24 research outputs found
Outskirts of Distant Galaxies In Absorption
QSO absorption spectroscopy provides a sensitive probe of both the neutral
medium and diffuse ionized gas in the distant Universe. It extends 21cm maps of
gaseous structures around low-redshift galaxies both to lower gas column
densities and to higher redshifts. Combining galaxy surveys with
absorption-line observations of gas around galaxies enables comprehensive
studies of baryon cycles in galaxy outskirts over cosmic time. This Chapter
presents a review of the empirical understanding of the cosmic neutral gas
reservoir from studies of damped Lya absorbers (DLAs). It describes the
constraints on the star formation relation and chemical enrichment history in
the outskirts of distant galaxies from DLA studies. A brief discussion of
available constraints on the ionized circumgalactic gas from studies of lower
column density Lya absorbers and associated ionic absorption transitions is
presented at the end.Comment: 45 pages, 7 figures, invited review, Book chapter in "Outskirts of
Galaxies", Eds. J. H. Knapen, J. C. Lee and A. Gil de Paz, Astrophysics and
Space Science Library, Springer, in pres
HI in the Outskirts of Nearby Galaxies
The HI in disk galaxies frequently extends beyond the optical image, and can
trace the dark matter there. I briefly highlight the history of high spatial
resolution HI imaging, the contribution it made to the dark matter problem, and
the current tension between several dynamical methods to break the disk-halo
degeneracy. I then turn to the flaring problem, which could in principle probe
the shape of the dark halo. Instead, however, a lot of attention is now devoted
to understanding the role of gas accretion via galactic fountains. The current
cold dark matter theory has problems on galactic scales, such as
the core-cusp problem, which can be addressed with HI observations of dwarf
galaxies. For a similar range in rotation velocities, galaxies of type Sd have
thin disks, while those of type Im are much thicker. After a few comments on
modified Newtonian dynamics and on irregular galaxies, I close with statistics
on the HI extent of galaxies.Comment: 38 pages, 17 figures, invited review, book chapter in "Outskirts of
Galaxies", Eds. J. H. Knapen, J. C. Lee and A. Gil de Paz, Astrophysics and
Space Science Library, Springer, in pres
Stellar structure and compact objects before 1940: Towards relativistic astrophysics
Since the mid-1920s, different strands of research used stars as "physics
laboratories" for investigating the nature of matter under extreme densities
and pressures, impossible to realize on Earth. To trace this process this paper
is following the evolution of the concept of a dense core in stars, which was
important both for an understanding of stellar evolution and as a testing
ground for the fast-evolving field of nuclear physics. In spite of the divide
between physicists and astrophysicists, some key actors working in the
cross-fertilized soil of overlapping but different scientific cultures
formulated models and tentative theories that gradually evolved into more
realistic and structured astrophysical objects. These investigations culminated
in the first contact with general relativity in 1939, when J. Robert
Oppenheimer and his students George Volkoff and Hartland Snyder systematically
applied the theory to the dense core of a collapsing neutron star. This
pioneering application of Einstein's theory to an astrophysical compact object
can be regarded as a milestone in the path eventually leading to the emergence
of relativistic astrophysics in the early 1960s.Comment: 83 pages, 4 figures, submitted to the European Physical Journal
Anatomy of Pilostyles hamiltonii C. A. Gardner (Rafflesiaceae) in stems of Daviesia
In Daviesia stems the vegetative body of Pilostyles hamiltonii occurs as thin strands of undifferentiated cells within the secondary phloem of the host. Parasite cells have prominent nuclei, extended plasmalemma, and lack chloroplasts and amyloplasts. Plasmodesmata are abundant between parasite and host cells. Early vegetative growth of the parasite appears to depend on host phloem tissues for its nutrient requirements. At flower initiation Pilostyles taps the host xylem by producing pegs of tissue across the vascular cambium of the host
Retention of transmitter attachments on black cockatoos (Calyptorhynchus spp.)
Despite the widespread use of telemetry to track the movements of many different avian species, there are few published studies describing tracking methods for large psittacine birds. Due to their powerful bills and inquisitive demeanours, large parrots may damage valuable transmitters and confound telemetry studies. We undertook a captive trial of three attachment methods (collar, harness and tail-mount) and a novel weak-link harness design for black cockatoos (Calyptorhynchus latirostris, C. baudinii and C. banksii naso). Mean retention times for the transmitter packages ranged from 44 to 384 days. There was no skin or feather damage to the birds associated with transmitter attachments. The results showed sufficient transmitter retention times to allow for the collection of valuable movement and survival data, with no obvious ill effects on animal welfare, and are a first step towards using transmitters on wild cockatoos
Ecosystem development on a titanium dioxide residue pond after five years in Capel, Western Australia
Fireāmediated habitat change regulates woodland bird species and functional group occurrence
In an era characterized by recurrent large wildfires in many parts of the globe, there is a critical need to understand how animal species respond to fires, the rates at which populations can recover, and the functional changes fires may cause. Using quantified changes in habitat parameters over a ~400āyr postāfire chronosequence in an obligateāseeding Australian eucalypt woodland, we build and test predictions of how birds, as individual species and aggregated into functional groups according to their use of specific habitat resources, respond to time since fire. Individual bird species exhibited four generalized response types to time since fire: incline, decline, delayed, and bell. All significant relationships between bird functional group richness or abundance and time since fire were consistent with predictions based on known timeāsinceāfireāassociated changes in habitat features putatively important for these bird groups. Consequently, we argue that the bird community is responding to postāfire successional changes in habitat as per the habitat accommodation model, rather than to time since fire per se, and that our functional framework will be of value in predicting bird responses to future disturbances in this and other obligateāseeder forest and woodland ecosystems. Most bird species and functional groups that were affected by time since fire were associated with longāunburned woodlands. In the context of recent large, standāreplacement wildfires that have affected a substantial proportion of obligateāseeder eucalypt woodlands, and the multiācentury timescales over which postāfire succession occurs, it would appear preferable from a bird conservation perspective if fires initiating loss of currently longāunburned woodlands were minimized. Once longāunburned woodlands are transformed by fire into recently burned woodlands, there is limited scope for alternative management interventions to accelerate the rate of habitat development after fire, or supplement the resources formerly provided to birds by longāunburned woodlands, with the limited exception of augmenting hollow availability for key hollowānesting species
Multi-century periods since fire in an intact woodland landscape favour bird species declining in an adjacent agricultural region
Habitat modification by fire and habitat loss via anthropogenic vegetation clearance and fragmentation both impact animal populations. Yet, there has been limited investigation as to whether animals that decline under one of these types of habitat change also decline under the other, and how their cumulative impacts affect the status of species and communities. Using a ~400-year chronosequence in the world's largest extant temperate woodland in south-western Australia, we examine how time since fire affects bird community richness, reporting rates and composition, and whether taxa grouped on the basis of responses to vegetation clearance and fragmentation in an adjoining agricultural landscape are associated with either recently-burnt or long-unburnt woodlands. Consistent with substantial changes in vegetation composition and structure after fire in obligate-seeder eucalypt woodlands, woodland bird communities were strongly affected by fire. Species richness and total reporting rates increased with time since fire, and community composition changed across the entire multi-century span of the chronosequence. Woodland birds most negatively impacted by vegetation clearance and fragmentation were strongly associated with long-unburnt woodlands. In a regional south-western Australian context, where extensive vegetation clearance has substantially reduced the range and populations of many woodland bird species, the ability of remaining unfragmented woodlands to support populations of these species will be strongly contingent on appropriate fire management. Specifically, as stand-replacement fires have affected 25ā30% of extant woodland over recent decades, management to limit the extent of fire in remaining long-unburnt woodlands would appear a priority for conservation of woodland bird diversity