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Stellar Feedback and Hot Gaseous Halos of Galaxies

Stellar Feedback and Hot Gaseous Halos of Galaxies. Q. Daniel Wang University of Massachusetts, Amherst. IRAC 8 micro K-band ACIS diffuse 0.5-2 keV. Galaxy formation and evolution context. Toft et al. (2002). The “overcooling” problem:

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Stellar Feedback and Hot Gaseous Halos of Galaxies

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  1. Stellar Feedback and Hot Gaseous Halos of Galaxies Q. Daniel Wang University of Massachusetts, Amherst IRAC 8 micro K-band ACIS diffuse 0.5-2 keV

  2. Galaxy formation and evolution context Toft et al. (2002) • The “overcooling” problem: • Too much condensation to be consistent with observations (e.g., White & Rees 1978; Navarro & Steinmetz 1997)

  3. The “missing” baryon problem • Stars and the ISM accounts for 1/3-1/2 of the baryon expected from the gravitational mass of a galaxy. • Where is the remaining baryon matter? • In a hot gaseous galactic halo? • Or having been pushed away? • Both are related to the galactic energy feedback!

  4. Origins of the galactic feedback • AGNs (jets) • Nuclear starbursts: • Radiation pressure • Superwinds • Gradual energy inputs • Galactic disks: massive star formation • Galactic bulges: Type Ia SNe.

  5. X-ray absorption line spectroscopy:adding depth into the map 4U1957+11 X-ray binary AGN Wang et al. 05, Yao & Wang 05/06, Yao et al. 06/07 ROSAT all-sky survey in the ¾-keV band X-ray binary

  6. Galactic global hot gas properties • Structure: • A thick Galactic disk with a scale height 1-2 kpc/f, ~ the values of OVI absorbers and free electrons • Enhanced hot gas around the Galactic bulge • Thermal property: • mean T ~ 106.3 K toward the inner region • ~ 106.1 K at solar neighborhood • Velocity dispersion from ~200 km/s to 80 km/s • Abundance ratios consistent with solar • But a large-scale hot gaseous halo is required to explain HVCs! • Confinement • Head-tail morphology • OVI absorption

  7. Hot gas in the M31 bulge • L(0.5-2 keV) ~ 31038 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! IRAC 8 micro, K-band, 0.5-2 keV Li & Wang (2007); Bogdan & Gilfanov 2008

  8. Mass-loading from the nuclear spiral? • Correlation of diffuse X-ray with the H emission  evaporation via thermal conduction? • SMBH is not active • No SF in the bulge Li & Wang (2008) H image with 0.5-2 keV contours

  9. Feedback from disk-wide star formation NGC 5775 • Scale height ~ 2 kpc + more distant blubs. • T1 ~ 106.3 K, T2> 107.1 K • Lx(diffuse) ~ 4x1039 erg/s Red – H Green – R-band Blue – 0.3-1.5 keV Li et al. (2008)

  10. NW SE NGC 2841 (Sb) • D=15 Mpc • Vc = 317 km/s • Lx ~ 7 x 1039 ergs/s Red: optical Blue: 0.3-1.5 keV diffuse emission Wang et al 2008

  11. NGC 4594 (Sa) • Average T ~ 6 x 106 K • Lx ~ 4 x 1039 erg/s, ~ 2% of Type Ia SN energy • Not much cool gas to hide/convert the SN energy • Mass and metals are also missing! • Mass input rate of evolved stars ~ 1.3 Msun/yr • Each Type Ia SN  0.7 Msun Fe Li et al. 2007

  12. Observations vs. simulations • X-ray-emitting gas in normal massive disk galaxies: • Disk – driven by massive star formation • Bulge – heated primarily by Type-Ia SNe • Extent ~ a few kpc • temperature ~ 0.3 keV • A possible very hot component (T > 107 K) is poorly constrained • Little evidence for X-ray emission or absorption from IGM accretion. • No “overcooling” problem • Instead, we have a missing feedback problem! Galaxy Vc NGC 4565 250 NGC 2613 304 NGC 5746 307 NGC 2841 317 NGC 4594 370 Simulations by Toft et al. (2003)

  13. Problems with the existing models • Model for stellar feedback • Typically with no consideration of the evolving galactic environment • Fixed outer boundary  unstable subsonic solution • No additional mass-loading • Such a superwind model fails: too low Lx, too high T, and too steep surface brightness profile. • Model for galaxy evolution via IGM accretion • Typically with no stellar feedback • If implemented, receipts are used, typically with an injection of energy or momentum or in form of an assumed preheating. • Predicted massive cooling hot gaseous halos are not observed. • But a large-scale, low-density hot gaseous halo is required to explain HVCs around the MW.

  14. 1- and 2-D simulations of galaxy evolution with the stellar feedback • Both dark and baryon matters trace each other initially and evolve with to a final mass of 1012 Msun (see also Birnboim & Dekel 03) • A blastwave is initiated by the SB (+AGN) and maintained by the Type Ia SN feedback + stellar winds from evolved stars. • IGM is heated beyond the virial radius, and accretion can be stopped. Density evolution; size of box = 1.5 Mpc See the poster by Tang & Wang Tang et al., Tang & Wang 2008

  15. Stellar feedback with mass-loading • With mass-loading, the wind can evolve into a subsonic outflow. • This outflow can be stable and long-lasting  higher Lx, lower T, and more extended. • Consistent with observations of galactic bulges and Lx/Lb ellipticals! • For massive ellipticals, the outflow can be completely stopped. z=1.4 z=0.5 z=0

  16. Total baryon before the SB Cosmological baryon fraction Total baryon at present Hot gas Galaxies such as the MW evolve in hot bubbles of baryon deficit! • Explains the lack of large-scale X-ray halos. • Bulge outflow drives away the present stellar feedback. • Allows later starbursts to develop high-velocity superwinds.

  17. 3-D simulations of a galactic bulge wind • Adaptive mesh refinement, down to 6 pc • Stellar mass injection and sporadic SNe, following the stellar light. 10x10x10 kpc3 box density distribution Tang et al. (2008)

  18. Sedov solution does apply for individual SNRs • Emission primarily from shells and filaments. • Fe-rich ejecta dominate the high-T emission and are not well-mixed with the ambient medium • Consistent with the low metallicity inferred from X-ray spectral observations

  19. 1-D Low Res. Log(T(K)) 3-D Effects • Large dispersion  • enhanced emission at both low and high temperatures • Overall luminosity increase by a factor of ~ 3. • Low metallicity if modeled with a 1-T plasma. • Consistent with the 1-D radial density and temperature distributions, except for the center region. 1-D

  20. Conclusions • Diffuse hot gas is strongly concentrated toward galactic disks/bulges (< 20 kpc) due to the feedback. • But the bulk of the feedback is not detected and is probably propagated into very hot (~107 K) halos. • The feedback from a galactic bulge likely plays a key role in galaxy evolution: • Initial burst led to the heating and expansion of gas beyond the virial radius • Ongoing feedback keeps the gas from forming a cooling flow and starves SMBHs • Mass-loaded outflows account for diffuse X-ray emission from galactic bulges. • Condensation of the initial starburst material may account for some HVCs. • Galaxies like ours reside in hot bubbles! • No overcooling or missing energy problem!

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