X-Ray Scaling Relations of Galaxy Groups in a Hydrodynamic Cosmological Simulation

We examine the scalings of X-ray luminosity, temperature, and dark matter or galaxy velocity dispersion for galaxy groups in an LCDM cosmological simulation, which incorporates gravity, gas dynamics, radiative cooling, and star formation, but no substantial non-gravitational heating. In agreement with observations, the simulated L_X-sigma and L_X-T_X relations are steeper than those predicted by adiabatic simulations or self-similar models, with L_X\propto sigma^{4.4} and L_X\propto T_X^{2.6} for massive groups and significantly steeper relations below a break at sigma~180 km/s (T_X~0.7 keV), but T_X-sigma is fairly close to self-similar, with T_X\propto sigma^{1.75}. The entropy of hot gas in low mass groups is higher than predicted by self-similar scaling, and agrees with observations that suggest an "entropy floor". The steeper scalings of the luminosity relations are driven by radiative cooling, which reduces the hot gas fraction from 50% of the total baryons at sigma \approx 500 km/s to 20% at sigma \approx 100 km/s. A secondary effect is that hot gas in smaller systems is less clumpy, further driving down L_X. A smaller volume simulation with eight times higher mass resolution predicts nearly identical X-ray luminosities at a given group mass, demonstrating the insensitivity of the predicted scaling relations to numerical resolution. There remain some quantitative discrepancies: the predicted mass scale of the L_X-T_X and L_X-sigma breaks is somewhat too low, and the luminosity-weighted temperatures are too high at a given sigma. We conclude that radiative cooling has an important quantitative impact on group X-ray properties and can account for many of the observed trends that have been interpreted as evidence for non-gravitational heating. (abridged)Comment: 29 pages, ApJ submitte

The phase-diagram of the IGM and the entropy floor of groups and clusters: are clusters born warm?

We point out that two problems of observational cosmology, the facts i) that > 60% of the baryonic content of the universe is not observed at z=0 and ii) that the properties of small clusters do not agree with simple expectations, could be closely related. As shown by recent studies, the shock-heating associated with the formation of large-scale structures heats the intergalactic medium (IGM) and leads to a ``warm IGM'' component for the gas. In the same spirit, we suggest the intracluster medium (ICM) to be a mixture of galaxy-recycled, metal enriched gas and intergalactic gas, shock-heated by the collapsing much larger scales. This could be obtained through two processes: 1) the late infalling gas from the external warm IGM is efficiently mixed within the halo and brings some additional entropy, or 2) the shocks generated by larger non-linear scales are also present within clusters and can heat the ICM. We show that if assumption (1) holds, the entropy brought by the warm IGM is sufficient to explain the observed properties of clusters, in particular the entropy floor and the LX-T relation. On the other hand, we briefly note that the scenario (2) would require a stronger shock-heating because of the larger density of the ICM as compared with filaments. Our scenario of clusters being "born warm" can be checked through the predicted redshift evolution of the entropy floor.Comment: 8 pages, final version published in MNRA

Humanistic counselling plus pastoral care as usual versus pastoral care as usual for the treatment of psychological distress in adolescents in UK state schools (ETHOS):a randomised controlled trial

Background About one in seven adolescents have a mental health disorder in England, UK. School counselling is one of the most common means of trying to address such a problem. We aimed to determine the effectiveness and cost-effectiveness of school-based humanistic counselling (SBHC) for the treatment of psychological distress in young people in England, UK. Methods We did a two-arm, individually randomised trial in 18 secondary state-funded schools across the Greater London area of the UK. Participants were randomly assigned (1:1) using a centrally secure randomisation procedure with random permuted blocks to either SBHC plus schools' pastoral care as usual (PCAU), or PCAU alone. Participants were pupils aged 13–16 years who had moderate-to-severe levels of emotional symptoms (measured by a score of ≥5 on the Strengths and Difficulties Questionnaire Emotional Symptoms scale) and were assessed as competent to consent to participate in the trial. Participants, providers, and assessors (who initially assessed and enrolled participants) were not masked but testers (who measured outcomes) were masked to treatment allocation. The primary outcome was psychological distress at 12 weeks (Young Person's Clinical Outcomes in Routine Evaluation measure [YP-CORE]; range 0–40), analysed on an intention-to-treat basis (with missing data imputed). Costs were assessed at 24 weeks (Client Service Receipt Inventory and service logs). The trial was registered with ISRCTN, number ISRCTN10460622. Findings 329 participants were recruited between Sept 29, 2016, and Feb 8, 2018, with 167 (51%) randomly assigned to SBHC plus PCAU and 162 (49%) to PCAU. 315 (96%) of 329 participants provided data at 12 weeks and scores were imputed for 14 participants (4%). At baseline, the mean YP-CORE scores were 20·86 (SD 6·38) for the SBHC plus PCAU group and 20·98 (6·41) for the PCAU group. Mean YP-CORE scores at 12 weeks were 16·41 (SD 7·59) for the SBHC plus PCAU group and 18·34 (7·84) for the PCAU group (difference 1·87, 95% CI 0·37–3·36; p=0·015), with a small effect size (0·25, 0·03–0·47). Overall costs at 24 weeks were £995·20 (SD 769·86) per pupil for the SBHC plus PCAU group and £612·89 (1224·56) for the PCAU group (unadjusted difference £382·31, 95% CI £148·18–616·44; p=0·0015). The probability of SBHC being more cost-effective reached 80% at a willingness to pay of £390 for a 1-point improvement on the YP-CORE. Five serious adverse events occurred for four participants in the SBHC plus PCAU group, all involving suicidal intent. Two serious adverse events occurred for two participants in the PCAU group, one involving suicidal intent. Interpretation The addition of SBHC to PCAU leads to small reductions in psychological distress, but at an additional economic cost. SBHC is a viable treatment option but there is a need for equally rigorous evaluation of alternative interventions. Funding This work was supported by the Economic and Social Research Council (grant reference ES/M011933/1)

The Allen Telescope Array Pi GHz Sky Survey I. Survey Description and Static Catalog Results for the Bootes Field

The Pi GHz Sky Survey (PiGSS) is a key project of the Allen Telescope Array. PiGSS is a 3.1 GHz survey of radio continuum emission in the extragalactic sky with an emphasis on synoptic observations that measure the static and time-variable properties of the sky. During the 2.5-year campaign, PiGSS will twice observe ~250,000 radio sources in the 10,000 deg^2 region of the sky with b > 30 deg to an rms sensitivity of ~1 mJy. Additionally, sub-regions of the sky will be observed multiple times to characterize variability on time scales of days to years. We present here observations of a 10 deg^2 region in the Bootes constellation overlapping the NOAO Deep Wide Field Survey field. The PiGSS image was constructed from 75 daily observations distributed over a 4-month period and has an rms flux density between 200 and 250 microJy. This represents a deeper image by a factor of 4 to 8 than we will achieve over the entire 10,000 deg^2. We provide flux densities, source sizes, and spectral indices for the 425 sources detected in the image. We identify ~100$ new flat spectrum radio sources; we project that when completed PiGSS will identify 10^4 flat spectrum sources. We identify one source that is a possible transient radio source. This survey provides new limits on faint radio transients and variables with characteristic durations of months.Comment: Accepted for publication in ApJ; revision submitted with extraneous figure remove

The Allen Telescope Array Twenty-centimeter Survey - A 690-Square-Degree, 12-Epoch Radio Dataset - I: Catalog and Long-Duration Transient Statistics

We present the Allen Telescope Array Twenty-centimeter Survey (ATATS), a multi-epoch (12 visits), 690 square degree radio image and catalog at 1.4GHz. The survey is designed to detect rare, very bright transients as well as to verify the capabilities of the ATA to form large mosaics. The combined image using data from all 12 ATATS epochs has RMS noise sigma = 3.94mJy / beam and dynamic range 180, with a circular beam of 150 arcsec FWHM. It contains 4408 sources to a limiting sensitivity of S = 20 mJy / beam. We compare the catalog generated from this 12-epoch combined image to the NRAO VLA Sky Survey (NVSS), a legacy survey at the same frequency, and find that we can measure source positions to better than ~20 arcsec. For sources above the ATATS completeness limit, the median flux density is 97% of the median value for matched NVSS sources, indicative of an accurate overall flux calibration. We examine the effects of source confusion due to the effects of differing resolution between ATATS and NVSS on our ability to compare flux densities. We detect no transients at flux densities greater than 40 mJy in comparison with NVSS, and place a 2-sigma upper limit on the transient rate for such sources of 0.004 per square degree. These results suggest that the > 1 Jy transients reported by Matsumura et al. (2009) may not be true transients, but rather variable sources at their flux density threshold.Comment: 41 pages, 19 figures, ApJ accepted; corrected minor typo in Table

The Allen Telescope Array: The First Widefield, Panchromatic, Snapshot Radio Camera for Radio Astronomy and SETI

The first 42 elements of the Allen Telescope Array (ATA-42) are beginning to deliver data at the Hat Creek Radio Observatory in Northern California. Scientists and engineers are actively exploiting all of the flexibility designed into this innovative instrument for simultaneously conducting surveys of the astrophysical sky and conducting searches for distant technological civilizations. This paper summarizes the design elements of the ATA, the cost savings made possible by the use of COTS components, and the cost/performance trades that eventually enabled this first snapshot radio camera. The fundamental scientific program of this new telescope is varied and exciting; some of the first astronomical results will be discussed.Comment: Special Issue of Proceedings of the IEEE: "Advances in Radio Telescopes", Baars,J. Thompson,R., D'Addario, L., eds, 2009, in pres