1,749 research outputs found
An Extremely Luminous Galaxy at z=5.74
We report the discovery of an extremely luminous galaxy lying at a redshift
of z=5.74, SSA22-HCM1. The object was found in narrowband imaging of the SSA22
field using a 105 Angstrom bandpass filter centered at 8185 Angstroms during
the course of the Hawaii narrowband survey using LRIS on the 10 m Keck II
Telescope, and was identified by the equivalent width of the emission
W_lambda(observed)=175 Angstroms, flux = 1.7 x 10^{-17} erg cm^{-2} s^{-1}).
Comparison with broadband colors shows the presence of an extremely strong
break (> 4.2 at the 2 sigma level) between the Z band above the line, where the
AB magnitude is 25.5, and the R band below, where the object is no longer
visible at a 2 sigma upper limit of 27.1 (AB mags). These properties are only
consistent with this object's being a high-z Ly alpha emitter. A 10,800 s
spectrum obtained with LRIS yields a redshift of 5.74. The object is similar in
its continuum shape, line properties, and observed equivalent width to the
z=5.60 galaxy, HDF 4-473.0, as recently described by Weymann et al. (1998), but
is 2-3 times more luminous in the line and in the red continuum. For H_0 = 65
km s^{-1} Mpc^{-1} and q_0 = (0.02, 0.5) we would require star formation rates
of around (40, 7) solar masses per year to produce the UV continuum in the
absence of extinction.Comment: 5 pages, 4 figures, Latex with emulateapj style file; to appear in
the Astrophysical Journal (Letters
Underpricing, underperformance and overreaction in initial public offerings : evidence from investor attention using online searches
Online activity of Internet users has proven very useful in modeling various phenomena across a wide range of scientific disciplines. In our study, we focus on two stylized facts or puzzles surrounding the initial public offerings (IPOs) - the underpricing and the long-term underperformance. Using the Internet searches on Google, we proxy the investor attention before and during the day of the offering to show that the high attention IPOs have different characteristics than the low attention ones. After controlling for various effects, we show that investor attention still remains a strong component of the high initial returns (the underpricing), primarily for the high sentiment periods. Moreover, we demonstrate that the investor attention partially explains the overoptimistic market reaction and thus also a part of the long-term underperformance
Time evolution of spin state of radical ion pair in microwave field: An analytical solution
The paper reports an exact solution for the problem of spin evolution of
radical ion pair in static magnetic and resonant microwave field taking into
account Zeeman and hyperfine interactions and spin relaxation. The values of
parameters that provide one of the four possible types of solution are
analysed. It is demonstrated that in the absence of spin relaxation, besides
the zero field invariant an invariant at large amplitudes of the resonant
microwave field can be found. The two invariants open the possibility for
simple calculation of microwave pulses to control quantum state of the radical
pair. The effect of relaxation on the invariants is analysed and it is shown
that changes in the high field invariant are induced by phase relaxation.Comment: 18 pages, 7 figure
The Density of Lyman-alpha Emitters at Very High Redshift
We describe narrowband and spectroscopic searches for emission-line star
forming galaxies in the redshift range 3 to 6 with the 10 m Keck II Telescope.
These searches yield a substantial population of objects with only a single
strong (equivalent width >> 100 Angstrom) emission line, lying in the 4000 -
10,000 Angstrom range. Spectra of the objects found in narrowband-selected
samples at lambda ~5390 Angstroms and ~6741 Angstroms show that these very high
equivalent width emission lines are generally redshifted Lyman alpha 1216
Angstrom at z~3.4 and 4.5. The density of these emitters above the 5 sigma
detection limit of 1.5 e-17 ergs/cm^2/s is roughly 15,000 per square degree per
unit redshift interval at both z~3.4 and 4.5. A complementary deeper (1 sigma
\~1.0 e-18 ergs/cm^2/s) slit spectroscopic search covering a wide redshift
range but a more limited spatial area (200 square arcminutes) shows such
objects can be found over the redshift range 3 to 6, with the currently highest
redshift detected being at z=5.64. The Lyman alpha flux distribution can be
used to estimate a minimum star formation rate in the absence of reddening of
roughly 0.01 solar masses/Mpc^3/year (H_0 = 65 km/s/Mpc and q_0 = 0.5).
Corrections for reddening are likely to be no larger than a factor of two,
since observed equivalent widths are close to the maximum values obtainable
from ionization by a massive star population. Within the still significant
uncertainties, the star formation rate from the Lyman alpha-selected sample is
comparable to that of the color-break-selected samples at z~3, but may
represent an increasing fraction of the total rates at higher redshifts. This
higher-z population can be readily studied with large ground-based telescopes.Comment: 7 pages, 5 encapsulated figures; aastex, emulateapj, psfig and lscape
style files. Separate gif files for 2 gray-scale images also available at
http://www.ifa.hawaii.edu/faculty/hu/emitters.html . Added discussion of
foreground contaminants. Updated discussion of comparison with external
surveys (Sec. 5 and Fig. 5). Note: continuum break strength limits (Fig. 3
caption) are correct here -- published ApJL text has a sign erro
Near-Infrared Spectroscopy of 0.4<z<1.0 CFRS Galaxies: Oxygen Abundances, SFRs and Dust
Using new J-band VLT-ISAAC and Keck-NIRSPEC spectroscopy, we have measured
Halpha and [NII] line fluxes for 0.47<z<0.92 CFRS galaxies which have [OII],
Hbeta and [OIII]a line fluxes available from optical spectroscopy, to
investigate how the properties of the star forming gas in galaxies evolve with
redshift. We derive the extinction and oxygen abundances for the sample using a
method based on a set of ionisation parameter and oxygen abundance diagnostics,
simultaneously fitting the [OII], Hbeta,[OIII], Halpha, and [NII] line fluxes.
The individual reddening measurements allow us to accurately correct the
Halpha-based star formation rate (SFR) estimates for extinction. Our most
salient conclusions are: a) in all 30 CFRS galaxies the source of gas
ionisation is not due to AGN activity; b) we find a range of 0<AV<3, suggesting
that it is important to determine the extinction for every single galaxy in
order to reliably measure SFRs and oxygen abundances in high redshift galaxies;
c) high values of [NII]/Halpha >0.1 for most (but not all) of the CFRS galaxies
indicate that they lie on the high-metallicity branch of the R23 calibration;
d) about one third of the 0.47<z<0.92 CFRS galaxies in our sample have lower
metallicities than local galaxies with similar luminosities and star formation
rates; e) comparison with a chemical evolution model indicates that these low
metallicity galaxies are unlikely to be the progenitors of metal-poor dwarf
galaxies at z~0.Comment: Accepted for publication in the Astrophysical Journa
Dependence of Dust Obscuration on Star Formation Rates in Galaxies
Many investigations of star formation rates (SFRs) in galaxies have explored
details of dust obscuration, with a number of recent analyses suggesting that
obscuration appears to increase in systems with high rates of star formation.
To date these analyses have been primarily based on nearby (z < 0.03) or UV
selected samples. Using 1.4 GHz imaging and optical spectroscopic data from the
Phoenix Deep Survey, the SFR-dependent obscuration is explored. The use of a
radio selected sample shows that previous studies exploring SFR-dependent
obscurations have been biased against obscured galaxies. The observed relation
between obscuration and SFR is found to be unsuitable to be used as an
obscuration measure for individual galaxies. Nevertheless, it is shown to be
successful as a first order correction for large samples of galaxies where no
other measure of obscuration is available, out to intermediate redshifts (z ~
0.8).Comment: 9 pages (including 5 encapsulated postscript figures), aastex, uses
emulateapj5.sty. Accepted for publication in Ap
Physical Conditions of Accreting Gas in T Tauri Star Systems
We present results from a low resolution (R~300) near-infrared spectroscopic
variability survey of actively accreting T Tauri stars (TTS) in the
Taurus-Auriga star forming region. Paschen and Brackett series H I
recombination lines were detected in 73 spectra of 15 classical T Tauri
systems. The values of the Pan/PaB, Brn/BrG, and BrG/Pan H I line ratios for
all observations exhibit a scatter of < 20% about the weighted mean, not only
from source to source, but also for epoch-to-epoch variations in the same
source. A representative or `global' value was determined for each ratio in
both the Paschen and Brackett series as well as the BrG/Pan line ratios. A
comparison of observed line ratio values was made to those predicted by the
temperature and electron density dependent models of Case B hydrogen
recombination line theory. The measured line ratios are statistically well-fit
by a tightly constrained range of temperatures (T < 2000 K) and electron
densities 1e9 < n_e < 1e10 cm^-3. A comparison of the observed line ratio
values to the values predicted by the optically thick and thin local
thermodynamic equilibrium cases rules out these conditions for the emitting H I
gas. Therefore, the emission is consistent with having an origin in a non-LTE
recombining gas. While the range of electron densities is consistent with the
gas densities predicted by existing magnetospheric accretion models, the
temperature range constrained by the Case B comparison is considerably lower
than that expected for accreting gas. The cooler gas temperatures will require
a non-thermal excitation process (e.g., coronal/accretion-related X-rays and UV
photons) to power the observed line emission.Comment: 12 pages, emulateapj format, Accepted for publication in Ap
Theoretical He I Emissivities in the Case B Approximation
We calculate the He I case B recombination cascade spectrum using improved
radiative and collisional data. We present new emissivities over a range of
electron temperatures and densities. The differences between our results and
the current standard are large enough to have a significant effect not only on
the interpretation of observed spectra of a wide variety of objects but also on
determinations of the primordial helium abundance.Comment: Accepted to ApJ
Perinatal outcomes after maternal 2009/H1N1 infection: national cohort study
Objectives To follow up a UK national cohort of women admitted to hospital with confirmed 2009/H1N1 influenza in pregnancy in order to obtain a complete picture of pregnancy outcomes and estimate the risks of adverse fetal and infant outcomes
Maternal and perinatal outcomes in women planning vaginal birth after caesarean (VBAC) at home in England: secondary analysis of the Birthplace national prospective cohort study
OBJECTIVE: To compare vaginal birth rates in women planning vaginal birth after caesarean (VBAC) at home versus in an obstetric unit (OU) and explore transfer rates in women planning home VBAC. DESIGN: Prospective cohort study. SETTING: OUs and planned home births in England. POPULATION: 1436 women planning VBAC in the Birthplace cohort, including 209 planning home VBAC. METHODS: We used Poisson regression to calculate relative risks adjusted for maternal characteristics. MAIN OUTCOME MEASURES: MAIN OUTCOMES: (i) vaginal birth and (ii) transfer from planned home birth to OU during labour or immediately after birth. SECONDARY OUTCOMES: (i) composite of maternal blood transfusion or admission to higher level care, (ii) stillbirth or Apgar score <7 at 5Â minutes, (iii) neonatal unit admission. RESULTS: Planned VBAC at home was associated with a statistically significant increase in the chances of having a vaginal birth compared with planned VBAC in an OU (adjusted relative risk 1.15, 95% confidence interval 1.06-1.24). The risk of an adverse maternal outcome was around 2-3% in both settings, with a similar risk of an adverse neonatal outcome. Transfer rates were high (37%) and varied markedly by parity (para 1, 56.7% versus para 2+, 24.6%). CONCLUSION: Women in the cohort who planned VBAC at home had an increased chance of a vaginal birth compared with those planning VBAC in an OU, but transfer rates were high, particularly for women with only one previous birth, and the risk of an adverse maternal or perinatal outcome was around 2-3%. No change in guidance can be recommended. TWEETABLE ABSTRACT: Higher vaginal birth rates in planned VBAC at home versus in OU but 2-3% adverse outcomes and high transfer rate
- âŠ