Tidal Dwarf Galaxies at Intermediate Redshifts

We present the first attempt at measuring the production rate of tidal dwarf galaxies (TDGs) and estimating their contribution to the overall dwarf population. Using HST/ACS deep imaging data from GOODS and GEMS surveys in conjunction with photometric redshifts from COMBO-17 survey, we performed a morphological analysis for a sample of merging/interacting galaxies in the Extended Chandra Deep Field South and identified tidal dwarf candidates in the rest-frame optical bands. We estimated a production rate about 1.4 {\times} 10^{-5} per Gyr per comoving volume for long-lived TDGs with stellar mass 3 {\times} 10^{8-9} solar mass at 0.5<z<1.1. Together with galaxy merger rates and TDG survival rate from the literature, our results suggest that only a marginal fraction (less than 10%) of dwarf galaxies in the local universe could be tidally-originated. TDGs in our sample are on average bluer than their host galaxies in the optical. Stellar population modelling of optical to near-infrared spectral energy distributions (SEDs) for two TDGs favors a burst component with age 400/200 Myr and stellar mass 40%/26% of the total, indicating that a young stellar population newly formed in TDGs. This is consistent with the episodic star formation histories found for nearby TDGs.Comment: 9 pages, 5 figures, Accepted for publication in Astrophysics & Space Scienc

CANDELS : constraining the AGN-merger connection with host morphologies at z ~ 2

Using Hubble Space Telescope/WFC3 imaging taken as part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, we examine the role that major galaxy mergers play in triggering active galactic nucleus (AGN) activity at z ~ 2. Our sample consists of 72 moderate-luminosity (L X ~ 1042-44 erg s-1) AGNs at 1.5 < z < 2.5 that are selected using the 4 Ms Chandra observations in the Chandra Deep Field South, the deepest X-ray observations to date. Employing visual classifications, we have analyzed the rest-frame optical morphologies of the AGN host galaxies and compared them to a mass-matched control sample of 216 non-active galaxies at the same redshift. We find that most of the AGNs reside in disk galaxies (51.4+5.8 - 5.9%), while a smaller percentage are found in spheroids (27.8+5.8 - 4.6%). Roughly 16.7+5.3 - 3.5% of the AGN hosts have highly disturbed morphologies and appear to be involved in a major merger or interaction, while most of the hosts (55.6+5.6 - 5.9%) appear relatively relaxed and undisturbed. These fractions are statistically consistent with the fraction of control galaxies that show similar morphological disturbances. These results suggest that the hosts of moderate-luminosity AGNs are no more likely to be involved in an ongoing merger or interaction relative to non-active galaxies of similar mass at z ~ 2. The high disk fraction observed among the AGN hosts also appears to be at odds with predictions that merger-driven accretion should be the dominant AGN fueling mode at z ~ 2, even at moderate X-ray luminosities. Although we cannot rule out that minor mergers are responsible for triggering these systems, the presence of a large population of relatively undisturbed disk-like hosts suggests that the stochastic accretion of gas plays a greater role in fueling AGN activity at z ~ 2 than previously thought

A multi-center individual-randomized controlled trial of screening and brief alcohol intervention to prevent risky drinking in young people aged 14–15 in a high school setting

Background: Young people are a greater risk of problem drinking and are vulnerable to the effects of alcohol consumption, linked to early drinking and also the physiological and social consequences of alcohol use. The SIPS JR-HIGH study is a multicenter Randomized Controlled Trial (RCT) aiming to assess the effectiveness and cost-effectiveness of alcohol screening and brief intervention to reduce risky drinking in those aged 14–15 years in the English high school setting. Materials and methods: Thirty schools in England were recruited into the trial: 4 in London; 6 in the North West, 7 in Kent, and 13 in the North East. A baseline survey was undertaken between December 2015 and June 2016 by young people in school. Young people who screened positive for risky drinking using a single item screen (ASAQ) were allocated with equal probability to either a control arm consisting of usual school-based education on alcohol issues, or to the intervention arm augmenting usual education with a 30 min brief intervention, both delivered by school pastoral staff. At 12-month follow-up the primary outcome of total alcohol consumed is being measured using the Timeline Follow Back (TLFB). Qualitative interviews with young people, parents, and school staff supplement the main trial, by exploring the barriers and facilitators to the effectiveness and implementation of the intervention. Results: In total, 4587 young people were surveyed at baseline, with 586 randomized. So far, thirty-one (n = 109) percent of the target (n = 352) follow-up sample have completed a survey at their 12 month time point, with ongoing follow-ups continuing until June 2017. In total, 27 qualitative interviews with school staff were conducted in 2016, and interviews with young people and parents are currently being conducted. Conclusions: Of 4587 young people surveyed, 1044 young people scored positive for risky drinking, and 586 are taking part in the trial. Qualitative interviews with school staff have indicated that they see the benefit of the intervention to schools, that there is staff support for the intervention, and that is easy to undertake by school staff and to roll-out in schools should it be shown to be effective and cost-effective