Zone Of Avoidance Research Articles

Parkes H I observations of galaxies behind the southern Milky Way

As part of our program to map the large-scale distribution of galaxies behind the Milky Way, we used the Parkes 210 ft (64 m) radio telescope for pointed HI observations of a sample of low surface-brightness (due to heavy obscuration) spiral galaxies selected from the deep optical Zone of Avoidance (ZOA) galaxy catalog in the Hydra/Antlia region (Kraan-Korteweg 2000a). Searching a simultaneous velocity range of either 300 to 5500 km/s or 300 to 10500 km/s to an rms level of typically 2 - 4 mJy resulted in detections in 61 of the 139 pointings, leading to a total of 66 detections (an additional detection was made in a reference position, and two other pointings revealed two and four independent signals respectively). Except for 2 strong HI emitters identified in the shallow Zone of Avoidance HI survey (Henning et al. 2000), all HI detections are new. An analysis of the properties of the observed and detected galaxies prove that pointed HI observations of highly obscured galaxies allow the tracing of a population of nearby, intrinsically large and bright spiral galaxies that otherwise would not be recovered. The new data identified a previously unrecognized nearby group at l=287.5, b=-9.5, V=1700 km/s, the continuation of the Hydra/Antlia filament on the opposite side of the Galactic plane, and helped to delimit a distinct void in the ZOA centered at 2000 km/s.

A Blind H [CSC]i[/CSC] Survey for Galaxies in the Zone of Avoidance, 308° ≤ [CLC][ITAL]l[/ITAL][/CLC] ≤ 332°

We report on a blind neutral hydrogen survey for galaxies using the 21 cm multibeam receiver on the Parkes 64 m telescope. The surveyed region covers |b| ≤ 5° in the zone of avoidance (ZOA) from Galactic longitude 308° to 332°. The survey represents the first phase of a blind H I survey covering the southern ZOA (l = 212° to 36°). We have detected H I in 42 galaxies above a 3 σ limit of 60 mJy. The galaxies detected in this survey have velocities out to 6000 km s-1 and H I masses in the range 4 × 107 to 3 × 1010M⊙ (h). Only eight of the 42 galaxies have velocities previously measured. A further nine galaxies appear to have optical counterparts in the Woudt's 1998 catalog. In total, 16 of the galaxies appear to be associated with IRAS sources, although only three of these are without optical counterparts. The estimated median extinction for the 20 galaxies with optical or IR counterparts is AB = 3.8 mag. For the 22 galaxies with no counterparts, the estimated median extinction is AB = 5.6 mag. The distribution of galaxies is suggestive of a connection between the Centaurus supercluster above the Galactic plane and the Pavo-Indus supercluster beneath the plane. No previously hidden concentrations of galaxies were found.

DENIS Observations of Multibeam Galaxies in the Zone of Avoidance

AbstractRoughly 25% of the optical extragalactic sky is obscured by the dust and stars of our Milky Way. Dynamically important structures might still lie hidden in this zone. Various surveys are presently being employed to uncover the galaxy distribution in the Zone of Avoidance (ZOA), but all suffer from (different) limitations and selection effects. We illustrate the promise of using a multi-wavelength approach for extragalactic large-scale studies behind the ZOA, i.e. a combination of three surveys, optical, systematic blind HI and near-infrared (NIR), which will allow the mapping of the peculiar velocity field in the ZOA through the NIR Tully–Fisher relation. In particular, we present here the results of cross-identifying HI-detected galaxies with the DENIS NIR survey, and the use of NIR colours to determine foreground extinctions.

Overview of Uncovered and Suspected Large-scale Structures behind the Milky Way

AbstractVarious dynamically important extragalactic large-scale structures in the local Universe lie behind the Milky Way. Most of these structures (predicted and unexpected) have only recently been made ‘visible’ through dedicated deep surveys at various wavelengths. The wide range of observational searches (optical, near infrared, far infrared, radio and X-ray) for galaxies in the Zone of Avoidance (ZOA) will be reviewed and the uncovered and suspected large-scale structures summarised. Particular emphasis is given to the Great Attractor region where the existence of yet another cluster is suspected (Woudt 1998). Predictions from reconstructions of the density field in the ZOA are discussed and compared with observational evidence. Although no major structures are predicted out to about v ≲ 10,000 km s−1 for which no observational evidence exists, the comparison between reconstructed density fields and the observed galaxy distribution remain important as they allow derivations of the density and biasing parameters.

Blind HI Survey in the Great Attractor Region

AbstractOptically, the Zone of Avoidance (ZOA) can only be explored to within a few degrees of the Galactic Equator. This restriction does not apply to radio wavelengths where we are able to detect galaxies at great distances behind the Galactic Plane. Using the Parkes 21 cm multibeam instrument we have detected neutral hydrogen (HI) in 42 galaxies in the region of the Great Attractor. We have been able to identify nine galaxies and make positional associations with a further six from existing optical catalogues, which makes at least 60% of these galaxies new discoveries.

Galaxy candidates in the Zone of Avoidance

Motivated by recent discoveries of nearby galaxies in the Zone of Avoidance (ZOA), we conducted a pilot study of galaxy candidates at low galactic latitude, near galactic longitude l ∼135°, where the Supergalactic plane is crossed by the Galactic plane. We observed with the 1-m Wise Observatory in the l band 17 of the ‘promising’ candidates identified by visual examination of Palomar red plates by Hau et al. A few candidates were also observed in R or B bands, or had spectroscopic observations performed at the Isaac Newton Telescope and at the Wise Observatory. Our study suggests that there are probably 10 galaxies in this sample. We also identify a probable planetary nebula. The final confirmation of the nature of these sources must await the availability of full spectroscopic information. The success rate of ∼50 per cent in identifying galaxies at galactic latitude ǀbǀ < 5° indicates that the ZOA is a promising region to discover new galaxies.

Penetrating the "zone of avoidance”

As the fourth part in a series of papers on galaxies in the zone of avoidance (ZOA) of the Milky Way we present a compilation of 1067 galaxies discovered during a systematic search on Palomar Observatory Sky Survey I (POSS I) red-sensitive prints. The region searched comprises 500 square degrees, at 130° 180°, -5° +5°. In addition to galactic and equatorial coordinates, we list maximum and minimum optical diameters derived from both the red- and blue-sensitive prints and made cross checks with the IRAS PSC catalogue. An asymmetric distribution of the galaxies with respect to the galactic equator is found and is compared to the locations of optically visible dust clouds and/or the distribution of IR-emitting dust material. There is a pronounced bridge of galaxies across the galactic plane at 160° which will be discussed according to recent results on the extension of the Pisces-Perseus supercluster.