Time‐dependent Circulation Flows: Iron Enrichment in Cooling Flows with Heated Return Flows

Abstract

We describe a new type of dynamical model for hot gas in galaxy groups and clusters in which gas moves simultaneously in both radial directions. The observational motivations for this type of flow are compelling. X-ray spectra indicate that little or no gas is cooling to low temperatures. Bubbles of hot gas typically appear in Chandra X-ray images and XMM-Newton X-ray spectra within $50 kpc of the central elliptical galaxy. These bubbles must be buoyant. Furthermore, the elemental composition and total mass of gas-phase iron observed within $100 kpc of the center can be understood as the accumulated outflow of most or all of the iron produced by Type Ia supernovae in the central galaxy over time. This gaseous iron has been circulating for many gigayears, unable to cool. As dense inflowing gas cools, it produces a positive central temperature gradient, a characteristic feature of normal cooling flows. This gas dominates the local X-ray spectrum but shares the total available volume with centrally heated, outflowing gas. Circulating flows eventually cool catastrophically if the outflowing gas transports mass but no heat; to maintain the circulation both mass and energy must be supplied to the inflowing gas over a large volume, extending to the cooling radius. The rapid radial recirculation of gas within $50 kpc results in a flat core in the gas iron abundance, similar to many group and cluster observations. We believe the circulation flows described here are the first gasdynamic, long-term evolutionary models that are in good agreement with all essential features observed in the hot gas: little or no gas cools as required by XMM spectra, the gas temperature increases outward near the center, and the gaseous iron abundance is about solar near the center and decreases outward.

Feedback Heating with Slow Jets in Cooling Flow Clusters

“…Our proposed scenario is also different from the circulation flow proposed by Mathews et al (2004); in their scenario the gas does not cool below X-ray emission temperature. This is a significant difference, as basically they do not consider the presence of a CF at low temperatures (T < 10 4 K), while we do.…”

“…The approach we adopt here differs from those adopted by most authors (e.g., Binney & Tabor 1995;Tucker & David 1997;Ciotti & Ostriker 2001;Binney 2004;Mathews et al 2004; for more references, see Peterson et al 2004), in that we do consider a CF, albeit a moderate one. We conclude that the best agreement with the available data occurs if the jets are not well collimated.…”

SpitzerObservations of Transient, Extended Dust in Two Elliptical Galaxies: New Evidence of Recent Feedback Energy Release in Galactic Cores

“…Based on the collective Balmer line luminosities of normal elliptical galaxies, we conclude that this warm gas can only last for $10 5 yr before it thermally melts into the dominant hot interstellar phase. Finally, the buoyant outflow described here is an essential feature of flows that successfully resolve the cooling flow problem with the outward transport of both mass and energy from the galactic core to large radii, i.e., a circulation flow (Mathews et al 2004). …”

Baryonically Closed Galaxy Groups

“…Nevertheless, substantial ongoing AGN-related heating is currently observed near the center of the NGC 5044 group (Buote et al 2003;Mathews et al 2004). The nongravitational energy received by the hot intracluster gas from supernovae can be estimated from the total mass of iron observed in the NGC 5044 group, …”