Mergers lighting the early Universe: enhanced star formation, AGN triggering, and Ly$α$ emission in close pairs at $z=3-9$
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| Format: | Preprint |
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2025
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| _version_ | 1866914096600842240 |
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| author | Puskás, Dávid Tacchella, Sandro Simmonds, Charlotte Jones, Gareth C. Juodžbalis, Ignas Scholtz, Jan Baker, William M. Bunker, Andrew J. Carniani, Stefano Curtis-Lake, Emma Duan, Qiao Eisenstein, Daniel J. Hainline, Kevin Johnson, Benjamin D. Maiolino, Roberto Rieke, Marcia Robertson, Brant Williams, Christina C. Witstok, Joris |
| author_facet | Puskás, Dávid Tacchella, Sandro Simmonds, Charlotte Jones, Gareth C. Juodžbalis, Ignas Scholtz, Jan Baker, William M. Bunker, Andrew J. Carniani, Stefano Curtis-Lake, Emma Duan, Qiao Eisenstein, Daniel J. Hainline, Kevin Johnson, Benjamin D. Maiolino, Roberto Rieke, Marcia Robertson, Brant Williams, Christina C. Witstok, Joris |
| contents | Galaxy mergers and interactions are often invoked to explain enhanced star formation, black hole growth, and mass build-up of galaxies at later cosmic times, but their effect is poorly understood at high redshift ($z>2$). We use JADES data to analyse a mass-complete sample of 2095 galaxies at $z=3-9$ with ${\rm log}(M_\star/{\rm M_\odot}) = [8, 10]$, identifying major merger pairs (projected separation of $5-100$ pkpc, mass ratio $\geq 1/4$) using a probabilistic method. To look for signatures of enhancement in multiple physical properties, we carefully build a control sample of non-pairs that are simultaneously matched in redshift, stellar mass, isolation, and environment to the pair sample. We find a moderate enhancement in specific star formation rate (sSFR) of $1.12 \pm 0.05$ at separations $\lesssim 20$ kpc, which is weakly detectable out to $\sim50$ kpc. We find that at longer averaging timescales (50-100 Myr) the sSFR is more affected by interactions and environment, whereas at shorter timescales (5-10 Myr) it is dominated by internal feedback and burstiness. By averaging star formation histories, we find two distinct populations: pre-first passage/coalescence (monotonically rising SFR) and post-pericentre pairs (earlier peak in SFR). Finally, we find no significant excess of AGN in pairs, suggesting galaxy interactions are not effectively triggering black hole activity at separations $>5$ kpc. Similarly, we also do not detect an excess in the fraction of Lyman-$α$ emitters in pairs, implying that at the probed separations, galaxy interactions are not efficient at enhancing Lyman-$α$ photon production and escape, which may only become important at the smallest scales. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2510_14743 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Mergers lighting the early Universe: enhanced star formation, AGN triggering, and Ly$α$ emission in close pairs at $z=3-9$ Puskás, Dávid Tacchella, Sandro Simmonds, Charlotte Jones, Gareth C. Juodžbalis, Ignas Scholtz, Jan Baker, William M. Bunker, Andrew J. Carniani, Stefano Curtis-Lake, Emma Duan, Qiao Eisenstein, Daniel J. Hainline, Kevin Johnson, Benjamin D. Maiolino, Roberto Rieke, Marcia Robertson, Brant Williams, Christina C. Witstok, Joris Astrophysics of Galaxies Galaxy mergers and interactions are often invoked to explain enhanced star formation, black hole growth, and mass build-up of galaxies at later cosmic times, but their effect is poorly understood at high redshift ($z>2$). We use JADES data to analyse a mass-complete sample of 2095 galaxies at $z=3-9$ with ${\rm log}(M_\star/{\rm M_\odot}) = [8, 10]$, identifying major merger pairs (projected separation of $5-100$ pkpc, mass ratio $\geq 1/4$) using a probabilistic method. To look for signatures of enhancement in multiple physical properties, we carefully build a control sample of non-pairs that are simultaneously matched in redshift, stellar mass, isolation, and environment to the pair sample. We find a moderate enhancement in specific star formation rate (sSFR) of $1.12 \pm 0.05$ at separations $\lesssim 20$ kpc, which is weakly detectable out to $\sim50$ kpc. We find that at longer averaging timescales (50-100 Myr) the sSFR is more affected by interactions and environment, whereas at shorter timescales (5-10 Myr) it is dominated by internal feedback and burstiness. By averaging star formation histories, we find two distinct populations: pre-first passage/coalescence (monotonically rising SFR) and post-pericentre pairs (earlier peak in SFR). Finally, we find no significant excess of AGN in pairs, suggesting galaxy interactions are not effectively triggering black hole activity at separations $>5$ kpc. Similarly, we also do not detect an excess in the fraction of Lyman-$α$ emitters in pairs, implying that at the probed separations, galaxy interactions are not efficient at enhancing Lyman-$α$ photon production and escape, which may only become important at the smallest scales. |
| title | Mergers lighting the early Universe: enhanced star formation, AGN triggering, and Ly$α$ emission in close pairs at $z=3-9$ |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2510.14743 |