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  1. The SRG/eROSITA All-Sky Survey: Constraints on ultralight axion dark matter through galaxy cluster number counts

    Zelmer, S. ; Artis, E. ; Bulbul, E. ; ... - Astronomy and Astrophysics
    Ultralight axions are hypothetical scalar particles that influence the evolution of large-scale structures of the Universe. Depending on their mass, they can potentially be part of the dark matter component of the Universe as candidates commonly referred to as fuzzy dark matter. While strong constraints have been established for pure fuzzy dark matter models, the more general scenario where ultralight axions constitute only a fraction of the dark matter has been limited to only a few observational probes. In this work, we use the galaxy cluster number counts obtained from the first All-Sky Survey (eRASS1) of the SRG/eROSITA mission togethermore » with gravitational weak lensing data from the Dark Energy Survey, the Kilo-Degree Survey, and the Hyper Suprime-Cam to constrain the fraction of ultralight axions in the mass range 10−32 eV to 10−24 eV. We put upper bounds on the ultralight axion relic density Ωa in independent logarithmic axion mass bins by performing a full cosmological parameter inference. We find an exclusion region in the intermediate ultralight axion mass regime with the tightest bounds reported so far in the mass bins around ma = 10−27 eV with Ωa < 0.0035 and ma = 10−26 eV with Ωa < 0.0079; both are at a 95% confidence level. When combined with cosmic microwave background probes, these bounds are tightened to Ωa < 0.0030 in the ma = 10−27 eV mass bin and Ωa < 0.0058 in the ma = 10−26 eV mass bin, with both at a 95% confidence level. This is the first time that constraints on ultralight axions have been obtained using the growth of structure measured by galaxy cluster number counts. These results pave the way for large surveys, which can be utilized to obtain tight constraints on the mass and relic density of ultralight axions with better theoretical modeling of the abundance of halos.« less

  2. Spectroscopic Characterization of redMaPPer Galaxy Clusters with DESI

    Myles, J ; Gruen, D ; Jeltema, T ; ... - Monthly Notices of the Royal Astronomical Society
    Optical galaxy cluster identification algorithms such as redMaPPer promise to enable an array of astrophysical and cosmological studies, but suffer from biases whereby galaxies in front of and behind a galaxy cluster are mistakenly associated with the primary cluster halo. These projection effects caused by irreducible photometric redshift uncertainty must be quantified to facilitate the use of optical cluster catalogues. We present measurements of galaxy cluster projection effects and velocity dispersion using spectroscopy from the Dark Energy Spectroscopic Instrument. Our findings are as follows: we confirm that the fraction of redMaPPer putative member galaxies mistakenly associated with cluster haloes ismore » richness dependent, being more than twice as large at low richness than high richness; we present the first spectroscopic evidence of an increase in projection effects with increasing redshift, by as much as 25 per cent from $$z\sim 0.1$$ to $$z\sim 0.2$$; moreover, we find qualitative evidence for luminosity dependence in projection effects, with fainter galaxies being more commonly far behind clusters than their bright counterparts; finally, we fit the scaling relation between measured mean spectroscopic richness and velocity dispersion, finding an implied linear scaling between spectroscopic richness and halo mass. We discuss further directions for the application of spectroscopic data sets to improve use of optically selected clusters to test cosmological models.« less

  3. DESI Emission-line Galaxies: Clustering Dependence on Stellar Mass and [O II] Luminosity

    Hagen, T. ; Dawson, K. S. ; Zheng, Z. ; ... - The Astrophysical Journal
    We measure the projected two-point correlation functions of emission-line galaxies (ELGs) from the Dark Energy Spectroscopic Instrument One-Percent Survey and model their dependence on stellar mass and [O II] luminosity. We select ∼180,000 ELGs with redshifts of 0.8 < z < 1.6, and define 27 samples according to cuts in redshift and both galaxy properties. Following a framework that describes the conditional [O II] luminosity–stellar mass distribution as a function of halo mass, we simultaneously model the clustering measurements of all samples at fixed redshift. Based on the modeling result, most ELGs in our samples are classified as central galaxies,more » residing in halos of a narrow mass range with a typical median of ∼1012.2−12.4 h−1 M⊙. We observe a weak dependence of clustering amplitude on stellar mass, which is reflected in the model constraints and is likely a consequence of the 0.5 dex measurement uncertainty in the stellar mass estimates. The model shows a trend between galaxy bias and [O II] luminosity at high redshift (1.2 < z < 1.6) that is otherwise absent at lower redshifts.« less

  4. Evidence for large baryonic feedback at low and intermediate redshifts from kinematic Sunyaev-Zel’dovich observations with ACT and DESI photometric galaxies

    Hadzhiyska, B. ; Ferraro, S. ; Ried Guachalla, B. ; ... - Physical Review. D.
    Recent advances in cosmological observations have provided an unprecedented opportunity to investigate the distribution of baryons relative to the underlying matter. In this work, we show that the gas is more extended than the dark matter, and the amount of baryonic feedback at $$z \lesssim 1$$ disfavors low-feedback models such as that of state-of-the-art hydrodynamical simulation IllustrisTNG compared with high-feedback models such as that of the original Illustris simulation. This has important implications for bridging the gap between theory and observations and understanding galaxy formation and evolution. Furthermore, a better grasp of the baryon-dark matter link is critical to futuremore » cosmological analyses, which are currently impeded by our limited knowledge of baryonic feedback. Here, we measure the kinematic Sunyaev-Zel'dovich (kSZ) effect from the Atacama Cosmology Telescope (ACT), stacked on the luminous red galaxy (LRG) sample of the Dark Energy Spectroscopic Instrument (DESI) imaging survey. This is the first analysis to use photometric redshifts for reconstructing galaxy velocities. Due to the large number of galaxies comprising the DESI imaging survey, this is the highest signal-to-noise stacked kSZ measurement to date: we detect the signal at 13$$σ$$, finding strong evidence that the gas is more spread out than the dark matter, as well as a preference for larger feedback compared to some commonly used state-of-the-art hydrodynamical simulations. Here, our work opens up the possibility of recalibrating large hydrodynamical simulations using the kSZ effect. In addition, our findings highlight the importance of properly accounting for baryonic feedback with future surveys such as LSST through direct probes such as the kSZ, and shed light on long-standing enigmas in astrophysics, such as the “missing baryon” problem.« less

  5. Enhanced Star Formation and Black Hole Accretion Rates in Galaxy Mergers in IllustrisTNG50

    Schechter, Aimee L. ; Genel, Shy ; Terrazas, Bryan ; ... - The Astrophysical Journal
    Many theoretical and observational studies have suggested that galaxy mergers may trigger enhanced star formation or active galactic nucleus activity. We present an analysis of merging and nonmerging galaxies from 0.2 ≤ z ≤ 3 in the IllustrisTNG50 simulation. These galaxies encompass a range of masses (M⋆ > 108 M⊙) and mass ratios (≥1:10) and multiple merger stages. We examine the effect that galaxy mergers have on star formation and black hole accretion rates in the TNG50 universe. We additionally investigate how galaxy and black hole mass, merger stage, merger mass ratio, and redshift affect these quantities. Mergers in ourmore » sample show excess specific star formation rates (sSFR) at z ≤ 3 and enhanced specific black hole accretion rates (sBHAR) at z ≲ 2. The difference between sSFRs and sBHARs in the merging sample compared to the nonmerging sample increases as redshift decreases. Additionally, we show that these enhancements persist for at least ∼1 Gyr after the merger event. Investigating how mergers behave in the TNG50 simulation throughout cosmic time enables both a better appreciation of the importance of spatial resolution in cosmological simulations and a better basis to understand our high-z Universe with observations from JWST.« less

  6. The DESI One-Percent Survey: Modelling the clustering and halo occupation of all four DESI tracers with UCHUU

    Prada, F. ; Ereza, J. ; Smith, A. ; ... - Astronomy and Astrophysics
    We present results from a set of mock lightcones for the DESI One-Percent Survey, created from the UCHUU simulation. This 8 h−3 Gpc3 N-body simulation comprises 2.1 trillion particles and provides high-resolution dark matter (sub)haloes in the framework of the Planck-based ΛCDM cosmology. Employing the subhalo abundance matching (SHAM) technique, we populated the UCHUU (sub)haloes with all four DESI tracers – Bright Galaxy Survey (BGS), luminous red galaxies (LRGs), emission line galaxies (ELGs), and quasars (QSOs) – to z = 2.1. Our method accounts for redshift evolution as well as the clustering dependence on luminosity and stellar mass. The two-pointmore » clustering statistics of the DESI One-Percent Survey generally agree with predictions from UCHUU across scales ranging from 0.3 h−1 Mpc to 100 h−1 Mpc for the BGS and across scales ranging from 5 h−1 Mpc to 100 h−1 Mpc for the other tracers. We observed some differences in clustering statistics that can be attributed to incompleteness of the massive end of the stellar mass function of LRGs, our use of a simplified galaxy-halo connection model for ELGs and QSOs, and cosmic variance. We find that at the high precision of UCHUU, the shape of the halo occupation distribution (HOD) of the BGS and LRG samples is smaller bias values, likely due to cosmic variance. The bias dependence on absolute magnitude, stellar mass, and redshift aligns with that of previous surveys. These results provide DESI with tools to generate high-fidelity lightcones for the remainder of the survey and enhance our understanding of the galaxy-halo connection.« less

  7. PAC in DESI. I. Galaxy stellar mass function into the 106 M⊙ frontier

    Xu, Kun ; Jing, Y. P. ; Cole, S. ; ... - Monthly Notices of the Royal Astronomical Society
    The Photometric objects Around Cosmic webs (PAC) method integrates cosmological photometric and spectroscopic surveys, offering valuable insights into galaxy formation. PAC measures the excess surface density of photometric objects, $$\bar{n}_2w_{{\rm {p}}}$$, with specific physical properties around spectroscopic tracers. In this study, we improve the PAC method to make it more rigorous and eliminate the need for redshift bins. We apply the enhanced PAC method to the DESI Y1 BGS Bright spectroscopic sample and the deep Dark Energy Camera Legacy Survey (DECaLS) photometric sample, obtaining $$\bar{n}_2w_{{\mathrm {p}}}$$ measurements across the complete stellar mass range, from $$10^{5.3}$$ to $$10^{11.5}\,{\rm M}_{\odot }$$ formore » blue galaxies, and from $$10^{6.3}$$ to $$10^{11.9}\,{\rm M}_{\odot }$$ for red galaxies. We combine $$\bar{n}_2w_{{\rm {p}}}$$ with $$w_{{\rm {p}}}$$ measurements from the BGS sample, which is not necessarily complete in stellar mass. Assuming that galaxy bias is primarily determined by stellar mass and colour, we derive the galaxy stellar mass functions (GSMFs) down to $$10^{5.3}\,{\rm M}_{\odot }$$ for blue galaxies and $$10^{6.3}\,{\rm M}_{\odot }$$ for red galaxies, while also setting lower limits for smaller masses. The blue and red GSMFs are well described by single and double Schechter functions, respectively, with low-mass end slopes of $$\alpha _{\rm {blue}}=-1.54^{+0.02}_{-0.02}$$ and $$\alpha _{\rm {red}}=-2.50^{+0.08}_{-0.08}$$, resulting in the dominance of red galaxies below $$10^{7.6}\,{\rm M}_{\odot }$$. Stage-IV cosmological photometric surveys, capable of reaching 2–3 mag deeper than DECaLS, present an opportunity to explore the entire galaxy population in the local universe with PAC. This advancement allows us to address critical questions regarding the nature of dark matter, the physics of reionization, and the formation of dwarf galaxies.« less

  8. Probing signals of self-interacting dark matter core collapse in HI-rich galaxies

    Kong, Demao ; Yu, Hai-Bo - Physics of the Dark Universe
    Here, we analyze rotation curves of five Hi-rich galaxies recently discovered with MeerKAT. These galaxies exhibit sharply rising rotation curves, while their baryonic components are not dynamically dominant, suggesting that their dark matter halos have high inner densities. When fitting the standard Navarro–Frenk–White (NFW) halo model, four galaxies require extremely high halo concentrations, exceeding the cosmological median by 5σ. In contrast, self-interacting dark matter (SIDM) halos in the core-collapse phase naturally account for the high densities in these galaxies. For halos with masses around 1011 M⊙, those in cosmic filaments exhibit concentrations consistent with the cosmological average, while halos inmore » cosmic nodes show relatively higher concentrations that align with the SIDM fits but remain insufficient for the NFW fits. Our analysis indicates that these Hi-rich galaxies may have formed in cosmic nodes of dark matter with significant self-interactions.« less

  9. DESI peculiar velocity survey – Fundamental Plane

    Said, Khaled ; Howlett, Cullan ; Davis, Tamara ; ... - Monthly Notices of the Royal Astronomical Society
    The Dark Energy Spectroscopic Instrument (DESI) peculiar velocity survey aims to measure the peculiar velocities of early- and late-type galaxies within the DESI footprint using both the Fundamental Plane and optical Tully–Fisher relations. Direct measurements of peculiar velocities can significantly improve constraints on the growth rate of structure, reducing uncertainty by a factor of approximately 2.5 at redshift 0.1 compared to the DESI Bright Galaxy Survey’s redshift space distortion measurements alone. We assess the quality of stellar velocity dispersion measurements from DESI spectroscopic data. These measurements, along with photometric data from the Legacy Survey, establish the Fundamental Plane relation andmore » determine distances and peculiar velocities of early-type galaxies. During survey validation, we obtain spectra for 6698 unique early-type galaxies, up to a photometric redshift of 0.15. 64 per cent of observed galaxies (4267) have relative velocity dispersion errors below 10 per cent. This percentage increases to 75 per cent if we restrict our sample to galaxies with spectroscopic redshifts below 0.1. We use the measured central velocity dispersion, along with photometry from the DESI Legacy Imaging Surveys, to fit the Fundamental Plane parameters using a 3D Gaussian maximum likelihood algorithm that accounts for measurement uncertainties and selection cuts. In addition, we conduct zero-point calibration using the absolute distance measurements to the Coma cluster, leading to a value of the Hubble constant, H0 = 76.05 ± 0.35 (statistical) ±0.49 (systematic Fundamental Plane) ±4.86 (statistical due to calibration) km s–1 Mpc–1⁠. This H0 value is within 2σ of Planck cosmic microwave background results and within 1σ of other low-redshift distance indicator-based measurements.« less

  10. Nearby stellar substructures in the Galactic halo from DESI Milky Way Survey Year 1 Data Release

    Kim, Bokyoung ; Koposov, Sergey E ; Li, Ting S ; ... - Monthly Notices of the Royal Astronomical Society
    We report five nearby ($$d_{\mathrm{helio}} < 5$$ kpc) stellar substructures in the Galactic halo from a subset of 138 661 stars in the Dark Energy Spectroscopic Instrument (DESI) Milky Way Survey Year 1 Data Release. With an unsupervised clustering algorithm, HDBSCAN*, these substructures are independently identified in Integrals of Motion ($$E_{\rm tot}$$, $$L_{\rm z}$$, $$\log {J_r}$$, $$\log {J_z}$$) space and Galactocentric cylindrical velocity space ($$V_{R}$$, $$V_{\phi }$$, $$V_{z}$$). We associate all identified clusters with known nearby substructures (Helmi streams, M18-Cand10/MMH-1, Sequoia, Antaeus, and ED-2) previously reported in various studies. With metallicities precisely measured by DESI, we confirm that the Helmimore » streams, M18-Cand10, and ED-2 are chemically distinct from local halo stars. We have characterized the chemodynamic properties of each dynamic group, including their metallicity dispersions, to associate them with their progenitor types (globular cluster or dwarf galaxy). Our approach for searching substructures with HDBSCAN* reliably detects real substructures in the Galactic halo, suggesting that applying the same method can lead to the discovery of new substructures in future DESI data. With more stars from future DESI data releases and improved astrometry from the upcoming Gaia Data Release 4, we will have a more detailed blueprint of the Galactic halo, offering a significant improvement in our understanding of the formation and evolutionary history of the Milky Way Galaxy.« less
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