Interstellar Grains in Elliptical Galaxies: Grain Evolution

Abstract

We consider the lifecycle of dust introduced into the hot interstellar medium in isolated elliptical galaxies. Dust grains are ejected into galactic-scale cooling flows in large ellipticals by normal mass loss from evolving red giants. Newly introduced dust rapidly enters the hot gas environment and is sputtered away by thermal collisions with ions. Before the grains are completely sputtered away, they emit prodigious amounts of infrared radiation which may contribute to the large far infrared luminosities observed in ellipticals. In order to study the global properties of grains in ellipticals we construct a new series of King-type galactic models which are consistent with the fundamental plane, galactic mass to light ratios and other relevant observational correlations. We describe a new ``continuity'' procedure to construct simple time-dependent gas dynamic models for cooling flows. In all galaxy models, although grains can flow a considerable distance from their radius of origin before being sputtered away, the grain size distribution is accurately determined by assuming {\it in situ} sputtering, completely ignoring advection. The dominant source of grain heating is absorption of starlight; grain heating by collisions with energetic thermal electrons or X-ray absorption are negligible. However, we also show that when self-consistent grain sputtering is included the dust-to-gas ratio is reduced and radiative cooling, not electron-grain interactions dominates plasma cooling, even for the most massive ellipticals.Comment: 30 pages plain TeX, figures available by request to tsai@cita.utoronto.ca, to appear in ApJ

The dust content of galaxies from z = 0 to z = 9

“…We follow the work by Tsai & Mathews (1995), Hirashita et al (2015), and to include the effects of thermal sputtering. The sputtering rate for a grain of radius a in gas with a density ρ and temperature T is…”

Simulating the dust content of galaxies: successes and failures

“…It is expected that other grain destruction mechanisms, like grain-grain collisions and cosmic ray-driven sputtering, are subdominant compared to non-thermal SN shocks and thermal sputtering (Barlow 1978;Draine & Salpeter 1979a,b;Jones et al 1994). We follow thermal sputtering prescriptions as used in previous galaxy modelling (Tsai & Mathews 1995;Hirashita et al 2015) for simplicity of implementation.…”

TheHerschelVirgo Cluster Survey

“…Sadler & Gerhard 1985) and many that have been detected by IRAS at 60 and 100 μm (Knapp et al 1989) and Spitzer at 70 and 160 μm (Kaneda et al 2007) may also host low levels of star formation. Intriguigly, of the 7 ellipticals detected at 70 and 160 μm by Kaneda et al (2007) the only object not showing PAH emission features is actually a radio source, so that the far-infrared emission is probably synchrotron ! Tsai & Mathews (1995) studied dust destruction in ETGs via thermal sputtering in the hot (10 6 −10 7 K), low density (n H ∼ 0.1 cm −3 ) gas, and found that the destruction time-scale is short compared to any cooling flow or dust transport time-scale.…”