Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.naic.edu/alfa/ealfa/papers/ZOA-AAS208.pdf Дата изменения: Wed Jun 14 01:43:39 2006 Дата индексирования: Sat Dec 22 05:36:22 2007 Кодировка: Поисковые слова: monoceros

Surveying the Zone of Avoidance with the Arecibo L-Band Feed Array
P.A. Henning (UNM), C.M. Springob (NRL), B. Catinella, E. Momjian (NAIC), B. Koribalski (ATNF), K. Masters (CfA), E. Muller (ATNF), C. Pantoja (UPR), M. Putman (U. Michigan), J.L. Rosenberg (CfA), S. Schneider (UMass), L. Staveley-Smith (ATNF)

Why Survey the Zone of Avoidance?
The obscuration due to dust and the high stellar density in our Galaxy blocks our optical view of the extragalactic Universe over 20% of the sky, somewhat less in the infrared, the "Zone of Avoidance" (ZOA). Accurate knowledge of the mass distribution within the local Universe is essential if we are to understand the dynamical evolution of the Local Group from kinematic s tudies (e.g. Peebles et al. 2001). In addition the discovery of previously unknown galaxies would further efforts to understand the dipole in the CMB, caused by the net gravitational acceleration of the Local Group due to the inhomogeneous mass distribution in the surrounding 4 steradians of the sky, and other velocity flow fields which require all-sky mapping of mass inhomogeneities to understand. Mapping hidden galaxies over a range of redshifts also allows the connectivity in three dimensions of large-scale structures across the Galactic plane to be explored. Many of the known nearby large-scale structures, eg. the Pisces-Perseus supercluster and the Great Attractor, are partially hidden by the Milky Way, and have not yet been satisfactorily mapped. Are there other dynamically important structures which remain hidden?

ZOA in the Arecibo Sky
Our Plan: Map the ZOA accessible to Arecibo, using the Arecibo L-Band Feed Array (ALFA)
Top panel shows LEDA galaxies within 12,000 km/s in and near the two ZOA regions accessible to Arecibo, the inner (left) and outer Galaxy (right). Dashed curves show the regions of sky Arecibo can see. The rectangles containing the Galactic equator show the overlap with the HI Parkes ZOA survey, with galaxies detected by Parkes plotted with heavy dots. The bottom panels indicate the Galactic extinction from the 100µm DIRBE experiment (Schlegel et al. 1998) with contours at AB = 1 mag (outer) and 3 mag (inner).

Results from Precursor Observations
We have mapped and reduced a 38 square degree field, using a meridian-nodding "basketweave" mode, near Galactic longitude 40°, achieving 4 sec per Nyquist pixel, ~6 mJy/ beam rms noise. Observations were conducted in "commensal" mode with a Galactic HI survey (GALFA). Data reduced using software originally developed for the Parkes Multibeam surveys (LiveData, Gridzilla), adapted for Arecibo. Data are gridded using a median filter, taking advantage of the re-observations of sky pointings afforded by the basketweave technique. Cubes are searched by eye, parameters fit in miriad. 9 Galaxies were uncovered in this precursor region, 6 previously known from HIZOA, and 3 new HI detections. For ALFA detections of HIZOA sources, all measured positions and heliocentric velocities are within beam size, and velocity resolution for HIZOA. No systematic difference for fluxes.
RA 18h 18 19 19 19 19 19 19 19 44m 55 01 06 08 17 20 20 22 (J2000) 38.4s 13.3 34.6 33.8 25.9 23.7 03.3 43.2 02.2 5° 7 6 7 5 7 6 6 8 Dec 54ґ 37 51 35 59 50 11 11 18 18" 06 44 03 29 21 10 42 21 l 3 7.42 40.15 40.19 41.40 40.20 42.87 41.71 41.80 43.82 Flux Int. J y km/s ° 4 .20° 1.15 2.63 5.39 0.88 11.36 0.11 6.26 ­1 .03 3.48 ­2 .17 6.18 ­3 .50 1.14 ­3 .64 6.72 ­2 .94 6.10 b V h el W 50 Ident? km/s km/s 9656 63 None 6156 294 HIZOA J1855+07 2950 81 HIZOA J1901+06 3081 196 HIZOA J1906+07 4564 178 HIZOA J1908+05 3029 217 HIZOA J1917+07 6215 109 None 6341 425: IRAS 19182+0604 3094 137 HIZOA J1921+08

Profile of an ALFA ZOA detected galaxy, also known from the P arkes HIZOA survey

A newly-discovered galaxy from ALFA ZOA precursor observations.

Why Survey the ZOA at 21-cm?
The ZOA has been successfully narrowed by deep searches in the optical and IR, but both fail in regions of high extinction and stellar confusion. Galaxies which contain HI can be found in regions of thickest obscuration and worst IR confusion. The HI Parkes Zone of Avoidance Survey (HIZOA) surveyed the southern ZOA to 6 mJy/beam, and the Dwingeloo northern ZOA survey to a shallow 40 mJy/beam.
How a 21-cm survey fills in the ZOA: Top panel shows galaxies from the LEDA database with velocities measured within 10,000 km/s. Dashed lines show the borders of the P arkes ZOA search area in the southern hemisphere, and extension to the north, to Dec +20° . The lower panel adds the galaxies uncovered by the HI Parkes ZOA Survey (Henning et al. in prep.). The HI-detected objects fill in the optical ZOA remarkably well. The Great Attractor region is seen as an overdensity at l 300° 340°, the Hydra-Antlia f ilament at l 280° and the Puppis filament crosses the Galactic plane at l 240°. The Local and Sagittarius voids are visible as an underdensity at l 350° 52°.

A 100 square degree field near l=190° has been observed, reductions are ongoing.

Conclusion
The ALFA ZOA team intends to map the full ZOA in the Arecibo sky, starting with the inner Galaxy, l = 30° - 75°, to b = ±10° commensally with GALFA. Extrapolating from the detection rate of the l ~40° region and the HIZOA, this should yield ~500 galaxies in the inner Galaxy region alone. We also plan to map the outer Galaxy l = 170° - 215° area as well. When new spectrometer development allows, we will also map the ZOA over all longitudes within ± 5° of the plane commensally with a deep PALFA pulsar project, with effective integration time ~30 times longer per pointing.
P.A.H. acknowledges support from NSF grant AST-0506676 References
Fairall, A.P. 1998, Large-Scale Structures in the Local Universe (Chichester: Wiley) Henning, P.A., K raan- K orteweg, R.C., & S taveley - Smith, L. 2005, in workshop on " N earby Large-Scale Structures and the Zone of Avoidance " , ASP Conf. Ser. 329, eds. A.P. F airall & P.A. W oudt, (San Francisco: ASP), 199 Kraan- K orteweg, R.C., K oribalski, B.S., & Juraszek, S. 1999, in ESO/ATNF Workshop on " L ooking Deep in the Southern Sky" , eds. R. M organti & W. Couch, Springer, 23 Kraan- K orteweg, R.C., S taveley-Smith, L., Donley, J., K oribalski , B., & Henning, P.A. 2005 in IAU Symp. 216, " Maps of the Cosmos" , eds., M. Colless, L. S taveley- Smith, and R. S tathakis, (San Francisco: ASP), 203 Peebles, P.J.E., Phelps, S.D., S haya, E.J., & Tully, R.B. 2001, A pJ, 554, 104 Schlegel, D.J., F inkbeiner , D.P., & Davis, M. 1998, A pJ 5 00, 525

Redshift s lices of known galaxies in and near the inner and outer Galaxy regions accessible to Arecibo. Top panels show galaxies with v hel < 3500 km/s, middle panels with 3500 < v hel < 6500 km/s, and bottom panels with 6500 < v hel < 9500 km/s. Known and suspected large-scale structures are labeled (Fairall 1998).

The ALFA ZOA Survey will:
Define the edges of the Gemini, Canis Major, Microscopium, and Cygnus voids; probe contents of Delphinus void Determine the reality of the Orion void Map end of the "sine wave" feature, indicated by southern surveys (Kraan-Korteweg et al.1999) Map the newly-discovered nearby Monoceros filament (Henning et al. 2005, Kraan-Korteweg et al. 2005) Almost certainly uncover new large-scale structures

UNM

University of New Mexico Department of Physics and Astronomy

P. Henning: henning@as.unm.edu