J/ApJ/758/44 The GALFA-HI compact cloud catalog (Saul+, 2012)
The GALFA-H I compact cloud catalog.
Saul D.R., Peek J.E.G., Grcevich J., Putman M.E., Douglas K.A.,
Korpela E.J., Stanimirovic S., Heiles C., Gibson S.J., Lee M., Begum A.,
Brown A.R.H., Burkhart B., Hamden E.T., Pingel N.M., Tonnesen S.
<Astrophys. J., 758, 44 (2012)>
=2012ApJ...758...44S 2012ApJ...758...44S
ADC_Keywords: H I data ; Diffuse clouds ; Surveys
Keywords: galaxies: formation; Galaxy: halo; intergalactic medium; ISM: clouds
Abstract:
We present a catalog of 1964 isolated, compact neutral hydrogen clouds
from the Galactic Arecibo L-Band Feed Array Survey Data Release One.
The clouds were identified by a custom machine-vision algorithm
utilizing the difference of Gaussian kernels to search for clouds
smaller than 20'. The clouds have velocities typically between
|VLSR|=20 and 400km/s, line widths of 2.5-35km/s, and column
densities ranging from 1 to 35x1018/cm2. The distances to the clouds
in this catalog may cover several orders of magnitude, so the masses
may range from less than a solar mass for clouds within the Galactic
disk, to greater than 104M☉for high-velocity clouds (HVCs) at
the tip of the Magellanic Stream. To search for trends, we separate
the catalog into five populations based on position, velocity, and
line width: HVCs; galaxy candidates; cold low-velocity clouds (LVCs);
warm, low positive-velocity clouds in the third Galactic quadrant; and
the remaining warm LVCs. The observed HVCs are found to be associated
with previously identified HVC complexes. We do not observe a large
population of isolated clouds at high velocities as some models
predict. We see evidence for distinct histories at low velocities in
detecting populations of clouds corotating with the Galactic disk and
a set of clouds that is not corotating.
Description:
The catalog is generated using the GALFA-HI Survey DR1. GALFA-HI is a
survey of the 1420MHz hyperfine transition of neutral hydrogen in the
Galaxy using the Arecibo 305m telescope and the ALFA seven-beam feed
array. The survey is completed commensally with other Arecibo
extragalactic and Galactic surveys (Giovanelli et al.
2005AJ....130.2598G 2005AJ....130.2598G; Guram & Taylor 2009ASPC..407..282G 2009ASPC..407..282G). GALFA-HI
data provide a channel spacing of 0.184km/s and cover a velocity range
of ±650km/s in the local standard of rest (LSR) with a spatial
resolution of 4'. The DR1 data cover 7520deg2 of sky in an area
between δ=38° and δ=-1° (see the bottom panel of
Figure 1, and Figure 2), with a range of sensitivity from 120mK to
50mK in 0.74km/s channels. The details of GALFA-HI observing and data
reduction, along with the specifics of the DR1 data set, can be found
in Peek et al. (2011ApJS..194...20P 2011ApJS..194...20P).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 99 1964 DR1 GALFA-HI cloud catalog
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See also:
VIII/76 : Leiden/Argentine/Bonn (LAB) Survey of Galactic HI (Kalberla+ 2005)
VI/128 : Log of CGPS exposures (Taylor+, 2003-)
J/ApJS/209/12 : High-velocity clouds from GASS. I. (Moss+, 2013)
J/AJ/142/170 : ALFALFA survey: α.40 HI source (Haynes+, 2011)
J/ApJ/722/367 : HI clouds in Quadrant I of the Milky Way (Ford+, 2010)
J/AJ/138/338 : Arecibo Legacy Fast ALFA Survey. IX. (Stierwalt+, 2009)
J/ApJ/688/290 : GASS HI survey of the lower halo (Ford+, 2008)
J/AJ/131/1501 : Intermediate-velocity clouds in the CGPS (Kerton+, 2006)
J/ApJ/626/887 : HI clouds in Southern Galactic Plane Survey (Kavars+, 2005)
J/ApJ/626/195 : HI self-absorption (HISA) survey in the CGPS (Gibson+, 2005)
J/ApJS/140/331 : High-velocity HI observations at 21cm (Lockman+, 2002)
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/122/3155 : Peculiar HI cloud near galactic plane (Higgs+, 2001)
J/ApJS/136/463 : Distances and metallicities of HVCs and IVCs (Wakker, 2001)
J/ApJS/79/77 : Bell Lab. H I Survey - High Velocity Clouds (Stark+ 1992)
http://purcell.ssl.berkeley.edu/ : GALFA HI Data Archive
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- ID Cloud identifier (DDD.d+DD.d+VVV) (1)
16- 17 I2 h RAh [0/23] Hour of Right Ascension (J2000) (2)
19- 20 I2 min RAm Minute of Right Ascension (J2000) (2)
22- 23 I2 s RAs Second of Right Ascension (J2000) (2)
25 A1 --- DE- [+] Sign of Declination (J2000) (2)
26- 27 I2 deg DEd [0/37] Degree of Declination (J2000) (2)
29- 30 I2 arcmin DEm Arcminute of Declination (J2000) (2)
32- 37 F6.2 deg GLON Galactic longitude
39- 44 F6.2 deg GLAT Galactic latitude
46- 50 F5.1 --- Sig [6/276] Significance of the cloud (3)
52- 55 F4.1 arcmin Size [2.3/20.5] Angular FWHM of cloud (4)
57- 63 F7.2 km/s VLSR [-448/615] Local Standard of Rest velocity
of the peak of the fit to the average spectrum
65- 71 F7.2 km/s VGSR Galactic Standard of Rest velocity (5)
73- 77 F5.2 km/s DelV [1.7/82.3] FWHM in velocity of the fit to
the average spectrum
79- 83 F5.2 K Tp [0/11.5] Peak brightness temperature at 1420MHz
after Galactic subtraction
85- 87 I3 10+18/cm2 NHI [0/197] Maximum HI column density (6)
88 A1 --- f_NHI [*] NHI is a lower limit (7)
90- 94 F5.1 Jy.km/s Stot [0.6/118] Total HI flux of cloud (1420MHz) (8)
96- 99 A4 --- Pop Cloud population classification (9)
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Note (1): Clouds are named by the right ascension (in degrees), declination,
and VLSR velocity of the peak in the convolved cube.
Note (2): Of the peak in the convolved cube. Note that this is not necessarily
the location of peak flux, or the spatial center of the region of
interest (see Section 3.1).
Note (3): Maximum S/N of cloud in the convolved cube
Note (4): Assuming a circular cloud, 2(Area/π)0.5, where the area is that
of the half maximum value contour shown in the catalog images
(Figure 5). Due to our size constraint of 20' along any axis, the
selection function for elongated clouds drops below 20'.
Note (5): Defined by VGSR=VLSR+220sin(GLON)cos(GLAT).
Note (6): Calculated using the fit of the spectrum through the peak of the
cloud in the unconvolved data.
Note (7): * = the fitting failed on the maximum spectrum thus the average
column density is reported as a lower limit.
Note (8): Determined by summing over the region of interest (ROI) in the
Galactic background subtracted data.
Note (9): Using the scheme detailed in Section 4. Population as follows:
HVC = (high velocity cloud) |VLSR|>90km/s and near a known HVC complex;
GC = (galaxy candidate) |VLSR|>90km/s and far from known HVC complex;
CLVC = (cold low-velocity cloud) |VLSR|<90km/s and DelV<15km/s;
WLVC = (warm low-velocity cloud) |VLSR|<90km/s, DelV>15km/s, and not Q3;
Q3 = (warm, positive low-velocity cloud in the third Galactic quadrant)
90>VLSR>0km/s, DelV>15km/s, and 270>GLON>180.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 03-Jul-2014