[en] Indoor radon exposure is estimated to be one of the leading causes of lung cancer. Radon can enter the home through cracks in the foundation floor and walls, drains, and other openings. Indoor radon concentration depends on the material from which buildings have been constructed. Indoor radon progeny accounts for more than 50% of the total background radiation received by the Indian people. Hence there is a need of continuous monitoring of this source of indoor air pollution. This study is aimed at collecting scattered information about the radon measurements by various workers in India. (author)

[en] The research on perovskite oxide thin films, interfaces, and super-lattices demands the need for the atomically flat surface of the substrate to realize high-quality epitaxial thin films. In this paper, we report the pH-dependent Buffered NH₄F-HF (BHF) etching and concentration-dependent ACID etching of the SrTiO₃ substrate in different orientations [(001), (110), and (111)]. We have optimized the etching time for both kinds of etching processes. A high-quality step–terrace structure without etch pits is obtained for 2% BHF and 100% ACID solution having a pH value of ~ 3.30. For BHF etching, the optimum etching time depends on the substrate orientation [30 s for STO (001), 40 s for STO (110), and 60 s for STO (111)]. On the other hand, for ACID etching, the optimum etching time is more or less constant for all the orientations. This study might be extended to similar oxides substrates, especially on the exciting KTaO₃. (author)

[en] The present study investigated the comprehensive chemical composition [organic carbon (OC), elemental carbon (EC), water-soluble inorganic ionic components (WSICs), and major & trace elements] of particulate matter (PM_2.5) and scrutinized their emission sources for urban region of Delhi. The 135 PM_2.5 samples were collected from January 2013 to December 2014 and analyzed for chemical constituents for source apportionment study. The average concentration of PM_2.5 was recorded as 121.9 ± 93.2 μg m⁻³ (range 25.1–429.8 μg m⁻³), whereas the total concentration of trace elements (Na, Ca, Mg, Al, S, Cl, K, Cr, Si, Ti, As, Br, Pb, Fe, Zn, and Mn) was accounted for ∼17% of PM_2.5. Strong seasonal variation was observed in PM_2.5 mass concentration and its chemical composition with maxima during winter and minima during monsoon seasons. The chemical composition of the PM_2.5 was reconstructed using IMPROVE equation, which was observed to be in good agreement with the gravimetric mass. Source apportionment of PM_2.5 was carried out using the following three different receptor models: principal component analysis with absolute principal component scores (PCA/APCS), which identified five major sources; UNMIX which identified four major sources; and positive matrix factorization (PMF), which explored seven major sources. The applied models were able to identify the major sources contributing to the PM_2.5 and re-confirmed that secondary aerosols (SAs), soil/road dust (SD), vehicular emissions (VEs), biomass burning (BB), fossil fuel combustion (FFC), and industrial emission (IE) were dominant contributors to PM_2.5 in Delhi. The influences of local and regional sources were also explored using 5-day backward air mass trajectory analysis, cluster analysis, and potential source contribution function (PSCF). Cluster and PSCF results indicated that local as well as long-transported PM_2.5 from the north-west India and Pakistan were mostly pertinent.

[en] Recent observations of galaxies in a cluster at z = 0.35 show that their integrated gas-phase metallicities increase with decreasing cluster-centric distance. To test whether ram pressure stripping (RPS) is the underlying cause, we use a semianalytic model to quantify the “observational bias” that RPS introduces into the aperture-based metallicity measurements. We take integral field spectroscopy of local galaxies, remove gas from their outer galactic disks via RPS, and then conduct mock slit observations of cluster galaxies at z = 0.35. Our RPS model predicts a typical cluster-scale metallicity gradient of −0.03 dex/Mpc. By removing gas from the outer galactic disks, RPS introduces a mean metallicity enhancement of $+0.02$ dex at a fixed stellar mass. This gas removal and subsequent quenching of star formation preferentially removes low-mass cluster galaxies from the observed star-forming population. As only the more massive star-forming galaxies survive to reach the cluster core, RPS produces a cluster-scale stellar mass gradient of $-<!--\; ???\; -->0.05\mathrm{l}\mathrm{o}\mathrm{g}(M_{\ast <!--\; ???\; -->}/M_{\odot <!--\; ???\; -->})$/Mpc. This mass segregation drives the predicted cluster-scale metallicity gradient of −0.03 dex/Mpc. However, the effects of RPS alone cannot explain the higher metallicities measured in cluster galaxies at z = 0.35. We hypothesize that additional mechanisms including steep internal metallicity gradients and self-enrichment due to gas strangulation are needed to reproduce our observations at z = 0.35.

[en] Using the TNG100 (100 Mpc)³ simulation of the IllustrisTNG project, we demonstrate a strong connection between the onset of star formation quenching and the stellar size of galaxies. We do so by tracking the evolutionary history of extended and normal-size galaxies selected at z = 2 with $\mathrm{l}\mathrm{o}\mathrm{g}(M_{\ast <!--\; ???\; -->}/M_{\odot <!--\; ???\; -->})$ $=10.2\text{--}11$ and stellar-half-mass-radii above and within 1σ of the stellar size–stellar mass relation, respectively. We match the stellar mass and star formation rate distributions of the two populations. By z = 1, only 36% of the extended massive galaxies have quenched, in contrast to a quenched fraction of 69% for the normal-size massive galaxies. We find that normal-size massive galaxies build up their central stellar mass without a significant increase in their stellar size between $z=2\text{--}4$, whereas the stellar size of the extended massive galaxies almost doubles in the same time. In IllustrisTNG, lower black hole masses and weaker kinetic-mode feedback appears to be responsible for the delayed quenching of star formation in the extended massive galaxies. We show that relatively gas-poor mergers may be responsible for the lower central stellar density and weaker supermassive black hole feedback in the extended massive galaxies.

[en] We use ZFIRE and ZFOURGE observations with the spectral energy distribution fitting tool PROSPECTOR to reconstruct the star formation histories (SFHs) of protocluster and field galaxies at z ∼ 2 and compare our results to the TNG100 run of the IllustrisTNG cosmological simulation suite. In the observations, we find that massive protocluster galaxies ($\mathrm{l}\mathrm{o}\mathrm{g}[M_{\ast <!--\; ???\; -->}/M_{\odot <!--\; ???\; -->}]$ > 10.5) form 45% ± 8% of their total stellar mass in the first 2 Gyr of the universe, compared to 31% ± 2% formed in the field galaxies. In both observations and simulations, massive protocluster galaxies have a flat/declining SFH with decreasing redshift compared to rising SFH in their field counterparts. Using IllustrisTNG, we find that massive galaxies ($\mathrm{l}\mathrm{o}\mathrm{g}[M_{\ast <!--\; ???\; -->}/M_{\odot <!--\; ???\; -->}]⩾<!--\; ???\; -->10.5$) in both environments are on average ≈190 Myr older than low-mass galaxies ($\mathrm{l}\mathrm{o}\mathrm{g}[M_{\ast <!--\; ???\; -->}/M_{\odot <!--\; ???\; -->}]=9\text{--}9.5$). However, the difference in mean stellar ages of cluster and field galaxies is minimal when considering the full range in stellar mass ($\mathrm{l}\mathrm{o}\mathrm{g}[M_{\ast <!--\; ???\; -->}/M_{\odot <!--\; ???\; -->}]⩾<!--\; ???\; -->9$). We explore the role of mergers in driving the SFH in IllustrisTNG and find that massive cluster galaxies consistently experience mergers with low gas fraction compared to other galaxies after 1 Gyr from the big bang. We hypothesize that the low gas fraction in the progenitors of massive cluster galaxies is responsible for the reduced star formation.

[en] To understand how strong emission-line galaxies (SELGs) contribute to the overall growth of galaxies and star formation history of the universe, we target SELGs from the ZFOURGE imaging survey that have blended Hβ+[O iii] rest-frame equivalent widths of >230 Å and 2.5 < $z_{\mathrm{p}\mathrm{h}\mathrm{o}\mathrm{t}}$ < 4.0. Using Keck/MOSFIRE, we measure 49 redshifts for galaxies brighter than K _s = 25 mag as part of our Multi-Object Spectroscopic Emission Line (MOSEL) survey. Our spectroscopic success rate is ∼53% and $z_{\mathrm{p}\mathrm{h}\mathrm{o}\mathrm{t}}$ uncertainty is ${\mathrm{\sigma <!--\; ??\; -->}}_z$ = [Δz/(1+z)] = 0.0135. We confirm 31 ELGs at $3<<!--\; <\; -->z_{\mathrm{s}\mathrm{p}\mathrm{e}\mathrm{c}}<<!--\; <\; -->3.8$, and show that SELGs have spectroscopic rest-frame [O iii]5007 Å equivalent widths of 100–500 Å and tend to be lower-mass systems [$\mathrm{l}\mathrm{o}\mathrm{g}(M_{\star <!--\; ???\; -->}/M_{\odot <!--\; ???\; -->})$ ∼ 8.2–9.6] compared with more typical star-forming galaxies. The SELGs lie ∼0.9 dex above the star-forming main sequence at z ∼ 3.5 and have high inferred gas fractions of $f_{\mathrm{g}\mathrm{a}\mathrm{s}}$ ≳ 60%, i.e., the inferred gas masses can easily fuel a starburst to double stellar masses within ∼10–100 Myr. Combined with recent results using ZFOURGE, our analysis indicates that (1) strong [O iii]5007 Å emission signals an early episode of intense stellar growth in low-mass [$M_{\star <!--\; ???\; -->}<<!--\; <\; -->0.1M^{\star <!--\; ???\; -->}$] galaxies and (2) many, if not most, galaxies at z > 3 go through this starburst phase. If true, low-mass galaxies with strong [O iii]5007 Å emission (EW_rest > 200 Å) may be an increasingly important source of ionizing UV radiation at z > 3.