40 research outputs found
Gemini Follow-up of two massive HI clouds discovered with the Australian Square Kilometer Array Pathfinder
Using the Gemini Multi Object Spectrograph (GMOS) we search for optical
counterparts of two massive (~10^9 solar masses) neutral hydrogen clouds near
the spiral galaxy IC 5270, located in the outskirts of the IC 1459 group. These
two HI clouds were recently discovered using the Australian Square Kilometer
Array Pathfinder (ASKAP). Two low surface brightness optical counterparts to
one of these HI clouds are identified in the new Gemini data that reaches down
to magnitudes of ~27.5 mag in the g-band. The observed HI mass to light ratio
derived with these new data, M_(HI)/L_g =242, is among the highest reported to
date. We are also able to rule out that the two HI clouds are dwarf companions
of IC 5270. Tidal interactions and ram pressure stripping are plausible
explanations for the physical origin of these two clouds.Comment: The journal version contains high-resolution images:
http://iopscience.iop.org/article/10.3847/2041-8213/aaaa1
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
The Host Galaxy of FRB 20171020A Revisited
The putative host galaxy of FRB 20171020A was first identified as ESO
601-G036 in 2018, but as no repeat bursts have been detected, direct
confirmation of the host remains elusive. In light of recent developments in
the field, we re-examine this host and determine a new association confidence
level of 98%. At 37 Mpc, this makes ESO 601-G036 the third closest FRB host
galaxy to be identified to date and the closest to host an apparently
non-repeating FRB (with an estimated repetition rate limit of < 0.011 bursts
per day above 10 erg). Due to its close distance, we are able to perform
detailed multi-wavelength analysis on the ESO 601-G036 system. Follow-up
observations confirm ESO 601-G036 to be a typical star-forming galaxy with HI
and stellar masses of log(M_HI/M_sol) ~ 9.2 and log(M_*/M_sol) = 8.64, and a
star formation rate of SFR = 0.09 +/- 0.01 M_sol/yr. We detect, for the first
time, a diffuse gaseous tail (log(M_HI/M_sol) ~ 8.3) extending to the
south-west that suggests recent interactions, likely with the confirmed nearby
companion ESO 601-G037. ESO 601-G037 is a stellar shred located to the south of
ESO 601-G036 that has an arc-like morphology, is about an order of magnitude
less massive, and has a lower gas metallicity that is indicative of a younger
stellar population. The properties of the ESO 601-G036 system indicate an
ongoing minor merger event, which is affecting the overall gaseous component of
the system and the stars within ESO 601-G037. Such activity is consistent with
current FRB progenitor models involving magnetars and the signs of recent
interactions in other nearby FRB host galaxies.Comment: 16 pages, 9 figures, accepted for publication in PAS
WALLABY Pilot Survey: Hydra Cluster Galaxies UV and HI morphometrics
Galaxy morphology in atomic hydrogen (HI) and in the ultra-violet (UV) are
closely linked. This has motivated their combined use to quantify morphology
over the full H i disk for both H i and UV imaging. We apply galaxy
morphometrics: Concentration, Asymmetry, Gini, M20 and
Multimode-Intensity-Deviation statistics to the first moment-0 maps of the
WALLABY survey of galaxies in the Hydra cluster center. Taking advantage of
this new HI survey, we apply the same morphometrics over the full HI extent on
archival GALEX FUV and NUV data to explore how well HI truncated, extended
ultraviolet disk (XUV) and other morphological phenomena can be captured using
pipeline WALLABY data products. Extended HI and UV disks can be identified
relatively straightforward from their respective concentration. Combined with
WALLABY HI, even the shallowest GALEX data is sufficient to identify XUV disks.
Our second goal is to isolate galaxies undergoing ram-pressure stripping in the
H i morphometric space. We employ four different machine learning techniques, a
decision tree, a k-nearest neighbour, a support-vector machine, and a random
forest. Up to 80% precision and recall are possible with the Random Forest
giving the most robust results.Comment: 17 figures, 12 figures, 7 tables, accepted by MNRA
WALLABY Pilot Survey: HI gas kinematics of galaxy pairs in cluster environment
We examine the H I gas kinematics of galaxy pairs in two clusters and a group using Australian Square Kilometre Array Pathfinder (ASKAP) WALLABY pilot survey observations. We compare the H I properties of galaxy pair candidates in the Hydra I and Norma clusters, and the NGC 4636 group, with those of non-paired control galaxies selected in the same fields. We perform H I profile decomposition of the sample galaxies using a tool, BAYGAUD which allows us to de-blend a line-of-sight velocity profile with an optimal number of Gaussian components. We construct H I super-profiles of the sample galaxies via stacking of their line profiles after aligning the central velocities. We fit a double Gaussian model to the super-profiles and classify them as kinematically narrow and broad components with respect to their velocity dispersions. Additionally, we investigate the gravitational instability of H I gas disks of the sample galaxies using Toomre Q parameters and H I morphological disturbances. We investigate the effect of the cluster environment on the H I properties of galaxy pairs by dividing the cluster environment into three subcluster regions (i.e., outskirts, infalling and central regions). We find that the denser cluster environment (i.e., infalling and central regions) is likely to impact the H I gas properties of galaxies in a way of decreasing the amplitude of the kinematically narrow H I gas (MnarrowHI role= presentation style= box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative; \u3eMHInarrowMnarrowHI/MtotalHI role= presentation style= box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative; \u3eMHItotalMtotalHI), and increasing the Toomre Q values of the infalling and central galaxies. This tendency is likely to be more enhanced for galaxy pairs in the cluster environment
WALLABY Pre-Pilot and Pilot Survey: the Tully Fisher Relation in Eridanus, Hydra, Norma and NGC4636 fields
The WALLABY pilot survey has been conducted using the Australian SKA Pathfinder (ASKAP). The integrated 21-cm HI line spectra are formed in a very different manner compared to usual single-dish spectra Tully-Fisher measurements. It is thus extremely important to ensure that slight differences (e.g. biases due to missing flux) are quantified and understood in order to maximise the use of the large amount of data becoming available soon. This article is based on four fields for which the data are scientifically interesting by themselves. The pilot data discussed here consist of 614 galaxy spectra at a rest wavelength of 21cm. Of these spectra, 472 are of high enough quality to be used to potentially derive distances using the Tully-Fisher relation. We further restrict the sample to the 251 galaxies whose inclination is sufficiently close to edge-on. For these, we derive Tully-Fisher distances using the deprojected WALLABY velocity widths combined with infrared (WISE W1) magnitudes. The resulting Tully-Fisher distances for the Eridanus, Hydra, Norma and NGC 4636 clusters are 21.5, 53.5, 69.4 and 23.0 Mpc respectively, with uncertainties of 5–10%, which are better or equivalent to the ones obtained in studies using data obtained with giant single dish telescopes. The pilot survey data show the benefits of WALLABY over previous giant single-dish telescope surveys. WALLABY is expected to detect around half a million galaxies with a mean redshift of 푧 = 0.05(200푀 푝푐). This study suggests that about 200,000 Tully-Fisher distances might result from the survey
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 ∼60 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 − 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 ∼0.5 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
The Rapid ASKAP Continuum Survey I: Design and First Results
The Rapid ASKAP Continuum Survey (RACS) is the first large-area survey to be
conducted with the full 36-antenna Australian Square Kilometre Array Pathfinder
(ASKAP) telescope. RACS will provide a shallow model of the ASKAP sky that will
aid the calibration of future deep ASKAP surveys. RACS will cover the whole sky
visible from the ASKAP site in Western Australia, and will cover the full ASKAP
band of MHz. The RACS images are generally deeper than the existing
NRAO VLA Sky Survey (NVSS) and Sydney University Molonglo Sky Survey (SUMSS)
radio surveys and have better spatial resolution. All RACS survey products will
be public, including radio images (with arcsecond resolution) and
catalogues of about three million source components with spectral index and
polarisation information. In this paper, we present a description of the RACS
survey and the first data release of 903 images covering the sky south of
declination made over a 288 MHz band centred at 887.5 MHz.Comment: 24 pages, 17 figures, 4 tables. For associated data see
https://data.csiro.au/collections/domain/casdaObservation/results/PRAS110%20-%20The%20Rapid%20ASKAP%20Continuu
Genomic epidemiology of SARS-CoV-2 in a UK university identifies dynamics of transmission
AbstractUnderstanding SARS-CoV-2 transmission in higher education settings is important to limit spread between students, and into at-risk populations. In this study, we sequenced 482 SARS-CoV-2 isolates from the University of Cambridge from 5 October to 6 December 2020. We perform a detailed phylogenetic comparison with 972 isolates from the surrounding community, complemented with epidemiological and contact tracing data, to determine transmission dynamics. We observe limited viral introductions into the university; the majority of student cases were linked to a single genetic cluster, likely following social gatherings at a venue outside the university. We identify considerable onward transmission associated with student accommodation and courses; this was effectively contained using local infection control measures and following a national lockdown. Transmission clusters were largely segregated within the university or the community. Our study highlights key determinants of SARS-CoV-2 transmission and effective interventions in a higher education setting that will inform public health policy during pandemics.</jats:p