291 research outputs found
Dynamical Characterization of Galaxies at z~4-6 via Tilted Ring Fitting to ALMA [CII] Observations
Until recently, determining the rotational properties of galaxies in the
early universe (z>4, Universe age <1.5Gyr) was impractical, with the exception
of a few strongly lensed systems. Combining the high resolution and sensitivity
of ALMA at (sub-) millimeter wavelengths with the typically high strength of
the [CII] 158um emission line from galaxies and long-developed dynamical
modeling tools raises the possibility of characterizing the gas dynamics in
both extreme starburst galaxies and normal star forming disk galaxies at z~4-7.
Using a procedure centered around GIPSY's ROTCUR task, we have fit tilted ring
models to some of the best available ALMA [CII] data of a small set of
galaxies: the MS galaxies HZ9 & HZ10, the Damped Lyman-alpha Absorber (DLA)
host galaxy ALMA J0817+1351, the submm galaxies AzTEC/C159 and COSMOS
J1000+0234, and the quasar host galaxy ULAS J1319+0950. This procedure directly
derives rotation curves and dynamical masses as functions of radius for each
object. In one case, we present evidence for a dark matter halo of O(10^11)
solar masses. We present an analysis of the possible velocity dispersions of
AzTEC/C159 and ULAS J1319+0950 based on matching simulated observations to the
integrated [CII] line profiles. Finally, we test the effects of observation
resolution and sensitivity on our results. While the conclusions remain limited
at the resolution and signal-to-noise ratios of these observations, the results
demonstrate the viability of the modeling tools at high redshift, and the
exciting potential for detailed dynamical analysis of the earliest galaxies, as
ALMA achieves full observational capabilities.Comment: 20 pages, 6 figures, Accepted for publication in Ap
An Introduction to Gas Accretion onto Galaxies
Evidence for gas accretion onto galaxies can be found throughout the
universe. In this chapter, I summarize the direct and indirect signatures of
this process and discuss the primary sources. The evidence for gas accretion
includes the star formation rates and metallicities of galaxies, the evolution
of the cold gas content of the universe with time, numerous indirect indicators
for individual galaxies, and a few direct detections of inflow. The primary
sources of gas accretion are the intergalactic medium, satellite gas and
feedback material. There is support for each of these sources from observations
and simulations, but the methods with which the fuel ultimately settles in to
form stars remain murky.Comment: 14 pages, 5 figures, Invited review to appear in Gas Accretion onto
Galaxies, Astrophysics and Space Science Library, eds. A. J. Fox & R. Dav\'e,
to be published by Springe
Reverberation Mapping of the Kepler-Field AGN KA1858+4850
KA1858+4850 is a narrow-line Seyfert 1 galaxy at redshift 0.078 and is among
the brightest active galaxies monitored by the Kepler mission. We have carried
out a reverberation mapping campaign designed to measure the broad-line region
size and estimate the mass of the black hole in this galaxy. We obtained 74
epochs of spectroscopic data using the Kast Spectrograph at the Lick 3-m
telescope from February to November of 2012, and obtained complementary V-band
images from five other ground-based telescopes. We measured the H-beta light
curve lag with respect to the V-band continuum light curve using both
cross-correlation techniques (CCF) and continuum light curve variability
modeling with the JAVELIN method, and found rest-frame lags of lag_CCF = 13.53
(+2.03, -2.32) days and lag_JAVELIN = 13.15 (+1.08, -1.00) days. The H-beta
root-mean-square line profile has a width of sigma_line = 770 +/- 49 km/s.
Combining these two results and assuming a virial scale factor of f = 5.13, we
obtained a virial estimate of M_BH = 8.06 (+1.59, -1.72) x 10^6 M_sun for the
mass of the central black hole and an Eddington ratio of L/L_Edd ~ 0.2. We also
obtained consistent but slightly shorter emission-line lags with respect to the
Kepler light curve. Thanks to the Kepler mission, the light curve of
KA1858+4850 has among the highest cadences and signal-to-noise ratios ever
measured for an active galactic nucleus; thus, our black hole mass measurement
will serve as a reference point for relations between black hole mass and
continuum variability characteristics in active galactic nuclei
Suicide among Arab-Americans
BACKGROUND: Arab-American (AA) populations in the US are exposed to discrimination and acculturative stress-two factors that have been associated with higher suicide risk. However, prior work suggests that socially oriented norms and behaviors, which characterize recent immigrant ethnic groups, may be protective against suicide risk. Here we explored suicide rates and their determinants among AAs in Michigan, the state with the largest proportion of AAs in the US. METHODOLOGY/PRINCIPAL FINDINGS: ICD-9/10 underlying cause of death codes were used to identify suicide deaths from among all deaths in Michigan between 1990 and 2007. Data from the 2000 U.S. Census were collected for population denominators. Age-adjusted suicide rates among AAs and non-ethnic whites were calculated by gender using the direct method of standardization. We also stratified by residence inside or outside of Wayne County (WC), the county with the largest AA population in the state. Suicide rates were 25.10 per 100,000 per year among men and 6.40 per 100,000 per year among women in Michigan from 1990 to 2007. AA men had a 51% lower suicide rate and AA women had a 33% lower rate than non-ethnic white men and women, respectively. The suicide rate among AA men in WC was 29% lower than in all other counties, while the rate among AA women in WC was 20% lower than in all other counties. Among non-ethnic whites, the suicide rate in WC was higher compared to all other counties among both men (12%) and women (16%). CONCLUSIONS/SIGNIFICANCE: Suicide rates were higher among non-ethnic white men and women compared to AA men and women in both contexts. Arab ethnicity may protect against suicide in both sexes, but more so among men. Additionally, ethnic density may protect against suicide among Arab-Americans
On the form-function dichotomy in linguistic theory
This paper focuses on an important divide in theoretical linguistics between two broad perspectives on the structural properties of human languages, generative and functionalist. In the former, linguistic structure is explained in terms of discrete categories and highly abstract principles, which may be language-independent or language-specific and purely formal or functional in nature. In the latter, explanation for why languages have the structure that they do is found ‘outside’ language, in the general principles of human cognition and the communicative functions of language. The aim of this paper is to highlight the need for abstractness, explicitness, simplicity and theoretical economy in linguistic description and explanation. The question is not whether principles of grammar are formal or functional. The question is whether the principles that are postulated to explain linguistic structure express true generalizations
Observational Diagnostics of Gas Flows: Insights from Cosmological Simulations
Galactic accretion interacts in complex ways with gaseous halos, including
galactic winds. As a result, observational diagnostics typically probe a range
of intertwined physical phenomena. Because of this complexity, cosmological
hydrodynamic simulations have played a key role in developing observational
diagnostics of galactic accretion. In this chapter, we review the status of
different observational diagnostics of circumgalactic gas flows, in both
absorption (galaxy pair and down-the-barrel observations in neutral hydrogen
and metals; kinematic and azimuthal angle diagnostics; the cosmological column
density distribution; and metallicity) and emission (Lya; UV metal lines; and
diffuse X-rays). We conclude that there is no simple and robust way to identify
galactic accretion in individual measurements. Rather, progress in testing
galactic accretion models is likely to come from systematic, statistical
comparisons of simulation predictions with observations. We discuss specific
areas where progress is likely to be particularly fruitful over the next few
years.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics
and Space Science Library, eds. A. J. Fox & R. Dave, to be published by
Springer. Typos correcte
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