J/ApJ/914/54 Deep FUV observations of NGC6946, NGC628 & NGC5457 (Yadav+, 2021)
Comparing the inner and outer star-forming complexes in the nearby spiral
galaxies NGC 628, NGC 5457, and NGC 6946 using UVIT observations.
Yadav J., Das M., Patra N.N., Dwarakanath K.S., Rahna P.T., McGaugh S.S.,
Schombert J., Murthy J.
<Astrophys. J., 914, 54 (2021)>
=2021ApJ...914...54Y 2021ApJ...914...54Y
ADC_Keywords: Galaxies, nearby; Ultraviolet; Star Forming Region
Keywords: Ultraviolet astronomy ; Spiral galaxies ; Galaxy interactions ;
Star forming regions ; HI shells
Abstract:
We present a far-UV (FUV) study of the star-forming complexes (SFCs)
in three nearby galaxies using the Ultraviolet Imaging Telescope. The
galaxies are close to face-on and show significant outer disk star
formation. Two of them are isolated (NGC 628 and NGC 6946), and one is
interacting with distant companions (NGC 5457). We compared the
properties of the SFCs inside and outside the optical radius (R25). We
estimated the sizes, star formation rates (SFRs), metallicities, and
Toomre Q parameter of the SFCs. We find that the outer disk SFCs are
at least 10 times smaller in area than those in the inner disk. The
SFRs per unit area (ΣSFR) in both regions have similar mean
values, but the outer SFCs have a much smaller range of ΣSFR.
They are also metal-poor compared to the inner disk SFCs. The FUV
emission is well correlated with the neutral hydrogen gas (HI)
distribution and detected within and near several HI holes. Our
estimation of the Q parameter in the outer disks of the two isolated
galaxies suggests that their outer disks are stable (Q>1). However,
their FUV images indicate that there is ongoing star formation in
these regions. This suggests that there may be some nonluminous mass
or dark matter in their outer disks, which increases the disk surface
density and supports the formation of local gravitational
instabilities. In the interacting galaxy, NGC 5457, the baryonic
surface density is sufficient (Q<1) to trigger local disk
instabilities in the outer disk.
Description:
We performed deep FUV imaging observations of the galaxy NGC 6946
using the Ultraviolet Imaging Telescope (UVIT) on board the AstroSat
Satellite (FUV:1300-1800Å and NUV:2000-3000Å).
We observed NGC 6946 and used archival UVIT data for NGC628 and
NGC5457. The UVIT NUV data were not available for NGC 6946 and
NGC5457. Hence, to constrain the metallicity of the SFCs using UV
colors, which requires both FUV and NUV emission, we used GALEX images
(FUV:1344-1786Å and NUV:1771-2831Å).
We have also used the HI total intensity (MOMNT0) maps of our sample
galaxies from the HI Nearby Galaxy Survey (THINGS;
Walter+ 2008, J/AJ/136/2563). See Section 3.2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 81 3 Properties of galaxies
table5.dat 75 2675 Properties of FUV bright complexes in
NGC 0628, NGC 5457, NGC 6946
table6.dat 59 142 Q value of star-forming complexes (SFCs)
in the outer disk
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See also:
J/ApJS/65/485 : 1.49GHz Atlas of Spiral Galaxies (Condon, 1987)
J/MNRAS/382/1552 : Multiwavelength study of nearby galaxy nuclei (Lira+, 2007)
J/ApJS/173/538 : XUV-Disk galaxies in the Local Universe (Thilker+, 2007)
J/AJ/136/2782 : Star formation efficiency in nearby galaxies (Leroy+, 2008)
J/AJ/136/2563 : HI Nearby Galaxy Survey, THINGS (Walter+, 2008)
J/AJ/140/1194 : FUV/HI relations in nearby galaxies (Bigiel+, 2010)
J/MNRAS/403/683 : GALEX Arecibo SDSS survey (GASS) (Catinella+, 2010)
J/AJ/141/23 : HI holes in THINGS galaxies (Bagetakos+, 2011)
J/ApJ/733/74 : GALEX - SDSS properties of local galaxies (Lemonias+, 2011)
J/A+A/545/A43 : HII regions in NGC 628 and NGC 6946 (Cedres+, 2012)
J/AJ/151/136 : LITTLE THINGS dwarf galaxies FUV regions (Hunter+, 2016)
J/A+A/600/A6 : NGC628 3.1GHz intensity & polarised images (Mulcahy+, 2017)
J/AJ/158/229 : Properties of FUV bright SFRs in IC 2574 (Mondal+, 2019)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [NGC]
5- 8 I04 --- NGC Galaxy name
10- 11 I2 h RAh Hour of right ascension (J2000) (1)
13- 14 I2 min RAm Minute of right ascension (J2000)
16- 19 F4.1 s RAs Second of right ascension (J2000)
21 A1 --- DE- Sign of declination (J2000) (1)
22- 23 I2 deg DEd Degree of declination (J2000) (1)
25- 26 I2 arcmin DEm Arcminute of declination (J2000)
28- 29 I2 arcsec DEs Arcsecond of declination (J2000)
31- 33 F3.1 Mpc Dist [5.9/7.4] Distance (1)
35- 36 I2 deg Inc [7/33] Inclination (1)
38- 40 I3 deg PA [20/243] Position angle
42- 58 A17 --- Type Galaxy type as listed in NED
60- 63 F4.1 pc/arcsec Scale [28.6/36] Spatial scale of galaxy
65- 69 F5.2 arcmin R25 [4.89/12] Optical radius R25 (1)
71- 75 F5.3 mag E(B-V) [0.008/0.3] Foreground Galactic
extinction taken from Schlafly and
Finkbeiner (2011ApJ...737..103S 2011ApJ...737..103S)
77- 81 F5.2 [Msun/yr/kpc2] logSFR [-2.92/-2.25] Log of stellar formation
rate surface density (2)
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Note (1): The RA, DEC, distance, inclination, and R25 are listed from
Walter+ (2008, J/AJ/136/2563).
Note (2): SFR surface density for NGC 628 and NGC 5457 from
Thilker+ (2007, J/ApJS/173/538) and NGC 6946 from
Leroy+ (2008, J/AJ/136/2782).
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [NGC]
4- 7 I04 --- NGC Galaxy name
10- 11 I2 h RAh [1/20] Hour of Right Ascension (J2000)
13- 14 I2 min RAm Minute of Right Ascension (J2000)
16- 20 F5.2 s RAs Second of Right Ascension (J2000)
22 A1 --- DE- [+] Sign of Declination (J2000)
23- 24 I2 deg DEd [15/60] Degree of Declination (J2000)
26- 27 I2 arcmin DEm Arcminute of Declination (J2000)
29- 33 F5.2 arcsec DEs Arcsecond of Declination (J2000)
35- 39 F5.2 arcsec amaj [0.7/38.1] Semi-major axis
41- 45 F5.2 arcsec bmin [0.27/22] Semi-minor axis
47- 49 I3 deg PA [0/359] Position angle, South of East
51- 55 F5.3 Msun/yr/kpc2 SFRuv [0.002/3.1] Specific star formation rate
from UV
57- 62 F6.4 Msun/yr/kpc2 e_SFRuv [0.0009/0.13] Uncertainty in SFR-UV
64- 69 F6.4 kpc2 Area [0.0001/0.0012] Area
71- 75 A5 --- Loc Location in Galaxy
("Inner": 2534 occurrences or
"Outer": 141 occurrences)
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Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- --- [NGC]
4- 7 I4 --- NGC Galaxy name
9- 10 I2 h RAh [1/20] Hour of right ascension (J2000)
12- 13 I2 min RAm Minute of right ascension (J2000)
15- 19 F5.2 s RAs Second of right ascension (J2000)
21 A1 --- DE- [+] Sign of declination (J2000)
22- 23 I2 deg DEd [15/60] Degree of declination (J2000)
25- 26 I2 arcmin DEm Arcminute of declination (J2000)
28- 32 F5.2 arcsec DEs Arcsecond of declination (J2000)
34- 37 F4.1 --- amaj [0.7/12.9] Semi-major axis
39- 42 F4.1 --- bmin [0.5/10] Semi-minor axis
44- 46 I3 deg PA [1/360] Position angle
48- 53 F6.2 --- Q [0.07/248.36] the Toomre Q value (1)
55- 59 F5.2 --- e_Q [0.01/37.52] Q uncertainty
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Note (1): The local gravitational stability of differentially rotating disks
can be investigated using the Toomre Q parameter
(Binney & Tremaine 2008gady.book.....B 2008gady.book.....B) which is given by:
Q=(Kσg)/(πGΣ); Equation (5)
where K is the epicyclic frequency, σg is the velocity
dispersion, G is the gravitational constant, and Σ is the disk
mass surface density. See Section 4.6.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 08-Dec-2022