7 research outputs found
The column densities of molecular gas across cosmic time: bridging observations and simulations
International audienceObservations of the cosmic evolution of different gas phases across time indicate a marked increase in the molecular gas mass density towards z ~ 2-3. Such a transformation implies an accompanied change in the global distribution of molecular hydrogen column densities (). Using observations by PHANGS-ALMA/SDSS and simulations by GRIFFIN/IllustrisTNG we explore the evolution of this H2 column density distribution function []. The H2 (and H I) column density maps for TNG50 and TNG100 are derived in post-processing and are made available through the IllustrisTNG online API. The shape and normalization of of individual main-sequence star-forming galaxies are correlated with the star formation rate (SFR), stellar mass (M*), and H2 mass () in both observations and simulations. TNG100, combined with H2 post-processing models, broadly reproduces observations, albeit with differences in slope and normalization. Also, an analytically modelled f(N), based on exponential gas discs, matches well with the simulations. The GRIFFIN simulation gives first indications that the slope of might not majorly differ when including non-equilibrium chemistry in simulations. The by TNG100 implies that higher molecular gas column densities are reached at z = 3 than at z = 0. Further, denser regions contribute more to the molecular mass density at z = 3. Finally, H2 starts dominating compared to H I only at column densities above log( at both redshifts. These results imply that neutral atomic gas is an important contributor to the overall cold gas mass found in the ISM of galaxies including at densities typical for molecular clouds at z = 0 and 3
Preventing Plasmon Coupling between Gold Nanorods Improves the Sensitivity of Photoacoustic Detection of Labeled Stem Cells <i>in Vivo</i>
Gold
nanorods are excellent contrast agents for imaging technologies which
rely on near-infrared absorption such as photoacoustic imaging. For
cell tracking applications, the cells of interest are labeled with
the contrast agent prior to injection. However, after uptake into
cells by endocytosis, the confinement and high concentration in endosomes
leads to plasmon band broadening and reduced absorbance. This would
limit the potential of multispectral optoacoustic tomography in terms
of spectral processing and, consequently, sensitivity. Here, we show
that steric hindrance provided by silica coating of the nanorods leads
to the preservation of their spectral properties and improved photoacoustic
sensitivity. This strategy allowed the detection and monitoring of
as few as 2 Ă 10<sup>4</sup> mesenchymal stem cells in mice over
a period of 15 days with a high spatial resolution. Importantly, the
silica-coated nanorods did not affect the viability or differentiation
potential of the transplanted mesenchymal stem cells