1,153 research outputs found
Neutral gas in Lyman-alpha emitting galaxies Haro 11 and ESO 338-IG04 measured through sodium absorption
Context. The Lyman alpha emission line of galaxies is an important tool for
finding galaxies at high redshift, and thus probe the structure of the early
universe. However, the resonance nature of the line and its sensitivity to dust
and neutral gas is still not fully understood.
Aims. We present measurements of the velocity, covering fraction and optical
depth of neutral gas in front of two well known local blue compact galaxies
that show Lyman alpha in emission: ESO 338-IG 04 and Haro 11. We thus test
observationally the hypothesis that Lyman alpha can escape through neutral gas
by being Doppler shifted out of resonance.
Methods. We present integral field spectroscopy from the GIRAFFE/Argus
spectrograph at VLT/FLAMES in Paranal, Chile. The excellent wavelength
resolution allows us to accurately measure the velocity of the ionized and
neutral gas through the H-alpha emission and Na D absorption, which traces the
ionized medium and cold interstellar gas, respectively. We also present
independent measurements with the VLT/X-shooter spectrograph which confirm our
results.
Results. For ESO 338-IG04, we measure no significant shift of neutral gas.
The best fit velocity is -15 (16) km/s. For Haro 11, we see an outflow from
knot B at 44 (13) km/s and infalling gas towards knot C with 32 (12) km/s.
Based on the relative strength of the Na D absorption lines, we estimate low
covering fractions of neutral gas (down to 10%) in all three cases.
Conclusions. The Na D absorption likely occurs in dense clumps with higher
column densities than where the bulk of the Ly-alpha scattering takes place.
Still, we find no strong correlation between outflowing neutral gas and a high
Lyman alpha escape fraction. The Lyman alpha photons from these two galaxies
are therefore likely escaping due to a low column density and/or covering
fraction.Comment: 9 pages, 3 figure
Movement and habitat selection of a large carnivore in response to human infrastructure differs by life stage
BackgroundThe movement extent of mammals is influenced by human-modified areas, which can affect population demographics. Understanding how human infrastructure influences movement at different life stages is important for wildlife management. This is true especially for large carnivores, due to their substantial space requirements and potential for conflict with humans.MethodsWe investigated human impact on movement and habitat selection by GPS-collared male brown bears (Ursus arctos) in two life stages (residents and dispersers) in central Sweden. We identified dispersers visually based on their GPS locations and used hidden Markov models to delineate dispersal events. We used integrated step selection analysis (iSSA) to infer movement and habitat selection at a local scale (availability defined by hourly relocations), and resource selection functions (RSFs) to infer habitat selection at a landscape scale (availability defined by the study area extent).ResultsMovement of residents on a local scale was facilitated by small forestry roads as they moved faster and selected areas closer to forestry roads, and they avoided areas closer to larger public roads and buildings on both scales. Dispersers were more ambivalent in their response to human infrastructure. Dispersers increased their speed closer to small forestry roads and larger public roads, did not exhibit selection for or against any road class, and avoided areas closer to buildings only at local scale. Dispersers did not select for any features on the landscape, which is likely explained by the novelty of the landscape or their naivety towards it.ConclusionOur results show that movement in male brown bears is life stage-dependent and indicate that connectivity maps derived from movement data of dispersing animals may provide more numerous and more realistic pathways than those derived from resident animal data alone. This suggests that data from dispersing animals provide more realistic models for reconnecting populations and maintaining connectivity than if data were derived from resident animals alone
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