25 research outputs found
Relics of structure formation: extra-planar gas and high-velocity clouds around the Andromeda Galaxy
Using the 100-m radio telescope at Effelsberg, we mapped a large area around
the Andromeda Galaxy in the 21-cm line emission of neutral hydrogen to search
for high-velocity clouds (HVCs) out to large projected distances in excess of
100 kpc. Our 3-sigma HI mass sensitivity for the warm neutral medium is 8x10^4
solar masses. We can confirm the existence of a population of HVCs with typical
HI masses of a few times 10^5 solar masses near the disc of M31. However, we
did not detect any HVCs beyond a projected distance of about 50 kpc from M31,
suggesting that HVCs are generally found in proximity of large spiral galaxies
at typical distances of a few 10 kpc. Comparison with CDM-based models and
simulations suggests that only a few of the detected HVCs could be associated
with primordial dark-matter satellites, whereas others are most likely the
result of tidal stripping. The lack of clouds beyond a projected distance of 50
kpc from M31 is also in conflict with the predictions of recent CDM structure
formation simulations. A possible solution to this problem could be ionisation
of the HVCs as a result of decreasing pressure of the ambient coronal gas at
larger distances from M31. A consequence of this scenario would be the presence
of hundreds of mainly ionised or pure dark-matter satellites around large
spiral galaxies like the Milky Way and M31.Comment: 21 pages, 15 figures, accepted for publication in MNRA
Source finding, parametrization and classification for the extragalactic Effelsberg-Bonn HI Survey
Context. Source extraction for large-scale HI surveys currently involves
large amounts of manual labor. For data volumes expected from future HI surveys
with upcoming facilities, this approach is not feasible any longer.
Aims. We describe the implementation of a fully automated source finding,
parametrization, and classification pipeline for the Effelsberg-Bonn HI Survey
(EBHIS). With future radio astronomical facilities in mind, we want to explore
the feasibility of a completely automated approach to source extraction for
large-scale HI surveys.
Methods. Source finding is implemented using wavelet denoising methods, which
previous studies show to be a powerful tool, especially in the presence of data
defects. For parametrization, we automate baseline fitting, mask optimization,
and other tasks based on well-established algorithms, currently used
interactively. For the classification of candidates, we implement an artificial
neural network which is trained on a candidate set comprised of false positives
from real data and simulated sources. Using simulated data, we perform a
thorough analysis of the algorithms implemented.
Results. We compare the results from our simulations to the parametrization
accuracy of the HI Parkes All-Sky Survey (HIPASS) survey. Even though HIPASS is
more sensitive than EBHIS in its current state, the parametrization accuracy
and classification reliability match or surpass the manual approach used for
HIPASS data.Comment: 13 Pages, 13 Figures, 1 Table, accepted for publication in A&
HI observations of three compact high-velocity clouds around the Milky Way
We present deep HI observations of three compact high-velocity clouds
(CHVCs). The main goal is to study their diffuse warm gas and compact cold
cores. We use both low- and high-resolution data obtained with the 100 m
Effelsberg telescope and the Westerbork Synthesis Radio Telescope (WSRT). The
combination is essential in order to study the morphological properties of the
clouds since the single-dish telescope lacks a sufficient angular resolution
while the interferometer misses a large portion of the diffuse gas. Here
single-dish and interferometer data are combined in the image domain with a new
combination pipeline. The combination makes it possible to examine interactions
between the clouds and their surrounding environment in great detail. The
apparent difference between single-dish and radio interferometer total flux
densities shows that the CHVCs contain a considerable amount of diffuse gas
with low brightness temperatures. A Gaussian decomposition indicates that the
clouds consist predominantly of warm gas.Comment: 11 pages, 7 figures, accepted for publication by A&
A dynamical transition from atomic to molecular intermediate-velocity clouds
Towards the high galactic latitude sky, the far-infrared (FIR) intensity is
tightly correlated to the total hydrogen column density which is made up of
atomic (HI) and molecular hydrogen (H. Above a certain column density
threshold, atomic hydrogen turns molecular. We analyse gas and dust properties
of intermediate-velocity clouds (IVCs) in the lower galactic halo to explore
their transition from the atomic to the molecular phase. Driven by
observations, we investigate the physical processes that transform a purely
atomic IVC into a molecular one. Data from the Effelsberg-Bonn HI-Survey
(EBHIS) are correlated to FIR wavebands of the Planck satellite and IRIS.
Modified black-body emission spectra are fitted to deduce dust optical depths
and grain temperatures. We remove the contribution of atomic hydrogen to the
FIR intensity to estimate molecular hydrogen column densities. Two IVCs show
different FIR properties, despite their similarity in HI, such as narrow
spectral lines and large column densities. One FIR bright IVC is associated
with H, confirmed by CO emission; the other IVC
is FIR dim and shows no FIR excess, which indicates the absence of molecular
hydrogen. We propose that the FIR dim and bright IVCs probe the transition
between the atomic and molecular gas phase. Triggered by dynamical processes,
this transition happens during the descent of IVCs onto the galactic disk. The
most natural driver is ram pressure exerted onto the cloud by the increasing
halo density. Because of the enhanced pressure, the formation timescale of
H is reduced, allowing the formation of large amounts of H within a
few Myr.Comment: 13 pages, 14 figures, accepted for publication by A&
Far-infrared excess emission as a tracer of disk-halo interaction
Given the current and past star-formation in the Milky Way in combination
with the limited gas supply, the re-fuelling of the reservoir of cool gas is an
important aspect of Galactic astrophysics. The infall of \ion{H}{i} halo clouds
can, among other mechanisms, contribute to solving this problem. We study the
intermediate-velocity cloud IVC135+54 and its spatially associated
high-velocity counterpart to look for signs of a past or ongoing interaction.
Using the Effelsberg-Bonn \ion{H}{i} Survey data, we investigated the interplay
of gas at different velocities. In combination with far-infrared Planck and
IRIS data, we extended this study to interstellar dust and used the correlation
of the data sets to infer information on the dark gas. The velocity structure
indicates a strong compression and deceleration of the infalling high-velocity
cloud (HVC), associated with far-infrared excess emission in the
intermediate-velocity cloud. This excess emission traces molecular hydrogen,
confirming that IVC135+54 is one of the very few molecular halo clouds. The
high dust emissivity of IVC135+54 with respect to the local gas implies that it
consists of disk material and does not, unlike the HVC, have an extragalactic
origin. Based on the velocity structure of the HVC and the dust content of the
IVC, a physical connection between them appears to be the logical conclusion.
Since this is not compatible with the distance difference between the two
objects, we conclude that this particular HVC might be much closer to us than
complex C. Alternatively, the indicators for an interaction are misleading and
have another origin.Comment: 11 pages, 10 figures, accepted for publication in A&
The eROSITA view of the Abell 3391/95 field: The Northern Clump. The largest infalling structure in the longest known gas filament observed with eROSITA, XMM-Newton, and Chandra
SRG/eROSITA PV observations revealed the A3391/95 cluster system and the
Northern Clump (MCXC J0621.7-5242 galaxy cluster) are aligning along a cosmic
filament in soft X-rays, similarly to what has been seen in simulations before.
We aim to understand the dynamical state of the Northern Clump as it enters the
atmosphere () of A3391. We analyzed joint eROSITA, XMM-Newton,
and Chandra observations to probe the morphological, thermal, and chemical
properties of the Northern Clump from its center out to a radius of 988 kpc
(). We utilized the ASKAP/EMU radio data, DECam optical image, and
Planck y-map to study the influence of the WAT radio source on the Northern
Clump central ICM. From the Magneticum simulation, we identified an analog of
the A3391/95 system along with an infalling group resembling the Northern
Clump. The Northern Clump is a WCC cluster centered on a WAT radio galaxy. The
gas temperature over is keV. We
employed the scaling relation and obtained a mass estimate of
and kpc. Its
atmosphere has a boxy shape and deviates from spherical symmetry. We identify a
southern surface brightness edge, likely caused by subsonic motion relative to
the filament gas. At , the southern atmosphere appears to be
42% hotter than its northern atmosphere. We detect a downstream tail pointing
toward the north with a projected length of kpc, plausibly the result
of ram pressure stripping. The analog group in the Magneticum simulation is
experiencing changes in its gas properties and a shift between the position of
the halo center and that of the bound gas, while approaching the main cluster
pair.Comment: 24 pages, 17 figures (main text), 6 figures (appendix). Submitted to
A&A for the Special Issue: The Early Data Release of eROSITA and Mikhail
Pavlinsky ART-XC on the SRG Mission. For more information, see
https://astro.uni-bonn.de/~averonica/NorthernClump/eROSITA_A3391_Northern_Clump_AIfA.htm
Kinematic analysis of the super-extended HI disk of the nearby spiral galaxy M 83
Funding: CE, FB, AB, IB, JdB and JP acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No.726384/Empire). TGW acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 694343). JMDK gratefully acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme via the ERC Starting Grant MUSTANG (grant agreement number 714907). SCOG acknowledges funding from the European Research Council via the ERC Synergy Grant “ECOGAL – Understanding our Galactic ecosystem: From the disk of the Milky Way to the formation sites of stars and planets” (project ID 855130). WJGdB received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 882793 ‘MeerGas’).We present new HI observations of the nearby massive spiral galaxy M83, taken with the VLA at 21″ angular resolution (≈500 pc) of an extended (1.5 deg2) 10-point mosaic combined with GBT single dish data. We study the super-extended HI disk of M83 (∼50 kpc in radius), in particular disc kinematics, rotation and the turbulent nature of the atomic interstellar medium. We define distinct regions in the outer disk (rgal > central optical disk), including ring, southern area, and southern and northern arm. We examine HI gas surface density, velocity dispersion and non-circular motions in the outskirts, which we compare to the inner optical disk. We find an increase of velocity dispersion (σv) towards the pronounced HI ring, indicative of more turbulent HI gas. Additionally, we report over a large galactocentric radius range (until rgal ∼ 50 kpc) that σv is slightly larger than thermal (i.e. > 8 km s-1). We find that a higher star formation rate (as traced by FUV emission) is not always necessarily associated with a higher HI velocity dispersion, suggesting that radial transport could be a dominant driver for the enhanced velocity dispersion. We further find a possible branch that connects the extended HI disk to the dwarf irregular galaxy UGCA365, that deviates from the general direction of the northern arm. Lastly, we compare mass flow rate profiles (based on 2D and 3D tilted ring models) and find evidence for outflowing gas at rgal ∼ 2 kpc, inflowing gas at rgal ~ 5.5 kpc and outflowing gas at rgal ~ 14 kpc. We caution that mass flow rates are highly sensitive to the assumed kinematic disk parameters, in particular, to the inclination.Publisher PDFPeer reviewe
Comment on the letter of the Society of Vertebrate Paleontology (SVP) dated April 21, 2020 regarding 'Fossils from conflict zones and reproducibility of fossil‑based scientific data': Myanmar amber
Recently, the Society of Vertebrate Paleontology (SVP) has sent around a letter, dated 21st April, 2020 to more than 300 palaeontological journals, signed by the President, Vice President and a former President of the society (Rayfield et al. 2020). The signatories of this letter request significant changes to the common practices in palaeontology. With our present, multi-authored comment, we aim to argue why these suggestions will not lead to improvement of both practice and ethics of palaeontological research but, conversely, hamper its further development. Although we disagree with most contents of the SVP letter, we appreciate this initiative to discuss scientific practices and the underlying ethics. Here, we consider different aspects of the suggestions by Rayfield et al. (2020) in which we see weaknesses and dangers. It is our intent to compile views from many different fields of palaeontology, as our discipline is (and should remain) pluralistic. This contribution deals with the aspects concerning Myanmar amber. Reference is made to Haug et al. (2020a) for another comment on aspects concerning amateur palaeontologists/citizen scientists/private collectors