J/ApJ/731/28 UV star-forming association in spiral galaxies (Alberts+, 2011)
The evolution of stellar populations in the outer disks of spiral galaxies. Alberts S., Calzetti D., Dong H., Johnson L.C., Dale D.A., Bianchi L., Chandar R., Kennicutt R.C., Meurer G.R., Regan M., Thilker D. <Astrophys. J., 731, 28 (2011)> =2011ApJ...731...28A
ADC_Keywords: Galaxies, photometry ; Ultraviolet ; Photometry, infrared ; Associations, stellar Keywords: galaxies: spiral - galaxies: star clusters: general - galaxies: star formation Abstract: We investigate recent star formation in the extended ultraviolet (XUV) disks of five nearby galaxies (NGC 0628, NGC 2090, NGC 2841, NGC 3621, and NGC 5055) using a long wavelength baseline comprised of ultraviolet and mid-infrared imaging from the Galaxy Evolution Explorer and the Spitzer Infrared Array Camera. We identify 229 unresolved stellar complexes across targeted portions of their XUV disks and utilize spectral energy distribution fitting to measure their stellar ages and masses through comparison with Starburst99 population synthesis models of instantaneous burst populations. We find that the median age of outer-disk associations in our sample is ∼100Myr with a large dispersion that spans the entire range of our models (1Myr to 1Gyr). This relatively evolved state for most associations addresses the observed dearth of Hα emission in some outer disks, as Hα can only be observed in star-forming regions younger than ∼10Myr. The large age dispersion is robust against variations in extinction (in the range E(B-V)=0-0.3mag) and variations in the upper end of the stellar initial mass function (IMF). In particular, we demonstrate that the age dispersion is insensitive to steepening of the IMF, up to extreme slopes. Description: In this paper, we aim to determine the age range and age distribution of star-forming associations in the outer disks of five galaxies assuming a standard Kroupa IMF (Kroupa 2001MNRAS.322..231K) and utilizing a long wavelength baseline by combining GALEX FUV (∼1529Å) and NUV (∼2312Å) imaging (galaxies from GALEX Atlas of Nearby Galaxies; Gil de Paz et al. 2007, Cat. J/ApJS/173/185) with Spitzer mid-infrared (MIR; 3.6-8.0um) bands. For the infrared observations, the Spitzer IRAC instrument observed the outer-disk fields as part of GO Program 30753 (PI: D. Calzetti). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table4.dat 117 229 Source list table5.dat 71 229 Derived ages and masses for all associations
See also: J/ApJS/192/6 : A GALEX UV imaging survey of nearby galaxies (Lee+, 2011) J/AJ/140/1194 : FUV/HI relations in nearby galaxies (Bigiel+, 2010) J/ApJ/714/1256 : Far-IR star formation rate indicators (Calzetti+, 2010) J/ApJ/706/599 : Hα and UV SFR in the local volume (Lee+, 2009) J/ApJ/706/553 : Fluxes in nearby star-forming galaxies (Boquien+, 2009) J/ApJ/703/1672 : Far-IR and Hα fluxes in galaxies (Kennicutt+, 2009) J/ApJ/703/517 : The Spitzer Local Volume Legacy: IR photometry (Dale+, 2009) J/other/RMxAA/44.161 : HII regions in NGC 5055 (Rozas+, 2008) J/ApJS/173/538 : XUV-Disk galaxies in the Local Universe (Thilker+, 2007) J/ApJS/173/185 : GALEX UV atlas of nearby galaxies (Gil de Paz+, 2007) J/AJ/133/791 : Spitzer photometry of galaxies (Smith+, 2007) J/ApJ/656/770 : Mid-IR spectrum of star-forming galaxies (Smith+, 2007) J/ApJ/586/794 : Multiwavelength luminosities of galaxies (Bell, 2003) J/A+AS/114/527 : UV properties of normal galaxies. III. (Rifatto+, 1995) Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 3 A3 --- --- [NGC] 5- 8 I4 --- NGC Galaxy NC identification 10- 11 I2 --- Seq [1/75] UV-bright star-forming association identification number 13- 14 I2 h RAh Hour of Right Ascension (J2000) 16- 17 I2 min RAm Minute of Right Ascension (J2000) 19- 23 F5.2 s RAs Second of Right Ascension (J2000) 25 A1 --- DE- Sign of the Declination (J2000) 26- 27 I2 deg DEd Degree of Declination (J2000) 29- 30 I2 arcmin DEm Arcminute of Declination (J2000) 32- 35 F4.1 arcsec DEs Arcsecond of Declination (J2000) 37- 44 F8.2 zW/m2/nm FUV GALEX FUV band flux (1) 46- 51 F6.2 zW/m2/nm e_FUV The 1σ uncertainty in FUV (1) 53- 59 F7.2 zW/m2/nm NUV GALEX NUV band flux (1) 61- 66 F6.2 zW/m2/nm e_NUV The 1σ uncertainty in NUV (1) 68- 73 F6.2 zW/m2/nm F3.6 Spitzer/IRAC 3.6 micron flux (1) 75- 78 F4.2 zW/m2/nm e_F3.6 The 1σ uncertainty in F3.6 (1) 80- 84 F5.2 zW/m2/nm F4.5 Spitzer/IRAC 4.5 micron flux (1) 86- 90 F5.3 zW/m2/nm e_F4.5 The 1σ uncertainty in F4.5 (1) 92- 99 F8.2 zW/m2/nm F5.8 Spitzer/IRAC 5.8 micron flux (1) 101-104 F4.2 zW/m2/nm e_F5.8 The 1σ uncertainty in F5.8 (1) 106-112 F7.3 zW/m2/nm F8.0 Spitzer/IRAC 8.0 micron flux (1) 114-117 F4.2 zW/m2/nm e_F8.0 The 1σ uncertainty in F8.0 (1)
Note (1): In units of 10-19ergs/s/cm2/Å. For FUV and NUV band, the flux has been corrected for the foreground Milky Way extinction.
Byte-by-byte Description of file: table5.dat
Bytes Format Units Label Explanations
1- 3 A3 --- --- [NGC] 5- 8 I4 --- NGC Galaxy NC identification 10 A1 --- f_Seq [nd] Best fit with (n)o dust or with (d)ust 12- 13 I2 --- Seq Association identification number 14 A1 --- n_Seq [ab] Note on fitting (2) 16- 19 I4 Myr Age0 Age with E(B-V)=0 21 A1 --- lEAge0 [>] Limit flag on E_Age0 22- 24 I3 Myr E_Age0 Positive error on Age0 26- 28 I3 Myr e_Age0 Negative error on Age0 30- 32 I3 Myr Age Age with E(B-V)=0.3 34 A1 --- lEAge [>] Limit flag on E_Age 35- 37 I3 Myr E_Age Positive error on Age 39- 41 I3 Myr e_Age Negative error on Age 43- 46 F4.2 [Msun] logM0 Log of Mass with E(B-V)=0 48- 51 F4.2 [Msun] E_logM0 Positive error on logMass0 53- 56 F4.2 [Msun] e_logM0 Negative error on logMass0 58- 61 F4.2 [Msun] logM Log of Mass with E(B-V)=0.3 63- 66 F4.2 [Msun] E_logM Positive error on logMass 68- 71 F4.2 [Msun] e_logM Negative error on logMass
Note (2): Flag as follows: a = These associations are missing their 4.5um point and are thus only fit with three data points. b = These associations display an inverse correlation between age and mass for E(B-V)=0.
History: From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 17-Oct-2012
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