KMTNet Nearby Galaxy Survey III. Deficient H$\alpha$ flux in the Extended Disks of Spiral Galaxies

Abstract

We perform a deep wide-field imaging survey of nearby galaxies using H$\alpha$ and broadband filters to investigate the characteristics of star formation in galaxies. Motivated by the finding that star formation rates (SFRs) derived from H$\alpha$ fluxes in dwarf galaxies are systematically lower than those inferred from far-ultraviolet (FUV) fluxes, we attempt to determine whether the same trend exists in the extended disks of two star-forming galaxies. We perform spatially resolved photometry using grid-shaped apertures to measure the FUV and H$\alpha$ fluxes of star-forming regions. We also perform spectral energy distribution (SED) fittings using 11 photometric data (FUV-to-MIR) including data from the literature to estimate the local properties such as internal attenuation of individual star-forming clumps. Comparing SFR${}_{\mathrm{FUV}}$ and SFR${}_{\mathrm{H}\alpha }$, which are converted from the H$\alpha$ and FUV fluxes corrected for the local properties, we find that SFR${}_{\mathrm{H}\alpha }$/SFR${}_{\mathrm{FUV}}$ tends to decrease as the SFR decreases. We evaluate possible causes of this discrepancy between the two SFRs by restricting parameters in the SED fitting and conclude that deficient H$\alpha$ fluxes in the extended disks of galaxies are tightly correlated with recent starbursts. The strong and short starburst which is being rapidly suppressed over the last 10 Myr seems to induce a significant discrepancy between the SFR${}_{\mathrm{H}\alpha }$ and SFR${}_{\mathrm{FUV}}$. In addition, the recent bursts in the extended disks of galaxies appear to have occurred azimuth-symmetrically, implying that these were likely triggered by gas accretion or internal processes rather than external perturbation.

17 pages, 13 figures, Accepted for publication in ApJ

References in corpus (18)

• UV Star Formation Rates in the Local Universe
• A simple model to interpret the ultraviolet, optical and infrared emission from galaxies
• An H-alpha Imaging Survey of Galaxies in the Local 11 Mpc Volume
• H-alpha Observations of a Large Sample of Galaxies at z~2: Implications for Star Formation in High Redshift Galaxies
• A Search for Extended Ultraviolet Disk (XUV-disk) Galaxies in the Local Universe
• The First Billion Years Project: The escape fraction of ionizing photons in the epoch of reionization
• GOODS-HERSCHEL: star formation, dust attenuation and the FIR-radio correlation on the Main Sequence of star-forming galaxies up to z~4
• A Local Clue to the Reionization of the Universe
• Radial distribution of dust, stars, gas, and star-formation rate in DustPedia face-on galaxies
• Diverging UV and Halpha fluxes of star forming galaxies predicted by the IGIMF theory
• SLUG - Stochastically Lighting Up Galaxies. II: Quantifying the Effects of Stochasticity on Star Formation Rate Indicators
• Do galaxy global relationships emerge from local ones? The SDSS IV MaNGA surface mass density-metallicity relation
• SDSS-IV MANGA: Spatially Resolved Star Formation Main Sequence and LI(N)ER Sequence
• On The Extended Knotted Disks of Galaxies
• A panchromatic spatially-resolved analysis of nearby galaxies -- I. Sub-kpc scale Main Sequence in grand-design spirals
• SDSS-IV MaNGA: spatially resolved dust attenuation in spiral galaxies
• An $\mathrm{H}\alpha$ Imaging Survey of the Low Surface Brightness Galaxies Selected from the Spring Sky Region of the 40% ALFALFA HI Survey
• Physical Properties of H II Regions in M51 from Spectroscopic Observations

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