1o semestre de 2015

Data

Apresentador

Título

18/08

Marcus Duarte

Retired galaxies: not to be forgotten in the quest of the star formation - AGN connection

25/08

Marcio Avellar

Possibility of life sustained by radioactive decay

01/09

Andres Paez

Theoretical analysis of the formation conditions of Kelvin-Helmholtz instability in a CME

08/09

Semana da Pátria

15/09

Raniere Menezes

Another new horizon

22/09

Maria Luiza Linhares Dantas

Astrostatistics: An Arising Field in Astrophysics

29/09

Cancelado: Semana do Encontro Anual da SAB



Retired galaxies: not to be forgotten in the quest of the star formation - AGN connection
Marcus Duarte
Resumo
We propose a fresh look at the Main Galaxy Sample of the Sloan Digital Sky Survey by packing the galaxies in stellar mass and redshift bins. We show how important it is to consider the emission-line equivalent widths, in addition to the commonly used emission-line ratios, to properly identify retired galaxies (i.e. galaxies that have stopped forming stars and are ionized by their old stellar populations) and not mistake them for galaxies with low-level nuclear activity. We find that the proportion of star-forming galaxies decreases with decreasing redshift in each mass bin, while that of retired galaxies increases. Galaxies with M⋆ > 1011.5 M⊙ have formed all their stars at redshift larger than 0.4. The population of AGN hosts is never dominant for galaxy masses larger than 1010 M⊙. We warn about the effects of stacking galaxy spectra to discuss galaxy properties. We estimate the lifetimes of active galactic nuclei (AGN) relying entirely on demographic arguments - i.e. without any assumption on the AGN radiative properties. We find upper-limit lifetimes of about 1-5 Gyr for detectable AGN in galaxies with masses between 1010-1012 M⊙. The lifetimes of the AGN-dominated phases are a few 108 yr. Finally, we compare the star formation histories of star-forming, AGN and retired galaxies as obtained by the spectral synthesis code STARLIGHT. Once the AGN is turned on, it inhibits star formation for the next ˜0.1 Gyr in galaxies with masses around 1010 M⊙, ˜ 1 Gyr in galaxies with masses around 1011 M⊙.
Referências
- Stasinska et al. (2015)


Possibility of life sustained by radioactive decay
Marcio Avellar
Resumo
The amazing capacity of life to adapt itself endowed the so-called extremophiles with capabilities that are only now being discovered and studied, such the production of proteins stable at temperatures above at 100 oC or the product ion of enzymes such as reverse gyrase, which can prevent the loss of biological activity of DNA, also due to high temperatures. In addition, other classes of beings are capable to extract energy from alternative sources, such as the reduction of iron or sulphate. In this work, we study the feasibility of microorganisms like the bacterium Candidatus Desulforudis audaxviator, an extremophile found in a gold mine in South Africa surviving at depths up to 4 km, with temperatures between 45 oC and 60 oC, few nutrients available and some concentration of radioactive minerals such as uraninite, to survive in satellites or in planets similar to the Jovian moon Europa by extracting energy from the radioactive decay of uranium, thorium and potassium. Knowing the metabolic pathway of Candidatus Desulforudis audaxviator we are developing a simple ecosystem model with the basic ingredients for support this kind of microbial life.
Referências
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Theoretical analysis of the formation conditions of Kelvin-Helmholtz instability in a CME
Andres Paez
Resumo
The Kelvin-Helmholtz instability (KHI) observed in the sheath of the Coronal Mass Ejection (CME) has motivated several analysis and simulations to test their existence. In this work we assume the existence of the KHI and propose a method to identify the regions where it is possible the development of KH for a CME propagating in a fast and slow solar wind. We build functions for the velocities, densities and magnetic fields for two different zones of interaction between the solar wind and a CME. We adjusted the theory of magnetic KHI proposed by Chandrasekhar (1961) and we found conditions for the existence of KHI in the CME sheath. Using this method it is possible to determine the intervals of KHI existence linked to the values of CME magnetic fields, this mode we can be interpreted the existence KHI as a tool to measure CME magnetic fields. We conclude that KHI may exist in the two CME flanks and it is perceived that the zone with boundaries with the slow solar wind is more appropriated for the formation of the KH vortex.
Referências
- Foullon et al. (2001) ;
- Mostl et al. (2013) ;
- Foullon et al 2013 (ApJ:767)


Another new horizon
Raniere Menezes
Resumo
This lecture is an overview about the gamma-ray sky. Fascinating phenomena such as giant gamma-ray bubbles, SNR and even a new horizon will be discussed (how far can we see a blazar?).
Referências
- Ackermann et al. (2015);
- Guobin Mou et al. (2015);


Astrostatistics: An Arising Field in Astrophysics
Maria Luiza Linhares Dantas
Resumo
Why is robust Statistics important for Astronomers? In the context of the era of Big Data, I will give an overview of the statistical approaches to handle data that have been arising within a few groups of Astrophysicists/Astrostatisticians. I will, furthermore, address a little bit about the history of the IAA (The International Astrostatistics Association), as well as newborn Astrostatistics groups, e.g. COIN (The Cosmostatistics Initiative).
Referências
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