Confronting Stellar Feedback Simulations with Observations of Hot Gas in Elliptical Galaxies Q. Daniel Wang, Shikui Tang, Yu Lu, Houjun Mo (UMass) Mordecai Mac-Low (AMNH), Ryan Joung (Princeton) NGC 4697: X-ray intensity contours 3-D stellar feedback simulation
Key questions to address Why do elliptical galaxies evolve passively? Understanding of the color bi-modality of galaxy evolution What is the role of stellar feedback? Mass loss from evolved stars: ~ 0.2 M /10 10 L B /yr Energy input from Ia SNe: ~ 0.2 /10 10 L B /100yr + velocity dispersion among stars Fe abundance ~Z * +5(M SN /0.7M sun ) Specific temperature: k T ~ 1-2 kev traced by X-ray
Observations of stellar feedback Both gas temperature and Fe abundance are less than the expected. Bregman et al (2004) Humphrey & Buote (2006) OSullivan & Ponman (2004), Irwin et al (2001), Irwin (2008)
Observations of stellar feedback Observed Lx is <10% of the energy inputs for low and intermediate mass ellipticals Large scattering in L X for galaxies of same stellar mass Mass of diffuse hot gas ~ 10 6 – 10 7 M, can be replenished within 10 8 yrs Hardly any accumulation of hot gas! David et al (2006) AGN SNe
Gone with the wind? The overall dynamics of hot gas may be described by a 1-D wind model (e.g., Ciotti et al. 1991) But it is inconsistent with the observations: Too high Temperature, fixed by the specific energy input Too steep radial X-ray intensity profile Too small Lx (by a factor > 10) with little dispersion Too high Fe abundance X-ray emission is sensitive to the structure in density, temperature, and metal distributions. Can 3-D effects alleviate these inconsistencies?
Galactic wind: 3-D simulations Initialized from a 1-D solution for a 5 x 10 10 M sun spheroid Adaptive mesh refinement ~2 pc spatial resolution Continuous and smooth mass injection, following stellar light Sporadic Sne in both time and space 10x10x10 kpc 3 Box Density snapshot Tang, Wang, et al 2009a Tang & Wang 2009
3-D effects Broad temperature and density distributions Lower metal abundance if modeled with a 1- or 2-T plasma by a factor of 2-3 X-ray measured temperature is a factor of ~2 lower Overall Lx is enhanced by a factor of ~ 3. Differential Emission Measure
Galactic wind model limitations Only reasonable for low-mass galaxies, where wind materials can escape. For more massive galaxies Hot gas may not be able to escape from the dark matter halo IGM accretion needs to be considered Hot gas properties thus depend on the environment and galaxy history.
Feedback and galaxy formation: 1-D simulations Evolution of both dark and baryon matters (with the final total mass of 10 12 M ) Initial spheroid formation (5x10 10 M ) starburst shock-heating and expanding of surrounding gas Later Type Ia SNe wind/outflow, maintaining a low-density, high-T gas halo and preventing a cooling flow The wind can be shocked at a large radius. Tang, Wang, et al 2009b z=1.4 z=0.5 z=0
Dependence of outflow dynamics on the feedback strength, galaxy mass, and environment For an intermediate mass galaxy, the wind may have evolved into a subsonic outflow. This outflow can be stable and long-lasting higher Lx and more extended profile, as indicated by the observations.
Starting from a 1-D outflow simulation 3-D Lx is a factor of ~5 higher Fe ejecta moves much faster than stellar mass-loss materials. Fe abundance map Tang & Wang in prep Subsonic Outflow: 3-D Simulations
3-D Subsonic Outflow Simulations: Results Positive temperature gradient, mimicking a cooling flow! 1-D wind model 1-D outflow model 3-D simulation Positive Fe abundance gradient, as observed in central regions of ellipticals 3-D results
Conclusions Hot gas in (low- and intermediate mass) ellipticals is likely in outflows (mostly subsonic) driven by Ia SNe 1-D supersonic wind model cannot explain observed diffuse X-ray emission 3-D structures significantly affect X-ray measurements (Lx, T, intensity profile, and Fe abundance) Stellar feedback can play a key role in galaxy evolution: Initial burst leads to the heating and expansion of gas beyond the virial radius Ongoing feedback can keep the circum-galactic medium from cooling and maintain a hot halo passive evolution of such galaxies.
Galaxies such as the MW evolves in hot bubbles of baryon deficit! Explains the lack of large-scale X- ray halos. Bulge wind drives away the present stellar feedback. Hot gas Total baryon before the SB Total baryon at present Cosmologi cal baryon fraction
Hot gas in the M31 bulge L (0.5-2 keV) ~ 3 10 38 erg/s ~1% of the SN mechanical energy input! T ~ 0.3 keV ~10 times lower than expected from Type Ia heating and mass-loss from evolved stars! Mental abundance ~ solar inconsistent with the SN enrichment! Li & Wang (2007); Li, Wang, Wakker (2009); Bogdan & Gilfanov 2008 IRAC 8 micro, K-band, 0.5-2 keV