The next Student Seminar on Monday, July 06, in the seminar room 0.02 of the MPIfR will feature the following talks, in this order:

1. Sylvia Adscheid: "A star is born: the CIB as a window into star formation"

In order to understand the formation of stars across cosmic time, it is crucial to study the environments from which they originate. The interstellar medium of highly star-forming galaxies is particularly interesting in this endeavour, as these galaxies evidently offer ideal conditions for the formation of great quantities of stars in comparatively short times. Representative samples of such highly star-forming galaxies are required to allow a systematic and unbiased view of this population and their modes of star formation. One way to do this is through the cosmic infrared background (CIB), which is the integrated stellar and dust emission from earlier cosmic times, and which serves as a beacon for highly star-forming galaxies. The elusive far-infrared (FIR) part of the CIB deserves particular attention, as it reveals the dust-obscured part of star-formation activity, which is not visible in rest-frame UV-to-optical wavelengths. In this talk, I will present the results from our work on a large sample of 260 ALMA-detected galaxies from the A3COSMOS project. These constitute a representative galaxy sample, used to infer (sub)mm number counts, making up between ∼4 and ∼40% of the CIB in four different ALMA bands. With this sample, we are able to dissect part of the FIR/(sub)mm CIB into individual sources and characterise its origin, also making use of near-infrared (NIR) imaging from the JWST COSMOS-Web and JADES programmes, and SED-fitting using CIGALE. We find that the morphologies of most galaxies in our sample appear irregular in rest-frame UV and optical wavelengths, and disk-like in the rest-frame NIR, indicating that these are predominantly highly dust-obscured, normal star-forming galaxies, as opposed to merger-driven starburst galaxies. Our galaxies are located at high redshift (median z ∼ 2.5) and have high stellar masses, sitting in massive haloes, requiring fast and efficient stellar build-up at early cosmic times to explain their existence. Our findings reveal that a large part of the stars in the early Universe are born in dust-obscured regions of massive star-forming galaxies, which show hints at a potentially increased cosmic star-formation efficiency at early cosmic times, close to theoretical expectations for the conversion of baryons into stars.


2. Andrea Guerrero: "CIB modeling to constrain the faint-end slope of galaxy number counts"

The Cosmic Infrared Background (CIB) encodes the integrated infrared emission of star-forming galaxies across cosmic history. Decomposing this background into individual source contributions through differential number counts dN/dS is therefore directly linked to understanding galaxy evolution. While current observations resolve the bright end of the number counts, the faint-end slope (e.g. fluxes below ~2 mJy at 350µm) remains poorly constrained.
The FYST/CCAT telescope, currently under construction, will map the FIR/submm sky to sensitivities three times deeper than Herschel, opening a new window onto faint source populations at large angular scales. In preparation for these observations, we generate simulated point-source CIB maps for different dN/dS models and analyze their flux distributions. We further exploit gravitational lensing by galaxy clusters, using LENSTOOL to simulate lensed fields in which magnification shifts faint sources into higher flux bins, making faint-end slope variations more distinguishable. We present our simulated CIB maps and lensed flux distributions, with the aim of parametrizing these to identify optimal fields for constraining the faint-end slope with future FYST observations.

3. Ankur Dev: "Atmospheric noise mitigation for line-intensity mapping with CCAT"

The Epoch of Reionization Spectrometer (EoR-Spec) on the Fred Young Submillimeter Telescope (FYST/ CCAT) will perform line-intensity mapping (LIM) of redshifted [C II] emission to probe the high-redshift Universe. Atmospheric 1/f noise in the sub-millimeter wavelengths and data-reduction filtering can significantly affect the recovery of the LIM power spectrum. We present realistic end-to-end simulations of EoR-Spec observations, including astrophysical sky emission, atmospheric fluctuations, instrumental effects, and the observing strategy, together with a filter-and-bin map-making pipeline. We show that the pipeline effectively suppresses atmospheric noise and enables recovery of the small-scale power spectrum, while the filtering attenuates the largest spatial modes. These results provide an important validation of the EoR-Spec analysis pipeline and quantify the impact of atmospheric mitigation on future CCAT Deep Spectroscopic Survey observations.

4. Prachi Prajapati: "Vz-GAL: Revisiting the CO--H2 Conversion Factor Tension"

The CO-H2 conversion factor (αCO) remains one of the largest sources of uncertainty in determining molecular gas masses of high-redshift dusty star-forming galaxies (DSFGs). Scaling up the inferences from local ULIRGs to DSFGs, dynamical studies have often favored values lower than the canonical Galactic calibration; however, the origin of αCO tension in early DSFGs remains less understood. In this talk, I will present a revisit to the long-standing αCO discrepancy using the largest homogeneous sample of unlensed Vz-GAL DSFGs at z=1-4 with integrated CO(1-0) measurements and resolved ALMA 1 mm continuum observations. I will discuss two independent approaches for estimating molecular gas masses: the dust SED-based method and TUNER LVG modeling. The resulting gas masses will be compared with dynamical constraints derived from both the isotropic virial mass estimator and a mixed dynamical mass estimator that assumes DSFGs as rotating, pressure-supported thick disks. Finally, I will discuss whether the inferred molecular gas masses are consistent with the available dynamical upper limits across the sample, highlighting the archetype DSFG GN20 (z=4.055) as a case study.