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For refcode 1992AJ....104.1505L:
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1992AJ....104.1505L A SURVEY OF SMALL-SCALE EXTREMES IN EXTINCTION AT LOW GALACTIC LATITUDES USING IRAS GALAXIES N. Y. LU, J. R. HOUCK, AND E. E. SALPETER Center for Radiophysics and Space Research, Cornell University, Ithaca, New York 14853 B. M. LEWIS Arecibo Observatory, National astronomy and Ionosphere Center, P.O. Box 995, Arecibo, Puerto Rico 00613 Received 9 March 1992; revised 2 June 1992 ABSTRACT We report V- and I-band CCD photometry of 94 IRAS galaxies of which 46 are at high Galactic latitudes (|b| > 35^deg^) and the remaining 48 are at low Galactic latitudes (2^deg^ < |b| < 16^deg^). For each observed wavelength band, the Tully-Fisher relation based on the high latitude galaxies is used to infer the expected optical apparent magnitudes of the low latitude galaxies free from Galactic obscuration. Comparison of such expected magnitudes with the observed ones gives an estimate of the Galactic extinction and reddening in the direction towards each low latitude galaxy. The systematic survey in this paper (1) is optically unbiased in selecting target positions for survey, (2) explored absolute Galactic latitudes below 10^deg^ where no systematic survey was available before, and (3) revealed the properties of Galactic extinction over angular scales of a few arcminutes. Extinctions with an error of order ~0.45 mag are obtained towards 28 low latitude spiral galaxies in both V and I. The following results are found. (a) Extinctions in V and I bands are linearly correlated with A_I_0.58 A_V_ (with rms scatter of ~0.31 mag), with no noticeable environmental dependence and consistent with existing results of Galactic reddening. (b) There is a large scatter in the simple linear relation with csc |b|, confirming the existence of "holes" and patches at low Galactic latitudes. The median csc |b| relation has a slope close to 0.1, similar to that at high latitudes. (c) The mean correlation between Galactic extinction and H I column density over a comparable angular scale is also found to be consistent with those at high latitudes over larger angular scales. This correlation is slightly better than the csc |b| law, with rms scatter of ~0.38 mag in V band and -0.30 mag in I band. (d) Correlation is also found between optical extinction and the IRAS 100 micron sky brightness, and this sky brightness is only slightly worse than H I column density as a indicator for optical extinction. No compact Bok globules with sizes larger than ~5" and A_V_=>2 mag were found over the surfaces of the 26 low latitude galaxies with |b| < 10^deg^. This also implies that any fluctuations of A_V_ over subarcminute scale are probably much less than 0.5 mag for |b| > 3^deg^. A comparison of our results with Burstein and Heiles reddening survey [AJ,87,1165(1982)] suggests that fluctuations over scales of arcminutes are not great either (probably <1 mag in visual) for |b| > 10^deg^.
Retrieve 97 NED objects in this reference.
Please click here for ADS abstract

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