1 of 31

Deep sub-arcsecond calibration and imaging of ELAIS-N1

Searching for radio galaxies below 40”

�Collaborators:�R. van Weeren, F. Sweijen, R. Oonk, H. Röttgering

Science at low frequencies 2023

2 of 31

Radio galaxy morphology evolution

See: de Jong et al. accepted (A&A)

See: https://github.com/jurjen93/redshifting

  • Catalogues Mingo et al. 2019/2022�
  • Sources at 6” and 144 MHz�

​

SALF 2023

3 of 31

Radio galaxy morphology evolution

See: de Jong et al. accepted (A&A)

See: https://github.com/jurjen93/redshifting

  • Catalogues Mingo et al. 2019/2022�
  • Sources at 6” and 144 MHz�
  • 100x more FRIs above z=0.3�
  • Space density enhancements�
  • Selection biases below 40”�

SALF 2023

4 of 31

Radio galaxy morphology evolution

See: de Jong et al. accepted (A&A)

See: https://github.com/jurjen93/redshifting

  • Catalogues Mingo et al. 2019/2022�
  • Sources at 6” and 144 MHz�
  • 100x more FRIs above z=0.3�
  • Space density enhancements�
  • Selection biases below 40”�

SALF 2023

5 of 31

LOw-Frequency ARray (LOFAR)

  • Pan-European radio telescope

​

  • HBA at ~144 MHz�
  • High sensitivity

SALF 2023

6 of 31

LOFAR Dutch (~6”)

SALF 2023

7 of 31

LOFAR International (~0.3”)

SALF 2023

8 of 31

Sub-arcsecond and arcsecond resolutions with 8 hours data

Sweijen et al 2022

Ye et al (submitted)

SALF 2023

9 of 31

High-res ELAIS-N1

  • 4 observations (32 hours)�
  • 3 resolutions: 1.2”, 0.6” and 0.3”�
  • 2 times deeper → going �from 35 to 17 μJy/beam

SALF 2023

10 of 31

Strategy

  1. Dutch calibration (prefactor/LINC, DDF pipeline)
  2. Subtract sources outside 2.5x2.5 degrees
  3. Direction-independent (DI) calibration
  4. Direction-dependent (DD) calibration
  5. Imaging

SALF 2023

11 of 31

Strategy

  • Dutch calibration (prefactor/LINC, DDF pipeline)
  • Subtract sources outside 2.5x2.5 degrees
  • Direction-independent (DI) calibration
  • Direction-dependent (DD) calibration
  • Imaging

Reduce human interaction

LOFAR VLBI pipeline

SALF 2023

12 of 31

Direction-independent calibration

Kickstart the international calibration!

Requirements

  • Bright
  • Compact
  • Near pointing center

SALF 2023

13 of 31

Direction-dependent calibration

SALF 2023

14 of 31

Pre-selection

Need enough signal-to-noise at long baselines�

​

​

SALF 2023

15 of 31

Pre-selection

Need enough signal-to-noise at long baselines�

Solution:�Select sources with lowest XX-YY phase difference at longest baselines

SALF 2023

16 of 31

Pre-selection

Need enough signal-to-noise at long baselines�

Solution:�Select sources with lowest XX-YY phase difference at longest baselines

SALF 2023

17 of 31

After selection

SALF 2023

18 of 31

Mosaicing

SALF 2023

19 of 31

0.6”

0.3”

1.2”

6”

SALF 2023

20 of 31

6”

FRI

Blob

Blob

SALF 2023

21 of 31

FRI

FRII?

FRI

0.3”

SALF 2023

22 of 31

Blob

FRII

6”

45”

SALF 2023

23 of 31

FRII?

FRII

0.3”

5”

36”

SALF 2023

24 of 31

6”

SALF 2023

25 of 31

0.3”

SALF 2023

26 of 31

0.3”

SALF 2023

27 of 31

3 Gaussians

6”

SALF 2023

28 of 31

point source

FRI

FRII?

0.3”

SALF 2023

29 of 31

Polarization

SALF 2023

30 of 31

Summary

  • Deepest 0.3” wide-field image with LOFAR at 17 µJy/beam
  • Implemented more automation in VLBI pipeline

�Future prospects

  • Fully automated pipeline
  • Go below 10 µJy/beam
  • Radio galaxy evolution at small angular scales
  • High-resolution polarization studies
  • And more…! Stay tuned.

SALF 2023

31 of 31

Acknowledgement

This presentation is part of the project CORTEX (NWA.1160.18.316) of the research programme NWA-ORC which is (partly) financed by the Dutch Research Council (NWO). This work made use of the Dutch national e-infrastructure with the support of the SURF Cooperative using grant no. EINF-6218. This work is co-funded by the EGI-ACE project (Horizon 2020) under Grant number 101017567.

This work was sponsored by NWO Domain Science for the use of the national computer facilities.