the mojave program: studying the relativistic kinematics of agn jets jansky postdoctoral fellow...

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

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

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

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?

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

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

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

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

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

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

Polarization ImagesPolarization Images

Quasar 1222+216 (z = 0.435)

Polarization contours

Total intensity contours

Fractional Polarization

BL Lacertae – first two epochsBL Lacertae – first two epochs

Feb 2003June 2002

Polarized Jet ComponentsPolarized Jet Components

BL Lac jets are typically more polarized than quasars – (K-S test -> 99.95% confidence)

Investigating Jet Magnetic FieldsInvestigating Jet Magnetic Fields

How do polarizations of jet features evolve?– magnetic field changes

with bending events

Homan et al. (2003)

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?

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