798 research outputs found
VLT Spectroscopy of the z=4.11 Radio Galaxy TN J1338-1942
We present optical, infrared and radio data of the z=4.11 radio galaxy TN
J1338-1942, including an intermediate resolution spectrum obtained with FORS1on
the VLT Antu telescope. TN J1338-1942 was the first z>4 radio galaxy to be
discovered in the southern hemisphere and is one of the most luminous Ly-alpha
objects in its class. The Ly-alpha and rest-frame optical emission appear
co-spatial with the brightest radio hotspot of this very asymmetric radio
source, suggesting extremely strong interaction with dense ambient clouds. The
VLT observations are sufficiently sensitive to detect the continuum flux both
blue-ward and red-ward of the Ly-alpha emission, allowing us to measure the
Ly-alpha forest continuum break (Ly-alpha 'discontinuity', D_A) and the Lyman
limit. We measure a D_A=0.37+-0.1, which is ~0.2 lower than the values found
for quasars at this redshift. We interpret this difference as possibly due to a
bias towards large D_A introduced in high--redshift quasar samples that are
selected on the basis of specific optical colors. If such a bias would exist in
optically selected quasars, - and even in samples of Lyman break galaxies -,
then the space density of both classes of object will be underestimated.
Furthermore, the average HI column density along cosmological lines of sight as
determined using quasar absorption lines would be overestimated. Because of
their radio-based selection, we argue that z>4 radio galaxies are excellent
objects for investigating D_A statistics. [abridged]Comment: 6 Pages, including 4 PostScript figures. Accepted for publication in
the Astronomy & Astrophysics Letter
Time-series analysis of seasonal patterns for pneumonia deaths in Peru, 2003-2017 period
Introduction. It is generally accepted that respiratory infections are seasonal, but high-frequency periods are rarely identified at the local level in a country with diverse climates. Anticipating the pneumonia season locally can provide a better use of critical resources. Objective. The aim of the study was to examine seasonal variability in monthly deaths due to pneumonia in Peru. Methods. Observational retrospective study using time series analysis to identify periods of high pneumonia mortality in seven cities in Peru. We reviewed administrative reports from the Ministry of Health for pneumonia deaths during 2003-2017. Descriptive statistics were calculated and a time series analysis at a monthly scale was performed on the frequency of deaths due to pneumonia, cumulative rainfall, and maximum and minimum environmental temperatures. Results: 94.4% of pneumonia deaths (N = 166,844) were reported as pneumonia due to “unspecified organism”, and 75.6% were adults older than 65 years. In the cities of Tarma, Arequipa and Cusco, minimum ambient temperature is negatively correlated to pneumonia deaths in all age groups and at least one risk group. In Iquitos, minimum temperature is positively correlated with deaths among children under 5 years of age. The cities of Pucallpa and Cajamarca reported no statistically significant correlation. The climate in Lima is a peculiar case. The distribution of pneumonia deaths throughout the year suggests a north-south sequence, while the climate space-time analysis suggests a south-north pattern. Conclusion: Results show different seasonal patterns for pneumonia deaths in different cities and risk groups.Revisión por pare
Photometric variability of candidate white dwarf binary systems from Palomar Transient Factory archival data
We present a sample of 59 periodic variables from the Palomar Transient
Factory, selected from published catalogues of white dwarf (WD) candidates. The
variability can likely be attributed to ellipsoidal variation of the tidally
distorted companion induced by the gravity of the primary (WD or hot subdwarf)
or to the reflection of hot emission by a cooler companion. We searched 11311
spectroscopically or photometrically selected WD candidates from three hot
star/WD catalogues, using the Lomb-Scargle periodogram to single out promising
sources. We present period estimates for the candidates, 45 of which were not
previously identified as periodic variables, and find that most have a period
shorter than a few days. Additionally, we discuss the eclipsing systems in our
sample and present spectroscopic data on selected sources
A Radio Galaxy at z=5.19
We report the discovery of the most distant known AGN, the radio galaxy TN
J0924-2201 at z = 5.19. The radio source was selected from a new sample of
ultra-steep spectrum (USS) sources, has an extreme radio spectral index
alpha_365MHz^1.4GHz = -1.63, and is identified at near-IR wavelengths with a
very faint, K = 21.3 +- 0.3 object. Spectroscopic observations show a single
emission line at lambda ~ 7530A, which we identify as Ly-alpha. The K-band
image, sampling rest frame U-band, shows a multi-component, radio-aligned
morphology, typical of lower-redshift radio galaxies. TN J0924-2201 extends the
near-IR Hubble, or K-z, relation for powerful radio galaxies to z > 5, and is
consistent with models of massive galaxies forming at even higher redshifts.Comment: 11 Pages, including 3 PostScript figures. Accepted for publication in
the Astrophysical Journal Letter
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