J/ApJ/768/77 Ultra-compact high velocity clouds from ALFALFA (Adams+, 2013)
A catalog of ultra-compact high velocity clouds from the ALFALFA survey:
local group galaxy candidates?
Adams E.A.K., Giovanelli R., Haynes M.P.
<Astrophys. J., 768, 77 (2013)>
=2013ApJ...768...77A 2013ApJ...768...77A
ADC_Keywords: Diffuse clouds ; Radio lines ; Redshifts ; Surveys ; H I data
Keywords: galaxies: distances and redshifts; galaxies: dwarf; galaxies: halos;
galaxies: ISM; Local Group; radio lines: galaxies
Abstract:
We present a catalog of 59 ultra-compact high velocity clouds (UCHVCs)
extracted from the 40% complete ALFALFA HI-line survey. The ALFALFA
UCHVCs have median flux densities of 1.34Jy.km/s, median angular
diameters of 10', and median velocity widths of 23km/s. We show that
the full UCHVC population cannot easily be associated with known
populations of high velocity clouds. Of the 59 clouds presented here,
only 11 are also present in the compact cloud catalog extracted from
the commensal GALFA-HI survey, demonstrating the utility of this
separate dataset and analysis. Based on their sky distribution and
observed properties, we infer that the ALFALFA UCHVCs are consistent
with the hypothesis that they may be very low mass galaxies within the
Local Volume. In that case, most of their baryons would be in the form
of gas, and because of their low stellar content, they remain
unidentified by extant optical surveys. At distances of ∼1Mpc, the
UCHVCs have neutral hydrogen (HI) masses of ∼105-106M☉, HI
diameters of ∼2-3kpc, and indicative dynamical masses within the HI
extent of ∼107-108M☉, similar to the Local Group ultra-faint
dwarf Leo T. The recent ALFALFA discovery of the star-forming,
metal-poor, low mass galaxy Leo P demonstrates that this hypothesis is
true in at least one case. In the case of the individual UCHVCs
presented here, confirmation of their extragalactic nature will
require further work, such as the identification of an optical
counterpart to constrain their distance.
Description:
The sources presented here are found within the footprint of the
α.40 release of the ALFALFA survey (Haynes et al. 2011,
Cat. J/AJ/142/170) but correspond to a separate analysis of the same
spectral data cubes. ALFALFA is an extragalactic spectral line survey
making use of the Arecibo 305m telescope. The survey maps 7000deg2
of sky in the HI 21cm line, covering the spectral range between 1335
and 1435MHz, with a spectral resolution of 25kHz (at z=0) and with an
angular resolution of ∼3.5'.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 103 59 ALFALFA ultra-compact high velocity clouds
(UCHVCs) in the α.40 survey
table2.dat 101 10 UCHVCs from Giovanelli+ (2010ApJ...708L..22G 2010ApJ...708L..22G)
that fail UCHVC criteria
table3.dat 54 59 Inferred cloud properties
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See also:
VIII/73 : HI Parkes All Sky Survey Catalogue (HIPASS) (Meyer+, 2004)
VIII/54 : Atlas of Galactic Neutral Hydrogen (Hartmann+, 1997)
J/ApJS/209/12 : High-velocity clouds from GASS. I. (Moss+, 2013)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/ApJ/758/44 : The GALFA-HI compact cloud catalog (Saul+, 2012)
J/ApJ/756/79 : Opt. photometry in 3 Local Group dwarf galaxies (Sand+, 2012)
J/MNRAS/415/1105 : Intermediate high-velocity clouds distances (Smoker+, 2011)
J/AJ/142/170 : ALFALFA survey: α.40 HI source catalog (Haynes+, 2011)
J/ApJ/722/367 : HI clouds in Quadrant I of the Milky Way (Ford+, 2010)
J/ApJ/711/361 : Local Group dE galaxies. II. (Geha+, 2010)
J/ApJ/702/940 : Radio and UV spectra of HVC toward the MC (Lehner+, 2009)
J/AJ/133/2569 : Arecibo legacy fast ALFA survey III. (Giovanelli+, 2007)
J/ApJ/653/240 : Low-mass SDSS dwarf galaxy properties (Geha+, 2006)
J/ApJ/623/181 : Compact HVC photometry catalog (Siegel+, 2005)
J/MNRAS/346/787 : HIDEEP survey (Minchin+, 2003)
J/A+A/391/159 : A search for Compact High-Velocity Clouds (De Heij+, 2002)
J/AJ/123/873 : HIPASS high-velocity clouds (Putman+, 2002)
J/AJ/113/1197 : 21cm Spectra (Haynes+ 1997)
J/ApJS/79/77 : Bell Lab. H I Survey - High Velocity Clouds (Stark+ 1992)
Byte-by-byte Description of file: table[12].dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- --- [HVC]
4- 19 A16 --- HVC HVC designation (LLL.ll+BB.bb+Vlsr) (G1)
21- 23 A3 --- f_HVC [sabc, ] Flag on source (1)
25- 30 I6 --- AGC Arecibo General Catalog number (2)
32- 33 I2 h RAh Hour of right ascension (J2000) (3)
34- 35 I2 min RAm Minute of right ascension (J2000)
36- 39 F4.1 s RAs Second of right ascension (J2000)
40 A1 --- DE- [+] Sign of declination (J2000) (3)
41- 42 I2 deg DEd Degree of declination (J2000) (3)
43- 44 I2 arcmin DEm Arcminute of declination (J2000)
45- 46 I2 arcsec DEs Arcsecond of declination (J2000)
48- 51 I4 km/s cz [-461/323] Heliocentric cz
53- 56 I4 km/s Vlsr [-454/327] LSR velocity (assumed solar motion
of 20km/s toward l=57°, b=25°)
58- 61 I4 km/s Vgsr [-282/298] Velocity in the Galactic standard
of rest frame (GSR; Vgsr=Vlsr+225sinlcosb)
63- 66 I4 km/s VLG [-294/264] Velocity with respect to the
Local Group (LG) reference (4)
68- 69 I2 km/s W50 [15/62] HI line FWHM (W50)
71- 72 I2 km/s e_W50 [1/15] W50 uncertainty
74- 75 I2 arcmin a [4/29] Estimated cloud major diameter (5)
76 A1 --- --- [x]
77- 78 I2 arcmin b [3/16] Estimated cloud minor diameter (5)
80- 83 F4.2 Jy.km/s S21 [0.2/8.6] 21cm integrated flux density
85- 86 I2 --- S/N [4/44] Signal-to-noise ratio of the line (6)
88 I1 --- N3 [0/5] The number of α.40 HVC neighbors
within D=3° (for f=0.2°/km/s)
90- 91 I2 --- N10 [0/42] The number of α.40 HVC neighbors
within D=10° (for f=0.2°/km/s)
93-103 A11 --- Notes Notes (7)
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Note (1): Flag as follows:
s = Part of the extremely isolated MIS ("most isolated" subsample; with no
more than four neighbors within D=10°). See section 2.4.
a = Not included in the α.40 catalog.
b = Also included in the compact cloud catalog of Saul et al. (2012,
J/ApJ/758/44).
c = Possible kinematic association with larger structure.
Note (2): Identification number in the Arecibo General Catalog (AGC), an
internal database maintained by M. Haynes and R. Giovanelli,
included to ease cross-reference with our archival system and the
α.40 catalog.
Note (3): Equatorial coordinates of the centroid, epoch J2000. Typical errors
are less than 1'.
Note (4): Velocity with respect to the LG reference frame from Karachentsev
& Makarov (1996AJ....111..794K 1996AJ....111..794K).
Note (5): Sizes are measured at approximately the level encircling half the
total flux density. In many cases, the outer contours are more
elongated than indicated by the ratio axb. The half-power ellipses
are also shown in the HI column density contour plots in Figure 7.
Note (6): Signal-to-noise ratio (S/N) of the line, defined as:
S/N=(1000S21/W50).(Wsmo1/2/σrms) (Equation (4))
where S21 is the integrated flux density in Jy.km/s; the ratio
1000S21/W50 is the mean flux density across the feature in mJy;
Wsmo is W50/(2x10), a smoothing width; and σrms is the rms
noise figure across the spectrum measured in mJy. More details on the
S/N calculation are available in Haynes et al. (2011, J/AJ/142/170).
Note (7): Note as follows:
G10 = UCHVCs that are part of the original sample of UCHVCs discussed by
Giovanelli et al. 2010ApJ...708L..22G 2010ApJ...708L..22G
O = UCHVCs that lie outside the area considered by Giovanelli et al.
2010ApJ...708L..22G 2010ApJ...708L..22G
S12 = UCHVCs that are also in the GALFA compact cloud catalog of Saul et al.
(2012, J/ApJ/758/44)
g = Gaussian fit to measure W50.
p = Single peaks fit to measure W50.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [HVC]
4- 19 A16 --- HVC HVC designation (LLL.ll+BB.bb+Vlsr) (G1)
21 A1 --- f_HVC [s] s: part of the extremely isolated MIS
subsample
23- 28 I6 --- AGC Arecibo General Catalog number
30- 32 F3.1 kpc DHI [1.2/6.2] HI diameter at d=1Mpc (Equation 9)
34- 38 F5.2 [cm-3] nHI [-3.7/-2.1] Log of the mean atomic HI density
at d=1Mpc (Equation 5)
40- 44 F5.2 [cm-2] logNHI [18.3/19.3] Log of the mean HI column density
(Equation 6)
46- 49 F4.2 [Msun] logMHI [5/6.3] Log of the HI mass at d=1Mpc (Equation 7)
51- 54 F4.2 [Msun] logMdyn [6.8/8.4] Log of the indicative dynamical mass
within DHI at d=1Mpc (Equation 8)
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Global Notes:
Note (G1): The HVC designation was completed with leading zeroes at CDS,
e.g. names like "5.58+52.07+163" are here written as "005.58+52.07+163"
in order to comply to the "IAU recommendations on Nomenclature".
History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 26-Nov-2014