3,151 research outputs found
A Magnified View of the Kinematics and Morphology of RCSGA 032727-132609: Zooming in on a Merger at z=1.7
We present a detailed analysis of multi-wavelength HST/WFC3 imaging and
Keck/OSIRIS near-IR AO-assisted integral field spectroscopy for a highly
magnified lensed galaxy at z=1.70. This young starburst is representative of
UV-selected star-forming galaxies (SFG) at z~2 and contains multiple individual
star-forming regions. Due to the lensing magnification, we can resolve spatial
scales down to 100pc in the source plane of the galaxy. The velocity field
shows disturbed kinematics suggestive of an ongoing interaction, and there is a
clear signature of a tidal tail. We constrain the age, reddening, SFR and
stellar mass of the star-forming clumps from SED modelling of the WFC3
photometry and measure their H-alpha luminosity, metallicity and outflow
properties from the OSIRIS data. With strong star formation driven outflows in
four clumps, RCSGA0327 is the first high redshift SFG at stellar mass <10^10
M_sun with spatially resolved stellar winds. We compare the H-alpha
luminosities, sizes and dispersions of the star-forming regions to other high-z
clumps as well as local giant HII regions and find no evidence for increased
clump star formation surface densities in interacting systems, unlike in the
local Universe. Spatially resolved SED modelling unveils an established stellar
population at the location of the largest clump and a second mass concentration
near the edge of the system which is not detected in H-alpha emission. This
suggests a picture of an equal-mass mixed major merger, which has not triggered
a new burst of star formation or caused a tidal tail in the gas-poor component.Comment: 22 pages, 16 figures, accepted to Ap
Erasure Correction for Noisy Radio Networks
The radio network model is a well-studied model of wireless, multi-hop networks. However, radio networks make the strong assumption that messages are delivered deterministically. The recently introduced noisy radio network model relaxes this assumption by dropping messages independently at random.
In this work we quantify the relative computational power of noisy radio networks and classic radio networks. In particular, given a non-adaptive protocol for a fixed radio network we show how to reliably simulate this protocol if noise is introduced with a multiplicative cost of poly(log Delta, log log n) rounds where n is the number nodes in the network and Delta is the max degree. Moreover, we demonstrate that, even if the simulated protocol is not non-adaptive, it can be simulated with a multiplicative O(Delta log ^2 Delta) cost in the number of rounds. Lastly, we argue that simulations with a multiplicative overhead of o(log Delta) are unlikely to exist by proving that an Omega(log Delta) multiplicative round overhead is necessary under certain natural assumptions
Probing Individual Star Forming Regions Within Strongly Lensed Galaxies at z > 1
Star formation occurs on physical scales corresponding to individual star
forming regions, typically of order ~100 parsecs in size, but current
observational facilities cannot resolve these scales within field galaxies
beyond the local universe. However, the magnification from strong gravitational
lensing allows us to measure the properties of these discrete star forming
regions within galaxies in the distant universe. New results from
multi-wavelength spectroscopic studies of a sample of extremely bright, highly
magnified lensed galaxies are revealing the complexity of star formation on
sub-galaxy scales during the era of peak star formation in the universe. We
find a wide range of properties in the rest-frame UV spectra of individual
galaxies, as well as in spectra that originate from different star forming
regions within the same galaxy. Large variations in the strengths and velocity
structure of Lyman-alpha and strong P Cygni lines such as C IV, and MgII
provide new insights into the astrophysical relationships between extremely
massive stars, the elemental abundances and physical properties of the nebular
gas those stars ionize, and the galactic-scale outflows they power.Comment: 4 pages, 3 figures. To be published in the Proceedings of IAU
Symposium 309. For more details and closely related work see also
arXiv:1310.6695 and arXiv:1406.335
Searching for Cooling Signatures in Strong Lensing Galaxy Clusters: Evidence Against Baryons Shaping the Matter Distribution in Cluster Cores
The process by which the mass density profile of certain galaxy clusters
becomes centrally concentrated enough to produce high strong lensing (SL)
cross-sections is not well understood. It has been suggested that the baryonic
condensation of the intra-cluster medium (ICM) due to cooling may drag dark
matter to the cores and thus steepen the profile. In this work, we search for
evidence of ongoing ICM cooling in the first large, well-defined sample of
strong lensing selected galaxy clusters in the range 0.1 < z < 0.6. Based on
known correlations between the ICM cooling rate and both optical emission line
luminosity and star formation, we measure, for a sample of 89 strong lensing
clusters, the fraction of clusters that have [OII]3727 emission in their
brightest cluster galaxy (BCG). We find that the fraction of line-emitting BCGs
is constant as a function of redshift for z > 0.2 and shows no statistically
significant deviation from the total cluster population. Specific star
formation rates, as traced by the strength of the 4000 angstrom break, D_4000,
are also consistent with the general cluster population. Finally, we use
optical imaging of the SL clusters to measure the angular separation, R_arc,
between the arc and the center of mass of each lensing cluster in our sample
and test for evidence of changing [OII] emission and D_4000 as a function of
R_arc, a proxy observable for SL cross-sections. D_4000 is constant with all
values of R_arc, and the [OII] emission fractions show no dependence on R_arc
for R_arc > 10" and only very marginal evidence of increased weak [OII]
emission for systems with R_arc < 10". These results argue against the ability
of baryonic cooling associated with cool core activity in the cores of galaxy
clusters to strongly modify the underlying dark matter potential, leading to an
increase in strong lensing cross-sections.Comment: 9 Pages, 5 Figures, 1 Tabl
Spatially Resolved Galactic Wind in Lensed Galaxy RCSGA 032727-132609
We probe the spatial distribution of outflowing gas along four lines of sight
separated by up to 6 kpc in a gravitationally-lensed star-forming galaxy at
z=1.70. Using MgII and FeII emission and absorption as tracers, we find that
the clumps of star formation are driving galactic outflows with velocities of
-170 to -250 km/sec. The velocities of MgII emission are redshifted with
respect to the systemic velocities of the galaxy, consistent with being
back-scattered. By contrast, the FeII fluorescent emission lines are either
slightly blueshifted or at the systemic velocity of the galaxy. Taken together,
the velocity structure of the MgII and FeII emission is consistent with arising
through scattering in galactic winds. Assuming a thin shell geometry for the
out owing gas, the estimated masses carried out by these outfows are large (>
30 - 50 ), with mass loading factors several times the
star-formation rate. Almost 20% to 50% of the blueshifted absorption probably
escapes the gravitational potential of the galaxy. In this galaxy, the outflow
is "locally sourced", that is, the properties of the outflow in each line of
sight are dominated by the properties of the nearest clump of star formation;
the wind is not global to the galaxy. The mass outflow rates and the momentum
flux carried out by outflows in individual star forming knots of this object
are comparable to that of starburst galaxies in the local Universe.Comment: 19 pages, 10 figure, accepted for publication in MNRA
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