475 research outputs found
The Tully-Fisher relation for low surface brightness galaxies - implications for galaxy evolution
We present the B band Tully-Fisher relation for Low Surface Brightness (LSB)
galaxies. These LSB galaxies follow the same Tully-Fisher relation as normal
spiral galaxies. This implies that the mass-to-light ratio (M/L) of LSB
galaxies is typically a factor of 2 larger than that of normal galaxies of the
same total luminosity and morphological type. Since the dynamical mass of a
galaxy is related to the rotation velocity and scale length via M \propto V^2
h, at fixed linewidth LSB galaxies must be twice as large as normal galaxies.
This is confirmed by examining the relation between scale length and linewidth
for LSB and normal galaxies. The universal nature of the Tully-Fisher relation
can be understood if LSB galaxies are galaxies with low mass surface density,
\sigma. The mass surface density apparently controls the luminosity evolution
of a galaxy such as to keep the product \sigma M/L constant.Comment: 9 pages, PostScript. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Comparing Galaxies and Lyman Alpha Absorbers at Low Redshift
A scenario is explored in which Lyman alpha absorbers at low redshift arise
from lines of sight through extended galaxy disks, including those of dwarf and
low surface brightness galaxies. A population of galaxies is simulated based
upon observed distributions of galaxy properties, and the gas disks are modeled
using pressure and gravity confinement. Some parameter values are ruled out by
comparing simulation results with the observed galaxy luminosity function, and
constraints may be made on the absorbing cross sections of galaxies. Simulation
results indicate that it is difficult to match absorbers with particular
galaxies observationally since absorption typically occurs at high impact
parameters (>200 kpc) from luminous galaxies. Low impact parameter absorption
is dominated by low luminosity dwarfs. A large fraction of absorption lines is
found to originate from low surface brightness galaxies, so that the absorbing
galaxy is likely to be misidentified. Low redshift Lyman alpha absorber counts
can easily be explained by moderately extended galaxy disks when low surface
brightness galaxies are included, and it is easily possible to find a scenario
which is consistent with observed the galaxy luminosity function, with low
redshift Lyman limit absorber counts, and with standard nucleosynthesis
predictions of the baryon density, Omega_Baryon.Comment: 17 pages, 8 figures, accepted to the Astrophysical Journa
The Ursa Major association of galaxies - VI: a relative dearth of gas-rich dwarf galaxies
We determined the HI mass function of galaxies in the Ursa Major association
of galaxies using a blind VLA-D array survey, consisting of 54 pointings in a
cross pattern, covering the centre as well as the outskirts of the Ursa Major
volume. The calculated HI mass function has best-fitting Schechter parameters
{\theta}^* = 0.19+/-0.11 Mpc^{-3}, log(M^*_{HI}/M_{\odot}) = 9.8+/-0.8 and
{\alpha} = -0.92+/-0.16. The high-mass end is determined by a complementary,
targeted WSRT survey, the low-mass end is determined by the blind VLA survey.
The slope is significantly shallower than the slopes of the HIPASS ({\alpha} =
-1.37+/-0.03+/-0.05) and ALFALFA ({\alpha} = -1.33+/-0.02) HI mass functions,
which are measured over much larger volumes and cover a wider range of cosmic
environments: There is a relative lack of low HI mass galaxies in the Ursa
Major region. This difference in the slope strongly hints at an environmental
dependence of the HI mass function slope.Comment: 19 pages, 15 figures. Accepted for publication in MNRA
Giant star-forming clumps?
With the spatial resolution of the Atacama Large Millimetre Array (ALMA),
dusty galaxies in the distant Universe typically appear as single, compact
blobs of dust emission, with a median half-light radius, 1 kpc.
Occasionally, strong gravitational lensing by foreground galaxies or galaxy
clusters has probed spatial scales 1-2 orders of magnitude smaller, often
revealing late-stage mergers, sometimes with tantalising hints of
sub-structure. One lensed galaxy in particular, the Cosmic Eyelash at 2.3,
has been cited extensively as an example of where the interstellar medium
exhibits obvious, pronounced clumps, on a spatial scale of 100 pc.
Seven orders of magnitude more luminous than giant molecular clouds in the
local Universe, these features are presented as circumstantial evidence that
the blue clumps observed in many 2-3 galaxies are important sites of
ongoing star formation, with significant masses of gas and stars. Here, we
present data from ALMA which reveal that the dust continuum of the Cosmic
Eyelash is in fact smooth and can be reproduced using two S\'ersic profiles
with effective radii, 1.2 and 4.4 kpc, with no evidence of significant
star-forming clumps down to a spatial scale of 80 pc and a
star-formation rate of 3 M yr.Comment: 5 pages; 3 figures; in press as a Letter to MNRA
Normal Globular Cluster Systems in Massive Low Surface Brightness Galaxies
We present the results of a study of the globular cluster systems of 6
massive spiral galaxies, originally cataloged as low surface brightness
galaxies but here shown to span a wide range of central surface brightness
values, including two intermediate to low surface brightness galaxies. We used
the Advanced Camera for Surveys on board HST to obtain photometry in the F475W
and F775W bands and select sources with photometric and morphological
properties consistent with those of globular clusters. A total of 206
candidates were identified in our target galaxies. From a direct comparison
with the Galactic globular cluster system we derive specific frequency values
for each galaxy that are in the expected range for late-type galaxies. We show
that the globular cluster candidates in all galaxies have properties consistent
with globular cluster systems of previously studied galaxies in terms of
luminosity, sizes and color. We establish the presence of globular clusters in
the two intermediate to low surface brightness galaxies in our sample and show
that their properties do not have any significant deviation from the behavior
observed in the other sample galaxies. Our results are broadly consistent with
a scenario in which low surface brightness galaxies follow roughly the same
evolutionary history as normal (i.e. high surface) brightness galaxies except
at a much lower rate, but require the presence of an initial period of star
formation intense enough to allow the formation of massive star clusters.Comment: 14 pages, 6 figures. AJ accepte
The stellar disk thickness of LSB galaxies
We present surface photometry results for a sample of eleven edge-on galaxies
observed with the 6m telescope at the Special Astrophysical Observatory
(Russia). The photometric scale length, scale height, and central surface
brightness of the stellar disks of our sample galaxies are estimated. We show
that four galaxies in our sample, which are visually referred as objects of the
lowest surface brightness class in the Revised Flat Galaxies Catalog, have bona
fide low surface brightness (LSB) disks. We find from the comparison of
photometric scales that the stellar disks of LSB galaxies are thinner than
those of high surface brightness (HSB) ones. There is a clear correlation
between the central surface brightness of the stellar disk and its vertical to
radial scale ratio. The masses of spherical subsystems (dark halo + bulge) and
the dark halo masses are obtained for the sample galaxies based on the
thickness of their stellar disks. The LSB galaxies tend to harbor more massive
spherical subsystems than the HSB objects, whereas no systematic difference in
the dark halo masses between LSB and HSB galaxies is found. At the same time,
the inferred mass-to-luminosity ratio for the LSB disks appears to be
systematically higher than for HSB disks.Comment: 33 pages with 17 Postscript figures, uses aastex.cls, accepted by Ap
Reconciling the local galaxy population with damped Ly-alpha cross sections and metal abundances
A comprehensive analysis of 355 high-quality WSRT HI 21-cm line maps of
nearby galaxies shows that the properties and incident rate of Damped
Lyman-alpha (DLA) absorption systems observed in the spectra of high redshift
QSOs are in good agreement with DLAs originating in gas disks of galaxies like
those in the z~0 population. Comparison of low-z DLA statistics with the HI
incidence rate and column density distribution f(N) for the local galaxy sample
shows no evidence for evolution in the integral "cross section density" below
z~1.5, implying that there is no need for a hidden population of galaxies or HI
clouds to contribute significantly to the DLA cross section. Compared with z~4,
our data indicates evolution of a factor of two in the comoving density along a
line of sight. We find that dN/dz(z=0)=0.045 +/- 0.006. The idea that the local
galaxy population can explain the DLAs is further strengthened by comparing the
properties of DLAs and DLA galaxies with the expectations based on our analysis
of local galaxies. The distribution of luminosities of DLA host galaxies, and
of impact parameters between QSOs and the centres of DLA galaxies, are in good
agreement with what is expected from local galaxies. Approximately 87% of low z
DLA galaxies are expected to be fainter than L* and 37 per cent have impact
parameters less than 1'' at z=0.5. The analysis shows that some host galaxies
with very low impact parameters and low luminosities are expected to be missed
in optical follow up surveys. The well-known metallicity-luminosity relation in
galaxies, in combination with metallicity gradients in galaxy disks, cause the
expected median metallicity of low redshift DLAs to be low (~1/7 solar), which
is also in good agreement with observations of low z DLAs. (Abridged)Comment: 22 pages, 22 figures. Accepted for publication in MNRAS. Fixed typo
Testing the Hypothesis of Modified Dynamics with Low Surface Brightness Galaxies and Other Evidence
The rotation curves of low surface brightness galaxies provide a unique data
set with which to test alternative theories of gravitation over a large dynamic
range in size, mass, surface density, and acceleration. Many clearly fail,
including any in which the mass discrepancy appears at a particular
length-scale. One hypothesis, MOND [Milgrom 1983, ApJ, 270, 371], is consistent
with the data. Indeed, it accurately predicts the observed behavior. We find no
evidence on any scale which clearly contradicts MOND, and a good deal which
supports it.Comment: Accepted for publication in the Astrophysical Journal. 35 pages
AAStex + 9 figures. This result surprised the bejeepers out of us, to
Exploring Neutral Hydrogen and Galaxy Evolution with the SKA
One of the key science drivers for the development of the SKA is to observe
the neutral hydrogen, HI, in galaxies as a means to probe galaxy evolution
across a range of environments over cosmic time. Over the past decade, much
progress has been made in theoretical simulations and observations of HI in
galaxies. However, recent HI surveys on both single dish radio telescopes and
interferometers, while providing detailed information on global HI properties,
the dark matter distribution in galaxies, as well as insight into the
relationship between star formation and the interstellar medium, have been
limited to the local universe. Ongoing and upcoming HI surveys on SKA
pathfinder instruments will extend these measurements beyond the local universe
to intermediate redshifts with long observing programmes. We present here an
overview of the HI science which will be possible with the increased
capabilities of the SKA and which will build upon the expected increase in
knowledge of HI in and around galaxies obtained with the SKA pathfinder
surveys. With the SKA1 the greatest improvement over our current measurements
is the capability to image galaxies at reasonable linear resolution and good
column density sensitivity to much higher redshifts (0.2 < z < 1.7). So one
will not only be able to increase the number of detections to study the
evolution of the HI mass function, but also have the sensitivity and resolution
to study inflows and outflows to and from galaxies and the kinematics of the
gas within and around galaxies as a function of environment and cosmic time out
to previously unexplored depths. The increased sensitivity of SKA2 will allow
us to image Milky Way-size galaxies out to redshifts of z=1 and will provide
the data required for a comprehensive picture of the HI content of galaxies
back to z~2 when the cosmic star formation rate density was at its peak.Comment: 25 pages, 5 figures, 3 tables. Contribution to the conference
'Advancing Astrophysics with the Square Kilometre Array', June 8-13, 2014,
Giardini Naxos, Ital
Management of cerebral azole-resistant Aspergillus fumigatus infection : a role for intraventricular liposomal-amphotericin B
Objectives: In the pre-azole era, central nervous system (CNS) infections with Aspergillus had a dismal outcome. Survival improved with voriconazole but CNS infections caused by azole-resistant Aspergillus fumigatus preclude its use. Intravenous liposomal-amphotericin B (L-AmB) is the preferred treatment option for azole-resistant CNS infections but has suboptimal brain concentrations. Methods: We describe three patients with biopsy-proven CNS aspergillosis where intraventricular L-AmB was added to systemic therapy. Two patients with azole-resistant aspergillosis and one patient with azole-susceptible CNS aspergillosis were treated with intraventricular L-AmB at a dose of 1 mg weekly. Results: We describe three patients successfully treated with a combination of intravenous and intraventricular L-AmB. All three patients survived but one patient developed serious headaches, most likely not related to this treatment. Conclusions: Intraventricular L-AmB may have a role in the treatment of therapy-refractory CNS aspergillosis when added to systemic therapy. (C) 2020 The Author(s). Published by Elsevier Ltd on behalf of International Society for Antimicrobial Chemotherapy
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