The evolution of radio luminosity
function of star forming galaxies
and AGNs up to 𝑧 ∼ 5.5
Kai Kono, Tsutomu T. Takeuchi
Nagoya University
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1. Introduction
 Cosmological evolution of physical properties of galaxy

2. Data VLA-COSMOS 3GHz large survey (Smolcic et al. 2017)

3. Method 𝐶 − method

4. Result

5. Discussion
 The differential number counts, redshift distribution,
SFRD evolution, NC+GL

Introduction: galaxy evolution
The physical properties of galaxies evolves through cosmic time(e.g., star formation rate density (SFRD), SMBH accretion rate).
Look back time Gyrlog SFRD, 𝜓 𝑀⊙ yr −1 Mpc −3

The Cosmic Noon
The peak of galaxy
interaction and star forming
activity (Hopkins et al. 2008,Popping et al. 2017).
The mass accretion rate onto
SMBH is also the highest(Caplar et al. 2018).
redshift
Madau & Dickinson (2014)

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Introduction: galaxy evolution
The physical properties of galaxies evolves through cosmic time(e.g., star formation rate density (SFRD), SMBH accretion rate).

log SFRD, 𝜓 𝑀⊙ yr −1 Mpc −3

Look back time Gyr

The Cosmic Dawn
Active galaxy formation.
Epoch of reionization:𝑧 = 6 ∼ 15 − 20

Observational constraint
Galaxy number counts &Luminosity function
redshift
Madau & Dickinson (2014)

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The aim of this study
Assess the parameter of luminosity
function for each redshift ranges
Construct a evolution model onstar forming galaxy (SFG) andactive galactic nuclei (AGN)
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Galaxy number counts sr −1

Introduction: empirical constrains on galaxy evolution
through number counts (NC)constant

In the past, the luminosityof galaxy is…
brighter
The NC increases
fainter
The NC decreaseslog(Flux μJy )4/16

Introduction: gravitational lensing (GL)Bias on number counts: gravitational lensing
Differential number counts Jy −1 deg −2

Increase of NC due tothe effect of GL.
In submillimeter band,
approximately 60% of NC
shows effect of GL atmaximum.

Flux Jy

Lima et al. (2010)

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Data: VLA-COSMOS 3GHz Large ProjectRegion

VLA-COSMOS field(1.77deg 2 )Number ofsample

10,830 (𝑆 𝑁>5)

Reference

The deepest radio survey

𝑆lim = 11.0 μJy , 𝑧 < 5.5

Dec.

Feature1.4deg × 1.4degSmolcic et al. (2017)

Karl G. Jansky Very large array (VLA)

R.A.
redshift
www.vla.nrao.edu/

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Data: selection
Color (Ilbert et al. 2010)

Blue & Green: 𝑀NUV − 𝑀𝑟 < 3.5
Radio excess; 3𝜎 (Delvecchio et al. 2017)

𝐿1.4GHzlog> 21.984 1 + 𝑧 0.013
SFR IR

Red: 𝑀NUV − 𝑀𝑟 > 3.5
Herschel detection

SFG (4,647)

Non Herschel detection

AGN (1,814)
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𝐶 − method (Lynden-Bell 1971)
 𝐶 − method is not affected by cosmic variance.
Luminosity function inferred from mock sample with a cluster.
𝐶 − method

Distortedby cluster

Absolute magnitude [mag]𝜙 [Mpc −3 mag −1 ]𝜙 [Mpc −3 mag −1 ]1 𝑉max method

No distortion

Absolute magnitude [mag]Takeuchi et al. (2000)

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Results: 3GHz luminosity function
The bright end of luminosity function is dominated by AGN andthe faint end is dominated by SFG for all nine redshift ranges.
𝑧 = 0.7 − 1.0

𝜙 Mpc −3 dex −1

We assumed pure luminosity
evolution model (PLE) and theredshift dependency of parameter𝐿∗ is modeled as below.

𝐿∗ 𝑧 = 𝐿∗,0 1 + 𝑧 𝑄 𝑧with 𝑄 𝑧 = 𝛼1 + 𝛼2 𝑧
log L3GHz [W Hz −1 ](The error shows 95% confidence interval estimated with bootstrap method)

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Results: redshift dependency of 𝐿∗
The SFG has a peak at 𝑧 ∼ 3 𝑡cos ∼ 2.2 Gyr and AGN have apeak at z ∼ 2 𝑡cos ∼ 3.3 Gyr .

Star formation triggered bygalaxy merger.
𝜏 = 0.5 − 1 Gyr
Mancuso et al. (2016)

log 𝐿∗ [W Hz −1 ]The time lag is Δ𝑡cos ∼ 1Gyr.

SF suppression due to AGN
feedback.
redshift

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Square Kilometre Array: SKAComparison

All skyarea (deg 2 )WideDeep
Ultradeep

sensitivity:
102 timesarea:
104 times

VLACOSMOS

Detection limit
𝑆lim,1.4GHz
Prandoni & Seymour (2015)

High angular resolution,
High sensitivity,
Large observation area
Constraints on highredshift universe physics.
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Discussion
Redshift dependency of 𝐿∗ 𝑧 Redshift distribution, SFRD history
 Estimation of number counts in the SKA
surveys

Assessment of the effect of gravitational lensing
on galaxy number counts.
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Discussion: galaxy number counts

Differential number counts Jy1.5 sr −1The comparison of Euclid normalized differential galaxy number
counts between the model and observation.
 Bright end (𝑆3GHz > 1 mJy)
𝑆1GHz = 1 μJy

About 90% of NC isdominated by AGN.

 Faint end (𝑆3GHz < 10 𝜇Jy)
With SKA-wide survey
detection limit, about 90% ofNC is dominated by SFG.
Flux μJy

13/16Discussion: galaxy number counts

Differential number counts Jy1.5 sr −1

The comparison of Euclid normalized differential galaxy number
counts between the model and observation.
 Bright end (𝑆3GHz > 1 mJy)𝑆1GHz = 1 μJy

About 90% of NC isdominated by AGN.

 Faint end (𝑆3GHz < 10 𝜇Jy)
With SKA-wide survey
detection limit, about 90% of
NC is dominated by SFG.
Flux μJy

13/16Discussion: redshift dependency of SFRD
• SFR estimation from 3GHz radio datalog(SFRD) 𝑀⊙ yr −1 Mpc −3

3GHz
𝑞 = 2.34 (Dale & Helou 2002)

FIR
𝐿IR = 1.91𝐿FIR (Magnelli et al.
2015)

IRSFR 𝑀⊙

redshift

SFRyr −1

𝐿IR 𝐿⊙=5.8 × 109(Kennicutt 1998)

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Discussion: redshift dependency of SFRD
For 𝑧 < 2:log(SFRD) 𝑀⊙ yr −1 Mpc −3

The SFRD is consistent with thevalue estimated from UV andIR observations.
For 𝑧 > 2:
The SFRD is larger by factor 2-3.

The results with radio observation(Karim et al. 2014, 𝑧 < 3) isconsistent with this model.
redshift

This result indicates the 𝑞 value (or IR-radio ratio) has lower
value at high redshift (c.f., Magnelli et al. 2015).
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Discussion: NC + GL
Differential number counts Jy1.5 sr −1

The assessment of the effect of lensing magnification on galaxy
number counts.
As for SFG, the contributionof lensed galaxies is up to 3%at S3GHz ∼ 100 μJy.

Approx. 3%
contributionlog(Flux[μJy])

As for AGN, the contributionis less than 0.5%.

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Conclusions
1. We assessed the 3GHz luminosity function
for samples 𝑧 < 5.5 with 𝐶 − method andconstructed the evolution model of galaxies.
2. SFRD history indicates the non-constancyof the radio-FIR relation at 𝑧 > 2.
3. The effect of gravitational lensing on thedifferential number counts is about 3% at𝑆3GHz ∼ 100 μJy for SFGs at most.
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