1,328 research outputs found
Large-scale structure in a new deep IRAS galaxy redshift survey
We present here the first results from two recently completed, fully sampled redshift surveys comprising 3703 IRAS Faint Source Survey (FSS) galaxies. An unbiased counts-in-cells analysis finds a clustering strength in broad agreement with other recent redshift surveys and at odds with the standard cold dark matter model. We combine our data with those from the QDOT and 1.2 Jy surveys, producing a single estimate of the IRAS galaxy clustering strength. We compare the data with the power spectrum derived from a mixed dark matter universe. Direct comparison of the clustering strength seen in the IRAS samples with that seen in the APM-Stromlo survey suggests b_O/b_I=1.20+/-0.05 assuming a linear, scale independent biasing. We also perform a cell by cell comparison of our FSS-z sample with galaxies from the first CfA slice, testing the viability of a linear-biasing scheme linking the two. We are able to rule out models in which the FSS-z galaxies identically trace the CfA galaxies on scales 5-20h^{-1}Mpc. On scales of 5 and 10h^{-1}Mpc no linear-biasing model can be found relating the two samples. We argue that this result is expected since the CfA sample includes more elliptical galaxies which have different clustering properties from spirals. On scales of 20h^{-1}Mpc no linear-biasing model with b_O/b_I < 1.70 is acceptable. When comparing the FSS-z galaxies to the CfA spirals, however, the two populations trace the same structures within our uncertaintie
Scattering of Straight Cosmic Strings by Black Holes: Weak Field Approximation
The scattering of a straight, infinitely long string moving with velocity
by a black hole is considered. We analyze the weak-field case, where the impact
parameter () is large, and obtain exact solutions to the equations of
motion. As a result of scattering, the string is displaced in the direction
perpendicular to the velocity by an amount , where . The second
term dominates at low velocities . The late-time
solution is represented by a kink and anti-kink, propagating in opposite
directions at the speed of light, and leaving behind them the string in a new
``phase''. The solutions are applied to the problem of string capture, and are
compared to numerical results.Comment: 19 pages, 5 figure
The first VLBI image of an Infrared-Faint Radio Source
Context: To investigate the joint evolution of active galactic nuclei and
star formation in the Universe. Aims: In the 1.4 GHz survey with the Australia
Telescope Compact Array of the Chandra Deep Field South and the European Large
Area ISO Survey - S1 we have identified a class of objects which are strong in
the radio but have no detectable infrared and optical counterparts. This class
has been called Infrared-Faint Radio Sources, or IFRS. 53 sources out of 2002
have been classified as IFRS. It is not known what these objects are. Methods:
To address the many possible explanations as to what the nature of these
objects is we have observed four sources with the Australian Long Baseline
Array. Results: We have detected and imaged one of the four sources observed.
Assuming that the source is at a high redshift, we find its properties in
agreement with properties of Compact Steep Spectrum sources. However, due to
the lack of optical and infrared data the constraints are not particularly
strong.Comment: Accepted for publication in Astronomy and Astrophysics, 5 pages,
needs aa.cl
High-velocity-resolution observations of OH main line lasers in the M82 starburst
Using the VLA, a series of high velocity resolution observations have been
made of the M82 starburst at 1.6 GHz. These observations follow up on previous
studies of the main line OH maser emission in the central kiloparsec of this
starburst region, but with far greater velocity resolution, showing significant
velocity structure in some of the maser spots for the first time. A total of
thirteen masers were detected, including all but one of the previously known
sources. While some of these masers are still unresolved in velocity, these new
results clearly show velocity structure in spectra from several of the maser
regions. Position-velocity plots show good agreement with the distribution of
H{\sc i} including interesting velocity structure on the blueward feature in
the west of the starburst which traces the velocity distribution seen in the
ionised gas.Comment: MNRAS in press. 15 pages, 9 figure
The remarkable infrared galaxy ARP 220 = IC 4553
IRAS observations of the peculiar galaxy Arp 220 = IC 4553 show that it is extremely luminous in the far-infrared with a total luminosity of - 2 X 10^(12) L_☉. The infrared-to-blue luminosity ratio of this galaxy is - 80, which is the largest value of the ratio for galaxies in the UGC catalog, and places it in the range of the
"unidentified" infrared sources recently reported by Houck et al. in the IRAS all-sky survey. Other observations of Arp 220, combined with the luminosity in the infrared, allow either a Seyfert-like or starburst origin for this luminosity
VLBI Imaging of Luminous Infrared Galaxies: AGN Cores in Mrk231, UGC 5101 & NGC 7469
We report 18cm VLBI continuum imaging observations at 5 mas resolution for
UGC 5101, NGC 7469, and Mrk 231, all part of a sample of Luminous Infrared
Galaxies which have been shown to have strong VLBI radio cores. The radio
morphology of these three systems on VLBI scales is AGN-like, with well-defined
ridgelines and high-brightness yet spatially resolved components. The structure
and flux densities of these VLBI components are not consistent with starburst
generated radio supernovae of the type found in Arp 220. On scales of 100pc the
radio continuum in all three objects appears to be dominated by an AGN, not a
starburst. Radio emission on larger scales may well originate in a less compact
circumnuclear star-forming region.
Confirming and extending VLBI imaging of Mrk 231 by Ulvestad et al. (1999),
our continuum image shows a triple structure, with a core and two lobes,
classifying it as a Compact Symmetric Object (CS0). If the southern (primary)
lobe/hot-spot in Mrk 231 is confined by ram pressure, we estimate a lobe
advance speed, , and an age for the jet/compact source, . We have also imaged the 1667 MHz OH maser emission in Mrk 231, which
is extended on scales of 50--100 milliarcsec (40--80 pc) and probably coincides
with the inner region of the disk which is seen in CO emission and HI
absorption. Among OH megamasers studied at high sensitivity with mas
resolution, Mrk 231 is unique in the stringent upper limits placed upon the
flux density of compact OH structures of the type found in Arp 220 and other
LIGs. It is possible that the circumnuclear environment of Mrk 231 has been
sufficiently disrupted by the emergent QSO that the cool, dense clouds
necessary for such compact masers no longer exist.Comment: 43 pages, 7 figure
The radio spectra of the compact sources in Arp 220: A mixed population of supernovae and supernova remnants
We report the first detection at multiple radio wavelengths (13, 6 and 3.6
cm) of the compact sources within both nuclei of the Ultra Luminous Infra-Red
Galaxy Arp 220. We present the radio spectra of the 18 detected sources. In
just over half of the sources we find that these spectra and other properties
are consistent with the standard model of powerful Type IIn supernovae
interacting with their pre-explosion stellar wind. The rate of appearance of
new radio sources identified with these supernova events suggests that an
unusually large fraction of core collapse supernovae in Arp 220 are highly
luminous; possibly implying a radically different stellar initial mass function
or stellar evolution compared to galactic disks. Another possible explanation
invokes very short (~3 x 10^5 year) intense (~10^3 M_Sol year^-1) star
formation episodes with a duty cycle of ~10%. A second group of our detected
sources, consisting of the brightest and longest monitored sources at 18 cm do
not easily fit the radio supernova model. These sources show a range of
spectral indexes from -0.2 to -1.9. We propose that these are young supernova
remnants which have just begun interacting with a surrounding ISM with a
density between 10^4 and 10^5 cm^-3. One of these sources is probably resolved
at 3.6 cm wavelength with a diameter 0.9 pc. In the western nucleus we estimate
that the ionized component of the ISM gives rise to foreground free-free
absorption with opacity at 18 cm of <0.6 along the majority of lines of sight.
Other sources may be affected by absorption with opacity in the range 1 to 2.
These values are consistent with previous models as fitted to the radio
recombination lines and the continuum spectrum.Comment: 44 pages, 9 figures, 2 tables. Accepted for publication in Ap
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