Jorryt Matthee
@jorryt.bsky.social
Extragalactic astrophysicist. Assistant Prof @ IST Austria - PI of ERC StG-2022 AGENTS. PhD Leiden 2018, Zwicky fellow @ ETH Zurich,2018-2023.
The FMR appears to be weaker at high-redshift, possibly because the gas flow response to variations in star formation rate are different than in the local Universe. However, this needs to be tested with larger samples of individual measurements rather than stacks -- ideally to lower masses as well!
October 31, 2025 at 10:53 AM
The FMR appears to be weaker at high-redshift, possibly because the gas flow response to variations in star formation rate are different than in the local Universe. However, this needs to be tested with larger samples of individual measurements rather than stacks -- ideally to lower masses as well!
With toy models, we investigate how selection effects impact the observed MZR, and whether an intrinsically steep MZR may be masqueraded. The direction of this effect depends on whether the 3D correlation between stellar mass, star formation rate and metallicity known at z=0 evolves or not.
October 31, 2025 at 10:53 AM
With toy models, we investigate how selection effects impact the observed MZR, and whether an intrinsically steep MZR may be masqueraded. The direction of this effect depends on whether the 3D correlation between stellar mass, star formation rate and metallicity known at z=0 evolves or not.
However, our measurements (and thus the literature implied) do not match recent galaxy simulations, especially once we account for our known selection effects. This implies that the MZR is flatter than expected, suggestive of more rapid chemical enrichment in low-mass galaxies.
October 31, 2025 at 10:53 AM
However, our measurements (and thus the literature implied) do not match recent galaxy simulations, especially once we account for our known selection effects. This implies that the MZR is flatter than expected, suggestive of more rapid chemical enrichment in low-mass galaxies.
The mass-metallicity relation of our sample confirms that early galaxies have a lower oxygen abundance than galaxies in the local Universe, with values and a mass-dependence in broad agreement with recent measurements in the literature based on other surveys and instruments.
October 31, 2025 at 10:53 AM
The mass-metallicity relation of our sample confirms that early galaxies have a lower oxygen abundance than galaxies in the local Universe, with values and a mass-dependence in broad agreement with recent measurements in the literature based on other surveys and instruments.
We use these stacks to measure the direct Te-based gas-phase oxygen abundance in various stacks of galaxies, and we demonstrate that previously calibrated strong line calibrations between the [OIII]/Hb ratio and metallicity are also applicable to our sample.
October 31, 2025 at 10:53 AM
We use these stacks to measure the direct Te-based gas-phase oxygen abundance in various stacks of galaxies, and we demonstrate that previously calibrated strong line calibrations between the [OIII]/Hb ratio and metallicity are also applicable to our sample.
By combining deep NIRCam grism data from the EIGER, ALT and COLA1 surveys, we assembled a clean oxygen emission-line selected sample of nearly 1000 galaxies in the early Universe at z~6. In stacked spectra, we detect feature as faint as [OIII]4364.
October 31, 2025 at 10:53 AM
By combining deep NIRCam grism data from the EIGER, ALT and COLA1 surveys, we assembled a clean oxygen emission-line selected sample of nearly 1000 galaxies in the early Universe at z~6. In stacked spectra, we detect feature as faint as [OIII]4364.
Each of these effects should be quantified with future observations, to improve our ability to use Halpha-based SFRs to map the variability of galaxy star formation histories as a more precise test of galaxy formation models.
October 28, 2025 at 11:02 AM
Each of these effects should be quantified with future observations, to improve our ability to use Halpha-based SFRs to map the variability of galaxy star formation histories as a more precise test of galaxy formation models.
2) a significant population of quenched galaxies at low masses and/or 3) an under-estimate in the dust attenuation from SED modeling at the massive end.
October 28, 2025 at 11:02 AM
2) a significant population of quenched galaxies at low masses and/or 3) an under-estimate in the dust attenuation from SED modeling at the massive end.
As discussed in the paper, the flat main sequence can be reconciled in various ways: 1) a new conversion between Halpha luminosity and SFR that is more applicable to metal-poor starbursts. See: arxiv.org/abs/2509.05403
Hydrogen-Alpha as a Tracer of Star Formation in the SPHINX Cosmological Simulations
The Hydrogen-alpha (Ha) emission line in galaxies is a powerful tracer of their recent star formation activity. With the advent of JWST, we are now able to routinely observe Ha in galaxies at high red...
arxiv.org
October 28, 2025 at 11:02 AM
As discussed in the paper, the flat main sequence can be reconciled in various ways: 1) a new conversion between Halpha luminosity and SFR that is more applicable to metal-poor starbursts. See: arxiv.org/abs/2509.05403
With boundary constraints from simulations ("the slope must be 1"), our data does prefer an increasing scatter towards low masses, which confirms the picture of bursty star formation in low mass galaxies.
October 28, 2025 at 11:02 AM
With boundary constraints from simulations ("the slope must be 1"), our data does prefer an increasing scatter towards low masses, which confirms the picture of bursty star formation in low mass galaxies.
We show that the flat slope is partly due to the flux-limited nature of our survey. Yet, even correcting for this with a Bayesian model, our data prefers a flatter slope, with a scatter that we cannot constrain on our data alone.
October 28, 2025 at 11:02 AM
We show that the flat slope is partly due to the flux-limited nature of our survey. Yet, even correcting for this with a Bayesian model, our data prefers a flatter slope, with a scatter that we cannot constrain on our data alone.
At face value, our data yields a relatively flat slope of the main sequence, which other work recently also reported, but which is at odds with virtually every galaxy simulation and with the relative constant low mass slope of the galaxy stellar mass function.
October 28, 2025 at 11:02 AM
At face value, our data yields a relatively flat slope of the main sequence, which other work recently also reported, but which is at odds with virtually every galaxy simulation and with the relative constant low mass slope of the galaxy stellar mass function.
Thanks to JWST grism spectroscopy behind a lensing cluster, we can now obtain large samples of uniformly selected galaxies at redshifts z~5, whose star formation rates we accurately estimate with the Halpha line, and characterize the main sequence across three orders of magnitude in mass.
October 28, 2025 at 11:02 AM
Thanks to JWST grism spectroscopy behind a lensing cluster, we can now obtain large samples of uniformly selected galaxies at redshifts z~5, whose star formation rates we accurately estimate with the Halpha line, and characterize the main sequence across three orders of magnitude in mass.
Early JWST results indicate that the first galaxies had "bursty" star formation histories, this impacts the observed UV luminosity function, leads to detection of "napping"/mini-quenched galaxies but also causes a larger scatter in the main sequence.
October 28, 2025 at 11:02 AM
Early JWST results indicate that the first galaxies had "bursty" star formation histories, this impacts the observed UV luminosity function, leads to detection of "napping"/mini-quenched galaxies but also causes a larger scatter in the main sequence.
Puzzled by all the latest developments and observed features in LRDs? We tried to summarize the key features, our interpretation, alternatives and challenges in this table:
October 3, 2025 at 7:54 AM
Puzzled by all the latest developments and observed features in LRDs? We tried to summarize the key features, our interpretation, alternatives and challenges in this table:
What does this mean? This very luminous LRD likely resides in a very low mass galaxy. The BH mass is unlikely as high as the virial indicators suggest, because the broadening is not dynamical. What the BH mass is.. a wide range is still possible, and we should find new ways of figuring that out!
October 3, 2025 at 7:54 AM
What does this mean? This very luminous LRD likely resides in a very low mass galaxy. The BH mass is unlikely as high as the virial indicators suggest, because the broadening is not dynamical. What the BH mass is.. a wide range is still possible, and we should find new ways of figuring that out!
Despite most of the light being dominated by the "LRD" (which we think is an accreting SMBH highly covered by dense gas), there are some indications of host galaxy light, in particular the extremely narrow [OIII] emission and some (similarly) narrow Hgamma emission that pops up
October 3, 2025 at 7:54 AM
Despite most of the light being dominated by the "LRD" (which we think is an accreting SMBH highly covered by dense gas), there are some indications of host galaxy light, in particular the extremely narrow [OIII] emission and some (similarly) narrow Hgamma emission that pops up
Using Cloudy modeling, we can connect the various observed features: [FeII], scattering & collisionally dominated Balmer emission and the now well-known Balmer break of LRDs: a warm layer of dense gas (T~7000 K, ne~10^9 cm3) is responsible.
October 3, 2025 at 7:54 AM
Using Cloudy modeling, we can connect the various observed features: [FeII], scattering & collisionally dominated Balmer emission and the now well-known Balmer break of LRDs: a warm layer of dense gas (T~7000 K, ne~10^9 cm3) is responsible.
The most surprising observed feature is a forest of [FeII] emission lines -- these lines are commonly observed in quasars but they tend to be much broader. This is further evidence that the dense gas is not moving as rapidly as the line-widths of the Balmer lines suggest.
October 3, 2025 at 7:54 AM
The most surprising observed feature is a forest of [FeII] emission lines -- these lines are commonly observed in quasars but they tend to be much broader. This is further evidence that the dense gas is not moving as rapidly as the line-widths of the Balmer lines suggest.
Together, this is a radically different explanation than is common, where line-profiles are explained as a composite of narrow emission from low density gas and broad emission from fast moving regions of gas, and the absorber would be a decoupled cloud of gas.
October 3, 2025 at 7:54 AM
Together, this is a radically different explanation than is common, where line-profiles are explained as a composite of narrow emission from low density gas and broad emission from fast moving regions of gas, and the absorber would be a decoupled cloud of gas.
The wings are exponential with an indistinguishable width, suggesting they emerge from electron scattering -- likely in the same layer of dense gas. Another exciting feature are the line-ratios: Ha/Hb~10. This is likely because of collisional effects in this dense gas.
October 3, 2025 at 7:54 AM
The wings are exponential with an indistinguishable width, suggesting they emerge from electron scattering -- likely in the same layer of dense gas. Another exciting feature are the line-ratios: Ha/Hb~10. This is likely because of collisional effects in this dense gas.
The P Cygni profile emerges because there is a layer of partially excited, very dense gas with a significant population of H atoms in the n=2 state. Resonant scattering in this layer (and complicated decay effects of Hb photons) cause the differences in the cores.
October 3, 2025 at 7:54 AM
The P Cygni profile emerges because there is a layer of partially excited, very dense gas with a significant population of H atoms in the n=2 state. Resonant scattering in this layer (and complicated decay effects of Hb photons) cause the differences in the cores.