Starbursts in Low Luminosity Active Galactic Nuclei Rosa M. González Delgado Instituto de Astrofísica de Andalucía (CSIC, Granada, Spain) Roberto Cid Fernandes Universidade Federal de Santa Catarina (Florianópolis, Brasil)  L. Colina (IEM-CSIC, Spain), T. Heckman (JHU, USA), C. Leitherer and L. Martins (STScI, USA), J.M. Mas-Hesse (CAB-CSIC, Spain), E. Pérez (IAA-CSIC, Spain), T. Storchi-Bergmann (UF Porto Alegre, Brasil), H. Schmitt (NRAO, USA), D. Schaerer (Geneva) Starbursts From 30 Dor to Lyman Break Galaxies Cambridge 2004

Outline Motivation: Techniques to detect Starbursts in the nuclei of active galaxies Starbursts in active galaxies: Seyferts, Radio Galaxies, QSOs Low Luminosity Active Galactic Nuclei (LLAGN) Sample and observations of LLAGNs Stellar population in the nuclei (Cid Fernandes et al. 2004, ApJ, 605, 105 & González Delgado et al. 2004, ApJ, 605, 127) Stellar population gradient (Cid Fernandes et al. 2004, MNRAS, submitted) Central morphology (González Delgado et al. in preparation) UV-optical SED (González Delgado et al. in preparation) Connection LLAGN-Starbursts

Techniques to detect starbursts 1.UV emission: Wind lines

Techniques to detect starbursts Optical spectrum: Emission lines, WR features, HOBL (H8, H9,…) and HeI in absorption After the first 6 Myr, HOBL in absorption dominate over nebular emission González Delgado, Leitherer & Heckman (1999)

Previous work: Nuclear Starburst in Seyfert 2 NGC 7130 González Delgado et al (1998) Heckman et al (1997) HST+FOC + + New HST ~ U-band snapshot survey by Schmitt et al 2004 (see POSTER#) IC pc

l Nuclear Starburst of size a few 100 pc (similar size to NLR) l Starburst dominates the UV light l < L Bol < L  : Similar to the estimated AGN luminosity Previous work: Nuclear Starburst in Seyfert 2

All Sy2 with nuclear Starbursts detected at UV show HOBS in absorption: intermediate age population Nuclear Starburst in Seyfert 2: HOBS in absorption 40% of Seyfert 2 show compact (100 pc) and powerful (L>10 10 Lsol) nuclear starburst González Delgado et al (1998) González Delgado, Heckman, Leitherer (2001) Cid Fernandes et al (2001) HOBL

Low-Luminosity AGN (LLAGNs) LLAGNs They are located in about 30% of the nearby and luminous galaxies (B T < 12.5) (Ho, Filippenko & Sargent 1995)  Liners/HII (Transitions Objects=TO) (weak Liners): weak [OI]/H   Classical Liners : strong [OI] 6300/H  Do LINERs & Transition Objects also have nuclear starbursts? Are they similar to those in Seyfert 2s? Is there a link between st pops & ionization? Previous work  Massive stars (Filippenko & Terlevich 1992)  Starburst in the Wolf-Rayet phase (Barth & Shields 2000)  Post-AGB (Binette et al 1994) and PN (Taniguchi et al 2000)

Stellar Population in LLAGNs  HST observations (from the archive):  STIS  G430L ( Å)  Nuclear spectra: 0.2x0.3 arcsec and 0.2x1 arcsec  28 LLAGNs  Ground-based observations:  Telescope: NOT (ALFOSC) and 2.1m at KPNO  Å  Nuclear spectra: 1x1 arcsec (100 pc)  51 LLAGNs + 2 HII + 7 non-active galaxies  Strong-[OI]: [OI]/H  > LINERs  Weak-[OI]: [OI]/H  < TOs

Strong-[OI] LLAGNs Strong-[OI] LLAGNs: All Liners (>90%) are dominated by old stellar population. Very few Liners (< 10%) have intermediate age, 100 Myr to 1 Gyr, population

Weak-[OI] LLAGNs Many TOs (50%): are dominated by intermediate age, 100 Myr to 1 Gyr, population Many TOs (50%): have HOBL in absorption, and relative weak metal lines

Stellar Population in LLAGNs Non-detection of Woft-Rayet features

[OI]/H  -Stellar population connection 90% objects with HOBL: (i) have weak metallic lines, (ii) are weak-[OI] LLAGNs  Strong-[OI]: LINERs [OI]/H  > 0.25  Weak-[OI]: TO [OI]/H  < 0.25

Summary of the tour through the data “Young” LINERs Old LINERs “Young” TOs Old TOs Stellar pop / age [OI] / H 

Stellar population Synthesis (code by M. Cerviño) Spectral Evolution (Geneva and Padova track at solar metallicity) High spectral resolution models ( A) * Isochrones: Padova and Geneva groups * Stellar library: 2 solar, solar, half and 1/10 solar * Stellar atmospheres: TLUSTY, Kurucz, and Phoenix * Spectral sampling 0.3 A Models: González Delgado, Cerviño, Martins, Leitherer, Hauschildt, 2004, MNRAS Library: Martins, González Delgado, Leitherer, Cerviño, Hauschildt, 2004, MNRAS

Stellar population Synthesis: ages Young-TO : 10 8 —10 9 yr Old-Liners and TO: >10 Gyr Very young (<10 Myr) stellar population contributes 10% of the 4000 A light in the young-TO EPS algorithm by Cid Fernandes et at (2001): inputs: Base of synthetic spectra covering from few Myr to 13 Gyr at different metallicities outputs: x (%), Av correspond to a likelihood- weighted mean of combinations obtained from a Metropolis tour through the (x, Av) -space

Summary of the nuclear spectra (100 pc) High Order Balmer Absorption Lines are very common (~ 50% of TOs) No WR bump Intermediate age populations (10 8 – 10 9 yr) are very common (~ 50% of TOs) Very young starbursts ( ≤ 10 7 yr), if present, are very weak

Stellar population gradient Spatially resolved spectra (500 extractions in 47 objects)

Stellar population gradient Radial profiles of Ew(CaIIK) Ew(CaIIK) < 15 A--- Intermediate age stellar population Young-TO have a diluted profiles The dilution is produced by the intermediate age population

Extinction profiles Young-TO have larger central extinction than Old-LLAGN The extinction profiles of young-TO are more complex that those of old LLAGN, which are often approximatelly flat. Young-TO have centrally peaked extinction profiles Young-TO have larger central extinction (Av= 0.5 mag) than Old-LLAGN

Central morphology: HST+WFPC2 (optical filter) Young-TO have dustier central emission than Liners

Central morphology: HST+WFPC2 (optical filter) Old-TO and Old-Liners

Sizes of the intermediate age stellar population (< 100 pc) X(%) SB FWHM=size

Comparison with Seyfert 2s & speculations... “Young” TOs evolve to Old TOs or Old LINERs on ~ 1 Gyr Only starburst+Seyfert 2 composites may evolve to “Young” TOs Other Seyfert 2s will end up as Old LINERs or Old TOs

Comparison with Radio Galaxies (FRII) Tadhunter, Robinson, González Delgado, et al 2004, MNRAS,submitted Are ULIRG the precursors of Radio Galaxies with (Post)-Starbursts?

Summary of the optical results Old-TO and Old-Liners have spatially uniform stellar population with very little amount of dust. Young-TO have stronger stellar population gradients, intermediate age population, and moderate dust content. This population is compact (< 100 pc) and has mass 10 7 —10 8 Msol These intermediate age populations were times more luminous in their formation epoch, at which time massive stars (starbursts) dominated the bulge light.

Is the star formation proceed at a residual level? UV emission in the core of some Young-TO: NGC 4303 STIS/MAMA (FUV) Size of the central knot (nucleus): 3 pc STIS/MAMA (G140L) E(B-V)= 0.1 Age= 4 Myr Mass= 2-3 X 10 5 M sol Lbol= 2 x 10 8 L sol Colina, González Delgado, Mas-Hesse, Leithere, Jiménez Jailon, 2002,ApJ, 579, 545

UV emission: evidence that the star formation proceeds at some level in Young-TO STIS (G140L) NGC 3507 and NGC 4303 NGC 4569 WFPC2 (F220W) A compact but resolved source: Stellar cluster?

Conclusions Young-TO are clearly separated from the Old-TO and Liners in terms of the properties and spatial distribution of the stellar population. Young-TO have stronger stellar population gradients, a luminous intermediate age stellar population which is concentrated in the nucleus (< central 100 pc) and larger amount of extinction than Old-TO and Liners. These Young-TO could be classified as Starbursts 1 Gyr ago or as “composite” Seyfert 2 (Seyfert + nuclear starburst) Young-TO will become old-LLAGN in a few Gyr.