the mojave program: studying the relativistic kinematics of agn jets jansky postdoctoral fellow...
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The MOJAVE Program:The MOJAVE Program:Studying the Relativistic Kinematics of AGN JetsStudying the Relativistic Kinematics of AGN Jets
Jansky Postdoctoral Fellow
National Radio Astronomy Observatory
Matthew Lister
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Team MembersTeam Members
●M. L. Lister, D. C. Homan, K. I. Kellermann, Y. Kovalev● National Radio Astronomy Observatory, USA
●M. Kadler, A. P. Lobanov, E. Ros, J. A. Zensus● Max Planck Institut fur Radioastronomie, Germany
●R. C. Vermeulen● ASTRON, The Netherlands
●M. H. Cohen● California Institute of Technology, USA
●H. D. Aller & M. F. Aller● University of Michigan, USA
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What is MOJAVE?What is MOJAVE?MonitoringOfJets inActive Galaxies withVLBAExperiments
● Physics of pc-scale AGN jets• 3 yr multi-epoch survey program
• follow-up to VLBA 2cm Survey
● New aspects/advantages:●complete flux-limited AGN sample●VLBA imaging in full Stokes●supporting single-dish observations●10-year baseline to study:
● intrinsically slow & high-z jets● slow nozzle precession● stable calibrator candidates
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AGN Jets: AGN Jets: FundamentalFundamental Questions Questions
● AGN jet speed distribution:– is the universe dominated by fast or slow jets?– what is the maximum jet speed?
● Relation of jet speed to other AGN properties: – dependence on black hole mass? optical class?– are more powerful/luminous jets necessarily faster?– which AGN are expected to have the fastest jets?
● Evolution of jet magnetic fields:● do the fields track the motions? ● consistent with streaming along bent paths?● how does circular polarization relate to jet structure/kinematics?
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Studying AGN Jets on Parsec-ScalesStudying AGN Jets on Parsec-Scales
Jets seen face-on (radio galaxies) – smaller projection and aberration effects
– jets are weak (beamed away from us)
– samples not selected by jet emission
– change Lorentz factor:
– --> very little change in apparent speed
Jets seen end-on (blazars)– strong, flat-spectrum cores– fastest motions– need large samples – projection and selection effects
Image: Alan Bridle
VLBA 2cm Survey
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Sample Selection Sample Selection
How to select a sample of end-on jets (blazars)?– want to minimize biases
● Logical choice: compact (VLBI) radio flux density
● all AGN jets are radio-loud (not true for other bands)● complete all-sky flux-limited radio surveys are available● emission is from same region where apparent speeds are
measured
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The MOJAVE Jet Sample The MOJAVE Jet Sample
Brightest AGN jets in the northern sky as seen by the VLBA at 15 GHz
Sky region: -20 < dec < +90excludes galactic plane region (|b| < 2.5)
Lower limit on VLBA 15 GHz flux density:1.5 Jy (>2 Jy for southern sources)include any source that has ever exceeded this limit since 1995
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The MOJAVE Jet Sample The MOJAVE Jet Sample
121 confirmed and 16 candidate AGN jets– 120/137 have measured redshifts
– 72 have measured jet speeds from 2cm Survey
Optical identifications:– 96 quasars
– 22 BL Lacertae objects
– 10 radio galaxies
– 9 unidentified objects
40 gamma-ray sources from third EGRET catalog
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ObservationsObservations
One of two current 'Large' VLBA programs
–observations started in May 2002
–new 24 hr session every 6 to 8 weeks
–18 sources per session
Current Status:
–eight sessions observed, five fully reduced
–90 full polarization jet images• resolution: 0.5-1 mas
• rms ~ 0.2 mJy/beam
• peak/rms ~ 5000:1
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Supporting ObservationsSupporting Observations
Current:
–single-dish polarization (UMRAO)
–broad-band radio spectrum (RATAN 600 m)
Proposed:
–x-ray (XMM; M. Kadler)
–low frequency radio (GMRT / WSRT)
–optical polarization
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Polarization ImagesPolarization Images
Quasar 1222+216 (z = 0.435)
Polarization contours
Total intensity contours
Fractional Polarization
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BL Lacertae – first two epochsBL Lacertae – first two epochs
Feb 2003June 2002
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Polarized Jet ComponentsPolarized Jet Components
BL Lac jets are typically more polarized than quasars – (K-S test -> 99.95% confidence)
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Investigating Jet Magnetic FieldsInvestigating Jet Magnetic Fields
How do polarizations of jet features evolve?– magnetic field changes
with bending events
Homan et al. (2003)
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Circular PolarizationCircular Polarization
Schedule ideally suited for CP studies• lots of strong sources• interleaved scans
Results so far: CP detected in 6 of 50 jets
Important questions:– how does CP depend on linear polarization?– does the sign of the CP remain constant?– why do only some sources show CP?
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SummarySummary
MOJAVE is a complete sample of the brightest AGN jets in the northern sky
Will lead to a better understanding of• magnetic field evolution in jets
• circular polarization mechanisms
• how jet kinematics depend on other AGN properties
• distribution and upper limit of jet speeds
Large amount of data available to community:
–http://www.nrao.edu/~mlister/MOJAVE
•VLBA and single-dish polarization data
•multi-epoch radio spectra