46 research outputs found
Cold gas outflows from the Small Magellanic Cloud traced with ASKAP
Feedback from massive stars plays a critical role in the evolution of the
Universe by driving powerful outflows from galaxies that enrich the
intergalactic medium and regulate star formation. An important source of
outflows may be the most numerous galaxies in the Universe: dwarf galaxies.
With small gravitational potential wells, these galaxies easily lose their
star-forming material in the presence of intense stellar feedback. Here, we
show that the nearby dwarf galaxy, the Small Magellanic Cloud (SMC), has atomic
hydrogen outflows extending at least 2 kiloparsecs (kpc) from the star-forming
bar of the galaxy. The outflows are cold, , and may have formed
during a period of active star formation million years (Myr) ago. The
total mass of atomic gas in the outflow is solar masses, , or % of the total atomic gas of the galaxy. The inferred
mass flux in atomic gas alone, , is up to an order of magnitude greater than the star
formation rate. We suggest that most of the observed outflow will be stripped
from the SMC through its interaction with its companion, the Large Magellanic
Cloud (LMC), and the Milky Way, feeding the Magellanic Stream of hydrogen
encircling the Milky Way.Comment: Published in Nature Astronomy, 29 October 2018,
http://dx.doi.org/10.1038/s41550-018-0608-
WALLABY Early Science - I. The NGC 7162 Galaxy Group
We present Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY) early
science results from the Australian Square Kilometre Array Pathfinder (ASKAP)
observations of the NGC 7162 galaxy group. We use archival HIPASS and Australia
Telescope Compact Array (ATCA) observations of this group to validate the new
ASKAP data and the data reduction pipeline ASKAPsoft. We detect six galaxies in
the neutral hydrogen (HI) 21-cm line, expanding the NGC 7162 group membership
from four to seven galaxies. Two of the new detections are also the first HI
detections of the dwarf galaxies, AM 2159-434 and GALEXASC J220338.65-431128.7,
for which we have measured velocities of and km s,
respectively. We confirm that there is extended HI emission around NGC 7162
possibly due to past interactions in the group as indicated by the
offset between the kinematic and morphological major axes for NGC 7162A, and
its HI richness. Taking advantage of the increased resolution (factor of
) of the ASKAP data over archival ATCA observations, we fit a tilted
ring model and use envelope tracing to determine the galaxies' rotation curves.
Using these we estimate the dynamical masses and find, as expected, high dark
matter fractions of for all group members. The
ASKAP data are publicly available.Comment: 20 pages, 11 figures, accepted for publication in MNRA
Electrical Control of Plasmon Resonance with Graphene
Surface plasmon, with its unique capability to concentrate light into
sub-wavelength volume, has enabled great advances in photon science, ranging
from nano-antenna and single-molecule Raman scattering to plasmonic waveguide
and metamaterials. In many applications it is desirable to control the surface
plasmon resonance in situ with electric field. Graphene, with its unique
tunable optical properties, provides an ideal material to integrate with
nanometallic structures for realizing such control. Here we demonstrate
effective modulation of the plasmon resonance in a model system composed of
hybrid graphene-gold nanorod structure. Upon electrical gating the strong
optical transitions in graphene can be switched on and off, which leads to
significant modulation of both the resonance frequency and quality factor of
plasmon resonance in gold nanorods. Hybrid graphene-nanometallic structures, as
exemplified by this combination of graphene and gold nanorod, provide a general
and powerful way for electrical control of plasmon resonances. It holds promise
for novel active optical devices and plasmonic circuits at the deep
subwavelength scale
Atomically thin three-dimensional membranes of van der Waals semiconductors by wafer-scale growth
We report wafer-scale growth of atomically thin, three-dimensional (3D) van der Waals (vdW) semiconductor membranes. By controlling the growth kinetics in the near-equilibrium limit during metal-organic chemical vapor depositions of MoS2 and WS2 monolayer (ML) crystals, we have achieved conformal ML coverage on diverse 3D texture substrates, such as periodic arrays of nanoscale needles and trenches on quartz and SiO2/Si substrates. The ML semiconductor properties, such as channel resistivity and photoluminescence, are verified to be seamlessly uniform over the 3D textures and are scalable to wafer scale. In addition, we demonstrated that these 3D films can be easily delaminated from the growth substrates to form suspended 3D semiconductor membranes. Our work suggests that vdW ML semiconductor films can be useful platforms for patchable membrane electronics with atomic precision, yet large areas, on arbitrary substrates.11Ysciescopu
The Look-back Time Evolution of Far-Ultraviolet Flux from the Brightest Cluster Elliptical Galaxies at z < 0.2
We present the GALEX UV photometry of the elliptical galaxies in Abell
clusters at moderate redshifts (z < 0.2) for the study of the look-back time
evolution of the UV upturn phenomenon. The brightest elliptical galaxies (M_r <
-22) in 12 remote clusters are compared with the nearby giant elliptical
galaxies of comparable optical luminosity in the Fornax and Virgo clusters. The
sample galaxies presented here appear to be quiescent without signs of massive
star formation or strong nuclear activity, and show smooth, extended profiles
in their UV images indicating that the far-UV (FUV) light is mostly produced by
hot stars in the underlying old stellar population. Compared to their
counterparts in nearby clusters, the FUV flux of cluster giant elliptical
galaxies at moderate redshifts fades rapidly with ~ 2 Gyrs of look-back time,
and the observed pace in FUV - V color evolution agrees reasonably well with
the prediction from the population synthesis models where the dominant FUV
source is hot horizontal-branch stars and their progeny. A similar amount of
color spread (~ 1 mag) in FUV - V exists among the brightest cluster elliptical
galaxies at z ~ 0.1, as observed among the nearby giant elliptical galaxies of
comparable optical luminosity.Comment: Accepted for publication in the Special GALEX ApJ Supplement,
December 200
Neutral hydrogen (H I) gas content of galaxies at z â 0.32
We use observations made with the Giant Metrewave Radio Telescope (GMRT) to probe the neutral hydrogen (H I) gas content of field galaxies in the VIMOS VLT Deep Survey (VVDS) 14h field at z â 0.32. Because the HI emission from individual galaxies is too faint to detect at this redshift, we use an HI spectral stacking technique using the known optical positions and redshifts of the 165 galaxies in our sample to co-add theirHI spectra and thus obtain the average HI mass of the galaxies. Stacked HI measurements of 165 galaxies show that âł95 per cent of the neutral gas is found in blue, star-forming galaxies. Among these galaxies, those having lower stellar mass are more gas rich than more massive ones. We apply a volume correction to our HI measurement to evaluate the HI gas density at zâ0.32 asΩHI = (0.50 ± 0.18) Ă 10-3 in units of the cosmic critical density. This value is in good agreement with previous results at z < 0.4, suggesting no evolution in the neutral hydrogen gas density over the last ~4Gyr. However the z â 0.32 gas density is lower than that at z ~ 5 by at least a factor of two.This research was funded by an Australian Indian Strategic Research Fund (AISRF) grant. This fund was jointly administered by the Department of Innovation, Industry, Science and Research in Australia and by the Department of Science and Technology in India. The project title was âGas in Galaxies in the Distant Pastâ. Parts of this research were conducted by the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020. Funding for the SDSS and SDSSâII has been provided by the Alfred P. Sloan Foundation,
the Participating Institutions, the National Science Foundation, the
U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society and the Higher Education Funding Council for England
Deep Investigation of Neutral Gas Origins (DINGO): HI stacking experiments with early science data
We present early science results from Deep Investigation of Neutral Gas
Origins (DINGO), an HI survey using the Australian Square Kilometre Array
Pathfinder (ASKAP). Using ASKAP sub-arrays available during its commissioning
phase, DINGO early science data were taken over 60 deg of the
Galaxy And Mass Assembly (GAMA) 23 h region with 35.5 hr integration time. We
make direct detections of six known and one new sources at . Using HI
spectral stacking, we investigate the HI gas content of galaxies at for different galaxy colours. The results show that galaxy morphology
based on optical colour is strongly linked to HI gas properties. To examine
environmental impacts on the HI gas content of galaxies, three sub-samples are
made based on the GAMA group catalogue. The average HI mass of group central
galaxies is larger than those of satellite and isolated galaxies, but with a
lower HI gas fraction. We derive a variety of HI scaling relations for physical
properties of our sample, including stellar mass, stellar mass surface density,
colour, specific star formation rate, and halo mass. We find that the
derived HI scaling relations are comparable to other published results, with
consistent trends also observed to 0.5 dex lower limits in stellar mass
and stellar surface density. The cosmic HI densities derived from our data are
consistent with other published values at similar redshifts. DINGO early
science highlights the power of HI spectral stacking techniques with ASKAP.Comment: 27 pages, 25 figures, 10 tables, accepted for publication in MNRA
Deep Investigation of Neutral Gas Origins (DINGO): HI stacking experiments with early science data
We present early science results from Deep Investigation of Neutral Gas Origins (DINGO), an H I survey using the Australian Square Kilometre Array Pathfinder (ASKAP). Using ASKAP subarrays available during its commissioning phase, DINGO early science data were taken over âŒ60 deg2 of the Galaxy And Mass Assembly (GAMA) 23 h region with 35.5 h integration time. We make direct detections of six known and one new sources at z \u3c 0.01. Using H I spectral stacking, we investigate the H I gas content of galaxies at 0.04 \u3c z \u3c 0.09 for different galaxy colours. The results show that galaxy morphology based on optical colour is strongly linked to H I gas properties. To examine environmental impacts on the H I gas content of galaxies, three subsamples are made based on the GAMA group catalogue. The average H I mass of group central galaxies is larger than those of satellite and isolated galaxies, but with a lower H I gas fraction. We derive a variety of H I scaling relations for physical properties of our sample, including stellar mass, stellar mass surface density, NUV â r colour, specific star formation rate, and halo mass. We find that the derived H I scaling relations are comparable to other published results, with consistent trends also observed to âŒ0.5 dex lower limits in stellar mass and stellar surface density. The cosmic H I densities derived from our data are consistent with other published values at similar redshifts. DINGO early science highlights the power of H I spectral stacking techniques with ASKA
FAST-ASKAP Synergy: Quantifying Coexistent Tidal and Ram-Pressure Strippings in the NGC 4636 Group
Combining new HI data from a synergetic survey of ASKAP WALLABY and FAST with
the ALFALFA data, we study the effect of ram-pressure and tidal interactions in
the NGC 4636 group. We develop two parameters to quantify and disentangle these
two effects on gas stripping in HI-bearing galaxies: the strength of external
forces at the optical-disk edge, and the outside-in extents of HI-disk
stripping. We find that gas stripping is widespread in this group, affecting
80% of HI-detected non-merging galaxies, and that 34% are experiencing both
types of stripping. Among the galaxies experiencing both effects, the strengths
(and extents) of ram-pressure and tidal stripping are independent of each
other. Both strengths are correlated with HI-disk shrinkage. The tidal strength
is related to a rather uniform reddening of low-mass galaxies
() when tidal stripping is the dominating effect. In
contrast, ram pressure is not clearly linked to the color-changing patterns of
galaxies in the group. Combining these two stripping extents, we estimate the
total stripping extent, and put forward an empirical model that can describe
the decrease of HI richness as galaxies fall toward the group center. The
stripping timescale we derived decreases with distance to the center, from
around to
near the center. Gas-depletion happens
since crossing for HI-rich galaxies,
but much quicker for HI-poor ones. Our results quantify in a physically
motivated way the details and processes of environmental-effects-driven galaxy
evolution, and might assist in analyzing hydrodynamic simulations in an
observational way.Comment: 44 pages, 22 figures, 5 tables, accepted for publication in ApJ.
Tables 4 and 5 are also available in machine-readable for