arXiv subjects

Abilio Mateus Jr.

Publications and source records attributed to Abilio Mateus Jr..

2 recordsLinked to original sources

arXiv2004

Star formation and the environment of nearby field galaxies

We investigate the environmental dependence of galaxies with star formation from a volume-limited sample of 4782 nearby field galaxy spectra extracted from the 2dF Galaxy Redshift Survey final data release. The environment is characterized by the local spatial density of galaxies, estimated from the distance to the 5th nearest neighbour. Extensive simulations have been made to estimate correction factors for the local density due to sample incompleteness. We discriminate the galaxies in distinct spectral classes -- passive, star-forming, and short starburst galaxies -- by the use of the equivalent widths of [{\sc O ii}]$λ$3727 and H$δ$. The frequency of galaxies of different classes are then evaluated as a function of the environment. We show that the fraction of star-forming galaxies decreases with increasing density, whereas passive galaxies present the opposite behaviour. The fraction of short starburst galaxies -- that suffered a starburst at $\sim$ 200 Myr ago -- do not present strong environmental dependence. The fraction of this class of galaxies is also approximately constant with galaxy luminosity, except for the faintest bins in the sample, where their fraction seems to increase. We find that the star-formation properties are affected in all range of densities present in our sample (that excludes clusters), what supports the idea that star-formation in galaxies is affected by the environment everywhere. We suggest that mechanisms like tidal interactions, which act in all environments, do play a relevant role on the star-formation in galaxies.

astro-ph↗

arXiv2002

The Environmental Dependence of Star Formation in the Nearby Universe

We have investigated how the incidence of star-forming galaxies varies with the environment using a volume-limited sample of nearby galaxy spectra extracted from the 2dF Galaxy Redshift Survey. The environment is characterized by the local number density of galaxies, corrected for sample incompleteness and border effects. Using the equivalent widths of [O II]$λ$3727 and H$δ$ we discriminate the star-forming galaxies in two classes, starbursts and ordinary star-forming galaxies, and evaluate their properties as a function of the local density. We show that the fraction of ordinary star-forming galaxies decreases regularly with increasing density, indicating that star formation is sensitive to the environment for all range of densities present in the sample. The fraction of starbursts is approximately independent of the density and, consequently, the fraction of starbursts relative to star-forming galaxies increases with local density. This suggests that a mechanism that acts everywhere, like tidal interactions, is the responsible for triggering starbursts. We also show that while the mean EW(H$α$) of ordinary star-forming galaxies is progressively reduced as density increases, for starbursts it suffers a strong decrease at densities corresponding to scales of $ρ^{-1/3} \sim 2.5 ~h^{-1}$ Mpc. A visual inspection of starburst images in the {\it Digital Sky Survey} reveals that this corresponds to a change in the morphology of starburst galaxies, from mainly apparently normal spirals and galaxies with apparently compact morphologies at low densities, to tidally distorted spirals at high densities.

astro-ph↗