Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.naic.edu/alfa/ealfa/papers/2006AAS...209.9504S.pdf Дата изменения: Thu Jan 4 19:06:25 2007 Дата индексирования: Sat Dec 22 19:16:11 2007 Кодировка: Поисковые слова: dust

The ALFA Zone of Avoidance Survey: Results from the Precursor Observations
C.M. Springob (NRC-Naval Research Lab), P.A. Henning (UNM), B. Catinella (NAIC), F. Day (UNM), R. Minchin, E. Momjian (NAIC), B. Koribalski (ATNF), K.L. Masters (CfA), E. Muller (ATNF), C. Pantoja (U. Puerto Rico), M. Putman (U. Michigan), J.L. Rosenberg (George Mason U.), S. Schneider (U. Mass.), L. Staveley-Smith (U. Western Australia)

Introduction
We present new extragalactic 21 cm observations in the Galactic Plane region. These observations are a precursor to a large scale, extragalactic, Zone of Avoidance (ZOA) survey with the Arecibo L-band Feed Array (ALFA). The data for this survey are being taken concurrently with a Galactic survey and a pulsar survey. Full survey observations, which will begin in 2007, will reveal local large scale structure in a part of the extragalactic sky that is relatively unexplored due to the obscuration of optical light by dust in our Galaxy. One of these surveys will have an integration time of 268 seconds per point in the inner Galaxy and 134 seconds in the outer Galaxy, covering |b|<5o, while the other will have an integration time of only 5 seconds per point, covering |b|<10o with an rms of roughly 6 mJy. No other extragalactic ALFA survey will cover these latitudes. Precursor observations have been made using the latter observational setup on two patches of sky totaling 140 deg2 (one near l=40o, and the other near l=192o ). We have measured HI parameters for detections from these observations, and cross-correlated with the NASA/IPAC Extragalactic Database. A significant fraction of the objects are new, having never been detected at any wavelength. For those galaxies that have been previously detected, about half have no previously known redshift, and no previous HI detection.

Data Reduction
Data reduced using software originally developed for the Parkes Multibeam surveys (L iveData, 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. Data reduction has been completed for the entire l~40o region and 2/7ths of the l~192o region.

Why survey the ZOA in HI?

Figure 3 Spectrum of a previously unknown galaxy from the precursor observations.

Figure 4 HI Image of the galaxy from Figure 3.

The ZOA has been narrowed by deep optical / IR searches, but both fail in regions Results of high extinction and stellar confusion. Galaxies which contain HI can be found in regions of thickest obscuration and worst IR confusion. 34 galaxies detected in the Goals of the survey: 70 deg2 of sky reduced so Reveal large scale structure in an unexplored region of the local universe far. Combine with HI detections of other ALFA surveys to produce HI mass Figure 5 Left heliocentric function for tens of thousands of galaxies redshift and right HI flux distributions for the 34 detections. Combine with 2MASS photometry, and HI spectroscopy from the rest of the Of the 34 sky to produce an all sky TF catalog, producing distances and peculiar velocities detections: for ~5000 galaxies, extending deep into ZOA (Masters et al. 2005) 9 have no known counterpart--obser ved here for the first time But only 15 of the 25 known objects have previously known redshifts (mostly radio) 13 objects with previously known HI fluxes and widths Figure 1 (From Henning et al. 2006) redshift slices of known galaxies in and near the inner
and outer Galaxy regions accessible to Arecibo. Top panels show galaxies with vhel < 3500 km/s, middle panels with 3 500 < vhel < 6500 km/s, and bottom panels with 6500 < vhel < 9500 km/s. Known and suspected large-scale structures are labeled (Fairall 1998).
b

Figure 6 Left HI fluxes and right H I widths for galaxies with H I parameters in the literature--comparison between our values and literature values. Our fluxes correlate more strongly with values from literature than our widths. However, width errors are typically of order ~10-15%, so most of our values are in agreement.

Precursor Observations
While the full survey will not begin until the spring of 2007, we conducted precursor observations in 2005-2006 on a 40 deg2 patch of sky, in the vicinity of l~40o, and a separate 100 deg2 patch of sky near l~192o . Each point on the sky is covered by two passes, of ~2.5 sec. integration time each.

Conclusions
- We intend to map the full ZOA in the Arecibo sky to b = ± 10°, with 5 sec int. time. Extrapolating from the detection rate of the precursor regions, this should yield ~900 galaxies. - Will also map the ZOA over all longitudes within ± 5° of the plane with ~30 times longer integration time. - The majority of our detections have known counterparts in the literature, but no previously known redshifts--exploring new part of LSS. - We find a strong correlation between our HI parameters and those from the literature.
100 80 60 40 20 l 220 200 180 160

Figure 2 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. Green boxes indicate ALFA ZOA precursor regions.

Acknowledgements
This research was performed while C.M.S. held a National Research Council Research Associateship Award at the Naval Research Laboratory. Basic research in astronomy at the Naval Research Laboratory is supported by 6.1 base funding. P.A.H. acknowledges support from NSF grant AST-0506676. The Arecibo Observatory is part of the National Astronomy and Ionosphere Center, which is operated by Cornell University under a cooperative agreement with the National Science Foundation.

References
Donley et al. 2005 AJ 129, 220. Fairall 1998, Large-Scale Structures in the Local Universe (Chichester: Wiley). Henning et al. 2006 BAAS 208.5304. Masters et al. 2005 BAAS 37, 1427. Pantoja et al. 1997 AJ 113, 905. Wong et al. 2006 MNRAS in press (astro-ph/0607491).