LOFAR Survey of Spatially ResolvedUltra-Steep Spectrum Sources(High-redshift Radio Galaxies at Low Frequencies)

Leah Morabito

Adam Deller, Javier Moldon, Raymond Oonk, George Miley, Huub

Röttgering, + LB working group

Leiden Observatory

The Many Facets of Extragalactic Radio Surveys

23 October 2015

Why are HzRGs important?

environments

protocluster

False color Herschel/SPIRE, Rigby+ (2014)

formation & evolution

radio galaxy

Image Credit: www.firstgalaxies.org

Morabito USS @ low-ν 1/16

HzRGs: Characteristics

Radio Synchrotron Relativistic plasma (Carilli et al)

Lyα Ionized gas (Kurk et al)

HzRGS  ARE  MASSIVE  GALAXIES    EMBEDDED  IN  HUGE  IONIZED  GAS  HALOs  

 SPIDERWEB  GALAXY  z  =  2.2    DEEP  IMAGE  WITH  HST    

(Miley et al. 2006, Astrophys. J. 650, 29L)  

~ 200 kpc

Huge ionized halosLyα (Kurk et al.)

Extended radio jets

Local overdensities of galaxies

- Optical alignment

- Ultra steep spectra- Energetic:> 1060 ergs

Morabito USS @ low-ν 2/16

Open questions...Selection from Miley & De Breuck (2008):

* What is the particle acceleration mechanism in the relativis-

tic plasma and why do HzRGs have much steeper radio spectra

than nearby radio sources?

* What are the detailed processes by which the radio jets in-

teract with the gas and trigger starbursts and how important is

jet-induced star formation for producing stars in the early Uni-

verse?

* What effect does feedback between the AGN and the galaxy

have on the evolution of HzRGs and the general evolution of

massive galaxies?

* What is the detailed mechanism by which the SMBHs produce

quasars and luminous collimated jets?

* What is the size distribution of radio-selected protoclusters

and what is is the topology of the cosmic web in the neighbour-

hood of the HzRGS?

Morabito USS @ low-ν 3/16

Open questions...Selection from Miley & De Breuck (2008):

* What is the particle acceleration mechanism in the relativis-

tic plasma and why do HzRGs have much steeper radio spectra

than nearby radio sources?

* What are the detailed processes by which the radio jets in-

teract with the gas and trigger starbursts and how important is

jet-induced star formation for producing stars in the early Uni-

verse?

* What effect does feedback between the AGN and the galaxy

have on the evolution of HzRGs and the general evolution of

massive galaxies?

* What is the detailed mechanism by which the SMBHs produce

quasars and luminous collimated jets?

* What is the size distribution of radio-selected protoclusters

and what is is the topology of the cosmic web in the neighbour-

hood of the HzRGS?

Morabito USS @ low-ν 3/16

Ultra Steep SpectraWhy do high-z sources have USS?

De Breuck et al. (2000)

Miley & De Breuck (2008)

Chambers et al. (1990)

Morabito USS @ low-ν 4/16

Ultra Steep SpectraWhy do high-z sources have USS?

De Breuck et al. (2000)

Miley & De Breuck (2008)

Chambers et al. (1990)

Morabito USS @ low-ν 4/16

Ultra Steep Spectra (USS)Why do high-z sources have USS?* Concavity at lower frequencies + K-correction

- Higher redshift : probe higher rest frequenciesAfonso et al. (2011), Miley & De Breuck (2008), Klamer et al. (2006), Athreya et al. (1998)

* Higher ambient density

- Reduce bulk velocity : steeper spectraKlamer et al. (2006), Miley & De Breuck (2008), Athreya et al. (1998)

* Luminosity–α relation + observational flux limits

- Higher L :more powerful jets : steeper spectraBlundell et al. (1999)

External: environmental, observationalvs.

Internal: particle acceleration processes

To resolve: need low frequencies & high resolution

Morabito USS @ low-ν 5/16

Ultra Steep Spectra (USS)Why do high-z sources have USS?* Concavity at lower frequencies + K-correction

- Higher redshift : probe higher rest frequenciesAfonso et al. (2011), Miley & De Breuck (2008), Klamer et al. (2006), Athreya et al. (1998)

* Higher ambient density

- Reduce bulk velocity : steeper spectraKlamer et al. (2006), Miley & De Breuck (2008), Athreya et al. (1998)

* Luminosity–α relation + observational flux limits

- Higher L :more powerful jets : steeper spectraBlundell et al. (1999)

External: environmental, observationalvs.

Internal: particle acceleration processes

To resolve: need low frequencies & high resolution

Morabito USS @ low-ν 5/16

Ultra Steep Spectra (USS)Why do high-z sources have USS?* Concavity at lower frequencies + K-correction

- Higher redshift : probe higher rest frequenciesAfonso et al. (2011), Miley & De Breuck (2008), Klamer et al. (2006), Athreya et al. (1998)

* Higher ambient density

- Reduce bulk velocity : steeper spectraKlamer et al. (2006), Miley & De Breuck (2008), Athreya et al. (1998)

* Luminosity–α relation + observational flux limits

- Higher L :more powerful jets : steeper spectraBlundell et al. (1999)

External: environmental, observationalvs.

Internal: particle acceleration processes

To resolve: need low frequencies & high resolutionMorabito USS @ low-ν 5/16

USS Survey

180 210 240 270 300 330 0 30 60 90 120 150 180

−60

−30

0

30

60

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● USS SampleHzRGs

3C 93C 368

4C 41.174C 39.37

4C 60.07

4C 72.26

4C 28.584C 24.28

4C 43.154C 48.48

4C 19.71

• z > 2• α < −1.0• &10 Jy at 30 MHz

• LAS > 5′′ 10 HzRGs

+ 1 low-z analog

Morabito USS @ low-ν 6/16

USS Survey: GoalsLow resolution Imaging

1. Characterize integrated low-ν spectra

High resolution Imaging

2. Study spatially resolved spectra to constrain

physical processes

• Determine spatial distribution of low-ν electrons• Compare lobes with each other as probe of

environmental conditions

3. Search for carbon radio recombination lines

• Probe of cold neutral medium

Morabito USS @ low-ν 7/16

USS Survey: GoalsLow resolution Imaging

1. Characterize integrated low-ν spectra

High resolution Imaging

2. Study spatially resolved spectra to constrain

physical processes

• Determine spatial distribution of low-ν electrons• Compare lobes with each other as probe of

environmental conditions

3. Search for carbon radio recombination lines

• Probe of cold neutral medium

Morabito USS @ low-ν 7/16

USS Survey: GoalsLow resolution Imaging

1. Characterize integrated low-ν spectra

High resolution Imaging

2. Study spatially resolved spectra to constrain

physical processes

• Determine spatial distribution of low-ν electrons• Compare lobes with each other as probe of

environmental conditions

3. Search for carbon radio recombination lines

• Probe of cold neutral medium

Morabito USS @ low-ν 7/16

USS Survey: Instruments

van Haarlem et al. (2013)

LBA

Carilli et al. (1997)

HBA

Morabito USS @ low-ν 8/16

USS Survey: Instruments

van Haarlem et al. (2013)

LBA

Carilli et al. (1997)

HBA

Morabito USS @ low-ν 8/16

USS Survey: Instruments

van Haarlem et al. (2013)

LBA

Carilli et al. (1997)

HBA

Morabito USS @ low-ν 8/16

USS Survey: Instruments

van Haarlem et al. (2013)

LBA

Carilli et al. (1997)

HBA

Morabito USS @ low-ν 8/16

186.00°188.00°190.00°192.00°RA (J2000)

+36.00°

+37.00°

+38.00°

+39.00°

+40.00°

+41.00°

+42.00°

Dec

(J2

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Low Resolution Imaging• baselines up to 83 km

• FoV: 8◦ @ 60MHz

• FWHM: 10′′@ 60MHz

• HzRGs not resolved

7 deg / 1.95MHz bandwidth / 7.5mJy rms

186.00°188.00°190.00°192.00°RA (J2000)

+36.00°

+37.00°

+38.00°

+39.00°

+40.00°

+41.00°

+42.00°

Dec

(J2

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Low Resolution ImagingPreliminary Results

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1e+01 1e+02 1e+03 1e+04 1e+05

1e+

27

1e+

28

1e+

29

1e+

30

1e+

31

Rest Frequency [MHz]

Res

t Fra

me

Lu

min

osit

y [W

Hz−1

]

4C +41.17α = 1.21

z = 3.79

LAS 11"

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1e+01 1e+02 1e+03 1e+04 1e+05

1e+

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1e+

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1e+

31

Rest Frequency [MHz]R

est

Fra

me

Lu

min

osit

y [W

Hz−1

]

4C +39.37α = 1.11

z = 3.22

LAS 11"

Some ultra-steep spectra remain ultra steep. Others may be

starting to turn over. Can spatially resolved images help solve

this?

Morabito USS @ low-ν 10/16

High Resolution ImagingWhat are some of the issues?

Sensitivity LBA has poor signal to noise

Clocks All stations are connected, only CS

are on the same clock

Correlator Model Baselines up to 1300 km lead to ge-

ometric errors/delays

Ionosphere Can be wildly varying, larger differ-

ential impact on long baselines

Calibrators Need compact, bright sources at

low-ν ... very few known

Traditional VLBI techniques can be used

(fringe-fitting)

Morabito USS @ low-ν 11/16

High Resolution ImagingWhat are some of the issues?

Sensitivity LBA has poor signal to noise

Clocks All stations are connected, only CS

are on the same clock

Correlator Model Baselines up to 1300 km lead to ge-

ometric errors/delays

Ionosphere Can be wildly varying, larger differ-

ential impact on long baselines

Calibrators Need compact, bright sources at

low-ν ... very few known

Traditional VLBI techniques can be used

(fringe-fitting)

Morabito USS @ low-ν 11/16

High Resolution ImagingWhat are some of the issues?

Sensitivity LBA has poor signal to noise

Clocks All stations are connected, only CS

are on the same clock

Correlator Model Baselines up to 1300 km lead to ge-

ometric errors/delays

Ionosphere Can be wildly varying, larger differ-

ential impact on long baselines

Calibrators Need compact, bright sources at

low-ν ... very few known

Traditional VLBI techniques can be used

(fringe-fitting)

Morabito USS @ low-ν 11/16

High Resolution Imaging

Now in official pipeline

Morabito USS @ low-ν 12/16

High Resolution Imaging: HBA145 MHz 1.6 GHz

LOFAR HBA MERLIN

Akujor et al. (1990)

3C 147

3C 295

Morabito USS @ low-ν 13/16

High Resolution Imaging: HBA

4.7 GHzCarilli+ (1997)

4C +39.37

Still see lobe-like structure at

low frequencies

Morabito USS @ low-ν 14/16

High Resolution Imaging: HBA

4.7 GHzCarilli+ (1997)

4C +39.37

Still see lobe-like structure at

low frequencies

Morabito USS @ low-ν 14/16

High Resolution Imaging: HBA

4.7 GHzCarilli+ (1997)

4C +39.37

Still see lobe-like structure at

low frequencies

Morabito USS @ low-ν 14/16

High Resolution Imaging: LBA

53 MHz

4.8 GHz

4C +43.15

Carilli et al. (1997)

∆ν =14 MHzrms=150 mJy bm−1

4.25 hr

PRELIMINARYPRELIMINARY

First LBA image using full International LOFAR!

Morabito USS @ low-ν 15/16

High Resolution Imaging: LBA

53 MHz

4.8 GHz

4C +43.15

Carilli et al. (1997)

∆ν =14 MHzrms=150 mJy bm−1

4.25 hr

PRELIMINARYPRELIMINARY

First LBA image using full International LOFAR!

Morabito USS @ low-ν 15/16

High Resolution Imaging: LBA

53 MHz

4.8 GHz

4C +43.15

Carilli et al. (1997)

∆ν =14 MHzrms=150 mJy bm−1

4.25 hr

PRELIMINARYPRELIMINARY

First LBA image using full International LOFAR!

Morabito USS @ low-ν 15/16

High Resolution Imaging: LBA

53 MHz

4.8 GHz

4C +43.15

Carilli et al. (1997)

∆ν =14 MHzrms=150 mJy bm−1

4.25 hr

PRELIMINARYPRELIMINARY

First LBA image using full International LOFAR!

Morabito USS @ low-ν 15/16

186.00°188.00°190.00°192.00°RA (J2000)

+36.00°

+37.00°

+38.00°

+39.00°

+40.00°

+41.00°

+42.00°

Dec

(J2

00

0)

0.00

0.01

0.02

0.03

0.04

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Summary

High resolution imaging at low-ν is possible!

Low Frequency observations are revealing:

1. HzRG integrated spectra show variety

2. Spatial distribution is similar to higher frequencies

Future work:

• Calibration of intermediate baselines

• Tie together flux scale of longest & shortest

baselines

Processing rest of survey ... stay tuned!

Morabito USS @ low-ν 16/16

183.00°186.00°189.00°192.00°195.00°RA (J2000)

+33.00°

+36.00°

+39.00°

+42.00°

+45.00°

Dec

(J2

00

0)

0.4

0.0

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0.8

1.2

1.6

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2.4

2.8

Flux d

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eam−

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4C +39.37, 30.4 MHz