The luminosity-dependent evolution of the radio luminosity function

The luminosity-dependent evolution of the radio luminosity function

The luminosity-dependent evolution of the radio luminosity function

Emma RigbyEmma RigbyUniversity of NottinghamUniversity of Nottingham

Collaborators: P. Best, M. Brookes, J. Dunlop, J. Collaborators: P. Best, M. Brookes, J. Dunlop, J. Peacock, L. Ker, H. Rottgering, J. WallPeacock, L. Ker, H. Rottgering, J. Wall

Emma RigbyEmma RigbyUniversity of NottinghamUniversity of Nottingham

Collaborators: P. Best, M. Brookes, J. Dunlop, J. Collaborators: P. Best, M. Brookes, J. Dunlop, J. Peacock, L. Ker, H. Rottgering, J. WallPeacock, L. Ker, H. Rottgering, J. Wall

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Why study radio galaxy evolution?Why study radio galaxy evolution?

• Important for Important for galaxy evolution galaxy evolution models via models via feedbackfeedback

• Radio-loud AGN Radio-loud AGN powered by most powered by most massive black massive black holes so provide holes so provide information on information on upper end of black upper end of black hole mass function hole mass function

• Important for Important for galaxy evolution galaxy evolution models via models via feedbackfeedback

• Radio-loud AGN Radio-loud AGN powered by most powered by most massive black massive black holes so provide holes so provide information on information on upper end of black upper end of black hole mass function hole mass function

Model of a radio-loud AGN (Urry & Padovani)

Model of a radio-loud AGN (Urry & Padovani)

The evolving radio luminosity function (RLF)

The evolving radio luminosity function (RLF)

• Comoving space density of radio galaxies increases to z Comoving space density of radio galaxies increases to z ~2 (Dunlop & Peacock 1990), with indications of a ~2 (Dunlop & Peacock 1990), with indications of a decline at higher redshiftdecline at higher redshift

• Previous work lacked depth & volume necessary to probe Previous work lacked depth & volume necessary to probe high-z behaviorhigh-z behavior• Motivated development of Motivated development of CENSORSCENSORS - a faint radio source - a faint radio source

sample (Ssample (S1.4GHz1.4GHz > 7.2 mJy) > 7.2 mJy)• 73% spectroscopically complete (Brookes et al. 2008)73% spectroscopically complete (Brookes et al. 2008)

• Investigate using a grid-based modelling technique with Investigate using a grid-based modelling technique with no assumptions made about the RLF behaviorno assumptions made about the RLF behavior

• Comoving space density of radio galaxies increases to z Comoving space density of radio galaxies increases to z ~2 (Dunlop & Peacock 1990), with indications of a ~2 (Dunlop & Peacock 1990), with indications of a decline at higher redshiftdecline at higher redshift

• Previous work lacked depth & volume necessary to probe Previous work lacked depth & volume necessary to probe high-z behaviorhigh-z behavior• Motivated development of Motivated development of CENSORSCENSORS - a faint radio source - a faint radio source

sample (Ssample (S1.4GHz1.4GHz > 7.2 mJy) > 7.2 mJy)• 73% spectroscopically complete (Brookes et al. 2008)73% spectroscopically complete (Brookes et al. 2008)

• Investigate using a grid-based modelling technique with Investigate using a grid-based modelling technique with no assumptions made about the RLF behaviorno assumptions made about the RLF behavior

RLF Modelling: input dataRLF Modelling: input data• 5 input radio source samples5 input radio source samples

• Wall & Peacock 1985,Wall & Peacock 1985,• Parkes selected regions, Parkes selected regions,

(Downes et al 1986),(Downes et al 1986),• CENSORS (Best et al. 2003)CENSORS (Best et al. 2003)• Hercules, (Waddington et al. Hercules, (Waddington et al.

2001)2001)• VLA-COSMOS, (Smolcic et al. VLA-COSMOS, (Smolcic et al.

2008)2008)

• Local radio luminosity Local radio luminosity functions covering ~20 < Log functions covering ~20 < Log PP1.4GHz1.4GHz < 27 < 27 (Best et al., 2010; Sadler et al., (Best et al., 2010; Sadler et al., 2002; Mauch et al., 2007)2002; Mauch et al., 2007)

• Integrated source counts Integrated source counts covering 0.05 mJy to 94 Jy covering 0.05 mJy to 94 Jy (Bondi et al. 2008; Seymour et al. (Bondi et al. 2008; Seymour et al. 2004; Windhorst et al. 1984; 2004; Windhorst et al. 1984; White et al. 1997; Kellermann & White et al. 1997; Kellermann & Wall 1987)Wall 1987)

• 5 input radio source samples5 input radio source samples• Wall & Peacock 1985,Wall & Peacock 1985,• Parkes selected regions, Parkes selected regions,



2008)2008)



The radio-power - redshift plane covered by the 5 samples

The radio-power - redshift plane covered by the 5 samples

RLF Modelling: input dataRLF Modelling: input data• 5 input radio source samples5 input radio source samples

• Wall & Peacock 1985,Wall & Peacock 1985,• Parkes selected regions, Parkes selected regions,



2008)2008)



• 5 input radio source samples5 input radio source samples• Wall & Peacock 1985,Wall & Peacock 1985,• Parkes selected regions, Parkes selected regions,



2008)2008)


• Integrated source counts Integrated source counts covering 0.05 mJy to 94 Jy covering 0.05 mJy to 94 Jy (Bondi et al. 2008; Seymour et al. (Bondi et al. 2008; Seymour et al. 2004; Windhorst et al. 1984; 2004; Windhorst et al. 1984; White et al. 1997; Kellermann & White et al. 1997; Kellermann & Wall 1987)Wall 1987) The CENSORS redshift distributionThe CENSORS redshift distribution





Modelling TechniqueModelling Technique

RedshiftRedshift

Radio PowerRadio Power

Space densitiesSpace densities

RLFRLF Cosmic evolutionCosmic evolution

Modelling TechniqueModelling Technique3 input radio-luminosity - redshift (P,z) density grids: 21 points in

log P (19.25 < Log P < 29.25) and 8 points in z (0.1 < z < 6)3 input radio-luminosity - redshift (P,z) density grids: 21 points in

log P (19.25 < Log P < 29.25) and 8 points in z (0.1 < z < 6)

Steep Steep spectrum spectrum

gridgrid


gridgrid

Flat Flat spectrum spectrum

gridgrid


gridgrid

Starforming Starforming gridgrid


Created by evolving the local starforming

galaxy luminosity function

Created by evolving the local starforming

galaxy luminosity function

Taken as the median of the

evolutionary models of Dunlop &

Peacock 1990

Taken as the median of the

evolutionary models of Dunlop &

Peacock 1990

Starting estimate created by evolving the local AGN RLF

by (1+z)3

Starting estimate created by evolving the local AGN RLF

by (1+z)3

Modelling TechniqueModelling Technique3 input radio-luminosity - redshift

(P,z) density grids3 input radio-luminosity - redshift

(P,z) density grids


gridgrid


gridgrid


gridgrid


gridgrid



Integrate to form 3 flux-density - redshift (S,z) grids containing source numbers


Compare to input datasets


Amoeba minimisation - varies

steep grid only


steep grid only

Modelling TechniqueModelling Technique3 input radio-luminosity - redshift

(P,z) density grids3 input radio-luminosity - redshift

(P,z) density grids


gridgrid


gridgrid


gridgrid


gridgrid








steep grid only


steep grid only

Assuming = 0.83+0.4log(1+z) for

steep; = 0.8 for starforming & = 0

for flat grids

Assuming = 0.83+0.4log(1+z) for

steep; = 0.8 for starforming & = 0

for flat grids

Marginalised errors calculated from a Hessian

matrix

Marginalised errors calculated from a Hessian

matrix

Results: dataset comparisonResults: dataset comparison

Local radio luminosity function

Local radio luminosity function

Radio source samples

Radio source samples

Integrated source counts

Integrated source counts

Model good fit to input data

Model good fit to input data

Results: model luminosity functions


Dashed line: median of Dunlop & Peacock (1990) resultsDashed line: median of Dunlop & Peacock (1990) results





Blue: lack of coverage in local RLF Green: Incomplete coverage of radio power - redshift planeBlue: lack of coverage in local RLF Green: Incomplete coverage of radio power - redshift plane

Robustness testingRobustness testing

Randomly moving the redshift limits to higher valuesRandomly moving the redshift limits to higher values

Varying the spectral index used to calculate the steep source number grid

Varying the spectral index used to calculate the steep source number grid

Redshift cutoffs still presentRedshift cutoffs still present

The high redshift cutoffThe high redshift cutoff

• High redshift cutoffs seen High redshift cutoffs seen across the radio power rangeacross the radio power range

• Cutoffs still present when Cutoffs still present when model parameters are variedmodel parameters are varied

• Need ~5 extra sources in Need ~5 extra sources in CENSORS sample to reduce CENSORS sample to reduce the cutoff strength to <3the cutoff strength to <3 for 27 < log P < 28for 27 < log P < 28

• Position of cutoff appears to Position of cutoff appears to be radio luminosity -be radio luminosity -dependent dependent

• High redshift cutoffs seen High redshift cutoffs seen across the radio power rangeacross the radio power range

• Cutoffs still present when Cutoffs still present when model parameters are variedmodel parameters are varied

• Need ~5 extra sources in Need ~5 extra sources in CENSORS sample to reduce CENSORS sample to reduce the cutoff strength to <3the cutoff strength to <3 for 27 < log P < 28for 27 < log P < 28

• Position of cutoff appears to Position of cutoff appears to be radio luminosity -be radio luminosity -dependent dependent

The future…The future…

• Larger radio source samplessamples will mean RLF evolution of different populations can be studied individually

• e.g. FRI vs FRII or Low vs High excitation sources

• Larger radio source samplessamples will mean RLF evolution of different populations can be studied individually

• e.g. FRI vs FRII or Low vs High excitation sources

Predictions for the LOFAR-deep survey [dashed line - FRIs, solid line - starforming galaxies, dot-dashed line - radio quiet quasars, dotted line - FRIIs]

Predictions for the LOFAR-deep survey [dashed line - FRIs, solid line - starforming galaxies, dot-dashed line - radio quiet quasars, dotted line - FRIIs]

FRIs

FRIIs

Starforming galaxies

The future…The future…• Luminosity dependence seen for cutoff needs to be

incorporated into SKA population models• Luminosity dependence seen for cutoff needs to be

incorporated into SKA population models

Red dashed line computed from S3 SKADS simulations (Wilman et al. 2008)

ConclusionsConclusionsConclusionsConclusions

• Using our new grid-based modelling have Using our new grid-based modelling have found clear high-redshift cutoff in the RLFfound clear high-redshift cutoff in the RLF

• Cutoff appears to move to higher redshift Cutoff appears to move to higher redshift

at higher radio powerat higher radio power

• Results still limited by uncertain redshifts Results still limited by uncertain redshifts & small radio samples& small radio samples

Documents

The luminosity-dependent evolution of the radio luminosity function