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Title
(G)old mining in high-redshift galaxies: Application of SED fitting in the era of JWST
Abstract
With recent progress in observational astronomy, we are now able to characterize spectral energy distributions (SEDs) of high-redshift galaxies well. Constraining galaxy SEDs is critically important, as they can be used to infer not only current properties but past evolutionary histories too. However, results from this technique need to be carefully assessed, as they may only represent a subset of the intrinsic distribution depending on e.g., data quality, underlying assumptions, and fitting methodology. With this in mind, in this seminar I will start by presenting our recent effort in inferring formation histories of massive galaxies at z~2 using deep grism datasets taken in multiple HST programs, aiming to understand galaxy mass assembly and quenching at high redshifts. I will then introduce our JWST ERS program, and discuss how we should utilize this new dataset to advance our understanding of galaxy evolution in the first billion years of the universe.
Title
Abstract
The Evolving Interstellar Medium of Star-Forming Galaxies
In this talk I would like to provide a status update regarding the current and upcoming projects of my PhD. This week we have passed a milestone by submitting our work where we analyse the far-infrared properties of ∼4,700 star-forming galaxies at z <4.5, drawn from the deepest, super-deblended catalogues in the GOODS-N and COSMOS fields. We develop a novel panchromatic SED fitting algorithm, STARDUST, that models the emission from stars, AGN, and infrared emission arising from dust heated by star formation without relying on energy balance assumptions. With our code we recover robust estimates of FIR properties of our objects, and through a set of simulations we quantify how the quality of our estimates is affected by the photometric coverage and uncertainty in photoz. In particular, we focus on the dust-to-stellar mass ratio, which we find to be increasing by a factor of 10 from z= 0 to z= 2, while remaining flat at higher−z, mirroring the evolution of the gas fraction. Finally, we construct the dust mass functions (DMF) of star-forming galaxies up to z=1 by the transforming the stellar mass function to DMF through the scaling relations, that we derive in our work. Reassuringly, we find that the evolution off dust-to-stellar mass ratio, and the recovered DMFs are in good agreement both with observational data, and the theoretical predictions of the Horizon-AGN and IllustrisTNG simulations.
100-pc resolution of z~2 quasar host galaxies with ALMA: witnessing the formation of compact spheroids
With the advent of ALMA, the interstellar medium of high-redshift galaxies can be probed at remarkable resolution and sensitivity. We push the limits of ALMA even further by studying strongly lensed galaxies where we are able to probe structures of 10s–100s parsecs in scale. Using novel lens modelling techniques, we reconstruct the molecular interstellar medium (ISM) structure and kinematics of z~2 galaxies hosting luminous quasars, to give a new perspective on the physical processes that drive the formation and evolution of quiescent galaxies, from birth to quiescence. A key aspect in this study is how spheroids formed very high stellar densities and grew concurrently with their supermassive black holes. We find evidence the quasar host galaxies are observed in a stage during a rapid transformation into compact spheroids, where a high density of dynamically unstable gas leads to efficient star formation and black hole accretion. Furthermore, I present first results of mapping the structure and kinematics across the CO ladder – the highest resolution of the molecular ISM for a quasar host at cosmic noon – which demonstrates a highly non-homogeneous ISM.
The X-SHOOTER Lyman-α survey at z = 2
The Lyman-α line has recently emerged as a powerful tool to measure the HI column density in and around galaxies. Its line profile has been suggested to be an excellent tracer of the escape fraction of ionising photons.
The Lyα equivalent width and escape fraction are used as a tracer of the neutral fraction of the Universe at the end stages of cosmic reionisation. However, empirically, the Lyα escape fraction and the line profile emerging from the ISM are poorly understood at high-redshift (z>3) due to the typical limited spectral resolution and the lack of rest-frame optical spectroscopy.
Currently, Lyα emitters (LAEs) at z~2 are the ideal “middle-redshift” analogs of the earliest galaxies. Their formation times are similarly short, they have specific SFRs and sizes comparable to galaxies at z>7 and similarly high equivalent widths in the rest-frame optical lines, which are still observable from the ground.
In my talk, I will present the first results of the spectroscopic component of our XLS-z2 survey which is based on ~100 hours of VLT/X-SHOOTER observations of 30 LAEs at z~2. I will present the average UV to optical SED of z~2 LAEs and present early results on the diversity in the (high resolution) Lyα line profiles. Finally I will discuss what these measurements in middle-redshift analogs imply for the production and escape fraction of ionising photons in typical galaxies in the epoch of reionisation.
Towards an Atacama Large Aperture Submillimeter Array (AtLAST)
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?
Abstract
No
The furthest QSOs in the X-rays
Abstract
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.
