Items filtered by date: July 2020

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Items filtered by date: July 2020

A new estimator of resolved molecular gas in nearby galaxies

Stars form out of molecular hydrogen in cold, dense regions of the interstellar medium (ISM). Empirically this picture is supported by correlations between tracers of cold gas and the radiation output from young stars such as the Kennicutt-Schmidt (KS) law. One manifestation of the KS law is the correlation between 12 micron luminosity, measured with the Wide-field Infrared Survey Explorer (WISE; Wright et al. 2010), and CO luminosity measured by ground-based radio telescopes. The 12 micron band spans mid-infrared wavelengths of 8 to 16 microns. In nearby galaxies, 12 micron emission traces star-formation rate (SFR), vibrational emission lines from polycyclic aromatic hydrocarbons (PAHs), and warm dust emission. Galaxy-integrated 12 micron luminosity is strongly correlated with CO(1-0) and CO(2-1) luminosity in nearby galaxies (Jiang et al., 2015; Gao et al., 2019). This correlation is useful for predicting molecular gas masses in galaxies since 12 micron images already exist thanks to the WISE survey (which covers the full sky), whereas CO luminosities require dedicated observations.

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Constraining the density and temperature of circumgalactic media with the SZ effect and X-ray data

Galaxies are believed to form and evolve in dark matter halos through the cooling and condensation of hot/warm gas around galaxies, usually termed as Circum-Galactic Medium (CGM). As the repository of baryons, the CGM is important for star formation, gas accretion and the gas-star-gas cycling in/around galaxies. The CGM can be probed by X-ray emission produced by the hot gas in galaxy clusters, which mainly depends on the temperature and density of the gas. The Sunyaev-Zel'dovich effect (SZE) of galaxy clusters on the spectrum of the cosmic microwave background (CMB) provides a complementary way to probe the CGM. The thermal SZE (tSZE) is proportional to the line-of-sight integral of the electron pressure (or thermal energy density), while the kinetic SZE (kSZE) is proportional to the integral of the momentum density along a given line of sight. Measurements of the X-ray emission, tSZE and kSZE have been made for a number of galaxy clusters in the local Universe, and these data should in principle be able to constrain the properties of the IGM. In particular, it is unclear whether the halo gas of clusters is always at the virial temperature and whether the gas can be described simply by a single-phase component or whether it consists of multiple phases.

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