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Conference: The many faces of Centaurus A

Is Centaurus A a typical Radio Galaxy?
(A neutral hydrogen perspective)
Christian Struve
Raffaella Morganti Tom Oosterloo Bjorn Emonts

July 1st 2009 Sydney - Australia


Why are we interested in Centaurus A?

Because it is a Radio Galaxy ! It is the closest of its kind



Questions of interest
Formation and evolution of RGs:
Which mechanisms trigger radio activity? - mergers/collisions/interactions/cold accretion What is feeding the black hole? - circumnuclear regions: accretion disks/tori/infall/outflow Why are some galaxies active while others are not? Do all galaxies experience a phase of AGN activity? Do different classes of radio sources get triggered in the same way? How long does a burst of activity last (re-current phases of activity)? Impact on cosmology (e.g. feedback) Evolution of nuclear activity with redshift



Questions of interest
Formation and evolution of RGs:
Which mechanisms trigger radio activity? - mergers/collisions/interactions/cold accretion What is feeding the black hole? - circumnuclear regions: accretion disks/tori/infall/outflow Why are some galaxies active while others are not? Do all galaxies experience a phase of AGN activity? Do different classes of radio sources get triggered in the same Is way? Centaurus A How long does a burst of activity last (re-current phases of a special case? activity)? Impact on cosmology (e.g. feedback) Evolution of nuclear activity with redshift



Outline





A complete sample of nearby Radio Galaxies (RGs) - large-scale properties Circumnuclear regions - circumnuclear disks/infall/outflow Summary and Outlook


A complete sample of nearby Radio Galaxies
(Emonts et al. 2007; Emonts, Morganti, Struve et al. in prep.)


Radio Galaxy sample
Sample selection:


All low-luminosity radio galaxies selected from the B2-catalogue (Colla et al. 1970) with:






F408MHz > 0.2 Jy (Flux limit) z < 0.041 (Redshift limit) Excluding cluster galaxies



23 sources in total


Radio Galaxy sample
Distances B2 sample:

Cen A: D = 3.5 Mpc


Radio Galaxy sample
Average resolution (D = 70 Mpc):

~ 7 kpc
emission beam


Radio Galaxy sample
7 detections in emission:




Different morphologies HI mass range from few 1e7 to 1e10 Msun

B2 0055+30


radio-loud vs. radio-quiet:


radio-loud vs. radio-quiet:

Morganti et al. 2006, Oosterloo et al. 2009


B2 0258+35

radio-loud vs. radio-quiet:

?
Morganti et al. 2006, Oosterloo et al. 2009

B2 0331+39


Radio Galaxy sample


Radio Galaxy sample
Radio source size:

FR-I vs. Compact:

(Emonts et al. 2007)


Radio Galaxy sample
Radio source size:
Cen A

FR-I vs. Compact:

(Emonts et al. 2007)


Radio continuum size
WSRT

Cen A
Morganti et al 1999

HI observations

B2 0258+35
Struve et al in prep

WSRT 21cm continuum map


Radio Galaxy sample
Conclusions:





HI - detection rate 7/23 (~30%) Often no evidence for on-going or recent gas-rich mergers/collisions HI structures are old (>Gyr) and hence not directly linked to the current phase of radio activity ( same for Centaurus A!)



Detection rate agrees to first order with radio-quiet comparison sample. AGN activity cycle part of many (all) early-types?


Circumnuclear regions
Disks/Infall/Outflow


Circumnuclear absorption
van Gorkom et al. 1989




Originally only redshifted absorption detected (including Cen A, van der Hulst et al 1983) e.g. van Gorkom et al 1989 More recent results suggest that blueshifted absorption occurs at least as often as redshifted e.g. Vermeulen et al 2003,
Morganti et al 2005



Often red- and blueshifted absorption together detected (e.g. Cen A, B2 sample, ...)

Morganti et al. 2005


Centaurus A: The central ~100pc
Position-velocity diagram:

Morganti et al. 2008


Centaurus A: LBA observations
Peak spectrum:

On-going data reduction !!!


Centaurus A: LBA observations
Peak spectrum: Comparison:


Centaurus A: LBA observations
Peak spectrum: Comparison:


Circumnuclear disks


Circumnuclear disks
Other sources:






NGC 1275: Vermeulen et al 1994 Hydra A: Taylor 1996 NGC 4261: van Langevelde et al 2000 1946+708: Peck & Taylor 2001
Cygnus A: Struve & Conway 2009

Cygnus A

-------------------------------------

1946+708
Peck & Taylor 2001

Hydra A
Jones 1996


Summary


Centaurus A is by far the closest FR-I galaxy

Large-scale properties


: Classical FR-I sources like Cen A do not contain large amounts of HI (>1e9Msun) but can contain some HI Often no evidence for on-going or recent gas-rich mergers/collisions causing the current phase of AGN activity No apparent difference between radio-loud and radio-quiet early-type galaxies Broad red- and blueshifted absorption around Vsys detected in Cen A and many other sources Evidence for atomic circumnuclear disks in a number of sources, including Cen A No evidence for direct HI fuelling of the BH is found

Circumnuclear region:



Future Work
Near future:


Analyse LBA observations of Centaurus A

Future (ideas):


Larger statistical sample to confirm trends (which are based on very small numbers) ­ investigate findings in more detail: - ASKAP HI all-sky proposal: Radio Galaxies are part of it (~150 detections expected) - CO ALMA follow-up of the detections (central beam) (pilot study with Apex started)