The ALFALFA Catalog Data
All sources have been extracted from three-dimensional spectral data cubes exploiting a matched filtering technique and then examined interactively to yield global HI parameters. Catalog details can be found in the first ALFALFA catalog paper Giovanelli et al. 2007 AJ 133, 2559 which describes the survey and how the catalogues are constructed.
Variable Name Format Data Content
Object A17 A temporary entry identifier for this Catalog. Note:
Since the astrometry may be updated after the source is extracted,
this designation is for INTERNAL PURPOSES only!
AGC A6 The source number in the AGC, a private database
of extragalactic objects maintained by M.P.H. and
R.G. The AGC entry normally correspnds to the optical
counterpart except in the cases of HI sources that
cannot be associated with and optical object with any
high degree of probability.
Other A8 Alternative source name.
Ellipse Center A15 Center (J2000) of the ellipse bounding the HI source after
correction for systematic telescope pointing errors, with a
range between a few and about a dozen arcseconds. On average,
the positional accuracy is about 24". Measured in RA and DEC,
where the units of right ascension are hours, minutes, and
seconds, and units of declination are degrees, arcminutes,
dRA I3 Difference in the degrees RA of the Ellipse Center and the
dDEC I3 Difference in the degrees DEC of the Ellipse Center and the
Optical Center A15 Center (J2000.0) of the optical galaxy found to provide a
reasonable optical counterpart. For objects with no
discernible optical counterpart and those for which such
assignment is ambiguous, due to the presence of more than
one equally possible optical counterpart, no optocal
position is listed. The latter set includes HVCs.
v50 I5 Heliocentric velocity, in km/s, of the HI source
measured as the midpoint between the channels at
which the flux density drops to 50% of the two peaks.
Verr I2 The error of v50 adopted as half the error on the
width, tabulated in W50
W50 I3 Velocity width of the source line profile, W50,
measured at 50% level of each two peaks.
Werr I3 Error in W50 measured as the sum in quadrature of two
components: the first is a statistical error, the
second is a systematic error associated with the
subjective guess with which the observer estimates
the spectral boundaries of the feature.
SintP F5.2 Integrated HI line flux density in Jy-km/s
Serr F4.2 Error of the integrated flux density.
Sintmap F5.2 (in general, not of use)
S/N F5.1 S/N of the detection
rms F4.2 Noise figure of the spatially integrated spectral
profile in mJy. The noise figure as tabulated is
the rms and measured over the signal- and RFI-free
portions of the spectrum, after Hanning smooting to
a spectral resolution of 10 km/s
code I1 Object code defined as follows:
Code 1 refers to sources of S/N and general quantities
that make it a reliable detection.
Code 2 refers to sources of low S/N (<6.5), which
would ordinarily not be considered reliable detections
by the criteria set for code 1.
Code 9 refers to objects assumed to be HVC's; no
estimate of their distances is made.
Grid A8 grid of pre-processed raw data on which the source can
ALFALFA Catalog records are now 156 characters in length:
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Last modified: Fri Jun 24 18:06:37 EDT by martha