Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.naic.edu/alfa/galfa/meetings/3/galfa3_science_goals.pdf Äàòà èçìåíåíèÿ: Wed Sep 29 01:51:29 2004 Äàòà èíäåêñèðîâàíèÿ: Sun Dec 23 03:55:44 2007 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: molecular cloud

GALFA
GALACTIC ASTRONOMY WITH ALFA
Three 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-CONSORTIUM
Unravel 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-CONSORTIUM
12 RRLs of H, He, C, and heavy elements (dn = 1) fall within ALFA passband: n = 174 @ 1238 MHz t o n = 1 6 3 @ 1 5 0 5 MH z
11 useful (RFI) 3 MHz BW each Spaced 2030 MHz


GALFA RRL SUB-CONSORTIUM
MAJOR THEMES
·Turbulence in ionized regions ·Galactic Structure incl. Te gradient ·Kinematics & Dynamics of HII regions and PDRs ·Galactic Diffuse Medium

RRL SURVEY
0.5 km/s resolution Galactic 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-CONSORTIUM
MAJOR 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 a n d t h e H a lo ? ·What are high latitude clouds and clouds in the Galactic Halo?


GALFA HI SUB-CONSORTIUM
· · · · · · · Galactic High­Latitude 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 Low­Latitude 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 STRATEGIES
If 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 13CO Integrated 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

I f a t 1 0 0 pc 0.4 solar masses 1045 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 ANY COMPLETE SINGLE DISH SURVEY: find what was missed with lower resolution / coarser / less complete surveys
SCIENTIFIC 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 ­ Surveys
DETAILS TIME (hr) 300s per position 2000 Fast scanning 1.3s/Nyquist sample 1000 Piggyback on other data sets Taurus+Perseus 1000 deg2 ; massive starforming regions; isolated clouds 1600 CNM 12 regions x 100 deg2 + other larger regions 1400 Disk-Halo 2500 deg2 1400 15600 Clouds in Halo All sky 13,600 deg2 [COMMENSAL] High Lat. Clouds same data set as Molecular Clouds 460 Low Latitude Plane 800 deg2 ? FV Wings ~ 10 x DD Area TBD PROJECT RRL C ON Turbulence Molecular Clouds