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Register a new userNew HI-detected Galaxies in the Zone of Avoidance
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Lister Staveley-Smith
Publication date
1998
fields
Physics
and research's language is
English
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We present the first results of a blind HI survey for galaxies in the southern Zone of Avoidance with a multibeam receiver on the Parkes telescope. This survey is eventually expected to catalog several thousand galaxies within Galactic latitude |b|<5 degrees, mostly unrecognised before due to Galactic extinction and confusion. We present here results of the first three detections to have been imaged with the Australia Telescope Compact Array (ATCA). The galaxies all lie near Galactic longitude 325 degrees and were selected because of their large angular sizes, up to 1.3 degrees. Linear sizes range from 53 to 108 kpc. The first galaxy is a massive 5.7x10^11 solar mass disk galaxy with a faint optical counterpart, SGC 1511.1--5249. The second is probably an interacting group of galaxies straddling the Galactic equator. No optical identification is possible. The third object appears to be an interacting pair of low column density galaxies, possibly belonging to an extended Circinus or Centaurus A galaxy group. No optical counterpart has been seen despite the predicted extinction (A(B) = 2.7 - 4.4 mag) not being excessive. We discuss the implications of the results, in particular the low HI column densities (~10^19 atoms/sq.cm) found for two of the three galaxies.
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We present a catalogue of galaxies in the northern Zone of Avoidance (ZoA), extracted from the shallow version of the blind HI survey with the Effelsberg 100 m radio telescope, EBHIS, that has a sensitivity of 23 mJy/beam at 10.24 km/s velocity resolution. The catalogue comprises 170 detections in the region Dec >= -5 degrees and |b| < 6 degrees. About a third of the detections (N=67) have not been previously recorded in HI. While 29 detections have no discernible counterpart at any wavelength other than HI, 48 detections (28%) have a counterpart visible on optical or NIR images but are not recorded as such in the literature. New HI detections were found as close as 7.5 Mpc (EZOA J2120+45), and at the edge of the Local Volume, at 10.1 Mpc, we have found two previously unknown dwarf galaxies (EZOA J0506+31 and EZOA J0301+56). Existing large-scale structures crossing the northern ZoA have been established more firmly by the new detections, with the possibility of new filaments. We conclude that the high rate of 39% new HIdetections in the northern ZoA, which has been extensively surveyed with targeted observations in the past, proves the power of blind HI surveys. The full EBHIS survey, which will cover the full northern sky with a sensitivity comparable to the HIPASS survey of the southern sky, is expected to add many new detections and uncover new structures in the northern ZoA.
To complement the 2MASS Redshift Survey (2MRS) and the 2MASS Tully-Fisher survey (2MTF) a search for 21cm HI line emission of 2MASS bright galaxy candidates has been pursued along the dust-obscured plane of the Milky Way with the 100m Nancay Radio Telescope. For our sample selection we adopted an isophotal extinction-corrected K-band magnitude limit of $K_s^o = 11.25$mag, corresponding to the first 2MRS data release and 2MTF, for which the 2MASX completeness level remains fairly constant deep into the Zone of Avoidance (ZoA). About one thousand galaxies without prior redshift measurement accessible from Nancay (Dec > -40deg) were observed to an rms noise level of ~3 mJy for the velocity range -250 to 10600 km/s. This resulted in 220 clear and 12 marginal detections of the target sample. Only few detections have redshifts above 8000 km/s due to recurring radio frequency interference (RFI). A further 29 detections and 6 marginals have their origin in non-target galaxies in the telescope beam. The newly detected galaxies are on average considerably more HI-rich (mostly $10^9 - 10^{10}$M$_odot$) compared to systematic (blind) HI surveys. The HI detections reveal various new filaments crossing the mostly uncharted northern ZoA (e.g. at $ell sim 90deg, 130deg, 160deg$), whilst consolidating galaxy agglomerations in Monoceros and Puppis ($ell sim 220deg, 240deg$). Considerably new insight has been gained about the extent of the Perseus-Pisces Supercluster through the confirmation of a ridge ($ell sim 160deg$) encompassing the 3C129 cluster that links Perseus-Pisces to Lynx, and the continuation of the second Perseus-Pisces arm ($ell sim 90deg$) across the ZoA.
A blind HI survey of the extragalactic sky behind the southern Milky Way has been conducted with the multibeam receiver on the 64-m Parkes radio telescope. The survey covers the Galactic longitude range 212 < l < 36 and Galactic latitudes |b| < 5, and yields 883 galaxies to a recessional velocity of 12,000 km/s. The survey covers the sky within the HIPASS area to greater sensitivity, finding lower HI-mass galaxies at all distances, and probing more completely the large-scale structures at and beyond the distance of the Great Attractor. Fifty-one percent of the HI detections have an optical/NIR counterpart in the literature. A further 27% have new counterparts found in existing, or newly obtained, optical/NIR images. The counterpart rate drops in regions of high foreground stellar crowding and extinction, and for low-HI mass objects. Only 8% of all counterparts have a previous optical redshift measurement. A notable new galaxy is HIZOA J1353-58, a possible companion to the Circinus galaxy. Merging this catalog with the similarly-conducted northern extension (Donley et al. 2005), large-scale structures are delineated, including those within the Puppis and Great Attractor regions, and the Local Void. Several newly-identified structures are revealed here for the first time. Three new galaxy concentrations (NW1, NW2 and NW3) are key in confirming the diagonal crossing of the Great Attractor Wall between the Norma cluster and the CIZA J1324.7-5736 cluster. Further contributors to the general mass overdensity in that area are two new clusters (CW1 and CW2) in the nearer Centaurus Wall, one of which forms part of the striking 180 deg (100/h Mpc) long filament that dominates the southern sky at velocities of ~3000 km/s, and the suggestion of a further Wall at the Great Attractor distance at slightly higher longitudes.
We present the results of the northern extension of the HI Parkes Zone of Avoidance Survey, a blind HI survey utilizing the multibeam receiver on the Parkes 64-m telescope. In the two regions studied here, l=36 to 52 deg. and l=196 to 212 deg., |b|<5 deg., we have detected 77 HI galaxies, twenty of which have been previously detected in HI. The survey has a median rms noise of 6.0 mJy/beam and is complete to a mean flux density of 22 mJy. We have searched for multiwavelength counterparts to the 77 galaxies detected here: 19, 27, and 11 have a likely optical, 2MASS, and IRAS cataloged counterpart, respectively. A further 16 galaxies have likely visible counterparts on the Digitized Sky Survey. The detection of these 77 galaxies allows a closer inspection of the large-scale structures in these regions. We see several filaments crossing the Galactic plane, one of which appears to be the continuation of a sine-wave like feature that can be traced across the whole southern sky. An analysis of the HI mass function suggests that the regions studied here may be underdense. One particularly noteworthy galaxy is HIZOA J0630+08 (l,b = 203 deg., -0.9 deg.) with a velocity of 367 km/s. We suggest that it belongs to the nearby Orion Group which includes a small number of dwarf galaxies. The newly detected galaxies improve our understanding of the properties of several voids, such as the Orion, Gemini, and Canis Major Voids.
We report the discovery of twenty-five previously unknown galaxies in the Zone of Avoidance. Our systematic search for extended extra-galactic sources in the GLIMPSE and MIPSGAL mid-infrared surveys of the Galactic plane has revealed two overdensities of these sources, located around l ~ 47 and 55 degrees and |b| less than 1 degree in the Sagitta-Aquila region. These overdensities are consistent with the local large-scale structure found at similar Galactic longitude and extending from |b| ~ 4 to 40 degrees. We show that the infrared spectral energy distribution of these sources is indeed consistent with those of normal galaxies. Photometric estimates of their redshift indicate that the majority of these galaxies are found in the redshift range z = 0.01 - 0.05, with one source located at z = 0.07. Comparison with known sources in the local Universe reveals that these galaxies are located at similar overdensities in redshift space. These new galaxies are the first evidence of a bridge linking the large-scale structure between both sides of the Galactic plane at very low Galactic latitude and clearly demonstrate the feasibility of detecting galaxies in the Zone of Avoidance using mid-to-far infrared surveys.
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