Transcript Studies of Extragalactic SNR

Jodrell Bank Observatory
University of Manchester UK
Starburst Galaxies
A brief introduction to star-forming galaxies, both
nearby and at high redshift – with regard to what
high resolution radio observations have revealed
Tom Muxlow
,
8th EVN Symposium, Torun
Sept 27 2006
What is a starburst galaxy?
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High star-formation rate ~ 10 – 100 M๏/year
– much higher than normal gas-rich galaxies
(eg Milky Way star-formation rate ~ 1 – 5 M๏/year)
Total gas content can be estimated
from integrated line profiles
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Integrated HI profile  HI Mass
From gas available to fuel the star-formation event
lifetimes
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~few x 109 years for Milky Way – can be maintained for the
lifetime of the galaxy
~108 years for starburst galaxy - short compared with the
galaxy lifetime
 Implies a ‘burst’ of star-formation

What is a starburst galaxy?
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Typically they are disturbed galaxies, many involved in
mergers
Star-formation sites are marked out by the rare highlyluminous high-mass stars
SED often dominated by strong (F)IR emission
NGC 1808
NGC 4038 /4039
Starburst galaxies
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Size of starburst region typically ~ kpc
Radio synchrotron emission from plasma (SNR)
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Strong FIR emission from UV-heated dust (O stars)
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LFIR >1010 Lo (ULIRGS>1012 Lo)
Thermal free-free emission from HII regions
Radio
FIR
Estimating star-formation rate (SFR)
SFR indicators are many and varied

Extensively studied -
eg Cram et al 1998 ApJ 507 155
 FIR, Radio Continuum, UV, SN etc….
 SFR estimated from FIR and radio are found to be
highly correlated over many orders of magnitude
 SFR can also be estimated from the numbers of O stars
required to ionize the medium and produce thermal freefree continuum emission and forbidden lines (eg [NeII])
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Measuring UV flux directly suffers from extinction problems
No dust extinction problems for thermal free-free emission,
to convert
to SFR over
complete
stellar
butx5.5
difficult
to separate
from
non-thermal
component
 SN rateBothcanFIRbeandused
to derive the SFR for stars more
radio emission determined by the
mass range (>0.1 M๏) [Salpeter IMF]
massive
than 8M๏
properties
of high-mass stars
Nearby starburst galaxies

Arp 220 and M82
Arp 220 HST ACS
M82 Spitzer
Arp220
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Merging ULIRG 77Mpc
HI emission VLA C+D array
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Low angular resolution
(Hibberd et al NRAO)
Dominated by HI absorption
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HI absorption studies at high angular
resolution probe the merger dynamics
MERLIN - Mundell, Ferruit & Pedlar (2001)
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Two counter-rotating disks – original galaxy cores that
have survived the initial encounter
Now in final stages of merger
OH mega-masers within eastern
disk show a velocity gradient of
320 km s-1 kpc-1
Rovilos, Diamond et al (2003)
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Masers are excellent
tracers of star-formation
See Sessions 7 & 8 this
afternoon – and Megan
Argo’s poster on OH
masers in M82
Radius ~80pc  Enclosed mass
~1.2x107 M๏
No 108M๏ BH… but Chandra finds
hard X-rays in western disk Clements et al 2002
Arp220 Global VLBI
Lonsdale, Lonsdale, Diamond, Conway, Smith, Rovilos, Parra, Thrall… et al
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Latest
images
- New
detectionsshow
+ variability
Both east
and west
components
radio Sn and SNR.
No
obvious
but Rodrigo
in west component
some
Sn +
SNR +AGN
AGNseen
? - –See
Parra’s presentation
unusual structures & velocity gradients detected……
MERLIN
Starbursts can have embedded AGN
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Often the AGN is obscured and may only contribute
a small proportion of the total flux density
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eg ULIRG Mkn273 – twin merging nuclei
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Flat spectrum radio component detected
Contours:
MERLIN 5GHz
Greyscale:
CFHT K-Band
HST
Knapen et al 1997
Mkn273
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Dynamical signature of super-massive object
 MERLIN HI absorption (Cole et al 1999)
Rotating disk
 M<500pc ~1.4x1010 Mo
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VLBA
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(Carilli & Taylor 2000)
M<220pc ~2x109 Mo
EVN
(Bondi et al 2005)
Compact AGN candidate
 Could be a compact RSn
 Hard X-rays  AGN
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M82
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One of the nearest (3.2 Mpc) & best studied starburst galaxies
 Starburst located in central ~1 kpc
 Starburst driven wind
(Ha) - Subaru image, X-rays - (Chandra)
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Triggering the starburst
tidal interaction over the past ~200 x 106 years
Interaction with M81/NGC3077 – M82 in high-speed
motion with respect to the M81/NGC3077 group
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HI observations Yun et al (1994)
M82
+203 km/s
-34 km/s
+14 km/s
NGC3077
M81
Previous Starburst Activity ?
- evidence from optical clusters
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Several ‘super’ starclusters identified
~ 1kpc NE of the centre of M82
N
E
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Correspond to 109 year old fossil starburst. Ages derived from
evolutionary spectral synthesis models
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Last close encounter with M81 (de Grijs et al 2001)
Current starburst:
- has existed for at least 50 x 106 years
- heavily obscured optically ~ 20-30 Mv
Tidal interaction has
channeled large amounts of
gas into the central region of
M82 inducing a burst of starformation
Current supernova rate
~ 0.1 yr-1
Current star-formation rate
(for M > 5 M๏) ~ 2 M๏ yr-1
M82 VLA HI absorption
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(Wills et al 2000)
Velocity field shows strong rotation
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Detailed fit along major axis suggests an inner bar
which is thought to be fuelling the central starburst
Also seen in molecular
lines (eg CO)
M82 Supernova remnants
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O & B stars are tracers recent star-formation
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Typically these become supernovae after ~ 107 years
SNR trace out star-formation sites ~107 years old
50-60 compact sources discovered in M82
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All resolved with MERLIN+VLBI
Most are SNR
Although ~16 are compact HII regions
M82 SNR – How old are they?
MERLIN resolves all the SNR visible
in M82 – derive size distribution
Assuming an initial expansion
rate ~ 5000km/s  ages ~1000
yr with a SNR appearing every
~ 20-40 yr
Expansion velocities of ~5-10,000km/s
are detected by MERLIN and VLBI
Cumulative number-size
diagram infers that SNR
expansion slows with time:
MERLIN (MFS) +VLA 1995
D ~ t 0.6
VLBI Imaging of SNR
- in M82 and other nearby starburst galaxies
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Measure expansion velocities and deceleration
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Probe the nature of the environment – thought to be
extremely clumpy
Investigate how the ejecta interact with the
environment and eventually move into the Sedov
phase of expansion
Do SN in environmental voids produce no observable
remnant? In M82, SFR  SN rate of 1 every ~12
years (cf SNR rate of 1 every ~30 years)
M82 SNR43.31+592
See review talk by Rob
Beswick on SNR-Session 9
See talk by Danielle
Fenech on M82 SNR
0.5 pc
SN43.31+592:
SN1993J:
Beswick et al 2006
Marcaide et al
Bietenholz, Bartel,
Rupen et al
M81
VLBI Imaging of SNR - 41.95+575
An unusual object in M82 !!
41.95+575 has decreased in flux density by 8.5% per year since
monitoring began in
the 1970s. 100 years
at 8.5%/yr  x 3500 !!!
Structurally-evolving
double-lobed
structure unlike ring/partial rings seen
allaother
M82 SNRof 24mJy – at birth 100 years
In 2000 41.95+575for
had
flux density
ago it would have been ~100 Jy !!!!
Expansion velocity(<1800km/s)
 age ~ 100 years
What sort of violent event is this ??
-
GRB afterglow ??
Star-formation at High Redshift
HDF (N)
Multi-wavelength studies of a number of fields
including deep radio observations involving VLA,
ATCA, MERLIN, EVN… have shown that at flux
densities <1mJy (1.4GHz) there is new population
of faint radio sources that are associated with
distant star-forming galaxies
Richards, Fomalont, Kellermann, Windhorst, Norris, Garrett, Muxlow…….
•Deep galaxy studies
indicate that early
galaxies merge to form
larger systems in a
‘bottom-up’ scenario of
galaxy assembly
•This implies that galaxygalaxy interactions were
common at early epochs
•Such interactions are
likely to trigger major
star-formation activity.
Deep HDF-N MERLIN + VLA data
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Covers ~10 arcmin2 centred on the HDF-N (Lovell telescope beam)
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High angular resolution ~0.2-0.5 arcsec
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rms ~3.3µJybm-1 - one of the most sensitive 1.4GHz images made
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Precis of results:
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92 radio sources with flux densities >40µJy.
Angular sizes of 0.2”–3”
85% are associated with galaxies brighter than 25th mag
Remaining 15% are optically faint EROs at high redshift (some seen at sub-mm)
Below ~60Jy sources are dominated by starburst systems
Some starbursts show evidence for embedded AGN – See latest VLBI results...
VLA: Richards et al 2000
MERLIN+VLA: Muxlow et al 2005
VLBI: Garrett et al 2001
Seungyoup Chi - this meeting
Contours: Radio linear CI=10µJy/bm
Image: Optical colour
One of the brighter
(~200µJy) starburst
galaxies in the NDF-N
GOODS NORTH: New ACS & Spitzer data
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The historical HDF-N is coincident with the GOODS north
field.
 deeper wider field HST ACS images + deep Spitzer
images
8.5’ x 8.5’ MERLIN+VLA radio field centred on HDF-N
intersects with 13030 galaxies brighter that 28.3mag in
ACS z-band field
Using these new data we can now extend the analysis,
to investigate statistically the very weak radio source
population below 20µJy.
Rob Beswick, Hanna Thrall, Tom Muxlow, Anita Richards, Simon Garrington….
Radio emission from ACS galaxies
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Radio flux density
within 0.75 arcsecond
of all 13030 z-band
optical galaxies in the
8.5’ field, binned by
magnitude
(Note: excluding all brighter radio
sources with S1.4>40µJy)
927 23mag galaxies
Control incorporates a random
7 arcsecond shift
Of the ~2700 galaxies brighter than Z=24mag, around 1400 will
have radio flux densities of ~4µJy or greater
(~8σ for a deep e-MERLIN/EVLA image)
Radio source sizes:
very weak (sub-20µJy) radio sources
Average radio source
sizes in each
magnitude bin can be
derived from flux
densities found in
annuli over radii of
0.25-2 arcsec
For detected systems
(brighter than 25mag)
average radio source
radii are in the range
0.6 – 0.8 arcsec
Next generation radio
interferometers will
need sub-arcsec
angular resolution !!
Starburst Luminosities
For those weak
sources
which
we
Measured
redshifts
can
at present
only
binned
by magnitude.
At present……
statistically...
We
now
SKAstudy
andmay
ALMA
willderive
Only
~1000
of
the
average
luminosities
for
Can
that
the
SFR
ultimately
extend
this
by
eshow
-MERLIN,
EVLA
~13000
galaxies
have
brighter
density
an galaxies
additional
order
ofthan
and
eincreases
-VLBI
should
mag
published
spectroscopic
~24
dramatically
to
magnitude.
image
>1000z~1 and
redshifts available
then
flattens…
starburst
systems to
With
more (Keck)
redshifts,
~4µJy with
perhaps
At higher
redshifts,
the
improved
SED templates,
150-200
at
high
position
of the turnover
and extinction-free
SFR
redshift
in
a
single
point
remains
uncertain
indicators
 solve
for !!
field.star-formation
cosmic
The next few years will be
history
– thousands
Madau diagram
Many
of
very
exciting…
systems with radio
flux densities <1µJy
will be studied
statistically
● Starburst
Sub-mm
Average
luminosities for
systems with
spectroscopic
redshifts
40µJy
377 Spitzer 24µm in 8.5’ field >20µJy
303 (80%) detected in radio (>3σ)
4µJy
 213 with redshifts
Beswick et al – work in progress….
0.4µJy