784 research outputs found
Establishing an analogue population for the most distant galaxies
Lyman break analogues (LBAs) are local galaxies selected to match a more
distant (usually z~3) galaxy population in luminosity, UV-spectral slope and
physical characteristics, and so provide an accessible laboratory for exploring
their properties. However, as the Lyman break technique is extended to higher
redshifts, it has become clear that the Lyman break galaxies (LBGs) at z~3 are
more massive, luminous, redder, more extended and at higher metallicities than
their z~5 counterparts. Thus extrapolations from the existing LBA samples
(which match z=3 properties) have limited value for characterising z>5
galaxies, or inferring properties unobservable at high redshift. We present a
new pilot sample of twenty-one compact star forming galaxies in the local
(0.05<z<0.25) Universe, which are tuned to match the luminosities and star
formation volume densities observed in z>~5 LBGs. Analysis of optical emission
line indices suggests that these sources have typical metallicities of a few
tenths Solar (again, consistent with the distant population). We also present
radio continuum observations of a subset of this sample (13 sources) and
determine that their radio fluxes are consistent with those inferred from the
ultraviolet, precluding the presence of a heavily obscured AGN or significant
dusty star formation.Comment: 13 pages, MNRAS accepte
Kant on welfare: five unsuccessful defences
This article discusses five attempts at justifying the provision of welfare on Kantian grounds. I argue that none of the five proposals is satisfactory. Each faces a serious challenge on textual or systematic grounds. The conclusion to draw from this is not that a Kantian cannot defend the provision of welfare. Rather, the conclusion to draw is that the task of defending the provision of welfare on Kantian grounds is a difficult one whose success we should not take for granted
Radio Observations of GRB Host Galaxies
We present 5.5 and 9.0 GHz observations of a sample of seventeen GRB host
galaxies at 0.5<z<1.4, using the radio continuum to explore their star
formation properties in the context of the small but growing sample of galaxies
with similar observations. Four sources are detected, one of those (GRB
100418A) likely due to lingering afterglow emission. We suggest that the
previously-reported radio afterglow of GRB 100621A may instead be due to host
galaxy flux. We see no strong evidence for redshift evolution in the typical
star formation rate of GRB hosts, but note that the fraction of `dark' bursts
with detections is higher than would be expected given constraints on the more
typical long GRB population. We also determine the average radio-derived star
formation rates of core collapse supernovae at comparable redshift, and show
that these are still well below the limits obtained for GRB hosts, and show
evidence for a rise in typical star formation rate with redshift in supernova
hosts.Comment: 15 pages, MNRAS accepte
Physical properties of local star-forming analogues toz∼ 5 Lyman break galaxies
Intense, compact, star-forming galaxies are rare in the local Universe but ubiquitous at high redshift. We interpret the 0.1-22 μm spectral energy distributions (SED) of a sample of 180 galaxies at 0.05 < z < 0.25 selected for extremely high surface densities of inferred star formation in the ultraviolet. By comparison with well-established stellar population synthesis models we find that our sample comprises young (∼ 60 - 400 Myrs), moderate mass (∼6 × 109 M⊙) star-forming galaxies with little dust extinction (mean stellar continuum extinction Econt(B − V) ∼ 0.1) and find star formation rates of a few tens of Solar masses per year. We use our inferred masses to determine a mean specific star formation rate for this sample of ∼10−9 yr−1, and compare this to the specific star formation rates in distant Lyman break galaxies (LBGs), and in other low redshift populations. We conclude that our sample's characteristics overlap significantly with those of the z ∼ 5 LBG population, making ours the first local analogue population well tuned to match those high redshift galaxies. We consider implications for the origin and evolution of early galaxies
Radio observations confirm young stellar populations in local analogues to z ~5 Lyman break galaxies
We present radio observations at 1.5 GHz of 32 local objects selected to reproduce the physical properties of z .5 star-forming galaxies. We also report non-detections of five such sources in the sub-millimetre. We find a radio-derived star formation rate which is typically half that derived from Hα emission for the same objects. These observations support previous indications that we are observing galaxies with a young dominant stellar population, which has not yet established a strong supernova-driven synchrotron continuum. We stress caution when applying star formation rate calibrations to stellar populations younger than 100 Myr. We calibrate the conversions
for younger galaxies, which are dominated by a thermal radio emission component.
We improve the size constraints for these sources, compared to previous unresolved ground-based optical observations. Their physical size limits indicate very high star formation rate surface densities, several orders of magnitude higher than the local galaxy
population. In typical nearby galaxies, this would imply the presence of galaxy-wide winds. Given the young stellar populations, it is unclear whether a mechanism exists in our sources that can deposit sufficient kinetic energy into the interstellar medium to drive such outflows
Natural and anthropogenic drivers of Bornean elephant movement strategies
Endangered Bornean elephants are severely threatened by ongoing habitat transformation and increasing levels of human-elephant conflict. Understanding how elephants move across intact and transformed landscapes, as well as within them, is therefore of vital importance for the successful implementation of conservation management initiatives. We combined remote sensing and GPS telemetry data to identify broad habitat utilization and key movement areas to aid elephant management and conflict mitigation in three spatially-isolated populations in central and eastern Sabah, Malaysian Borneo. Home ranges were estimated using Brownian Bridge Movement Models and specific behavioral movement traits were identified by pathway analyses. These behavioral traits enabled a fine-scale evaluation of movements between and adjacent to forest patches and the role of large-scale agriculture in shaping elephant movements. Both natural (topological) and anthropogenic (agricultural) landscape features were found to have a broad influence on elephant movements. All elephant populations exhibited human-mediated behavioral responses, regardless of disturbance level. Throughout their range, elephants appeared to actively select relatively degraded forests, as measured by aboveground carbon density. However, elephants actively avoided urbanized areas, including roads and villages. Throughout the elephant range, high-speed, low-trajectory movements were found at low aboveground carbon locations, with 27% of all such movements located in large-scale agriculture. Our results suggest that agriculture impacts movement strategies of elephants, with evidence of repeat agricultural use pointing towards an active rationale for this behavior. Elephants were also found to use ridgelines as movement pathways, providing further context for the protection of such forested areas. The Lower Kinabatangan population, located in small remnant forests, travelled further to meet their ecological needs, suggesting the population is under added strain. Our work represents the broadest landscape assessment of Bornean elephant movements to-date and has important implications for both future work and habitat-level protected area management strategies
Managing hostile subsoils in the high rainfall zone of south-western Australia
This report is designed to complement existing information on the management of crops in the High Rainfall Zone of south-western Australia and to identify limitations for crop production arising from the soil properties in this area
Large Scale Structure traced by Molecular Gas at High Redshift
We present observations of redshifted CO(1-0) and CO(2-1) in a field
containing an overdensity of Lyman break galaxies (LBGs) at z=5.12. Our
Australia Telescope Compact Array observations were centered between two
spectroscopically-confirmed z=5.12 galaxies. We place upper limits on the
molecular gas masses in these two galaxies of M(H_2) <1.7 x 10^10 M_sun and
<2.9 x 10^9 M_sun (2 sigma), comparable to their stellar masses. We detect an
optically-faint line emitter situated between the two LBGs which we identify as
warm molecular gas at z=5.1245 +/- 0.0001. This source, detected in the CO(2-1)
transition but undetected in CO(1-0), has an integrated line flux of 0.106 +/-
0.012 Jy km/s, yielding an inferred gas mass M(H_2)=(1.9 +/- 0.2) x 10^10
M_sun. Molecular line emitters without detectable counterparts at optical and
infrared wavelengths may be crucial tracers of structure and mass at high
redshift.Comment: 4 pages, accepted for publication in ApJ Letter
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