106 research outputs found
Submm/mm Galaxy Counterpart Identification Using a Characteristic Density Distribution
We present a new submm/mm galaxy counterpart identification technique which
builds on the use of Spitzer IRAC colors as discriminators between likely
counterparts and the general IRAC galaxy population. Using 102 radio- and
SMA-confirmed counterparts to AzTEC sources across three fields (GOODS-N,
GOODS-S, and COSMOS), we develop a non-parametric IRAC color-color
characteristic density distribution (CDD), which, when combined with positional
uncertainty information via likelihood ratios, allows us to rank all potential
IRAC counterparts around SMGs and calculate the significance of each ranking
via the reliability factor. We report all robust and tentative radio
counterparts to SMGs, the first such list available for AzTEC/COSMOS, as well
as the highest ranked IRAC counterparts for all AzTEC SMGs in these fields as
determined by our technique. We demonstrate that the technique is free of radio
bias and thus applicable regardless of radio detections. For observations made
with a moderate beamsize (~18"), this technique identifies ~85 per cent of SMG
counterparts. For much larger beamsizes (>30"), we report identification rates
of 33-49 per cent. Using simulations, we demonstrate that this technique is an
improvement over using positional information alone for observations with
facilities such as AzTEC on the LMT and SCUBA-2 on JCMT.Comment: 30 pages, 9 figures, 5 tables. Accepted for publication in MNRA
Spatial correlation between submillimetre and Lyman-alpha galaxies in the SSA 22 protocluster
Lyman-alpha emitters are thought to be young, low-mass galaxies with ages of
~10^8 yr. An overdensity of them in one region of the sky (the SSA 22 field)
traces out a filamentary structure in the early Universe at a redshift of z =
3.1 (equivalent to 15 per cent of the age of the Universe) and is believed to
mark a forming protocluster. Galaxies that are bright at (sub)millimetre
wavelengths are undergoing violent episodes of star formation, and there is
evidence that they are preferentially associated with high-redshift radio
galaxies, so the question of whether they are also associated with the most
significant large-scale structure growing at high redshift (as outlined by
Lyman-alpha emitters) naturally arises. Here we report an imaging survey of
1,100-um emission in the SSA 22 region. We find an enhancement of submillimetre
galaxies near the core of the protocluster, and a large-scale correlation
between the submillimetre galaxies and the low-mass Lyman-alpha emitters,
suggesting synchronous formation of the two very different types of
star-forming galaxy within the same structure at high redshift. These results
are in general agreement with our understanding of the formation of cosmic
structure.Comment: Published in Nature (7th May 2009 issue). The astro-ph paper includes
the main text (10 pages, 2 figures, 1 table) and supplementary material (6
pages, 4 figures, 1 table
Material properties of a low contraction and resistivity silicon-aluminum composite for cryogenic detectors
We report on the cryogenic properties of a low-contraction silicon-aluminum
composite, namely Japan Fine Ceramics SA001, to use as a packaging structure
for cryogenic silicon devices. SA001 is a silicon--aluminum composite material
(75% silicon by volume) and has a low thermal expansion coefficient (1/3
that of aluminum). The superconducting transition temperature of SA001 is
measured to be 1.18 K, which is in agreement with that of pure aluminum, and is
thus available as a superconducting magnetic shield material. The residual
resistivity of SA001 is 0.065 , which is considerably
lower than an equivalent silicon--aluminum composite material. The measured
thermal contraction of SA001 immersed in liquid nitrogen is
%, which is
consistent with the expected rate obtained from the volume-weighted mean of the
contractions of silicon and aluminum. The machinability of SA001 is also
confirmed with a demonstrated fabrication of a conical feedhorn array, with a
wall thickness of 100 . These properties are suitable for
packaging applications for large-format superconducting detector devices.Comment: 8 pages, 4 figures, 1 table, accepted for the Journal of Low
Temperature Physics for the LTD19 special issu
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