Starburst GalaxiesStarburst Galaxies

Tom MuxlowTom Muxlow88thth EVN Symposium, Torun Sept 27 EVN Symposium, Torun Sept 27

20062006

Jodrell Bank ObservatoryJodrell Bank Observatory University of Manchester UKUniversity of Manchester UK

A brief introduction to star-forming A brief introduction to star-forming galaxies, both nearby and at high redshift – galaxies, both nearby and at high redshift –

with regard to what high resolution radio with regard to what high resolution radio observationsobservations have revealedhave revealed

,

What is a starburst galaxy?What is a starburst galaxy? High star-formation rate ~ 10 – 100 MHigh star-formation rate ~ 10 – 100 M๏๏/year /year

– much higher than normal gas-rich galaxies – much higher than normal gas-rich galaxies (eg Milky Way star-formation rate ~ (eg Milky Way star-formation rate ~ 1 – 5 M1 – 5 M๏๏/year)/year)

Total gas content can be estimated Total gas content can be estimated from integrated line profiles from integrated line profiles Integrated HI profile Integrated HI profile HI Mass HI Mass

From gas available to fuel the star-formation From gas available to fuel the star-formation event event lifetimes lifetimes ~few x 10~few x 1099 years for Milky Way – can be maintained for years for Milky Way – can be maintained for

the lifetime of the galaxythe lifetime of the galaxy ~10~1088 years for starburst galaxy - short compared with years for starburst galaxy - short compared with

the galaxy lifetimethe galaxy lifetime Implies a ‘burst’ of star-formationImplies a ‘burst’ of star-formation

What is a starburst galaxy?What is a starburst galaxy?

Typically they are disturbed galaxies, many involved Typically they are disturbed galaxies, many involved in mergersin mergers

Star-formation sites are marked out by the rare highly-Star-formation sites are marked out by the rare highly-luminous high-mass starsluminous high-mass stars

SED often dominated by strong (F)IR emissionSED often dominated by strong (F)IR emission

NGC 1808 NGC 4038 /4039

Starburst galaxiesStarburst galaxies Size of starburst region typically ~ kpc Size of starburst region typically ~ kpc Radio synchrotron emission from plasma Radio synchrotron emission from plasma

(SNR)(SNR) Strong FIR emission from UV-heated dust (O Strong FIR emission from UV-heated dust (O

stars)stars) LLFIRFIR >10 >1010 10 LLo o (ULIRGS>10(ULIRGS>101212 L Loo))

Radio

FIR

Thermal free-free emission from HII regionsThermal free-free emission from HII regions

Estimating star-formation rate Estimating star-formation rate (SFR)(SFR)

SFR indicators are many and variedSFR indicators are many and varied

Extensively studied - Extensively studied - eg eg Cram et al 1998 ApJ Cram et al 1998 ApJ 507 155507 155

FIRFIR, , Radio ContinuumRadio Continuum, , UV, SN etc….UV, SN etc…. SFR estimated from FIR and radio are found to SFR estimated from FIR and radio are found to

be highly correlated over many orders of be highly correlated over many orders of magnitudemagnitude

x5.5 to convert to SFR over complete stellar mass range (>0.1 M๏) [Salpeter IMF]

Both FIR and radio emission determined by the properties of high-mass stars

SFR can also be estimated from the numbers of O stars required to SFR can also be estimated from the numbers of O stars required to ionize the medium and produce thermal free-free continuum emission ionize the medium and produce thermal free-free continuum emission and forbidden lines (eg [NeII])and forbidden lines (eg [NeII])

Measuring UV flux directly suffers from extinction problemsMeasuring UV flux directly suffers from extinction problems No dust extinction problems for thermal free-free emission, but difficult to No dust extinction problems for thermal free-free emission, but difficult to

separate from non-thermal componentseparate from non-thermal component SN rate can be used to derive the SFR for stars more massive than 8MSN rate can be used to derive the SFR for stars more massive than 8M๏๏

Arp 220 and M82Arp 220 and M82

Nearby starburst galaxiesNearby starburst galaxies

Arp 220 HST ACS

M82 Spitzer

Arp220Arp220 Merging ULIRG 77MpcMerging ULIRG 77Mpc HI emission VLA C+D arrayHI emission VLA C+D array

Low angular resolutionLow angular resolution

(Hibberd et al NRAO)(Hibberd et al NRAO) Dominated by HI absorptionDominated by HI absorption

HI absorption studies at high angular HI absorption studies at high angular resolution probe the merger dynamics resolution probe the merger dynamics

Two counter-rotating disks – original galaxy Two counter-rotating disks – original galaxy cores that have survived the initial encountercores that have survived the initial encounter

Now in final stages of merger Now in final stages of merger

MERLIN - Mundell, Ferruit & Pedlar (2001)MERLIN - Mundell, Ferruit & Pedlar (2001)

OH mega-masers within eastern OH mega-masers within eastern disk show a velocity gradient of disk show a velocity gradient of 320 km s320 km s-1-1 kpc kpc-1-1

Radius ~80pc Radius ~80pc Enclosed mass Enclosed mass ~1.2x10~1.2x107 7 MM๏๏

No 10No 1088MM๏๏ BHBH… but Chandra … but Chandra

finds hard X-rays in western finds hard X-rays in western diskdisk Clements et al 2002Clements et al 2002

Rovilos, Diamond et al Rovilos, Diamond et al (2003)(2003)

Masers are excellent tracers of star-formation See Sessions 7 & 8 this afternoon – and Megan Argo’s poster on OH masers in M82

Arp220 Global VLBIArp220 Global VLBILonsdale, Lonsdale, Diamond, Conway, Smith, Rovilos, Parra, Lonsdale, Lonsdale, Diamond, Conway, Smith, Rovilos, Parra,

Thrall… et alThrall… et al

Both east and west components show radio Sn Both east and west components show radio Sn and SNR. No obvious AGN seen – but in west and SNR. No obvious AGN seen – but in west component some unusual structures & velocity component some unusual structures & velocity gradients detected……gradients detected……

MERLIN

Latest images Latest images - - New detections + variabilityNew detections + variability

Sn + SNR + AGN ? - See Rodrigo Parra’s Sn + SNR + AGN ? - See Rodrigo Parra’s presentationpresentation

Starbursts can have embedded Starbursts can have embedded AGNAGN

Often the AGN is obscured and may only Often the AGN is obscured and may only contribute a small proportion of the total flux contribute a small proportion of the total flux densitydensity eg ULIRG Mkn273 – twin merging nuclei eg ULIRG Mkn273 – twin merging nuclei Knapen et al Knapen et al

19971997 Flat spectrum radio component detectedFlat spectrum radio component detected

HST

Contours: MERLIN 5GHz

Greyscale: CFHT K-Band

Mkn273Mkn273 Dynamical signature of super-massive Dynamical signature of super-massive

objectobject MERLIN HI absorption MERLIN HI absorption (Cole et al 1999)(Cole et al 1999)

Rotating diskRotating disk M<500pc ~1.4x10M<500pc ~1.4x1010 10 MMoo

VLBA VLBA (Carilli & Taylor 2000)(Carilli & Taylor 2000)

M<220pc ~2x10M<220pc ~2x109 9 MMoo EVN EVN (Bondi et al 2005)(Bondi et al 2005)

Compact AGN Compact AGN candidatecandidate

Could be a compact Could be a compact RSnRSn

Hard X-rays Hard X-rays AGN AGN

M82M82 One of the nearest (3.2 Mpc) & best studied starburst One of the nearest (3.2 Mpc) & best studied starburst

galaxiesgalaxies Starburst located in central ~1 kpc Starburst located in central ~1 kpc SStarburst driven tarburst driven windwind (H (H) - ) - Subaru image, X-rays - Subaru image, X-rays -

(Chandra)(Chandra)

Triggering the starburst Triggering the starburst - - tidal interaction over the past ~200 x 10tidal interaction over the past ~200 x 1066

yearsyears

Interaction with M81/NGC3077 – M82 in high-Interaction with M81/NGC3077 – M82 in high-speed motionspeed motion with respect to the with respect to the M81/NGC3077 groupM81/NGC3077 group HI observations Yun et al (1994)HI observations Yun et al (1994)

M82

M81

NGC3077

-34 km/s

+14 km/s

+203 km/s

Previous Starburst Activity ? Previous Starburst Activity ? - evidence from optical - evidence from optical

clustersclusters Several ‘super’ starclusters identified ~ Several ‘super’ starclusters identified ~

1kpc NE of the centre of M821kpc NE of the centre of M82

Correspond to 10Correspond to 1099 year old fossil starburst. Ages derived from year old fossil starburst. Ages derived from evolutionary spectral synthesis modelsevolutionary spectral synthesis models Last close encounter with M81 Last close encounter with M81 (de Grijs et al 2001)(de Grijs et al 2001)

N

E

Current starburst:Current starburst:- has existed for at least 50 x 10- has existed for at least 50 x 1066 years years- heavily obscured optically ~ 20-30 M- heavily obscured optically ~ 20-30 Mvv

Tidal interaction has Tidal interaction has channeled large amounts channeled large amounts of gas into the central of gas into the central region of M82 inducing a region of M82 inducing a burst of star-formationburst of star-formation

Current supernova rate Current supernova rate ~ 0.1 yr ~ 0.1 yr-1-1

Current star-formation Current star-formation rate (for M > 5 Mrate (for M > 5 M๏๏) ~ ) ~ 2 M2 M๏๏ yryr-1-1

M82 VLA HI absorptionM82 VLA HI absorption (Wills et al 2000)(Wills et al 2000)

Velocity field shows strong rotationVelocity field shows strong rotation Detailed fit along major axis suggests an Detailed fit along major axis suggests an

inner bar which is thought to be fuelling the inner bar which is thought to be fuelling the central starburstcentral starburst Also seen in Also seen in molecular lines (eg molecular lines (eg CO)CO)

M82 M82 Supernova remnantsSupernova remnants O & B stars are tracers recent star-formationO & B stars are tracers recent star-formation

Typically these become supernovae after ~ 10Typically these become supernovae after ~ 1077 yearsyears

SNR trace out star-formation sites ~10SNR trace out star-formation sites ~1077 years old years old

50-6050-60 compact sources discovered in M82compact sources discovered in M82 All resolved with MERLIN+VLBIAll resolved with MERLIN+VLBI Most are SNRMost are SNR Although ~16 are compact HII regionsAlthough ~16 are compact HII regions

MERLIN (MFS) +VLA 1995

M82 SNR – How old are they?M82 SNR – How old are they?MERLIN resolves all the SNR MERLIN resolves all the SNR visible in M82 – derive size visible in M82 – derive size distributiondistribution

Cumulative number-size Cumulative number-size diagram infers that SNR diagram infers that SNR expansion slows with time: expansion slows with time:

D ~ t D ~ t 0.60.6

Assuming an initial Assuming an initial expansion rate ~ 5000km/s expansion rate ~ 5000km/s ages ~1000 yr with a SNR ages ~1000 yr with a SNR appearing every ~ 20-40 yrappearing every ~ 20-40 yr

Expansion velocities of ~5-Expansion velocities of ~5-10,000km/s are detected by MERLIN 10,000km/s are detected by MERLIN and VLBIand VLBI

VLBI Imaging of SNR VLBI Imaging of SNR - in M82 and other nearby starburst galaxies- in M82 and other nearby starburst galaxies

Measure expansion velocities and Measure expansion velocities and decelerationdeceleration

Probe the nature of the environment – thought Probe the nature of the environment – thought to be extremely clumpyto be extremely clumpy

Investigate how the ejecta interact with the Investigate how the ejecta interact with the environment and eventually move into the environment and eventually move into the Sedov phase of expansionSedov phase of expansion

Do SN in environmental voids produce no Do SN in environmental voids produce no observable remnant? In M82, SFR observable remnant? In M82, SFR SN rate of SN rate of 1 every ~12 years (cf SNR rate of 1 every ~30 1 every ~12 years (cf SNR rate of 1 every ~30 years) years) M82

SNR43.31+592

0.5 pc

M81

SN1993J:SN1993J:

Marcaide et alMarcaide et al

Bietenholz, Bartel, Bietenholz, Bartel, Rupen et alRupen et al

SN43.31+592:SN43.31+592:

Beswick et al 2006Beswick et al 2006

See review talk by Rob See review talk by Rob Beswick on SNR-Beswick on SNR-Session 9Session 9

See talk by Danielle See talk by Danielle Fenech on M82 SNRFenech on M82 SNR

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 !!!

In 2000 41.95+575 had a flux density of 24mJy – at birth 100 years ago it would have been ~100 Jy !!!!

What sort of violent event is this ??

- GRB afterglow ??

VLBI Imaging of SNR - 41.95+575VLBI Imaging of SNR - 41.95+575An unusual object in M82 !!An unusual object in M82 !!

Structurally-evolving double-lobed structure unlike ring/partial rings seen for all other M82 SNR

Expansion velocity(<1800km/s) age ~ 100 years

•Deep galaxy studies Deep galaxy studies indicate that early indicate that early galaxies merge to galaxies merge to form larger systems in form larger systems in a ‘bottom-up’ scenario a ‘bottom-up’ scenario of galaxy assemblyof galaxy assembly

•This implies that This implies that galaxy-galaxy galaxy-galaxy interactions were interactions were common at early common at early epochs epochs

•Such interactions are Such interactions are likely to trigger major likely to trigger major star-formation star-formation activity.activity.

Star-formation at High Star-formation at High RedshiftRedshift

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 HDF-N MERLIN + VLA dataDeep HDF-N MERLIN + VLA data

Covers ~10 arcminCovers ~10 arcmin2 2 centred on the HDF-N (Lovell telescope centred on the HDF-N (Lovell telescope beam)beam)

High angular resolution ~0.2-0.5 arcsecHigh angular resolution ~0.2-0.5 arcsec

rms ~3.3rms ~3.3µJybmµJybm-1-1 - one of the most sensitive 1.4GHz images - one of the most sensitive 1.4GHz images mademade

Precis of results:Precis of results: 92 radio sources with flux densities >4092 radio sources with flux densities >40µµJy.Jy. Angular sizes of 0.2”–3”Angular sizes of 0.2”–3” 85% are associated with galaxies brighter than 25th mag85% are associated with galaxies brighter than 25th mag Remaining 15% are optically faint EROs at high redshift (some seen at sub-Remaining 15% are optically faint EROs at high redshift (some seen at sub-

mm)mm) Below ~60Below ~60Jy sources are dominated by starburst systemsJy sources are dominated by starburst systems Some starbursts show evidence for embedded AGN – See latest VLBI Some starbursts show evidence for embedded AGN – See latest VLBI

results...results...

VLA: VLA: Richards et al 2000Richards et al 2000 VLBI: VLBI: Garrett et al 2001Garrett et al 2001 Seungyoup Chi - this Seungyoup Chi - this

meetingmeeting MERLIN+VLA: MERLIN+VLA: Muxlow et al 2005Muxlow et al 2005

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 dataGOODS NORTH: New ACS & Spitzer data

The historical HDF-N is coincident with the The historical HDF-N is coincident with the GOODS north field.GOODS north field.

deeper wider field HST ACS images + deep deeper wider field HST ACS images + deep Spitzer imagesSpitzer images

8.5’ x 8.5’ MERLIN+VLA radio field centred on 8.5’ x 8.5’ MERLIN+VLA radio field centred on HDF-N intersects with 13030 galaxies brighter HDF-N intersects with 13030 galaxies brighter that 28.3that 28.3magmag in ACS z-band field in ACS z-band field

Using these new data we can now extend the Using these new data we can now extend the analysis, to investigate statistically the very weak analysis, to investigate statistically the very weak radio source population below 20radio source population below 20µJyµJy. . Rob Beswick, Hanna Thrall, Tom Muxlow, Anita Rob Beswick, Hanna Thrall, Tom Muxlow, Anita Richards, Simon Garrington….Richards, Simon Garrington….

Radio emission from ACS Radio emission from ACS galaxiesgalaxies

Radio flux density Radio flux density within 0.75 arcsecond within 0.75 arcsecond of all 13030 z-band of all 13030 z-band optical galaxies in the optical galaxies in the 8.5’ field, binned by 8.5’ field, binned by magnitude magnitude

(Note: excluding all brighter (Note: excluding all brighter radio sources with radio sources with SS1.41.4>40>40µJyµJy))

Control incorporates a random Control incorporates a random 7 arcsecond shift 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)

927 23mag galaxies

Radio source sizes:Radio source sizes:very weak (sub-20very weak (sub-20µµJy) radio sourcesJy) radio sources

Average radio Average radio source sizes in source sizes in

each magnitude each magnitude bin can be derived bin can be derived from flux densities from flux densities

found in annuli found in annuli over radii of 0.25-2 over radii of 0.25-2

arcsec arcsec For detected For detected

systems (brighter systems (brighter than 25than 25magmag) average ) average radio source radii radio source radii are in the range are in the range 0.6 – 0.8 arcsec0.6 – 0.8 arcsec

Next generation Next generation radio radio

interferometers interferometers will need sub-will need sub-arcsec angular arcsec angular resolution !!resolution !!

Starburst LuminositiesStarburst Luminosities

Only ~1000 of the Only ~1000 of the ~13000 galaxies ~13000 galaxies have published have published spectroscopic spectroscopic

redshifts available redshifts available (Keck)(Keck)

Measured redshifts Measured redshifts binned by magnitude.binned by magnitude.

We may now derive We may now derive average luminosities average luminosities for galaxies brighter for galaxies brighter

than ~24than ~24magmag

40µJy

4µJy

0.4µJy

● Starburst

Sub-mm

Average Average luminosities luminosities for systems for systems

with with spectroscopic spectroscopic

redshiftsredshifts

For those weak For those weak sources which we sources which we can at present can at present only study only study statistically...statistically...

ee-MERLIN, EVLA -MERLIN, EVLA and and ee-VLBI should -VLBI should image >1000 image >1000 starburst systems starburst systems to ~4to ~4µJy with µJy with perhaps 150-200 perhaps 150-200 at high redshift in at high redshift in a single field. a single field.

Many thousands of Many thousands of systems with radio systems with radio flux densities flux densities <1µJy will be <1µJy will be studied studied statisticallystatistically

SKA and ALMA will SKA and ALMA will ultimately extend this ultimately extend this by an additional order by an additional order of magnitude. of magnitude.

With more redshifts, With more redshifts, improved SED improved SED templates, and templates, and extinction-free SFR extinction-free SFR indicators indicators solve for solve for cosmic star-formation cosmic star-formation history – Madau history – Madau diagramdiagram

377 Spitzer 24377 Spitzer 24µm in 8.5’ field µm in 8.5’ field >20>20µJyµJy

303 (80%) detected in radio 303 (80%) detected in radio (>3(>3σσ))

213 with redshifts213 with redshifts

Beswick et alBeswick et al – work in – work in progress….progress….

At present……At present……

Can show that the SFR Can show that the SFR density increases density increases dramatically to z~1 dramatically to z~1 and then flattens…and then flattens…

At higher redshifts, the At higher redshifts, the position of the position of the turnover point remains turnover point remains uncertain !!uncertain !!

The next few years will The next few years will be very exciting…be very exciting…