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A study was performed to investigate the experimental conditions and systematic uncertainties that need to be considered in order to precisely characterize quantum efficiency (QE). Measurements were performed on a HAWAII-2RG1.7 μm detector but the methodology of characterization is applicable to other detectors as well and may be useful in characterization of detectors used in future ground and space based surveys. For this study the detector QE as a function of illumination intensity, total integrated signal, and temperature was measured. A 3% relative systematic uncertainty on the measured QE value was achieved at wavelengths longer than 800 nm but the total uncertainty in the determination of absolute QE is dominated by the uncertainty in the conversion gain, which adds an additional 3.4% scale uncertainty. It was found that the measured detector QE depends on illumination intensity and that temperature dependence of QE can, at least in part, be attributed to reciprocity failure. Well-chosen detector bias voltages can reduce integrated signal nonlinearity.

Recent baryon acoustic oscillation (BAO) measurements by the Dark Energy Spectroscopic Instrument (DESI) provide evidence that dark energy (DE) evolves with time, as parameterized by a \\(w_0 w_a\\) equation of state. Cosmologically coupled black holes (BHs) provide a DE source that naturally evolves with time, because BH production tracks cosmic star-formation. Using DESI BAO measurements and priors informed by Big Bang Nucleosynthesis, we measure the fraction of baryonic density converted into BHs, assuming that all DE is sourced by BH production. We find that the best-fit DE density tracks each DESI best-fit \\(w_0w_a\\) model within \\(1\\), except at redshifts \\(z 0.2\\), highlighting limitations of the \\(w_0w_a\\) parameterization. Cosmologically coupled BHs produce \\(H_0 = (69.94 0.81)~km\\,s^-1\\,Mpc^-1\\), with the same \\(^2\\) as \\(\\)CDM, and with two fewer parameters than \\(w_0w_a\\). This value reduces tension with SH0ES to \\(2.7\\) and is in excellent agreement with recent measurements from the Chicago-Carnegie Hubble Program. Because cosmologically coupled BH production depletes the baryon density established by primordial nucleosynthesis, these BHs provide a physical explanation for the ``missing baryon problem'' and the anomalously low sum of neutrino masses preferred by DESI. The global evolution of DE is an orthogonal probe of cosmological coupling, complementing constraints on BH mass-growth from elliptical galaxies, stellar binaries, globular clusters, the LIGO-Virgo-KAGRA merging population, and X-ray binaries. A DE density that correlates with cosmic star-formation: 1) is a natural outcome of cosmological coupling in BH populations; 2) eases tension between early and late-time cosmological probes; and 3) produces time-evolution toward a late-time \\(\\)CDM cosmology different from Cosmic Microwave Background projections.

Nearly a half century after the discovery of the antiproton the study of cosmic-ray antimatter continues to be an exciting and fertile field. Sensitive searches for heavy cosmic-ray antimatter continue, although in recent years their value as a probe of universal baryon symmetry has all but evaporated. Antiprotons and positrons have opened new windows on the origin and history of cosmic rays. The rarity of antimatter as compared to ordinary cosmic-ray species has posed substantial experimental challenges. Early reports of significant enhancements of antiprotons and high-energy positrons fueled speculation that non-baryonic dark matter had been found. A new generation of balloon-borne magnetic spectrometers employing powerful particle identification techniques to eliminate background have finally managed to uncover the true antimatter signal. These new measurements support simple models of secondary production but also suggest the possibility of a small yet interesting primary component.

Black holes, dark energy, and the Higgs field are all currently established, exciting, and mysterious, each in its own way. Cosmological data show that dark energy may evolve with time. The electroweak phase transition during stellar collapse can provide a mechanism via the Higgs field for dark energy to be trapped inside black holes at the time of their formation. Using the Oppenheimer-Snyder model of collapse, we calculate the total matter and dark energy densities in a black hole, to be in the ratio of 2 to 1 at the start of collapse. The solution for the scale factor a(t) is a cycloid with a collapse time of 57 s. If black holes are cosmologically coupled and grow in mass as the universe expands, they can account for the evolution and quantity of the dark energy of the universe.

We present an efficient estimator for higher-order galaxy clustering using small groups of nearby galaxies, or multiplets. Using the Luminous Red Galaxy (LRG) sample from the Dark Energy Spectroscopic Instrument (DESI) Data Release 2, we identify galaxy multiplets as discrete objects and measure their cross-correlations with the general galaxy field. Our results show that the multiplets exhibit stronger clustering bias as they trace more massive dark matter halos than individual galaxies. When comparing the observed clustering statistics with the mock catalogs generated from the N-body simulation AbacusSummit, we find that the mocks underpredict multiplet clustering despite reproducing the galaxy two-point auto-correlation reasonably well. This discrepancy indicates that the standard Halo Occupation Distribution (HOD) model is insufficient to describe the properties of galaxy multiplets, revealing the greater constraining power of this higher-order statistic on galaxy-halo connection and the possibility that multiplets are specific to additional assembly bias. We demonstrate that incorporating secondary biases into the HOD model improves agreement with the observed multiplet statistics, specifically by allowing galaxies to preferentially occupy halos in denser environments. Our results highlight the potential of utilizing multiplet clustering, beyond traditional two-point correlation measurements, to break degeneracies in models describing the galaxy-dark matter connection.

In this paper, we study how absorption-line systems affect the spectra and redshifts of quasars (QSOs), using catalogs of Mg II absorbers from the early data release (EDR) and first data release (DR1) of the Dark Energy Spectroscopic Instrument (DESI). We determine the reddening effect of an absorption system by fitting an un-reddened template spectrum to a sample of 50,674 QSO spectra that contain Mg II absorbers. We find that reddening caused by intervening absorbers (voff > 3500 km/s) has an average color excess of E(B-V) = 0.04 magnitudes. We find that the E(B-V) tends to be greater for absorbers at low redshifts, or those having Mg II absorption lines with higher equivalent widths, but shows no clear trend with voff for intervening systems. However, the E(B-V) of associated absorbers, those at voff < 3500 km/s, shows a strong trend with voff , increasing rapidly with decreasing voff and peaking (approximately 0.15 magnitudes) around voff = 0 km/s. We demonstrate that Mg II absorbers impact redshift estimation for QSOs by investigating the distributions of voff for associated absorbers. We find that at z > 1.5 these distributions broaden and bifurcate in a nonphysical manner. In an effort to mitigate this effect, we mask pixels associated with the Mg II absorption lines and recalculate the QSO redshifts. We find that we can recover voff populations in better agreement with those for z < 1.5 absorbers and in doing so typically shift background QSO redshifts by delta_z approximately equal to plus or minus 0.005.

The gas density profile around galaxies, shaped by feedback and affecting the galaxy lensing signal, is imprinted on the cosmic microwave background (CMB) by the kinematic Sunyaev-Zel'dovich effect (kSZ). We precisely measure this effect (\\(S/N\\approx 10\\)) via velocity stacking with more than 800,000 spectroscopically confirmed luminous red galaxies (LRG) from the Dark Energy Spectroscopic Instrument (DESI) Y1 survey, which overlap with the Atacama Cosmology Telescope (ACT) Data Release 6 temperature maps over \\(\\geq\\) 4,000 deg\\(^2\\). We explore the kSZ dependence with various galaxy parameters and find no significant trend with redshift, but clear trends with stellar mass and absolute magnitude in \\(g\\), \\(r\\), and \\(z\\) bands. Our analysis suggests that the gas extends beyond the dark matter halo (99.5\\% confidence, i.e. PTE = 0.005). We find a tentative preference for hydrodynamical simulation models with stronger feedback that drives gas further out (Illustris \\(z=0.5\\), PTE = 0.37) over weaker-feedback cases (IllustrisTNG \\(z=0.8\\), PTE = 0.045), though with limited statistical significance. In all cases, a free multiplicative amplitude was fit to the simulated profiles, and further modeling work is required to firm up these conclusions. We find consistency between kSZ profiles around spectroscopic and photometric LRG, with comparable statistical power, thus increasing our confidence in the photometric analysis. Additionally, we present the first kSZ measurement around DESI Y1 bright galaxy sample (BGS) and emission-line galaxies (ELG), whose features match qualitative expectations. Finally, we forecast \\(S/N \\sim 50\\) for future stacked kSZ measurements using data from ACT, DESI Y3, and Rubin Observatory. These measurements will serve as an input for galaxy formation models and baryonic uncertainties in galaxy lensing.

High-ionization iron coronal lines (CLs) are a rare phenomenon observed in galaxy and quasi-stellar object spectra that are thought to be created by high-energy emission from active galactic nuclei and certain types of transients. In cases known as extreme coronal line emitting galaxies (ECLEs), these CLs are strong and fade away on a timescale of years. The most likely progenitors of these variable CLs are tidal disruption events (TDEs), which produce sufficient high-energy emission to create and sustain the CLs over these timescales. To test the possible connection between ECLEs and TDEs, we present the most complete variable ECLE rate calculation to date and compare the results to TDE rates from the literature. To achieve this, we search for ECLEs in the Sloan Digital Sky Survey (SDSS). We detect sufficiently strong CLs in 16 galaxies, more than doubling the number previously found in SDSS. We find that none of the nine new ECLEs evolve in a manner consistent with that of the five previously discovered variable ECLEs. Using this sample of five variable ECLEs, we calculate the galaxy-normalized rate of variable ECLEs in SDSS to be \\(R_\\mathrm{G}=3.6~^{+2.6}_{-1.8}~(\\mathrm{statistical})~^{+5.1}_{-0.0} (\\mathrm{systematic})\\times10^{-6}~\\mathrm{galaxy}^{-1}~\\mathrm{yr}^{-1}\\). The mass-normalised rate is \\(R_\\mathrm{M}=3.1~^{+2.3}_{-1.5}~(\\mathrm{statistical})~^{+4.4}_{-0.0}~(\\mathrm{systematic})\\times10^{-17}~\\mathrm{M_\\odot^{-1}}~\\mathrm{yr}^{-1}\\) and the volumetric rate is \\(R_\\mathrm{V}=7~^{+20}_{-5}~(\\mathrm{statistical})~^{+10}_{-0.0}~(\\mathrm{systematic})\\times10^{-9}~\\mathrm{Mpc}^{-3}~\\mathrm{yr}^{-1}\\). Our rates are one to two orders of magnitude lower than TDE rates from the literature, which suggests that only 10 to 40 per cent of all TDEs produce variable ECLEs. Additional uncertainties in the rates arising from the structure of the interstellar medium have yet to be included.

The estimation of uncertainties in cosmological parameters is an important challenge in Large-Scale-Structure (LSS) analyses. For standard analyses such as Baryon Acoustic Oscillations (BAO) and Full Shape, two approaches are usually considered. First: analytical estimates of the covariance matrix use Gaussian approximations and (nonlinear) clustering measurements to estimate the matrix, which allows a relatively fast and computationally cheap way to generate matrices that adapt to an arbitrary clustering measurement. On the other hand, sample covariances are an empirical estimate of the matrix based on en ensemble of clustering measurements from fast and approximate simulations. While more computationally expensive due to the large amount of simulations and volume required, these allow us to take into account systematics that are impossible to model analytically. In this work we compare these two approaches in order to enable DESI's key analyses. We find that the configuration space analytical estimate performs satisfactorily in BAO analyses and its flexibility in terms of input clustering makes it the fiducial choice for DESI's 2024 BAO analysis. On the contrary, the analytical computation of the covariance matrix in Fourier space does not reproduce the expected measurements in terms of Full Shape analyses, which motivates the use of a corrected mock covariance for DESI's Full Shape analysis.

The Large Magellanic Cloud (LMC) is a Milky Way (MW) satellite that is massive enough to gravitationally attract the MW disc and inner halo, causing significant motion of the inner MW with respect to the outer halo. In this work, we probe this interaction by constructing a sample of 9,866 blue horizontal branch (BHB) stars with radial velocities from the DESI spectroscopic survey out to 120 kpc from the Galactic centre. This is the largest spectroscopic set of BHB stars in the literature to date, and it contains four times more stars with Galactocentric distances beyond 50 kpc than previous BHB catalogues. Using the DESI BHB sample combined with SDSS BHBs, we measure the bulk radial velocity of stars in the outer halo and observe that the velocity in the Southern Galactic hemisphere is different by 3.7\\(\\sigma\\) from the North. Modelling the projected velocity field shows that its dipole component is directed at a point 22 degrees away from the LMC along its orbit, which we interpret as the travel direction of the inner MW. The velocity field includes a monopole term that is -24 km/s, which we refer to as compression velocity. This velocity is significantly larger than predicted by the current models of the MW and LMC interaction. This work uses DESI data from its first two years of observations, but we expect that with upcoming DESI data releases, the sample of BHB stars will increase and our ability to measure the MW-LMC interaction will improve significantly.