Starbursts and the triggering of the activity in low redshift radio galaxies

1
Starbursts and the triggering of the activity in
low redshift radio galaxies

• Clive Tadhunter
• University of Sheffield

Collaborators J. Holt, D. Dicken, C. Ramos
Almeida, R. Gonzalez Delgado, R. Morganti, J.
Rodriguez-Zaurin, K. Inskip, K. Wills
2
Triggering mechanisms

• Galaxy mergers and interactions (Heckman et al.
  1986, Smith Heckman 1989)
• Accretion of gas from hot X-ray haloes
• - Bondi accretion of hot gas (Allen et al.
  2006,
• Best et al. 2006, Hardcastle et al.
  2007, Buttiglione et al. 2009)
• - Accretion of cool gas from cooling flow
• (e.g. Bremer et al. 1997)
• Cold accretion from large-scale filamentary
  structures (e.g. Keres 2005, Dekel et al. 2009)

3
Evidence for galaxy interactions and mergers in
non-starburst radio galaxies
Deep GeminiGMOS imaging observations of 2Jy
sample
A large proportion of nearby radio galaxies show
evidence for morphological disturbance consistent
with triggering in major galaxy mergers and
interactions (see talk by Cristina Ramos Almeida)
4
Triggering starbursts in major galaxy mergers
Cox et al. (2008)
5
Starbursts in radio galaxies occurrence

• Starburst rate from optical spectroscopy I
• - 2Jy(0.15 lt z lt 0.7) 20 -- 35 (22
  objects)
• Tadhunter et al. (2002)
• - 3CR(zlt0.2) 33 (14 objects)
• Aretxaga et al. (2001), Wills et al.
  (2002)
• - 2Jy (zlt0.08, FRIs) 25 (12 objects)
• Wills et al. (2004)
• UV imaging with HST
• - 3C (zlt0.1) 100 HEG (6 objects) 5 LEG
• Baldi et al. (2008)
• Detection of PAH at mid-IR wavelengths
• - 3C (zlt0.1, FRIs) 75 (24 objects)
• Leipski et al. (2009)
• Combined opticalfar-IR continuum excessMFIR
  coloursPAH
• - 2Jy(0.05 lt z lt 0.7) 15--35
• Dicken et al. (2009,2010)

UV and PAH techniques particularly sensitive
to low levels of SF, especially if level of AGN
activity weak
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The reddened nuclear starburst in 3C305
WHT/ISIS
Starburst Properties Age 0.4 - 0.9
Gyr E(B-V)0.4 - 0.8 mag Mass1.5/-0.5x1010
Msun (16 - 40 of total stellar mass)
Hd
Bruzual Charlot(1996) models Salpeter IMF
(0.1-125 Msun)
CaII K
3C305 (z0.042) Heckman et al. 1986
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Starburst dominated Objects (zgt0.15)
3C459 (z0.22) NTTEMMI
YSP Properties Age 0.05 Gyr Mass4x109 Msun (gt5
of total stellar mass in slit)
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Objects with v.young starburst components
PKS0023-26 (z0.340) - VLT/FORS2
PKS0409-75 (z0.69) - VLT/FORS2
YSP age 30Myr Reddening E(B-V)0.8 YSP mass
proportion 9
YSP age 10Myr Reddening E(B-V)0.9 YSP mass
proportion 4
These objects have - Low UV polarization -
Relatively weak narrow lines - No broad lines
detected
Holt et al. (2007)
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The Ages of the YSP in ULIRG and PRG
Tadhunter et al. (2005) Holt et al.
(2006,2007) Wills et al. (2008) Tadhunter et al.
(2010)
Rodriguez-Zaurin et al. (2007,2008,2009,2010)
Typical maximum age of radio source
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Two main groups of starburst radio galaxies

• LIRG/ULIRG-like systems (tysp lt 0.1Gyr)
• - Most have
• - Radio source triggered quasi-simultaneously
  
• with starburst
• Post-starburst systems (tysp gt 0.2 Gyr)
• - Most have
• - Radio source triggered (or retriggered) a
  significant period after the starburst episode

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Starburst radio galaxies general properties

• Based on a detailed spectrosynthesis modelling of
  a sample of
• 22 radio galaxies with good evidence for YSP
• 95 of starburst radio galaxies show signs of
  morphological disturbance (tidal tails, fans,
  shells, dust lanes, double nuclei etc.)
• Young stellar populations (YSP) contribute a
  significant proportion of the total stellar
  masses (5-40)
• The YSP are spatially extended -- they generally
  detected across the full extents of the host
  galaxies over which accurate measurements can be
  made (although brightest in the nuclei)

Overall, the results are consistent with the
triggering of the activity in major, gas-rich
galaxy mergers/interactions
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Merger sequence for starburst radio galaxies
3C459
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Cooling flow driven activity in Hydra A?
GeminiGMOS
Hydra A, z0.054, FRI
SpitzerIRS
The similarity between the SRF rate and hot
X-ray cooling rate is consistent with triggering
by a cooling flow
Rafferty et al. (2006)
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PKS0023-26 a compact radio source at the centre
of a cluster
PKS0023-26 z0.322, CSS
SpitzerIRS
PAH
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Star Formation in 4C41.17 at z3.8?
La
Dunlop et al. 1994
Star formation rate 2,000 - 10,000 M0/yr
Dey et al. 1997
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3C Radio Galaxies at 60mm with IRAS
Only 30 of 3CR radio galaxies at zlt0.5 were
detected by IRAS at 60mm
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Spitzer/MIPS observations of complete samples of
radio-loud AGN

• 2Jy sample
• S2.7GHz gt 2.0 Jy
• Intermediate redshifts (0.05 lt z lt 0.7)
• Steep radio spectra (a1.4-5GHz lt -0.5)
• 46 objects

• 3CRR sample
• S178MHz gt 10.0 Jy
• Low redshifts (z lt 0.1)
• FRII only
• 19 objects

• Spitzer/MIPS detection rates 100 at 24?m and
  90 at 70?m
• All objects have deep optical spectra, allowing
  accurate
• spectral classification, measurements of
  emission line
• luminosities, and assessment of stellar
  population mix

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Correlations between MFIR and optical properties

• The 24?m luminosity is
• strongly correlated with the
• OIII?5007 emission line
• luminosity
• The 70?m luminosity is
• also strongly correlated with
• the OIII luminosity, but
• with increased scatter
• The slopes of the 24?m and
• 70?m correlations are similar

Tadhunter et al. (2007), Dicken et al. (2008,2009)
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The starburst contribution to the far-IR
SB Heating
AGN Heating

• The far-IR emitting dust is predominantly heated
  by AGN illumination
• Starburst heating only significant in a minority
  of objects (17 -- 35)

Tadhunter et al. (2007) Dicken et al. (2009, 2010)
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A simple model for the dust/emission line
structures

• Assume that both the emission lines and MFIR
  emission produced by AGN illumination
• Covering factors of mid-IR
• and far-IR emitting dust structures, and NLR
• Cmir, Cfir and Cnlr

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Energetic feasibility of AGN illumination
Dicken et al. (2009)

• Allowing for a modest amount of intrinsic
  extinction, it is
• plausible that much of the far-IR continuum is
  in most radio
• galaxies is produced by AGN illumination of the
  NLR clouds

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Triggering non-starburst radio galaxies

• Non-starburst radio galaxies make up gt60 of the
  population of powerful radio galaxies
• Most non-starburst RG belong to the class of
  strong-lined objects that are thought to be
  powered by cold accretion
• Triggering possibilities include
• - Gas accretion in a tidal encounter, or
  around the time of
• first pass of nuclei in a merger
• - Re-triggering the activity a substantial
  period
• (gt1Gyr) after the major merger-induced
  starburst
• - Minor mergers (gt31 mass ratio)

23
Triggering starbursts in major galaxy mergers
Cox et al. (2008)
24
Evidence for galaxy interactions and mergers in
non-starburst radio galaxies
Deep GeminiGMOS imaging observations of 2Jy
sample 0.05 lt z lt 0.7, 46 objects, r or i band
85 of the non-starburst radio galaxies in 2Jy
sample show signs of morphological disturbance
(Ramos Almeida et al. 2009)
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How do the WLRG fit in?

• Commonly proposed that weak line radio galaxies
  (WLRG) are triggered/fuelled by Bondi accretion
  of the hot ISM in the host galaxies/clusters
• But significant proportion of the optical
  starburst radio galaxies (40) -- particularly
  those with older young stellar populations --
  are WLRG (e.g. Fornax A, Cen A, Hydra A,
  PKS034709, PKS0620-52, 3C213.1, 3C236, 3C292,
  NGC612)
• The presence of SF provides evidence of cold
  accretion into the circum-nuclear regions of some
  WLRG
• Most such objects show evidence for a rich ISM in
  the form of dust lanes many also show PAH
  features in their mid-IR spectra

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Star formation in Fornax A
Evidence for young stellar populations -
Diffuse stellar light has luminosity weighted
age 2-3 Gyr (Kuntschner 2002) - Globular
clusters have ages 3/-0.5 Gyr (Goudfrooij et
al. 2003) ----gt current galaxy formed from a
major merger of gas-rich galaxies 2-3 Gyr ago
HSTACS Goudfrooij et al. (2005)
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The double AGN in PKS034705
WLRG
SpitzerIRS
This WLRG is clearly in an interacting system
with a rich ISM and plenty of star formation.
PAH
Sy 1
z0.339, FRII
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A torus in the WLRG PKS0043-42?
PKS0043-42 z0.116, FRII
SpitzerIRS
Silicate absorption
Dicken et al. (2010)
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Detection of weak PAH in nearby FRI galaxies

• 75 of the sample of 24 nearby FRI radio galaxies
  presented by Leipski et al.(2009) show PAH
  features
• Possible evidence for low-level star formation in
  the circum-nuclear regions

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Evidence for a rich ISM in the nuclear regions of
WLRG

• Dust lanes (e.g. Fornax A, Cen A, Hydra A)
• Circum-nuclear (warm) gas disks (e.g. M87), and
  cool molecular disks
• Detection of hot dust emission at mid-IR
  wavelengths (e.g. PKS0043-42, Leipski et al.
  2009)
• Detection of PAH features in mid-IR spectra of a
  large proportion of nearby FRI sources (Leipski
  et al. 2009)
• Detection of compact emission line regions
  associated with the compact optical cores of FRI
  radio sources (e.g. Capetti et al. 2005)

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Conclusions

• Most SB radio galaxies consistent with triggering
  in major gas-rich mergers but triggering can
  occur before, around or a long time after the
  coalescence of the merging nuclei
• Non-starburst radio galaxies also likely to be
  triggered in galaxy mergers and interactions (but
  much earlier or later in sequence, or by more
  minor mergers)
• Radio-loud AGN activity is not solely associated
  with a particular phase of unique type of gas
  accretion event
• The heating of the far-IR emitting dust is likely
  to be dominated by AGN illumination in the
  majority of PRG the far-IR doesnt always
  provide a good diagnostic of SF
• Evidence for cool/warm gas accretion into the
  circum-nuclear regions of WLRG

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Correlation analysis -- 2Jy sample
L24 vs Lrad
L24 vs LOIII
LOIII vs Lrad
L24 vs z
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An evolutionary link with ULIRGs?

• Some powerful radio galaxies are ULIRGs (3C48,
  PKS134512, PKS1549-79, PKS2135-20, 3C459)
• ULIRG radio galaxies have stellar populations
  properties similar to the general population of
  ULIRGs (tysp lt 0.1 Gyr)
• The stellar masses of the intermediate age,
  post-starburst stellar populations in some radio
  galaxies are consistent with the idea that they
  have evolved from ULIRG/LIRGs

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ULIRG/starburst radio galaxy stellar mass
comparison
Nearby 1Jy ULIRGs (zlt0.18) (Rodriguez Zaurin et
al. 2009, 2010)
Not all starburst radio galaxies can have
evolved from ULIRGs
Starburst radio galaxies (zlt0.7) (Tadhunter et
al. 2010)
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Star formation in major mergers
Springel et al. (2005)
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Activity and galaxy evolution
Evolution of activity and star formation
Black hole vs. galaxy bulge properties
z
Dunlop Peacock 1990, Madau 1987
Tremaine et al. (2002)
Triggering?
Feedback?
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Outstanding questions