J/ApJ/855/33 Compact clouds in a sensitive GBT HI survey (Di Teodoro+, 2018)
Blowing in the Milky Way wind: neutral hydrogen clouds tracing the Galactic
nuclear outflow.
Di Teodoro E.M., McClure-Griffiths N.M., Lockman F.J., Denbo S.R.,
Endsley R., Ford H.A., Harrington K.
<Astrophys. J., 855, 33 (2018)>
=2018ApJ...855...33D 2018ApJ...855...33D
ADC_Keywords: Galactic center; Molecular clouds; H I data; Surveys
Keywords: Galaxy: center; Galaxy: nucleus; ISM: clouds; ISM: jets and outflows;
ISM: kinematics and dynamics
Abstract:
We present the results of a new sensitive survey of neutral hydrogen
above and below the Galactic Center with the Green Bank Telescope. The
observations extend up to Galactic latitude |b|<10° with an
effective angular resolution of 9.5' and an average rms brightness
temperature noise of 40mK in a 1km/s channel. The survey reveals the
existence of a population of anomalous high-velocity clouds extending
up to heights of about 1.5kpc from the Galactic plane and showing no
signature of Galactic rotation. These clouds have local standard of
rest velocities |VLSR|≲360km/s, and assuming a Galactic Center
origin, they have sizes of a few tens of parsec and neutral hydrogen
masses spanning 10-105M☉. Accounting for selection effects,
the cloud population is symmetric in longitude, latitude, and VLSR. We
model the cloud kinematics in terms of an outflow expanding from the
Galactic Center and find the population consistent with being material
moving with radial velocity Vw∼330km/s distributed throughout a
bicone with opening angle α>140°. This simple model implies
an outflow luminosity Lw>3x1040erg/s over the past 10Myr,
consistent with star formation feedback in the inner region of the
Milky Way, with a cold gas mass-loss rate ≲0.1M☉/yr. These
clouds may represent the cold gas component accelerated in the nuclear
wind driven by our Galaxy, although some of the derived properties
challenge current theoretical models of the entrainment process.
Description:
Our new survey extends the Australia Telescope Compact Array (ATCA)
observations used by MCG13 (McClure-Griffiths+, 2013, J/ApJ/770/L4) to
higher latitude regions where the biconical wind is expected to
expand. The survey covers several areas at longitudes
0°≲l≲10° and latitudes 3°≲|b|≲10°. Observations of
the 21cm line were made with the Robert C. Byrd Green Bank Telescope
(GBT) of the Green Bank Observatory with an angular resolution of 9.1'
at 1.4GHz.
The survey was made in two parts: in the first part, a region
approximately symmetric about the GC in longitude and latitude was
observed under GBT proposals 14A_302, 14B_076 and 14B_461.
In the second phase of the survey, observations were made under GBT
proposals 15B_139 and 16B_419.
Compared to the ATCA survey used by MCG13, the GBT data cover a wider
area (215deg2 versus 100deg2) and a larger velocity range (VLSR:
±670km/s versus ±350km/s, with a better sensitivity (σrms:
0.04K versus 0.7K) and a coarser spatial resolution (beam FWHM: 570"
versus 145").
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 61 106 Cloud observed properties
table2.dat 72 106 Cloud derived (model-dependent) properties
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See also:
J/AJ/123/873 : HIPASS high-velocity clouds (Putman+, 2002)
J/ApJ/722/367 : HI clouds in Quadrant I of the Milky Way (Ford+, 2010)
J/A+A/510/A54 : NaI and CaII interstellar absorption (Welsh+, 2010)
J/ApJ/770/L4 : HI clouds around the Galactic Center (McClure-Griffiths+, 2013)
J/ApJS/209/12 : High-velocity clouds from GASS. I. (Moss+, 2013)
J/A+A/562/A21 : AGN feedback from CO observations (Cicone+, 2014)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- Name Assigned HI cloud name
16- 21 F6.2 deg GLON [0/360] Galactic Longitude cloud centroids
23- 27 F5.2 deg GLAT [-7.6/9.8] Galactic latitude cloud centroids
29- 34 F6.1 km/s VLSR [-291/366] LSR velocity (1)
36- 39 F4.1 km/s dV [4.2/40.1] FWHM velocity width
(Δν) (1)
41- 44 F4.2 K Tbmax [0.07/1.2] Peak brightness temperature
(Tb,max)
46- 49 F4.2 10+19cm-2 NHImax [0.1/6] Maximum HI column density (NHI,max)
51- 54 F4.2 [Msun] logMHI8.2 [1.1/5.6] Logarithm of HI mass
assuming a distance of 8.2kpc (log(MHI))
56- 59 F4.1 pc Rcl8.2 [6.4/53.5] Cloud radius
assuming a distance of 8.2kpc (Rcl)
61- 61 I1 --- Ref ?=- Previous detections of a cloud (2)
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Note (1): VLSR and dV from Gaussian fit of the integrated HI line.
Note (2): Previous detections of a cloud; reference code as follows:
1 = Putman et al. (2002, J/AJ/123/873);
2 = Moss et al. (2013, J/ApJS/209/12).
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- Name Assigned HI cloud name
16- 16 A1 --- flag [m ] m: this cloud can not be reproduced w/model
18- 22 F5.2 kpc x-kpc [-2.4/1.8]? Cartesian X coordinate (3)
24- 28 F5.2 kpc y-kpc [-1.3/1.7]? Cartesian Y coordinate (3)
30- 34 F5.2 kpc z-kpc [-1.3/1.7]? Cartesian Z coordinate (3)
36- 39 F4.2 kpc R [0.5/2.7]? Distance of clouds from
the Galactic Center (r)
41- 45 F5.2 kpc Dist [6/10.1]? Distance of clouds from
the Sun location (D) (4)
47- 50 F4.2 Myr t [1.6/8]? Cloud lifetime, t=r/Vw
52- 55 F4.2 [Msun] logMHI [1.3/5.7]? Cloud HI mass assuming
the distance, Dist
57- 60 F4.1 pc Rcl [6/59.3]? Cloud radius assuming the distance,
Dist
62- 66 I5 K Tkin [386/35341] Maximum cloud kinetic temperature (5)
68- 72 F5.2 cm-3 nHI [0.2/26.1]? Neutral hydrogen number density (6)
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Note (3): Cartesian coordinates (x,y,z) of clouds in the Galactic frame of
reference (see Figure 6). Clouds with negative x coordinate lie between
the Sun and the Galactic Center.
Note (4): Distance of clouds from the Sun location at (x,y,z)=(-8.2,0,0)kpc.
Note (5): Maximum cloud kinetic temperature Tk=mH*dv2/(8k*ln2), where mH
is the HI atom mass, k the Boltzmann constant and dv the FWHM linewidth
of the integrated HI line.
Note (6): Neutral hydrogen number density nHI=3*MHI/(4π*mH*Rcl3), where
mH is the HI atom mass, MHI is the cloud HI mass (logMHI) and the cloud
radius (Rcl).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 15-Nov-2018