The Effects of Environment on radio-loud AGN Activity in Stripe 82

126 Pages·2016·11.69 MB·English

by  Sthabile Kolwa

University of the Western Cape

Magister Scientiae

The Effects of Environment on radio-loud AGN Activity in
Stripe 82
Supervisors:
Author:
Prof. Matt Jarvis
Sthabile Kolwa
Dr Kim McAlpine
A thesis submitted in fulfilment of the requirements
for the degree of Magister Scientiae
in the
UWC Astrophysics Group
Department of Physics
June 2016
ii
Keywords

Catalogues - galaxies

Radio continuum - galaxies

Accretion-disk physics
Black-hole physics
Evolution - galaxies
Environment - galaxies
Surveys - galaxies
Active - galaxies
Photometry - infrared
Statistics - galaxies
Declaration of Authorship
I, Sthabile Kolwa, declare that The Effects of Environment on radio-loud AGN Activity
in Stripe 82 is my own work, that it hasnot been submitted forany degree or examination
in any other university, and that all the sources I have used or quoted have been indicated
and acknowledged by complete references.
Full name: Sthabile Kolwa
Signed:
Date:
iii
“Sanity is not statistical.”
George Orwell in his novel, Nineteen Eighty-Four
UNIVERSITY OF THE WESTERN CAPE

Abstract
Natural Sciences
Department of Physics
Magister Scientiae
The Effects of Environment on radio-loud AGN Activity in Stripe 82
by Sthabile Kolwa
We investigate the link between environment and radiative accretion efficiency using a
sample of 8946 radio-loud AGN detected at 1 2 GHz in the SDSS Stripe 82 region.
−
We quantify their environments using the surface-density parameter, Σ , which measures
N
galaxy density based on distances to Nth nearest neighbours. Comparing Σ and Σ
2 5
between AGN and control galaxies, we obtain relative densities that quantify the degree
of galaxy clustering around each AGN. Using this, we examine the relation between
density and the HERG-LERG dichotomy (accretion-modes) classified using a 1.4 GHz
luminosity (L ) threshold. Our results indicate that, in the low-redshift interval
1.4GHz
(0.1 < z < 0.2), LERGs occupy environments denser than the field. At intermediate
redshifts (0.2 < z < 1.2), both LERGs and HERGs occupy regions denser than the field.
Spearman’s rank tests show that correlationsbetween density andL in bothredshift
1.4GHz
intervals are weak. We conclude that the absence of a strong correlation is confirmation
of the idea that galaxy density plays a more secondary role on AGN activity and also,
accretion-mode classification (both measured using L ). It is likely that the rate of
1.4GHz
gas accretion or properties of galactic-scale magnetic fields correlate more strongly with
L , hence being primarily influential.
1.4GHz
Acknowledgements

Thank you to the SKA Division of the National Research Foundation for funding my
studies continuously for five years and counti ng. Dr McAlpine, your attention to detail is
superb, you’re a champion. Prof Jarvis, thanks for the trip to Oxford and all the wisdom

that you have shared. Mother and family, thank you for your continual support.

vi
Contents

Declaration of Authorship iii
Abstract v
Acknowledgements vi
Contents vi
List of Figures ix
List of Tables xi
Abbreviations xiii
1 Introduction 1
1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Brief History of AGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3 AGN Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3.1 Unified AGN Model . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3.2 Radio-Loudness . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.4 Accretion-Mode Dichotomy . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.5 AGN Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1.5.1 Galaxy Interactions and AGN . . . . . . . . . . . . . . . . . . . . 19
1.5.2 Secular Processes and AGN . . . . . . . . . . . . . . . . . . . . . 22
1.6 AGN Environment and Accretion-Mode . . . . . . . . . . . . . . . . . . 24
1.7 Thermal Dust Re-emission in WISE . . . . . . . . . . . . . . . . . . . . . 26
1.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2 Methodology 31
2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.2 The Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.2.1 JVLA Radio Data . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.2.2 SDSS Optical Data . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2.2.3 WISE Mid-Infrared Data . . . . . . . . . . . . . . . . . . . . . . . 39
2.2.4 UKIDSS Near-Infrared Data . . . . . . . . . . . . . . . . . . . . . 40
2.3 Multiwavelength Cross-match . . . . . . . . . . . . . . . . . . . . . . . . 42
vii
Contents viii
2.3.1 JVLA and SDSS Cross-match . . . . . . . . . . . . . . . . . . . . 42
2.3.2 WISE Cross-match . . . . . . . . . . . . . . . . . . . . . . . . . . 45

2.3.3 UKIDSS Cross-match . . . . . . . . . . . . . . . . . . . . . . . . . 45
2.4 Environment Quantifier . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

2.5 AGN Sample . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
2.6 Control Sample . . . . . . . . . . .  . . . . . . . . . . . . . . . . . . . . . 54
2.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

3 WISE Results 61
3.1 WISE Photometry of a radio-loud AGN Sample . . . . . . . . . . . . . . 62
3.2 WISE Mid-IR Two-colour Diagrams . . . . . . . . . . . . . . . . . . . . . 66
4 Environment Results 73
4.1 1.4 GHz Radio Luminosity and Surface-Density Measure . . . . . . . . . 75
4.1.1 Low Redshift Interval . . . . . . . . . . . . . . . . . . . . . . . . . 77
4.1.2 Intermediate Redshift Interval . . . . . . . . . . . . . . . . . . . . 83
4.2 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
5 Conclusions 93
5.1 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 93
5.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
A Measured Quantities 95
A.1 Cosmological Distance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
A.2 Error Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
B Neighbour Search and Cross-match Tools 99
C Computing the Surface-density Parameter 101
Bibliography 103
List of Figures

1.1 Schematic diagram of the Unified AGN Model . . . . . . . . . . . . . . . 10
1.2 Cross-sectional schematic of the Unified AGN Model . . . . . . . . . . . 11
1.3 Schematic of accretion-modes in Heckman and Best (Fig. 3) . . . . . . . 13
1.4 M and M as functions of L in Best and Heckman (Fig. 7) . . . . 15
∗ BH NVSS
1.5 HERG-LERG radio-luminosity function in Heckman and Best (Fig. 11) . 15
1.6 EW as a function of EI in Best and Heckman (Fig. 1) . . . . . . . . 17
[OIII]
1.7 AGN fraction as function of environment in Silverman et al. (Fig. 5) . . 20
1.8 Galaxy fraction as a function of density in Miller et al. (Fig. 8) . . . . . 22
1.9 AGN activity as a function of environment in Sabater et al. (Fig. 5) . . . 23
1.10 SFR of radio-loud LERGs and HERGs in Janssen et al. (Fig. 6) . . . . . 25
1.11 WISE two-colour diagram in Wright et al. (Fig. 12) . . . . . . . . . . . . 27
1.12 WISE two-colour diagram in Gu¨rkan et al. (Fig. 3) . . . . . . . . . . . . 28
2.1 JVLA survey coverage of Stripe 82 in Heywood et al. (Fig. 1) . . . . . . 35
2.2 Scanning procedure for SDSS telescope . . . . . . . . . . . . . . . . . . . 37
2.3 SDSS DR7 coverage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
2.4 Percentage of WISE full-sky coverage over time . . . . . . . . . . . . . . 40
2.5 UKIDSS DR10 coverage map . . . . . . . . . . . . . . . . . . . . . . . . 41
2.6 Cross-match radius determination for JVLA-SDSS catalogue . . . . . . . 45
2.7 Photometric redshifts of all JVLA-SDSS sources . . . . . . . . . . . . . . 46
2.8 L as function of photo-z for JVLA-SDSS sources . . . . . . . . . . . 47
1.4GHz
2.9 Cross-match radius determination for JVLA-SDSS-WISE catalogue . . . 47
2.10 Cross-match radius determination for JVLA-SDSS-UKIDSS catalogue . . 48
2.11 Petrosian K as a function of redshift . . . . . . . . . . . . . . . . . . . . 48
s
2.12 JVLA-SDSS and SDSS DR7 survey coverage . . . . . . . . . . . . . . . . 51
2.13 Distribution for K K 0.05 . . . . . . . . . . . . . . . . . . . . 57
s,agn s,cont
− ≤
2.14 Distribution for K K 0.1 . . . . . . . . . . . . . . . . . . . . 57
s,agn s,cont
− ≤
2.15 Distribution for z z 0.05 . . . . . . . . . . . . . . . . . . . . . . 58
agn cont
− ≤
2.16 Distribution for z z 0.1 . . . . . . . . . . . . . . . . . . . . . . 58
agn cont
− ≤
3.1 Spectral line method on W12 vs W23 for Best and Heckman sample . . . 63
3.2 W4-luminosity method on W12 vs W23 for Best and Heckman sample . . 63
3.3 Spectral line method on W12 vs W24 for Best and Heckman sample . . . 64
3.4 W4-luminosity classification on W12 vs W24 Best and Heckman sample . 64
3.5 W12 vs W23 for JVLA-SDSS-WISE radio sources . . . . . . . . . . . . . 68
3.6 W12 vs W24 for JVLA-SDSS-WISE radio sources . . . . . . . . . . . . . 69
3.7 W1 (3.4 µm magnitude) luminosity as a function of redshift . . . . . . . 69
3.8 W2 (4.6 µm magnitude) luminosity as a function of redshift . . . . . . . 70
ix
List of Figures x
3.9 W3 (12 µm magnitude) luminosity as a function of redshift . . . . . . . . 70
3.10 W4 (22 µm magnitude) luminosity as a function of redshift . . . . . . . . 71

4.1 Low redshift: Σ as a function of L . . . . . . . . . . . . . . . . . 79
2,R 1.4GHz

4.2 Low redshift: magnified rendition of Fig. 4.1 . . . . . . . . . . . . . . . . 79
4.3 Low redshift: Σ as a function of L . . . . . . . . . . . . . . . . . 80
2,D   1.4GHz
4.4 Low redshift: magnified rendition of Fig. 4.3 . . . . . . . . . . . . . . . . 80
4.5 Low redshift: Σ5,R as a function of  L1.4GHz . . . . . . . . . . . . . . . . . 81
4.6 Low redshift: magnified rendition of Fig. 4.5 . . . . . . . . . . . . . . . . 81
4.7 Low redshift: Σ as a function of L . . . . . . . . . . . . . . . . . 82
5,D 1.4GHz
4.8 Low redshift: magnified rendition of Fig. 4.7 . . . . . . . . . . . . . . . . 82
4.9 Intermediate redshift: Σ as a function of L . . . . . . . . . . . . 85
2,R 1.4GHz
4.10 Intermediate redshift: magnified rendition of Fig. 4.9 . . . . . . . . . . . 85
4.11 Intermediate redshift: Σ as a function of L . . . . . . . . . . . . 86
2,D 1.4GHz
4.12 Intermediate redshift: magnified rendition of Fig. 4.11 . . . . . . . . . . 86
4.13 Intermediate redshift: Σ as a function of L . . . . . . . . . . . . 87
5,R 1.4GHz
4.14 Intermediate redshift: magnified rendition of Fig. 4.13 . . . . . . . . . . 87
4.15 Intermediate redshift: Σ as a function of L . . . . . . . . . . . . 88
5,D 1.4GHz
4.16 Intermediate redshift: magnified rendition of Fig. 4.15 . . . . . . . . . . 88