Probing star formation in five of the most massive spiral galaxies observed through $\textit{ASTROSAT UltraViolet Imaging Telescope}$

Abstract

We present highly resolved and sensitive imaging of the five nearby massive spiral galaxies (with rotation velocities $\rm > 300 km s^{-1}$) observed by the UltraViolet Imaging Telescope onboard India's multi-wavelength astronomy satellite ASTROSAT, along with other archival observations. These massive spirals show a far-ultraviolet star formation rate in the range of $\sim$$\rm 1.4$$-$$\rm13.7 M_{\odot} yr^{-1}$ and fall in the `Green Valley' region with a specific star formation rate within $\sim$$\rm10^{-11.5}$$-$$\rm10^{-10.5}yr^{-1}$. Moreover, the mean star formation rate density of the highly resolved star-forming clumps of these objects are in the range $\rm 0.011$$-$$\rm 0.098 M_{\odot} yr^{-1}kpc^{-2}$, signifying localised star formation. From the spectral energy distributions, under the assumption of a delayed star formation model, we show that the star formation of these objects had peaked in the period of $\sim$ $\rm0.8$$-$$\rm2.8$ Gyr after the `Big Bang' and the object that has experienced the peak sooner after the `Big Bang' show relatively less star-forming activity at $\rm\it{z}$$\sim$0 and falls below the main-sequence relation for a stellar content of $\rm \gtrsim 10^{11} M_{\odot}$. We also show that these objects accumulated much of their stellar mass in the early period of evolution with $\sim31$$-$$42$ per cent of the total stellar mass obtained in a time of $(1/16)$$-$$(1/5)^{\rm th}$ the age of the Universe. We estimate that these massive objects convert their halo baryons into stars with efficiencies falling between $\sim 7-31$ percent.