190 research outputs found
Tidal Dwarf Galaxies at Intermediate Redshifts
We present the first attempt at measuring the production rate of tidal dwarf
galaxies (TDGs) and estimating their contribution to the overall dwarf
population. Using HST/ACS deep imaging data from GOODS and GEMS surveys in
conjunction with photometric redshifts from COMBO-17 survey, we performed a
morphological analysis for a sample of merging/interacting galaxies in the
Extended Chandra Deep Field South and identified tidal dwarf candidates in the
rest-frame optical bands. We estimated a production rate about 1.4 {\times}
10^{-5} per Gyr per comoving volume for long-lived TDGs with stellar mass 3
{\times} 10^{8-9} solar mass at 0.5<z<1.1. Together with galaxy merger rates
and TDG survival rate from the literature, our results suggest that only a
marginal fraction (less than 10%) of dwarf galaxies in the local universe could
be tidally-originated. TDGs in our sample are on average bluer than their host
galaxies in the optical. Stellar population modelling of optical to
near-infrared spectral energy distributions (SEDs) for two TDGs favors a burst
component with age 400/200 Myr and stellar mass 40%/26% of the total,
indicating that a young stellar population newly formed in TDGs. This is
consistent with the episodic star formation histories found for nearby TDGs.Comment: 9 pages, 5 figures, Accepted for publication in Astrophysics & Space
Scienc
Influence of edapho-climatic factors on the sporulation and colonization of arbuscular mycorrhizal fungi in two Amazonian native fruit species
Arbuscular mycorrhizal fungi (AMF) colonization and spore numbers in the rhizosphere of two fruit species, Paullinia cupana Mart. and Theobroma grandiflorum Schum., growing in a terra firme ecosystem in Central Amazonia were studied from August 1998 to May 2000. Climatic and edaphic factors were also determined to investigate their influence on mycorrhizal variables. Soil pH, Al, Mn and effective cation exchange capacity exhibited seasonal variations during the investigation period. Temporal variations in mycorrhizal colonization levels and spore numbers occurred, indicating seasonality. Moreover, the patterns of mycorrhizal colonization levels and spore numbers for both host species were similar during the studied period. Mycorrhizal variables were related to climatic and edaphic factors, however, the intensity and type of influence of climatic and soil characteristics on AMF development tended to vary with the season and host plant species in Central Amazonia conditions
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