GALFAGALACTIC ASTRONOMY

WITH ALFAThree Major Science Areas:

CON Radio Continuum (incl. Polarimetry)

RRL Radio Recombination Line (Spectroscopy)

HI (Spectroscopy)

GALFA CONTINUUM

SUB-CONSORTIUM•Synchrotron emission gives steep spectrum with substantial linear polarization•Whole sky surveys @ 408 MHz (51’) 1400 MHz (36’)•Low and intermediate b surveys @ 1.4 GHz (10’), 2.7 GHz (5’), and 4.8 GHz (3’)

Have yielded extremely curious “disembodied” polarization features – could be due to differential Faraday rotation (angle ~ wavelength2)

GALFA CONTINUUM

SUB-CONSORTIUM

9’ BEAM

GALFA CON SUB-CONSORTIUMUnravel RM with “FARADAY TOMOGRAPHY” to obtain unique view of B-field in Milky Way

GALFA Continuum Transit Survey (GALFACTS)•Full ALFA bandwidth+Full Stokes Parameters obtained with PALFA Spectrometer (1024 ch/par.)•Scan fast (in ZA) giving zig-zag on sky filled in on successive days. 1000 hr for AO sky•Polarimetric confusion (20 microJy/beam) << Stokes I (2 mJy/beam)•Issues: -8 dB coma lobes & polariz. of outer beams

GALFA RADIO RECOMBINATION

LINE (RRL) SUB-CONSORTIUM12 RRLs of H, He, C, and heavy elements (dn = 1) fall within ALFA passband: n = 174 @ 1238 MHz to n = 163 @ 1505 MHz

11 useful (RFI)3 MHz BW eachSpaced 20-30 MHz

GALFA RRL SUB-CONSORTIUMMAJOR THEMES

•Turbulence in ionized regions•Galactic Structure incl. Te gradient•Kinematics & Dynamics of HII regions and PDRs•Galactic Diffuse Medium

RRL SURVEY0.5 km/s resolutionGalactic Plane with |b| < 5o 300 s integration time per pointing - 10mK sens.Several to many transitions observed simultaneously (for sensitivity)2000 hrs total time required (commensal candidate)

GALFA HI SUB-CONSORTIUMMAJOR THEMES

•What are the critical physical processes that determine the structure and evolution of the interstellar medium?•What are the CONNECTIONS -- between atomic and molecular ISM, between the “cold” and “normal” neutral medium, and between the Disk and the Halo?•What are high latitude clouds and clouds in the Galactic Halo?

GALFA HI SUB-CONSORTIUMGalactic High–Latitude HI

•Interstellar Turbulence (low & high – b)•Neutral Hydrogen as Probe of the Origin & Evolution of Molecular Clouds•The Cold Neutral Medium•The Disk-Halo Connection•HI Clouds in the Galactic Halo•High-Latitude Line Wings & Turbulence•High-Latitude Clouds

GALFA HI SUB-CONSORTIUM

Galactic Low–Latitude HI

•Low-Latitude HI Study of the Galactic Plane

•21-cm Emission Line Wings at Forbidden Velocities

GALFA – HI MAPPING STRATEGIES•Rotating array by ~ 22 deg gives 7 equally spaced beams on the sky•Beam spacing is 125”•Nyquist sampling interval perpendicular to scan direction is 95”• Average FWHM beam size is 215”•A single drift scan pass with this configuration yields a somewhat undersampled map in direction perpendicular to scan•Integration time along scan direction is ~4 s/sample in order not to smear beam (equivalent to 1’)•Successive strips are offset by 875”•Mapping rate is 3.5 deg2 hr-1 with 4 s integration time/pixel

SINGLE-DRIFT MAPPING

GALFA – HI MAPPING STRATEGIESIf Nyquist sampling is desired, single-drift mapping will not be satisfactory and interleaved drift scans offset by 62” can be profitably employed (mapping rate is 1.83 deg2 hr-1)

Exact effective integration time depends on precise beam reconstruction function employed, but will typically be about 10 seconds/beam

With 2 polarizations and noiseless reference position

–Rms = 0.18 K for velocity resolution = 0.2 km/s

–Rms = 0.08 K for velocity resolution = 1.0 km/s

DOUBLE-DRIFT MAPPING

GALFA HI – High Latitude Surveys:

Interstellar Turbulence

Critical mechanism for determining structure of ISM

•Intermittency

•Energy Injection

•Relationship with Theory

Require l-b-v cubes for which you can calculate velocity-density correlations

GALFA HI – HI & Molecular Clouds

•What is the origin of molecular clouds

•What is the relationship between atomic and molecular components in present day clouds and cloud complexes

–Does atomic ISM provide external pressure for

molecular clouds?–What is the evolutionary connection between

atomic and molecular phases?

~ 50 Sq. Degree Image of 13COIntegrated Intensity in Taurus

FCRAO 14m with Sequoia Array 55” res.

GALFA HI – High Latitude Surveys:

Cold Neutral Medium (CNM)Characteristics:

Cold, thermally stable phase of HI

Temperature 15 to 300 K

40% of HI by mass

Some questions:

Why such a large range of temperatures?

Why such extreme geometries – sheets & filaments?

How much CNM is there, really?

What are its relationships with other phases of ISM including molecular clouds?

GALFA HI – High Latitude Surveys:

The Disk – Halo Connection•Total kinetic energy of halo gas probably exceeds that of disk due to large velocity dispersion

•Flow of hot gas from disk to halo seen in edge-on spiral galaxies with active star formation

•Interstellar “chimneys” and “fountains” are plausibly the conduit for energy and matter transport

Need relatively high sensitivity

Must have high spatial resolution of Arecibo

Large area coverage of about 2500 deg2 is required (in and out of Galatic Plane)

GALFA HI – High Latitude Surveys:HI Clouds in the Galactic Halo

Gas at high latitudes not consistent with Galactic rotation models – clouds are clearly outside the galactic disk

–Intermediate Velocity Clouds (IVCs): distances between few hundred pc and 2 kpc; solar metallicities; may be the final stage of a Galatic fountain–High Velocity Clouds (HVCs): deviate by > 50 km from Galactic rotation; metallicity = 0.1 solar; two-phase structure with cold cores embedded in warm envelope; DISTANCE UNCERTAIN–Magellanic Stream: only HVC complex with known origin, namely that they are tidal debris of Magellanic Clouds; total mass of HI almost 5x108 solar masses; –Compact High Velocity Clouds (CHVCs): separate class spatially and kinematically; visible counterparts of Dark Matter Halos?–QUESTIONS: Structure, physical conditions, interactions, origin

High Latitude Surveys: Line Wings - An Unrecognized Source of Turbulence

If at 100 pc0.4 solar masses1045 erg

GALFA HI – High Latitude Surveys: High Latitude Clouds

•Dust and dust evolution–Relatively simple “laboratories” to study key physical processes

•High-latitude translucent clouds –Statistics, turbulence, formation & evolution–Relationship between atomic and molecular gas

Galfa HI – Low Latitude Surveys: Survey of the Galactic Plane at |b| < 5 deg•800 deg2 in first and third quadrants•Nyquist sampling•High spectral resolution

HIGHEST ANGULAR RESOLUTION OF ANYCOMPLETE SINGLE DISH SURVEY: find what was missed with lower resolution / coarser / less complete surveysSCIENTIFIC GOALS

(1) Use HI self-absorption (HISA) to map spiral arms in first quadrant (resolve distance ambiguities)

(2) Study atomic and molecular gas in Giant Molecular Clouds (sites of formation of massive stars)

(3) Infrared Luminosity Function of the Inner Galaxy – correlations with MSX and other surveys

GALFA HI – Low Latitude Surveys:

Forbidden Velocity Line Wings

•Old, previously-unkown supernovae remants?•Stellar wind-blown bubbles?

Time Requirements for GALFA – SurveysPROJECT DETAILS TIME (hr)RRL 300s per position 2000CON Fast scanning 1.3s/Nyquist sample 1000Turbulence Piggyback on other data sets -Molecular Clouds Taurus+Perseus 1000 deg2 ; massive star-

forming regions; isolated clouds 1600CNM 12 regions x 100 deg2 + other larger

regions 1400Disk-Halo 2500 deg2 1400Clouds in Halo All sky 13,600 deg2 [COMMENSAL] 15600High Lat. Clouds same data set as Molecular Clouds -Low Latitude Plane 800 deg2 460FV Wings ~ 10 x DD Area TBD ?