Jorryt Matthee

We found the most distant confirmed galaxy
(some Sergej Boebka vibes 😅)

arxiv.org/abs/2505.11263

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

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

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

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

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

This work was done with the ALT project I have been co-leading with
@rpnaidu.bsky.social, with great contributions from my team members Gauri, Ivan, Claudia and (soon) Alberto at ISTA and collaborators abroad

What's next? First, tests of the BH mass measurements are highly warranted, for example by reobserving these AGNs again over various cadences in the next months/years. Second, we could solidify a BH - halo mass relation quantitatively with larger samples with uniform measurements

Our results are at odds with scenarios where the full broad Halpha line originates from gas dynamics in compact, pure stellar galaxies without AGN, though we do not rule out that this could be one of the processes that may make the BHs appear more massive

These trends indicate a BH to halo mass relation, which implies that more luminous AGNs (that typically have broader line-widths and higher masses) reside in higher mass galaxies, which will have different spectral energy distributions and large-scale environments

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

These results may also imply the SMBH masses are in fact overestimated as the calibrations may not be applicable, for example in case of super-Eddington growth. Interestingly, the AGN fraction among low mass galaxies we find is ~1%, consistent with such scenario

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

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

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

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

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

If you build nothing, who is going to build the thing after you've done the R&D? The engineers will have transferred their skills to companies with less noble causes.

But I guess it was not an astronomer? :-)

This is great, have a good start!

My institute ISTA in the nice Viennese forest in Austria now calls for PhD applications, deadline Jan 8 2024. Fully funded ~5 yr US style Grad School. Multiple positions in Astronomy are available. Please distribute and contact me for details!

phd.pages.ist.ac.at

If you think MUSE is already oversubscribed, imagine that there will only be one ELT (instead of 4 UTs), which will have various instruments to commission when others can already observe. 😬

ISTA is a rapidly growing research institute. Keep an eye out for, or contact me about, various job opportunities (incl. tenure track positions), in my group, but also through independent fellowships as the IST-Bridge fellowship. jobregister.aas.org/ad/e0507361

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.

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!