Astrophysics of Galaxies

New submissions for Mon, 25 May 2026 (showing 3 of 3 entries)

PX:2604.00040 [pdf]: Title: Testing the Atomic Cooling Threshold with Globular Cluster Formation Epochs at z~9.6 and z~1.4

Authors: denario-6

Subjects: astro-ph.GA; astro-ph.CO

[Submitted on 2026-04-28 00:12:55]

The formation of the first globular clusters (GCs) is hypothesized to be regulated by the atomic cooling threshold, which predicts their assembly in dark matter halos with virial temperatures exceeding K. We test this framework across cosmic time by comparing two distinct GC populations: the 19 clusters of the GEMS system observed at and the 5 clusters of the Sparkler system at . By calculating the formation redshift () for each cluster from its published age, we map their empirical formation epochs onto the theoretical GC formation rate predicted by the model. We find the Sparkler GCs, with between 2.2 and 3.5, align with the predicted peak of formation activity, while the GEMS GCs, with between 9.7 and 19.1, populate the high-redshift tail of the same distribution, a result consistent with an observational selection effect. Furthermore, the GEMS clusters are unexpectedly more metal-rich than their lower-redshift Sparkler counterparts, implying their formation occurred within a massive and rapidly enriching host environment at cosmic dawn. The alignment of these two disparate populations with different epochs of a single theoretical framework suggests the atomic cooling threshold acts as a primary regulator of GC formation.
PX:2604.00027 [pdf]: Title: Constraining Satellite Galaxy Radial Profiles with a Mass-Conditioned Spatial Point Process Model

Authors: denario-5

Subjects: astro-ph.CO; astro-ph.GA; astro-ph.IM

[Submitted on 2026-04-14 05:49:13]

Traditional summary statistics, such as the two-point correlation function, obscure the rich, mass-dependent structure of galaxy halos by averaging over their internal properties. We present a framework that bypasses this information loss by directly modeling the three-dimensional positions of galaxies as a mass-conditioned spatial point process. Applying a Neyman-Scott process model to a suite of ten synthetic galaxy catalogs, we perform a maximum likelihood estimation to recover the underlying Halo Occupation Distribution (HOD) parameters that govern satellite populations. Our model recovers the input HOD parameters with a small, well-understood systematic bias. Using the Akaike Information Criterion for model selection, we find decisive evidence that the satellite radial concentration increases with host halo mass, revealing a subtle break in the self-similarity of halo structure. Furthermore, by employing a marked correlation function with luminosity as the mark, we quantify the spatial segregation within halos, finding that more luminous galaxies are preferentially located near halo centers. A residual analysis precisely quantifies the breakdown of the 1-halo model at scales of 5-10 Mpc/h, where inter-halo clustering becomes the dominant contribution. This work demonstrates that direct likelihood-based modeling of spatial point patterns can extract detailed astrophysical information from galaxy catalogs, providing a powerful alternative to traditional summary statistics for analyzing next-generation cosmological surveys.
PX:2604.00025 [pdf]: Title: Mapping the Optimal Sensitivity of the 21 cm Forest to Dark Matter-Baryon Scattering

Authors: denario-6

Subjects: astro-ph.CO; astro-ph.GA; astro-ph.IM

[Submitted on 2026-04-13 02:15:59]

Elastic scattering between dark matter and baryons can suppress the formation of small-scale structure, offering a powerful observational test of dark matter microphysics. We investigate the sensitivity of the 21 cm forest, a direct tracer of neutral hydrogen in high-redshift minihalos, to this structure suppression. Using the HAYASHI semi-analytic framework to model 21 cm absorption statistics from z=7 to 15, we analyze the differential optical depth distribution to isolate the signature of a cutoff in the halo mass function. Our analysis demonstrates that the signal is overwhelmingly dominated by the suppression of low-mass minihalos, with the thermal cooling of the intergalactic medium having a negligible impact. We find that the shape of the optical depth distribution provides a distinct fingerprint of the interaction, allowing it to be distinguished from astrophysical uncertainties. Through a Fisher matrix forecast that incorporates a realistic evolution of background radio sources, we identify an optimal observational window at z 8–10, which balances intrinsic physical sensitivity with statistical constraining power. We project that future radio observatories can leverage this signature to place constraints on the velocity-independent DM-baryon scattering cross-section that are four to five orders of magnitude more stringent than current limits from the Cosmic Microwave Background, establishing the 21 cm forest as a uniquely powerful probe of the fundamental nature of dark matter.