1. The AMUSE surveys: Down-sizing in black hole accretion
Elena Gallo | University of Michigan
B. Miller & K. Gultekin (U. of Michigan), T. Treu & R. Antonucci (UCSB), J.-H. Woo (Seoul U.)
12 Years of Science with Chandra, 218th AAS

2. Black holes and bulge relations
Empirical correlation between super-massive black hole mass and bulge properties (central stellar velocity dispersion, luminosity, Sersic index, etc) suggest deep evolutionary link
However, poorly constrained at the low mass end
Gultekin+09

3. Evolution of quasar LF Quasar density peaked near redshift z~2
Lower-luminosity quasars peak at lower redshifts (“downsizing”)
Quasars accrete/radiate at Eddington, but only for relatively short lifetimes (~108 yr)
Ciotti & Ostriker 07

4. Low-level SMBH activity
Post-quasar phase: highly sub-Eddington, radiatively inefficient accretion (Sgr A*: Lx/LEdd~1e-9)
Simulations indicate “radio mode” feedback at low redshift is required to quench cooling and inhibit star formation (e.g., to match observed galaxy colors)
Croton+06

5. X-rays: AGN vs. ‘inactive’ galaxies
X-rays from inactive galaxies:
ROSAT effectively sensitive down to 1e40 erg/sec for nearby galaxies
Chandra bridges the gap between active (>1E-2 L_Edd) and (formally) inactive galaxies
Sub-arcsec angular resolution is key
Pellegrini 05

6. The AMUSE surveys: science goals
Two Large Chandra Programs (~1Msec) to bridge the gap between AGN and formally inactive galaxies. Specifically, to:
Investigate highly sub-Eddington (Lx/Ledd<1e-5) activity in local super-massive BHs
Quantify active fraction as a function of BH/host mass, corrected for ‘Eddington incompleteness’
Constrain the local BH occupation fraction
Control for environmental effects on the nuclear activity (cluster members vs. isolated galaxies)

7. AMUSE-Virgo: the survey
Targets 100 Virgo early type galaxies which compose the HST ACS Virgo Cluster Survey (VCS, Cote’ et al 2004):
84 new targets with Chandra ACIS-S (454 ksec Cycle 8, PI: Treu) archival (>1 Msec)
Complete down to Ledd for a 3 Msun object
57 new targets with Spitzer MIPS (9.5 hr) + 43 archival
Archival HST ACS g- & z-band (100 orbits)
Nuclear black hole mass distribution

8. Black holes, star clusters & LMXBs
1. Diffuse gas emission modeled and removed: search for nuclear BH limited to hard X-rays (>2keV)
2. Astrometry matched to SDSS, positional accuracy: arcsec
3. Contamination from Low-Mass X-ray Binaries (LMXBs) addressed quantitatively based on X-ray luminosity function of LMXBs:
Gilfanov04) in the absence of nuclear star
Sivakoff in the presence of a nuclear cluster

9. AMUSE-Virgo:Nuclear X-ray census
32/100 show a nuclear X-ray source
51/100 show a massive nuclear star cluster (HST)
6/100 show both a nuclear X-ray source and a star cluster
After accounting for LMXB contamination: 24-34% of the galaxies host an active super- massive black hole (95% C.L.)
Next: ACTIVE FRACTION as a function of host stellar mass and MBH

10. AMUSE-Virgo: Active fraction
Active fraction raises with host stellar mass
Mostly due to ‘Eddington incompleteness’: Dealing with `Eddington-limited’ sub-samples results in no evidence that the fraction of active black holes depends on host mass
(see Ho+97 Kaufmann+03, Decarli+07, Seth+08,10)
(Gallo+10)

11. AMUSE-Virgo: Down-sizing
Assume: Log( LX,38 )=A + B log( M BH,8)
Bayesian code handles limits, errors; Uncertainties: 0.44 dex on MBH to be 0.44 dex, 30% on Lx ; include intrinsic scatter
Priors: MBH mass function power- law index -1, rotational invariance for slope
Most likely parameter value taken to be median of random draws from posterior distribution
DOWN-SIZING: Lx/Ledd increases with decreasing BH mass
‹LX / MBH ›MBH-0.62
log LX
log (MBH)

12. AMUSE-Virgo: Summary
32/100 nuclear X-ray sources ; 51/100 nuclear clusters ; 6/100 hybrids
Bona fide active black holes (after LMXB contamination assessment): between 24-34% host an accreting black hole. Strong lower limit to occupation fraction in the local universe.
AVERAGE Lx/Ledd DECREASES WITH INCREASING BLACK HOLE MASS (Gallo+08,10)
PLUS :
Spizter MIPS results: absorption, dust reprocessing etc. (Leipski+ Paper III, submitted)
Off-nuclear X-ray source population (Katolik+ Paper IV, in prep.)

13. Influence of environment
Relative to their cluster counterparts, local field early- type galaxies tend to:
Have a lower incidence of past major mergers
Face reduced ram pressure stripping, but outflows less confined
Generally have more cold gas (e.g., higher HI content) along with younger stellar populations

14. AMUSE-Field
Chandra snapshots of 75 field spheroids (PI Gallo, Cycle 11, 479 ks), plus 25 archival within 30 Mpc
Sensitive down to the Eddington limit for a 6 Msun BH
Sample drawn from HyperLeda catalog, with following criteria:
Spheroidal, MB<-13
v<1800 km/s and d<30 Mpc
b>294o or b<230o (no Virgo or Fornax)
l>30o or l<-30o (avoids absorption from Galactic plane)

15. AMUSE-Field: Active Fraction
34/75 X-ray nuclei
Detection fraction increases with Mstar
Assuming LMXB contamination as for Virgo (red), ~40% X-ray active fraction (filled histogram, upper)
Comparable to Virgo; (dashed lines, lower)
B.Miller+ in prep.

16. AMUSE-Field: Stacking
Stacked keV images of snapshot observations lacking nuclear X-ray detection (after removing off-nuclear X-ray sources) 291 ks of net exposure
31 net counts within 5’’ aperture (2.8 sigma)
log(Lx) = 37.7, consistent with LMXB origin
B.Miller+ in prep.

17. Virgo vs Field: Eddington ratios
Lx/LEdd versus MBH and Mstar for field (blue, purple) and Virgo (red)
Lx/LEdd declines with increasing MBH, Mstar
Field sample includes relatively more low MBH, Mstar objects: all comparisons based on weighted subsamples consistent with Virgo

18. Virgo vs Field: Down-sizing
Assume: Log( LX,38 )=A + B log( M BH,8)
Bayesian code handles limits, errors; Uncertainties: 0.44 dex on MBH to be dex, 30% on Lx ; include intrinsic scatter
Priors: MBH mass function power-law index -1, rotational invariance
Most likely parameter value taken to be median of random draws from posterior distribution
DOWN-SIZING IN BOTH SAMPLES: Lx/Ledd increases with decreasing BH/host mass
B.Miller+ in prep.

19. Virgo vs Field: Down-sizing
Slopes consistent between the field and Virgo samples; also holds for detections only, as well as for the weighted subsamples
Intercept slightly higher for the field sample
B.Miller+ in prep.

20. The AMUSE-surveys
Two Large Chandra Programs (Cycle 8 & 11) to investigate the rate of highly sub-Eddington accretion onto nuclear super- massive BHs in nearby early type galaxies: 200 objects (100 in Virgo, 100 field, D<30 Mpc)
Overall active fraction: 30% (Virgo), 40% (Field); does NOT increase with host mass
Evidence for DOWN-SIZING: ‘smaller’ BHs shine closer to their Eddington limit
The large-scale environment does not appear to influence strongly activity in local spheroids; Field galaxies show modestly enhanced nuclear X-ray emission, perhaps due to greater access to fuel supply