Cosmology

Abstract:

The Cosmic Infrared Background (CIB) traces the emission of star-forming galaxies throughout all cosmic epochs. Breaking down the contribution from galaxies at different redshifts to the observed CIB maps would allow us to probe the history of star formation. In this paper, we cross-correlate maps of the CIB with galaxy samples covering the range 푧 . 2 to measure the bias-weighted star-formation rate (SFR) density h푏휌SFRi as a function of time in a model independent way. This quantity is complementary to direct measurements of the SFR density 휌SFR, giving a higher weight to more massive haloes, and thus provides additional information to constrain the physical properties of star formation. Using cross-correlations of the CIB with galaxies from the DESI Legacy Survey and the extended Baryon Oscillation Spectroscopic Survey, we obtain high signal-to-noise ratio measurements of h푏휌SFRi, which we then use to place constraints on halo-based models of the star-formation history. We fit halo-based SFR models to our data and compare the recovered 휌SFR with direct measurements of this quantity. We find a qualitatively good agreement between both independent datasets, although the details depend on the specific halo model assumed. This constitutes a useful robustness test for the physical interpretation of the CIB, and reinforces the role of CIB maps as valuable astrophysical probes of the large-scale structure. We report our measurements of h푏휌SFRi as well as a thorough account of their statistical uncertainties, which can be used to constrain star-formation models in combination with other data.

Abstract:

Residuals between measured galactic radii and those predicted by the Fundamental Plane (FP) are possible tracers of weak lensing magnification. However, observations have shown these to be systematically correlated with the large-scale structure. We use the Horizon-AGN hydrodynamical cosmological simulation to analyse these intrinsic size correlations (ISCs) for both elliptical (early-type) and spiral (late-type) galaxies at z = 0.06. We fit separate FPs to each sample, finding similarly distributed radius residuals, λ, in each case. We find persistent λλ correlations over three-dimensional separations 0.5–17h⁻¹ Mpc in the case of spiral galaxies, at >3σ significance. When relaxing a mass-selection, applied for better agreement with galaxy clustering constraints, the spiral λλ detection strengthens to 9σ; we detect a 5σ density-λ correlation; and we observe intrinsically-large spirals to cluster more strongly than small spirals over scales ≲10h⁻¹ Mpc at >5σ significance. Conversely, and in agreement with the literature, we observe lower-mass, intrinsically-small ellipticals to cluster more strongly than their large counterparts over scales 0.5–17h⁻¹ Mpc at >5σ significance. We model λλ correlations using a phenomenological non-linear size model, and predict the level of contamination for cosmic convergence analyses. We find the systematic contribution to be of similar order to, or dominant over the cosmological signal. We make a mock measurement of an intrinsic, systematic contribution to the projected surface mass density Σ(r), and find statistically significant low-amplitude, positive (negative) contributions from lower-mass spirals (ellipticals), which may be of concern for large-scale (⁠≳7h⁻¹ Mpc) measurements.

Abstract:

Cluster galaxies exhibit substantially lower star formation rates than field galaxies today, but it is conceivable that clusters were sites of more active star formation in the early universe. Herein, we present an interpretation of the star formation history (SFH) of group/cluster galaxies based on the large-scale cosmological hydrodynamic simulation, Horizon-AGN. We find that massive galaxies in general have small values of e-folding timescales of star formation decay (i.e., "mass quenching") regardless of their environment, while low-mass galaxies exhibit prominent environmental dependence. In massive host halos (i.e., clusters), the e-folding timescales of low-mass galaxies are further decreased if they reside in such halos for a longer period of time. This "environmental quenching" trend is consistent with the theoretical expectation from ram pressure stripping. Furthermore, we define a "transition epoch" as where cluster galaxies become less star-forming than field galaxies. The transition epoch of group/cluster galaxies varies according to their stellar and host-cluster halo masses. Low-mass galaxies in massive clusters show the earliest transition epoch of ∼7.6 Gyr ago in lookback time. However, this decreases to ∼5.2 Gyr for massive galaxies in low-mass clusters. Based on our findings, we can describe a cluster galaxy's SFH with regard to the cluster halo-to-stellar mass ratio.