129 research outputs found
Multi-object spectroscopy of the field surrounding PKS 2126-158: Discovery of a z=0.66 galaxy group
The high-redshift radio-loud quasar PKS 2126-158 is found to have a large
number of red galaxies in close apparent proximity. We use the Gemini
Multi-Object Spectrograph (GMOS) on Gemini South to obtain optical spectra for
a large fraction of these sources. We show that there is a group of galaxies at
, coincident with a metal-line absorption system seen in the
quasar's optical spectrum. The multiplexing capabilities of GMOS also allow us
to measure redshifts of many foreground galaxies in the field surrounding the
quasar.
The galaxy group has five confirmed members, and a further four fainter
galaxies are possibly associated. All confirmed members exhibit early-type
galaxy spectra, a rare situation for a Mg II absorbing system. We discuss the
relationship of this group to the absorbing gas, and the possibility of
gravitational lensing of the quasar due to the intervening galaxies.Comment: Monthly Notices of the Royal Astronomical Society, in press. 10
pages, 8 figure
The Optical/Near-IR Colours of Red Quasars
We present quasi-simultaneous multi-colour optical/near-IR photometry for 157 radio selected quasars, forming an unbiassed sub-sample of the Parkes Flat-Spectrum Sample. Data are also presented for 12 optically selected QSOs, drawn from the Large Bright QSO Survey. The spectral energy distributions of the radio- and optically-selected sources are quite different. The optically selected QSOs are all very similar: they have blue spectral energy distributions curving downwards at shorter wavelengths. Roughly 90% of the radio-selected quasars have roughly power-law spectral energy distributions, with slopes ranging from FÎœ â Îœ0 to FÎœ, â Îœ-2. The remaining 10% have spectral energy distributions showing sharp peaks: these are radio galaxies and highly reddened quasars. Four radio sources were not detected down to magnitude limits of H ⌠19 · 6. These are probably high redshift (z > 3) galaxies or quasars. We show that the colours of our red quasars lie close to the stellar locus in the optical: they will be hard to identify in surveys such as the Sloan Digital Sky Survey. If near-IR photometry is added, however, the red power-law sources can be clearly separated from the stellar locus: IR surveys such as 2MASS should be capable of finding these sources on the basis of their excess flux in the K-band
The Spectra of Red Quasars
We measure the spectral properties of a representative sub-sample of 187
quasars, drawn from the Parkes Half-Jansky, Flat-radio-spectrum Sample (PHFS).
Quasars with a wide range of rest-frame optical/UV continuum slopes are
included in the analysis: their colours range from 2 < B-K < 7.
The median H-beta and [O III] emission-line equivalent widths of the red
quasar sub-sample are a factor of ten weaker than those of the blue quasar
sub-sample. Both the colours and the emission-line equivalent widths of the red
quasars can be explained by the addition of a featureless red synchrotron
continuum component to an otherwise normal blue quasar spectrum. The relative
strengths of the blue and red components span two orders of magnitude at
rest-frame 500nm. The blue component is weaker relative to the red component in
low optical luminosity sources. This suggests that the fraction of accretion
energy going into optical emission from the jet is greater in low luminosity
quasars.
This synchrotron model does not, however, fit around 10% of the quasars,
which have both red colours and high equivalent width emission-lines. We
hypothesise that these red, strong-lined quasars have intrinsically weak Big
Blue Bumps.
There is no discontinuity in spectral properties between the BL Lac objects
in our sample and the other quasars. The synchrotron emission component only
dominates the spectrum at longer wavelengths, so existing BL Lac surveys will
be biassed against high redshift objects.Comment: 22 pages, 12 figures, accepted for publication in PASA. Data tables
and composite spectra from the paper can be found at
http://msowww.anu.edu.au/~pfrancis
Observations of cold extragalactic gas clouds at towards PKS 1610-771
We present results from MUSE observations of a 21-cm HI absorption system
detected with the Australian Square Kilometre Array Pathfinder radio telescope
at redshift towards the quasar PKS 1610-771. We
identify four galaxies (A, B, X and Y) at the same redshift as the 21-cm H I
Damped Lyman-{\alpha} (DLA) absorption system, with impact parameters ranging
from less than 10 kpc to almost 200 kpc from the quasar sightline. Ca II and Na
I absorption is seen in the MUSE spectrum of the background QSO, with
velocities coinciding with the initial HI 21-cm detection, but tracing less
dense and warmer gas. This metal-line component aligns with the rotating
ionised disc of galaxy B (impact parameter 18 kpc from the QSO) and appears to
be co-rotating with the galaxy disc. In contrast, the 21-cm HI absorber is
blueshifted relative to the galaxies nearest the absorber and has the opposite
sign to the velocity field of galaxy B. Since galaxies A and B are separated by
only 17 kpc on the sky and km s in velocity, it appears likely that
the 21-cm detection traces extragalactic clouds of gas formed from their
interaction. This system reveals that the cold 100 K neutral gas critical for
star formation can be associated with complex structures beyond the galaxy
disc, and is a first case study made in preparation for future large 21-cm
absorption surveys like the ASKAP First Large Absorption Survey in HI.Comment: Accepted. 13 pages, 7 figure
Duchamp: a 3D source finder for spectral-line data
This paper describes the Duchamp source finder, a piece of software designed
to find and describe sources in 3-dimensional, spectral-line data cubes.
Duchamp has been developed with HI (neutral hydrogen) observations in mind, but
is widely applicable to many types of astronomical images. It features
efficient source detection and handling methods, noise suppression via
smoothing or multi-resolution wavelet reconstruction, and a range of graphical
and text-based outputs to allow the user to understand the detections. This
paper details some of the key algorithms used, and illustrates the
effectiveness of the finder on different data sets.Comment: MNRAS, in press. 17 pages, 8 figure
A successful search for intervening 21 cm HI absorption in galaxies at 0.4 < z <1.0 with the Australian Square Kilometre Array Pathfinder (ASKAP)
We have used the Australian Square Kilometre Array Pathfinder (ASKAP) radio
telescope to search for intervening 21 cm neutral hydrogen (HI) absorption
along the line of sight to 53 bright radio continuum sources. Our observations
are sensitive to HI column densities typical of Damped Lyman Alpha absorbers
(DLAs) in cool gas with an HI spin temperature below about 300-500 K. The
six-dish Boolardy Engineering Test Array (BETA) and twelve-antenna Early
Science array (ASKAP-12) covered a frequency range corresponding to redshift
and respectively for the HI line. Fifty of the 53
radio sources observed have reliable optical redshifts, giving a total redshift
path = 21.37. This was a spectroscopically-untargeted survey, with
no prior assumptions about the location of the lines in redshift space. Four
intervening HI lines were detected, two of them new. In each case, the
estimated HI column density lies above the DLA limit for HI spin temperatures
above 50-80 K, and we estimate a DLA number density at redshift of
. This value lies somewhat above the
general trend of with redshift seen in optical DLA studies. Although the
current sample is small, it represents an important proof of concept for the
much larger 21cm First Large Absorption Survey in HI (FLASH) project to be
carried out with the full 36-antenna ASKAP telescope, probing a total redshift
path .Comment: 21 pages, 11 figures. Accepted for publication in MNRA
Ricci flow and black holes
Gradient flow in a potential energy (or Euclidean action) landscape provides
a natural set of paths connecting different saddle points. We apply this method
to General Relativity, where gradient flow is Ricci flow, and focus on the
example of 4-dimensional Euclidean gravity with boundary S^1 x S^2,
representing the canonical ensemble for gravity in a box. At high temperature
the action has three saddle points: hot flat space and a large and small black
hole. Adding a time direction, these also give static 5-dimensional
Kaluza-Klein solutions, whose potential energy equals the 4-dimensional action.
The small black hole has a Gross-Perry-Yaffe-type negative mode, and is
therefore unstable under Ricci flow. We numerically simulate the two flows
seeded by this mode, finding that they lead to the large black hole and to hot
flat space respectively, in the latter case via a topology-changing
singularity. In the context of string theory these flows are world-sheet
renormalization group trajectories. We also use them to construct a novel free
energy diagram for the canonical ensemble.Comment: 31 pages, 14 color figures. v2: Discussion of the metric on the space
of metrics corrected and expanded, references adde
Temperature-ramped 129Xe spin-exchange optical pumping
We describe temperature-ramped spin-exchange optical pumping (TR-SEOP) in an automated high-throughput batch-mode 129Xe hyperpolarizer utilizing three key temperature regimes: (i) âhotâwhere the 129Xe hyperpolarization rate is maximal, (ii) âwarmâ-where the 129Xe hyperpolarization approaches unity, and (iii) âcoolâ where hyperpolarized 129Xe gas is transferred into a Tedlar bag with low Rb content (<5 ng per âŒ1 L dose) suitable for human imaging applications. Unlike with the conventional approach of batch-mode SEOP, here all three temperature regimes may be operated under continuous high-power (170 W) laser irradiation, and hyperpolarized 129Xe gas is delivered without the need for a cryocollection step. The variable-temperature approach increased the SEOP rate by more than 2-fold compared to the constant-temperature polarization rate (e.g., giving effective values for the exponential buildup constant ÎłSEOP of 62.5 ± 3.7 Ă 10â3 minâ1 vs 29.9 ± 1.2 Ă 10â3 minâ1) while achieving nearly the same maximum %PXe value (88.0 ± 0.8% vs 90.1% ± 0.8%, for a 500 Torr (67 kPa) Xe cell loadingcorresponding to nuclear magnetic resonance/magnetic resonance imaging (NMR/MRI) enhancements of âŒ3.1 Ă 105 and âŒ2.32 Ă 108 at the relevant fields for clinical imaging and HP 129Xe production of 3 T and 4 mT, respectively); moreover, the intercycle âdeadâ time was also significantly decreased. The higher-throughput TR-SEOP approach can be implemented without sacrificing the level of 129Xe hyperpolarization
or the experimental stability for automation-making this approach beneficial for improving the overall 129Xe production rate in clinical settings
Does a radio jet drive the massive multi-phase outflow in the ultra-luminous infrared galaxy IRAS 10565+2448?
We present new upgraded Giant Metrewave Radio Telescope (uGMRT) HI 21-cm
observations of the ultra-luminous infrared galaxy IRAS 10565+2448, previously
reported to show blueshifted, broad, and shallow HI absorption indicating an
outflow. Our higher spatial resolution observations have localised this
blueshifted outflow, which is 1.36 kpc southwest of the radio centre and
has a blueshifted velocity of and a full width at
half maximum (FWHM) of . The spatial extent and
kinematic properties of the HI outflow are consistent with the previously
detected cold molecular outflows in IRAS 10565+2448, suggesting that they
likely have the same driving mechanism and are tracing the same outflow. By
combining the multi-phase gas observations, we estimate a total outflowing mass
rate of at least and a total energy loss rate of
at least , where the contribution from the
ionised outflow is negligible, emphasising the importance of including both
cold neutral and molecular gas when quantifying the impact of outflows. We
present evidence of the presence of a radio jet and argue that this may play a
role in driving the observed outflows. The modest radio luminosity
of the jet in IRAS
10565+2448 implies that the jet contribution to driving outflows should not be
ignored in low radio luminosity AGN.Comment: 12 pages, 9 figures, accepted for publication in MNRA
Single-copy nuclear genes resolve the phylogeny of the holometabolous insects
Background: Evolutionary relationships among the 11 extant orders of insects that undergo complete metamorphosis, called Holometabola, remain either unresolved or contentious, but are extremely important as a context for accurate comparative biology of insect model organisms. The most phylogenetically enigmatic holometabolan insects are Strepsiptera or twisted wing parasites, whose evolutionary relationship to any other insect order is unconfirmed. They have been controversially proposed as the closest relatives of the flies, based on rDNA, and a possible homeotic transformation in the common ancestor of both groups that would make the reduced forewings of Strepsiptera homologous to the reduced hindwings of Diptera. Here we present evidence from nucleotide sequences of six single-copy nuclear protein coding genes used to reconstruct phylogenetic relationships and estimate evolutionary divergence times for all holometabolan orders. Results: Our results strongly support Hymenoptera as the earliest branching holometabolan lineage, the monophyly of the extant orders, including the fleas, and traditionally recognized groupings of Neuropteroidea and Mecopterida. Most significantly, we find strong support for a close relationship between Coleoptera (beetles) and Strepsiptera, a previously proposed, but analytically controversial relationship. Exploratory analyses reveal that this relationship cannot be explained by long-branch attraction or other systematic biases. Bayesian divergence times analysis, with reference to specific fossil constraints, places the origin of Holometabola in the Carboniferous (355 Ma), a date significantly older than previous paleontological and morphological phylogenetic reconstructions. The origin and diversification of most extant insect orders began in the Triassic, but flourished in the Jurassic, with multiple adaptive radiations producing the astounding diversity of insect species for which these groups are so well known. Conclusion: These findings provide the most complete evolutionary framework for future comparative studies on holometabolous model organisms and contribute strong evidence for the resolution of the 'Strepsiptera problem', a long-standing and hotly debated issue in insect phylogenetics
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