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A virtual seminar on COSMOS2020
This week the speaker at the IAP seminar will be our very own John Weaver, who is going to present the COSMOS2020 catalog and (ongoing) scientific projects related to it.
Is the Stellar Initial Mass Function Universal?
The furthest QSOs in the X-rays
In the last 20 years, more than 200 accreting supermassive black holes (SMBHs), shining as quasi-stellar objects (QSOs), have been discovered at z>6, i.e., only <1 Gyr after the Big Bang. The very existence of these objects is a currently unsolved challenge to our theoretical knowledge of SMBH formation. X-ray observations provide a direct view into the very inner regions of the accretion disk/hot corona system, allowing us to study the SMBH accretion physics and possible evolution in the early universe. I will present the main results of recent X-ray observations of the first statistically significant samples of z>6 QSOs, focusing on the observables that we use to study the physics of SMBH accretion (e.g., the relations between Lx and LUV) and their possible evolution in the first Gyr of the universe. I will also present new follow-up observations of two high-redshift QSOs that showed noticeable properties. The first QSO, PSO167 at z=6.5, shows evidence of extremely weak X-ray emission, due to either uncommon accretion physics or heavy obscuration. The second QSO, J1641 at z=6.05, has been found to be an extremely variable (by a factor of >7) X-ray source on timescale of a few months in the rest frame.
Peculiar objects like these might provide unique information on the physics behind the fast growth of high-redshift SMBHs.
Molecular gas in high-redshift quiescent galaxies
Cold molecular gas represents the fuel for star formation and plays a key role in galaxy quenching. However, it is observationally challenging to detect CO emission in gas-poor quiescent galaxies, particularly at high redshift. Using deep observations with the NOEMA interferometer, we have detected CO emission in three galaxies that are undergoing quenching at z~1. Additionally, we characterized their stellar populations by fitting models to the combined optical spectroscopy and multi-band photometry.
By comparing the properties of the cold gas to those of the stars, we can place new constraints on the physical processes that drive galaxy quenching.
PASSAGES: A Multi-J CO and [CI] line study of single dish observations of the lensed Planck selected starbursts at cosmic noon
ALMA Lensing Cluster Survey: A Sub-kpc View of [CII] emission from a Sub-L* Galaxy in the epoch of reionization
Half of all cosmic starlight is absorbed and reprocessed by dust, which means that the widely-accepted cosmic history generated by visible-light telescopes is incomplete. The consequences of our biases are apparent in our most modern cosmological simulations, which struggle to produce sufficient populations of massive galaxies (M > 3 x 10^10 Msun) to match observations of the first 2 Gyr of the cosmos. These giants likely underwent rapid, violent, and bursty phases of star formation in order to reach such extreme masses, so early on. Such rapid stellar growth produces an overabundance of dust that obscures starlight, rendering the galaxies near-invisible at UV/optical wavelengths. In this work, I compile empirical data on massive, dusty, star-forming galaxies to create a numerical model that re-derives the primary function describing stellar mass assembly in the Universe: the stellar mass function (SMF). With my model, I extend the massive end of the SMF and create more massive star-forming galaxies throughout cosmic time. I forward evolve the model and show that, to first order, we can also successfully model the rapid build up of the massive quiescent galaxy population at z > 1 — aka the fated descendants of dusty, star-forming galaxies. I detail the impact of this model on our understanding of massive galaxy assembly, and briefly review our next steps towards predicting and characterizing the evolutionary properties of these massive, dust-obscured galaxies using next-generation telescopes.