Institute of Astrophysics and Space Sciences

Funder

Organizational Unit

Publications

Calibration light sources for high accuracy photometry instruments

Publication . Pereira, Cédric P.; Abreu, Manuel Adler Sanchez de; Cabral, Alexandre

The exoplanet field is a scientific area that has been growing with exciting discoveries every year. More and more missions are emerging, and their complexity has been increasing. The latest instruments are designed to operate with extreme precision and stability, allowing the detection of smaller exoplanets and the characterisation of these other worlds. The fast evolution of this field constantly requires new technology and new strategies to meet its scientific objectives. Many of these missions use observation techniques based on the transit method, including photometers and spectrometers in their instruments. To successfully use these techniques, it is necessary to mitigate different sources of noise and systematic errors caused by effects such as pointing jitter, thermal and optomechanical stability, wavelength and photometric calibration, detector stability, among others. Therefore, it is essential to characterise the impact of these noise sources on the instruments and, consequently, on the critical calibration of scientific data. The characterisation of high accuracy photometers requires a calibration system in which the main component is a light source. The photometric stability of this light source, both in flux and spectra, must be better than the goal stability of the photometer to be tested. This thesis aims to research and develop an on-ground method capable of characterising and calibrating space-based instruments (with a particular focus on high accuracy photometers). It must be able to achieve state-of-the-art stability, allowing it to be integrated into the most modern exoplanet space missions, a truly impressive challenge when stabilisation levels of few parts-per-million (ppm) are required up to several hours of observation. The future ARIEL space mission is here considered as a reference, defining the top-level requirements of a high accuracy photometric instrument: a challenging target photometric precision/stability of 20 ppm to 100 ppm, over a 10 hour observation period.

2025-01-08Doctoral thesis

Open access

Towards the detection of the earliest supermassive black holes with the future radio and X-ray surveys

Publication . Amarantidis, Stergios; Afonso, José; Matute, Israel; Messias, Hugo

One of the fundamental topics in extragalactic astronomy concerns the formation and evolution of galaxies through cosmic time. A common approach for shedding more light on this subject is the exploration of the young stages of the Universe, when the first stars and Super Massive Black Holes (SMBHs) were formed and therefore started ionising the intergalactic medium. This Epoch of Re-ionisation (EoR) is considered one of the key areas of extragalactic research that only recently we were able to explore, mostly due to the growing number of identified high-redshift Active Galactic Nuclei (AGNs). In this thesis, we focus on the exploration of the EoR and the SMBH/AGN population, both from the theoretical and observational point of view. Regarding the former, we employ eight state-of-the-art cosmological galaxy formation and evolution models with the main goal of exploring their predictions regarding the number of AGNs that the current and next surveys would observe at the EoR. Furthermore, we combine one of these models with a software that simulates the observations from X-ray telescopes, generating a future possible survey of 1 deg2 using the next-generation telescope, Athena. Having these predictions in hand, the project advances by trying to identify high-redshift radio galaxies in deep and well-studied surveys. In this regard, we explore two selection criteria that are widely used and were successful in the past in detecting high-redshift galaxies, aiming to provide further evidence regarding their efficiency of studying the EoR.

2021-05Doctoral thesis

Open access

Q-Matter coupling in modified gravity

Publication . Correia, Filipe Guedes Pinto de Rosado; Lobo, Francisco Sabélio Nobrega; Frusciante, Noemi

O Cosmos tem sido um tema de interesse para a humanidade durante grande parte da nossa história neste planeta. Ao longo dos séculos, a nossa compreensão do Cosmos evoluiu através do desenvolvimento de teorias que vão desde a astronomia básica até às mais avançadas, como a da gravidade newtoniana. No entanto, foi apenas em 1915 que Einstein desenvolveu a teoria da gravidade atualmente aceite - a sua teoria da Relatividade Geral. As suas equações são notavelmente precisas na descrição do nosso Universo só que apresenta algumas incompatibilidades com o que observamos como, por exemplo, a presença de uma constante cosmológica nas suas equações ser necessária para explicar a expansão do Universo (que é atribuída àquilo que se denomina por energia escura) ou o facto da constante de Hubble apresentar valores diferentes consoante o método de observação. Neste trabalho, derivaram-se as equações de campo de Einstein e discutiu-se um pouco da termodinâmica da Relatividade Geral no contexto de sistemas abertos e o que isso implica para o nosso Universo. Apesar da teoria de Einstein descrever o nosso Universo a um nível extremo de detalhe, ainda faltam algumas peças do puzzle e, neste trabalho, destacaram-se algumas das motivações para irmos além da GR e procurarmos teorias da gravidade que descrevam melhor o nosso Cosmos. Começou-se por recapitular o que é a Relatividade Geral e quais os passos que Einstein deu para chegar à sua teoria. Em seguida, seguiu-se o raciocínio de Prigogine e dos seus colegas para indagarmos sobre a termodinâmica de sistemas abertos e como reconciliá-la com a teoria de Einstein, e explorou-se muito brevemente o modelo atual da cosmologia - o modelo ΛCDM. Apresentaram-se alguns dos argumentos que sustentam a ideia de que a Relatividade Geral não é a teoria final da gravidade e explorou-se algumas das teorias já propostas, como a gravidade f(R) e f(T ), e alguns dos seus resultados mais importantes, e focou-se, depois, na teoria f(Q) em que Q representa a não-metricidade. Nestas teorias, diferentes quantidades são responsáveis pela assinatura do espaço-tempo. Em f(R), R (curvatura) descreve a rotação de um vetor quando transportado ao longo de um circuito fechado. Em f(T ), T (torção) representa o não-fecho de um paralelogramo formado quando dois vectores são transportados um ao longo do outro e em f(Q), Q (não-metricidade) representa a variação do comprimento de um vetor quando este é transportado em paralelo. Em seguida, derivaram-se as equações de campo de f(Q) para o casos em que não existe acoplamento entre a matéria e o espaço-tempo através do princípio variacional tanto no formalismo da métrica como no formalismo da conexão. Deduziram-se as equações de Friedmann para este caso e consideraram-se algumas aplicações cosmológicas, nomeadamente derivaram-se alguns dos parâmetros mais relevantes para a descrição do nosso Universo - o parâmetro de desaceleração e o parâmetro da equação de estado da energia escura. Terminou-se o capítulo mostrando qual a família de funções que recupera o modelo ΛCDM e qual a função para a qual se obtém a solução de De Sitter. Posteriormente, fez-se a mesma análise para o caso em que há acoplamento entre a geometria do espaçotempo e a matéria e calculou-se a divergência do tensor energia-momento. Contrariamente à Relatividade Geral, este tensor não é conservado no caso em que há acoplamento em gravidade f(Q) que leva à presença de uma força extra que pode ser interpretada como uma força “normal” ao vetor quadrimomento. No contexto da termodinâmica de sistemas abertos, estabeleceu-se um paralelo entre o que foi feito por Prigogine e seus pares para a Relatividade Geral e o que se obtém para o caso da gravidade f(Q) no caso de acoplamento. Com base na não-conservação do tensor energia-momento derivada na secção anterior, pode-se deduzir que existe uma transferência de energia entre o espaço-tempo e a matéria que pode levar à criação de partículas. Seguindo o raciocínio de Prigogine, obtiveram-se expressões para a taxa de criação de partículas e para a pressão de criação.

2024Master thesis

Open access

Photometric and spectroscopic tracers of the inside-out growth of massive galaxies

Publication . dos Reis, Sandra N.; Buitrago, Fernando; Papaderos, Polychronis; Matute, Israel

The most massive (Mstellar > 1011M_) galaxies of the Universe experience a dramatic evolution in their observational properties (size, morphology, kinematics, star formation rates) across cosmic time. This metamorphosis, which implies an accelerated evolution of this galaxy population in comparison with lower mass galaxies, is not well understood. This thesis explores the structural properties and spectroscopic evolution of massive galaxies in the nearby Universe (z < 0:5) by conducting two different but complementary studies: one employing surface photometry using deep photometric data from the Hubble Space Telescope (HST), and another one exploiting spectral synthesis using state-of-the-art integral field spectroscopy (IFS) from MUSE. The first study makes use of HST CANDELS data to analyze a sample of 17 nearby (z < 0:5) massive (Mstellar > 1011M_) galaxies, with the aim to disentangle the structural components of these systems and study possible faint non-axissymmetric features. The excellent HST spatial resolution for intermediate redshift objects justifies a detailed structural analysis that combines two parametric components for the disk and bulge, instead of a purely automatic application of one single Sérsic model. Therefore careful single Sérsic fits and bulge-disk decompositions are performed to model the galaxy surface brightness profiles. The model color profiles are compared with the observed ones, and multi-component global effective radii are derived in order to obtain more accurate measurements of the size of galaxies and their position on the mass-size relation. It was found that the Sérsic index does not offer a good proxy for the visual morphology of our sample of massive galaxies. The derived multi-component effective radii offer a better description of the size of the sample galaxies than those inferred from single Sérsic models with GALFIT. The galaxies in our sample lie on the scatter of the local masssize relation, indicating that these massive objects have not experienced a significant growth in size since z ~ 0.5. Interestingly, the few outliers in the local mass-size relation are late-type galaxies, suggesting that spheroids must have reached the local mass-size relation earlier. For most of our sample, both single and multi-component Sérsic models retrieved with GALFIT show considerable systematic deviations from the observed surface brightness profiles in the galaxy peripheries that consequently propagate into significant uncertainties in the Sérsic fit parameters. In several cases they also indicate that colors inferred from Sersic fits show strong discrepancies from the observed colors. The second study explores the build-up process of massive galaxies by examining IFS MUSE data. We conduct a direct comparison between the spatially resolved stellar populations of the largest galaxy known in the Universe – IC1101 – and four other nearby early-type massive galaxies (ETGs), which represent the predominant morphological massive class in the nearby Universe. The IFS data were spatially-binned using Voronoi tesselation and modeled with our in-house spectral fitting pipeline Porto3D, enabling us to study the galaxy stellar populations, and focusing on the stellar age and metallicity radial profiles and their corresponding gradients. It was found a diversity in the radial distribution of equivalent width (EW) of H α) supporting a subdivision of ETGs into two groups: type i and type ii ETGs. The ones classified as type ii ETGs show an outwardly increasing EW(H α) whereas type i show a nearly constant EW(Hα) with values being consistent with gas photoionization by post-AGB stellar populations. All but one of the analyzed galaxies show LINER-specific spectroscopic properties out to several kpc from their nucleus. Old stellar ages (above 9 Gyr) and negative radial gradients are found for all galaxies, supporting an inside-out formation scenario. Stellar metallicities are over-solar for all galaxies with only a single exception. The main difference in the comparison of IC1101 with the rest of the sample lies on its positive stellar metallicity gradient. This result is atypical for ETGs in the low-redshift Universe and may be an indication of different evolutionary mechanisms for this galaxy. We tentatively propose plausible scenarios to explain the metal-enriched periphery of IC1101, being (i) a contribution of metal-rich intra-cluster stellar light, and (ii) a self-enrichment by “wet” mergers of accreted satellites that fed star formation. We also conjecture that this might partly be an artifact created by the astonishing large velocity dispersion determined in the outskirts of IC1101.

2021-04Doctoral thesis

Open access

Towards better selection and characterisation criteria for high-redshift radio galaxies using machine-assisted pattern recognition

Publication . Carvajal, Rodrigo; Afonso, José; Matute, Israel; Messias, Hugo G.

Understanding how galaxies and their constituents, like active galactic nuclei (AGN), evolve and interact across cosmic timescales remains a key challenge in astrophysics, especially during the epoch of reionisation (EoR), when the early Universe transitioned from a neutral to an ionised state. Even though star formation (SF) is considered to be its main contributor, the impact of AGN remains elusive. Recently, huge efforts have been put into the determination of the AGN bolometric radiation output via their search using a multi-wavelength approach. To address such challenge, this thesis presents a novel machine learning (ML) tool –a pipeline of models– for the efficient selection and redshift characterisation of radio-detectable AGN by using multi-wavelength photometry of sources detected in the infrared (IR). By analysing sources in a wide range of redshift values, this tool enables the exploration of theAGN-galaxy co-evolution across cosmic times. Applied to millions of sources in the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) Spring and the Stripe 82 (S82) fields, our pipeline has identified almost 100 thousand radio-AGN candidates, with predicted redshift values up to 4.4. Beyond classification, we can extract the key parameters that most significantly impact candidate selection in our pipeline. This investigation has led to the design of a new AGN colour-colour selection criterion, offering a useful, ML-based, tool for the community. Furthermore, by extracting radio-AGN candidates from the Evolutionary Map of the Universe Pilot Survey (EMU-PS), we can generate radio luminosity functions (RLFs) with highly constrained uncertainties. Our results are compatible with current knowledge and hint at the existence of a distinct population of bright sources. Finally, this thesis explores the potential application of our tool to future surveys like the Square Kilometre Array (SKA), that is expected to generate immense radio datasets. Our rapid and reliable method will be instrumental in separating AGN from star-forming galaxies (SFGs) while helping to unveil their interplay across the history of the Universe.

2024-12-19Doctoral thesis

Open access