85 research outputs found
A magnified view of star formation at redshift 0.9 from two lensed galaxies
We present new narrow-band H alpha imaging from the Hubble Space Telescope of
two redshift 0.91 galaxies that have been lensed by foreground galaxy cluster
Abell 2390. These data probe spatial scales as small as 0.3 kpc, providing a
magnified look at the morphology of star formation at an epoch when the global
star formation rate was high. However, dust attenuates our spatially resolved
star formation rate (SFR) indicators, the H alpha and rest-UV emission, and we
lack a direct measurement of extinction. Other studies have found that ionized
gas in galaxies tends to be roughly 50 percent more obscured than stars;
however, given an unextincted measurement of the SFR we can quantify the
relative stellar to nebular extinction and the extinction in H{\alpha}. We
infer SFRs from Spitzer and Herschel mid- to far-infrared observations and
compare these to integrated H alpha and rest-UV SFRs; this yields stellar to
nebular extinction ratios consistent with previous studies. We take advantage
of high spatial resolution and contextualize these results in terms of the
source-plane morphologies, comparing the distribution of H alpha to that of the
rest-frame UV and optical light. In one galaxy, we measure separate SFRs in
visually distinct clumps, but can set only a lower limit on the extinction and
thus the star formation. Consequently, the data are also consistent with there
being an equal amount of extinction along the lines of sight to the ionized gas
as to the stars. Future observations in the far-infrared could settle this by
mapping out the dust directly.Comment: Published as 2014, The Astronomical Journal, 148, 6
A new introductory quantum mechanics curriculum
The Institute of Physics New Quantum Curriculum consists of freely available
online learning and teaching materials (quantumphysics.iop.org) for a first
course in university quantum mechanics starting from two-level systems. This
approach immediately immerses students in inherently quantum mechanical aspects
by focusing on experiments that have no classical explanation. It allows from
the start a discussion of interpretive aspects of quantum mechanics and quantum
information theory. This article gives an overview of the resources available
at the IOP website. The core text is presented as around 80 articles
co-authored by leading experts that are arranged in themes and can be used
flexibly to provide a range of alternative approaches. Many of the articles
include interactive simulations with accompanying activities and problem sets
that can be explored by students to enhance their understanding. Much of the
linear algebra needed for this approach is part of the resource. Solutions to
activities are available to instructors. The resources can be used in a variety
of ways from supplements to existing courses to a complete programme.Comment: 10 pages, 2 figures, 1 table; submitted to the European Journal of
Physic
The Emission Line Properties of Gravitationally-lensed 1.5 < z < 5 Galaxies
We present and analyse near-infrared spectroscopy for a sample of 28
gravitationally- lensed star-forming galaxies in the redshift range 1.5 < z <
5, observed mostly with the Keck II telescope. With typical magnifications of
~1.5-4 magnitudes, our survey provides a valuable census of star formation
rates, gas-phase metallicities and dynamical masses for a representative sample
of low luminosity galaxies seen at a formative period in cosmic history. We
find less evolution in the mass-metallicity relation compared to earlier work
that focused on more luminous systems with z - 2-3, especially in the low mass
(- 10^9 Msol) where our sample is - 0.25 dex more metal-rich. We interpret this
offset as a result of the lower star formation rates (typically a factor of -10
lower) for a given stellar mass in our sub-luminous systems. Taking this effect
into account, we conclude our objects are consistent with a fundamental
metallicity relation recently proposed from unlensed observations.Comment: 22 pages, 12 figures, MNRAS, version including proof correction
An ALMA survey of Sub-millimeter Galaxies in the Extended Chandra Deep Field South: Physical properties derived from ultraviolet-to-radio modelling
[abridged] The ALESS survey has followed-up a sample of 122 sub-millimeter
sources in the Extended Chandra Deep Field South at 870um with ALMA, allowing
to pinpoint the positions of sub-millimeter galaxies (SMGs) to 0.3'' and to
find their precise counterparts at different wavelengths. This enabled the
first compilation of the multi-wavelength spectral energy distributions (SEDs)
of a statistically reliable survey of SMGs. In this paper, we present a new
calibration of the MAGPHYS modelling code that is optimized to fit these
UV-to-radio SEDs of z>1 star-forming galaxies using an energy balance technique
to connect the emission from stellar populations, dust attenuation and dust
emission in a physically consistent way. We derive statistically and physically
robust estimates of the photometric redshifts and physical parameters for the
ALESS SMGs. We find that they have a median stellar mass
, SFR/yr, overall
V-band dust attenuation mag, dust mass
M_\rm{dust}=(5.6\pm1.0)\times10^8 M_\odot, and average dust temperature
Tdust~40 K. The average intrinsic SED of the ALESS SMGs resembles that of local
ULIRGs in the IR range, but the stellar emission of our average SMG is brighter
and bluer, indicating lower dust attenuation, possibly because they are more
extended. We explore how the average SEDs vary with different parameters, and
we provide a new set of SMG templates. To put the ALESS SMGs into context, we
compare their stellar masses and SFRs with those of less actively star-forming
galaxies at the same redshifts. At z~2, about half of the SMGs lie above the
star-forming main sequence, while half are at the high-mass end of the
sequence. At higher redshifts (z~3.5), the SMGs tend to have higher SFR and
Mstar, but the fraction of SMGs that lie significantly above the main sequence
decreases to less than a third.Comment: 22 pages, 14 figures, 2 tables. Accepted for publication in the
Astrophysical Journal. The new MAGPHYS model libraries used in this paper
will appear in www.iap.fr/magphys. The SMG SED templates shown in Section 6.1
are available at
http://astronomy.swinburne.edu.au/~ecunha/ecunha/SED_Templates.htm
The behaviour of dark matter associated with 4 bright cluster galaxies in the 10kpc core of Abell 3827
Galaxy cluster Abell 3827 hosts the stellar remnants of four almost equally
bright elliptical galaxies within a core of radius 10kpc. Such corrugation of
the stellar distribution is very rare, and suggests recent formation by several
simultaneous mergers. We map the distribution of associated dark matter, using
new Hubble Space Telescope imaging and VLT/MUSE integral field spectroscopy of
a gravitationally lensed system threaded through the cluster core. We find that
each of the central galaxies retains a dark matter halo, but that (at least)
one of these is spatially offset from its stars. The best-constrained offset is
1.62+/-0.48kpc, where the 68% confidence limit includes both statistical error
and systematic biases in mass modelling. Such offsets are not seen in field
galaxies, but are predicted during the long infall to a cluster, if dark matter
self-interactions generate an extra drag force. With such a small physical
separation, it is difficult to definitively rule out astrophysical effects
operating exclusively in dense cluster core environments - but if interpreted
solely as evidence for self-interacting dark matter, this offset implies a
cross-section sigma/m=(1.7+/-0.7)x10^{-4}cm^2/g x (t/10^9yrs)^{-2}, where t is
the infall duration.Comment: 15 pages, 9 figure
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