6 research outputs found
Detection of broad 21-cm absorption at z = 0.656 in the complex sight-line towards 3C336
We report the detection of 21-cm absorption at z = 0.656 towards 1622+238
(3C336). The line is very broad with a Full-Width Half Maximum (FWHM) of 235
km/s, giving a velocity integrated optical depth of 2.2 km/s. The centroid of
the line is offset from that of the known damped Lyman-alpha absorption (DLA)
system by 50 km/s, and if the Lyman-alpha and 21-cm absorption are due to the
same gas, we derive a spin temperature of < 60 K, which would be the lowest yet
in a DLA. The wide profile, which is over four times wider than that of any
other DLA, supports the hypothesis that the hydrogen absorption is occurring
either in the disk of a large underluminous spiral or a group of dim
unidentified galaxies, associated with the single object which has been
optically identified at this redshift.Comment: 5 pages, 3 figures, accepted by MNRAS Letter
A Thin HI Circumnuclear Disk in NGC4261
We report on high sensitivity, spectral line VLBI observations of the HI
absorption feature in the radio galaxy NGC4261. Although absorption is only
detectable on the most sensitive baseline, it can be unambiguously associated
with the counterjet and is interpreted to originate in a thin atomic
circumnuclear disk. This structure is probably a continuation of the dusty
accretion disk inferred from HST imaging, which could be feeding the massive
black hole. HI column densities in front of the counterjet of the order of
10^{21}(T_sp/100 K) cm^{-2} are derived, consistent with X-ray data and VLBI
scale free-free absorption. The data presented here are the result of the first
scientific project processed on the new EVN MkIV data processor.Comment: 4 pages, 3 postscript figures, Astronomy and Astrophysics Letters, in
pres
A 22GHz search for molecular absorption at z~3 with the upgraded ATCA
We report a lambda > 1cm search for rotational molecular absorption towards
quasars, now possible with the upgraded Australia Telescope Compact Array
(ATCA). The targets were PKS 0201+113, PKS 0336-017 and Q 0537-286, where known
damped Lyman-alpha absorption systems (DLAs) could cause redshifted molecular
absorption in the 12mm band of the telescope. We place 3-sigma upper limits on
any HCO+ 0-1 absorption features of < 30mJy per 3.4km/s channel. The
non-detections could be attributed to the inherent low metallicities in DLAs
leading to generally low H_2, and thus HCO+, column densities. In general, the
detection of molecular rotational transitions in DLAs could be further hindered
by a lower than expected CO-to-H_2 conversion ratio, whether due either to
photoionization of carbon or its relative under-abundance at high redshift.Comment: 5 pages, 3 EPS figures, 2 tables, accepted by MNRA
The 1000 Brightest HIPASS Galaxies: HI Properties
(abridged) We present the HIPASS Bright Galaxy Catalog (BGC) which contains
the 1000 HI-brightest galaxies in the southern sky as obtained from the HI
Parkes All-Sky Survey (HIPASS). The selection of the brightest sources is based
on their HI peak flux density (Speak > 116 mJy) as measured from the spatially
integrated HIPASS spectrum. The derived HI masses range from about 10^7 to 4 x
10^10 Msun. While the BGC (z < 0.03) is complete in Speak, only a subset of
about 500 sources can be considered complete in integrated HI flux density (FHI
> 25 JY km/s). The HIPASS BGC contains a total of 158 new redshifts and yields
no evidence for a population of "free-floating" intergalactic HI clouds without
associated optical counterparts. HIPASS provides a clear view of the local
large-scale structure. The dominant features in the sky distribution of the BGC
are the Supergalactic Plane and the Local Void. In addition, one can clearly
see the Centaurus Wall which connects via the Hydra and Antlia clusters to the
Puppis filament. Some previously hardly noticed galaxy groups stand out quite
distinctively in the HI sky distribution. Several new structures are seen for
the first time, not only behind the Milky Way.Comment: AJ, accepted (scheduled for publication in July 2004). Latex, 46
pages. The HIPASS BGC paper, figures, tables, HI spectra and further
infromation are available at
http://www.atnf.csiro.au/research/multibeam/HIPASS-BG
Observations of HI absorbing gas in compact radio sources at cosmological redshifts Recommended Citation Observations of H i absorbing gas in compact radio sources at cosmological redshifts
Abstract. We present an overview of the occurrence and properties of atomic gas associated with compact radio sources at redshifts up to z = 0.85. Searches for H i 21 cm absorption were made with the Westerbork Synthesis Radio Telescope at UHF-high frequencies (725-1200 MHz). Detections were obtained for 19 of the 57 sources with usable spectra (33%). We have found a large range in line depths, from τ = 0.16 to τ ≤ 0.001. There is a substantial variety of line profiles, including Gaussians of less than 10 km s −1 , to more typically 150 km s −1 , as well as irregular and multi-peaked absorption profiles, sometimes spanning several hundred km s −1 . Assuming uniform coverage of the entire radio source, we obtain column depths of atomic gas between 1×10 19 and 3.3×10 21 (Tsp/100 K)(1/f ) cm −2 . There is evidence for significant gas motions, but in contrast to earlier results at low redshift, there are many sources in which the H i velocity is substantially negative (up to v = −1420 km s −1 ) with respect to the optical redshift, suggesting that in these sources the atomic gas, rather than falling into the centre, may be be flowing out, interacting with the jets, or rotating around the nucleus