Does galaxy evolution proceed through the green valley via multiple pathways or as a single population? Motivated by recent results highlighting radically different evolutionary pathways between ...early- and late-type galaxies, we present results from a simple Bayesian approach to this problem wherein we model the star formation history (SFH) of a galaxy with two parameters, t, τ and compare the predicted and observed optical and near-ultraviolet colours. We use a novel method to investigate the morphological differences between the most probable SFHs for both disc-like and smooth-like populations of galaxies, by using a sample of 126 316 galaxies (0.01 < z < 0.25) with probabilistic estimates of morphology from Galaxy Zoo. We find a clear difference between the quenching time-scales preferred by smooth- and disc-like galaxies, with three possible routes through the green valley dominated by smooth- (rapid time-scales, attributed to major mergers), intermediate- (intermediate time-scales, attributed to minor mergers and galaxy interactions) and disc-like (slow time-scales, attributed to secular evolution) galaxies. We hypothesize that morphological changes occur in systems which have undergone quenching with an exponential time-scale τ < 1.5 Gyr, in order for the evolution of galaxies in the green valley to match the ratio of smooth to disc galaxies observed in the red sequence. These rapid time-scales are instrumental in the formation of the red sequence at earlier times; however, we find that galaxies currently passing through the green valley typically do so at intermediate time-scales.
†
We report the detection of very high energy -ray emission from the intermediate-frequency-peaked BL Lacertae object W Comae by VERITAS. The source was observed between 2008 January and April. A ...strong outburst of -ray emission was measured in the middle of March, lasting for only 4 days. The energy spectrum measured during the two highest flare nights is fit by a power law and is found to be very steep, with a differential photon spectral index of image. The integral photon flux above image during those two nights corresponds to roughly image of the flux from the Crab Nebula. Quasi-simultaneous Swift observations at X-ray energies were triggered by the VERITAS observations. The spectral energy distribution of the flare data can be described by synchrotron self-Compton (SSC) or external Compton (EC) leptonic jet models.
Like other cultures, measures to accurately and sensitively assess and treat disruptive behaviors in Taiwanese children are necessary. This research provides normative and psychometric data (i.e., ...item-total correlations, split-half coefficients, internal consistency, and internal validity) on the Eyberg Child Behavior Inventory (ECBI), including clinical cut-off scores, with a Taiwanese community sample. The results suggest that the ECBI may be helpful in screening for disruptive behaviors in Taiwanese children, which may allow for appropriate prevention and intervention efforts. Although results are comparable to other research, cultural differences do exist, thereby highlighting the importance of cultural considerations in assessing child behavior, irrespective of country of treatment.
Galaxy Zoo Supernovae Smith, A. M.; Lynn, S.; Sullivan, M. ...
Monthly notices of the Royal Astronomical Society,
April 2011, Letnik:
412, Številka:
2
Journal Article
Recenzirano
Odprti dostop
This paper presents the first results from a new citizen science project: Galaxy Zoo Supernovae. This proof-of-concept project uses members of the public to identify supernova candidates from the ...latest generation of wide-field imaging transient surveys. We describe the Galaxy Zoo Supernovae operations and scoring model, and demonstrate the effectiveness of this novel method using imaging data and transients from the Palomar Transient Factory (PTF). We examine the results collected over the period 2010 April-July, during which nearly 14 000 supernova candidates from the PTF were classified by more than 2500 individuals within a few hours of data collection. We compare the transients selected by the citizen scientists to those identified by experienced PTF scanners and find the agreement to be remarkable - Galaxy Zoo Supernovae performs comparably to the PTF scanners and identified as transients 93 per cent of the ∼130 spectroscopically confirmed supernovae (SNe) that the PTF located during the trial period (with no false positive identifications). Further analysis shows that only a small fraction of the lowest signal-to-noise ratio detections (r > 19.5) are given low scores: Galaxy Zoo Supernovae correctly identifies all SNe with ≥8σ detections in the PTF imaging data. The Galaxy Zoo Supernovae project has direct applicability to future transient searches, such as the Large Synoptic Survey Telescope, by both rapidly identifying candidate transient events and via the training and improvement of existing machine classifier algorithms.
Multiwavelength observations of the high-frequency-peaked blazar 1ES 2344+514 were performed from 2007 October to 2008 January. The campaign represents the first contemporaneous data on the object at ...very high energy (VHE, E >100 GeV) Delta *g-ray, X-ray, and UV energies. Observations with VERITAS in VHE Delta *g-rays yield a strong detection of 20 Delta *s with 633 excess events in a total exposure of 18.1 hr live time. A strong VHE Delta *g-ray flare on 2007 December 7 is measured at F(>300 GeV) = (6.76 ? 0.62) X 10--11 photons cm--2 s--1, corresponding to 48% of the Crab Nebula flux. Excluding this flaring episode, nightly variability at lower fluxes is observed with a time-averaged mean of F(>300 GeV) = (1.06 ? 0.09) X 10--11 photons cm--2 s--1 (7.6% of the Crab Nebula flux). The differential photon spectrum between 390 GeV and 8.3 TeV for the time-averaged observations excluding 2007 December 7 is well described by a power law with a photon index of Delta *G = 2.78 ? 0.09stat ? 0.15syst. On the flaring night of 2007 December 7 the measured VHE Delta *g-ray photon index was Delta *G = 2.43 ? 0.22stat ? 0.15syst. Over the full period of VERITAS observations contemporaneous X-ray and UV data were taken with Swift and RXTE. The measured 2-10 keV flux ranged by a factor of ~7 during the campaign. On 2007 December 8 the highest ever observed X-ray flux from 1ES 2344+514 was measured by Swift X-ray Telescope at a flux of F(2-10 keV) = (6.28 ? 0.31) X 10--11 erg cm--2 s--1. Evidence for a correlation between the X-ray flux and VHE Delta *g-ray flux on nightly timescales is indicated with a Pearson correlation coefficient of r = 0.60 ? 0.11. Contemporaneous spectral energy distributions (SEDs) of 1ES 2344+514 are presented for two distinct flux states. A one-zone synchrotron self-Compton (SSC) model describes both SEDs using parameters consistent with previous SSC modeling of 1ES 2344+514 from non-contemporaneous observations.
Symptoms of posttraumatic stress disorder (PTSD) have been extensively studied in victim populations (e.g., survivors of sexual assault), but not nearly as thoroughly in the responders who come to ...the aid of those victims, particularly firefighters. The prevalence rates for PTSD (as defined by previous authors) in firefighters vary widely, from 6.5% to 37%, using various cutoff scores on a variety of measures (primarily self-report) with rather dissimilar samples and events. This study utilized the Posttraumatic Stress Disorder Checklist (PCL), a measure consistent with current DSM-IV criteria, to evaluate the prevalence of PTSD symptoms in 131 firefighters from two US states. Using a standard cutoff score on the PCL, a prevalence rate of 8% was found. When measures of fear, helplessness, or horror (DSM-IV Criterion A2) and functional impairment (Criterion F) were included, a lower prevalence rate of 5% was obtained, a rate lower than typically is found in previously published reports. Previous psychological treatment, age at which the firefighters started working, Miscellaneous Calls, and the response of horror following the firefighter's Single Worst Event predicted PTSD symptoms. The present findings highlight the importance of using a symptom measure consistent with the full DSM-IV criteria to more fully assess firefighters' responses of fear, helplessness, and horror.
Characterizing chemical changes within individual cells is important for determining fundamental mechanisms of biological processes that will lead to new biological insights and improved disease ...understanding. Analyzing biological systems with imaging and profiling mass spectrometry (MS) has gained popularity in recent years as a method for creating chemical maps of biological samples. To obtain mass spectra that provide relevant molecular information about individual cells, samples must be prepared so that salts and other cell culture components are removed from the cell surface and that the cell contents are rendered accessible to the desorption beam. We have designed a cellular preparation protocol for imaging/profiling MS that removes the majority of the interfering species derived from the cellular growth medium, preserves the basic morphology of the cells, and allows chemical profiling of the diffusible elements of the cytosol. Using this method, we are able to reproducibly analyze cells from three diverse cell types: MCF7 human breast cancer cells, Madin-Darby canine kidney (MDCK) cells, and NIH/3T3 mouse fibroblasts. This preparation technique makes possible routine imaging/profiling MS analysis of individual cultured cells, allowing for understanding of molecular processes within individual cells.
The VERITAS collaboration reports the detection of very-high-energy gamma-ray emission from the high-frequency-peaked BL Lac object 1ES 1218+304 located at a redshift of z = 0.182. A gamma-ray signal ...was detected with a statistical significance of 10.4 standard deviations (10.4s) for the observations taken during the first three months of 2007, confirming the discovery of this object made by the MAGIC collaboration. The photon spectrum between ~160 GeV and ~1.8 TeV is well described by a power law with an index of = 3.08 ± 0.34stat ± 0.2sys. The integral flux is (E>200GeV) = (12.2 ± 2.6) X 10-12 cm-2 s-1, which corresponds to ~6% of that of the Crab Nebula. The light curve does not show any evidence for very high energy flux variability. Using lower limits on the density of the extragalactic background light in the near to mid-infrared, we are able to limit the range of intrinsic energy spectra for 1ES 1218+304. We show that the intrinsic photon spectrum has an index that is harder than = 2.32 ± 0.37stat. When including constraints from the spectra of 1ES 1101-232 and 1ES 0229+200, the spectrum of 1ES 1218+304 is likely to be harder than = 1.86 ± 0.37stat.
Since 2005 September, the Whipple 10 m Gamma-ray Telescope has been operated primarily as a blazar monitor. The five northern hemisphere blazars that have already been detected at the Whipple ...Observatory, Markarian 421 (Mrk 421), H1426+428, Mrk 501, 1ES 1959+650, and 1ES 2344+514, are monitored routinely each night that they are visible. We report on the Mrk 421 observations taken from 2005 November to 2006 June in the gamma-ray, X-ray, optical, and radio bands. During this time, Mrk 421 was found to be variable at all wavelengths probed. Both the variability and the correlations among different energy regimes are studied in detail here. A tentative correlation, with large spread, was measured between the X-ray and gamma-ray bands, while no clear correlation was evident among the other energy bands. In addition to this, the well-sampled spectral energy distribution of Mrk 421 (1101+384) is presented for three different activity levels. The observations of the other blazar targets will be reported separately.
PDF
