65 research outputs found
Development in astronomy in Ethiopia and East-Africa through nuclear activity in galaxies
In this paper we summarise the research that is currently going on in
Ethiopia and East-Africa in extragalactic astronomy and physics of active
galaxies and active galactic nuclei (AGN). The study is focused on some of the
still open questions such as: what are the stellar ages and populations of
ultra hard X-ray detected AGN and connection between AGN and their host
galaxies?, what are the properties of AGN in galaxy clusters and the role that
environment has in triggering nuclear activity?, what are the morphological
properties of AGN and how precisely we can deal with morphological
classification of active galaxies?, what are the properties of galaxies in the
green valley and the role of AGN in galaxy evolution?, and what are the
properties of radio-loud and radio-quiet quasars (QSO) and dichotomy between
the two?. Each of these questions has been developed under one specific project
that will be briefly introduced. These projects involve 6 PhD and 3 MSc
students and collaborations between Ethiopia, Rwanda, South Africa, Uganda,
Tanzania, Spain, Italy, and Chile. With all projects we aim: first, to
contribute to our general knowledge about AGN, and second, to contribute to the
development in astronomy and science in Ethiopia and East-Africa.Comment: 5 pages; Proceedings paper of the IAU symposium 356 "Nuclear Activity
in Galaxies Across Cosmic Time" (Ethiopia) accepted to be published under the
Cambridge University Press, eds. M. Povi\'c, P. Marziani, J. Masegosa, H.
Netzer, S. H. Negu, and S. B. Tessem
Star formation and AGN activity in the most luminous LINERs in the local universe
This work presents the properties of 42 objects in the group of the most
luminous, highest star formation rate LINERs at z = 0.04 - 0.11. We obtained
long-slit spectroscopy of the nuclear regions for all sources, and FIR data
(Herschel and IRAS) for 13 of them. We measured emission line intensities,
extinction, stellar populations, stellar masses, ages, AGN luminosities, and
star-formation rates. We find considerable differences from other low-redshift
LINERs, in terms of extinction, and general similarity to star forming (SF)
galaxies. We confirm the existence of such luminous LINERs in the local
universe, after being previously detected at z ~ 0.3 by Tommasin et al. (2012).
The median stellar mass of these LINERs corresponds to 6 - 7
10M which was found in previous work to correspond to the peak
of relative growth rate of stellar populations and therefore for the highest
SFRs. Other LINERs although showing similar AGN luminosities have lower SFR. We
find that most of these sources have LAGN ~ LSF suggesting co-evolution of
black hole and stellar mass. In general among local LINERs being on the
main-sequence of SF galaxies is related to their AGN luminosity.Comment: submitted to MNRA
AGN and Star-Formation Properties of Inside-out Assembled Galaxy Candidates at z<0.1
We study a sample of 48127 galaxies selected from the SDSS MPA-JHU catalogue,
with and . Local galaxies in
this stellar mass range have been shown to have systematically shorter assembly
times within their inner regions () when compared to that of the
galaxy as a whole, contrary to lower or higher mass galaxies which show
consistent assembly times at all radii. Hence, we refer to these galaxies as
Inside-Out Assembled Galaxy (IOAG) candidates. We find that the majority of
IOAG candidates with well-detected emission lines are classified as either AGN
(40%) or composite (40%) in the BPT diagram. We also find that the majority of
our sources are located below the main sequence of star formation, and within
the green valley or red sequence. Most BPT-classified star-forming IOAG
candidates have spiral morphologies and are in the main sequence, whereas
Seyfert 2 and composites have mostly spiral morphologies but quiescent star
formation rates (SFRs). We argue that a high fraction of IOAG candidates seem
to be in the process of quenching, moving from the blue cloud to the red
sequence. Those classified as AGN have systematically lower SFRs than
star-forming galaxies suggesting that AGN activity may be related to this
quenching. However, the spiral morphology of these galaxies remains in place,
suggesting that the central star-formation is suppressed before the
morphological transformation occurs.Comment: 11 pages, 9 figure, accepted for publication in MNRAS. A video
description can be seen here https://youtu.be/oxfjbqMqeQ
Properties of X-ray detected far-IR AGN in the green valley
In this study, we analysed active galactic nuclei in the "green valley" by
comparing active and non-active galaxies using data from the COSMOS field. We
found that most of our X-ray detected active galactic nuclei with far-infrared
emission have star formation rates higher than the ones of normal galaxies of
the same stellar mass range.Comment: Proceedings paper of the IAU symposium "Nuclear Activity in Galaxies
Across Cosmic Time" (Ethiopia) accepted to be published under the Cambridge
University Press, eds. M. Povic, P. Marziani, J. Masegosa, H. Netzer, S. H.
Negu, and S. B. Tessem
Study of AGN contribution on morphological parameters of their host galaxies
We tested how the AGN contribution (5% - 75% of the total flux) may affect
different morphological parameters commonly used in galaxy classification. We
carried out all analysis at ,,0 and at higher redshifts that correspond
to the COSMOS field. Using a local training sample of ,2000 visually
classified galaxies, we carried out all measurements with and without the
central source and quantified how the contribution of a bright nuclear point
source could affect different morphological parameters, such as: Abraham and
Concelice-Bershady indices, Gini, Asymmetry, moment of light, and
Smoothness. We found that concentration indexes are less sensitive to both
redshift and brightness in comparison to the other parameters. We also found
that all parameters change significantly with AGN contribution. At 0,
up to a 10% of AGN contribution the morphological classification will not be
significantly affect, but for 25% of AGN contribution late-type spirals
follow the range of parameters of elliptical galaxies and can therefore be
misclassified early types.Comment: Proceedings paper of the IAU symposium "Nuclear Activity in Galaxies
Across Cosmic Time" (Ethiopia) accepted to be published under the Cambridge
University Press, eds. M. Povi\'c, P. Marziani, J. Masegosa, H. Netzer, S. H.
Negu, and S. B. Tessem
- …