J/ApJS/244/7 ATCA HI absorption survey in Magellanic clouds. I. (Jameson+, 2019)
An ATCA survey of H I absorption in the Magellanic Clouds.
I. HI gas temperature measurements in the Small Magellanic Cloud.
Jameson K.E., McClure-Griffiths N.M., Liu B., Dickey J.M.,
Staveley-Smith L., Stanimirovic S., Dempsey J., Dawson J.R., Denes H.,
Bolatto A.D., Li Di, Wong T.
<Astrophys. J. Suppl. Ser., 244, 7 (2019)>
=2019ApJS..244....7J 2019ApJS..244....7J
ADC_Keywords: Magellanic Clouds; H I data; Radio lines; Interstellar medium
Keywords: galaxies: ISM ; ISM: clouds ; Magellanic Clouds ; radio lines: ISM
Abstract:
We present the first results from the Small Magellanic Cloud portion
of a new Australia Telescope Compact Array HI absorption survey of
both of the Magellanic Clouds, comprising over 800hr of observations.
Our new HI absorption line data allow us to measure the temperature
and fraction of cold neutral gas in a low-metallicity environment. We
observed 22 separate fields, targeting a total of 55 continuum
sources, against 37 of which we detected HI absorption; from this we
measure a column-density-weighted mean average spin temperature of
<Ts≥150K. Splitting the spectra into individual absorption line
features, we estimate the temperatures of different gas components and
find an average cold gas temperature of ∼30K for this sample, lower
than the average of ∼40K in the Milky Way. The HI appears to be evenly
distributed throughout the SMC, and we detect absorption in 67% of the
lines of sight in our sample, including some outside the main body of
the galaxy (NHI>2x1021cm-2). The optical depth and temperature
of the cold neutral atomic gas show no strong trend with location
spatially or in velocity. Despite the low-metallicity environment, we
find an average cold gas fraction of ∼20%, not dissimilar from that of
the Milky Way.
Description:
Observations of the Small Magellanic Cloud (SMC) portion were
conducted with the Australia Telescope Compact Array (ATCA), between
2016 May 2 and 2018 January 14, in the 6km array configurations. At
1420MHz these array configurations return an angular resolution of
approximately 10".
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 94 55 Absorption spectra quantities of the continuum
sources in the SMC
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See also:
J/ApJS/145/329 : Millennium Arecibo 21-cm Survey (Heiles+, 2003)
J/MNRAS/355/44 : ATCA SMC Radio Continuum Source. II. (Payne+, 2004)
J/ApJ/793/132 : Perseus cloud sources Gaussian param. (Stanimirovic+, 2014)
J/MNRAS/490/1202 : ASKAP EMU ESP, SMC Radio Continuum Survey (Joseph+ 2020)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Field Field identifier (HHMM+DDMM)
11- 23 A13 --- Name Source name (HHMMSS-DDMMSS; J2000)
25- 31 F7.4 deg RAdeg [7.2/23.2] Right Ascension (J2000)
33- 40 F8.4 deg DEdeg [-74.4/-71] Declination (J2000)
42- 47 F6.2 mJy Scont [16/553] Continuum source flux
49- 52 F4.2 --- tauPk [0.04/9.4] Peak optical depth (1)
54- 57 F4.2 --- e_tauPk [0.01/1.3] 1σ uncertainty on the
optical depth (1)
59- 63 F5.1 km/s EW [-25.6/55.4] Absorption equivalent width (2)
65- 67 F3.1 km/s e_EW [0.1/7.4] Uncertainty in EW
69- 71 F3.1 10+21/cm2 NHI [0.4/9.1] HI column density (3)
73- 75 F3.1 10+21/cm2 e_NHI [0.1/0.6] Uncertainty in NHI
77- 80 F4.2 --- fHI [1.0/1.53] HI correction factor to the column
density for the isothermal case
82 A1 --- l_Ts Limit flag on Ts
83- 88 F6.1 K Ts [17/806] Weighted mean average spin
temperature
90- 94 F5.1 K e_Ts [4/267]? Uncertainty in <Ts>
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Note (1): In the spectra Hanning-smoothed to 0.6km/s spectral
resolution with 0.2km/s channels.
Note (2): The integral over the entire image velocity range
(∼70<vLSRK<270km/s).
Note (3): Uncorrected for optical depth using the integral of the spectrum
over the whole velocity range covered by the existing observations
(∼80<vLSRK<200km/s).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 11-Feb-2020