Sofia Rojas Ruiz

Sofia Rojas Ruiz   (Colombia)

rojas @

Quasars and Galaxies at the Epoch of Reionization

Quasars are highly energetic sources that provide important tools to understand the Epoch of Reionization, which is the time when the
universe transitioned from being completely neutral to ionized. Observational searches demonstrate that quasars in the early universe are
rare, however, it is not yet well-understood how these objects can form so early-on. I am investigating the quasar P352-15, one of the
most radio-loud quasar already near the end of Reionization at redshift z=5.83, which corresponds to approximately 950 million years after
the Big Bang. This is the only quasar at such high redshifts presenting evidence of extended radio jets at z~6, which makes it an ideal
laboratory to measure different quasar properties in the early universe. I have analysed radio and sub-mm data of this source to help
characterize the quasar’s radio emission and the cold dust properties of its host galaxy. The results suggest a break in the radio
synchrotron emission of the quasar and to confirm this, I have PI a VLA proposal to do multifrequency observations of P352-15 in all
available bands of this observatory to constrain the frequency of the break and from there find the age of the jet. Additionally, I have
VLT X-Shooter visible and near-infrared spectral data that will be used to calculate the black hole accretion timescale of P352-15, or its
quasar lifetime. Combining all these data sets we can study for the first time the coevolution of the host galaxy, black hole accretion
and jet launch of a source at such high redshift.

Another project I am working on is to probe whether the most distant quasars live in special environments. Quasars are believed to reside
in the most massive dark matter halos and therefore they are expected to live in overdensities probing proto-cluster structure, which is
still observationally controversial. I am looking for Lyman-break galaxies in the nearby proximity of one of the most distant quasars,
J1342+0928 at z=7.54. We have data from the Hubble Space Telescope in three filters covering continuous wavelength from optical to NIR. I
am using the photometric redshift technique to find galaxy candidates and this way confirm one of the first large-scale structures of the

Lastly, I have Co-PI a JWST project using NIRSpec IFU to confirm a subset of 11 galaxy candidates at z~9 selected from the Hubble Space
Telescope. We will confirm a catalog of galaxies deep in the Epoch of Reionization and will characterise their ionizing potential.

Supervisor:    Frederick Davies, Eduardo Banados   (MPIA)

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