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Zhiyuan Li (SAO) Galactic Center Workshop, Shanghai, 2009

Diffuse X-ray Emission: Diagnostics of AGN and Stellar Feedback in Galactic Circumnuclear Environments. Zhiyuan Li (SAO) Galactic Center Workshop, Shanghai, 2009. Q. D. Wang (UMass) , B.P. Wakker (UWisc) W. Forman, C. Jones, R. Kraft (SAO). Outline.

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Zhiyuan Li (SAO) Galactic Center Workshop, Shanghai, 2009

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  1. Diffuse X-ray Emission: Diagnostics of AGN and Stellar Feedback in Galactic Circumnuclear Environments Zhiyuan Li (SAO) Galactic Center Workshop, Shanghai, 2009 Q. D. Wang (UMass) , B.P. Wakker (UWisc) W. Forman, C. Jones, R. Kraft (SAO)

  2. Outline • An observational overview of the circumnuclear environment in M31 (the Andromeda galaxy) • A self-consistent scenario: the role of diffuse hot gas • Diffuse X-ray emission from the circumnuclear region of M81

  3. Why M31? • The nearest circumnuclear environment in an external galaxy similar to our Galaxy • Harbors an inactive SMBH and little (if any) recent star formation -- a quiescent view • Little foreground extinction, moderate inclination • Rich high-sensitivity, high-resolution, multiwavelength data, tracing nearly all stellar and interstellar components Credit: NOAO/NASA X-ray: 0.5-1 1-2 2-8 keV

  4. The nucleus • Double nuclei (P1 and P2; Lauer et al. 1998) – an eccentric disk of 107 M☺ old stars (Tremaine 1995) • A third nucleus (P3) – a 200 Myr-old starburst embedded in P2 (Bender et al. 2005) • A 108 M☺ SMBH (M31*) embedded in P2/P3 – inactive; detections only in radio (Crane et al. 1992) and X-ray (Garcia et al. 2005) Lauer et al. 1998 d=780 kpc; 1”~ 4 pc

  5. The nucleus • LX ≤ 1036 erg/s ~10-10LEdd second faintest SMBH detected in X-ray, after Sgr A* • Flux variation (≤10) seen in both X-ray and radio, but not detected simultaneously • Simultaneous monitoring of radio/X-ray variability; SED • Spatially-resolving the accretion flow (RBondi ~ 3” ) Garcia et al. 2009 greyscale: Chandra/ACIS 0.5-8 keV; contours: HST/ACS F330W Li, Wang & Wakker 2009

  6. The stars • 1010 M☺ old stellar populations in the central 500 pc: stellar mass loss rate of 0.02 M☺/yr • No evidence for recent star formation: non-dection of OB stars; FUV-NUV color; optical emission line ratios • The likely presence of a stellar bar: a potential driver of gas inflow from the outer disk

  7. The ionized gas • the nuclear spiral • -high [N II]/Hα ratio (~2; compared to ~0.5 in HII regions) • -low volume filling factor (<10-4) • probably formed by bar-induced gravitational perturbations • the ionizing source remains uncertain (no young stars!): post-AGB stars, but shocks and/or relativistic particles are likely needed Hα+[N II]; Devereux et al. 1994

  8. Neutral gas and dust • Atomic gas: non-detection; an upper limit of 106 M☺on the HI mass in the central 500 pc (Brinks 1984) • Molecular gas: single detection of CO to date • Dust: spatially follows the nuclear spiral; inferring 2x106 M☺neutral gas • Detection of molecular gas; physical and chemical properties Optical extinction; Melchior et al. 2000

  9. 8 μm 24 μm 70 μm 160 μm

  10. Neutral gas and dust • Atomic gas: non-detection; an upper limit of 106 M☺on the HI mass in the central 500 pc (Brinks 1984) • Molecular gas: single detection of CO to date • Dust: spatially follows the nuclear spiral; inferring 2x106 M☺neutral gas • Detection of molecular gas; physical and chemical properties Optical extinction; Melchior et al. 2000

  11. Cosmic-rays and magnetic field • Radio continuum emission follows the nuclear spiral; most likely non-thermal • The regular magnetic field is oriented along the nuclear spiral; 10-20 µG (Hoernes et al. 1998) • Source of CRs: nucleus? SNe? • Other CR component, e.g., bulge ? 21-cm radio continuum Walterbos & Grave 1985

  12. The hot gas • Hard (2-8 keV) unresolved emission follows the starlight: a stellar origin (CVs and ABs; Sazonov et al. 2006) • Soft (0.5-2 keV) unresolved emission shows an excess in the bulge: diffuse gas • Elongated morphology – a bulge outflow, likely a generic component in intermediate-mass early-type galaxies 0.5-2 keV diffuse X-ray, K-band, 24 μm Li & Wang 2007

  13. The hot gas • Within 200 pc, T ~ 0.3 keV; n ~ 0.1 cm-3; Z ~ Zʘ • LX ~ 7 1037erg/s; SNe Ia heating rate ~ 5 1039erg/s Gas Total CVs • MX ~ 105 Mʘ; stellar mass loss rate: 0.01 Mʘ/yr • Missing stellar feedback! – transported by an outflow of hot gas • Both T and Z appear to be lower than expected from stellar feedback Active binaries Spectrum of the unresolved X-ray emission Li, Wang & Bakker 2009

  14. The circumnuclear environment in M31 • the cold, dusty gas (with an ionized surface) in a nuclear spiral – inflow from outer disk, but only ~ 106 Mʘ in mass • The hot gas corona – forming a bulge outflow • The stellar sea – the dominant heating (SNe Ia) and ionizing (post-AGB stars) source for the ISM • The starving SMBH – heating via CRs?

  15. A self-consistent scenario: evaporation of the nuclear spiral • Explains: • the dearth of cold gas, despite the spiral inflow • a mass-loaded hot gas with low T and diluted Z (~5 times the stellar mass input rate) • the starved nucleus • Tests: • conductive interfaces: high [NII]/Hα ratio, FUV excess, soft X-ray peaks • molecular clumps (~pc size)

  16. * Collected from this workshop

  17. The circumnuclear environment in M81 Kaufman et al. 1996 Li et al. in prep.

  18. Summary and prospects • Our current understanding of the global properties and interaction of different ISM components in the circumnuclear region of M31 • A self-consistent scenario: role of stellar feedback • Multiwavelength studies of galactic circumnuclear environments to understand stellar and AGN feedback in nearby galaxies

  19. Thank you!

  20. The circumnuclear environment of M104

  21. The stars • 1010 Mʘ old stellar populations in the central 500 pc • no evidence of star formation (non-dection of OB stars; FUV-NUV color; optical emission line ratios) • The presence of a stellar bar (Athanassoula & Beaton 2006), a potential driver of gas inflow along the disk GALEXFUV/NUV; Thilker et al. 2005

  22. The ISM in multiwavelength Contours: 0.5-2 keV diffuse X-ray emission Hα contours on NUV-FUV color map

  23. A self-consistent scenario: thermal conduction OVI absorption lines in the FUSE spectrum • Evaporation of the nuclear spiral • - inevitable in the presence of multi-phase gas • - most likely powered by SNe Ia • - can explain • the inactivity of the SMBH • the dearth of cold gas • a mass-loaded hot gas with low T and Z • - conductive interfaces? supporting • evidence: high [N II]/Hα ratio, FUV • excess • - detection of O VI absorption lines • - probing molecular clouds (~pc size)

  24. Galactic circumnuclear environments • Both stars and the ISM are in a dense state • The (common) presence of an SMBH • The interplay among the nuclear, stellar and interstellar components - feeding and feedback of the SMBH - star formation and stellar feedback - phase transition of the ISM: heating, cooling, ionization • The global evolution of the host galaxy

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