADO (Gomes & Papaderos 2017).
This project provides an excellent combination of astrophysical theory with observations, and it will lead to valuable expertise on the field of spectral synthesis and AGN phenomenon. Several publications will support the future career of the student. Preferable computing languages are Fortran, Python or IDL.
2019/338 – Spatial distribution of α-elements in galaxies
Abstract: 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 e.g. Gomes et al. 2016b&c).
Only recently spatially-resolved data from Integral Field Spectroscopy (IFS) has become available, permit- ting the study of radial abundance patterns of α-elements in galaxies with unprecedented detail. An inno- vative aspect of this PhD research project is the use both the IFS data for 667 local Hubble-type galaxies from The Calar Alto Legacy Integral Field spectroscopy Area survey (CALIFA – http://califa.caha.es) andMapping Nearby Galaxies at APO (MaNGA) survey (last release ~5k galaxies) 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 devel- oping new evolutionary diagnostics for ETGs and shedding light into the origin of the α-element enhance- ment in these systems.
2019/339 - Dark matter and metal poor stars in Ultra Faint Dwarfs
Advisors: Jarle Brinchamnn (IA U.Porto)
Abstract: Ultra-faint dwarfs are the most dark matter dominated objects we know – in some there is 1000 times more dark matter than baryonic. They are also the faintest and lowest mass galaxies we know with the entire galaxy less bright than a single star. These facts combine to make these systems excellent places to look for dark matter and to explore the effect of stellar feedback on galaxy evolution in low mass dark matter halos. To that end I am carrying out a survey of 100hrs with MUSE on the VLT to study the make-up of these ultra-faint satellites and constrain their metal enrichment history and dark matter content. The student will be involved in both of these aspects, with a particular focus on the metal enrichment history and stellar make-up of the ultra-faint dwarfs.
2019/340 - Investigating Structure Formation around Massive Galaxies through a Radio-Infrared Synergy
Advisors: José Afonso (DF/FCUL & IA U.Lisboa), Hugo Messias (Joint ALMA Observatory)
Abstract: 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 extended Spitzer Extragalactic Representative Volume Survey (SERVS), now including over 2700 hours of deep mid-infrared observations and capable of finally overcoming long-standing observational limitations.
2019/341 - The First Radio Galaxies in the Universe
Abstract: 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.
Type: This topic may correspond to a mixed fellowship with up to 1 year abroad.
2019/342 - Fitting galaxies with MANGA
Advisors: Ciro Papparlardo (IA U.Lisboa)
Abstract: One of the biggest open questions of Astrophysics is to establish a comprehensive picture of galaxies evolution. This is a complicated task, and despite the huge effort of scientists, large uncertainties related to the interpretation of the observations are still present, together with oversimplification in the models. One of the largest projects in the world tackling the issues related to the evolution of galaxies is the Sloan Digital Sky Survey (SDSS, Eisenstein et al.2011). It started twenty years ago and recently, in December 2018, the data taken by the fourth phase of SDSS have been released, Data Release Fifteen (DR15). The main difference with respect to the previous releases is that for the first time the database contains also the spectra of about 5000 galaxies obtained with the revolutionary instrument MANGA, the integral field spectrograph unit mounted on the 2.5 m optical telescope at Apache Point Observatory (New Mexico). This is a unique database, where instead of a spectrum collecting the light from the entire galaxies, as it was for the previous releases, 17 different ’integral field unit’ (IFU) extract simultaneously different spectra from the same regions of the sky. The possibility to place the different IFU at small distances allows detailed studies of the chemical composition, the kinematic, and the stellar age distribution of each galaxies investigating its internal structure.
As already mentioned, previous SDSS releases extracted from each observed galaxy a single spectrum, sampling mostly the centre of target galaxies. Despite these limitations, the SDSS data have been crucial to discover the fundamental relations between the stellar mass of a galaxy and its star formation rate, the so-called ’main sequence’, and the link between the stellar mass and the mass of heavy elements available in a galaxy, also known as ’mass-metallicity relation’.
This project proposes a deep analysis of the ’MANGA’ extended data-set in DR15, in order to investigate the physical processes that determine the galaxy scaling relations mentioned above, considering also the internal structure of the galaxies, available for these 5000 objects. For such a purpose, different spectral fitting tools will be compared and mutually validated, to clarify possible bias and strengthen the conclusions of the work. In particular, the student will use a specific software developed within the IA (Porto node), FADO, which is an optimised spectral fitting algorithm able to disentangle the stellar and gaseous emission of medium resolution optical spectra, and for this reason suitable for the goal of the project.
2019/343 - Spectro Photometric Analysis of MOONS Galaxy Evolution Legacy
Advisors: Ciro Papparlardo (IA U.Lisboa)
Abstract: Galaxy evolution is one of the biggest open question in Astrophysics but, despite the huge effort of scientists, there are still large uncertainties in the observations and oversimplification in the models. The reasons for the lack of a comprehensive theory in this field, are twofold:
- on one side instrumental limitations have biased our knowledge of galaxies towards most luminous object, preventing then a statistical significance at higher distances. Most of the studies are focused on nearby galaxies, missing then the most relevant part of the Universe history.
- on the other side there are strong theoretical limitations to the informations that we can extract from the light that we observe. Most of the effort up to now focused on two distinct parallel paths: photometric approaches develop fitting methods to extract physical parameters from sparse data points sampling the galaxy spectral energy distribution; the other approach is spectroscopy, and in this direction different spectral fitting tools have become the more and more efficient in recovering reliable results from the analysis of moderate resolution spectra.
The combined action of these two factors hampered big step forwards in this field of Astrophysics. It is clear that in order to have really relevant improvement we must tackle the problem in two ways:
- build instruments able to observe galaxies at larger distances, where the Universe was younger;
- improve the efficiency of both spectroscopic and photometric approach.
The instrumental gap mentioned above will soon be challenged by the MOONS (Multi-Object Optical and Near-infrared Spectrograph) instrument, a spectrograph that will be mounted on the Very Large Telescope (VLT) in Chile and will trigger a step forward in our knowledge of the assembly history of galaxies. The Institute of Astronomy and Space Sciences (IA) in Portugal is strongly involved in the project, being part of the scientific consortium, and participating to the construction of the instrument.
This project proposes to participate to MOONS through two complementary actions, strongly related with the expertises grown within the IA:
- investigate the galaxies spectra provided by the MOONS consortium through specific spectral fitting tools developed within the IA: i.e. FADO.
- build a photometric data set for the same galaxies observed with MOONS in order to investigate the properties of their Spectral Energy dsitribution (SED).
2019/344 – Reconstruction of the mass assembly history of Active Galactic Nuclei with FADO
Abstract: 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-consist- ently reproduce the main nebular characteristics of star-forming (SF) galaxies. This unique con-cept 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 super-massive 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:
- 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;
- Disentangle the star-forming component from the non-thermal AGN component and estimate the AGN luminosity emission in various spectral bands;
- 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;
- 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.
2019/345 - Studying extended gas associated with distant AGN using MUSE observations of extended Lyman-alpha emission
Advisors: Andrew Humphrey (IA U.Porto)
Abstract: This project will use VLT MUSE observations of extended Lyman-alpha emitting gas to study the co-evolution between the interstellar medium, star formation activity and the outputs of the active nucleus itself, thereby obtaining new pieces of the jigsaw puzzle that is our understanding of the formation and evolution of galaxies. The student will process and analyse archival VLT MUSE integral field spectroscopy observations of high-redshift radio galaxies and/or quasars, and study in detail the morphological, kinematic, ionization and chemical enrichment properties of extended (>10 kpc) Lyman-alpha emitting gas halos associated with the active galaxies. Observational information will be compared with models from the literature, and the ionization and chemical enrichment properties will be modeled using state of the art ionization modeling codes. Important new information on cluster (or protocluster) environment will also be obtained.
2019/346 – Diffuse ionized gas and Lyman continuum photon escape in spiral galaxies
Abstract: Diffuse ionized gas (DIG) is an ubiquitous component in the disk and halo of late-type galaxies (LTGs). 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 image processing techniques, spatially resolved integral field spectroscopy 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 LTGs.
2019/347 – Uncovering the mass assembly history of late-type galaxies in different environments with IFS data
Abstract: Galaxy clusters and groups are gravitationally bound structures that contain hundreds to thousands of galaxies bonded by gravity and embedded in a dense medium. They are excellent laboratories for studying the impact of the environment on the mass assembly history of their member galaxies. As such, there is abundant literature on how several processes such as ram pressure stripping, strangulation, tidal effects and merging can lead to significant changes in the secular evolution of galaxies. A combination of these mechanisms is expected to explain some of the morphological transformations of galaxies and the quenching of their star formation activity. Pinning down the dominant mechanism responsible for these evolutionary trends is one of the key-questions in extragalactic astronomy, that is likely linked to the process of infall of galaxies into clusters occurring within the framework of the hierarchical growth of large scale structure. The cold gas medium of galaxies is expected to be tightly connected with their capacity to keep forming stars and is extremely sensitive, in small timescales, to the mechanisms mentioned above. It should thus provide indications of the relevant processes acting on galaxies located at different cluster centric radii and in the field. Recent studies that show abnormally strong and frequent cold gas interstellar medium interactions signatures in the late-type galaxies in merging clusters seem to indicate that this phase of the galactic content carries the signatures of the physical processes occurring in different environments.
This project proposes a systematic study of 2D integral field spectroscopy (IFS) from the MaNGA (Mapping Nearby Galaxies at APO) survey combined with HI and molecular gas ancillary data for a large sample of galaxies inhabiting different environments. In order to reconstruct the spatially resolved star-formation and chemical enrichment history of galaxies in distinct environments, the student will make use of the FADO population synthesis code and Porto3D post-processing IFS analysis pipeline.
This project provides an excellent combination of astrophysical theory with observations, and it will lead to valuable expertise in the field of spectral synthesis and environment of galaxies, i.e. cluster as compared to field galaxies. Several publications will support the future career of the student. Previous knowledge on one of the following computing languages is desirable: ESO-MIDAS script language, Fortran 77/2008+, C, C++, IDL or Python.