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

Abstract

We present highly resolved and sensitive imaging of the five nearby massive spiral galaxies (with rotation velocities $>300km{\mathrm{s}}^{-1}$) 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$$1.4$$-$$13.7{\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}$ and fall in the `Green Valley' region with a specific star formation rate within $\sim$$10^{-11.5}$$-$$10^{-10.5}\mathrm{y}{\mathrm{r}}^{-1}$. Moreover, the mean star formation rate density of the highly resolved star-forming clumps of these objects are in the range $0.011$$-$$0.098{\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}\mathrm{kp}{\mathrm{c}}^{-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 $\sim$ $0.8$$-$$2.8$ 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 $z$$\sim$0 and falls below the main-sequence relation for a stellar content of $\gtrsim 10^{11}{\mathrm{M}}_{\odot }$. We also show that these objects accumulated much of their stellar mass in the early period of evolution with $\sim 31$$-$$42$ per cent of the total stellar mass obtained in a time of $(1/16)$$-$$(1/5{)}^{\mathrm{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.

Accepted for publication in MNRAS