J/AJ/161/71 Parameters for 40 LITTLE THINGS galaxies (Hunter+, 2021)
Relationships between the stellar, gaseous, and star formation disks in LITTLE
THINGS dwarf irregular galaxies: indirect evidence for substantial fractions of
dark molecular gas.
Hunter D.A., Elmegreen B.G., Goldberger E., Taylor H., Ermakov A.I.,
Herrmann K.A., Oh S.-H., Malko B., Barandi B., Jundt R.
<Astron. J., 161, 71 (2021)>
=2021AJ....161...71H 2021AJ....161...71H
ADC_Keywords: Galaxies; H I data; Star Forming Region; Spectra, ultraviolet;
Keywords: Dwarf irregular galaxies ; Star formation ; Interstellar medium
Abstract:
The stellar, gaseous and young stellar disks in the LITTLE THINGS
sample of nearby dwarf irregular galaxies are fitted with functions to
search for correlations between the parameters. We find that the HI
radial profiles are generally flatter in the center and fall faster in
the outer regions than the V-band profiles, while young stars are more
centrally concentrated, especially if the HI is more centrally flat.
This pattern suggests that the HI is turning into molecules in the
center, and the molecular clouds are forming stars and FUV. A model
that assumes the molecular surface density is proportional to the
total gas surface density to a power of 1.5 or 2, in analogy with the
Kennicutt-Schmidt relation, reproduces the relationship between the
ratio of the visible to the HI scale length and the HI Sersic index.
The molecular fraction is estimated as a function of radius for each
galaxy by converting the FUV to a molecular surface density using
conventional calibrations. The average molecular fraction inside 3RD
is 23%±17%. However, the break in the stellar surface brightness
profile has no unified tracer related to star formation.
Description:
LITTLE THINGS is a multiwavelength survey aimed at determining what
drives star formation in dwarf galaxies. The LITTLE THINGS sample
includes 37 dIrr galaxies and 4 BCD galaxies, and is centered around
HI-emission data obtained with the National Science Foundation's Karl
G. Jansky Very Large Array (VLA10). The HI-line data are characterized
by high sensitivity (≤1.1mJy/beam per channel), high spectral
resolution (1.3 or 2.6km/s), and high angular resolution (typically
6"). The LITTLE THINGS ancillary data include far-ultraviolet (FUV)
images obtained with the NASA Galaxy Evolution Explorer satellite
(GALEX11) to trace star formation over the past 200Myr.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 112 40 The galaxy sample
table2.dat 59 40 Sersic fit parameters and radii for HI
table3.dat 37 40 FUV interior and exterior to RBr
table4.dat 43 36 Sersic fit parameters for FUV profiles
table5.dat 41 17 Rotation curve fit parameters
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See also:
J/AJ/114/2402 : Rotation curves of early-type galaxies (Courteau+, 1997)
J/AJ/128/2170 : Hα imaging of irregular galaxies (Hunter+, 2004)
J/ApJS/162/49 : UBV imaging of irregular galaxies (Hunter+, 2006)
J/ApJS/173/185 : GALEX UV atlas of nearby galaxies (Gil de Paz+, 2007)
J/A+A/465/71 : 21cm observations of 452 galaxies (Theureau+, 2007)
J/AJ/136/2782 : Star formation efficiency in nearby galaxies (Leroy+, 2008)
J/AJ/140/1194 : FUV/HI relations in nearby galaxies (Bigiel+, 2010)
J/AJ/144/134 : LITTLE THINGS survey of nearby dwarf galaxies (Hunter+,2012)
J/MNRAS/433/2240 : SALT2 parameters and distances for SNe (Ganeshalingam+,2013)
J/AJ/146/104 : Dwarf galaxies surface bright. profiles. I. (Herrmann+,2013)
J/A+A/566/A44 : gr photometry of Sextans A and Sextans B (Bellazzini+, 2014)
J/AJ/151/145 : Dwarf galaxies surface bright. profiles II. (Herrmann+,2016)
J/AJ/151/136 : LITTLE THINGS dwarf irregular galax. FUV reg. (Hunter+,2016)
J/AJ/157/241 : HI clouds LITTLE THINGS dwarf irregular galax (Hunter+,2019)
J/A+A/625/A36 : Breaks in surf. bright. prof. galaxy disks (Watkins+, 2019)
J/ApJ/882/5 : ALMA data for 5 luminous IR gal. (Wilson+, 2019)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Galaxy Galaxy identification
10- 28 A19 --- NED NED preferred identifier
30- 33 F4.1 Mpc Dist [0.7/10.3] Distance to galaxy (1)
35- 38 F4.2 Mpc e_Dist [0.04/0.8] Uncertainty in Dist (2)
40- 45 F6.2 mag MVmag [-18.3/-9.7] Absolute V band magnitude
47- 50 F4.2 mag e_MVmag [0.03/0.4] Uncertainty in MVmag (2)
52- 55 F4.2 kpc RHa [0.3/5.58]? Radius of furthest out
detected HII region (3)
57- 60 F4.2 kpc RFUV [0.29/6.79]? Radius of furthest out
detected FUV knot (4)
62- 65 F4.2 kpc e_RFUV [0.01/0.1]? Uncertainty in RFUV
67- 70 F4.2 kpc RD [0.15/2.24] Disk scale length (5)
72- 75 F4.2 kpc e_RD [0/0.25] Uncertainty in RD
77- 80 F4.2 kpc RBr [0.13/2.8]? Break radius (6)
82- 85 F4.2 kpc e_RBr [0/1.35]? Uncertainty in RBr
87- 91 F5.2 [Msun/yr/kpc2] logSFR [-3.75/-0.32]? Area normalized, FUV
based star formation rate (7)
93- 96 F4.2 [Msun/yr/kpc2] e_logSFR [0.04]? Uncertainty in logSFR
98-101 F4.2 --- C31 [2.02/5.29]? Central concentration (8)
103-107 F5.2 [-] logFUV [-0.14/1.76]? Ratio of the FUV emission
interior/exterior to RD (9)
109-112 F4.2 [-] e_logFUV [0.06]? Uncertainty in logFUV
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Note (1): Distance to the galaxy. References are given by
Hunter+, 2012, J/AJ/144/134
Note (2): Uncertainty in the distance is folded into the uncertainty of MVmag
Note (3): Radius of furthest out detected HII region RHa in each galaxy from
Hunter & Elmegreen, 2004, J/AJ/128/2170. Galaxies without HII regions
or with HII regions extending beyond the area imaged do not have RHa and
are marked as null values.
Note (4): Radius of furthest out detected FUV knot, RFUVknot, in each galaxy
from Hunter+, 2016, J/AJ/151/136. Galaxies without GALEX images
have no value for this radius.
Note (5): Disk scale length RD determined from the V-band image surface
photometry from Herrmann et al. (2013AJ....146..104H 2013AJ....146..104H). In the case of
galaxies with breaks in their surface brightness profiles, we have
chosen the scale length that describes the primary underlying stellar
disk.
Note (6): Break radius RBr where the V-band surface brightness profile
changes slope given by Herrmann+, 2013, J/AJ/146/104. Galaxies
without RBr do not have breaks in their profiles.
Note (7): SFR measured from the integrated FUV luminosity and normalized to
the area within one RD from Hunter+, 2010AJ....139..447H 2010AJ....139..447H. The
normalization is independent of the radial extent of the FUV emission in
a galaxy. We assume an uncertainty of 10%, which is greater than the
photometric uncertainty.
Note (8): A measure of the central concentration of stars - ratio of the
radii that encompass 75% and 25% of the total stellar mass, from
Zhang+, 2012AJ....143...47Z 2012AJ....143...47Z. A larger ratio means the stars are more
centrally concentrated.
Note (9): Ratio of the FUV emission within the inner disk scale length RD
and the FUV emission in the annulus from radius 1*RD to 3*RD. A larger
ratio means the FUV emission, and hence star formation, is centrally
concentrated. We assume an uncertainty of 10% in both the numerator and
the denominator.
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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- 8 A8 --- Galaxy Galaxy identification
10- 14 F5.2 [Msun/pc2] logS0 [-0.21/2.39] Extrapolated central surface
mass density
16- 19 F4.2 [Msun/pc2] e_logS0 [0.01/0.17] Uncertainty in logS0
21- 24 F4.2 kpc R0 [0.25/7.71] Characteristic radius
26- 29 F4.2 kpc e_R0 [0.02/0.29] Uncertainty in R0
31- 34 F4.2 --- nHI [0.2/1.65] Curvature of profile
36- 39 F4.2 --- e_nHI [0.0/0.12] Uncertainty in nHI
41- 44 F4.2 kpc R50 [0.29/5.03] Radius containing 50% HI gas
46- 49 F4.2 kpc e_R50 [0.01/0.14] Uncertainty in R50
51- 54 F4.2 --- R50/R90 [0.3/0.67] Central concentration of HI
56- 59 F4.2 --- e_R50/R90 [0.04/0.06] Uncertainty in R50/R90
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Galaxy Galaxy identification
11- 16 A6 --- Type Break Type (1)
18- 21 F4.2 [-] logFUV1 [0.39/2.19]? log, ratio interior/exterior FUV
flux ratio, normalized by area (2)
23- 26 F4.2 [-] e_logFUV1 [0.01/0.92]? Uncertainty in logFUVie1
28- 32 F5.2 [-] logFUV2 [-0.27/0.87]? log, ratio interior/exterior FUV
flux ratio, normalized by V band flux (2)
34- 37 F4.2 [-] e_logFUV2 [0/0.92]? Uncertainty in logFUVie2
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Note (1): Type of surface brightness profile break in the V-band
(Herrmann+, 2013, J/AJ/146/104). Types as follows:
FI = profile in which there is a short central segment that is flat or
rising and then the profile drops off exponentially
II = downward break
III = upward bend
FI+II = profile with two breaks
FI+III = profile with two breaks
I = the profile does not show any break
Galaxies without breaks and those without FUV images do not have
ratios of FUV interior to exterior of the break.
Note (2): flux ratio given interior and exterior to RBr, the break radius
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Galaxy Galaxy identification
10- 14 F5.2 [mag/arcsec2] logFUV [14.22/28.84] Extrapolated central
surface brightness
16- 19 F4.2 [mag/arcsec2] e_logFUV [0.01/0.64] Uncertainty in logmu0FUV
21- 26 F6.4 kpc R0FUV [0.0/2.91] Characteristic radius
28- 33 F6.4 kpc e_R0FUV [0.0/0.12] Uncertainty in R0-FUV
35- 38 F4.2 --- nFUV [0.21/4.17] Curvature of profile
40- 43 F4.2 --- e_nFUV [0.01/0.27] Uncertainty in nFUV
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Galaxy Galaxy identification
10- 13 F4.2 kpc Rt [0.32/4.18] Transition radius (1)
15- 18 F4.2 kpc e_Rt [0.02/0.34] Uncertainty in Rt
20- 24 F5.1 km/s Vc [13.1/160.9] Asymptotic velocity at large radii
26- 29 F4.1 km/s e_Vc [0.3/37.3] Uncertainty in Vc
31- 35 F5.2 --- gamma [0.89/20.88] Sharpness of transition (2)
37- 41 F5.2 --- e_gamma [0.12/15.38] Uncertainty in gamma
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Note (1): Transition radius at which the increase in rotation speed with radius
ends.
Note (2): The parameter Β was set equal to 0 in Equation 5.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 01-Apr-2021