The Influence of Environment on the Chemical Evolution in Low-mass Galaxies

The mean alpha-to-iron abundance ratio ([$\alpha$/Fe]) of galaxies is sensitive to the chemical evolution processes at early time, and it is an indicator of star formation timescale ($\tau_{{\rm SF}}$). Although the physical reason remains ambiguous, there is a tight relation between [$\alpha$/Fe] and stellar velocity dispersion ($\sigma$) among massive early-type galaxies (ETGs). However, no work has shown convincing results as to how this relation behaves at low masses. We assemble 15 data sets from the literature and build a large sample that includes 192 nearby low-mass ($18<\sigma<80$~\kms) ETGs. We find that the [$\alpha$/Fe]-$\sigma$ relation generally holds for low-mass ETGs, except in extreme environments. Specifically, in normal galaxy cluster environments, the [$\alpha$/Fe]-$\sigma$ relation and its intrinsic scatter are, within uncertainties, similar for low-mass and high-mass ETGs. However, in the most massive relaxed galaxy cluster in our sample, the zero point of the relation is higher and the intrinsic scatter is significantly larger. By contrast, in galaxy groups the zero point of the relation offsets in the opposite direction, again with substantial intrinsic scatter. The elevated [$\alpha$/Fe] of low-mass ETGs in the densest environments suggests that their star formation was quenched earlier than in high-mass ETGs. For the low-mass ETGs in the lowest density environments, we suggest that their more extended star formation histories suppressed their average [$\alpha$/Fe]. The large scatter in [$\alpha$/Fe] may reflect stochasticity in the chemical evolution of low-mass galaxies.Comment: 7 pages, 3 figures, accepted by ApJ

On the limits of measuring the bulge and disk properties of local and high-redshift massive galaxies

A considerable fraction of the massive quiescent galaxies at \emph{z} $\approx$ 2, which are known to be much more compact than galaxies of comparable mass today, appear to have a disk. How well can we measure the bulge and disk properties of these systems? We simulate two-component model galaxies in order to systematically quantify the effects of non-homology in structures and the methods employed. We employ empirical scaling relations to produce realistic-looking local galaxies with a uniform and wide range of bulge-to-total ratios ($B/T$), and then rescale them to mimic the signal-to-noise ratios and sizes of observed galaxies at \emph{z} $\approx$ 2. This provides the most complete set of simulations to date for which we can examine the robustness of two-component decomposition of compact disk galaxies at different $B/T$. We confirm that the size of these massive, compact galaxies can be measured robustly using a single S\'{e}rsic fit. We can measure $B/T$ accurately without imposing any constraints on the light profile shape of the bulge, but, due to the small angular sizes of bulges at high redshift, their detailed properties can only be recovered for galaxies with $B/T$ \gax\ 0.2. The disk component, by contrast, can be measured with little difficulty

Geotraces and Beyond: Studies of Trace Elements in Coastal and Open Ocean Waters with an Emphasis on the Effects of Oxygen Depletion and Hydrothermal Plumes

We investigated various dissolved trace element (dTE) distributions in two distinct areas: the coastal northern Gulf of Mexico and the eastern tropical Pacific Ocean. A multi-year (2007‒2011) chemical time series of eight stations in the western Mississippi Sound (MS) and northwestern Mississippi Bight (MB) was undertaken to examine the factors affecting chemical distributions in this dynamic region. Key findings include the frequent development of bottom water hypoxia in MB during late spring-summer, the likely contribution of submarine groundwater discharge (SGD) to the material flows, and observation of effects of episodic events including tropical storms and the opening of the Bonnet Carré Spillway. In hypoxic bottom waters, enriched nutrients, Mn, and Ba as well as depleted V and Cr were commonly observed. Contrasting with the northern Gulf section, we also examined dTE distributions in the eastern tropical Pacific Ocean in late 2013. Generally, a conservative dissolved Mo (dMo) distribution and surface dissolved V (dV) depletion were observed in the East Pacific Zonal Transect (EPZT) from Peru to Tahiti. Depleted dMo and dV in the oxygen deficient zone (ODZ) coincided with the nitrite maximum, suggesting association of these elements with the nitrogen cycle. Particulate Mo (pMo) and V (pV) enrichments in the ODZ indicate scavenging by Fe oxyhydroxides and/or biogenic particles. Depleted dMo and dV in hydrothermal plumes suggest a sink for Mo and V. Within the plumes, pV and pMo are adsorbed onto Fe oxyhydroxide and Fe/Mn (oxy)hydroxides, respectively. Low surface water dissolved Ga and Al, as well as high and variable surface Ga/Al ratios along the EPZT reflect low aeolian input and a longer Ga residence time than Al. Intermediate water dissolved Ga (removal) and Al (addition) behaved non-conservatively in the EPZT, having contrasting behaviors that remain to be explained. Generally, elevated Ga and Al concentrations were observed in deep water, indicating inputs from hydrothermal activity and resuspended sediments. Hydrothermal flux estimates for Ga and Al showed that hydrothermal inputs of these elements are likely to be of local, not global importance, with dust input still the likely major influence on the distributions of these elements

Global Water Vapor Estimates from Measurements from Active GPS RO Sensors and Passive Infrared and Microwave Sounders

Water vapor plays an important role in both climate change processes and atmospheric chemistry and photochemistry. Global water vapor vertical profile can be derived from satellite infrared and microwave sounders. However, no single remote sensing technique is capable of completely fulfilling the needs for numerical weather prediction, chemistry, and climate studies in terms of vertical resolution, spatial and temporal coverage, and accuracy. In addition to the passive infrared and microwave sounder observations, the active global positioning system (GPS) radio occultation (RO) technique can also provide all-weather temperature and moisture profiles. In this chapter, we describe the current developments of global water vapor vertical profile and total precipitable water derived from active GPS RO measurements. In addition, we also demonstrate the potential improvement of global water vapor estimates using combined active GPS RO and passive IR/MW particularly from Atmospheric InfraRed Sounder (AIRS) and Advanced Technology Microwave Sounder (ATMS) measurements. Results show that because RO data are very sensitive to water vapor variation in the moisture rich troposphere, the RO data are able to provide extra water vapor information for the combined AIRS/ATMS and RO retrievals in the lower troposphere