702 research outputs found
Remote sensing in the mixing zone
Characteristics of dispersion and diffusion as the mechanisms by which pollutants are transported in natural river courses were studied with the view of providing additional data for the establishment of water quality guidelines and effluent outfall design protocols. Work has been divided into four basic categories which are directed at the basic goal of developing relationships which will permit the estimation of the nature and extent of the mixing zone as a function of those variables which characterize the outfall structure, the effluent, and the river, as well as climatological conditions. The four basic categories of effort are: (1) the development of mathematical models; (2) laboratory studies of physical models; (3) field surveys involving ground and aerial sensing; and (4) correlation between aerial photographic imagery and mixing zone characteristics
Stellar abundances and molecular hydrogen in high-redshift galaxies -the far-ultraviolet view
FUSE spectra of star-forming regions in nearby galaxies are compared to
composite spectra of Lyman-break galaxies (LBGs), binned by strength of Lyman
alpha emission and by mid-UV luminosity. Several far-UV spectral features,
including lines dominated by stellar wind and by photospheric components, are
very sensitive to stellar abundances. Their measurement in Lyman-break galaxies
is compromised by the strong interstellar absorption features, allowing in some
cases only upper limits. The derived C and N abundances in the LBGs are no
higher than half solar (scaled to oxygen abundance for comparison with
emission-line analyses), independent of the strength of Lyman alpha emission. P
V absorption indicates abundances as low as 0.1 solar, with an upper limit near
0.4 solar in the reddest and weakest-emission galaxies. Unresolved interstellar
absorption components would further lower the derived abundances. Trends of
line strength, and derived abundances, are stronger with mid-UV luminosity than
with Lyman-alpha strength. H2 absorption in the Lyman and Werner bands is very
weak in the LBGs. Template H2 absorption spectra convolved to appropriate
resolution show that strict upper limits N(H2)< 10^18 cm^-2 apply in all cases,
with more stringent values appropriate for the stronger-emission composites and
for mixes of H2 level populations like those on Milky Way sight lines. Since
the UV-bright regions are likely to be widespread in these galaxies, these
results rule out massive diffuse reservoirs of H2, and suggest that the
dust/gas ratio is already fairly large at z~3.Comment: Astron J., in press (June 2006
Feedback in the local LBG Analog Haro 11 as probed by far-UV and X-ray observations
We have re-analyzed FUSE data and obtained new Chandra observations of Haro
11, a local (D_L=88 Mpc) UV luminous galaxy. Haro 11 has a similar far-UV
luminosity (10^10.3 L_\odot), UV surface brightness (10^9.4 L_\odot kpc^-2),
SFR, and metallicity to that observed in Lyman Break Galaxies (LBGs). We show
that Haro 11 has extended, soft thermal (kT~0.68 keV) X-ray emission with a
luminosity and size which scales with the physical properties (e.g. SFR,
stellar mass) of the host galaxy. An enhanced alpha/Fe, ratio of ~4 relative to
solar abundance suggests significant supernovae enrichment. These results are
consistent with the X-ray emission being produced in a shock between a
supernovae driven outflow and the ambient material. The FUV spectra show strong
absorption lines similar to those observed in LBG spectra. A blueshifted
absorption component is identified as a wind outflowing at ~200-280 km/s.
OVI\lambda\lambda1032,1038 emission, the dominant cooling mechanism for coronal
gas at T~10^5.5 K is also observed. If associated with the outflow, the
luminosity of the OVI emission suggests that <20% of the total mechanical
energy from the supernovae and solar winds is being radiated away. This implies
that radiative cooling through OVI is not significantly inhibiting the growth
of the outflowing gas. In contradiction to the findings of Bergvall et al 2006,
we find no convincing evidence of Lyman continuum leakage in Haro 11. We
conclude that the wind has not created a `tunnel' allowing the escape of a
significant fraction of Lyman continuum photons and place a limit on the escape
fraction of f_{esc}<2%. Overall, both Haro 11 and a previously observed LBG
analogue VV 114, provide an invaluable insight into the X-ray and FUV
properties of high redshift LBGs.Comment: Accepted for publication in ApJ, 40 pages, 17 figure
A Far-Ultraviolet View of Starburst Galaxies
Recent observational and theoretical results on starburst galaxies related to
the wavelength regime below 1200 A are discussed. The review covers stars,
dust, as well as hot and cold gas. This wavelength region follows trends
similar to those seen at longer wavelengths, with several notable exceptions.
Even the youngest stellar populations show a turn-over in their spectral energy
distributions, and line-blanketing is much more pronounced. Furthermore, the O
VI line allows one to probe gas at higher temperatures than possible with lines
at longer wavelengths. Molecular hydrogen lines (if detected) provide a glimpse
of the cold phase. I cover the crucial wavelength regime below 912 A and the
implications of recent attempts to detect the escaping ionizing radiation.Comment: 8 pages, 3 figures, Invited Talk, Starbursts--From 30 Doradus to
Lyman-Break Galaxies, ed. R. de Grijs & R. M. Gonzalez Delgado (Dordrecht:
Kluwer
Far-Ultraviolet & X-ray Observations of VV 114: Feedback in a Local Analog to Lyman Break Galaxies
We have analyzed FUSE, XMM, and Chandra observations of VV 114, a local
galaxy merger with strong similarities to typical high-redshift Lyman Break
Galaxies (LBGs). Diffuse thermal X-ray emission encompassing VV114 has been
observed by Chandra and XMM. This region of hot (kT~0.59 keV) gas has an
enhanced alpha to iron element ratio relative to solar abundances and follows
the same relation as typical starbursts between its properties (luminosity,
size, and temperature) and those of the starburst galaxy (star formation rate,
dust temperature, galaxy mass). These results are consistent with the X-ray gas
having been produced by shocks driven by a galactic superwind. The FUSE
observations of VV 114 show strong, broad interstellar absorption lines with a
pronounced blueshifted component(similar to what is seen in LBGs). This implies
an outflow of material moving at 300-400 km/s relative to VV 114. The
properties of the strong OVI absorption line are consistent with radiative
cooling at the interface between the hot outrushing gas seen in X-rays and the
cooler material seen in the other outflowing ions in the FUSE data. We show
that the wind in VV114 has not created a ``tunnel'' that enables more than a
small fraction (< few percent) of the ionizing photons from VV114 to escape
into the IGM. Taken together, these data provide a more complete physical basis
for understanding the outflows that seem to be generic in LBGs. This will lead
to improved insight into the role that such outflows play in the evolution of
galaxies and the inter-galactic medium.Comment: 33 pages, 13 figure
Parental bonding and identity style as correlates of self-esteem among adult adoptees and nonadoptees
Adult adoptees (n equals 100) and non-adoptees (n equals 100) were compared with regard to selfesteem, identity processing style, and parental bonding. While some differences were found with regard to self-esteem, maternal care, and maternal overprotection, these differences were
qualified by reunion status such that only reunited adoptees differed significantly from nonadoptees.
Moreover, hierarchical regression analyses indicated that parental bonding and identity processing style were more important than adoptive status per se in predicting self esteem. Implications for practitioners who work with adoptees are discussed
Forum 2: The migrant climate: resilience, adaptation and the ontopolitics of mobility in the Anthropocene
While modernist or âtop-downâ, âcommand-and-controlâ approaches to climate and migration worked at the surface or ontic level of the redistribution of entities in time and space, resilience approaches call for a different approach to mobility (for an extensive discussion of resilience as a distinctive governance regime see, for example, Grove, 2018; Chandler, 2014). These discourses construct mobilities that are more transformative, in fact, ones that question traditional liberal modernist notions of time and space and of entities with fixed essences. These mobilities do not concern moving entities in space but rethinking mobility in relation to space. Mobility then becomes more a matter of changing the understandings and practices relating to spaces and entities than of moving things from one place to another. Becoming âmobileâ thus would apply to the development of capabilities or âresponse-abilitiesâ (Haraway, 2016: 2) to sense, adapt, recompose, repurpose and reimagine problems and possibilities; taking responses to crises beyond the static and binary conceptions of mobility and space epitomised by The Clash lyrics in the epigraph
Abundances in the Neutral Interstellar Medium of I Zw 18 from FUSE Observations
We report on new FUSE far-UV spectroscopy of the most metal-poor blue compact
dwarf galaxy I Zw 18. The new data represent an improvement over previous FUSE
spectra by a factor of 1.7 in the signal-to-noise. Together with a larger
spectral coverage (917-1188 angstroms), this allows us to characterize
absorption lines in the interstellar medium with unprecedented accuracy. The
kinematics averaged over the large sampled region shows no clear evidence of
gas inflows or outflows. The H I absorption is interstellar with a column
density of 2.2 (+0.6,-0.5} * 10^21 cm^(-2). A conservative 3 sigma upper limit
of 5.25 * 10^(14) cm^(-2) is derived for the column density of diffuse H_2.
From a simultaneous fitting of metal absorption lines in the interstellar
medium, we infer the following abundances: [Fe/H] = -1.76 +/- 0.12, [O/H] =
-2.06 +/- 0.28, [Si/H] = -2.09 +/- 0.12, [Ar/H] = -2.27 +/- 0.13, and [N/H] =
-2.88 +/- 0.11. This is in general several times lower than in the H II
regions. The only exception is iron, whose abundance is the same. The abundance
pattern of the interstellar medium suggests ancient star-formation activity
with an age of at least a Gyr that enriched the H I phase. Around 470 SNe Ia
are required to produce the iron content. A more recent episode that started 10
to several 100 Myr ago is responsible for the additional enrichment of
alpha-elements and nitrogen in the H II regions.Comment: 48 pages including 3 tables (Latex) and 7 figures (postscript).
Accepted for publication in the Astrophysical Journa
The Contribution of Field OB Stars to the Ionization of the Diffuse Ionized Gas in M33
(Abridged) We present a study of the ionizing stars associated with the
diffuse ionized gas (DIG) and HII regions in the nearby spiral galaxy M33. We
compare our Schmidt H-alpha image to the far-ultraviolet (FUV, 1520A) image
from the Ultraviolet Imaging Telescope (UIT). The H-alpha/FUV ratio is higher
in HII regions than in the DIG, suggesting an older population of ionizing
stars in the DIG. When compared to models of evolving stellar populations, the
N(Lyc)/FUV ratio in HII regions is consistent with a young burst, while the DIG
ratio resembles an older burst population, or a steady state population built
up by constant star formation. The UIT data is complimented with archival FUV
and optical images of a small portion of the disk of M33 obtained with WFPC2 on
HST. Using the HST FUV and optical photometry, we assign spectral types to the
stars observed in DIG and HII regions. The photometry indicates that ionizing
stars are present in the DIG. We compare the predicted ionizing flux with the
amount required to produce the observed H-alpha emission, and find that field
OB stars in the HST images can account for 40% +/- 12% of the ionization of the
DIG, while the stars in HII regions can provide 107% +/- 26% of the H-alpha
luminosity of the HII regions. We do not find any correlation between leakage
of ionizing photons and H-alpha luminosity for the HII regions in these HST
fields. If stellar photons alone are responsible for ionizing the DIG, the
current results are consistent with no or few ionizing photons escaping from
the galaxy.Comment: 30 pages, 7 figures, accepted for publication in Ap
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