TY - JOUR

T1 - Galaxy Zoo: Clump Scout: Surveying the Local Universe for Giant Star-forming Clumps

AU - Adams, Dominic

AU - Mehta, Vihang

AU - Dickinson, Hugh

AU - Scarlata, Claudia

AU - Fortson, Lucy

AU - Kruk, Sandor

AU - Simmons, Brooke

AU - Lintott, Chris

PY - 2022/5/19

Y1 - 2022/5/19

N2 - Massive, star-forming clumps are a common feature of high-redshift star-forming galaxies. How they formed, and why they are so rare at low redshift, remains unclear. In this paper we identify the largest sample yet of clumpy galaxies (7050) at low redshift using data from the citizen science project Galaxy Zoo: Clump Scout, in which volunteers classified 58,550 Sloan Digital Sky Survey (SDSS) galaxies spanning redshift 0.02 < z < 0.15. We apply a robust completeness correction by comparing with simulated clumps identified by the same method. Requiring that the ratio of clump to galaxy flux in the SDSS u band be greater than 8% (similar to clump definitions used by other works), we estimate the fraction of local star-forming galaxies hosting at least one clump (f clumpy) to be 3.22−0.34+0.38% . We also compute the same fraction with a less stringent relative flux cut of 3% ( 12.68−0.88+1.38% ), as the higher number count and lower statistical noise of this fraction permit finer comparison with future low-redshift clumpy galaxy studies. Our results reveal a sharp decline in f clumpy over 0 < z < 0.5. The minor merger rate remains roughly constant over the same span, so we suggest that minor mergers are unlikely to be the primary driver of clump formation. Instead, the rate of galaxy turbulence is a better tracer for f clumpy over 0 < z < 1.5 for galaxies of all masses, which supports the idea that clump formation is primarily driven by violent disk instability for all galaxy populations during this period.

AB - Massive, star-forming clumps are a common feature of high-redshift star-forming galaxies. How they formed, and why they are so rare at low redshift, remains unclear. In this paper we identify the largest sample yet of clumpy galaxies (7050) at low redshift using data from the citizen science project Galaxy Zoo: Clump Scout, in which volunteers classified 58,550 Sloan Digital Sky Survey (SDSS) galaxies spanning redshift 0.02 < z < 0.15. We apply a robust completeness correction by comparing with simulated clumps identified by the same method. Requiring that the ratio of clump to galaxy flux in the SDSS u band be greater than 8% (similar to clump definitions used by other works), we estimate the fraction of local star-forming galaxies hosting at least one clump (f clumpy) to be 3.22−0.34+0.38% . We also compute the same fraction with a less stringent relative flux cut of 3% ( 12.68−0.88+1.38% ), as the higher number count and lower statistical noise of this fraction permit finer comparison with future low-redshift clumpy galaxy studies. Our results reveal a sharp decline in f clumpy over 0 < z < 0.5. The minor merger rate remains roughly constant over the same span, so we suggest that minor mergers are unlikely to be the primary driver of clump formation. Instead, the rate of galaxy turbulence is a better tracer for f clumpy over 0 < z < 1.5 for galaxies of all masses, which supports the idea that clump formation is primarily driven by violent disk instability for all galaxy populations during this period.

KW - 310

KW - Galaxies and Cosmology

U2 - 10.3847/1538-4357/ac6512

DO - 10.3847/1538-4357/ac6512

M3 - Journal article

VL - 931

JO - The Astrophysical Journal

JF - The Astrophysical Journal

SN - 0004-637X

IS - 1

M1 - 16

ER -