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Feb
4
Thu
Cake talk by Takahiro Morishita
Feb 4 @ 16:00 – 16:30
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.

Feb
11
Thu
Cake talk by Sam Cutler (University of Massachusetts Amherst)
Feb 11 @ 15:00 – 15:30

Title

Diagnosing DASH: A Morphological Catalog for the COSMOS-DASH Survey

Abstract

COSMOS-DASH is a 0.5 square degree survey of the COSMOS field, obtained utilizing the novel “Drift And SHift” (DASH) observing technique for HST-WFC3 imaging. While DASH observations are significantly more efficient than standard HST imaging, they also are shallower and have an unusual data reduction, both of which may impact morphology measurements for fainter galaxies. In this talk I will present the F160W morphological catalog for for 51,534 galaxies in the COSMOS-DASH survey. Using morphological measurements from GALFIT, we recover consistent results with those from the deeper 3D-HST morphological catalogs out to z=2 and logM~10. I will also discuss the parameter space where morphological fits of DASH galaxies are robustly recovered. At logM<10.5, we find a flattening of the quiescent size-mass relation, implying the sizes of low mass quiescent galaxies are more similar to star-forming galaxies with a similar redshift and mass. Trends with axis-ratio and environment also suggest that low mass galaxies that quench in low density environments may retain morphologies comparable to similar mass star-forming galaxies.
Feb
25
Thu
Cake talk by Vasily Kokorev (DAWN)
Feb 25 @ 14:00 – 14:30

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.

Mar
4
Thu
Cake talk by Hannah Stacey (MPA Garching)
Mar 4 @ 14:00 – 14:30

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.

Mar
11
Thu
Cake talk by Jorryt Matthee (ETH Zürich)
Mar 11 @ 14:00 – 14:30
Cake talk by Jorryt Matthee (ETH Zürich)

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.

Mar
18
Thu
Cake talk by Tony Mroczkowski (ESO)
Mar 18 @ 14:00 – 14:30
Cake talk by Tony Mroczkowski (ESO)

Towards an Atacama Large Aperture Submillimeter Array (AtLAST)

Astrophysical observations at (sub-)mm wavelengths (λ from ~300 μm to ~3mm) allow us to study the cold, dense molecular gas pervading the Universe, hence probing the formation of stars and planets, and the interstellar and circumgalactic medium within galaxies across cosmic time.  At the same time, these wavelengths access the warm and hot inter- and intra-cluster gas via the SZ effect.
The current generation of 10-meter-class single dish telescopes has delivered some of the first surveys at (sub-)mm wavelengths, complementing and allowing us to go far beyond the previously optical-biased view of the Universe.  At the same time their limited fields of view, low spatial resolutions, high confusion limits, and low sensitivities mean that (sub)mm studies are only just scratching the surface. These limitations cannot be fully mitigated by interferometers, which are intrinsically affected by a low mapping speed and by the loss of diffuse, large scale (> 1 arcminute) extended signals.
It is now clear that without a transformative change in the capabilities of single-dish facilities by 2030, interferometers (like the ALMA observatory) will also become source-starved. The Atacama Large Aperture Submillimeter Telescope (AtLAST) (Klaassen+ 2020) project aims to address this, and is a concept for a 50-meter diameter single dish observatory to be built near the ALMA site. With its extremely large field of view (the goal is ~ 2 degrees), high spatial resolution (up to ~1.5” at 350 μm), and high sensitivity to both point sources and large-scale structures, AtLAST will be transformational for all fields of Astronomy in the 2030s and beyond. Here we will describe the EU Horizon2020 project, which commenced earlier this month, to deliver a comprehensive design study for such a next-generation single-single dish facility.

Tony Mroczkowski’s profile

Mar
25
Thu
IAP seminar by John Weaver @ Zoom link by mail
Mar 25 @ 11:30 – 12:30

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.

 

Cake talk by Charles Steinhardt @ Zoom link by mail
Mar 25 @ 14:00 – 14:30

Is the Stellar Initial Mass Function Universal?

Abstract

No

Apr
8
Thu
Cake talk by Fabio Vito (Scuola Normale Superiore di Pisa)
Apr 8 @ 14:00 – 14:30

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.

Apr
15
Thu
Cake talk by Sirio Belli (Harvard CfA)
Apr 15 @ 16:00 – 16:30
Cake talk by Sirio Belli (Harvard CfA)

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.