200,431 research outputs found
Very compact millimeter sizes for composite star-forming/AGN submillimeter galaxies
We report the study of far-IR sizes of submillimeter galaxies (SMGs) in
relation to their dust-obscured star formation rate (SFR) and active galactic
nuclei (AGN) presence, determined using mid-IR photometry. We determined the
millimeter-wave (m) sizes of 69 ALMA-identified
SMGs, selected with confidence on ALMA images (--7.4 mJy). We found that all the SMGs are located above an
avoidance region in the millimeter size-flux plane, as expected by the
Eddington limit for star formation. In order to understand what drives the
different millimeter-wave sizes in SMGs, we investigated the relation between
millimeter-wave size and AGN fraction for 25 of our SMGs at --3. We found
that the SMGs for which the mid-IR emission is dominated by star formation or
AGN have extended millimeter-sizes, with respective median and 1.5 kpc. Instead, the SMGs for which
the mid-IR emission corresponds to star-forming/AGN composites have more
compact millimeter-wave sizes, with median
kpc. The relation between millimeter-wave size and AGN fraction suggests that
this size may be related to the evolutionary stage of the SMG. The very compact
sizes for composite star-forming/AGN systems could be explained by supermassive
black holes growing rapidly during the SMG coalescing, star-formation phase.Comment: 9 pages, 4 figures, 1 table. Accepted for publication in ApJ Lette
High-Rate Space Coding for Reconfigurable 2x2 Millimeter-Wave MIMO Systems
Millimeter-wave links are of a line-of-sight nature. Hence, multiple-input
multiple-output (MIMO) systems operating in the millimeter-wave band may not
achieve full spatial diversity or multiplexing. In this paper, we utilize
reconfigurable antennas and the high antenna directivity in the millimeter-wave
band to propose a rate-two space coding design for 2x2 MIMO systems. The
proposed scheme can be decoded with a low complexity maximum-likelihood
detector at the receiver and yet it can enhance the bit-error-rate performance
of millimeter-wave systems compared to traditional spatial multiplexing
schemes, such as the Vertical Bell Laboratories Layered Space-Time Architecture
(VBLAST). Using numerical simulations, we demonstrate the efficiency of the
proposed code and show its superiority compared to existing rate-two space-time
block codes
Maximum Throughput Scheduling for Multi-connectivity in Millimeter-Wave Networks
Multi-connectivity is emerging as promising solution to provide reliable
communications and seamless connectivity at the millimeter-wave frequency
range. Due to the obstacles that cause frequent interruptions at such high
frequency range, connectivity to multiple cells can drastically increase the
network performance in terms of throughput and reliability by coordination
among the network elements. In this paper, we propose an algorithm for the link
scheduling optimization that maximizes the network throughput for
multi-connectivity in millimeter-wave cellular networks. The considered
approach exploits a centralized architecture, fast link switching, proactive
context preparation and data forwarding between millimeter-wave access points
and the users. The proposed algorithm is able to numerically approach the
global optimum and to quantify the potential gain of multi-connectivity in
millimeter-wave cellular networks
MMIC technology for advanced space communications systems
The current NASA program for 20 and 30 GHz monolithic microwave integrated circuit (MMIC) technology is reviewed. The advantages of MMIC are discussed. Millimeter wavelength MMIC applications and technology for communications systems are discussed. Passive and active MMIC compatible components for millimeter wavelength applications are investigated. The cost of a millimeter wavelength MMIC's is projected
Dust in External Galaxies
Existing (Spitzer Space Telescope) and upcoming (Herschel Space Telescope)
facilities are deepening our understanding of the role of dust in tracing the
energy budget and chemical evolution of galaxies. The tools we are developing
while exploring the local Universe will in turn become pivotal in the
interpretation of the high redshift Universe when near--future facilities (the
Atacama Large Millimeter Array [ALMA], the Sub--Millimeter Array [SMA], the
Large Millimeter Telescope [LMT], the James Webb Space Telescope [JWST]), and,
possibly, farther--future ones, will begin operations.Comment: 14 pages, 5 figures, invited review at the conference `Cosmic Dust -
Near & Far', Heidelberg, Germany, September 2008. ASP Conference Series, Eds.
T. Henning et a
The sub-millimeter properties of broad absorption line quasars
We have carried out the first systematic survey of the sub-millimeter
properties of broad absorption line (BAL) quasars. 30 BAL quasars drawn from a
homogeneously selected sample from the Sloan Digital Sky Survey at redshifts
2<z<2.6 were observed with the SCUBA array at the JCMT to a typical rms
sensitivity of 2.5 mJy. Eight quasars were detected at > 2 sigma significance,
four of which are at > 3 sigma significance. The far-infrared luminosities of
these quasars are > 10^{13} L_solar. There is no correlation of sub-millimeter
flux with either the strength of the broad absorption feature or with absolute
magnitude in our sample. We compare the sub-millimeter flux distribution of the
BAL quasar sample with that of a sample of quasars which do not show BAL
features in their optical spectra and find that the two are indistinguishable.
BAL quasars do not have higher sub-millimeter luminosities than non-BAL
quasars. These findings are consistent with the hypothesis that all quasars
would contain a BAL if viewed along a certain line-of-sight. The data are
inconsistent with a model in which the BAL phenomenon indicates a special
evolutionary stage which co-incides with a large dust mass in the host galaxy
and a high sub-millimeter luminosity. Our work provides constraints on
alternative evolutionary explanations of BAL quasars.Comment: 8 pages, 2 figures, ApJ, in pres
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