Thus Far Intro / Some Definitions Hubble Classification Components of Galaxies Stars Gas Dust Black Holes Dark Matter Specific Galaxy Types Star Formation Clusters of Galaxies
Components of Galaxies: Black Holes Possible Evidence that Black Holes are the central engines of Quasars/QSOs Average QSO produces 10 12 L sun from its nucleus alone.
Evidence 2: Light variations in nuclear light are consistent With source sizes of ~ 0.1 pc Black Hole Narrow Line Region (NLR) (Lower velocity gas farther from black hole) Broad Line Region (BLR) (High velocity gas near black hole) Accretion Disk (feeds black hole)
Reverberation Technique Estimating sizes of BLR Ionized gas from BLR Continuum Emission Active galaxies vary in energy output
Reverberation (cont ) Time lag, t, between a change in the continuum emission (black hole + accretion disk) & BLR is used to estimate size, L, of the BLR.
Evidence 3: Powerful relativistic radio jets are seen emanating from either side of the nuclear region The highly collimated nature of the emission favors a single source of emission
Black Holes as Central Engines Lots of energy Emanating from a small space Model: Material from an accretion disk falling into a supermassive nuclear black hole. Energy: Gravitational energy of sources near dense massive object converted to radiative energy.
Counterpoint: Supernovae & not BH? Quasar SN Difficulty: Sustaining the SN Rate Needed to Power QSOs for ~ 10 8-9 yrs
Calculation of Black Hole Mass from the Eddingtion Luminosity Accretion Disk Black Hole (gravitational force) (radiative force)
Condition for accretion: F grav > F rad Solving for black hole mass yields, Where L edd is the Eddington Luminosity i.e., the Luminosity a source would have if the gravitational Force exactly balanced the radiative force. If 10% of the total mass/energy of the accreting material is converted to radiative energy, the mass accretion rate is,
Black Hole Mass: Size & Velocity Dispersion of the BLR Size of BLR: r ~ 0.1 pc = 3x10 15 m FWHM of gas in BLR Mass is thus,
Black Hole Mass: Quasar Co-moving Volume Density QSO density was higher in the past QSO density presently low FWHM is ~ QSO lifetime Maximum lifetime of QSO: + 0.68 M sun yr -1 accretion rate:
Dormant Black Holes in Nearby Normal Galaxies Qu: Given that the density of QSOs was higher in the past, & that QSOs built up black holes with masses on the order of 10 7-9 M sun, where are these dead QSOs? An: Perhaps these dormant QSOs are in the nuclear regions of nearby normal galaxies. The implication of this is that almost every massive galaxy has gone through an active galactic phase. Qu: Why aren t present day, nearly normal galaxies active? An: Because they re not being fed. [Quasars] can live forever, but they must fed.
Evidence for Mass of Central Black Holes in Nearby Galaxies If dead quasars are in the nuclear regions of nearby normal galaxies, how might we infer their presence? By their gravitational effect on stars & gas in the nuclear regions of galaxies
From Gas Kinematics Active Galaxy M87 M BH ~ 3x10 9 M sun
Evidence for Massive/Compact Central Energy from Maser Rotation Curve (Miyoshi et al. 1995, Nature 373, 127) V(r) = (832 ± 2) [r / (0.25)] -½ Mass interior to 0.18 pc is M = 4.1x10 7 M sun pc
Gas Dynamics (cont )
Qu: Is a Nuclear Cusp Evidence of a BH? (Shu, pg 330)
(Kormendy & Richstone 1995 ARAA, 33, 581) Answer: No.
From Stellar Kinematics: The Galaxy HST NICMOS Imaging of GC (Rieke et al., in prep) Change in stellar position Velocity Mass Keck Imaging of GC (Ghez et al. 1998, ApJ, 509, 678)
The Galactic Center M ~ 2.6x10 6 M sun Advantage: GC is close I.e., mass interior to stars being traced by velocity dispersion is likely dominated by black hole, not stars. Possible Problem: some stars may not be in the GC (Ghez et al. 1998, ApJ, 509, 678)
From M / L(r) How can a large sample of galaxies be searched for black holes? The method should involve stellar kinematics gas motion is subject to non-gravitational forces Method: M / L (r) of central regions of galaxies
Search criteria for black hole survey of nearby galaxies The galaxy should be edge-on to minimize (v sin i) effects The galaxy must be relatively nearby, so that the best possible resolution can be obtained The galaxy must have no recent history of star formation (old stellar populations do not vary much in M / L with r) The galaxies should rotate to minimize the effects of anisotropy (Note: Giant elliptical galaxies don t rotate) The galaxies must have no evidence of nuclear dust (dust absorbs optical light, which gives an erroneous values of M / L V )
Case Study: NGC 3115 Edge-on Disk Galaxy HST: rotating Nuclear region
Kinematic Evidence of Edge-on Disk (Kormendy & Richstone 1992, ApJ, 393, 559) No Minor Axis Rotation
Imaging Brightness Profiles Seeing is important! Surface Brightness (mag arcsec -2 ) radius as a function of radius
Brightness Profiles Data + Models Measure Projected Brightness Distribution Determine Unprojected/seeing corrected I(r). (K&R 1992)
Spectroscopy: Velocity Profiles Velocity Radius of 0 Spatial
Sometimes, AGN contribution to Galaxy Continuum must be Accounted for Sombrero Galaxy AGN Line emission Low Luminosity AGN Stellar Absorption Lines (Kormendy et al. 1996, ApJ 473, L91)
Fitting Velocity Profiles to Data Exponential Disk Keplerian V(r) = constant Same Process as for I(r) (K&R 1992)
M / L(r) vs. Radius M = 1x10 9 Msun (K&R 1992)
Another Example: M31 (Andromeda Galaxy) M ~ 3x10 7 M sun (Kormendy & Richstone 1995)
And Another: The Sombrero Galaxy M ~ 1x10 9 M sun (e.g., Kormendy et al. 1996, 473, 91)
A Less Convincing Example: NGC 3377 M / L V (r 0) not as Extreme M ~ 2x10 8 M sun (Kormendy, Bender, Evans & Richstone 1998, AJ, 115, 1823)
Alternatives Explanations 1) Anisotropies can cause errors in the estimation of nuclear black hole masses Line of Sight
2) Dust in the core of the galaxy can cause artificially high values of M / L. Check: Unsharp Masking Patchiness in focussed / unfocussed (or model) images is a likely sign of dust Due to disk in nucleus of Galaxy Due to disky isophotes (Kormendy & Richstone 1992, ApJ, 393 559)
3) Metallicities: metal-rich galaxies have high M/L V because of line blanketing M/L V ~ 1-10 for Old Stellar Populations M/L Spread in Elliptical Galaxies 1) Metallicities 2) Anisotropies M / L = 9σ 2 / 2πGΣ 0 r c M/L of Globular Clusters 1) Metallicity (Kormendy, in High Energy Neutrino Astrophysics)
4) Dense Star Clusters & Not Black Hole? Probably Not. σ c & r c of Galaxies with Supermassive Nuclear Black Holes are same as Other Elliptical Galaxies and Bulges. I.e., IMFs must be similar. (Kormendy, in Structure & Dynamics of Elliptical Galaxies, 17)
Log M vs. M B,Bulge (Kormendy et al. 1998, AJ, 115, 1823)
The Magorrian Relation log (Υ fit / Υ sun ) = -1.11±0.33 + (0.18±0.03) log (L / L sun ) log (M,fit / M sun ) = -1.79±1.35 + (0.96±0.12) log (M bulge / M sun ) (Magorrian et al. 1998, AJ, 115, 2285)
M - σ r e/8 Relation Best data: M ~ σ 4.8±0.5 (Ferrarese & Merritt 2000, ApJ, 539, L9)
A Check: M - v rms Relation σ c (r e / 8) v rms (r e / 4) M ~ (σ rms ) 4.6±0.8 Note: v rms = [(s 2 + v r / sin 2 i) re/4 ] ½ v r = mean line-of-sight velocity
M - σ e Relation M = 1.2(±0.2) x10 8 M sun (σ e / 200 km/s) 3.75±0.3 (Gebhardt et al. 2000, ApJ, 539, L13)
M - σ Relation Appears to Hold for Active Galaxies Also Stellar + AGN components to spectrum complicate matters (Ferrarese et al. 2001, ApJ, 555, 79)
M via Reverberation Mapping & Ionization Models also appear to work (Kormendy & Gebhardt 2001, in Relativistic Astrophysics)
Nearby Galaxy with no Black Hole: M 33 Disk Galaxy Negligible Bulge (e.g., Merritt, Ferrarese, & Joseph 2001, Science, 293, 1116)
Why is there a Relationship? A First Guess Stellar mass and Black Hole Mass are related And σ traces stellar mass better than, e.g., blue light does For early-type galaxies, M ~ L 5/4 Faber Jackson relation L ~ σ 4 Thus, M ~ σ 5 Universal fraction of baryonic mass is converted into Black Holes (Ferrarese & Merritt 2000)
Details to Come Detailed Discussion of Active Galactic Nuclei Profile Fits to Galaxies Elliptical/Bulge Core Parameterization