The Galaxy Starburst/Main-sequence Bimodality over Five Decades in Stellar Mass at z ≈ 3–6.5

Abstract

We study the relation between stellar mass (M *) and star formation rate (SFR) for star-forming galaxies over approximately five decades in stellar mass ( 5.5 ≲ log 10 ( M * / M ⊙ ) ≲ 10.5 ) at z ≈ 3–6.5. This unprecedented coverage has been possible thanks to the joint analysis of blank non-lensed fields (COSMOS/SMUVS) and cluster lensing fields (Hubble Frontier Fields) that allow us to reach very low stellar masses. Previous works have revealed the existence of a clear bimodality in the SFR–M * plane with a star formation Main Sequence and a starburst cloud at z ≈ 4–5. Here we show that this bimodality extends to all star-forming galaxies and is valid in the whole redshift range z ≈ 3–6.5. We find that starbursts constitute at least ≈20% of all star-forming galaxies with M * ≳ 109 M ⊙ at these redshifts and reach a peak of 40% at z = 4–5. More importantly, 60%–90% of the total SFR budget at these redshifts is contained in starburst galaxies, indicating that the starburst mode of star formation is dominant at high redshifts. Almost all the low stellar mass starbursts with log 10 ( M * / M ⊙ ) ≲ 8.5 have ages comparable to the typical timescales of a starburst event, suggesting that these galaxies are being caught in the process of formation. Interestingly, galaxy formation models fail to predict the starburst/main-sequence bimodality and starbursts overall, suggesting that the starburst phenomenon may be driven by physical processes occurring at smaller scales than those probed by these models.

Dynamical characterization of galaxies up toz∼ 7

“…Currently, at z ≃ 6 − 7 the serra suite has a total of ≃ 200 galaxies with mass range ∼ 10 8 −10 10 M ⊙ (Pallottini et al 2022). As shown in Pallottini et al (2022), serra galaxies have a specific SFR that ranges from sSFR ∼ 100 Gyr −1 for young (t ⋆ ≲ 100 Myr), small galaxies (M ⋆ ≲ 10 8 M ⊙ ) to sSFR ∼ 10 Gyr −1 for older (t ⋆ ≳ 200 Myr) more massive ones (M ⋆ ≳ 10 9 M ⊙ ), in good agreement with high-z data (Jiang et al 2013, Rinaldi et al 2022. In Fig.…”

A First Look into the Nature of JWST/MIRI 7.7 μm Sources from SMACS 0723

“…The z > 1 galaxies in our sample span stellar masses between 10 7 and 10 10 M e . The access to low stellar masses is facilitated thanks to the gravitational lensing effect, as it has been shown by previous works (e.g., Rinaldi et al 2022). We do not find any very massive >10 11 M e galaxies, but this is not surprising, given the small volume sampled by the SMACS 0723 field.…”

The merger–starburst connection across cosmic times

“…Furthermore, it suggests that the bimodality in the distribution of sSFRs of star forming galaxies (e.g. Sargent et al 2014;Rinaldi et al 2022) is not, or at least not solely, explained by starburst events as rapid transitions above the main sequence. The divergence between the merger rate and the number of outliers above the main sequence (Schreiber et al 2015;Pearson et al 2019) could thus be explained by a complex relation between outliers and starbursts, which depends on the phase of star formation.…”