J/AJ/170/76 Photometry of 10 dwarf irregular galaxies with LDT (Hunter+, 2025)
Ultradeep imaging of nearby dwarf irregular galaxies: Young objects in the far
outer disk.
Hunter D.A., Zhang H.-X., Elmegreen B.G., Castelloe E.R., Ledford H.M.,
Nisley I., Hatano R.
<Astron. J., 170, 76 (2025)>
=2025AJ....170...76H 2025AJ....170...76H
ADC_Keywords: Galaxies, dwarf; Galaxies, nearby; Photometry, UBVRI; H I data
Keywords: Dwarf irregular galaxies ; Star formation ; Galaxy evolution
Abstract:
Ultradeep UBVI imaging of 10 nearby (≤7.8Mpc) noninteracting
dwarf irregular galaxies are used to examine their far outer stellar
disks. The annulus between 26mag/arcsec2 and 29mag/arcsec2 in the
V band is what we define as the far outer disk and is our focus here.
Photometry of distinct objects in the far outer disks, including
far-UV images, is used to determine ages of the objects in order to
look for those that are young. In three of the galaxies we find
objects with high-confidence ages ≤30Myr. These objects are too
young to have scattered into the far outer disk from the central
regions. Therefore, they likely formed in situ. How star-forming gas
clouds formed in the extreme environment of the outer stellar disks of
dwarfs is a primary unanswered question.
Description:
The ultradeep imaging was done with Lowell Observatory's 4.3m
Lowell Discovery Telescope (LDT) and Large Monolithic Imager (LMI) in
Arizona, USA. The field of view (FOV) of the CCD is 12.5'x12 5'. Each
galaxy was observed for a total of 10/5/2.5/2.5hr in U/B/V/I filters
so as to reach a V-band surface brightness of 30 mag/arcsec2 with
averaging over several pixels (scale of 0.24") and be equally deep in
all four passbands so that all three colors would be good to the same
radial extent. The observing began 2014 October and went through to
2022 April.
The galaxies that were chosen for ultradeep imaging were 10 dwarf
irregular galaxies (dIrrs) selected from the Local Irregulars That
Trace Luminosity Extremes, The HI Nearby Galaxy Survey (LITTLE
THINGS) sample. LITTLE THINGS is a multiwavelength survey put together
for the purpose of determining what drives star formation in dwarf
galaxies (Hunter+2012, J/AJ/144/134). The LITTLE THINGS sample
includes 37 dIrr galaxies and four blue compact dwarf (or BCD)
galaxies, and is centered around HI emission data obtained with the
National Science Foundation's Karl G. Jansky Very Large Array (VLA).
The LITTLE THINGS ancillary data include FUV images obtained with the
NASA Galaxy Evolution Explorer satellite (GALEX).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 70 10 Galaxy sample
table7.dat 97 15233 Objects in far outer stellar disk
table12.dat 98 103813 Objects in background
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See also:
II/183A : UBVRI Photometric Standards (Landolt 1992)
J/AJ/112/1335 : Hubble Deep Field observations (Williams+ 1996)
J/AJ/123/3154 : RV light curves of variable stars in Leo A (Dolphin+, 2002)
J/A+A/398/479 : Local galaxy flows within 5 Mpc (Karachentsev+, 2003)
J/AJ/127/2031 : Catalog of neighboring galaxies (Karachentsev+, 2004)
J/ApJS/162/49 : UBV imaging of irregular galaxies (Hunter+, 2006)
J/AJ/144/134 : LITTLE THINGS survey of nearby dwarf galaxies (Hunter+, 2012)
J/AJ/146/104 : Dwarf galaxies surface brightn. profiles. I. (Herrmann+, 2013)
J/AJ/151/145 : Dwarf galaxies surface brightn. profiles. II. (Herrmann+, 2016)
J/AJ/157/241 : HI clouds in LITTLE THINGS dwarf irreg. galaxies (Hunter+, 2019)
J/A+A/667/A87 : Edges of galaxies. Limits of star formation (Chamba+, 2022)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Name Galaxy name
10- 11 I2 h RAh Hour of right ascension of the stellar disk
center (J2000) (1)
13- 14 I2 min RAm Minute of right ascension of the stellar
disk center (J2000) (1)
16- 19 F4.1 s RAs Second of right ascension of the stellar
disk center (J2000) (1)
21 A1 --- DE- Sign of declination of the stellar disk
center (J2000) (1)
22- 23 I2 deg DEd Degree of declination of the stellar disk
center (J2000) (1)
25- 26 I2 arcmin DEm Arcminute of declination of the stellar disk
center (J2000) (1)
28- 29 I2 arcsec DEs Arcsecond of declination of the stellar disk
center (J2000) (1)
31- 33 F3.1 Mpc Dist [0.7/8.7] Distance (2)
35- 39 F5.1 mag VMag [-17.1/-9.7] Absolute V magnitude (1)
41- 44 F4.2 kpc Rdisk [0.14/1.34] Stellar disk scale length (3)
46- 49 F4.2 kpc e_Rdisk [0.01/0.1] Rdisk uncertainty (3)
51- 55 F5.1 deg PA [-85/84] Position angle (1)
57- 60 F4.2 --- b/a [0.45/1] Minor-to-major disk axes ratio (1)
62- 65 F4.2 mag E(B-V)f [0/0.05] Foreground reddening from the Milky
Way (4)
67- 70 F4.2 [Msun] log(MHI) [5.19/8.59] Log of HI mass (1)
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Note (1): Stellar disk center positions (RA, DE), position angles (PA),
minor-to-major disk ratios (b/a), integrated HI masses (log(MHI)), and
absolute magnitudes (VMag) are from Hunter+2012 (J/AJ/144/134).
Note (2): Distances (Dist) are from Dalcanton+ (2009ApJS..183...67D 2009ApJS..183...67D),
Dolphin+2002 (J/AJ/123/3154), Karachentsev+ (2002A&A...383..125K 2002A&A...383..125K),
Karachentsev+2003 (J/A+A/398/479), Karachentsev+2004 (J/AJ/127/2031),
Karachentsev+ (2006AJ....131.1361K 2006AJ....131.1361K), Meschin+ (2009AJ....137.3619M 2009AJ....137.3619M), and
Miller+ (2001ApJ...562..713M 2001ApJ...562..713M).
Note (3): Stellar disk scale lengths (Rdisk) are from
Herrmann+2013 (J/AJ/146/104).
Note (4): Foreground reddening from the Milky Way (E(B-V)f) values are from
Burstein & Heiles (1984ApJS...54...33B 1984ApJS...54...33B).
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Byte-by-byte Description of file: table7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Name Galaxy name
10- 13 I4 --- ID [1/6131] Running ID number
15- 16 I2 h RAh Hour of right ascension (J2000)
18- 19 I2 min RAm Minute of right ascension (J2000)
21- 24 F4.1 s RAs Second of right ascension (J2000)
26 A1 --- DE- Sign of declination (J2000)
27- 28 I2 deg DEd Degree of declination (J2000)
30- 31 I2 arcmin DEm Arcminute of declination (J2000)
33- 36 F4.1 arcsec DEs Arcsecond of declination (J2000)
38- 41 F4.1 arcsec Rphot [0.3/18.4] Radius of aperture used for
photometry
43- 47 F5.2 mag Bmag [18.32/99.99]?=99.99 Apparent Johnson B
magnitude (1)
49- 52 F4.2 mag e_Bmag [0.0/9.99]?=9.99 Uncertainty in Bmag
54- 58 F5.2 mag Vmag [16.45/99.99]?=99.99 Apparent Johnson V
magnitude (1)
60- 63 F4.2 mag e_Vmag [0.0/9.99]?=9.99 Uncertainty in Vmag
65- 69 F5.2 mag U-B [-2.86/99.99]?=99.99 U-B color (1)
71- 74 F4.2 mag e_U-B [0.0/9.99]?=9.99 Uncertainty in U-B
76- 80 F5.2 mag B-V [-3.92/99.99]?=99.99 B-V color (1)
82- 85 F4.2 mag e_B-V [0.0/9.99]?=9.99 Uncertainty in B-V
87- 91 F5.2 mag V-I [-3.93/99.99]?=99.99 V-I color (1)
93- 97 F5.2 mag e_V-I [0.0/9.99]?=9.99 Uncertainty in V-I
--------------------------------------------------------------------------------
Note (1): Magnitudes are corrected for foreground extinction/reddening using
E(B-V)=0.02.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table12.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Name Galaxy name
10- 14 I5 --- ID [1/13640] Running ID number
16- 17 I2 h RAh Hour of right ascension (J2000)
19- 20 I2 min RAm Minute of right ascension (J2000)
22- 25 F4.1 s RAs Second of right ascension (J2000)
27 A1 --- DE- Sign of declination (J2000)
28- 29 I2 deg DEd Degree of declination (J2000)
31- 32 I2 arcmin DEm Arcminute of declination (J2000)
34- 37 F4.1 arcsec DEs Arcsecond of declination (J2000)
39- 42 F4.1 arcsec Rphot [0.1/17.9] Radius of aperture used for
photometry
44- 48 F5.2 mag Bmag [17.5/99.99]?=99.99 Apparent Johnson B
magnitude (1)
50- 53 F4.2 mag e_Bmag [0.0/9.99]?=9.99 Uncertainty in Bmag
55- 59 F5.2 mag Vmag [16.47/99.99]?=99.99 Apparent Johnson V
magnitude (1)
61- 64 F4.2 mag e_Vmag [0.0/9.99]?=9.99 Uncertainty in Vmag
66- 70 F5.2 mag U-B [-3.21/99.99]?=99.99 U-B color (1)
72- 75 F4.2 mag e_U-B [0.0/9.99]?=9.99 Uncertainty in U-B
77- 81 F5.2 mag B-V [-4.74/99.99]?=99.99 B-V color (1)
83- 86 F4.2 mag e_B-V [0.0/9.99]?=9.99 Uncertainty in B-V
88- 92 F5.2 mag V-I [-8.51/99.99]?=99.99 V-I color (1)
94- 98 F5.2 mag e_V-I [0.0/9.99]?=9.99 Uncertainty in V-I
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Note (1): Magnitudes are corrected for foreground extinction/reddening using
E(B-V)=0.02.
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History:
From electronic version of the journal
License: CC-BY-4.0
(End) Prepared by [AAS], Robin Leichtnam [CDS] 26-May-2026