UV and NIR size of the low-mass field galaxies: the UV compact galaxies

Abstract

Context. Most of the massive star-forming galaxies are found to have 'inside-out' stellar mass growth modes, which means the inner parts of the galaxies mainly consist of the older stellar population, while the star forming in the outskirt of the galaxy is still ongoing. Aims. The high-resolution HST images from Hubble Deep UV Legacy Survey (HDUV) and Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) projects with the unprecedented depth in both F275W and F160W bands are the perfect data sets to study the forming and formed stellar distribution directly. Methods. We selected the low redshift (0.05 < z spec < 0.3) galaxy sample from the GOODS-North field where the HST F275W and F160W images are available. Then we measured the half light radius in F275W and F160W bands, which are the indicators of the star formation and stellar mass. Results. By comparing the F275W and F160W half light radius, we find the massive galaxies are mainly follow the 'inside-out' growth mode, which is consistent with the previous results. Moreover, the HST F275W and F160W images reveal that some of the low-mass galaxies (< 10 8 M ⊙ ) have the 'outside-in' growth mode: their images show a compact UV morphology, implying an ongoing star formation in the galaxy centre, while the stars in the outskirts of the galaxies are already formed. The two modes transit smoothly at stellar mass range about 10 8−9 M ⊙ with a large scatter. We also try to identify the possible neighbour massive galaxies from the SDSS data, which represent the massive galaxy sample. We find that all of the spec-z selected galaxies have no massive galaxy nearby. Thus the 'outside-in' mode we find in the low-mass galaxies are not likely originated from the environment.

A kpc-scale-resolved study of unobscured and obscured star formation activity in normal galaxies at z = 1.5 and 2.2 from ALMA and HiZELS

“…For the ALMA non-detected galaxies, SHiZELS-10, -2, 3, and -21, the rest-frame UV and optical band images show compact cores at their centres (Fig. A2), evidencing compact UV star formation cores or regions of lower obscuration which is also found in the low-redshift low mass galaxies (Cheng et al 2020). We see that z ≃ 2.23 galaxies display more compact rest-frame UV morphologies than the z ≃ 1.47 sample, which is consistent with previous studies (Paulino-Afonso et al 2017).…”

UV and NIR size of the HI selected low surface brightness galaxies

“…LSBGs are mainly a population of low mass galaxies. To understand the LSBG properties in a wider picture, we compare the LSBG sample with the low mass galaxy sample in Cheng et al (2020), which includes the galaxies at 0.05 < z spec < 0.3, F 606W < 24 AB mag in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS, Grogin et al 2011;Koekemoer et al 2011) GOODS-North field (Barro et al 2019) with a stellar-mass range 10 7 < M * /M ⊙ < 10 11.4 . The CANDELS GOOD-North field has been covered by Hubble Deep UV Legacy Survey (HDUV, Oesch et al 2018) in F275W, F336W band.…”

“…By comparing the UV and NIR bands HST images in the GOODS-North field, we have found the low mass star-forming galaxies can have an "outside-in" growth mode, which means that the star formation is active in the galaxy centre, while the stars are already formed in a larger radius (Cheng et al 2020). Nevertheless, our previous results based on the HST images only covered the UV bright galaxy with optical spectroscopy redshift, which usually have a high centre surface brightness.…”

“…The study of the star formation in LSBG is crucially important to the understanding of the formation process in the young galaxy population with extreme properties such as low mass, low dust and low metallicity. One simple and yet fundamental parameter to show the galaxy formation and evolution path is the galaxy size in different bands (Cheng et al 2020). Previous studies show that massive star-forming galaxies have a larger star formation radius than that of the stellar distribution radius, implying an "inside-out" growth mode because most of the stars have concentrated in the galaxy centre region, while the star formation is more extended (Kelvin et al 2012).…”

“…Nevertheless, our previous results based on the HST images only covered the UV bright galaxy with optical spectroscopy redshift, which usually have a high centre surface brightness. LSBGs as an influential member of low mass galaxy population is absent in Cheng et al (2020). So in this work, we select a sample of HI bright LSBGs with GALEX and UKIRT detection, aiming to study the growth mode of the LSBGs.…”