The Galactic Plane Infrared Polarization Survey (GPIPS)

Current Members:Michael PavelDan Clemens (PI)Lauren CashmanSadia HoqJordan MontgomoryIan SantagataPantelis ThomaidisBrian Taylor

Former Members:April Pinnick

Robert MarchwinskiKatherine Jameson

Julie MoreauMeredith Bartlett

Nora WatsonCarol Carveth

(Supported by NSF grants AST 06-07500 and -07790)

Science Questions

1. Galactic Size Scales (1-5 kpc): • Magnetic Field (B-field) in and out of spiral arms? • Molecular clouds threaded by one B-field?• Large-scale B-field structure? Dynamo origin?

2. Cloud Size Scales (10 – 100 pc): • Role of B-field in cloud morphology?• B-field strength variations with gas density?• How do dust grains align with B-field?

3. Dense Cores and Star Forming Regions (0.1 – 1 pc): • B-fields in star-forming regions? • Quiescent cloud cores?• Magnetically sub- or super-critical?

Polarization of Background Starlight

Why H-band (1.6μm)?

(Serkowski 1973)

Optical Wavelengths - <P> ~ 5%

Near-Infrared (H-band) - <P> ~ 1%

Pro: Less dust extinction (probe more distant stars)Con: Weaker polarization signal

Observational Tools

Perkins 1.83m telescope outside of Flagstaff, AZ

Mimir instrument (Clemens et al. 2007) -10x10 arcmin imaging polarimetry FOV -0.6 arcsecond pixels -Cold (~70 K) polarization optics -Designed to be an imaging polarimeter!

Survey DetailsSurvey area: 18° < l < 56° 3237 Overlapping 9 x 9 arcmin fields

|b| < 1 ° Expect ~106 starlight polarizations

Data Release 1:June 2012

(Clemens et al. 2012a)(18% of data, red fields in figure)

Initial Observations are complete!

Now re-observing ‘Bad’ fields

Observing StrategyMimir uses a stepping zero-order half-wave plate (HWP) and fixed wire grid for polarimetric analysis.

For each of the 3237 fields:-Six sky dither positions (15 arcsec hexagon)-16 unique HWP position at each dither-2.5 second integrations per HWP

96 images per pointing4 minutes of on-target integration

13 minutes to complete each field

Instrumental Polarization: A 3-step Process

1. “Polarization” Flat-Fielding

• Correction with high SNR flat-fields taken in every HWP position angle used for polarimetry (16, for Mimir)

• SNR > 2000 per pixel

2.Instrumental Polarization Determination, Removal

• Observing lots of stars in globular clusters

• Mapped across full FOV

3.Position Angle Offset & Linear Polarimetric Efficiency Determination

• Observing lots of Polarization Standard Stars (Whittet et al. 1992)

• Observed every night

• Mapped across FOV

HWP=0 deg HWP=45 deg

M3 M2

Sco Field Cyg Field(Clemens et al. 2012b)

σPinst ≈ 0.02-0.04%

Large-Scale Galactic B-field

(Pavel et al. 2012)

Testing Galactic Magnetic Field Models

Polarization Properties Across the sky

3-D B-field Structure

Probing magnetic fields with distance(Pavel et al., submitted)

Using open star clusters as distance probes(Hoq et al., in prep)

ISM Interaction with B-fieldsMIR Galactic Bubbles

(Churchwell et al. 2006)

(Pavel et al., submitted)

Dark Clouds

(Cashman et al., submitted)

ISM Interaction with B-fields

Presence of MHD/Alfvén waves in ISM?(Clemens et al., in prep)

B-field strength mapping of GRSMC 45.60+0.30 using

Chandrasekhar-Fermi Method

(Marchwinski et al. 2012)

Direct measurement of magnetically-supported cores!

(Cho & Lazarian 2005)

Testing Dust Grain Alignment

Measure polarization efficiency in a variety of environments.

SummaryGPIPS can be used to:•Probe large-scale magnetic field structures (possibly in 3-D)

•Map magnetic fields in individual objects and provide magnetic context

•Estimate Magnetic field strengths in suitable objects

•Observe the interaction of magnetic fields with the ISM

•Test dust grain alignment theories

Data Release 1 is Here

DR1 (18% of survey) is live and available to the community via the GPIPS website.

Explore the initial data!

DR2 (additional ~18%) is expected Sept. 2012.

http://gpips0.bu.edu