17,593 research outputs found
Spatially Extended Low Ionization Emission Regions (LIERs) at
We present spatially resolved emission diagnostics for eight
galaxies that demonstrate extended low ionization emission-line regions (LIERs)
over kpc scales. Eight candidates are selected based on their spatial extent
and emission line fluxes from slitless spectroscopic observations with the
HST/WFC3 G141 and G800L grisms in the well-studied GOODS survey fields. Five of
the candidates (62.5%) are matched to X-ray counterparts in the \textit{Chandra
X-Ray Observatory} Deep Fields. We modify the traditional
Baldwin-Philips-Terlevich (BPT) emission line diagnostic diagram to use
[SII]/(H+[NII]) instead of [NII]/H to overcome the blending of
[NII] and H+[NII] in the low resolution slitless grism spectra. We
construct emission line ratio maps and place the individual pixels in the
modified BPT. The extended LINER-like emission present in all of our
candidates, coupled with X-Ray properties consistent with star-forming galaxies
and weak [OIII]5007\AA\ detections, is inconsistent with purely
nuclear sources (LINERs) driven by active galactic nuclei. While recent
ground-based integral field unit spectroscopic surveys have revealed
significant evidence for diffuse LINER-like emission in galaxies within the
local universe , this work provides the first evidence for the
non-AGN origin of LINER-like emission out to high redshifts.Comment: 11 pages, 1 table, 6 figures, accepted for publication in the
Astrophysics Journal (ApJ
Sub-Nyquist Sampling: Bridging Theory and Practice
Sampling theory encompasses all aspects related to the conversion of
continuous-time signals to discrete streams of numbers. The famous
Shannon-Nyquist theorem has become a landmark in the development of digital
signal processing. In modern applications, an increasingly number of functions
is being pushed forward to sophisticated software algorithms, leaving only
those delicate finely-tuned tasks for the circuit level.
In this paper, we review sampling strategies which target reduction of the
ADC rate below Nyquist. Our survey covers classic works from the early 50's of
the previous century through recent publications from the past several years.
The prime focus is bridging theory and practice, that is to pinpoint the
potential of sub-Nyquist strategies to emerge from the math to the hardware. In
that spirit, we integrate contemporary theoretical viewpoints, which study
signal modeling in a union of subspaces, together with a taste of practical
aspects, namely how the avant-garde modalities boil down to concrete signal
processing systems. Our hope is that this presentation style will attract the
interest of both researchers and engineers in the hope of promoting the
sub-Nyquist premise into practical applications, and encouraging further
research into this exciting new frontier.Comment: 48 pages, 18 figures, to appear in IEEE Signal Processing Magazin
Double-peaked Narrow Emission-line Galaxies in LAMOST Survey
We outline a full-scale search for galaxies exhibiting double-peaked profiles
of promi- nent narrow emission lines, motivated by the prospect of finding
objects related to merging galaxies, and even dual active galactic nuclei
candidates as by-product, from the Large Sky Area Multi-object Fiber
Spectroscopic Telescope (LAMOST) Data Re- lease 4. We assemble a large sample
of 325 candidates with double-peaked or strong asymmetric narrow emission
lines, with 33 objects therein appearing optically resolved dual-cored
structures, close companions or signs of recent interaction on the Sloan Dig-
ital Sky Survey images. A candidate from LAMOST (J074810.95+281349.2) is also
stressed here based on the kinematic and spatial decompositions of the
double-peaked narrow emission line target, with analysis from the
cross-referenced Mapping Nearby Galaxies at the Apache Point Observatory
(MaNGA) survey datacube. MaNGA en- ables us to constrain the origin of double
peaks for these sources, and with the IFU data we infer that the most promising
origin of double-peaked profiles for LAMOST J074810.95+281349.2 is the
`Rotation Dominated + Disturbance' structure.Comment: 13 pages, 9 figures, accepted by MNRA
The digital data processing concepts of the LOFT mission
The Large Observatory for X-ray Timing (LOFT) is one of the five mission
candidates that were considered by ESA for an M3 mission (with a launch
opportunity in 2022 - 2024). LOFT features two instruments: the Large Area
Detector (LAD) and the Wide Field Monitor (WFM). The LAD is a 10 m 2 -class
instrument with approximately 15 times the collecting area of the largest
timing mission so far (RXTE) for the first time combined with CCD-class
spectral resolution. The WFM will continuously monitor the sky and recognise
changes in source states, detect transient and bursting phenomena and will
allow the mission to respond to this. Observing the brightest X-ray sources
with the effective area of the LAD leads to enormous data rates that need to be
processed on several levels, filtered and compressed in real-time already on
board. The WFM data processing on the other hand puts rather low constraints on
the data rate but requires algorithms to find the photon interaction location
on the detector and then to deconvolve the detector image in order to obtain
the sky coordinates of observed transient sources. In the following, we want to
give an overview of the data handling concepts that were developed during the
study phase.Comment: Proc. SPIE 9144, Space Telescopes and Instrumentation 2014:
Ultraviolet to Gamma Ray, 91446
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