1,797 research outputs found
Feeding Records of Aphids (Hemiptera: Aphididae) From Wisconsin
Basic to our understanding of any animal and its habitat requirements is knowing what it eats. Reported here are observations of feeding by 27 species of aphids encountered in Wisconsin over 1992-2002
Feeding Records of Aphids (Hemiptera: Aphididae) From Wisconsin, Supplement
Basic to our understanding of any animal and its habitat requirements is knowing what it eats. Reported here are observations of feeding by 24 species of aphids encountered in Wisconsin over 2002-2010
The non-universality of the low-mass end of the IMF is robust against the choice of SSP model
We perform a direct comparison of two state-of-the art single stellar
population (SSP) models that have been used to demonstrate the non-universality
of the low-mass end of the Initial Mass Function (IMF) slope. The two public
versions of the SSP models are restricted to either solar abundance patterns or
solar metallicity, too restrictive if one aims to disentangle elemental
enhancements, metallicity changes and IMF variations in massive early-type
galaxies (ETGs) with star formation histories different from the solar
neighborhood. We define response functions (to metallicity and
\alpha-abundance) to extend the parameter space of each set of models. We
compare these extended models with a sample of Sloan Digital Sky Survey (SDSS)
ETGs spectra with varying velocity dispersions. We measure equivalent widths of
optical IMF-sensitive stellar features to examine the effect of the underlying
model assumptions and ingredients, such as stellar libraries or isochrones, on
the inference of the IMF slope down to ~0.1 solar masses. We demonstrate that
the steepening of the low-mass end of the Initial Mass Function (IMF) based on
a non-degenerate set of spectroscopic optical indicators is robust against the
choice of the stellar population model. Although the models agree in a relative
sense (i.e. both imply more bottom-heavy IMFs for more massive systems), we
find non-negligible differences on the absolute values of the IMF slope
inferred at each velocity dispersion by using the two different models. In
particular, we find large inconsistency in the quantitative predictions of IMF
slope variations and abundance patterns when sodium lines are used. We
investigate the possible reasons for these inconsistencies.Comment: 16 pages, 9 figures, 2 tables, accepted for publication on Ap
Rest-frame ultra-violet spectra of massive galaxies at z=3: evidence of high-velocity outflows
Galaxy formation models invoke the presence of strong feedback mechanisms
that regulate the growth of massive galaxies at high redshifts. In this paper
we aim to: (1) confirm spectroscopically the redshifts of a sample of massive
galaxies selected with photometric redshifts z > 2.5; (2) investigate the
properties of their stellar and interstellar media; (3) detect the presence of
outflows, and measure their velocities. To achieve this, we analysed deep,
high-resolution (R~2000) FORS2 rest-frame UV spectra for 11 targets. We
confirmed that 9 out of 11 have spectroscopic redshifts z > 2.5. We also
serendipitously found two mask fillers at redshift z > 2.5, which originally
were assigned photometric redshifts 2.0 < z < 2.5. In the four highest-quality
spectra we derived outflow velocities by fitting the absorption line profiles
with models including multiple dynamical components. We found strongly
asymmetric, high-ionisation lines, from which we derived outflow velocities
ranging from 480 to 1518 km/s. The two galaxies with highest velocity show
signs of AGN. We revised the spectral energy distribution fitting U-band
through 8 micron photometry, including the analysis of a power-law component
subtraction to identify the possible presence of active galactic nuclei (AGN).
The revised stellar masses of all but one of our targets are >1e10 Msun, with
four having stellar masses > 5e10 Msun. Three galaxies have a significant
power-law component in their spectral energy distributions, which indicates
that they host AGN. We conclude that massive galaxies are characterised by
significantly higher velocity outflows than the typical Lyman break galaxies at
z ~ 3. The incidence of high-velocity outflows (~40% within our sample) is also
much higher than among massive galaxies at z < 1, which is consistent with the
powerful star formation and nuclear activity that most massive galaxies display
at z > 2.Comment: 17 pages, 14 figures, Accepted for publication in A&
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