Observations of the initial formation and evolution of spiral galaxies at 1 < z < 3 in the CANDELS fields

Many aspects concerning the formation of spiral and disc galaxies remain unresolved, despite their discovery and detailed study over the past 150 yr. As such, we present the results of an observational search for proto-spiral galaxies and their earliest formation, including the discovery of a significant population of spiral-like and clumpy galaxies at z > 1 in deep Hubble Space Telescope CANDELS imaging. We carry out a detailed analysis of this population, characterizing their number density evolution, masses, star formation rates (SFR), and sizes. Overall, we find a surprisingly high overall number density of massive M-* > 10(10) M-circle dot spiral-like galaxies (including clumpy spirals) at z > 1 of 0.18 per arcmin(-2). We measure and characterize the decline in the number of these systems at higher redshift using simulations to correct for redshift effects in identifications, finding that the true fraction of spiral-like galaxies grows at lower redshifts as similar to (1 + z)(-1-1). This is such that the absolute numbers of spirals increases by a factor of similar to 10 between z = 2.5 and z = 0.5. We also demonstrate that these spiral-like systems have large sizes at z > 2, and high SFRs, above the main-sequence, These galaxies represent a major mode of galaxy formation in the early Universe, perhaps driven by the spiral structure itself. We finally discuss the origin of these systems, including their likely formation through gas accretion and minor mergers, but conclude that major mergers are an unlikely cause.

Automated summary

This study presents observational results on the formation of early spiral galaxies, which were discovered in deep Hubble Space Telescope CANDELS imaging. The study finds a significant population of spiral-like and clumpy galaxies at high redshifts, with a surprisingly high overall number density. The analysis also reveals the decline in the number of these galaxies at higher redshifts and their large sizes and high star formation rates. The study suggests that these spiral-like galaxies represent an important mode of galaxy formation in the early Universe, possibly driven by the spiral structure itself.