20,871 research outputs found
The dependence of the IR-radio correlation on the metallicity
We have compiled a sample of 26 metal-poor galaxies with 12 + log(O/H) < 8.1
with both infrared continuum and 1.4 GHz radio continuum data. By comparing to
galaxies at higher metallicity, we have investigated the dependence on the
metallicity of the IR-radio relationship at 24 um, 70 um, 100 um and 160 um
bands as well as the integrated FIR luminosity. It is found that metal-poor
galaxies have on average lower qIR than metal-rich ones with larger offsets at
longer IR wavelengths, from -0.06 dex in q24um to -0.6 dex in q160um. The qIR
of all galaxies as a whole at 160 um show positive trends with the metallicity
and IR-to-FUV ratio, and negative trends with the IR color, while those at
lower IR wavelengths show weaker correlations. We proposed a mechanism that
invokes combined effects of low obscured-SFR/total-SFR fraction and warm dust
temperature at low metallicity to interpret the above behavior of qIR, with the
former reducing the IR radiation and the latter further reducing the IR
emission at longer IR wavelength. Other mechanisms that are related to the
radio emission including the enhanced magnetic field strength and increased
thermal radio contribution are unable to reconcile the IR-wavelength-dependent
differences of qIR between metal-poor and metal- rich galaxies. In contrast to
qIR, the mean total-SFR/radio ratio of metal-poor galaxies is the same as the
metal-rich one, indicating the 1.4 GHz radio emission is still an effective
tracer of SFRs at low metallicity.Comment: 25 pages, 11 figures, 4 tables. ApJ in pres
Sampled in Pairs and Driven by Text: A New Graph Embedding Framework
In graphs with rich texts, incorporating textual information with structural
information would benefit constructing expressive graph embeddings. Among
various graph embedding models, random walk (RW)-based is one of the most
popular and successful groups. However, it is challenged by two issues when
applied on graphs with rich texts: (i) sampling efficiency: deriving from the
training objective of RW-based models (e.g., DeepWalk and node2vec), we show
that RW-based models are likely to generate large amounts of redundant training
samples due to three main drawbacks. (ii) text utilization: these models have
difficulty in dealing with zero-shot scenarios where graph embedding models
have to infer graph structures directly from texts. To solve these problems, we
propose a novel framework, namely Text-driven Graph Embedding with Pairs
Sampling (TGE-PS). TGE-PS uses Pairs Sampling (PS) to improve the sampling
strategy of RW, being able to reduce ~99% training samples while preserving
competitive performance. TGE-PS uses Text-driven Graph Embedding (TGE), an
inductive graph embedding approach, to generate node embeddings from texts.
Since each node contains rich texts, TGE is able to generate high-quality
embeddings and provide reasonable predictions on existence of links to unseen
nodes. We evaluate TGE-PS on several real-world datasets, and experiment
results demonstrate that TGE-PS produces state-of-the-art results on both
traditional and zero-shot link prediction tasks.Comment: Accepted by WWW 2019 (The World Wide Web Conference. ACM, 2019
Submillimeter Array Observations of the Molecular Outflow in High-mass Star-forming Region G240.31+0.07
We present Submillimeter Array observations toward the 10^{4.7} Lsun
star-forming region G240.31+0.07, in the J=2-1 transition of 12CO and 13CO and
at 1.3 mm continuum, as well as the 12CO and 13CO observations from the Caltech
Submillimeter Observatory to recover the extended emission filtered out by the
interferometer. Maps of the 12CO and 13CO emission show a bipolar, wide-angle,
quasi-parabolic molecular outflow, roughly coincident with an IR nebula
revealed by the Spitzer 3.6 and 4.5 micron emission. The outflow has ~98 Msun
molecular gas, making it one of the most massive molecular outflows known, and
resulting in a very high mass-loss rate of 4.1 by 10^{-3} Msun yr^{-1} over a
dynamical timescale of 2.4 by 10^4 yr. The 1.3 mm continuum observations with a
4" by 3" beam reveal a flattened dusty envelope of ~150 Msun, which is further
resolved with a 1.2" by 1" beam into three dense cores with a total mass of ~40
Msun. The central mm core, showing evidence of active star formation,
approximately coincides with the geometric center of the bipolar outflow thus
most likely harbors the powering source of the outflow. Overall our
observations provide the best case to date of a well-defined wide-angle
molecular outflow in a >10^4 Lsun star-forming region. The outflow is
morphologically and kinematically similar to low-mass protostellar outflows but
has two to three orders of magnitude greater mass, momentum, and energy, and is
apparently driven by an underlying wide-angle wind, hence further supports that
high-mass stars up to late-O types, even in a crowded clustering environment,
can form as a scaled-up version of low-mass star formation.Comment: accepted for publication in the Ap
- …