631 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
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
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
Galaxy quenching timescales from a forensic reconstruction of their colour evolution
The timescales on which galaxies move out of the blue cloud to the red
sequence () provide insight into the mechanisms driving
quenching. Here, we build upon previous work, where we showcased a method to
reconstruct the colour evolution of observed low-redshift galaxies from the
Galaxy And Mass Assembly (GAMA) survey based on spectral energy distribution
(SED) fitting with ProSpect, together with a statistically-driven definition
for the blue and red populations. We also use the predicted colour evolution
from the SHARK semi-analytic model, combined with SED fits of our simulated
galaxy sample, to study the accuracy of the measured and
gain physical insight into the colour evolution of galaxies. In this work, we
measure in a consistent approach for both observations and
simulations. After accounting for selection bias, we find evidence for an
increase in in GAMA as a function of cosmic time (from
Gyr to Gyr in the lapse of
Gyr), but not in SHARK ( Gyr). Our
observations and simulations disagree on the effect of stellar mass, with GAMA
showing massive galaxies transitioning faster, but is the opposite in SHARK. We
find that environment only impacts galaxies below M in
GAMA, with satellites having shorter than centrals by
Gyr, with SHARK only in qualitative agreement. Finally, we compare to
previous literature, finding consistency with timescales in the order of couple
Gyr, but with several differences that we discuss.Comment: 17 pages, 14 figures. Submitted to MNRAS. Updated to reflect changes
addressing the referee's comment
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