J/ApJ/845/96 [CII] emission in the ISM of 20 nearby galaxies (Croxall+, 2017)
The origins of [CII] emission in local star-forming galaxies.
Croxall K.V., Smith J.D., Pellegrini E., Groves B., Bolatto A.,
Herrera-Camus R., Sandstrom K.M., Draine B., Wolfire M.G., Armus L.,
Boquien M., Brandl B., Dale D., Galametz M., Hunt L., Kennicutt R.,
Kreckel K., Rigopoulou D., van der Werf P., Wilson C.
<Astrophys. J., 845, 96 (2017)>
=2017ApJ...845...96C 2017ApJ...845...96C
ADC_Keywords: Galaxies, nearby ; Interstellar medium ; Photometry, infrared ;
Spectra, infrared
Keywords: galaxies: ISM; ISM: lines and bands
Abstract:
The [CII]158µm fine-structure line is the brightest emission line
observed in local star-forming galaxies. As a major coolant of the
gas-phase interstellar medium, [CII] balances the heating, including
that due to far- ultraviolet photons, which heat the gas via the
photoelectric effect. However, the origin of [CII] emission remains
unclear because C+ can be found in multiple phases of the interstellar
medium. Here we measure the fractions of [CII] emission originating in
the ionized and neutral gas phases of a sample of nearby galaxies. We
use the [NII]205µm fine-structure line to trace the ionized
medium, thereby eliminating the strong density dependence that exists
in the ratio of [CII]/[NII]122µm. Using the FIR [CII] and [NII]
emission detected by the KINGFISH (Key Insights on Nearby Galaxies: a
Far- Infrared Survey with Herschel) and Beyond the Peak Herschel
programs, we show that 60%-80% of [CII] emission originates from
neutral gas. We find that the fraction of [CII] originating in the
neutral medium has a weak dependence on dust temperature and the
surface density of star formation, and has a stronger dependence on
the gas-phase metallicity. In metal-rich environments, the relatively
cooler ionized gas makes substantially larger contributions to total
[CII] emission than at low abundance, contrary to prior expectations.
Approximate calibrations of this metallicity trend are provided.
Description:
Our observations include photometric and spectral-line observations
from both the PACS and SPIRE instruments onboard Herschel, obtained as
part of the large KINGFISH (Key Insights on Nearby Galaxies: a Far-
Infrared Survey with Herschel, Kennicutt+ 2011PASP..123.1347K 2011PASP..123.1347K) and BtP
(Beyond the Peak; OT1_jsmith1; P.I. J.D. Smith) projects.
[NII]205um BtP observations were performed with SPIRE-FTS intermediate
mapping, which is a 4-point dither. E. Pellegrini et al. (2017, in
preparation) will contain a full description of the observations and
reductions.
[CII]158um and [NII]122um emission lines, and 70 and 160um continuum
maps have been observed as part the Herschel Open Time Key Program
KINGFISH. The data and the associated reduction are described in
Kennicutt+ (2011PASP..123.1347K 2011PASP..123.1347K) and Croxall+ (2013ApJ...777...96C 2013ApJ...777...96C).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
gal.dat 8 20 List of targeted galaxies; table added by CDS
table1.dat 92 280 *Line fluxes and associated uncertainties for
20 regions
--------------------------------------------------------------------------------
Note on table1.dat: Although NGC5457 (M101) showed a faint extranuclear target
with Herschel/SPIRE-FTS, this did not result in any detection of the lines
used in this paper; so this target is not included in the table.
--------------------------------------------------------------------------------
See also:
VI/139 : Herschel Observation Log (Herschel Science Centre, 2013)
J/ApJ/617/240 : Oxygen abundances in the GOODS-North field (Kobulnicky+, 2004)
J/ApJ/671/333 : Aperture photometry in NGC 5194 (Kennicutt+, 2007)
J/A+A/486/629 : Effective collision strengths for C II (Tayal, 2008)
J/ApJS/190/233 : Spectroscopy & abundances of SINGS galaxies (Moustakas+, 2010)
J/ApJ/745/95 : Herschel FIR + submm photom. of KINGFISH sample (Dale+, 2012)
J/A+A/539/A143 : Nearby B-stars stellar parameters & abundances (Nieva+, 2012)
J/ApJS/208/10 : Effects of κ-distribution in HII regions (Dopita+, 2013)
J/A+A/552/A19 : Radio-farIR correlation in NGC 6946 (Tabatabaei+, 2013)
J/A+A/578/A53 : Spectroscopy of Herschel Dwarf Galaxy Survey (Cormier+, 2015)
J/ApJ/814/133 : Herschel Galactic plane survey of [NII] (Goldsmith+, 2015)
J/A+A/575/A17 : NGC 891 Herschel PACS and SPIRE spectroscopy (Hughes+, 2015)
J/A+A/576/A33 : KINGFISH galaxy sample radial profile SED (Hunt+, 2015)
J/A+A/591/A33 : [CII]158um and [NII]205um IC 342 spectra (Roellig+, 2016)
Byte-by-byte Description of file: gal.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Name Galaxy Name
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Name Galaxy Name
10- 17 F8.4 deg RAdeg Right Ascension, decimal degrees (J2000)
19- 27 F9.5 deg DEdeg Declination, decimal degrees (J2000)
29- 32 F4.2 --- 70/160 [0.5/4] 70/160 far-infrared color,
nu*fnu(70um)/nu*fnu(160um)
34- 37 F4.2 --- e_70/160 [0.04/1] Uncertainty in 70/160
39- 43 F5.2 10-8W/m2/sr [CII]158 [0.6/59] Line flux, [CII] 158um
45- 48 F4.2 10-8W/m2/sr e_[CII]158 [0.1/0.2] Uncertainty in [CII]158
50- 55 F6.2 10-9W/m2/sr [NII]122 [0.01/110]? Line flux, [NII] 122um
57- 60 F4.2 10-9W/m2/sr e_[NII]122 [0.06/3.1]? Uncertainty in [NII]122
62- 66 F5.2 10-9W/m2/sr [NII]205 [0.5/32.2] Line flux, [NII] 205um
68- 71 F4.2 10-9W/m2/sr e_[NII]205 [0.1/1.1] Uncertainty in [NII]205
73- 74 A2 --- l_ne [≤ ] Limit flag on electron density
76- 78 I3 cm-3 ne [10/289] electron density
80- 85 F6.3 --- f[CII] [0.2/1] Fraction [CII] from neutral ISM
87- 92 F6.3 --- e_f[CII] [0.003/0.3] Uncertainty in f[CII]
--------------------------------------------------------------------------------
Acknowledgements:
John-David Smith [University of Toledo] for the note added on table 1.
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 03-Apr-2018