J/ApJ/722/395 Compact H I clouds from the GALFA-H I survey (Begum+, 2010)
Compact H I clouds from the GALFA-H I survey.
Begum A., Stanimirovic S.Z., Peek J.E., Ballering N.P., Heiles C.,
Douglas K.A., Putman M., Gibson S.J., Grcevich J., Korpela E.J., Lee M.-Y.,
Saul D., Gallagher III J.S.
<Astrophys. J., 722, 395-411 (2010)>
=2010ApJ...722..395B 2010ApJ...722..395B (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Molecular clouds ; Interstellar medium ; H I data
Keywords: Galaxy: evolution - Galaxy: halo - ISM: clouds -
ISM: kinematics and dynamics - ISM: structure - radio lines: ISM
Abstract:
The Galactic Arecibo L-band Feed Array H I (GALFA-H I) survey is
mapping the entire Arecibo sky at 21 cm, over a velocity range of -700
to +700 km/s (LSR), at a velocity resolution of 0.18 km/s, and a
spatial resolution of 3.5 arcmin. The unprecedented resolution and
sensitivity of the GALFA-H I survey have resulted in the detection of
numerous isolated, very compact H I clouds at low Galactic velocities,
which are distinctly separated from the H I disk emission. In the
limited area of ∼4600 deg2 surveyed so far, we have detected 96 such
compact clouds. The detected clouds are cold with a median
Tk,max (the kinetic temperature in the case in which there is no
non-thermal broadening) of 300 K. Moreover, these clouds are quite
compact and faint, with median values of 5 arcmin in angular size,
0.75 K in peak brightness temperature, and 5x1018/cm2 in H I column
density. Most of the clouds deviate from Galactic rotation at the
20-30 km/s level, and a significant fraction show evidence for a
multiphase medium and velocity gradients. No counterparts for these
clouds were found in other wave bands. From the modeling of spatial
and velocity distributions of the whole compact cloud population, we
find that the bulk of the compact clouds are related to the Galactic
disk, and their distances are likely to be in the range of 0.1 to a
few kpc. We discuss various possible scenarios for the formation and
maintenance of this cloud population and its significance for Galactic
interstellar medium studies.
Description:
The GALFA-H I survey consists of many individual projects, being
observed in both solo modes and commensally with the Arecibo Legacy
Fast ALFA Survey (ALFALFA; Giovanelli et al. 2005AJ....130.2598G 2005AJ....130.2598G),
Arecibo Galaxy Environment Survey (AGES; Auld et al. 2006MNRAS.371.1617A 2006MNRAS.371.1617A),
and the Galactic ALFA Continuum Transit Survey (GALFACTS; Guram & Taylor
2009ASPC..407..282G 2009ASPC..407..282G) as the Turn-On GALFA Spectrometer (TOGS) and
TOGS2 projects. Data cubes used for this study have been made by the
core GALFA-H I group and are based on the first data release
(released separately as "Spring" and "Fall" data cubes), which uses
data from TOGS and several smaller, targeted GALFA-H I projects.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 82 96 The Compact Cloud Sample with Derived Gaussian
Parameters
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See also:
VIII/76 : Leiden/Argentine/Bonn (LAB) Survey of Galactic HI
(Kalberla+ 2005)
J/ApJ/688/290 : GASS HI survey of the lower halo (Ford+, 2008)
J/AJ/142/170 : ALFALFA survey: α.40 HI source (Haynes+, 2011)
J/ApJ/758/44 : The GALFA-HI compact cloud catalog (Saul+, 2012)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Cloud [1/96] Cloud catalog number
4- 5 I2 h RAh Hour of Right Ascension (J2000)
7- 8 I2 min RAm Minute of Right Ascension (J2000)
10- 11 I2 s RAs Second of Right Ascension (J2000)
12 A1 --- DE- Sign of the Declination (J2000)
13- 14 I2 deg DEd Degree of Declination (J2000)
16- 17 I2 arcmin DEm Arcminute of Declination (J2000)
19- 20 I2 arcsec DEs Arcsecond of Declination (J2000)
22- 27 F6.2 deg GLON Galactic longitude
29- 34 F6.2 deg GLAT Galactic latitude
36- 39 F4.2 arcmin theta Size estimated as the geometrical mean of the
measured angular extent along the major and
minor axes (1)
41- 47 F7.2 km/s VLSR1 Central LSR velocity of the fitted Gaussian
components (2)
49- 54 F6.2 km/s VLSR2 ? Central LSR velocity of the fitted Gaussian
components (2)
56- 60 F5.2 km/s DeltaV1 Velocity FWHM line width of the fitted
Gaussian components (2)
62- 66 F5.2 km/s DeltaV2 ? Velocity FWHM line width of the fitted
Gaussian components (2)
68- 71 F4.2 K Tpk1 Peak brightness temperature of the fitted
Gaussian components (2)
73- 76 F4.2 K Tpk2 ? Peak brightness temperature of the fitted
Gaussian components (2)
78- 82 F5.2 10+18/cm2 NHI H I column density (3)
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Note (1): θ=sqrt(θmax*θmin).
Note (2): Only one value is given if the velocity profile can be well fit with
a single Gaussian function.
Note (3): NHI is derived under the assumption that the gas is optically thin.
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History:
From electronic version of the journal
(End) Prepared by Tiphaine Pouvreau [CDS] 17-Aug-2017