The Evolution of AGN over Cosmic Time
Current Status and Future Prospects
Matt Jarvis
University of Hertfordshire
• What have we learnt from radio surveys so far?
• What have we learnt from current multi-wavelength surveys?
• What will future surveys tell us?
Radio selection
• Free from dust obscuration
• 1.4GHz may not be the best frequency to search for HzRGs as
they have steep spectra (optically thin lobe emission).
• High frequency surveys at high flux density dominated by flatspectrum quasars
• Most searches for HzRGs have been conducted at low
frequency (<400 MHz)
Evolution of the high-luminosity population
Need COMPLETE radio
samples – in the past this
meant spectroscopic
completeness and using the
K-z diagram
Integrate under the LF to
measure the space density of
the radio sources as a
function of cosmic epoch
Dunlop & Peacock 1990
The first to find a “redshift cutoff” in the flat-spectrum radio
source population
Evolution of the high-luminosity population
Shaver et al. (1996)
followed this up with a
larger and more complete
data set of flat-spectrum
quasars.
Again found a sharp
decline at the high redshifts
Issues with spectral shapes
A selection of Shaver et al.’s FLAT-SPECTRUM objects!
Issues with Spectral Index
But steep spectrum
sources fall out of
flux-limited surveys
more quicky than flatspectrum sources.
Jarvis & Rawlings
2000
Means that if HzRGs have steep spectra then you need to
observe them at low frequency
Issues with Spectral Index
But steep spectrum
sources fall out of
flux-limited surveys
more quicky than flatspectrum sources.
Jarvis & Rawlings
2000
Means that if HzRGs have steep spectra then you need to
observe them at low frequency
Issues with Spectral Index
Profound effect on the
interpretation of a
redshift cut-off
Jarvis & Rawlings
2000
Evolution of the high-luminosity population
Flat-spectrum population of Shaver et al. was reanalysed fully
by Wall et al. (2005). Now a ~4sigma decline is found.
But still restricted to the bright, flat-spectrum quasars – which
again may not be fair to do and enforces small number
statistics.
So measuring the high-redshift evolution of
AGN is a tricky business
So measuring the high-redshift evolution of
AGN is a tricky business
What can we do?
The problem
For the FIRST survey at 1mJy (1.4GHz)…
• ~83 sources per sq.degree
• ~6 local(ish) starburst galaxies
• ~77 AGN (6 FRIIs where we should detect
emission lines)
Splitting in redshift…
• 57 AGN at z<2 (2 FRIIs)
• 67 AGN at z<3 (4 FRIIs)
• 73 AGN at z<4 (6 FRIIs)
Past searches for HzRGs…
Many have utilized the properties of the radio sources
themselves to filter out the low-z contaminant sources.
Steep spectral index
Blundell et al. 1999
De Breuck et al. 2000
Past searches for HzRGs…
Jarvis et al. 2001
The “lack” of a redshift cut-off in the
steep-spectrum population
Jarvis et al. 2001
The “lack” of a redshift cut-off in the
steep-spectrum population
Jarvis et al. 2001
But remember
steep-spectrum
selection
reduces the
accessible
volume
The “lack” of a redshift cut-off in the
steep-spectrum population
Jarvis et al. 2001
Not much progress
since!
The “lack” of a redshift cut-off in the
steep-spectrum population
Jarvis et al. 2001
Not much progress
since!
But see later
Can turn around the way we use radio surveys
Can turn around the way we use radio surveys
Optical
SDSS1-2 Pan-STARRS SDSS-3 DES
Now  2009  2010  2011
Near-IR
UKIDSS VISTA JWST ELT
Now  2009  2013  2020
Mid/Far-IR
Spitzer SCUBA2 Herschel WISE ALMA
Now  2010  2009  2010  2012
Radio
eMerlin
LOFAR eVLA KAT/ASKAP SKA
2010  2010  2011  2020
Combine existing survey data to infer the properties of
AGN
Evolution of the low-power radio
sources (not necessarily FRIs)
Clewley & Jarvis 2004
Combine existing survey data to infer the properties of
AGN
Evolution of the low-power radio
sources (not necessarily FRIs)
Sadler et al. 2007
Clewley & Jarvis 2004
Combine existing survey data to infer the properties of
AGN
Rigby, Best & Snellen 2008
Morphologically classified FRIs
at L(1.4)>1025 W/Hz
Combine existing survey data to infer the properties of
AGN
Rigby, Best & Snellen 2008
Morphologically classified FRIs
at L(1.4)>1025 W/Hz
As well as all of the good work
we’ve heard about this
morning
So what now?
So what now?
First go back to the high-luminosity sources…
Use the host galaxies
K-band samples the
old stellar population
– so bulk of the stellar
mass
Going back to the K-z relation…
Jarvis et al. 2001; Willott et al. 2003
Going back to the K-z relation…
Jarvis et al. 2001; Willott et al. 2003
Going back to the K-z relation…
Jarvis et al. 2001; Willott et al. 2003
Use this information at other wavelengths
to eliminate low-z contaminants
Jarvis et al. 2004
UKIDSS
Large Area Survey (LAS)
Galactic Plane Survey (GPS)
Galactic Clusters Survey (GCS)
Deep eXtragalactic Survey (DXS)
UltraDeep Survey (UDS)
Klim
4000
18.4
1800
19.0
1400
18.7
35
21.0
0.8
23.0
Declination
•
•
•
•
•
deg2
Right Ascension
Finding the highest-redshift radio galaxies
(similar strategy to CENSORS – Best et al. (2003), Brookes et al. (2006,2008)
Use UKIDSS-DXS +
Spitzer-SWIRE and a
variety of radio
surveys (e,g. FIRST).
Try and get spectra
for all of the objects
undetected in the
near-IR
In 10 sq. degrees to 10mJy at
1.4GHz
Jarvis, Simpson,
Teimourian, Smith &
Rawlings
PhD student
Hanifa
Teimourian
LOFAR Surveys KSP will need to adopt such a strategy to be most
efficient. Pan-STARRS/UKIDSS/VISTA/WISE
A demonstration of combining radio surveys with
multi-wavelength data…
A typical HzRG at z=4.88
Jarvis et al. 2009
Log(L(1.4))=26.5W/Hz/sr
=0.75
A demonstration of combining radio surveys with
multi-wavelength data…
α=0.9
Teimourian et al. 2010
What does this mean?
Teimourian et al. in prep.
But this survey is only
sensitive to the most
powerful sources. Due to
the need to obtain
spectroscopic redshifts and
the need for accurate
positions from the radio
survey.
To understand the whole radio source population at all luminosities (from SFGs to
powerful FRII radio galaxies) we need exquisite multi-wavelength data and deep
radio data.
LOFAR Surveys
Huub Rottgering (Chair), Peter Barthel, Philip Best, Marcus Brueggen,
Matt Jarvis, George Miley, Raffaella Morganti, Ignas Snellen
All Sky Survey
20,000 sq.degree survey at 15, 30, 60, 120MHz to 15, 5, 1.7 and 0.1mJy(rare
objects + unknown)
1000 sq.degree survey at 200MHz to 0.07mJy (Cluster relics/haloes, starburst
galaxies…)
Deep Survey
1200 sq.deg at 30 & 60MHz to 0.9 & 0.2mJy
220 sq.deg at 120MHz to 0.025mJy
80 sq.deg.at 200MHz to 0.018mJy (distant starbursts, AGN, clusters…)
Ultra-Deep Survey
1-2 pointings (4-8sq.deg) at 200MHz to 0.006mJy (confusion limited at subarcsec resolution) very high-z starbursts, RQ-AGN, …
Comparison of WENSS, FIRST, NVSS and LOFAR for detecting HzRGs
(FRIIs with =0.8)
Radio galaxies at
z>7 in Surveys
• More than 100 sufficiently
powerful sources at z>7
predicted in 2π survey.
• LOFAR’s wide area survey
multi-frequency capabilities are
essential.
• Isolate using ultra-steep radio spectrum, plus optically blank in deepest images
(eg. PanSTARRS/VISTA/UKIDSS)
• Ultra-deep images would also detect any clustered starforming galaxies around
radio source (would need high dynamic range though).
What the future has in store…
VISTA
Survey speed >3x faster than WFCAM and better sensitivity
in the Z,Y,J wavebands
The VIDEO Survey (PI Jarvis)
Filter
Time (per
source)
Time (full 5s AB
survey)
5s
Vega
UKIDSS Seei
-DXS
ng
Moon
Z
17.5 hours
456 hours
25.7
25.2
-
0.8
D
Y
6.7 hours
175 hours
24.6
24.0
-
0.8
G
J
8.0 hours
209 hours
24.5
23.7
22.3
0.8
G
H
8.0 hours
221 hours
24.0
22.7
22
0.8
B
Ks
6.7 hours
180 hours
23.5
21.7
20.8
0.8
B
VIDEO+SERVs+DES++
Spitzer Representative Volume Survey (SERVS) approved to
cover VIDEO survey regions + LH and Elais-N1
Elais-S1
1400 hours allocated – PI Mark Lacy
Management: Matt Jarvis, Seb Oliver and Duncan Farrah
Will provide 3.6 and 4.5um data to slightly deeper levels than
the VIDEO depths (L* at z>5)
XMM-LSS
VIDEO entering data sharing agreement with the Dark Energy
Survey. DES will have grizy photometry over VIDEO regions to
depths of AB~27 (5sigma)
Concentrating on SNe science initially.
Will be covered by Herschel-HerMES survey (100-500um)
CDF-S
Partly covered by SCUBA2
What can we learn about AGN?
L- and T-dwarfs
z=6 z=6.5
z=7
Depending on the
QSO LF slope
expect 10-30
z>6.5 QSOs in
VIDEO
Z-Y vs Y-J very efficient at selection z>6.5 QSOs. VIDEO+SERVs crucially allows us to
find the reddened high-z QSOs
Summary
• Radio surveys allow is a relatively unbiased view of this activity
• Past surveys have enabled us to put some constraints on the highredshift evolution, but much is still uncertain
• The way in which we carry out such studies in the future (and now)
will change.
• We must use the multi-wavelength data already in place and move
away from “follow-up” of radio surveys
• Initial results with such a strategy has allowed us to find the most
distant radio galaxy thus far in a far more efficient way than any
previous studies
• The prospects for this strategy in the future only get better with the
deep optical/IR datasets, combined with the SKA precursor telescopes
such as LOFAR, ASKAP and MeerKAT.