NUclei of GAlaxies: First results of NUGA

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NUclei of GAlaxiesFirst results of NUGA

Santiago GARCIA BURILLO
(burillo_at_oan.es) Observatorio Astronómico
Nacional (OAN)
The NUGA project People involved S
García-Burillo(1), F.Combes(2), A.Eckart(3),
L.Tacconi(4), L.Hunt(5), S.Leon(3), A.Baker(4),
P.Englmaier(4),F.Boone(2),E.Schinnerer(6),
R.Neri(7).
(1)OAN- Observatorio Astronomico Nacional,
Madrid, Spain(2) LERMA, Observatoire de Paris,
France (3) I. Physikalisches Institut,
Universitaet zu Koeln, Germany (4) MPE, Garching,
Germany (5) CAISMI-CNR, Florence, Italy (6)
Caltech, USA (7) IRAM, Grenoble, France
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FUELING THE AGNs IN SPIRALS

• AGN are fuelled with material(gas/stars)
  originally lying away from the gravitational
  field of the BH.
• For gas in-fall to occur we need to remove
  angular momentum.
• There is no consensus on the mechanisms driving
  the in-fall of gas towards the central BH do
  they depend on AGN luminosity/type?

• I/High-luminosity AGNs need large accretion
  rates (?102-3 M?/yr) which must involve
  large-scale gravitational instabilities. These
  can trigger a nuclear starburst. Mass-loss
  rate/stellar collisions/disruptions may account
  for the necessary fuel.

• I/Low-luminosity AGNs (Seyferts 1-2 and Liners)
  although they need smaller accre-tion rates
  (10-2 -10-1 M?/yr) , these probably involve also
  large-scale gravitational instabilities nuclear
  SB comes first?

• Different types of large-scale gravitational
  instabilities have been described for AGN in
  spirals
• 1/Large-scale stellar bars gas infall may stop
  at ILR barrier (Combes and Gerin 85)
• 2/Decoupled nuclear bars stellar (Friedli and
  Martinet 93) or gaseous (Shlosman et al 89) may
  drive gas to smaller scales lt 100pc.
• 3/Spiral gas waves probably effective at small
  scales effective even for low Mgas/Mtot ratios
  (Englmaier and Shlosman 2000) .
• 4/Micro-warpsdriven by pressure effects (Pringle
  1996, Schinnerer et al 2000).
• 5/Lopsided/m1 instabilities either related to
  indirect potentials due to off-centring of
  central mass (Shu et al 90), counter-rotation
  (Garcia-Burillo et al 2000) or BH-dominated
  potentials (Bacon et al 2000).
• Are large-scale instabilities different for Seyf
  1, 2, and Liners? (and starburst galaxies?)
• Are they equally efficient in driving the gas
  inwards?
• Are molecular gas tori in Seyferts extended to
  several hundred pc?

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NUCLEI OF GALAXIES the NUGA project
NEED OF A HIGH-RESOLUTION CO SURVEY ? No
interferometric CO survey of a significant sample
of AGNs has ever been published so far-Previous
surveys ? done with low-resolution single-dish
antennas (studying molecular gas on kpc scales).
High spatial resolution (lt1) will allow study
of molecular gas distribution/kinematics on
scales lt50-100pc. ?
restricted to very few cases (poor statistics).
See ongoing AGN surveys with OVRO (Baker et
al,2000-2002)-NUGA sample12 nearby AGNs
covering the whole sequence of activity types (1,
2, 3Liners)-NUGA aims at enlarging the sample
to 25-30 galaxies by adding available data on
AGNs observed by consortium members. Non active
galaxies are also available (comparison sample)
? CO maps provide information on the gas
kinematics velocity fields, velocity
dispersions....-Essential to characterise
gravitational instabilities
COMPLEMENTARY INFORMATION FROM OTHER WAVELENGTHS
? NUGA has a multi-wavelength approach HST and
ground-based optical/NIR images available to
derive stellar potentials/SF patterns, ... ? CO
observations can be confronted to numerical
simulations of gas dynamics based on stellar
potentials derived from NIR images.
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NUCLEI OF GALAXIES the NUGA sample
High-sensitivity of Bure array can give
high-dynamic range images after a standard
synthesis.-The survey will provide a unique
data set to be fully exploited on a detailed
case-by-case basis, and globally as a homogeneous
sample of nearby AGNs.
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First images of NUGA project
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First images of NUGA project
-The variety of morphologies of circumnuclear gas
disks is remarkably large unresolved compact
sources, nuclear spiral arms, rings, lopsided and
other asymmetric features.
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M1 instabilities

• The distribution and kinematics of molecular gas
  reveal the onset of m1 perturbations , shaped
  into one-arm spirals and lopsided disks in
  several galaxies. Perturbations appear at various
  scales, from several tens to several hundred pc.

LINER
Seyf 2
Seyf 1
NGC4826
NGC1961
NGC4579
AGN
AGN
?
Spiral arm structure detected in CO(2-1)
(colour) is off-centred with respect to AGN locus
(1mm continuum source-contours).
?
CO(2-1) map (contours) overlaid on Palpha HST
image. Lopsided inner diskone-arm spiral echoed
by star formation.
One-arm spiral revealed by CO distribution
kinematics (top) is detected in UMT HST NICMOS
image (bottom)).
?
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NGC4826 gas velocities

• Both m1 spirals (arms I/II) are revealed by
  noncircular motions.
• Noncircular motions are also associated with the
  nuclear lopsided disk.
• We have compared the observed deviations with
  the expected velocity residuals for stationary
  and fast m1 modes, either trailing or leading
  with respect to the gas flow.

Velocity patterns of stationary/fast m1 modes,
trailing/leading with respect to the gas flow.
Isovelocity maps in N4826
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NGC4826 the realm of m1 perturbations

• Do we expect the onset of a counterrotating
  instability in the inner disk where there is no
  two-stream flow?? Is there a missing (undetected)
  counterrotating stellar disk in the inner
  regions?
• Numerical simulations will test the viability of
  counterrotating instabilities in a N4826-like
  case...
• Discuss other mechanisms favouring m1 modes (see
  Shu et al 90 Junqueira and Combes, 1996).

• m1 modes in N4826
• The distribution and kinematics of molecular gas
  reveal several m1 modes (slow and fast).
• ---Fast m1 modes in the inner disk (50-500pc)
• ---Slow m1 modes in the outer disk
  (500pc-1.5kpc)
• Although N4826 has a counterrotating HI disk,
  the m1 modes observed in CO disk may not due to
  counterrotation, however...

?

• AGN fueling
• Inner m1 mode being fast, might not cooperate in
  AGN fueling (problem??)

• Are (all kind of ) m1 modes older than m2
  perturbations?

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NGC4826 star formation patterns

• Asymmetrical patterns in the disk are mimicked by
  star formation tracers, such as Paschen_alpha
  (color image)
• m1 outer arm
• off-centered bar-like structure
• inner disk in Paschen_alpha appears strongly
  lopsided

• We overlay the 1-0 (top) / 2-1 (bottom) Bure
  maps with the Paschen_alpha image obtained from
  HST data (Boeker et al 1999).

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M2 instabilities

• m2 perturbations such as two-arm spirals or
  gaseous bars dominate the response and kinematics
  of the gas in other galaxies.

Seyf 2
H/Seyf 1
Seyf 2
NGC6951
NGC2782
NGC3147
AGN
AGN
AGN
?
CO(1-0) map (color) shows nested two-arm spirals
compact source on AGN.
?
CO(2-1) map (color) shows regular two-arm spiral
structure in the nucleus. Gas kinematics strongly
disturbed (isovel contours).
CO(1-0) map (top) shows nuclear gas barouter
spiral. CO(2-1) map (bottom) resolves inner disk
into nuclear gas barmini two-arm spiral.
?
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Acoustic waves?
NGC7217
Most of the described gas perturbations observed
in the first NUGA galaxies are probably linked
with classical gravitational instabilities,
except for NGC7217.
LINER

• 12CO(1-0) map clearly shows molecular gas is
  related to the dust ring, but also to the
  filamentary stochastic multi-arm spiral pattern.

NGC7217
12co(2-1)
12CO(2-1) central source (contours) coincides
with mini-spiral (?) seen in V-I color image.
?
12CO(1-0) map overlaid with HST- V-I image
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NGC7217
Very regular LINER galaxy with 2 stellar /gas
rings
Slight oval distortion? A destroyed
bar
Spiral structure inside the ring, gaseous,
might be due to acoustic waves
An evolved system??
Palomar-5m
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SEYF 1/H
LINER
SEYF 1
SEYF 2
SEYF 2
LINER
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NUGA(preliminary) conclusions on first results...
?Wide range of morphologies detected... -----Are
AGN nuclear gas disks different from starbursts
or normal galaxies at scales of tens-to-hundred
parsecs?-----Any difference among the different
activity types? No clear PICTURE /EVOLUTIONARY
SEQUENCE emerging (so far!).WHY?? --- AGN sate
is episodic gravitational instabilities are
known to change during the evolution of galaxy
disks Are different mechanisms of fuelling
acting at different epochs? The problem of
time-scales.---Our Galaxy is known to have (at
the same time!)a large-scale bara nuclear bara
m1 inner mode !
? Importance of m1 instabilities one-arm
spirals, lopsided disks ...In some cases, they
do not help fuelling AGN however
? Most of m1m2 perturbations described are
roughly self-gravitating structures (low Q).
With notable exceptionN7217 (evidence of
acoustic waves?).
--More observations are needed -completion of
the NUGA supersample -forthcoming observations
(this winter) will reach subarsec resolution.
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The supersample beyond NUGA
NUGA aims at enlarging the sample to 25-30
galaxies by adding available data on AGNs
observed by consortium members. Non active
galaxies are also available (comparison sample).
We have compiled a tentative first list of 16
possible candidates to be included/added in a
follow-up study.