Post on 20-Jan-2016
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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
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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
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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