Stellar Populations in the Central 10 pc of low-luminosity AGNs and Seyfert 2

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Stellar Populations in the Central 10 pc of
low-luminosity AGNs and Seyfert 2

• Marc Sarzi
• (University of Hertfordshire, UK)
• In Collaboration with H.-W. Rix, J. Shields, A.
  Barth, L. Ho, A. Filippenko, W. Sargent, G.
  Rudnick, D. McIntosh, R. Pogge, P. Martini

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OUTLINE

• The SUrvey of Nearby Nuclei with STIS
• Nuclear Stellar Populations of LLAGN
• A STIS survey of Seyfert 2s
• New method
• Preliminary results
• ! Both studies are unique in that they probe
  the very central regions of galaxies, within
  10pc from the center

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SUNNS SUrvey of Nearby Nuclei with STIS

• G430L and G750M spectra for 24 S0-Sbc galaxies
  within 17 Mpc with EM-lines to study
• Emission-Line Kinematics (Sarzi et al. 2001,
  2002 Shields et al. 1999 Ho et al. 2000, 2002)
• Emission-Line Diagnostic (Shields et al. 2006)
• Nuclear Stellar Populations (Sarzi et al. 2005)
• Relative Role in powering AGNs of Accretion onto
  SMBH and Star Formation

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The Template Superposition Method

• Select a 1st guess template
• Find optimal kinematical broadening with 1st
  guess
• Broaden all templates with the same LOSVD and get
  templates weights
• With optimal templates run again through 2. 3.
  to improve both LOSVD and templates weights
• Reddening by dust or a polynomial adjustment can
  be included in 3.

From Bruzual Charlot (2003)
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Multiple Starburst Models

• Mostly old and reddened objects.

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NGC 4203

• A Liner with very broad H?

From Shields et al. (1999)

• True AGN, Powered by a SMBH

See also Ho et al. (2000) for NGC 4450
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Luminosity-Weighted Mean Ages

• 80 of our nuclei are very old (gt3 Gyr). This
  holds when considering super-solar metallicities.

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Very Young Stars can they power EM-lines?

• With such very conservative 3-s upper limits

• Seyferts no hope.
• L1 not really
• L2 maybe just 1
• T 2 yes, 2 no, 2 dont know
• HII ok for the 2 with EM-lines

This at 10 pc. At 100 it would be worse.
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Young Stars Correlations?
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SUNNS Conclusions

• 1) The Central 10 Parsec of Sb-S0 bulges are in
  80 of the cases dominated by very old (gt 3Gyr)
  stars.

2) 25 of them need some stars younger than
1Gyr, and their incidence depends on the nuclear
classification.
3) Reddening or Super-Solar metallicities do not
change these results.
4) Only 1 galaxy harbours a clearly young (3-Myr)
Nuclear Cluster
5) Only 2 out of 5 HII nuclei have young stars or
emission. Star formation in HII-nuclei may be
mainly circumnuclear.
6) O-stars could contribute to ionization of some
Liner2 and Transition objects.

• Gonzales-Delgado et al. (2004) reached
  independently similar conclusions

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Seyfert 2 Central Populations

• G430L and G750M spectra for 19 nearby Seyfert 2
  galaxies to zoom in the central 10 pc to
• Reveal the presence of BLRs hidden in
  ground-based observations
• Understand whether intrinsic Sy2 objects could
  exist
• Investigate the star formation history on small
  scales
• Now, this will more difficult than in the case of
  the SUNNS survey

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Seyfert 2 Central Populations
A New Method

• Abundant nebular emission reduces the information
  about the stellar population content.
• Iterative procedures involving masking to narrow
  the regions contaminated by emission may not
  converge.

• Solution a simultaneous fit of emission and
  absorption lines,
• treating the emission-lines as Gaussian
  template in addition to
• the stellar templates!

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Seyfert 2 Central Populations
A New Method

• Furthermore with the STIS wavelength range we
  can constrain the
• A) Diffuse reddening affecting gas stars
• (continuum slope)
• B) Internal reddening affecting gas
• (Balmer decrement)
• C) Contamination of Balmer emission in the
  age-sensitive
• corresponding absorption feature

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Seyfert 2 Central Populations
Preliminary Results

• Old Nuclei (10Gyr) - 9/21 including 3 Sy2 from
  SUNNS)

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Seyfert 2 Central Populations
Preliminary Results

• Nuclei of Intermediate Age (1-2Gyr) - 2/21

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Seyfert 2 Central Populations
Preliminary Results

• Old Nuclei with O-stars - 10/21 (2 with BLR, all
  with strong emission)

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Seyfert 2 Central Populations
Discussion

• The finding of a blue continuum could be
  consistent with star formation concomitant to
  intense AGN activity, which would subsequently
  fade.
• Alternatively, we could be looking at the
  accretion source without a BLR.
• We must keep in mind the relative shortage of
  intermediate stellar populations, which would be
  inconsistent with frequent and related
  star-formation and AGN episodes
• Future work will include seeking evidence for a)
  absorption feature dilution, b) correlation
  between the luminosity of the blue continuum and
  the eq. of emission, b) evidence for an impact of
  O-star in the emission-line ratios, and WR
  features

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Multiple Starburst Models

• NGC 4800

Typical 10-Gyr-old, reddened nucleus
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Multiple Starburst Models

• NGC 4459

Typical 10-Gyr-old, reddened nucleus
and a-enhanced
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Multiple Starburst Models

• Mostly old and reddened objects. 25 need younger
  components. But young stars do not always help

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Very Young Stars how many can we fit in?

• 3-s upper limits, in average 6. We could have
  not detect the MW central clusters, if observing
  from Virgo

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Multiple Starburst Models, Z 2.5 Zsun

• Supersolar models always work better, but AV0
  too often (40) The truth probably lies in
  between

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Contribution from Young Stars

• 5 nuclei certainly need some stars lt1 Gyr old. 4
  may need a featureless continuum instead of young
  stars.

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Young Stars vs Power -Law

• A dusty starburst gives a almost identical
  continuum slope than a power-law, but not
  entirely featureless !

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Young Stars Correlations?

• The presence of young stars does not correlate
  with either the Hubble type or s

• The presence of young stars correlates with the
  Nuclear Classification.

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Young Stars Correlations?
Bias?

• The presence of young stars does not correlate
  with either the Hubble type or s

• The presence of young stars correlates with the
  Nuclear Classification.

• The presence of young stars correlates with the
  Distance Hubble type. Even at HST resolution
  bulge-light contamination is important !!!

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Young Stars in Nuclear Clusters?

• Only one object with young stars is clearly a NC
  (NGC 278). The others could, but we need better
  images.

• 5/14 of our spirals have stars lt 1 Gyr old.
  Carollo et al. finds 50 of spirals have NCs.

• If 1 Gyr old we could have detect most of them.
  So some may be older, consistent with imaging
  results.

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Seyfert 2 Central Populations
A New Method

• Abundant Nebular Emission reduce the information
  about the stellar population content.
• Iterative procedures involving masking may not
  converge.
• Similar to the case of the SAURON integral-field
  survey

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Seyfert 2 Central Populations
A New Method

• Solution simultaneous fit of emission and
  absorption lines, treating the emission-lines as
  Gaussian template in addition to the stellar
  templates!

Hb Flux overstimate (here by 40)
Hb Flux and sgas overstimated (flux by 80)