Star formation in the outer regions of the early-type galaxy NGC 4203

Abstract

NGC 4203 is a nearby early-type galaxy surrounded by a very large, low-column-density H i disc. In this paper we study the star formation efficiency in the gas disc of NGC 4203 by using the UV, deep optical imaging and infrared data. We confirm that the H i disc consists of two distinct components: an inner star forming ring with radius from ∼1 to ∼3 R e f f , and an outer disc. The outer H i disc is 9 times more massive than the inner H i ring. At the location of the inner H i ring we detect spiral-like structure both in the deep g − r image and in the 8 µm Spitzer-IRAC image, extending in radius up to ∼ 3 R e f f . These two gas components have a different star formation efficiency likely due to the different metallicity and dust content. The inner component has a star formation efficiency very similar to the inner regions of late-type galaxies. Although the outer component has a very low star formation efficiency, it is similar to that of the outer regions of spiral galaxies and dwarfs. We suggest that these differences can be explained with different gas origins for the two components such as stellar mass loss for the inner H i ring and accretion from the inter galactic medium (IGM) for the outer H i disc. The low level star formation efficiency in the outer H i disc is not enough to change the morphology of NGC 4203, making the depletion time of the H i gas much too long.

Star formation in CALIFA early-type galaxies: a matter of discs

“…The presence of residual star formation in the outer parts of ETGs has been previously reported in the literature from measurements of either emission lines (Sarzi et al 2006;Gomes et al 2016a) or atomic/molecular gas (Yıldız et al 2015;Colombo et al 2018). However, our spectro-photometric decomposition analysis demonstrates that the star formation in not only present in the outer regions of ETGs, but at all galactocentric radii when considering the disc component.…”

“…Despite most of the stellar mass in ETGs is formed at high redshift (Cowie et al 1996;Thomas et al 2010;Sánchez et al 2019), the study of the recent star formation in these systems has provided new clues on their mass assembly. Studies of the ultra-violet (UV) emission in ETGs show that residual star formation is occurring in the outer parts of a non-negligible fraction of these galaxies (Jeong et al 2007;Salim & Rich 2010;Moffett et al 2012), generally follow-⋆ E-mail: jairomendezabreu@gmail.com ing distinctive spiral-like patterns noticeable in the ionisedgas (Gomes et al 2016b), that have been also detected in atomic Hydrogen (Yıldız et al 2015). Similarly, observations of molecular gas (mostly CO) have also proved its presence in ETGs and showed signatures of different modes of star formation (Shapiro et al 2010;Young et al 2011).…”

H i galaxies with little star formation: an abundance of LIERs

“…Some early-type galaxies (ETGs; ellipticals and lenticulars) have also been found to have H i gas masses similar to spirals (e.g, Knapp et al 1985;Sadler et al 2002;Oosterloo et al 2010;Serra et al 2012). However, while the H i column density distribution of spirals is very broad, reaching up to 10 21 cm −2 , most H i-rich ETGs have H i column densities < 5 × 10 20 cm −2 (Serra et al 2012;Yıldız et al 2015). ETGs have column densities that are similar to those observed in the outer regions of spirals where very little star formation occurs (Bigiel et al 2010).…”