14 research outputs found
HI scaling relations of galaxies in the environment of HI-rich and control galaxies observed by the Bluedisk project
Our work is based on the "Bluedisk" project, a program to map the neutral gas
in a sample of 25 HI-rich spirals and a similar number of control galaxies with
the Westerbork Synthesis Radio Telescope (WSRT). In this paper we focus on the
HI properties of the galaxies in the environment of our targeted galaxies. In
total, we extract 65 galaxies from the WSRT cubes with stellar masses between
and . Most of these galaxies are located on
the same HI mass-size relation and "HI-plane" as normal spiral galaxies. We
find that companions around HI-rich galaxies tend to be HI-rich as well and to
have larger R90,HI/R50,HI. This suggests a scenario of "HI conformity", similar
to the colour conformity found by Weinmann et al. (2006): galaxies tend to
adopt the HI properties of their neighbours. We visually inspect the outliers
from the HI mass-size relation and galaxies which are offset from the HI plane
and find that they show morphological and kinematical signatures of recent
interactions with their environment. We speculate that these outliers have been
disturbed by tidal or ram-pressure stripping processes, or in a few cases, by
accretion events.Comment: 16 pages, 12 figures; accepted for publication in MNRA
An HI View of Galaxy Conformity: HI-rich Environment around HI-excess Galaxies
Using data taken as part of the Bluedisk project we study the connection
between neutral hydrogen (HI) in the environment of spiral galaxies and that in
the galaxies themselves. We measure the total HI mass present in the
environment in a statistical way by studying the distribution of noise peaks in
the HI data cubes obtained for 40 galaxies observed with WSRT. We find that
galaxies whose HI mass fraction is high relative to standard scaling relations
have an excess HI mass in the surrounding environment as well. Gas in the
environment consists of gas clumps which are individually below the detection
limit of our HI data. These clumps may be hosted by small satellite galaxies
and\or be the high-density peaks of a more diffuse gas distribution in the
inter-galactic medium. We interpret this result as an indication for a picture
in which the HI-rich central galaxies accrete gas from an extended gas
reservoir present in their environment.Comment: 15 pages, 13 figures. Accepted for publication in MNRA
The Sudden Death of the Nearest Quasar
Galaxy formation is significantly modulated by energy output from
supermassive black holes at the centers of galaxies which grow in highly
efficient luminous quasar phases. The timescale on which black holes transition
into and out of such phases is, however, unknown. We present the first
measurement of the shutdown timescale for an individual quasar using X-ray
observations of the nearby galaxy IC 2497, which hosted a luminous quasar no
more than 70,000 years ago that is still seen as a light echo in `Hanny's
Voorwerp', but whose present-day radiative output is lower by at least 2 and
more likely by over 4 orders of magnitude. This extremely rapid shutdown
provides new insights into the physics of accretion in supermassive black
holes, and may signal a transition of the accretion disk to a radiatively
inefficient state.Comment: 4 pages, 2 figures. Astrophysical Journal Letters, in pres
The HI Tully-Fisher Relation of Early-Type Galaxies
We study the HI K-band Tully-Fisher relation and the baryonic Tully-Fisher
relation for a sample of 16 early-type galaxies, taken from the ATLAS3D sample,
which all have very regular HI disks extending well beyond the optical body (>
5 R_eff). We use the kinematics of these disks to estimate the circular
velocity at large radii for these galaxies. We find that the Tully-Fisher
relation for our early-type galaxies is offset by about 0.5-0.7 magnitudes from
the relation for spiral galaxies. The residuals with respect to the spiral
Tully-Fisher relation correlate with estimates of the stellar mass-to-light
ratio, suggesting that the offset between the relations is mainly driven by
differences in stellar populations. We also observe a small offset between our
Tully-Fisher relation with the relation derived for the ATLAS3D sample based on
CO data representing the galaxies' inner regions (< 1 R_eff). This indicates
that the circular velocities at large radii are systematically 10% lower than
those near 0.5-1 R_eff, in line with recent determinations of the shape of the
mass profile of early-type galaxies. The baryonic Tully-Fisher relation of our
sample is distinctly tighter than the standard one, in particular when using
mass-to-light ratios based on dynamical models of the stellar kinematics. We
find that the early-type galaxies fall on the spiral baryonic Tully-Fisher
relation if one assumes M/L_K = 0.54 M_sun/L_sun for the stellar populations of
the spirals, a value similar to that found by recent studies of the dynamics of
spiral galaxies. Such a mass-to-light ratio for spiral galaxies would imply
that their disks are 60-70% of maximal. Our analysis increases the range of
galaxy morphologies for which the baryonic Tully-Fisher relations holds,
strengthening previous claims that it is a more fundamental scaling relation
than the classical Tully-Fisher relation.Comment: Accepted for publication in Astronomy & Astrophysic
Searching for axion dark matter with MeerKAT Radio Telescope
Axions provide a natural and well-motivated dark matter candidate, with the
capability to convert directly to photons in the presence of an electromagnetic
field. A particularly compelling observational target is the conversion of dark
matter axions into photons in the magnetospheres of highly magnetised neutron
stars, which is expected to produce a narrow spectral peak centred at the
frequency of the axion mass. We point the MeerKAT radio telescope towards the
isolated neutron star J0806.44123 for -hours of observation and obtain
the radio spectra in the frequency range - MHz. By modelling the
conversion process of infalling axion dark matter (DM), we then compare these
spectra to theoretical expectations for a given choice of axion parameters.
Whilst finding no signal above in the data, we provide a unique
constraint on the Primakoff coupling of axion DM, at the
confidence level, in the mass range -eV. This result serves
the strongest constraint in the axion mass range -eV.Comment: 6 pages, 3 figures, accepted by Physical Review
Connecting MeerKAT radio continuum properties to GAMA optical emission-line and WISE mid-infrared activity
The identification of AGN in large surveys has been hampered by seemingly
discordant classifications arising from differing diagnostic methods, usually
tracing distinct processes specific to a particular wavelength regime. However,
as shown in Yao et al. (2020), the combination of optical emission line
measurements and mid-infrared photometry can be used to optimise the
discrimination capability between AGN and star formation activity. In this
paper we test our new classification scheme by combining the existing GAMA-WISE
data with high-quality MeerKAT radio continuum data covering 8 deg of the
GAMA G23 region. Using this sample of 1 841 galaxies (z < 0.25), we investigate
the total infrared (derived from 12m) to radio luminosity ratio, q(TIR),
and its relationship to optical-infrared AGN and star-forming (SF)
classifications. We find that while q(TIR) is efficient at detecting AGN
activity in massive galaxies generally appearing quiescent in the infrared, it
becomes less reliable for cases where the emission from star formation in the
host galaxy is dominant. However, we find that the q(TIR) can identify up to 70
% more AGNs not discernible at optical and/or infrared wavelengths. The median
q(TIR) of our SF sample is 2.57 0.23 consistent with previous local
universe estimates
The Bluedisks project, a study of unusually H I-rich galaxies - I. H I sizes and morphology
<p>We introduce the 'Bluedisk' project, a large programme at the Westerbork Synthesis Radio Telescope that has mapped the H i in a sample of 23 nearby galaxies with unusually high H i mass fractions, along with a similar-sized sample of control galaxies. This paper presents the sample selection, observational set-up, data reduction strategy and a first analysis of the sizes and structural properties of the H i discs. We find that the H i-rich galaxies lie on the same H i mass versus H i size relation as normal spiral galaxies, extending it to total H i masses of 2 x 10(10) M-circle dot and radii R1 of similar to 100 kpc. The H i-rich galaxies have significantly larger values of H i-to-optical size ratio and more clumpy H i discs than those of normal spirals. There is no evidence that the discs of H i-rich galaxies are more disturbed. In fact, the centre of the H i distribution corresponds more closely with the centre of the optical light in the H i-rich galaxies than in the controls. All these results argue against a scenario in which new gas has been brought in by mergers. It is possible that they may be more consistent with cooling from a surrounding quasi-static halo of warm/hot gas.</p>
MeerKLASS: MeerKAT Large Area Synoptic Survey
We discuss the ground-breaking science that will be possible with a wide area
survey, using the MeerKAT telescope, known as MeerKLASS (MeerKAT Large Area
Synoptic Survey). The current specifications of MeerKAT make it a great fit for
science applications that require large survey speeds but not necessarily high
angular resolutions. In particular, for cosmology, a large survey over for hours will potentially provide the first
ever measurements of the baryon acoustic oscillations using the 21cm intensity
mapping technique, with enough accuracy to impose constraints on the nature of
dark energy. The combination with multi-wavelength data will give unique
additional information, such as exquisite constraints on primordial
non-Gaussianity using the multi-tracer technique, as well as a better handle on
foregrounds and systematics. Such a wide survey with MeerKAT is also a great
match for HI galaxy studies, providing unrivalled statistics in the pre-SKA era
for galaxies resolved in the HI emission line beyond local structures at z >
0.01. It will also produce a large continuum galaxy sample down to a depth of
about 5\,Jy in L-band, which is quite unique over such large areas and
will allow studies of the large-scale structure of the Universe out to high
redshifts, complementing the galaxy HI survey to form a transformational
multi-wavelength approach to study galaxy dynamics and evolution. Finally, the
same survey will supply unique information for a range of other science
applications, including a large statistical investigation of galaxy clusters as
well as produce a rotation measure map across a huge swathe of the sky. The
MeerKLASS survey will be a crucial step on the road to using SKA1-MID for
cosmological applications and other commensal surveys, as described in the top
priority SKA key science projects (abridged).Comment: Larger version of the paper submitted to the Proceedings of Science,
"MeerKAT Science: On the Pathway to the SKA", Stellenbosch, 25-27 May 201
MIGHTEE-\HI: Possible interactions with the galaxy NGC~895
The transformation and evolution of a galaxy is strongly influenced by
interactions with its environment. Neutral hydrogen (\HI) is an excellent way
to trace these interactions. Here, we present \HI\ observations of the spiral
galaxy NGC~895, which was previously thought to be isolated. High-sensitivity
\HI\ observations from the MeerKAT large survey project MIGHTEE reveal possible
interaction features, such as extended spiral arms, and the two newly
discovered \HI\ companions, that drive us to change the narrative that it is an
isolated galaxy. We combine these observations with deep optical images from
the Hyper Suprime Camera to show an absence of tidal debris between NGC 895 and
its companions. We do find an excess of light in the outer parts of the
companion galaxy MGTHJ022138.1-052631 which could be an indication of
external perturbation and thus possible sign of interactions. Our analysis
shows that NGC~895 is an actively star-forming galaxy with a SFR of
, a value typical for high stellar mass
galaxies on the star forming main sequence. It is reasonable to state that
different mechanisms may have contributed to the observed features in NGC~895
and this emphasizes the need to revisit the target with more detailed
observations. Our work shows the high potential and synergy of using
state-of-the-art data in both \HI\ and optical to reveal a more complete
picture of galaxy environments.Comment: 14 pages, 10 figures. Accepted for publication in MNRA