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<!DOCTYPE HTML>
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<title>Research - Jan-Torge Schindler, PhD</title>
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<!-- <h1><a href="index.html">Jan-Torge Schindler</a></h1> -->
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<li><a href="index.html">Home</a></li>
<li><a href="aboutme.html">About Me</a></li>
<li><a href="research.html">Research</a></li>
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<p style="margin: 0 0 0 0"> The formation and evolution of </p>
<h2 style="margin: 0 0 0 0">Supermassive black holes in the early Universe</h2>
<p>as probes of cosmic structure formation. </p>
<!-- the central elements of galaxies and-->
</header>
<!-- General research nfo -->
<section class="wrapper style1 special">
<div class="inner align-left">
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<h2>Quasars and Supermassive Black Holes</h2>
</header>
<p> My main scientific interest lies in the to understand the emergence of galaxies in the early
Universe. I am particularly interested in the formation and evolution of supermassive black holes (SMBHS), which we can observe
during phases of active growth (mass accretion), when they shine as luminous quasars.
I study quasars in the first two billion years of the Universe to understand the processes by which SMBHs form, how they grow to their observed masses and how they influence the evolution of their host galaxies.
The first massive SMBHs are believed to reside in the most overdense regions of the Cosmic Web and observations of these environments allow us to test large-scale structure formation models.
Furthermore, quasars serve as bright beacons to study hydrogen reionization, the last major phase transition of the Universe, in absorption.
<!-- <br>-->
<!-- <br>-->
<!-- The upcoming Euclid mission and the Vera C. Rubin Observatory's Legacy Survey of Space and Time will re -->
</p>
<!-- <p> SMBHs are found in the centers of almost all massive galaxies.-->
<!-- During phases of active growth the infalling gas forms an accretion disk, which heats up and can outshine the stellar light from the host galaxy.-->
<!-- The objects are called active galactic nuclei (AGN) and the most luminous of them are historically refereed to as <b>quasars</b>.-->
<!-- <br>-->
<!-- <br>-->
<!-- Due to their extreme luminosities we can currently observe quasars at redshifts of up to 7.5, when the Universe was only 0.8 billion years old.-->
<!-- These high-redshift quasars are ideal probes of the formation of cosmic structures, the evolution of the intergalactic medium and the early growth of SMBHs.-->
<!-- <br>-->
<!-- <br>-->
<!-- Curiously, we measure black hole masses of up to 10<sup>10</sup> solar masses at these redshifts.-->
<!-- Assuming standard theories of SMBH formation and growth, it would take more than the age of the Universe at the time to grow these black holes to their observed masses.-->
<!-- How these SMBHs form and grow at the dawn of cosmic time constitutes one of the biggest puzzles in modern astrophysics.-->
<!-- </p>-->
</div>
</section>
<!-- Research projects -->
<section id="two" class="wrapper alt style2">
<section class="spotlight style1 orient-left">
<div class="image"><img src="images/Euclid_Perseus.png" alt=""/></div>
<div class="content">
<h2>The search for the most distant quasars</h2>
<p>
To understand the formation of supermassive black holes my group expands the quasar redshift
frontier using near-infrared, wide-area photometric surveys.
Applying careful completeness analyses we can statistically constrain the quasar number densities to understand the emergence of the first SMBHs.
<br>
<br>
The Euclid space mission, launched in 2023, and the Vera Rubin Observatory with its Legacy Survey of Space and Time, will provide the deepest optical and near-infrared surveys
of the extragalactic sky. These surveys will allow us to discover quasars up to redshifts of
~10 to truly understand their formation processes and early growth. My group works on
developing new quasar selection strategies tailored to these surveys to build the first census of the most distant quasars.
<br>
<br>
The image to the left shows <a href="https://www.esa.int/Science_Exploration/Space_Science/Euclid/Euclid_s_view_of_the_Perseus_cluster_of_galaxies" target="_blank" rel="noopener noreferrer">Euclid's view of the Perseus cluster</a>.
Many of the faint background galaxies were first unveiled by Euclid's novel observations.
<br>
</p>
<p>In past work I have designed and executed the <a href="https://ui.adsabs.harvard.edu/abs/2017ApJ...851...13S/abstract" target="_blank" rel="noopener noreferrer">Extremely Luminous Quasar Survey (ELQS)</a>
to <a href="https://ui.adsabs.harvard.edu/abs/2018ApJ...863..144S/abstract" target="_blank" rel="noopener noreferrer">discover the most luminous quasars at z=3-5 </a> for a more accurate measurement
of the <a href="https://ui.adsabs.harvard.edu/abs/2019ApJ...871..258S/abstract" target="_blank" rel="noopener noreferrer">z=3-5 bright-end quasar luminosity function</a>. This selection strategy applied random forest classification on panchromatic photometric data.
</p>
<p> I have also been an integral part of the <a href="https://ui.adsabs.harvard.edu/abs/2016ApJS..227...11B/abstract" >Pan-STARRS1 distant quasar survey</a> targeting quasars at z>6.
Following many observational campaigns in the last few years, we <a href="https://ui.adsabs.harvard.edu/abs/2022arXiv221204452B/abstract" target="_blank" rel="noopener noreferrer"> recently increased the discovery sample by
a 55 quasars</a>. Based on these number counts, I determined <a
href="https://ui.adsabs.harvard.edu/abs/2023ApJ...943...67S/abstract"
target="_blank" rel="noopener noreferrer">the most precise estimate of the z~6
quasar luminosity function</a> to date.</p>
</div>
</section>
<section class="spotlight style1 orient-right">
<div class="image"><img src="images/eso1327a.jpg" alt="" /></div>
<div class="content">
<h2>Characterization of supermassive black holes</h2>
<p>
Spectroscopic follow-up observations of quasars are not only essential to measure the mass of the SMBH and to understand the physics of the accretion process.
The spectra also allow us to investigate the chemical make-up of the accreted gas and provide insight into foreground galaxies as well as the state of the
intergalactic medium.
<br>
<br>
I have been leading one of the largest spectroscopic studies of high-redshift quasars, the <a href="https://ui.adsabs.harvard.edu/abs/2020ApJ...905...51S/abstract" target="_blank" rel="noopener noreferrer">
X-SHOOTER/ALMA Survey of Quasars in the Epoch of Reionization</a>.
Based on this sample of 38 reionization-era quasars, z>5.7, we concluded that quasars at these times are <a href="https://ui.adsabs.harvard.edu/abs/2022ApJ...941..106F/abstract" target="_blank" rel="noopener noreferrer">accreting more rapidly than their lower-redshift
cousins</a>. In addition, the spectra more commonly show large velocity shifts of high-ionization lines, indicative of vigorous (outflowing) gas motion
close to the accretion disk. Even 0.8 Gyr after the Big Bang the accreted gas is already chemically enriched, indicating a fast chemical evolution
at the centers of these early massive galaxies.
</p>
<p>I am also a member of the <a href="https://xqr30.inaf.it/" target="_blank" rel="noopener noreferrer">XQR-30 collaboration</a>,
which is centered on a large ESO/X-SHOOTER program to provide high signal-to-noise ratio spectra
of 30 quasars at z>5.7. This unprecedented data set has already led to some exciting results: in a study published in Nature, lead by Manuela Bischetti,
we show that <a href="https://ui.adsabs.harvard.edu/abs/2022Natur.605..244B/abstract" target="_blank" rel="noopener noreferrer"> fast outflowing dense gas is observed at a much higher incidence </a>
in the first 1 Gyr after Big Bang, possibly indicating more vigorous feedback
effects on the surrounding galactic gas. We furthermore use these spectra to understand the evolution and morphology of cosmic hydrogen reionization.
By measuring the <a href="https://ui.adsabs.harvard.edu/abs/2022MNRAS.514...55B/abstract" target="_blank" rel="noopener noreferrer">Lyman-α transmission </a>
<!-- and <a href="https://ui.adsabs.harvard.edu/abs/2021ApJ...923..223Z/abstract" >"dark gaps" in the Lyman-α forest</a>-->
we were able to conclude that the epoch of reionization extends to z~5.3,
later than originally thought.</p>
</div>
</section>
<section class="spotlight style1 orient-left">
<div class="image"><img src="images/jwst_artists_illustration.jpg" alt="" /></div>
<div class="content">
<h2>Probing the early Universe with the James Webb Space Telescope</h2>
<p>
The James Webb Space Telescope (JWST) opens up the near- and mid-infrared sky unhindered by the Earth's atmosphere.
It's unprecendent capabilities will revolutionize our understanding the population of less
luminous galaxies and lower mass supermassive black holes, which appear much fainter than quasars.
I am leading the data reduction and analysis of the JWST program
<a href="https://www.stsci.edu/jwst/science-execution/program-information.html?id=2073" target="_blank" rel="noopener noreferrer">
"Towards Tomographic Mapping of Reionization Epoch Quasar Light-Echoes with JWST" (PI: J. Hennawi) </a> to characterize the environments of two of the most distant quasars.
<br><br>
In the above program I discovered <a href="https://ui.adsabs.harvard.edu/abs/2024arXiv241111534S/abstract" target="_blank" rel="noopener noreferrer">a z~7.3 lower mass SMBH</a>, which belongs to the
puzzling
population of "Little Red Dots", an AGN population, whose properties have not been well understood so far.
With my JWST follow-up program <a
href="https://www.stsci.edu/jwst/science-execution/program-information.html?id=5734"
target="_blank" rel="noopener noreferrer">
"GO 5734" (PI: J. Schindler)
</a> I aim to understand the differences between these lower mass SMBHs and the more
luminous quasars in the context of cosmic structure formation.
<br><br>
My group is also heavily involved in the JWST program <a
href="https://www.stsci.edu/jwst/science-execution/program-information.html?id=5893"
target="_blank" rel="noopener noreferrer"> "GO 5734" (PI: K. Kakiichi) </a>, the
largest approved JWST program to date. Over an area of 0.33 deg<sup>2</sup>, this program
will provide the most comprehensive census of galaxies and active galactic nuclei at
z=7-9. The expected number densities will further allow us to place constraints on the
dark matter halo masses of these sources via clustering measurements.
<!-- I am involved as a Co-I in a range of other JWST programs on supermassive black holes and large scale structure, including:-->
<!-- <ul>-->
<!-- <li><a href="https://www.stsci.edu/jwst/science-execution/program-information.html?id=1764" target="_blank" rel="noopener noreferrer">-->
<!-- "A Comprehensive JWST View of the Most Distant Quasars Deep into the Epoch of Reionization" (PI: X. Fan) </a></li>-->
<!-- <li><a href="https://www.stsci.edu/jwst/science-execution/program-information.html?id=1554" target="_blank" rel="noopener noreferrer">-->
<!-- "Nebular Line Diagnostics in a Merger at Cosmic Dawn" (PI: R. Decarli) </a></li>-->
<!-- <li><a href="https://www.stsci.edu/jwst/science-execution/program-information.html?id=1967" target="_blank" rel="noopener noreferrer">-->
<!-- "A Complete Census of Supermassive Black Holes and Host Galaxies at z=6" (PI: M. Onoue) </a></li>-->
<!-- <li><a href="https://www.stsci.edu/jwst/science-execution/program-information.html?id=2078" target="_blank" rel="noopener noreferrer">-->
<!-- "A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE): A JWST Quasar Legacy Survey" (PI: F. Wang) </a></li>-->
<!-- </ul>-->
</p>
</div>
</section>
<section class="spotlight style1 orient-right">
<div class="image"><img src="images/artificial-intelligence-g1374cfcd7_1920.jpg" alt="" /></div>
<div class="content">
<h2>Machine learning in Astrophysics</h2>
<p>
My group applies machine learning techniques to search for rare high-redshift quasar candidates
in large astronomical datasets. For source classification and photometric redshift
estimation (regression problem), we currently employ random forests, eXtreme Gradient Boosting, and Bayesian
neural networks.
</p>
<p>
However, at high redshift, z>6, we run into the problem that there is not sufficient empirical
training data available for the rare luminous quasars we are interested in. Therefore, we are currently developing
a generative model based on a Variational Autoencoder that can produce synthetic quasar
spectra. Trained on a large sample of lower-redshift quasars, this model will allow us
to calculate synthetic photometry based on the spectra and reconstruct quasar spectra with
missing spectral coverage.
</p>
<p>
I am further interested to explore the vast data sets of the Euclid mission and the Vera C. Rubin
Observatory's Legacy Survey of Space and Time (LSST) to search for rare and exotic objects with
unsupervised machine learning methods.
</p>
</div>
</section>
<!-- <section class="spotlight style1 orient-right">-->
<!-- <div class="image"><img src="images/eso1327a.jpg" alt="" /></div>-->
<!-- <div class="content">-->
<!-- <h2>The Extremely Luminous Quasar Survey</h2>-->
<!-- <p>-->
<!-- Spectroscopic follow-up observations of quasars are essential to measure the mass of the SMBH and to understand the physics of the accretion process.-->
<!-- <br>-->
<!-- <br>-->
<!-- Over the past years, I have lead one of the largest spectroscopic studies of high-redshift quasars, the X-SHOOTER/ALMA Survey of Quasars in the Epoch of Reionization.-->
<!-- </p>-->
<!-- </div>-->
<!-- </section>-->
</section>
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