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

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!

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

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

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

• 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: (1) Low-luminosity AGN, as high-luminosity ones are dominated by outflows; (2) intermediate inclination to measure kinematics; (3) presence of ionized gas to allow optical IFU.

Signatures of feeding: gas kinematics

• 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 FR656N images of inner 500 pc: gas/dust filaments (Prieto et al. 2005; Fathi et al. 2006)

Results: 1) NGC 1097

Fathi et al. 2006:

Results:

(1) Non-circular motions: residuals (~50 km/s) delineate spiral arms (dots) seen in structure map;

(2) redshifts in the near side, blueshifts in the far side → streaming motions along spiral arms towards the nucleus

Fathi et al. 2006: Gemini IFU GMOS Hα spectra covering 715 (3 fields; 3000 spectra) →

Near side

Far side

Results: 2) NGC6951

• Galaxy• 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

IFU fields→

Structure map shows nuclear spirals →

Storchi-Bergmann et al. 2007

Results

• Streaming motions along nuclear spirals

• Plus: outflow produced by radio jet (Saikia et al. 2002)

Nea

r si

de

Far s

ide

Results: 3) M81 (preliminary)

• FOV too small to fit a kinematic model

• But distorted isovelocity curves evidentiate non-circular motions

• Location of the distortions ↔ dusty structures

1 1

2 2

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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 molecular mass ~ 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.)

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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 starburstsJon Lomberg: artistic view of mass

inflow along nuclear spiral arms