About

I am a 3rd year PhD student working in the Astrophysics Research Group at the University of Bath, under the supervision of Dr. Stijn Wuyts and Prof. Carole Mundell. I did my Master's degree at ETH Zurich, Switzerland, under the supervision of Dr Benny Trakhtenbrot in Kevin Schawinski's Black Hole Research Group.

In the context of galaxy evolution, my research focuses on dissecting galaxies into their different mass components (stellar populations, gas phases, dark matter) using multi-wavelength data, and weighing each of them. This will allow us to establish a robust observational foundation on which a cohesive theory of galaxy evolution can be built that incorporates the interplay of different galactic elements within the surrounding ecosystem. I have also worked on the demographics of supermassive black holes (could some of them escape detection?).

In more detail, my work includes for example: Please find a list of recent publications, projects and talks under 'Research'.


Research

Galaxies

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

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.


Black Hole Physics

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

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.


Conference talks & seminars (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

Since November 2016, I have been part of one of the University of Bath's outreach teams, led by Dr Ventsislav Valev. Our main focus lies on organising science workshops for primary school children on light. Hopefully, we may help to inspire the next generation of scientists!

We gratefully acknowledge funding from the Royal Society and the STFC, as well as support on our equipment by Thorlabs and Zeiss.

Click here to visit our team's official webpage.


CV

View/download CV


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