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J/AJ/122/3155 Peculiar HI cloud near galactic plane (Higgs+, 2001)
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A peculiar intermediate-velocity hydrogen cloud near the galactic plane.
Higgs L.A., Kerton C.R., Knee L.B.G.
<Astron. J. 122, 3155 (2001)>
=2001AJ....122.3155H (SIMBAD/NED BibCode)
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ADC_Keywords: Molecular clouds ; Galactic plane ; H I data ; Radial velocities
Keywords: Galaxy: kinematics and dynamics - ISM: H I - radio continuum -
radio emission lines
Abstract:
An H I cloud with a double-lobed structure and a radial velocity of
+50km/s has been found near l=92{deg}, b=-4{deg} in a low-resolution
H I survey carried out at the Dominion Radio Astrophysical Observatory
(DRAO). This velocity is forbidden for circular Galactic rotation.
Because of its unusual morphology and small variation in radial
velocity over the cloud, further observations of the area were made
with the DRAO Synthesis Telescope, both in the H I line and in the
radio continuum. The cloud has dimensions of about 3.3{deg}x0.5{deg},
and has a morphology somewhat similar to high-velocity H I clouds
(HVCs). Several possible associations with other objects are examined
in this paper. A variable inverted-spectrum radio continuum source
exists near the morphological center of the H I cloud. It is probably
a rare example of a gigahertz peaked spectrum (GPS) extragalactic
source having a peak above 5GHz. A luminous B star is found close to
the peculiar H I cloud, and the cloud is also located near the center
of an H I supershell, supposedly located at a distance of about 9kpc.
Energetic and other considerations lead to the conclusion that the
cloud is probably not related to the HVC phenomenon nor to any of the
above objects but is a relic of a nearby (D~1kpc) supernova event, all
other evidence of which has now dissipated. Maps of continuum radio
emission (at 1420 and 408MHz) in the area around the cloud are
presented, as well as lists of continuum radio sources. A few isolated
high-velocity knots of H I emission have also been detected in the
vicinity of the cloud.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 63 10 Parameters of H I knots
table4.dat 76 106 Point Sources Observed at 1420 MHz
table5.dat 76 56 Point Sources Observed at 408 MHz
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- [HKK2001] Knot number ([HKK2001] Knot NN)
4- 9 F6.3 deg GLON Galactic longitude
11- 16 F6.3 deg GLAT Galactic latitude
18- 21 F4.1 km/s RV LSR radial velocity
23- 25 F3.1 km/s e_RV rms uncertainty on RV
27- 29 F3.1 km/s DV Observed widths (1)
31- 33 F3.1 km/s e_DV rms uncertainty on DV
35- 37 F3.1 K Tb Peak brightness
39- 41 F3.1 arcmin theta1 Size of the knot
42 A1 --- --- [x]
43- 45 F3.1 arcmin theta2 Size of the knot
47- 57 A11 --- n_theta1 Note on the size
60- 63 F4.2 kpc2.solMass Mass HI mass in D^2^*solMass (2)
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Note (1): The 1.3km/s spectrometer resolution has not been removed.
Note (2): The H I masses of the knots are determined from the relation for a
Gaussian brightness distribution with peak brightness Tb (K) and
half-power widths theta1 x theta2 (arcmin^2^) and a Gaussian velocity
profile with half-power with DV (km/s), at a distance D (kpc):
M = 1.49*10^-3^*Tb*theta1*theta2*DV*D^2^
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Byte-by-byte Description of file: table4.dat table5.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Seq Designation number (1)
8- 13 F6.3 deg GLON Galactic longitude
15- 20 F6.3 deg GLAT Galactic latitude
22- 23 I2 h RAh Hour of Right Ascension (J2000)
25- 26 I2 min RAm Minute of Right Ascension (J2000)
28- 31 F4.1 s RAs Second of Right Ascension (J2000)
33- 35 F3.1 s e_RAs Error in RAs
37- 38 I2 deg DEd Degree of the Declination (J2000)
40- 41 I2 arcmin DEm Arcminute of the Declination (J2000)
43- 44 I2 arcsec DEs Arcsecond of the Declination (J2000)
46 I1 arcsec e_DEs Error in DEs
48- 53 F6.1 mJy FluxDen Integrated flux density
(1420MHz for table4, 408MHz for table5)
55- 58 F4.1 mJy e_FluxDen Error in FluxDen
60- 75 A16 --- Comm Comments (2)
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Note (1): Follows designation system for DRAO source lists
(Higgs, 1986JRASC..80...51H).
71PNNN in table4, 72PNN in table5
Note (2): Comments:
a = Parameters of this source were derived from integration of image
intensity, not by Gaussian fitting
b = This source is not visible in the 408-MHz image, so spectrum may
be ``inverted''.
c = Position given here differs by 19" from that in NVSS
(Condon et al., 1998AJ....115.1693C).
E = The source may be slightly resolved (one of the deconvolved
dimensions exceeds 15" in 1420MHz images).
V = The source may be variable.
F = The 408/1420 MHz spectral index is flat (0.25>{alpha}>-0.25)
where S_int_ {propto} {nu}^{alpha}^
I = The spectral index is ``inverted'' ({alpha}>0.25)
+ = 1420-MHz sources weaker than 10mJy contribute to the 408-MHz
source
? = A discrepancy of more than 45'' exists between the 1420-MHz
and 408-MHz positions.
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History:
From electronic version of the journal
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(End) Greg Schwarz [AAS], Patricia Bauer [CDS] 07-Mar-2002