On the Nature of NarrowLine Seyfert 1 Galaxies

1
On the Nature of Narrow-Line Seyfert 1 Galaxies

• Steve Kraemer (Catholic Univ. of America)

2
Properties of Seyfert Galaxies

• Relatively nearby (z lt 0.1), moderate luminosity
  (Lbol 1043 1045 ergs/sec) active galaxies
• Approximately 2 of Spiral galaxies are Seyfert
  galaxies they harbor an active galactic
  nucleus
• Optical and UV Spectra broad emission-lines,
  featureless continuum
• Strong X-ray sources (power-law continua)
• Radio quiet compared to other AGN, but often
  show jet-like structure
• IR often dominated by thermal emission from dust

3

• Two classes of Seyfert galaxies
• Type 1 broad permitted lines (FWHM
  several 1000 km/sec) narrower forbidden lines
  (FWHM lt 1000 km/sec) non-stellar continuum
• Type 2 narrow permitted and forbidden
  lines continuum dominated by host galaxy
• spectral-polarimetry results scattered broad
  line emission in Seyfert 2s (Antonucci Miller
  1983) hidden broad line region. Led to Unified
  Model (Antonucci 1993)

4

• Optical Spectra of Seyferts

Seyfert 1
Seyfert 2
5
(No Transcript)
6

• All galaxies with central bulges harbor
  supermassive black holes

7
AGN are powered by mass-accretion onto a
super-massive black hole.Ionization radiation
arises from accretion disk and hot corona.
8

• Various intermediate classes Seyfert 1.2, 1.5,
  1.8, 1.9 based on the strength of the broad and
  narrow components of the Balmer lines
• Detectable narrow Hß 1.2 or 1.5
• Weak broad wings 1.8 only observed in Ha
  1.9.
• This may be due to different obscuration of the
  BLR, or the relative strengths of the broad and
  narrow component.
• However there are Seyfert 1s which show only
  narrow permitted lines. Narrow-Line Seyfert 1s
  (NLSy1) (Osterbrock Pogge 1985)

9
BLR Spectrum (from a NLS1)
O III
(Peterson, p. 71)
10

• Characteristics of Narrow-Line Seyfert 1s
  (compared to Broad-Line Seyfert 1s)
• i. Relatively narrow permitted lines (FWHM
  lt 2000 km/sec)
• ii. Steeper continuum slopes in soft- and
  hard-Xray (Boller et al. 1996 Brandt et al.
  1997)
• iii. More rapid X-ray variability (Turner
  et al. 1999 Leighly 1999)
• iv. Optical X-ray continua have similar
  slopes to Broad-Line Seyferts (Grupe et al. 1998)

11
(No Transcript)
12

• v. High N V ?1240/C IV ?1550 ratios (Wills et
  al. 1999)
• vi. CIII ?1909 relatively weak compared to Al
  III ?1857 maybe higher BLR densities?
  (Kuraszkiewicz et al. 2000)
• vii. Strong Fe II, weak OIII ?5007 puts
  at one extreme of eigenvector 1 (principal
  component analysis Boroson Green 1992)
• Is there one intrinsic property that links all of
  these?

13
(No Transcript)
14

• Assuming the defining feature is the line width
  why are the permitted lines narrow?
• Widths thought to be due to Doppler broadening.
  In BLR, fast moving gas, in virialized system.
• Narrow lines?
• 1) gas is more distant
• 2) central potential is weaker (smaller black
  hole mass)
• Option 1 over-ionization of BLR (Wandel et al.
  1999)

15

• Ionization state of the gas can be characterized
  via the dimensionless Ionization Parameter

The denominator is the luminosity of the source
in ionizing photons/sec If large, for given R2,
ne, the emission-line gas can be over-ionized
Gas in which the Balmer lines form must be at
large distances, hence lower orbital velocities.
16

• Option2 the permitted lines are narrow because
  the black hole mass is relatively small.
• Reverberation mapping studies (e.g. Peterson et
  al. 2004) have found low mass black holes in
  NLSy1s (Mbh lt 107 Msun).
• The Black Hole is the engine of the AGN.
  Smaller engine should mean less power.
• Luminosities of NLSy1s span similar range to
  BLSy1s.

17

• From Grupe Mathur (2005) NLSy1s show
  systematically smaller masses.

18
From Bian Zhao (2003) bulge masses derived
from OIII, as In Grupe Mathur
19

• If Mbh is small, accretion rate, dM/dt, must be
  high.
• NLSy1s must radiate at large fraction of their
  Eddington Luminosity

• Radiation pressure balances gravity at higher
  luminosities, matter
• can no longer accrete
• BLSy1s radiate at smaller fraction of Ledd than
  NLSy1s

20

• High dM/dt accretion disks expected to be
  hotter (than in BLSy1s)
• Can be super-Eddington accretors due to advection
• Wang Netzer (2003) high dM/dt results in thin
  disk emits double-peaked continuum
• Peak in EUV-soft X-ray from disk
• Peak at high energies from corona

21
NLSy1s and BLSy1s span same Range in X-ray and
OIII
NLSy1s show stronger OIII as function of BH Mass
22

• Dust structure possibly indicative of fueling
  flows
• Often show kpc-scale starburst rings
• (Deo et al. 2006)

23
(No Transcript)
24

• To recap, NLSy1s
• i. smaller BH mass
• ii. higher accretion rates maybe seen
  as dust flows
• iii. higher heavy element abundances
  (N/C, strong Fe II) associated with star
  formation?
• iv. Different accretion disk conditions
• But, is this all certain? Can there be other
  explanations? More importantly, is there evidence
  to the contrary?

25
(No Transcript)
26

• Fe II emission I Zw 1 is used as a template for
  FeII and shows some of the strongest UV and
  optical FeII among NLSy1s
• However, numerous FeII lines can resemble a
  continuum if broadened.

27

• If the emission line region is flattened, and
  viewed face-on, the line profiles would be
  narrowed (Boller et al. 1996)
• Can this be the case?
• Radio maps NLSY1s appear compact (Ulvestad et.
  Al 1995)

Mrk 766 3.5 cm VLA
NGC 5548 6 cm
28

• The low OIII/Hß ratios are likely due to
  improper deconvolution of broad and narrow
  components (Veron-Cetty et al. 2001 Dietrich et
  al. 2005)
• No evidence for effect of soft Xray excess on
  emission-line fluxes, ratios (Dietrich et al.
  2005 Kraemer et al 2004)

29

• If the BH masses are underestimated by factor of
  3 5
• The are not high dM/dt
• The BH to bulge mass discrepancy goes away
• Reverberation mapping assumes virialized system.
  Flattened BLR means narrower lines, underestimate
  of BH masses
• However.
• X-ray properties still unusual
• Dust structure/star formation atypical
• They seem to be relatively weak in the very hard
  X-ray (14-195 keV Swift/Burst Alert Telescope
  survey detected only a few 5-s sources)