J/AJ/133/2569 Arecibo legacy fast ALFA survey III. (Giovanelli+, 2007)
The Arecibo legacy fast ALFA survey.
III. H I source catalog of the northern Virgo cluster region.
Giovanelli R., Haynes M.P., Kent B.R., Saintonge A., Stierwalt S.,
Altaf A., Balonek T., Brosch N., Brown S., Catinella B., Furniss A.,
Goldstein J., Hoffman G.L., Koopmann R.A., Kornreich D.A., Mahmood B.,
Martin A.M., Masters K.L., Mitschang A., Momjian E., Nair P.H.,
Rosenberg J.L., Walsh B.
<Astron. J., 133, 2569-2583 (2007)>
=2007AJ....133.2569G 2007AJ....133.2569G
ADC_Keywords: Surveys ; H I data ; Galaxies, radio ; Radial velocities
Keywords: galaxies: distances and redshifts - galaxies: halos
galaxies: luminosity function, mass function - galaxies: photometry
galaxies: spiral - radio lines: galaxies
Abstract:
We present the first installment of HI sources extracted from the
Arecibo Legacy Fast ALFA (ALFALFA) extragalactic survey, initiated in
2005. Sources have been extracted from three-dimensional spectral data
cubes exploiting a matched filtering technique and then examined
interactively to yield global HI parameters. A total of 730 HI
detections are cataloged within the solid angle
11h44<RA(J2000.0)<14h00 and +12°<DE(J2000.0)<+16° and
redshift range -1600km/s<cz<18000km/s. In comparison, the HI Parkes
All-Sky Survey (HIPASS, Meyer et al. 2004, Cat. VIII/73) detected 40 HI
signals in the same region. Optical counterparts are assigned via
examination of digital optical imaging databases.
Description:
ALFALFA uses the seven-feed ALFA receiver system and a spectral-line
back end capable of instantaneously producing spectra from the two
linear polarizations of each beam and covering a bandwidth of 100MHz.
Objects:
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RA (2000) DE Designation(s)
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12 26 32.1 +12 43 24 NAME VIRGO I = NAME VIRGO CLUSTER
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 106 730 HI Candidate Detections
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See also:
VIII/77 : HI spectral properties of galaxies (Springob+, 2005)
VIII/75 : HI survey of the sky DE<+25° (Bajaja+, 2005)
VIII/73 : HI Parkes All Sky Survey Catalogue (HIPASS) (Meyer+, 2004)
J/MNRAS/357/819 : Colours and HI line observations in Virgo (Sabatini+, 2005)
J/AJ/113/905 : HI observations of galaxies (Pantoja+ 1997)
J/AJ/130/2613 : The Arecibo Legacy Fast ALFA survey. II (Giovanelli+, 2005)
J/AJ/135/588 : Arecibo legacy fast ALFA survey V. (Saintonge+, 2008)
J/AJ/136/713 : Arecibo legacy fast ALFA survey. VI. (Kent+, 2008)
http://arecibo.tc.cornell.edu/hiarchive : ALFALFA data access
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- --- [1-]
3- 5 I3 --- ALFALFA1 Catalog entry number (1-NNN)
7- 12 I6 --- AGC Arecibo General Catalog number (1)
14- 15 I2 h RAh HI Right Ascension (J2000) (2)
17- 18 I2 min RAm HI Right Ascension (J2000) (2)
20- 23 F4.1 s RAs HI Right Ascension (J2000) (2)
25 A1 --- DE- HI Declination sign (J2000) (2)
26- 27 I2 deg DEd HI Declination (J2000) (2)
29- 30 I2 arcmin DEm HI Declination (J2000) (2)
32- 33 I2 arcsec DEs HI Declination (J2000) (2)
35- 36 I2 h RAOh ? Optical Right Ascension (J2000) (3)
38- 39 I2 min RAOm ? Optical Right Ascension (J2000) (3)
41- 44 F4.1 s RAOs ? Optical Right Ascension (J2000) (3)
46 A1 --- DEO- Optical Declination sign (J2000) (3)
47- 48 I2 deg DEOd ? Optical Declination (J2000) (3)
50- 51 I2 arcmin DEOm ? Optical Declination (J2000) (3)
53- 54 I2 arcsec DEOs ? Optical Declination (J2000) (3)
56- 60 I5 km/s cz Heliocentric radial velocity (4)
62- 64 I3 km/s W50 Velocity width of source line profile (5)
66- 68 I3 km/s e_W50 Estimated error in W50 (6)
70- 74 F5.2 Jy.km/s Fc Integrated flux density (7)
76- 79 F4.2 Jy.km/s e_Fc Estimated error in Fc (8)
81- 85 F5.1 --- S/N Signal-to-noise ratio (9)
87- 90 F4.2 mJy rms Noise figure of the spatially integrated
spectral profile (10)
92- 96 F5.1 Mpc Dist ? Adopted distance (11)
98-102 F5.2 [solMass] logM ? Log of the HI mass (12)
104 I1 --- Qual Source quality code (13)
106 A1 --- Note [*] *: Additional comment(s) available in
the text
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Note (1): A private database of extragalactic objects maintained by M.P.H.
and R.G. (see Cat. VIII/77). The AGC entry normally corresponds to the
optical counterpart except in the cases of HI sources which cannot be
associated with an optical object with any high degree of probability.
Numbers lower than 100000 are UGC number (Cat. VII/26).
Note (2): Center of the HI source, after correction for systematic
telescope pointing errors, which range between a few and about a dozen
arcsec, as described in Section 5. The accuracy of the HI positions
depends on source strength. On average, the positional accuracy is
about 24". See Section 5 for details.
Note (3): Center of the optical galaxy found to provide a reasonable
optical counterpart. This position has been checked for each listed
object and assessed using tools provided through the SDSS and Skyview
websites. Quality of centroids is estimated to be 2" or better. The
assessment of identification between optical and HI sources is based
on spatial proximity, redshift (if optical is available), morphology,
color and evidence for optical emission lines (if known). For sources
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 optical position is listed. The
latter set includes HVCs. For objects with more than one possible
candidate as an optical counterpart but such that one of the
candidates is significantly more preferable than the others, an
optical identification is made; however, a comment on the possible
ambiguity is added in the notes to this table, as alerted by an
asterisk in Code.
Note (4): Measured as the midpoint between the channels at which the flux
density drops to 50% of each of the two peaks (or of one, if only one
is present) at each side of the spectral feature. The error to be
adopted is half the error on W50.
Note (5): Measured at the 50% level of each of the two peaks. This value is
corrected for instrumental broadening. No corrections due to turbulent
motions, disk inclination or cosmological effects are applied.
Note (6): This error is the sum in quadrature of two components: the first
is a statistical error, principally dependent on the S/N ratio of the
feature measured; the second is a systematic error associated with the
subjective guess with which the observer estimates the spectral
boundaries of the feature: maximum and minimum guesses of the spectral
extent of the feature are flagged and the ratio of those values is
used to estimate systematic errors on the width, the velocity and the
flux integral. In the majority of cases, the systematic error is
significantly smaller than the statistical error; thus the former is
ignored.
Note (7): This is measured on the integrated spectrum, obtained by
spatially integrating the source image over a solid angle of at least
7'x7' and dividing by the sum of the survey beam values over the same
set of image pixels (see Shostak & Allen 1980, 1980A&A....81..167S 1980A&A....81..167S).
Estimates of integrated fluxes for very extended sources with
significant angular asymmetries can be misestimated by our algorithm,
which is optimized for measuring sources comparable with or smaller
than the survey beam. A special catalog with parameters of extended
sources will be produced after completion of the survey.
Note (8): Uncertainties associated with the quality of the baseline fitting
are not included; an analysis of that contribution to the error will
be presented elsewhere for the full survey. See description of e_W50
for the contribution of a possible systematic measurement error.
Note (9): estimated as S/N=(1000Fc/W50)(wsmo)1/2/σrms) where
the ratio 1000Fc/W50 is the mean flux across the feature in mJy,
wsmo is either W50/(2x10) for W50<400km/s or 400/(2x10)=20 for
W50≥400km/s [wsmo is a smoothing width expressed as the number of
spectral resolution bins of 10km/s bridging half of the signal width],
and σrms is the r.m.s noise figure across the spectrum
measured in mJy at 10km/s resolution, see column rms. In a similar
analysis, in Giovanelli et al. (Paper II, 2005, Cat. J/AJ/130/2613) we
adopted a maximum smoothing width W50/20=10. See Figure 6 and related
text below for details. The value of the smoothing width could be
interpreted as an indication of the degree to which spectral smoothing
aids in the visual detection of broad signals, against broad-band
spectral instabilities. The ALFALFA data quality appears to warrant a
more optimistic adoption of the smoothing width than previously
anticipated.
Note (10): The noise figure as tabulated is the r.m.s. and measured over
the signal- and rfi-free portions of the spectrum, after Hanning
smoothing to a spectral resolution of 10km/s.
Note (11): For objects with czcmb>3000, the distance is simply
czcmb/H0; czcmb is the recession velocity measured in the Cosmic
Microwave Background reference frame and H0 is the Hubble constant,
for which we use a value of 70km/s/Mpc. For objects of lower czcmb,
we use a peculiar velocity model for the local Universe, as described
in Giovanelli et al. (Paper II, 2005, Cat. J/AJ/130/2613). Objects
which are thought to be parts of clusters or groups are assigned the
czcmb of the cluster or group. Cluster and group membership are
assigned following the method described in Springob et al. (2007, Cat.
J/ApJS/172/599). A detailed analysis of group and cluster membership
of ALFALFA objects will be presented elsewhere. Note that the Virgo
cluster extends over much of the solid angle surveyed. This introduces
unavoidable ambiguities in the distance assignment, as the peculiar
flow model only corrects for large-scale perturbations in the velocity
field and is unable to deal effectively with regions in the immediate
vicinity of the cluster and along a section of a cone which contains
the cluster, up to cz∼2500km/s. The distance to the Virgo cluster was
assumed to be 16.7Mpc.
Note (12): Obtained by using the expression MHI=2.356x105DMpc2 Fc.
Note (13): Note as follows:
1 = sources of S/N and general qualities that make it a reliable detection.
By "general qualities" we mean that, in addition to an approximate
S/N threshold of 6.5, the signal should exhibit a good match between
the two independent polarizations and a spatial extent consistent with
expectations given the telescope beam characteristics. Thus, some
candidate detections with S/N>6.5 have been excluded on grounds of
polarization mismatch, spectral vicinity to rfi features or peculiar
spatial properties. Likewise, some features of S/N<6.5 are included
as reliable detections, due to optimal overall characteristics of the
feature. The S/N threshold for acceptance of a reliable detection
candidate is thus soft. In a preliminary fashion, we estimate that
detection candidates with S/N>6.5 in Table 1 are reliable, i.e. they
will be confirmed in follow-up observations in better than 95% of cases
(Saintonge 2007, Paper IV, 2007AJ....133.2087S 2007AJ....133.2087S). Follow-up observations
planned for 2007 will set this estimate on stronger statistical grounds.
2 = sources of low S/N (<6.5), which would ordinarily not be considered
reliable detections by the criteria set for code 1. However, those HI
candidate sources are matched with optical counterparts with known
optical redshifts which match those measured in the HI line. These
candidate sources, albeit "detected" by our signal finding algorithm,
are accepted as likely counterparts only because of the existence of
previously available, corroborating optical spectroscopy. We refer to
these sources as "priors". We include them in our catalog because
they are very likely to be real.
9 = objects assumed to be HVCs; no estimate of their distances is made.
Figure 2 shows a few examples of candidate detections.
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History:
From electronic version of the journal
References:
Giovanelli et al., Paper I 2005AJ....130.2598G 2005AJ....130.2598G
Giovanelli et al., Paper II 2005AJ....130.2613G 2005AJ....130.2613G, Cat. J/AJ/130/2613
Saintonge et al., Paper IV 2007AJ....133.2087S 2007AJ....133.2087S
Saintonge et al., Paper V 2008AJ....135.588S, Cat. J/AJ/135/588
Kent et al., Paper VI 2008AJ....136.713K, Cat. J/AJ/136/713
Kent et al., Paper VII 2009ApJ...691.1595K 2009ApJ...691.1595K
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 07-May-2009