iiinova — where your digital self keeps evolving

Jorryt Matthee @jorryt.bsky.social · 19/03/2026

A key implication of these results is that line-profiles (and line-widths specifically) are not set by the dynamics of the gas, but rather by radiative transfer effects. This is not something uncommon to happen and well understood in stellar phenomena as Type IIn supernova or luminous blue variables

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Jorryt Matthee @jorryt.bsky.social · 19/03/2026

As illustrated in these sketches, our trends could suggest that differences in viewing angle (and a non-spherically symmetric geometry) and/or different evolutionary phases (linked to accretion and outflow cycles) drive the variety among observed LRDs, warranting such geometries in new models.

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Jorryt Matthee @jorryt.bsky.social · 19/03/2026

To me the newest result is that the central velocity of the Balmer absorption correlates with the UV-optical color (Balmer break, HI column density). The reddest sources show redshifted absorption from (primarily) inflowing gas, whereas bluer sources have outflowing gas with lower column densities

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Jorryt Matthee @jorryt.bsky.social · 19/03/2026

The exponential wings are increasingly more dominant in redder sources. This means that the photons that experience higher column of HI gas also experience more free electrons: gas is partially ionised, likely clumpy. Scattering in a clumpy medium explains stronger Hbeta absorption.

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Jorryt Matthee @jorryt.bsky.social · 19/03/2026

The Balmer break strength depends on the column density of HI atoms. The HI column density also sets the resonant scattering opacity. From blue to red colors we indeed see line cores (subtracting the wing for visualisation purposes) showing increasingly strong scattering effects.

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Jorryt Matthee @jorryt.bsky.social · 19/03/2026

From blue to red (i.e. with increasing Balmer break strength), sources have broader and more dominant wings, steeper Balmer decrements and stronger Balmer absorption. Seeing absorption is not "random". Important: blue sources still lack various standard AGN indicators (X-ray, IR, MgII, [NeV])

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Jorryt Matthee @jorryt.bsky.social · 19/03/2026

This figure summarizes the results: the cores of the Balmer lines depend on UV to optical color, wings are exponential. Blue sources have core-dominated lines. Redder sources show P Cygni features with blue-shifted absorption and redshift emitted. The reddest sources have dominant central absorption

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Jorryt Matthee @jorryt.bsky.social · 19/03/2026

Paper Day! You may have heard about these "Little Red Dots" in JWST data. Here we use new high quality spectra to show that the their spectral appearance is primarily determined by the properties of surrounding gas. LRDs are hot engines covered by dense gas arxiv.org/abs/2603.17667

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Jorryt Matthee @jorryt.bsky.social · 31/10/2025

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.

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Jorryt Matthee @jorryt.bsky.social · 31/10/2025

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.

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Jorryt Matthee @jorryt.bsky.social · 31/10/2025

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.

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Jorryt Matthee @jorryt.bsky.social · 31/10/2025

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.

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Jorryt Matthee @jorryt.bsky.social · 31/10/2025

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.

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Jorryt Matthee @jorryt.bsky.social · 28/10/2025

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.

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Jorryt Matthee @jorryt.bsky.social · 28/10/2025

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.

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Jorryt Matthee @jorryt.bsky.social · 28/10/2025

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.

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Jorryt Matthee @jorryt.bsky.social · 28/10/2025

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.

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Jorryt Matthee @jorryt.bsky.social · 28/10/2025

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.

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Jorryt Matthee @jorryt.bsky.social · 28/10/2025

Delayed paper day! In work lead by my postdoc Claudia Di Cesare as part of the ALT survey, we provide a detailed census of the so-called star formation main sequence in the early Universe. arxiv.org/pdf/2510.19044

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Jorryt Matthee @jorryt.bsky.social · 03/10/2025

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:

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Jorryt Matthee @jorryt.bsky.social · 03/10/2025

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!

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Jorryt Matthee @jorryt.bsky.social · 03/10/2025

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

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Jorryt Matthee @jorryt.bsky.social · 03/10/2025

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.

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Jorryt Matthee @jorryt.bsky.social · 03/10/2025

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.

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Jorryt Matthee @jorryt.bsky.social · 03/10/2025

With our new deep JWST NIRspec IFU Prism+G395H data, we can characterize the Balmer lines in unprecedented detail; We confirm the absorption seen in grism data, show it's also present in other transitions, and we argue the line-profiles are best explained by exponential wings with P Cygni cores.

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Jorryt Matthee @jorryt.bsky.social · 03/10/2025

Object of interest: FRESCO-GN-9771, the most luminous LRD from my discovery paper (arxiv.org/abs/2306.05448). This object shows such luminous Halpha emission that I initially thought it must have been a very nearby object when I spotted it in the FRESCO data back in 2023.. Yet it's at z~5.5.

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Jorryt Matthee @jorryt.bsky.social · 03/10/2025

Delayed paper day! arxiv.org/abs/2510.00103 Led by Alberto Torralba, who is a postdoc in my group, we present the highest quality spectrum of a "Little Red Dot" yet known. This unveils new insights in the warm, dense layer of gas that is key to explain the most unusual spectral features of the LRDs!

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Jorryt Matthee @jorryt.bsky.social · 09/09/2025

We make these and various other new calibrations available in the paper, discuss what to do if you worry about attenuation due to dust and how biased various measurements of galaxy populations otherwise are. 6/..

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Jorryt Matthee @jorryt.bsky.social · 09/09/2025

However, fortunately, the Halpha equivalent width -- a measurement readily available for many galaxies -- correlates with both of these quantities and can be used to derive more accurate and bias-free measurements of the rates at which young galaxies form new stars .. 5/

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Jorryt Matthee @jorryt.bsky.social · 09/09/2025

Indeed, using the SPHINX20 simulation we show that the SFR-Bias (how wrong is your star formation rate if you use the standard calibration) correlates both with burst age and metallicity. Unfortunately, it is not very easy to simply measure these properties and use those to derive corrections... 4/.

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Jorryt Matthee @jorryt.bsky.social · 09/09/2025

The Halpha emission line has long been considered the "golden" indicator of the star formation rate of galaxies. However, various assumptions behind the standard calibrations are no longer applicable to galaxies in the early Universe such as those observed by the JWST, causing significant bias 2/..

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Jorryt Matthee @jorryt.bsky.social · 19/05/2025

We found the most distant confirmed galaxy (some Sergej Boebka vibes 😅) arxiv.org/abs/2505.11263

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Jorryt Matthee @jorryt.bsky.social · 09/12/2024

Last week we showed that the environments of typical faint Broad Halpha line emitters -- typically a few neighbours. This monster on the other hand sites in the largest over-density (on ~Mpc scales) in the entire field, supporting the massive galaxy *and* AGN interpretation

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Jorryt Matthee @jorryt.bsky.social · 09/12/2024

The high quality spectrum really enables detailed fitting of the stellar + AGN component of the galaxy, but higher resolution data would still help.

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Jorryt Matthee @jorryt.bsky.social · 09/12/2024

The ALT grism spectrum shows this very nice R~1600 Halpha spectrum with absorption.

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Jorryt Matthee @jorryt.bsky.social · 09/12/2024

These data speak for themselves, but note in particular the strong UV lines (including nitrogen), the Balmer break and the dominant & broad Balmer lines

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Jorryt Matthee @jorryt.bsky.social · 09/12/2024

More exciting measurements on the most luminous little red dot that I know of (F444W=22 at z=4.5!): an unambiguous AGN and a Balmer break in deep UNCOVER and ALT spectroscopy, led by Ivo Labbe arxiv.org/abs/2412.04557

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Jorryt Matthee @jorryt.bsky.social · 06/12/2024

Does this mean all BL Halpha emitters or Little Red Dots reside in such galaxies? No, very likely not. Our sample probes the low mass and luminosity and of the broad line population discovered so far, and we find evidence for a correlation between over-density and BH mass

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Jorryt Matthee @jorryt.bsky.social · 06/12/2024

Typical simulations of galaxy formation include the growth of SMBHs to reproduce realistic galaxies, with models mainly tuned for the present-day Universe. However, they are not able to reproduce such SMBH growth in such low-mass galaxies early on - unless they switch of feedback

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Jorryt Matthee @jorryt.bsky.social · 06/12/2024

This result is in line with other recent measurements with totally different techniques. It seems to suggest that this (luminosity-limited) sample consists of galaxies who have been able to very efficiently form and grow their supermassive black hole

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Jorryt Matthee @jorryt.bsky.social · 06/12/2024

Measuring the over-densities around a new sample of six faint Broad-Line selected AGNs (appearing as Little Red Dots in the NIRCam image), whose broad lines naively imply SMBH masses of ~6x10^6 Msun , we derive a stellar mass ~5x10^7 Msun, so the BH is ~10% the stellar mass

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Jorryt Matthee @jorryt.bsky.social · 06/12/2024

In the ALT data, we use a sample of 300 spectroscopically identified galaxies at z~4-5 to empirically measure a correlation between galaxy stellar mass and large (Mpc)-scale over-density

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Jorryt Matthee @jorryt.bsky.social · 06/12/2024

Yesterday was paper day! With deep JWST data from the ALT survey we provide new independent evidence that the new population of faint AGNs in the early Universe seems to have so-called overly massive black holes compared to their stellar mass arxiv.org/abs/2412.02846

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Jorryt Matthee @jorryt.bsky.social · 04/09/2023

My research group - supported by an ERC StG - will focus on understanding the formation and impact of the first stars, galaxies and supermassive black holes in the early Universe using observational data.

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Jorryt Matthee @jorryt.bsky.social · 04/09/2023

Hello Blue Sky! Very happy and grateful to be starting a research group in extragalactic astronomy and contribute to the development of astronomy at ISTA (ista.ac.at) as of this september!

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