Galaxy And Mass Assembly (GAMA): growing up in a bad neighbourhood - how do low-mass galaxies become passive?

Both theoretical predictions and observations of the very nearby Universe suggest that low-mass galaxies (log$_{10}$[M$_{*}$/M$_{\odot}$]<9.5) are likely to remain star-forming unless they are affected by their local environment. To test this premise, we compare and contrast the local environment of both passive and star-forming galaxies as a function of stellar mass, using the Galaxy and Mass Assembly survey. We find that passive fractions are higher in both interacting pair and group galaxies than the field at all stellar masses, and that this effect is most apparent in the lowest mass galaxies. We also find that essentially all passive log$_{10}$[M$_{*}$/M$_{\odot}$]<8.5 galaxies are found in pair/group environments, suggesting that local interactions with a more massive neighbour cause them to cease forming new stars. We find that the effects of immediate environment (local galaxy-galaxy interactions) in forming passive systems increases with decreasing stellar mass, and highlight that this is potentially due to increasing interaction timescales giving sufficient time for the galaxy to become passive via starvation. We then present a simplistic model to test this premise, and show that given our speculative assumptions, it is consistent with our observed results

Seasonal variations in carbon, nitrogen and phosphorus concentrations and C:N:P stoichiometry in different organs of a Larix principis-rupprechtii Mayr. plantation in the Qinling Mountains, China

Understanding how concentrations of elements and their stoichiometry change with plant growth and age is critical for predicting plant community responses to environmental change. Weusedlong-term field experiments to explore how the leaf, stem and root carbon (C), nitrogen (N) and phosphorous (P) concentrations and their stoichiometry changed with growth and stand age in a L.principis-rupprechtii Mayr. plantation from 2012–2015 in the Qinling Mountains, China. Our results showed that the C, N and P concentrations and stoichiometric ratios in different tissues of larch stands were affected by stand age, organ type andsampling month and displayed multiple correlations with increased stand age in different growing seasons. Generally, leaf C and N concentrations were greatest in the fast-growing season, but leaf P concentrations were greatest in the early growing season. However, no clear seasonal tendencies in the stem and root C, N and P concentrations were observed with growth. In contrast to N and P, few differences were found in organ-specific C concentrations. Leaf N:P was greatest in the fast-growing season, while C:N and C:P were greatest in the late-growing season. No clear variations were observed in stem and root C:N, C:P andN:Pthroughout the entire growing season, but leaf N:P was less than 14, suggesting that the growth of larch stands was limited by N in our study region. Compared to global plant element concentrations and stoichiometry, the leaves of larch stands had higher C, P, C:NandC:PbutlowerNandN:P,andtherootshadgreater PandC:NbutlowerN,C:Pand N:P. Our study provides baseline information for describing the changes in nutritional elements with plant growth, which will facilitates plantation forest management and restoration, and makes avaluable contribution to the global data pool on leaf nutrition and stoichiometry

Galaxy And Mass Assembly (GAMA): galaxy close pairs, mergers and the future fate of stellar mass

We use a highly complete subset of the Galaxy And Mass Assembly II (GAMA-II) redshift sample to fully describe the stellar mass dependence of close pairs and mergers between 10(8) and 10(12)M(circle dot). Using the analytic form of this fit we investigate the total stellar mass accreting on to more massive galaxies across all mass ratios. Depending on how conservatively we select our robust merging systems, the fraction of mass merging on to more massive companions is 2.0-5.6 per cent. Using the GAMA-II data we see no significant evidence for a change in the close pair fraction between redshift z = 0.05 and 0.2. However, we find a systematically higher fraction of galaxies in similar mass close pairs compared to published results over a similar redshift baseline. Using a compendium of data and the function gamma(M) = A(1 + z)(m) to predict the major close pair fraction, we find fitting parameters of A = 0.021 +/- 0.001 and m = 1.53 +/- 0.08, which represents a higher low-redshift normalization and shallower power-law slope than recent literature values. We find that the relative importance of in situ star formation versus galaxy merging is inversely correlated, with star formation dominating the addition of stellar material below M* and merger accretion events dominating beyond M*. We find mergers have a measurable impact on the whole extent of the galaxy stellar mass function (GSMF), manifest as a deepening of the &#39;dip&#39; in the GSMF over the next similar to Gyr and an increase in M* by as much as 0.01-0.05 dex.</p

Galaxy And Mass Assembly (GAMA): galaxy close pairs, mergers and the future fate of stellar mass

We use a highly complete subset of the GAMA-II redshift sample to fully describe the stellar mass dependence of close-pairs and mergers between 108M_ and 1012M_. Using the analytic form of this fit we investigate the total stellar mass accreting onto more massive galaxies across all mass ratios. Depending on how conservatively we select our robust merging systems, the fraction of mass merging onto more massive companions is 2:0%{5:6%. Using the GAMA-II data we see no significant evidence for a change in the close-pair fraction between redshift z = 0:05{0:2. However, we find a systematically higher fraction of galaxies in similar mass close-pairs compared to published results over a similar redshift baseline. Using a compendium of data and the function M = A(1+z)m to predict the major close-pair fraction, we find fitting parameters of A = 0:021 _ 0:001 and m = 1:53 _ 0:08, which represents a higher low-redshift normalisation and shallower power-law slope than recent literature values.We find that the relative importance of in-situ star-formation versus galaxy merging is inversely correlated, with star-formation dominating the addition of stellar material below M_ and merger accretion events dominating beyond M_. We find mergers have a measurable impact on the whole extent of the GSMF, manifest as a deepening of the `dip' in the GSMF over the next _Gyr and an increase in M_ by as much as 0.01{0.05 dex

Galaxy And Mass Assembly (GAMA): galaxy close pairs, mergers and the future fate of stellar mass

We use a highly complete subset of the GAMA-II redshift sample to fully describe the stellar mass dependence of close-pairs and mergers between 108M_ and 1012M_. Using the analytic form of this fit we investigate the total stellar mass accreting onto more massive galaxies across all mass ratios. Depending on how conservatively we select our robust merging systems, the fraction of mass merging onto more massive companions is 2:0%{5:6%. Using the GAMA-II data we see no significant evidence for a change in the close-pair fraction between redshift z = 0:05{0:2. However, we find a systematically higher fraction of galaxies in similar mass close-pairs compared to published results over a similar redshift baseline. Using a compendium of data and the function M = A(1+z)m to predict the major close-pair fraction, we find fitting parameters of A = 0:021 _ 0:001 and m = 1:53 _ 0:08, which represents a higher low-redshift normalisation and shallower power-law slope than recent literature values.We find that the relative importance of in-situ star-formation versus galaxy merging is inversely correlated, with star-formation dominating the addition of stellar material below M_ and merger accretion events dominating beyond M_. We find mergers have a measurable impact on the whole extent of the GSMF, manifest as a deepening of the `dip' in the GSMF over the next _Gyr and an increase in M_ by as much as 0.01{0.05 dex

A nocturnal atmospheric loss of CH2I2 in the remote marine boundary layer.

Ocean emissions of inorganic and organic iodine compounds drive the biogeochemical cycle of iodine and produce reactive ozone-destroying iodine radicals that influence the oxidizing capacity of the atmosphere. Di-iodomethane (CH2I2) and chloro-iodomethane (CH2ICl) are the two most important organic iodine precursors in the marine boundary layer. Ship-borne measurements made during the TORERO (Tropical Ocean tRoposphere Exchange of Reactive halogens and Oxygenated VOC) field campaign in the east tropical Pacific Ocean in January/February 2012 revealed strong diurnal cycles of CH2I2 and CH2ICl in air and of CH2I2 in seawater. Both compounds are known to undergo rapid photolysis during the day, but models assume no night-time atmospheric losses. Surprisingly, the diurnal cycle of CH2I2 was lower in amplitude than that of CH2ICl, despite its faster photolysis rate. We speculate that night-time loss of CH2I2 occurs due to reaction with NO3 radicals. Indirect results from a laboratory study under ambient atmospheric boundary layer conditions indicate a k CH2I2+NO3 of ≤4 × 10-13 cm3 molecule-1 s-1; a previous kinetic study carried out at ≤100 Torr found k CH2I2+NO3 of 4 × 10-13 cm3 molecule-1 s-1. Using the 1-dimensional atmospheric THAMO model driven by sea-air fluxes calculated from the seawater and air measurements (averaging 1.8 +/- 0.8 nmol m-2 d-1 for CH2I2 and 3.7 +/- 0.8 nmol m-2 d-1 for CH2ICl), we show that the model overestimates night-time CH2I2 by >60 % but reaches good agreement with the measurements when the CH2I2 + NO3 reaction is included at 2-4 × 10-13 cm3 molecule-1 s-1. We conclude that the reaction has a significant effect on CH2I2 and helps reconcile observed and modeled concentrations. We recommend further direct measurements of this reaction under atmospheric conditions, including of product branching ratios.LJC acknowledges NERC (NE/J00619X/1) and the National Centre for Atmospheric Science (NCAS) for funding. The laboratory work was supported by the NERC React-SCI (NE/K005448/1) and RONOCO (NE/F005466/1) grants.This is the final version of the article. It was first available from Springer via http://dx.doi.org/10.1007/s10874-015-9320-

Rapidity and Centrality Dependence of Proton and Anti-proton Production from Au+Au Collisions at sqrt(sNN) = 130GeV

We report on the rapidity and centrality dependence of proton and anti-proton transverse mass distributions from Au+Au collisions at sqrt(sNN) = 130GeV as measured by the STAR experiment at RHIC. Our results are from the rapidity and transverse momentum range of |y|<0.5 and 0.35 <p_t<1.00GeV/c. For both protons and anti-protons, transverse mass distributions become more convex from peripheral to central collisions demonstrating characteristics of collective expansion. The measured rapidity distributions and the mean transverse momenta versus rapidity are flat within |y|<0.5. Comparisons of our data with results from model calculations indicate that in order to obtain a consistent picture of the proton(anti-proton) yields and transverse mass distributions the possibility of pre-hadronic collective expansion may have to be taken into account.Comment: 4 pages, 3 figures, 1 table, submitted to PR