463 research outputs found
Photon dominated regions in the spiral arms of M83 and M51
We present CI 3P1-3P0 spectra at four spiral arm positions and the nuclei of
the nearby galaxies M83 and M51 obtained at the JCMT. This data is complemented
with maps of CO 1-0, 2-1, and 3-2, and ISO/LWS far-infrared data of CII (158
micron), OI (63 micron), and NII (122 micron) allowing for the investigation of
a complete set of all major gas cooling lines. From the intensity of the NII
line, we estimate that between 15% and 30% of the observed CII emission
originate from the dense ionized phase of the ISM. The analysis indicates that
emission from the diffuse ionized medium is negligible. In combination with the
FIR dust continuum, we find gas heating efficiencies below ~0.21% in the
nuclei, and between 0.25 and 0.36% at the outer positions. Comparison with
models of photon-dominated regions (PDRs) of Kaufman et al. (1999) with the
standard ratios OI(63)/CII_PDR and (OI(63)+CII_PDR) vs. TIR, the total infrared
intensity, yields two solutions. The physically most plausible solution
exhibits slightly lower densities and higher FUV fields than found when using a
full set of line ratios, CII_PDR/CI(1-0), CI(1-0)/CO(3-2), CO(3-2)/CO(1-0),
CII/CO(3-2), and, OI(63)/CII_PDR. The best fits to the latter ratios yield
densities of 10^4 cm^-3 and FUV fields of ~G_0=20-30 times the average
interstellar field without much variation. At the outer positions, the observed
total infrared intensities are in perfect agreement with the derived best
fitting FUV intensities. The ratio of the two intensities lies at 4-5 at the
nuclei, indicating the presence of other mechanisms heating the dust
Strong [CII] emission at high redshift
We report the detection of the [CII]157.74um fine-structure line in the
lensed galaxy BRI 0952-0115 at z=4.43, using the APEX telescope. This is the
first detection of the [CII] line in a source with L_FIR < 10^13 L_sun at high
redshift. The line is very strong compared to previous [CII] detections at
high-z (a factor of 5-8 higher in flux), partly due to the lensing
amplification. The L_[CII]/L_FIR ratio is 10^-2.9, which is higher than
observed in local galaxies with similar infrared luminosities. Together with
previous observations of [CII] at high redshift, our result suggests that the
[CII] emission in high redshift galaxies is enhanced relative to local galaxies
of the same infrared luminosity. This finding may result from selection effects
of the few current observations of [CII] at high redshift, and in particular
the fact that non detections may have not been published (although the few
published upper limits are still consistent with the [CII] enhancement
scenario). If the trend is confirmed with larger samples, it would indicate
that high-z galaxies are characterized by different physical conditions with
respect to their local counterparts. Regardless of the physical origin of the
trend, this effect would increase the potential of the [CII]158um line to
search and characterize high-z sources.Comment: Accepted for publication in A&A Letters, 5 pages, 2 figure
Critical Response Models for Foot-and-Mouth Disease Epidemics
28 pages, 1 article*Critical Response Models for Foot-and-Mouth Disease Epidemics* (Oritz, Johnsie; Rivera, Manuel A.; Rubin, Daniel; Ruiz, Israel; Hernandez, Carlos M.; Castillo-Chavez, Carlos) 28 page
Metals Removed by Outflows from Milky Way Dwarf Spheroidal Galaxies
The stars in the dwarf spheroidal satellite galaxies (dSphs) of the Milky Way
are significantly more metal-poor than would be expected from a closed box
model of chemical evolution. Gas outflows likely carried away most of the
metals produced by the dSphs. Based on previous Keck/DEIMOS observations and
models, we calculate the mass in Mg, Si, Ca, and Fe expelled from each of eight
dSphs. Essentially, these masses are the differences between the observed
amount of metals present in the dSphs' stars today and the inferred amount of
metals produced by supernovae. We conclude that the dSphs lost 96% to >99% of
the metals their stars manufactured. We apply the observed mass function of
Milky Way dSphs to the ejected mass function to determine that a single large
dSph, like Fornax, lost more metals over 10 Gyr than all smaller dSphs
combined. Therefore, small galaxies like dSphs are not significant contributors
to the metal content of the intergalactic medium. Finally, we compare our
ejected mass function to previous X-ray measurements of the metal content of
the winds from the post-starburst dwarf irregular galaxy NGC 1569. Remarkably,
the most recent starburst in that galaxy falls exactly on the ejected
mass-stellar mass relation defined by the Milky Way dSphs.Comment: 5 pages, 2 figures, accepted to ApJ
High-resolution mapping of the physical conditions in two nearby active galaxies based on 12CO(1-0), (2-1) and (3-2) lines
We present a detailed analysis of high resolution observations of the three
lowest CO transitions in two nearby active galaxies, NGC4569 and NGC4826. The
CO(1-0) and (2-1) lines were observed with the Plateau de Bure Interferometer
and the CO(3-2) line with the Submillimeter Array. Combining these data allows
us to compare the emission in the three lines and to map the line ratios,
R21=I_{CO(2-1)}/I_{CO(1-0)} and R32=I_{CO(3-2)}/I_{CO(1-0)} at a resolution of
~2", i.e., a linear resolution of 160 pc for NGC4569 and 40 pc for NGC4826. In
both galaxies the emission in the three lines is similarly distributed
spatially and in velocity, and CO is less excited (R32<0.6) than in the
Galactic Center or the centers of other active galaxies studied so far.
According to a pseudo-LTE model the molecular gas in NGC4569 is cold and mainly
optically thick in the CO(1-0) and (2-1) lines; less than 50% of the gas is
optically thin in the CO(3-2) line. LVG modeling suggests the presence of an
elongated ring of cold and dense gas coinciding with the ILR of the stellar
bar. More excited gas is resolved in the circumnuclear disk of NGC4826.
According to our pseudo-LTE model this corresponds to warmer gas with a ~50% of
the CO(3-2) emission being optically thin. LVG modeling indicates the presence
of a semicircular arc of dense and cold gas centered on the dynamical center
and ~70 pc in radius. The gas temperature increases and its density decreases
toward the center. A near side/far side asymmetry noticeable in the CO, R32 and
Pa-alpha maps suggests that opacity effects play a role. Examining published CO
maps of nearby active galaxies we find similar asymmetries suggesting that this
could be a common phenomenon in active galaxies. These mainly qualitative
results open new perspectives for the study of active galaxies with the future
Atacama Large Millimeter/submillimeter Array.Comment: accepted for publication in A&
Chern-Simons Modified General Relativity
Chern-Simons modified gravity is an effective extension of general relativity
that captures leading-order, gravitational parity violation. Such an effective
theory is motivated by anomaly cancelation in particle physics and string
theory. In this review, we begin by providing a pedagogical derivation of the
three distinct ways such an extension arises: (1) in particle physics, (2) from
string theory and (3) geometrically. We then review many exact and approximate,
vacuum solutions of the modified theory, and discuss possible matter couplings.
Following this, we review the myriad astrophysical, solar system, gravitational
wave and cosmological probes that bound Chern-Simons modified gravity,
including discussions of cosmic baryon asymmetry and inflation. The review
closes with a discussion of possible future directions in which to test and
study gravitational parity violation.Comment: 104 pages, 2 figures, 186 references, Invited Review accepted for
publication in Phys. Repts. This version corrects a minor typo in Eq. (174)
of the published versio
Entangled Stories: The Red Jews in Premodern Yiddish and German Apocalyptic Lore
“Far, far away from our areas, somewhere beyond the Mountains of Darkness, on the other side of the Sambatyon River…there lives a nation known as the Red Jews.” The Red Jews are best known from classic Yiddish writing, most notably from Mendele's Kitser masoes Binyomin hashlishi (The Brief Travels of Benjamin the Third). This novel, first published in 1878, represents the initial appearance of the Red Jews in modern Yiddish literature. This comical travelogue describes the adventures of Benjamin, who sets off in search of the legendary Red Jews. But who are these Red Jews or, in Yiddish, di royte yidelekh? The term denotes the Ten Lost Tribes of Israel, the ten tribes that in biblical times had composed the Northern Kingdom of Israel until they were exiled by the Assyrians in the eighth century BCE. Over time, the myth of their return emerged, and they were said to live in an uncharted location beyond the mysterious Sambatyon River, where they would remain until the Messiah's arrival at the end of time, when they would rejoin the rest of the Jewish people.
This article is part of a broader study of the Red Jews in Jewish popular culture from the Middle Ages through modernity. It is partially based on a chapter from my book, Umstrittene Erlöser: Politik, Ideologie und jüdisch-christlicher Messianismus in Deutschland, 1500–1600 (Göttingen: Vandenhoeck & Ruprecht, 2011). Several postdoctoral fellowships have generously supported my research on the Red Jews: a Dr. Meyer-Struckmann-Fellowship of the German Academic Foundation, a Harry Starr Fellowship in Judaica/Alan M. Stroock Fellowship for Advanced Research in Judaica at Harvard University, a research fellowship from the Heinrich Hertz-Foundation, and a YIVO Dina Abramowicz Emerging Scholar Fellowship. I thank the organizers of and participants in the colloquia and conferences where I have presented this material in various forms as well as the editors and anonymous reviewers of AJS Review for their valuable comments and suggestions. I am especially grateful to Jeremy Dauber and Elisheva Carlebach of the Institute for Israel and Jewish Studies at Columbia University, where I was a Visiting Scholar in the fall of 2009, for their generous encouragement to write this article. Sue Oren considerably improved my English. The style employed for Romanization of Yiddish follows YIVO's transliteration standards. Unless otherwise noted, translations from the Yiddish, Hebrew, German, and Latin are my own. Quotations from the Bible follow the JPS translation, and those from the Babylonian Talmud are according to the Hebrew-English edition of the Soncino Talmud by Isidore Epstein
A photoionization modeling study of 30 Doradus: the case for small-scale chemical inhomogeneity
Photoionization models of the giant HII region 30 Doradus are built and
confronted to available UV, optical, IR (ISO) and radio spectra, under
black-body or CoStar SEDs for the primary source and various density
distributions for the nebular gas. Chemically homogeneous models show very
small rms electron temperature fluctuations and fail to reproduce the heavy
element optical recombination line (ORL) spectrum of the nebula. Dual abundance
models incorporating small-scale chemical inhomogeneities in the form of
H-deficient inclusions which are in pressure balance with the normal
composition ambient gas, provide a better fit to the observed heavy element
ORLs and other nebular lines, while most spectral features are satisfactorily
accounted for. The inclusions, whose mass is ~2 per cent of the total gaseous
mass, are 2-3 times cooler and denser than the ambient nebula. Their O/H
abundance ratio is ~0.9 dex larger than in the normal composition gas and have
typical mass fractions of X = 0.687, Y = 0.273 and Z = 0.040. Helium is found
to be about as deficient as hydrogen in the inclusions, while elements heavier
than Ne, such as S and Ar, are quite possibly enhanced in proportions similar
to O. This suggests that the posited H-deficient inclusions may have arisen
from partial mixing of matter which was nucleosynthetically processed in a
supernova event with gas of normal LMC composition. Attention is drawn to a
bias in the determination of HII region helium abundances in the presence of
H-deficient inclusions. It is argued that these results provide evidence for
incomplete small-scale mixing of the ISM. The case for the existence of
abundance inhomogeneities in HII regions is examined in the light of current
theoretical considerations regarding the process of homogenization in the ISM.Comment: 19 pages; 8 figures; MNRAS in pres
A Spitzer Space Telescope far-infrared spectral atlas of compact sources in the Magellanic Clouds. I. The Large Magellanic Cloud
[abridged] We present 52-93 micron spectra obtained with Spitzer in the
MIPS-SED mode, of a representative sample of luminous compact far-IR sources in
the LMC. These include carbon stars, OH/IR AGB stars, post-AGB objects and PNe,
RCrB-type star HV2671, OH/IR red supergiants WOHG064 and IRAS05280-6910, B[e]
stars IRAS04530-6916, R66 and R126, Wolf-Rayet star Brey3a, Luminous Blue
Variable R71, supernova remnant N49, a large number of young stellar objects,
compact HII regions and molecular cores, and a background galaxy (z~0.175). We
use the spectra to constrain the presence and temperature of cold dust and the
excitation conditions and shocks within the neutral and ionized gas, in the
circumstellar environments and interfaces with the surrounding ISM. Evolved
stars, including LBV R71, lack cold dust except in some cases where we argue
that this is swept-up ISM. This leads to an estimate of the duration of the
prolific dust-producing phase ("superwind") of several thousand years for both
RSGs and massive AGB stars, with a similar fractional mass loss experienced
despite the different masses. We tentatively detect line emission from neutral
oxygen in the extreme RSG WOHG064, with implications for the wind driving. In
N49, the shock between the supernova ejecta and ISM is revealed by its strong
[OI] 63-micron emission and possibly water vapour; we estimate that 0.2 Msun of
ISM dust was swept up. Some of the compact HII regions display pronounced
[OIII] 88-micron emission. The efficiency of photo-electric heating in the
interfaces of ionized gas and molecular clouds is estimated at 0.1-0.3%. We
confirm earlier indications of a low nitrogen content in the LMC. Evidence for
solid state emission features is found in both young and evolved object; some
of the YSOs are found to contain crystalline water ice.Comment: Accepted for publication in The Astronomical Journal. This paper
accompanies the Summer 2009 SAGE-Spec release of 48 MIPS-SED spectra, but
uses improved spectrum extraction. (Fig. 2 reduced resolution because of
arXiv limit.
Gauge-invariant gravitational perturbations of maximally symmetric spacetimes
Gravitational perturbations of anti-deSitter spacetime play important roles
in AdS/CFT correspondence and the brane world scenario. In this paper, we
develop a gauge-invariant formalism of gravitational perturbations of maximally
symmetric spacetimes including anti-deSitter spacetime. Existence of
scalar-type master variables is shown and the corresponding master equations
are derived.Comment: Latex, 18 pages; references revised; accepted for publication in
Phys. Rev.
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