Research carried out under the extragalactic astronomy group (PI. Mirjana Pović)

The main objective of the ESSTI extragalactic astronomy group is to understand better the properties of active galaxies, the physics behind active galactic nuclei (AGN), and the role of nuclear activity in galaxy formation and evolution across cosmic time. We also aim in understanding better the morphological properties and classification of galaxies at different cosmic times and morphological transformation of galaxies, star formation in galaxies, and properties of galaxies in galaxy clusters. In addition to this, through fundamental research we aim to contribute to the human capacity developments in Ethiopia, and development of the high-education sector in the country, institutional development of the ESSTI, to give more visibility to the science carried out in Ethiopia, and to strengthen international collaborations.

List of Projects

Morphological properties of active galaxies in deep surveys

Under this project we want to do a more detailed study of morphological properties of active galaxies along the cosmic time using deep observations. For that purpose we are using the galSVM code (Huertas-Company et al. 2008). First, we want to test this code and its sensitivity to classify active galaxies when having different AGN contributions. Using a local training sample of thousands of galaxies, we are comparing morphologies derived with and without the central source and quantifying how it affects different morphological parameters and final morphological classification. Finally, we will test morphology of a large sample of active galaxies in the COSMOS and other deep surveys, and compare morphology with other properties of active galaxies.

Members: Tilahun Getachew (PhD student, ESSTI, Ethiopia), Mirjana Pović (ESSTI, Ethiopia), Josefa Masegosa (IAA-CSIC, Spain), Jaime Perea (IAA-CSIC, Spain), and Isabel Márquez-Pérez (IAA-CSIC, Spain).

Properties of galaxies in galaxy clusters up to z ~ 1.0

This project is carried out in collaboration with the GaLAxy Cluster Evolution  (GLACE) survey (Sánchez Portal et al. 2015), with the general aim to study the properties and evolution of galaxies in galaxy clusters up to redshift of z ~ 1. Two GLACE clusters, ZwCl0024.0+1652 at z = 0.395 and RXJ1257.2+4738 at z = 0.866 will be analysed using the tunable filters data from the GTC 10m telescope. We want to study the properties such as morphology, star formation, metallicity, and nuclear activity in relation to other cluster properties, including environment, density and size. Our main objective is to understand better some of the still open questions such are: the role of AGN, metallicity variability, and galaxy transformations and evolution in galaxy clusters at different cosmic time.

Members: Zeleke Beyoro-Amado (PhD student, ESSTI, Ethiopia), Mirjana Pović (ESSTI, Ethiopia), Miguel Sánchez-Portal (IRAM, Spain), Solomon Belay Tessema (MoIT, ESSTI, Ethiopia), and the GLACE team

Properties of green valley galaxies and the role of AGN in galaxy evolution (3 projects)

Several works are included under this project. We first studied the properties of active and non-active galaxies in the green valley using a sample of public data from the COSMOS field. In particular, we analyzed star formation rates (SFR) through the Spitzer MIR and public Herschel FIR data, and found that most of our green valley X-ray detected AGN with FIR emission have SFRs higher than the ones of non-active galaxies at fixed stellar mass ranges. We suggested that for these active galaxies if there is an influence of AGN feedback on star formation in the green valley the scenario of AGN positive feedback seem to take place, rather than the negative one. Using these results we got an observational time on the 11m SALT telescope, with aim to carry out spectroscopic observations of a selected sample of active and non-active galaxies and to search for signs of positive feedback through  emission line analysis. In addition, currently we are analyzing morphological properties of initial sample. This project resulted in a MSc dissertation of Antoine Mahore (Rwanda/Uganda), and is currently a part of his PhD. On the other side, using the SDSS optical and GALEX UV data we analyzed the six most commonly used green valley selection criteria and the properties of galaxies under each (paper in close submission). This part of project resulted in a MSc dissertation of  Beatrice Nyiransengiyumva, the first woman to hold MSc degree in astrophysics in Rwanda. Finally, more detailed study on green valley selection criteria and galaxies properties will be done in near future under the sciope of J-PAS survey.

Members: Antoine Mahoro (PhD student, SAAO, SA), Beatrice Nyiransengiyumva (PhD student, UoR, Rwanda), Mirjana Pović (ESSTI, Ethiopia), Pheneas Nkundabakura (UoR, Rwanda), Petri Vaisanen (SAAO, SA), Moses Mogotsi (SAAO, SA), Solohery Randriamamoandry (SAAO, SA), Josefa Masegosa (IAA-CSIC, Spain), Isabel Márquez-Pérez (IAA-CSIC, Spain), Sara Caziolli (IAA-CSIC, Spain), and J-PAS team.

Stellar ages, metallicities, and morphologies of ultra-hard X-ray AGN in the BASS survey (2 projects)

Using the optical spectra gathered under the BASS survey (Koss et al. 2017) and  data release DR1 we are carrying out spectral energy distribution (SED) fittings by using the STARLIGHT code (Cid Fernandes et al. 2004) with aim to study for the very first time stellar ages and populations of BASS ultra-hard X-ray AGN. Using the obtained emission spectra we will measure the properties of all emission lines. Metallicities will  be measured using the new Bayesian-like approach of Pérez-Montero et al. (2019) that has been tested on type-2 AGN. For type-1 AGN, taking into account their contribution to the whole spectrum, we are planning to first test different AGN templates and evaluate AGN contribution, before being able to carry-out the stellar populations study. In addition to this, the research will be combined by morphological study of the same sample. Visual multiwavelength classification has been already carried out, where we obtained that most of ultra hard X-ray detected AGN are hosted by spirals in optical, are radio-quiet, and have compact morphologies in X-rays. In addition, we are planning to measure and study different morphological parameters commonly used in morphological classification, and finally to study in more details how/if X-ray luminosities, SMBH masses, and accretion rates are correlated with obtained stellar ages, stellar populations, metallicities, and morphology, for understanding better the connection between ultra-hard AGN and their host galaxies.

Members: Mirjana Pović (ESSTI, Ethiopia), Betelehem Bilata (ESSTI, Ethiopia), Josefa Masegosa (IAA-CSIC, Spain), and Isabel Márquez-Pérez (IAA-CSIC, Spain).

Dichotomy of radio loud (RL) and radio quite (RQ) quasars

Using the spectroscopic data from CAHA and GTC observatories in Spain of ~ 60 RL QSOs, we aim to quantify broad emission line differences between RQ and RL sources, exploiting larger and more complete samples of QSOs with spectral coverage in Hβ, FeII, MgII and CIV emission lines than it was done previously, using SPECFIT to determine the main parameters of each component. This will allow us to verify whether the larger values of FWHM(Hβ) among RL sources can be due to orientation, and study the wind properties affecting the profiles of the CIV and MgII lines. We will focus our comparisons on RQ and RL sources that have the same mass and L/LEdd ranges. In addition, we are planing to use the sample of QSOs with FIRST and NVSS radio measurements available, which will allow us to separate the orientation part of broad line width from the part driven by RL physics, that is most likely connected with thermal gas entrained near the radio outflows, perhaps suppressing the wind observed in RQ QSOs. Initial analysis are applied on 12 sources, where we found very diverse scenarios (in terms of their morphologies, emission line properties, radio properties, etc.). 

Members: Shimeles Terefe (PhD student, ESSTI, Ethiopia), Ascensión del Olmo (IAA-CSIC, Spain), Paola Marziani (INAF, Italy), and Mirjana Pović (ESSTI, Ethiopia).

Variability of nearby QSOs (2 projects)

A subsample of 12 nearby QSOs selected in previous work will be monitored photometrically along 2021/22 using the Entoto 1m telescopes for understanding better their variability and for analysing variability in line with other properties mentioned above. In addition to this we are planing to analyse the SFR properties of a large sample of variable QSOs detected in e-BOSS survey for which variability properties have been already measured. We will measure the SFR using the FANTASY code that provides a separation between the QSO and its host.

Members: Jerusalem Tamirat (ESSTI, Ethiopia), Mirjana Pović (ESSTI, Ethiopia), Betelehem Bilata (ESSTI, Ethiopia), Shimeles Terefe (PhD student, ESSTI, Ethiopia), Ascensión del Olmo (IAA-CSIC, Spain), Paola Marziani (INAF, Italy)