The Evolution of Stellar Populations in the Outer Disks of Spiral Galaxies

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 ~100 Myr with a large dispersion that spans the entire range of our models (1 Myr-1 Gyr). This relatively evolved state for most associations addresses the observed dearth of Halpha emission in some outer disks, as Halpha can only be observed in star forming regions younger than ~10 Myr. The large age dispersion is robust against variations in extinction (in the range E(B-V)=0-0.3 mag) 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.

49 pages, 25 figures, 11 tables, accepted for publication in ApJ

References in corpus (13)

• Dust Masses, PAH Abundances, and Starlight Intensities in the SINGS Galaxy Sample
• The GALEX Ultraviolet Atlas of Nearby Galaxies
• The Spitzer Local Volume Legacy: Survey Description and Infrared Photometry
• Evidence for TP-AGB stars in high redshift galaxies, and their effect on deriving stellar population parameters
• A Search for Extended Ultraviolet Disk (XUV-disk) Galaxies in the Local Universe
• Metallicity Effects on Dust Properties in Starbursting Galaxies
• Radial variation of attenuation and star formation in the largest late-type disks observed with GALEX
• Specific SFR profiles in nearby spiral galaxies: quantifying the inside-out formation of disks
• Converting H$\alpha$ Luminosities into Star Formation Rates
• On The Extended Knotted Disks of Galaxies
• Spitzer Observations of Star Formation in the Extreme Outer Disk of M83 (NGC5236)
• The Metal-Enriched Outer Disk of NGC 2915
• On the Nature of Star Formation at Large Galactic Radii

Cited by in corpus (15)

• Legacy ExtraGalactic UV Survey (LEGUS) with The Hubble Space Telescope. I. Survey Description
• Radial Migration in Disk Galaxies I: Transient Spiral Structure and Dynamics
• Gas Metallicities in the Extended Disks of NGC 1512 and NGC 3621. Chemical Signatures of Metal Mixing or Enriched Gas Accretion?
• Quantified H i Morphology VII: The Morphology of Extended Disks in UV and H i
• CO map and steep Kennicutt-Schmidt relation in the extended UV disk of M63
• Radial Star Formation Histories in Fifteen Nearby Galaxies
• The multifarious ionization sources and disturbed kinematics of extraplanar gas in five low-mass galaxies
• Star-Forming Environments Throughout the M101 Group
• Star Cluster Populations in the Outer Disks of Nearby Galaxies
• First Detection of the Molecular Cloud Population in the Extended Ultraviolet (XUV) Disk of M83
• A Multi-Wavelength Study of Star Formation in 15 Local Star-Forming Galaxies
• A pilot study using deep infrared imaging to constrain the star formation history of the XUV stellar populations in NGC 4625
• KMTNet Nearby Galaxy Survey III. Deficient H$\alpha$ flux in the Extended Disks of Spiral Galaxies
• WALLABY Pilot Survey: Hydra Cluster Galaxies UV and HI morphometrics
• The Massive Star Population in M101. II. Spatial Variations in the Recent Star Formation History