Observational signatures of gas flows toward the center of galaxies

1. Observational signatures of gas flows toward the center of galaxies Thaisa Storchi Bergmann Instituto de Física, UFRGS, Brazil Collaborators:Barbosa, Riffel, Dors Jr., Simões Lopes, Winge, Axon, Robinson, Fathi, Ostlin, Marconi Gas accretion and Star Formation in Galaxies, Garching Research Center, Sept. 10-14 2007 Credit:Jon Lomberg

2. Motivation • AGN paradigm: Nuclear activity as phase in galaxy evolution triggered by mass accretion to the nuclear supermassive blackhole (SMBH) (Ferrarese & Merrit 2000; Tremaine 2002; Marconi & Hunt 2003, Peterson & collabs. 2000-2007) • Main unsolved questions in AGN research: • Origin of fuel; • Nature of triggering mechanism • How gas is transferred from galactic scales to the nucleus • →inflows! • But observations show outflows, not inflows!

3. Nuclear morphology:Simões Lopes, Storchi-Bergmann, Martini 2007: structure maps of HST images of paired sample active vs. non-active galaxy from Palomar survey; 68 pairs Active Non-active Active Non-active Active Non-active

4. Simões Lopes et al. 2007: Results for 34 early-type pairs: • Dust structures/spirals in ALL active galaxies but in only 27% of non-active → feeding material on its way in • Previous works: Van Dokkum & Franx 1995, Pogge & Martini, 2002; Martini et al. 2003, Xilouris & Papadakis 2002, Ferrarese et al. 2006, Lauer et al. 2005; Prieto et al. 2005→ association with activity not so clear • “Side result”: non-active galaxies have stellar disks (talk by Bureau, this conference) Active Non-active Active Non-active

5. Simões Lopes et al. 2007: Results for 34 late-type pairs: • Dust structures in both active and non-active galaxies • Many non-active galaxies have star-forming nuclei • → If dusty structures is the gas in its way towards the nucleus: nuclear spirals also responsible to send gas in to feed starbursts Active Non-active Active Non-active

6. Signatures of feeding: gas kinematics • Inner kpc morphology support nuclear spirals (~100 pc scales) as means to feed AGN and nuclear starbursts. • But:where are the kinematic signatures? • Storchi-Bergmann, Fathi, Axon, Robinson, Marconi, 2006-2007: proposed GMOS IFU observations to look for streaming motions along nuclear spirals in AGN hosts. Sample extracted from Simões Lopes et al. 2007 (structure maps). • Observational constraints: • Low-luminosity AGN, as high-luminosity ones are dominated by outflows; • intermediate inclination to measure kinematics; • presence of ionized gas to allow optical IFU.

7. Results: 1) NGC 1097 • Luminous (MB=-21.2) SBb galaxy at 17 Mpc with nuclear ring (700 pc); LLAGN with double-peaked Balmer lines (Storchi-Bergmann et al. 1993-2003) • HST ACS FR656Nimages of inner 500 pc: gas/dust filaments (Prieto et al. 2005; Fathi et al. 2006) Fathi et al. 2006:

8. Fathi et al. 2006: Gemini IFU GMOS Hαspectra covering715 (3 fields; 3000 spectra) → • Results: • Non-circular motions: residuals (~50 km/s) delineate spiral arms (dots) seen in structure map; • redshifts in the near side, blueshifts in the far side → streaming motions along spiral arms towards the nucleus Far side Near side

9. Results: 2) NGC6951 • SABbc galaxy at 24 Mpc with LLAGN (LINER/Sy 2) , with star-forming ring at ~ 500 pc from nucleus • Has radio, CO and HCN emission • Galaxy Structure map shows nuclear spirals → IFU fields→

10. Storchi-Bergmann et al. 2007 • Results • Streaming motions along nuclear spirals • Plus: outflow produced by radio jet (Saikia et al. 2002) Far side Near side

11. Results: 3) M81 (preliminary) 1 1 2 2 3 3 • FOV too small to fit a kinematic model • But distorted isovelocity curves evidentiate non-circular motions • Location of the distortions ↔ dusty structures

12. Relevance and implications • First time that streaming motions in nuclear spirals are mapped – previously only in large scale spiral arms and bars (Visser 1980; Tilanus & Allen 1991; Mundell 1999 for NGC4151; Adler & Westfall for M81; Emsellen, Fathi, Peletier et al. 2005-2007; van Gorkom, Blitz, Walter, this conference) • Nuclear spirals ubiquitous in active and late-type galaxies → material in its way in to feed the SMBH and star-forming nuclei; • Timescales: at 50 km/s, gas at ~1 kpc from center will reach the nucleus in ~107 yrs • Calculation of mass inflow rate (of ionized gas!): • ~ nuclear accretion rate to drive the luminosity of the low-lum. AGNs • BUT: ionized gas may be only the “tip of the iceberg”; neutral and molecular gas may dominate inflow (nuclear molecularmass ~ 107 Msun in NGC6951; Garcia-Burillo et al. 2000, Krips et al. 2007; nuclear starburst of 106 Msun in NGC1097, Storchi-Bergman et al. 2005, Davies et al. 2006; also strong CO recently measured from the nucleus, priv. comm.)

13. Conclusions • Strong correlation between dusty nuclear structures and activity → nuclear spirals can be channels to feed the nucleus; SMBH or starburst • First kinematic signatures of inflow towards low-lum. AGNs (in nuclear spirals) • More targets to be observed, including Seyferts and starbursts Jon Lomberg: artistic view of mass inflow along nuclear spiral arms