73 research outputs found
High-velocity OH megamasers in IRAS 20100-4156: Evidence for a Supermassive Black Hole
We report the discovery of new, high-velocity narrow-line components of the
OH megamaser in IRAS 20100-4156. Results from the Australian Square Kilometre
Array Pathfinder (ASKAP)'s Boolardy Engineering Test Array (BETA) and the
Australia Telescope Compact Array (ATCA) provide two independent measurements
of the OH megamaser spectrum. We found evidence for OH megamaser clumps at
409 and 562 km/s (blue-shifted) from the systemic velocity of the galaxy,
in addition to the lines previously known. The presence of such high velocities
in the molecular emission from IRAS 201004156 could be explained by a ~50 pc
molecular ring enclosing an approximately 3.8 billion solar mass black hole. We
also discuss two alternatives, i.e. that the narrow-line masers are dynamically
coupled to the wind driven by the active galactic nucleus or they are
associated with two separate galactic nuclei. The comparison between the BETA
and ATCA spectra provides another scientific verification of ASKAP's BETA. Our
data, combined with previous measurements of the source enabled us to study the
variability of the source over a twenty-six year period. The flux density of
the brightest OH maser components has reduced by more than a factor of two
between 1988 and 2015, whereas a secondary narrow-line component has more than
doubled in the same time. Plans for high-resolution VLBI follow-up of this
source are discussed, as are prospects for discovering new OH megamasers during
the ASKAP early science program.Comment: Accepted to MNRAS. Seven pages, three figure
Field sources near the southern-sky calibrator PKS B1934-638: effect on spectral line observations with SKA-MID and its precursors
Accurate instrumental bandpass corrections are essential for the reliable
interpretation of spectral lines from targeted and survey-mode observations
with radio interferometers. Bandpass correction is typically performed by
comparing measurements of a strong calibrator source to an assumed model,
typically an isolated point source. The wide field-of-view and high sensitivity
of modern interferometers means that additional sources are often detected in
observations of calibrators. This can introduce errors into bandpass
corrections and subsequently the target data if not properly accounted for.
Focusing on the standard calibrator PKS B1934-638, we perform simulations to
asses this effect by constructing a wide-field sky model. The cases of ASKAP
(0.7-1.9 GHz), MeerKAT (UHF: 0.58-1.05 GHz; L-band: 0.87-1.67 GHz) and Band 2
(0.95-1.76 GHz) of SKA-MID are examined. The use of a central point source
model during bandpass calibration is found to impart amplitude errors into
spectra measured by the precursor instruments at the ~0.2-0.5% level dropping
to ~0.01% in the case of SKA-MID. This manifests itself as ripples in the
source spectrum, the behaviour of which is coupled to the distribution of the
array baselines, the solution interval, the primary beam size, the hour-angle
of the calibration scan, as well as the weights used when imaging the target.
Calibration pipelines should routinely employ complete field models for
standard calibrators to remove this potentially destructive contaminant from
the data, a recommendation we validate by comparing our simulation results to a
MeerKAT scan of PKS B1934-638, calibrated with and without our expanded sky
model.Comment: 11 pages, 10 figures, accepted for publication in MNRA
The Spectral Energy Distribution of Powerful Starburst Galaxies I : Modelling the Radio Continuum
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We have acquired radio-continuum data between 70MHz and 48 GHz for a sample of 19 southern starburst galaxies at moderate redshifts (0.067 < z < 0.227) with the aim of separating synchrotron and free-free emission components. Using a Bayesian framework, we find the radio continuum is rarely characterized well by a single power law, instead often exhibiting lowfrequency turnovers below 500 MHz, steepening at mid to high frequencies, and a flattening at high frequencies where free-free emission begins to dominate over the synchrotron emission. These higher order curvature components may be attributed to free-free absorption across multiple regions of star formation with varying optical depths. The decomposed synchrotron and free-free emission components in our sample of galaxies form strong correlations with the total-infrared bolometric luminosities. Finally, we find that without accounting for free-free absorption with turnovers between 90 and 500MHz the radio continuum at low frequency (v < 200 MHz) could be overestimated by upwards of a factor of 12 if a simple power-law extrapolation is used from higher frequencies. The mean synchrotron spectral index of our sample is constrained to be α = -1.06, which is steeper than the canonical value of -0.8 for normal galaxies. We suggest this may be caused by an intrinsically steeper cosmic ray distribution.Peer reviewe
The Spectral Energy Distribution of Powerful Starburst Galaxies I: Modelling the Radio Continuum
We have acquired radio continuum data between 70\,MHz and 48\,GHz for a
sample of 19 southern starburst galaxies at moderate redshifts () with the aim of separating synchrotron and free-free emission
components. Using a Bayesian framework we find the radio continuum is rarely
characterised well by a single power law, instead often exhibiting low
frequency turnovers below 500\,MHz, steepening at mid-to-high frequencies, and
a flattening at high frequencies where free-free emission begins to dominate
over the synchrotron emission. These higher order curvature components may be
attributed to free-free absorption across multiple regions of star formation
with varying optical depths. The decomposed synchrotron and free-free emission
components in our sample of galaxies form strong correlations with the
total-infrared bolometric luminosities. Finally, we find that without
accounting for free-free absorption with turnovers between 90 to 500\,MHz the
radio-continuum at low frequency (\,MHz) could be overestimated by
upwards of a factor of twelve if a simple power law extrapolation is used from
higher frequencies. The mean synchrotron spectral index of our sample is
constrained to be , which is steeper then the canonical value of
for normal galaxies. We suggest this may be caused by an intrinsically
steeper cosmic ray distribution
The White Mountain Polarimeter Telescope and an Upper Limit on CMB Polarization
The White Mountain Polarimeter (WMPol) is a dedicated ground-based microwave
telescope and receiver system for observing polarization of the Cosmic
Microwave Background. WMPol is located at an altitude of 3880 meters on a
plateau in the White Mountains of Eastern California, USA, at the Barcroft
Facility of the University of California White Mountain Research Station.
Presented here is a description of the instrument and the data collected during
April through October 2004. We set an upper limit on -mode polarization of
14 (95% confidence limit) in the multipole range
. This result was obtained with 422 hours of observations of a 3
sky area about the North Celestial Pole, using a 42 GHz
polarimeter. This upper limit is consistent with polarization predicted
from a standard -CDM concordance model.Comment: 35 pages. 12 figures. To appear in ApJ
A pilot survey for transients and variables with the Australian Square Kilometre Array Pathfinder
We present a pilot search for variable and transient sources at 1.4 GHz with the Australian Square Kilometre Array Pathfinder (ASKAP). The search was performed in a 30 deg2 area centred on the NGC 7232 galaxy group over eight epochs and observed with a near-daily cadence. The search yielded nine potential variable sources, rejecting the null hypothesis that the flux densities of these sources do not change with 99.9 per cent confidence. These nine sources displayed flux density variations with modulation indices m = 0.1 above our flux density limit of ~1.5mJy. They are identified to be compact active galactic nucleus (AGN)/quasars or galaxies hosting an AGN, whose variability is consistent with refractive interstellar scintillation.We also detect a highly variable source with modulation index m > 0.5 over a time interval of a decade between the SydneyUniversity Molonglo Sky Survey (SUMSS) and our latest ASKAP observations. We find the source to be consistent with the properties of long-term variability of a quasar. No transients were detected on time-scales of days and we place an upper limit ?t < 0.01 deg-2 with 95 per cent confidence for non-detections on near-daily time-scales. The future VAST-Wide survey with 36-ASKAP dishes will probe the transient phase space with similar cadence to our pilot survey, but better sensitivity, and will detect and monitor rarer brighter events
Microbial engineering for production of N-functionalized amino acids and amines
Mindt M, Walter T, Kugler P, Wendisch VF. Microbial engineering for production of N-functionalized amino acids and amines. Biotechnology Journal . 2020;15(7): 1900451.N‐ functionalized amines play important roles in nature and occur, for example, in the antibiotic vancomycin, the immunosuppressant cyclosporine, the cytostatic actinomycin, the siderophore aerobactin, the cyanogenic glucoside linamarin, and the polyamine spermidine. In the pharmaceutical and fine‐chemical industries N‐ functionalized amines are used as building blocks for the preparation of bioactive molecules. Processes based on fermentation and on enzyme catalysis have been developed to provide sustainable manufacturing routes to N‐ alkylated, N‐ hydroxylated, N‐ acylated, or other N‐ functionalized amines including polyamines. Metabolic engineering for provision of precursor metabolites is combined with heterologous N‐ functionalizing enzymes such as imine or ketimine reductases, opine or amino acid dehydrogenases, N‐ hydroxylases, N‐ acyltransferase, or polyamine synthetases. Recent progress and applications of fermentative processes using metabolically engineered bacteria and yeasts along with the employed enzymes are reviewed and the perspectives on developing new fermentative processes based on insight from enzyme catalysis are discussed
WALLABY Early Science - II. The NGC 7232 galaxy group
We report on neutral hydrogen (HI) observations of the NGC 7232 group with
the Australian Square Kilometre Array Pathfinder (ASKAP). These observations
were conducted as part of the Wide-field ASKAP L-Band Legacy All-sky Blind
surveY (WALLABY) Early Science program with an array of 12 ASKAP antennas
equipped with Phased Array Feeds, which were used to form 36 beams to map a
field of view of 30 square degrees. Analyzing a subregion of the central beams,
we detect 17 HI sources. Eleven of these detections are identified as galaxies
and have stellar counterparts, of which five are newly resolved HI galaxy
sources. The other six detections appear to be tidal debris in the form of HI
clouds that are associated with the central triplet, NGC 7232/3, comprising the
spiral galaxies NGC 7232, NGC7232B and NGC7233. One of these HI clouds has a
mass of M_HI ~ 3 x 10^8 M_sol and could be the progenitor of a long-lived tidal
dwarf galaxy. The remaining HI clouds are likely transient tidal knots that are
possibly part of a diffuse tidal bridge between NGC 7232/3 and another group
member, the lenticular galaxy IC 5181.Comment: 18 pages (including appendix), 9 figures, accepted for publication in
MNRA
Connecting X-ray absorption and 21 cm neutral hydrogen absorption in obscured radio AGN
Many radio galaxies show the presence of dense and dusty gas near the active nucleus. This can be traced by both 21 cm H I absorption and soft X-ray absorption, offering new insight into the physical nature of the circumnuclear medium of these distant galaxies. To better understand this relationship, we investigate soft X-ray absorption as an indicator for the detection of associated H I absorption, as part of preparation for the First Large Absorption Survey in H I to be undertaken with the Australian Square Kilometre Array Pathfinder (ASKAP). We present the results of our pilot study using the Boolardy Engineering Test Array, a precursor to ASKAP, to search for new absorption detections in radio sources brighter than 1 Jy that also feature soft X-ray absorption. Based on this pilot survey, we detected H I absorption towards the radio source PKS 1657−298 at a redshift of z = 0.42. This source also features the highest X-ray absorption ratio of our pilot sample by a factor of 3, which is consistent with our general findings that X-ray absorption predicates the presence of dense neutral gas. By comparing the X-ray properties of active galactic nuclei with and without detection of H I absorption at radio wavelengths, we find that X-ray hardness ratio and H I absorption optical depth are correlated at a statistical significance of 4.71σ. We conclude by considering the impact of these findings on future radio and X-ray absorption studies
The Abell 3391/95 galaxy cluster system:A 15 Mpc intergalactic medium emission filament, a warm gas bridge, infalling matter clumps, and (re-) accelerated plasma discovered by combining SRG/eROSITA data with ASKAP/EMU and DECam data
We used dedicated SRG/eROSITA X-ray, ASKAP/EMU radio, and DECam optical
observations of a 15 sq.deg region around the interacting galaxy cluster system
A3391/95 to study the warm-hot gas in cluster outskirts and filaments, the
surrounding large-scale structure and its formation process. We relate the
observations to expectations from cosmological hydrodynamic simulations from
the Magneticum suite.
We trace the irregular morphology of warm-hot gas of the main clusters from
their centers out to well beyond their characteristic radii, . Between
the two main cluster systems, we observe an emission bridge; thanks to
eROSITA's unique soft response and large field of view, we discover tantalizing
hints for warm gas. Several matter clumps physically surrounding the system are
detected. For the "Northern Clump," we provide evidence that it is falling
towards A3391 from the hot gas morphology and radio lobe structure of its
central AGN. Many of the extended sources in the field detected by eROSITA are
known clusters or new clusters in the background, including a known SZ cluster
at redshift z=1. We discover an emission filament north of the virial radius,
, of A3391 connecting to the Northern Clump and extending south of
A3395 towards another galaxy cluster. The total projected length of this
continuous warm-hot emission filament is 15 Mpc, running almost 4 degrees
across the entire eROSITA observation. The DECam galaxy density map shows
galaxy overdensities in the same regions. The new datasets provide impressive
confirmation of the theoretically expected structure formation processes on the
individual system level, including the surrounding warm-hot intergalactic
medium distribution compared to the Magneticum simulation. Our spatially
resolved findings show that baryons indeed reside in large-scale warm-hot gas
filaments with a clumpy structure.Comment: 21 pages plus 16 figures in the main text and 13 pages plus 29
figures as appendix. Astronomy & Astrophysics, accepted on November 3, 2020.
A press release, full resolution images plus additional images and movies are
available at https://astro.uni-bonn.de/~reiprich/A3391_95
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