About

I am a postdoctoral researcher at the Astronomisches Recheninstitut (ARI) in Heidelberg working with Dr. Dominika Wylezalek in the DFG-funded GALENA group. I obtained my PhD in astrophysics from the University of Bath in 2020, and completed my Master's degree at ETH Zurich.

My research interests lie in the broad field of AGN and galaxy evolution.
In particular, how is the star formation in galaxies connected to:
I am a member of the MASCOT survey, the MaNGA-ARO Survey of CO Targets, an ongoing ESO Public Spectroscopic Survey conducted at the Arizona Radio Observatory (ARO). MASCOT is collecting CO-based molecular gas measurements for nearby galaxies with available optical-IFU data. The first data release is out - and here you can find the release paper!

I am also involved in the JWST Early Release Science program Q3D. Q3D is targeting 3 luminous quasars with powerful outflows at intermediate redshifts. Here you can find the press release accompanying our first results - presenting the complex environment of a z=3 quasar, and potentially one of the densest knots at that time!
Our team is also developing the q3dfit software package, a new public spectral analysis and PSF decomposition tool, for which I am one of the developers of the MIR pipeline.

My PhD thesis focused on dissecting galaxies into their different mass components (stellar populations, gas phases, dark matter), and weighing each of them.
Please find a list of publications, projects and talks under 'Research' and 'Talks' below.

Research

MASCOT: Molecular gas depletion times and metallicity gradients -- evidence for feedback in quenching active galaxies

Bertemes et al. (2023), MNRAS, 518, 5500

Left panel: Gas-phase metallicity gradients $\nabla Z$ plotted against the mean [O III] $W_{80} (< R_e)$ parameter (averaged over all spaxels out to $1 \ R_e$). We find a strong correlation between $\nabla Z$ and average [O iii] $W_{80}$ in Seyfert AGN (black datapoints) and LINERs/Composites (purple dots). We suggest that this relation emerges via weak chemically-enriched outflows. The targets plotted in grey are excluded from the fit due to exhibiting too many spaxels in which we deem the recovered $W_{80}$ values to be unreliable ($S/N < 10$, ‘DONOTUSE’ flag, or negative flux). Only targets with $>10$ % of reliable spaxels are included in the fit. The best linear fit is shown as a black solid line, while the red lines show fits recovered when perturbing the datapoints within their uncertainties. The r-value, p-value and coefficients of the best fit are further annotated in the top of the panel. Right panel: There is also a strong correlation between [O iii] $W_{80} (< R_e)$ and depletion times $t_\mathrm{dep}$, such that the AGN-like galaxies with the strongest [O iii] line broadening are the least efficient at forming stars out of the available molecular gas.

We present results from the first public data release of the MaNGA-ARO Survey of CO Targets (MASCOT), focussing our study on galaxies whose star-formation rates and stellar masses place them below the ridge of the star-forming Main Sequence. In optically-selected type 2 AGN/LINERs/Composites, we find an empirical relation between gas-phase metallicity gradients $\nabla Z$ and global molecular gas depletion times $t_\mathrm{dep} = M_\mathrm{H_2}/{\rm SFR}$ with ``more quenched'' systems showing flatter/positive gradients. Our results are based on the O3N2 metallicity diagnostic {(applied to star-forming regions within a given galaxy)} which was recently suggested to also be robust against emission by diffuse ionised gas (DIG) and low-ionisation nuclear emission regions (LINERs). We conduct a systematic investigation into possible drivers of the observed $\nabla Z - t_\mathrm{dep}$ relation (ouflows, gas accretion, in-situ star formation, mergers, and morphology). We find a strong relation between $\nabla Z$ or $t_\mathrm{dep}$ and centralised outflow strength traced by the [OIII] velocity broadening. We also find signatures of suppressed star-formation in the outskirts in AGN-like galaxies with long depletion times and an enhancement of metals in the outer regions. We find no evidence of inflows impacting the metallicity gradients, and none of our results are found to be significantly affected by merger activity or morphology. We thus conclude that the observed $\nabla Z - t_\mathrm{dep}$ relation may stem from a combination of metal redistribution via weak feedback, and a connection to in-situ star formation via a resolved mass-metallicity-SFR relation.

Cross-calibration of CO- versus dust-based gas masses and assessment of the dynamical mass budget in Herschel-SDSS Stripe82 galaxies

Bertemes et al. (2018), MNRAS, 478, 1442

We present a cross-calibration of CO- and dust-based molecular gas masses at $z \leqslant 0.2$. Our results are based on an IRAM survey collecting CO(1-0) measurements of 78 massive ($\log M_{*} > 10$) galaxies with known gas-phase metallicities, and with IR photometric coverage from WISE (22 $\mu{\rm m}$ ) and Herschel SPIRE ($250$, $350$, $500$ $\mu{\rm m}$).
We find a tight relation ($\sim 0.17$ dex scatter) between the gas masses inferred from CO and dust continuum emission, with a minor systematic offset of $0.05$ dex. The two methods can be brought into agreement by applying a metallicity-dependent adjustment factor ($\sim 0.13$ dex scatter). We illustrate that the observed offset is consistent with a scenario in which dust traces not only molecular gas, but also part of the ${\rm H}\,{\rm \small I}$ reservoir, residing in the ${\rm H_2}$-dominated region of the galaxy. Observations of the CO(2-1) to CO(1-0) line ratio for two thirds of the sample indicate a narrow range in excitation properties, with a median ratio of luminosities $ \left\langle R_{21} \right\rangle \sim 0.64 $. Finally, we find dynamical mass constraints from spectral line profile fitting to agree well with the anticipated mass budget enclosed within an effective radius, once all mass components (stars, gas and dark matter) are accounted for.

Comparison between dust-based gas masses and CO-based gas masses. Cold gas masses from the two methods correlate strongly, albeit with a modest offset towards higher values for the dust-based inference. The 1-to-1 line (black solid) and the median offset (black dashed) are shown for reference.

Testing the Completeness of the SDSS Colour Selection for Ultramassive, Slowly Spinning Black Holes

Bertemes et al. (2016), MNRAS, 463, 4041

Percentage of observable sources (i.e., within the flux limits) that are selected as possible quasar candidates in each bin of $\left(M_{BH},a_{\star}\right)$. Hatched bins indicate that all of the objects lie outside SDSS's flux limits. We stress that the number of observable objects varies between adjacent bins, even if they result in identical percentages of colour-selected objects.

We investigate the sensitivity of the colour-based quasar selection algorithm of the Sloan Digital Sky Survey to several key physical parameters of supermassive black holes (SMBHs), focusing on BH spin ($a_{\star}$) at the high BH-mass regime $M_{BH} \geq 10^{9} M_{\odot}$). We use a large grid of model spectral energy distributions, assuming geometrically-thin, optically-thick accretion discs, and spanning a wide range of five physical parameters: BH mass $M_{BH}$, BH spin $a_{\star}$, Eddington ratio $ L/L_{Edd}$, redshift $z$, and inclination angle $inc$.

Based on the expected fluxes in the SDSS imaging ugriz bands, we find that $\sim 99.8$ % of our models with $M_{BH} \leq 10^{9.5} M_{\odot}$ are selected as quasar candidates and thus would have been targeted for spectroscopic follow-up. However, in the extremely high-mass regime, $\geq 10^{10} M_{\odot}$, we identify a bias against slowly/retrograde spinning SMBHs. The fraction of SEDs that would have been selected as quasar candidates drops below $\sim 50$ % for $a_{\star} < 0$ across $0.5 < z < 2$. For particularly massive BHs, with $M_{BH} \sim 3 \cdot 10^{10} M_{\odot}$, this rate drops below $\sim 20$ %, and can be yet lower for specific redshifts. We further find that the chances of identifying any hypothetical sources with $M_{BH} = 10^{11} M_{\odot}$ by colour selection would be extremely low at the level of $\sim 3$ \%.

Our findings, along with several recent theoretical arguments and empirical findings, demonstrate that the current understanding of the SMBH population at the high-MBH, and particularly the low- or retrograde-spinning regime, is highly incomplete.

Talks & workshops (Selection)

I’m always happy to travel around and talk more!
If you’re interested in what I’m doing, please feel free to message me.
For a more complete list of talks, please see my CV below.

Outreach (Selection)

Aside from doing research, I enjoy engaging in outreach. Please find a selection of outreach activities here - for a more complete summary, please refer to my CV.

Current Outreach

At Heidelberg University, I am participating in the annual Girls' Day, where I co-organise the online workshop "Schwarze Löcher im Universum" open to 5th & 6th grade girls in Germany. Together with Dr Dominika Wylezalek, we craft a model of an actively accreting supermassive black hole while learning more about these fascinating objects in our Universe.

Past Outreach

During my time in Bath (2016-2019 roughly), I have been part of one of the University of Bath's outreach teams, led by Dr Ventsislav Valev. The main focus lies on organising science workshops for primary school children on light to help to inspire the next generation of scientists! The team gratefully acknowledges funding from the Royal Society and the STFC, as well as support on equipment by Thorlabs and Zeiss.

CV

For an up-to-date CV, please feel free to contact me.

I will also periodically upload updated versions here: View/download CV

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