3,680 research outputs found
Birds in a partly clearfelled dry eucalypt forest on dolerite in southeastern Tasmania
An area of dry eucalypt forest on dolerite in southeastern Tasmania was clearfelled in 1981. A portion of this area was subsequently slash-burnt and aerially sown in 1982, whilst the rest of the area was left unburnt and unsown. A monthly bird census was conducted during 1983-1984 in surrounding uncut, mature forest and also on the clearfelled area. Species were recorded together with the habitat in which they occurred and the particular plant species being utilised. A total of 46 avian species were recorded during the monthly censuses, with most species and individuals being observed in the spring months. The numbers of species and individuals recorded on the burnt and unburnt clearfelled areas were low in comparison with those observed in the uncut forest. In general, those species able to utilise open-ground habitats tended to be the least affected by clearfelling followed by slash-burning. However, the unburnt clearfelled area provided foraging sites for certain species, in preference to the nearby slash-burnt area. Many individuals recorded in the clearfelled areas made use of trees left standing after logging. The use of fire in dry forest management practice and the importance of cull trees are discussed
A model for atomic and molecular interstellar gas: The Meudon PDR code
We present the revised ``Meudon'' model of Photon Dominated Region (PDR
code), presently available on the web under the Gnu Public Licence at:
http://aristote.obspm.fr/MIS. General organisation of the code is described
down to a level that should allow most observers to use it as an interpretation
tool with minimal help from our part. Two grids of models, one for low
excitation diffuse clouds and one for dense highly illuminated clouds, are
discussed, and some new results on PDR modelisation highlighted.Comment: accepted in ApJ sup
The evolution of clustering and bias in the galaxy distribution
This paper reviews the measurements of galaxy correlations at high redshifts,
and discusses how these may be understood in models of hierarchical
gravitational collapse. The clustering of galaxies at redshift one is much
weaker than at present, and this is consistent with the rate of growth of
structure expected in an open universe. If , this observation would
imply that bias increases at high redshift, in conflict with observed
values for known high- clusters. At redshift 3, the population of
Lyman-limit galaxies displays clustering which is of similar amplitude to that
seen today. This is most naturally understood if the Lyman-limit population is
a set of rare recently-formed objects. Knowing both the clustering and the
abundance of these objects, it is possible to deduce empirically the
fluctuation spectrum required on scales which cannot be measured today owing to
gravitational nonlinearities. Of existing physical models for the fluctuation
spectrum, the results are most closely matched by a low-density spatially flat
universe. This conclusion is reinforced by an empirical analysis of CMB
anisotropies, in which the present-day fluctuation spectrum is forced to have
the observed form. Open models are strongly disfavoured, leaving CDM
as the most successful simple model for structure formation.Comment: Invited review at the Royal Society Meeting `Large-scale structure in
the universe', London, March 1998. 20 Pages LaTe
OH spectral evolution of oxygen-rich late-type stars
We investigated the main-line spectral evolution with shell thickness of
oxygen rich AGB stars. The study is based on a sample of 30 sources distributed
along the IRAS colour-colour diagram. The sources were chosen to trace the
Miras with thick shells and the whole range of OH/IR stars. The Miras exhibit a
1665 MHz emission strength comparable to that at 1667 MHz. Even though the
Miras of the study have quite thick shells, their spectral characteristics in
both main lines attest to a strong heterogeneity in their OH shell with, in
particular, the presence of significant turbulence and acceleration. The
expansion velocity has been found to be about the same at 1665 and 1667 MHz,
taking into account a possible velocity turbulence of 1-2km/s at the location
of the main-line maser emission. An increase in the intensity ratio 1667/1665
with shell thickness has been found. A plausible explanation for such a
phenomenon is that competitive gain in favour of the 1667 MHz line increases
when the shell is getting thicker. There is an evolution in the spectral
profile shape with the appearance of a substantial inter-peak signal when the
shell is getting thicker. Also, inter-peak components are found and can be as
strong as the external standard peaks when the shell is very thick. This trend
for an increase of the signal in between the two main peaks is thought to be
the result of an increase of the saturation with shell thickness. All sources
but two - a Mira and an OH/IR star from the lower part of the colour-colour
diagram - are weakly polarized. The strong polarization observed for those two
particular objects is thought to be the result of perturbations in their
shells.Comment: 19 pages, 12 figures, accepted for publication in A&
The Evolution of the Optical and Near-Infrared Galaxy Luminosity Functions and Luminosity Densities to z~2
Using Hubble Space Telescope and ground-based U through K- band photometry
from the Great Observatories Origins Deep Survey (GOODS), we measure the
evolution of the luminosity function and luminosity density in the rest-frame
optical (UBR) to z ~ 2, bridging the poorly explored ``redshift desert''
between z~1 and z~2. We also use deep near-infrared observations to measure the
evolution in the rest-frame J-band to z~1. Compared to local measurements from
the SDSS, we find a brightening of the characteristic magnitude, (M*), by ~2.1,
\~0.8 and ~0.7 mag between z=0.1 and z=1.9, in U, B, and R bands, respectively.
The evolution of M* in the J-band is in the opposite sense, showing a dimming
between redshifts z=0.4 and z=0.9. This is consistent with a scenario in which
the mean star formation rate in galaxies was higher in the past, while the mean
stellar mass was lower, in qualitative agreement with hierarchical galaxy
formation models. We find that the shape of the luminosity function is strongly
dependent on spectral type and that there is strong evolution with redshift in
the relative contribution from the different spectral types to the luminosity
density.
We find good agreement in the luminosity function derived from an R-selected
and a K-selected sample at z~1, suggesting that optically selected surveys of
similar depth (R < 24) are not missing a significant fraction of objects at
this redshift relative to a near-infrared-selected sample. We compare the
rest-frame B-band luminosity functions from z~0--2 with the predictions of a
semi-analytic hierarchical model of galaxy formation, and find qualitatively
good agreement. In particular, the model predicts at least as many optically
luminous galaxies at z~1--2 as are implied by our observations.Comment: 43 pages; 15 Figures; 5 Tables, Accepted for publication in Ap.
Clustering, host halos and environment of z2 galaxies as a function of their physical properties
Using a sample of 25683 star-forming and 2821 passive galaxies at ,
selected in the COSMOS field following the BzK color criterion, we study the
hosting halo mass and environment of galaxies as a function of their physical
properties. Spitzer and Herschel provide accurate SFR estimates for starburst
galaxies. We measure the auto- and cross-correlation functions of various
galaxy sub-samples and infer the properties of their hosting halos using both
an HOD model and the linear bias at large scale. We find that passive and
star-forming galaxies obey a similarly rising relation between the halo and
stellar mass. The mean host halo mass of star forming galaxies increases with
the star formation rate between 30 and 200 M.yr, but flattens
for higher values, except if we select only main-sequence galaxies. This
reflects the expected transition from a regime of secular co-evolution of the
halos and the galaxies to a regime of episodic starburst. We find similar large
scale biases for main-sequence, passive, and starburst galaxies at equal
stellar mass, suggesting that these populations live in halos of the same mass.
We detect an excess of clustering on small scales for passive galaxies and
showed, by measuring the large-scale bias of close pairs, that this excess is
caused by a small fraction () of passive galaxies being hosted by
massive halos ( M) as satellites. Finally,
extrapolating the growth of halos hosting the z2 population, we show that
M M galaxies at z2 will evolve, on average,
into massive (M M), field galaxies in the local
Universe and M M galaxies at z=2 into local,
massive, group galaxies. The most massive main-sequence galaxies and close
pairs of massive, passive galaxies end up in today's clusters.Comment: 18 pages, 16 figures, Accepted by A&
Physical properties of z~4 LBGs: differences between galaxies with and without Ly-alpha emission
We have analysed the physical properties of z~4 Lyman Break Galaxies observed
in the GOODS-S survey, in order to investigate the possible differences between
galaxies where the Ly-alpha is present in emission, and those where the line is
absent or in absorption. The objects have been selected from their optical
color and then spectroscopically confirmed by Vanzella et al. (2005). From the
public spectra we assessed the nature of the Ly-alpha emission and divided the
sample into galaxies with Ly-alpha in emission and objects without Ly-alpha
line (i.e. either absent or in absorption). We have then used the complete
photometry, from U band to mid infrared from the GOODS-MUSIC database, to study
the observational properties of the galaxies, such as UV spectral slopes and
optical to mid-infrared colors, and the possible differences between the two
samples. Finally through standard spectral fitting tecniques we have determined
the physical properties of the galaxies, such as total stellar mass, stellar
ages and so on, and again we have studied the possible differences between the
two samples. Our results indicate that LBG with Ly-alpha in emission are on
average a much younger and less massive population than the LBGs without
Ly-alpha emission. Both populations are forming stars very actively and are
relatively dust free, although those with line emission seem to be even less
dusty on average. We briefly discuss these results in the context of recent
models for the evolution of Lyman break galaxies and Ly-alpha emitters.Comment: Accepted for publication in A&A. Uses aa.cls, 6 pages, 3 figure
GOODS-: identification of the individual galaxies responsible for the 80-290m cosmic infrared background
We propose a new method of pushing to its faintest detection
limits using universal trends in the redshift evolution of the far infrared
over 24m colours in the well-sampled GOODS-North field. An extension to
other fields with less multi-wavelength information is presented. This method
is applied here to raise the contribution of individually detected
sources to the cosmic infrared background (CIRB) by a factor 5 close to its
peak at 250m and more than 3 in the 350m and 500m bands. We
produce realistic mock images of the deep PACS and SPIRE images of
the GOODS-North field from the GOODS- Key Program and use them to
quantify the confusion noise at the position of individual sources, i.e.,
estimate a "local confusion noise". Two methods are used to identify sources
with reliable photometric accuracy extracted using 24m prior positions.
The clean index (CI), previously defined but validated here with simulations,
which measures the presence of bright 24m neighbours and the photometric
accuracy index (PAI) directly extracted from the mock images. After
correction for completeness, thanks to our mock images, individually
detected sources make up as much as 54% and 60% of the CIRB in the PACS bands
down to 1.1 mJy at 100m and 2.2 mJy at 160m and 55, 33, and 13% of
the CIRB in the SPIRE bands down to 2.5, 5, and 9 mJy at 250m, 350m,
and 500m, respectively. The latter depths improve the detection limits of
by factors of 5 at 250m, and 3 at 350m and 500m as
compared to the standard confusion limit. Interestingly, the dominant
contributors to the CIRB in all bands appear to be distant siblings
of the Milky Way (0.96 for 300m) with a stellar mass
of 910M.Comment: 22 pages, 16 figures. Accepted for publication by Astronomy and
Astrophysic
AGN Emission Line Diagnostics and the Mass-Metallicity Relation up to Redshift z~2: the Impact of Selection Effects and Evolution
Emission line diagnostic diagrams probing the ionization sources in galaxies,
such as the Baldwin-Phillips-Terlevich (BPT) diagram, have been used
extensively to distinguish AGN from purely star-forming galaxies. Yet, they
remain poorly understood at higher redshifts. We shed light on this issue with
an empirical approach based on a z~0 reference sample built from ~300,000 SDSS
galaxies, from which we mimic selection effects due to typical emission line
detection limits at higher redshift. We combine this low-redshift reference
sample with a simple prescription for luminosity evolution of the global galaxy
population to predict the loci of high-redshift galaxies on the BPT and
Mass-Excitation (MEx) diagnostic diagrams. The predicted bivariate
distributions agree remarkably well with direct observations of galaxies out to
z~1.5, including the observed stellar mass-metallicity (MZ) relation evolution.
As a result, we infer that high-redshift star-forming galaxies are consistent
with having "normal" ISM properties out to z~1.5, after accounting for
selection effects and line luminosity evolution. Namely, their optical line
ratios and gas-phase metallicities are comparable to that of low-redshift
galaxies with equivalent emission-line luminosities. In contrast, AGN
narrow-line regions may show a shift toward lower metallicities at higher
redshift. While a physical evolution of the ISM conditions is not ruled out for
purely star-forming galaxies, and may be more important starting at z>2, we
find that reliably quantifying this evolution is hindered by selections
effects. The recipes provided here may serve as a basis for future studies
toward this goal. Code to predict the loci of galaxies on the BPT and MEx
diagnostic diagrams, and the MZ relation as a function of emission line
luminosity limits, is made publicly available.Comment: Main article: 15 pages, 7 figures; Appendix: 13 pages, 11 figures.
Revisions: Paper now accepted for publication in the Astrophysical Journal
(same scientific content as previous arXiv version). IDL routines to make
empirical predictions on the BPT, MEx, and M-Z plane are now released at
https://sites.google.com/site/agndiagnostics/home/me
- …