Past, Present and Future Star Formation in High Redshift Radio Galaxies

Nick Seymour (MSSL/UCL)

22nd Nov 2009 - Powerful Radio Galaxies

Past, Present and Future Star Formation in High Redshift Radio Galaxies

Nick Seymour (MSSL/UCL)

22nd Nov 2009 Powerful Radio Galaxies

IRAC false-colour image of 4C23.56

High-z Radio Galaxies

• Powerful active nuclei from massive black holes

High-z Radio Galaxies

• Powerful active nuclei from massive black holes

• High host galaxy masses imply DMH by z=0 of ~1014M

Connection Between Star Formation and Black Hole Growth

• Correlation between central black hole mass and host galaxy bulge mass

• Similar shape of black hole and galaxy mass function

• Similar evolution over cosmic time• Some direct evidence, e.g. outflows

Connection Between Star Formation and Black Hole Growth

• Correlation between central black hole mass and host galaxy bulge mass

• Similar shape of black hole and galaxy mass function

• Similar evolution over cosmic time• Some direct evidence, e.g. outflows• Keep the theoreticians happy!

High-z Radio Galaxies Are Unique Laboratories to Study Star Formation

• Past stellar assembly can be derived from current stellar population (near-IR: stellar mass)

• Current star formation (sub-mm: far-IR luminosities and PAH: UV ionisation strength)

• Future star formation (environmental studies: future mergers and tidal interactions)

Measures of Star Formation Past

K-z or Hubble diagram for radio galaxies

Rocca-Volmerange et al. 2004

K-z or Hubble diagram for radio galaxies

Rocca-Volmerange et al. 2004

1012M

H-band Stellar Luminosities of HzRGs

SHzRG sample: z>1 L3GHz>1026WHz-1 Seymour et al. 2007, De Breuck et al. 2010

StellarLuminosities

Stellar masses of HzRGs

Galaxy Mass(Kroupa IMF)

Now 7Gyr 10Gyr Look back time

Seymour et al. 2007, De Breuck et al. 2010

Stellar Mass/Radio Luminosity Relation

*

* selection function biased towards red ellipticals (Donoso et al. 2008) and 1.4GHz converted to 3GHz assuming spectral index of -0.8

Seymour, De Breuck et al. 2010

Measures of Star Formation Present

Current constrains on SFR

SFRs inferred from sub-mm detections

SFR

Current constrains on SFR

SFRs inferred from sub-mm detections

SFR/stellar mass

Current constrains on SFR

1/SSFR

Current constrains on SFR

Star formation in High Redshift Radio Galaxies

• PAH emission features + lots of cold dust = high star formation rate

• This massive galaxy is still growing extremely rapidly

• Direct observations of coeval black hole and host galaxy growth

Seymour et al. (2008)

Further IRS Spectroscopy of HzRGs

J. Rawlings et al. (2010)

Aim: to study SFR as function of radio luminosity and radio morphology at z~2.

Further IRS Spectroscopy of HzRGs

J. Rawlings et al. (2010)

Measures of Star Formation Yet to Come

Future of Growth of Radio Galaxies

• MRC 1138-262 (the Spiderweb galaxy) at z=2.157 will eat or destroy most of its companions by z=0 (Hatch et al. 2009).

• 4c23.56 (z=2.483) has a companion galaxy with similar mass, 4C23.56 ER1 (A. Stockton et al., 2004) at 30asec ~240kpc with a merging time of ~5Gyrs (hence likely major merger of ~5x1011M at z~0.6)

MRC 1138-262Spiderweb GalaxyMiley et al. (2006)

ACS greyscaleRadio contoursLyman Alpha

4c23.56 z=2.48

24um images

Over-densities at 24um Around Radio Galaxies

Other environmental evidence

• Red sequence seen around z~1.5 HzRGs, over abundance of AGN (Galametz et al. 2009)

• Red and passive galaxies seen around z~3 HzRGs (Doherty et al. 2009)

Questions related to star formation:

• Are all HzRG massive? Does radio luminosity depend on stellar mass (i.e. mass of the central black hole)?

• Are environments of HzRGs with given stellar mass the similar? Can we trace the stellar mass function in (HzRG-selected) over-dense environments?

• What is the present SFR of HzRGs? How is the SFR related to black hole accretion and jet activity?

• What is the future evolution of a HzRG and its proto-cluster?

“Galaxies' courses will foreshadow certain ends, to which they must lead”

- paraphrasing Charles Dickins