Abstract
ABSTRACT 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 $M_{*} \gt 10^{10}\, \mathrm{M}_{\odot }$ spiral-like galaxies (including clumpy spirals) at z > 1 of $0.18\, {\rm per}\, \mathrm{arcmin}^{-2}$. 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 ∼ (1 + z)−1.1. This is such that the absolute numbers of spirals increases by a factor of ∼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.
Highlights
Spiral structures are present in many disc galaxies in the local Universe with different morphologies, ranging from granddesign, in which prominent and well-defined spiral arms can be traced over large parts of the disc, to those with a flocculent pattern, with fragmented spiral arms that have a more limited spacial extent (Elmegreen et al 2011; Elmegreen & Elmegreen 2014)
We first begin by investigating the spiral galaxy fraction and how it evolves with time and characterise these systems before discussing their likely origin
We investigate how the fractions of the different types of disc galaxies vary as a function of redshift
Summary
Spiral structures are present in many disc galaxies in the local Universe with different morphologies, ranging from granddesign, in which prominent and well-defined spiral arms can be traced over large parts of the disc, to those with a flocculent pattern, with fragmented spiral arms that have a more limited spacial extent (Elmegreen et al 2011; Elmegreen & Elmegreen 2014). Since these spirals/discs make up the majority of the galaxy population in today’s universe (e.g., Conselice 2006), understanding their development is critical for any full picture of galaxy formation. By examining these systems in the distant universe we may be able to determine their formation history in an empirical way that can inform the physics for their development and long lasting nature
Sign-in/Register to view highlights & summary 
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
