Transcript SUMSS - 京都大学

Radio sources in the 2dF Galaxy
Redshift Survey (2dFGRS)
• With Russell Cannon (AAO), Carole Jackson (ANU), Vince McIntyre
(ATNF) and the 2DFGRS team (PIs Matthew Colless & John Peacock)
• Cross-match the 2dF Galaxy Redshift Survey
(spectra of 250,000 galaxies to bJ=19.4 mag)
with large-area radio continuum surveys (NVSS
at 1.4 GHz, SUMSS at 843 MHz)
• When 2dFGRS complete, will have good-quality
spectra of ~4000 radio-emitting galaxies to
z=0.3. Currently analysed ~900 galaxies (20%).
• Goal: Accurate study of local radio source
populations as benchmark for work at higher z
Main themes of this talk:
• Radio telescopes are highly efficient machines for
probing the distant universe and measuring the
cosmic evolution of galaxies.
• Developing a proper physical understanding of
galaxy formation and evolution requires data sets
much larger than those available in the past.
• “The astronomy of the 21st century will be dominated by
computer-based manipulation of huge homogeneous
surveys of various types of astronomical objects.’’
den Bergh (2000), PASP 112, 4.
Van
Optical and radio views of the sky
DSS B band
Optical - Galactic stars and a
few nearby galaxies
SUMSS 843 MHz
Radio - distant galaxies with median z~1
A brief history of the Universe
Redshift and lookback time for a
universe with Ho=50 km/s/Mpc, W=1
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Redshift
z
1400
20
10
5
3
2
1
0.5
0.3
0.2
0.1
0
Time Since Big Bang
(in Gyr=109 yr)
250,000 yr
0.1 Gyr
0.3
0.9
1.6
2.5
4.6
7.1
8.8
9 .9
11.3
13.0
Fraction of
current age
0.0019%
1.0 %
2.7 %
6.8 %
13 %
19 %
35 %
54 %
67 %
76 %
87 %
100 %
COBE
Peak of
Galaxy
formation?
.
2dF
Nearby galaxies: Hubble type is
related to star-formation history
Galaxy classification
scheme first proposed
by Hubble (1936)
The Milky Way Galaxy in far-IR
(COBE)
Much of what we currently know about galaxy formation comes from
studies of the stellar populations in our own Milky Way
Galactic archaeology: Stellar
populations in nearby galaxies
• Techniques: Spectroscopy of resolved stars/clusters
line-strength gradients, colour gradients.
• Spiral galaxies: Wide range in stellar ages (0 to 13
Gyr) and metalliciies. 10% (Sc) to 90%(Sa) of available
gas now converted to stars. Star formation continues to
present day.
• Elliptical galaxies: Age/metallicity degeneracy, but
stellar population all old (?). ‘Assembled’ from merger
of subsystems, but Mg/Fe ratio implies rapid formation
(<1Gyr). Kinematics, metallicity, luminosity etc. closely
linked (fundamental plane).
Radio galaxies in the local universe
Radio galaxy PKS
2356-61 (ATCA
image, radio emission
shown in red, optical
light in blue)
Radio synchrotron
emission, collimated
radio jets powered
by accretion disk
around supermassive
black hole (Blandford
& Rees 1978)
Unified model for Active Galactic
Nuclei (AGN) (Urry & Padovani)
Ingredients of
a model AGN:
• Black hole
• Accretion disk
• Collimated jets
M87 - a nearby radio galaxy with a
central supermassive black hole
(Harms
et al. 1994)
Correlation between bulge mass and
black hole mass (Kormendy & Richstone 1995)
Black hole mass-bulge
mass correlation implies
that formation of
galaxy and central
black hole (AGN)
are closely coupled
(i.e. in mergers, black
holes also merge?)
Explains how AGN
‘know’ what kind of
galaxy they live in.
Galactic time machines: Direct
observations at high redshift (z=0.1 to 5)
• Techniques: Selection of candidates by colour or other
criteria, spectroscopy with large optical/IR telescopes.
• Elliptical galaxies: Ellipticals at z~1 (lookback time
8-9 Gyr) still look ‘old’, main epoch of formation
probably earlier than z=3.
• Cosmic evolution: Powerful radio galaxies much
more common at high redshifts - energy output implies
supermassive black holes (~109 solar masses) in nuclei
of many ellipticals. Beyond z~2, radio galaxies have
‘disturbed’ optical morphology (Miley et al.), possibly
implying that black hole formation precedes star
formation?
Galaxies in the Hubble Deep Field
Our deepest view
of the Universe in
optical light:
Median redshift of
z~1 implies galaxies
typically appear as
they were when the
Universe was a third
of its current age.
The star formation history of
the Universe (Baugh et al. 1998)
The rise and fall of quasars
- evidence for an AGN/starburst link?
(Keel 2000)
High-redshift radio galaxies ancestors of present day ellipticals?
(Keel 2000)
Steep radio spectra
efficiently select
high-z galaxies.
Infrared K
magnitude can be
used as initial
redshift estimator.
The K-band Hubble diagram
(van Breughel et al. 1999)
Finding high-z
galaxies:
1) Radio filter
(e.g. spectral index)
2) IR (K-band)
imaging - estimate z
3) Optical/IR spectra
(8m-class telescopes)
Cosmic evolution of active
galaxies - interpreting radio data
• First need to disentangle the following:
• Orientation effects: Relativistic beaming for sources
oriented near line of sight. Differences in observed
emission-line widths, projected source sizes.
• Source lifetime: Typical AGN lifetime ~108 years,
expect correlation between age and source size and/or
luminosity. Onset of active phase may be related to
interaction/merger.
• Host galaxy luminosity: On average, bigger galaxies
have more massive BHs, stronger radio sources.
• Therefore need a large sample of nearby objects.
How large a sample of active
galaxies do we need at z~0?
• Need: At least 50 galaxies/bin for <15% error bars
• Radio power: At least 10 bins to cover full range
observed (at least 1021 to 1026 W/Hz).
• Host galaxy luminosity: At least 4 bins to cover full
range in optical luminosity. Plus, for sample as a whole:
• Orientation effects: Say 5 bins to cover full range in
orientation.
• Source lifetime: Say 5 bins to cover full age range and
investigate AGN/starburst connection.
• i.e. Need spectra of 5,000-10,000 galaxies as
local benchmark for studies of cosmic evolution.
The 2dF Galaxy Redshift Survey
Goal: 250,000 galaxy spectra in 1700 deg2 of sky (completion end 2001)
2dF corrector, robot positioner and
fibre-fed spectrographs on the AAT
Typical 2dFGRS radio-source spectra
(Sadler et al. 1999)
Ha
Hb
• Star-forming
galaxy, z=0.14
(40%)
[OIII]
• Emission-line
AGN, z=0.15
(10%)
• Absorption-line
AGN, z=0.14
(50%)
2dFGRS radio sources - progress
so far
• Have analysed data taken up to May 1999
(58,454 spectra, 20% of final 2dFGRS data set)
• 757 confirmed radio-source IDs - 1.5% of
2dFGRS galaxies
• Spectra classified by eye (60% AGN, 40% starforming galaxies)
• Cross-matching with far-infrared (IRAS) and
X-ray (ROSAT) catalogues
• 2dFGRS spectra cover the closest 5% of
NVSS/SUMSS radio sources (flux limit 2-3 mJy)
Redshift distribution of 2dFGRS
radio sources (and all galaxies)
(Colless 2001)
Spatially-resolved 2dFGRS radio
sources
Around 25% of 2dFGRS
radio sources are spatially
resolved by the 45 arcsec
radio beam, allowing us to
measure their projected
linear sizes.
3 GRGs
In star-forming galaxies,
radio emission is usually
confined to the galactic
disk (scales of a few tens
of kpc).
In active galaxies, sources
are often several hundred
kpc in size.
Local radio luminosity function (RLF)
for 2dFGRS radio sources (Sadler et al. 2001)
Mixture of
AGN and SF
galaxies
RLF measures
space density of
radio sources as
a function of
luminosity.
To account for
greater survey
depth for
luminous
sources, use
V/Vmax method
(Schmidt 1968)
Radio emission from star-forming
galaxies
UGC 09057
z=0.0054
NGC 5257/5258
z=0.0223
Derived star formation rate:
1.8 Msun/yr
120 Msun/yr
NGC 7252
z=0.0161
32 Msun/yr
(Radio emission is dominated by synchrotron radiation from electrons
accelerated by supernova remnants)
Far-infrared - radio correlation
for 2dFGRS galaxies
* AGN spectrum
o SF spectrum
In star-forming galaxies,
far-IR and radio
emission are tightly
correlated.
Above 1023 W/Hz (i.e.
implied star formation
rates of ~100 Msun/yr),
many star-forming
galaxies also have active
nuclei.
Normal galaxy line
Signs are Seyfert-like
emission-line ratios and
(sometimes) excess
radio emission
Local RLF for star-forming galaxies
RSA
2dFGRS
NVSS radio
limit (3mJy)
biases towards
high SFR
RLF derived from
2dFGRS data fits
onto values for
nearby bright
(RSA) galaxies
(Condon 1989).
Star formation
rates derived from
radio data are
typically 10-100
Msun/yr
(vs ~1 Msun/yr for
Milky Way).
Local star-formation density from
radio and Ha data
Ha
Local star formation
density (zero-point of
Madau diagram) in
Msun/yr/Mpc3 :
Ha: 0.013 +/-0.006
(Gallego et al. 1995)
Radio: 0.022 +/-0.004
(Sadler et al. 2001)
Radio
Radio data show more
galaxies with very high SFR
(> 30 Msun/yr), otherwise
very good agreement.
What are the “high SFR” galaxies?
• Radio LF for star-forming galaxies implies that galaxies with
SFR > 30 Msun/yr are far more common than Ha surveys
suggest, and may account for up to 40% of the local
star-formation density.
• Dust obscuration in star-forming regions could lead to
under-estimate of Ha line strength.
• Deep VLA studies of clusters at z~0.4 (Smail et al. 1999) and
local (z <0.5) “post-starburst” galaxies (Miller & Owen 2001) also
suggest that star-forming regions can be hidden by dust.
• Important to study the 2dFGRS “high-SFR” galaxies
in more detail (high-res. radio images, IR spectra...)
- are the high star-formation rates real?
Radio emission from active galaxies
TGN284Z051
z=0.1065
TGN348Z183
z=0.1790
1.4 GHz radio power and projected linear size:
1024.3 W/Hz
1025.0 W/Hz
327 kpc
475 kpc
TGS153Z214
z=0.2079
1024.8 W/Hz
471 kpc
Local radio LF for active galaxies
RLF derived from
2dFGRS data fits
onto values for
nearby bright E/S0
galaxies derived by
Sadler et al. (1989).
Power-law
F(P) a P0.62
RLF must turn over
not far below 1020
W/Hz to avoid
exceeding the space
density of early-type
galaxies.
Black hole mass spectrum for active
galaxies in the local universe
No turnover
in BH density
yet!
Can use radio LF for
AGN to estimate the
local mass density of
black holes (>3x107 Msun)
following relation from
Franchescini et al. (1998;
ADAF model) .
Total min. BH density
rBH=1.6x105 Msun/Mpc3
agrees with Choksi &
Turner QSO estimate
(rBH=1.4-2.2 x105
Msun/Mpc3).
Local radio luminosity function of
active and star-forming galaxies
Below 1025 W/Hz, the
local radio source
population is always
a mixture of AGN and
star-forming galaxies.
Low-lum AGN
are hard to find
i.e. There is probably
no observational
regime where radio
surveys detect only
star-forming galaxies.
Summary: Results so far
• The local radio source population is a mixture of starforming galaxies and AGN, but 2dFGRS spectra usually
allow us to distinguish them unambiguously.
• The local star-formation density derived from the radio
continuum is higher than the value measured from Ha
because we find more galaxies with SFR > 30-50 Msun/yr
(possibly dust-obscured in optical light).
• The black-hole mass density in AGN agrees with the
value derived for QSOs in the early Universe, suggesting
that local radio galaxies are the direct descendants of
high-z QSOs.
The next steps...
• With the full 2dFGRS data set: Evolution of the
AGN and SF luminosity functions to z~0.3, split by
radio spectral index.
• With the 6dF Galaxy Survey: From mid-2001,
expect ~12,000 radio-source spectra to z~0.1
(16% detection rate!), define faint end of RLF,
starburst/AGN connection, (Tom Mauch thesis).
• Going deeper: Deep 2dF spectroscopy to z~0.5,
photometric redshifts to z~1, steep-spectrum
sources + k-band imaging/8m spectroscopy to z>3.