Darkmatter Redshift Free Download
Berry Spitsberg
Following Edwin Hubble, it is widely believed that the universe is expanding, which is based on the red-shift of light from distant objects. Can dark matter cause light to be red-shifted and make it look like the universe is expanding while in fact it is not?
Dark matter does cause light to be red-shifted via gravitational redshift. The best example of this that relates to dark matter is light emitted from other galaxies (or clusters of galaxies, or any structure that is expected to he hosted in a dark matter "halo"). A photon emitted near the center of a deep gravitational potential well needs energy to "climb out" of the well; the required energy is released by a redshift of the photon. There is of course a corresponding blue-shift for a photon falling into a potential well.
A slightly more complicated example is for a photon passing through a galaxy cluster. As the photon falls into the cluster, it experiences a blueshift. Clusters are large, so it takes quite a long time (a few to tens of Myrs) for the photon to get across. During this time the cluster will typically accrete some mass, deepening its potential, so on the way out the photon will experience a redshift of a magnitude greater than the blueshift it experienced on the way in. A photon passing through a galaxy cluster therefore experiences a net redshift.
I gave these two examples because they are relevant to the second part of the question - could dark matter make the Universe appear to expand while in fact being static? The idea of an expanding Universe is indeed motivated by the observation that more distant galaxies have higher redshifts. The first example I gave doesn't scale the right way - it actually scales the other way since more massive structures form at later times, so we observe more massive structures nearby and these are the ones giving the strongest redshifts.
The second example actually does scale the right way because clusters accreted mass faster at earlier times than they do today, so the strongest redshifts from this effect will be from structures observed as they were a long time ago - those furthest away.
The reason we can't explain away cosmic expansion with all this is that the magnitude of gravitational redshift that we predict and observe in these scenarios is very small - much smaller than the redshift we attribute to cosmic expansion. Either the Universe is expanding, or something very fundamental about our understanding of gravity is flawed (my opinion is that the former is true, but people do research alternate theories of gravity; so far no breakthroughs, though).
Let us assume momentarily that your hypothesis is true. One consequence is that dark matter in different galaxies would redshift light by different amounts, in high correlation with the second distance measure given by luminosity of the baryonic matter in the galaxy. So you are back to correlating dark matter to distance, anyway. Unlikely.
The problem is cosmic dust can red-shift light without Universe expansion. Since cosmic dust is concentrated near the surface of galaxies, light travelling around a galaxy is most likely redshft by absorption in dust and not by gravitational attraction by dark matter. The error caused by cosmic dust can be corrected by measuring the difference in redshift between Lyman-alpha and H-alpha lines, but is never done. What this means the Universe is not expanding and dark matter does not exist. See at "Cosmology by Cosmic Dust"", 2014 and "Expanding Universe or Cosmic Dust?", 2015.
Methods. We compare properties of high-redshift galaxies observed by JWST with hydrodynamical simulations, in the standard cold dark matter model and in warm dark matter models with a suppressed linear matter power spectrum
Conclusions. We also show how two observables, the galaxy luminosity functions and the galaxy correlation function at small scales of faint objects, can be promising tools for discriminating between the different dark-matter scenarios. Further hints may come from early stellar-mass statistics and galaxy CO emission.
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License ( ), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The early data release of the James Webb Space Telescope (JWST) has shown, for the first time, the existence of primordial galaxies in the very distant Universe, deep in the first half billion years. These findings have profound implications on our understanding of primordial structure formation and can help pose tight constraints on the nature of dark matter. While the common paradigm of structure formation relies on cold dark matter (CDM), that is matter that is non-relativistic at decoupling, alternative possibilities advocated to solve small-scale problems of the standard CDM scenario rely on the hypothesis that dark matter is made of warm particles that possess a small, non-negligible, thermal velocity, that is to say warm dark matter (WDM).
Answering these questions is not a trivial task and requires detailed analysis of primordial structure formation, including the relevant chemical and physical mechanisms responsible for pristine-gas collapse and first-galaxy buildup. To address these open issues, in the next sections, we perform several numerical simulations under different assumptions for CDM and WDM, and we contrast the recent JWST observational determinations against the predictions of our updated non-equilibrium numerical model applied to different dark-matter scenarios.
The paper is structured as follows. In Sect. 2 we describe our methodology; in Sect. 3 we discuss our main results about early-galaxy properties in CDM and WDM universes; and, finally, we summarize and conclude in Sect. 4.
Fig. 1.Halo mass functions for the different dark-matter models at different redshifts. Numerical simulation fiducial results (histograms) are overplotted on the corresponding analytical expectations (lines) by Reed et al. (2007). These mass functions have been derived by considering hydro-dynamical simulations and are thereby incorporating baryonic effects.
Fig. 6.Expected dust-to-gas ratios, D/G, as a function of the total halo mass for galaxies in the CDM, 3 keV WDM, and 2 keV WDM fiducial runs (top) and corresponding relation with the local SFR (bottom).
In this work we have exploited the latest JWST observational determinations and novel up-to-date numerical simulations to put constraints on the nature of dark matter from high-redshift observations. We have compared the latest JWST-inferred high-z star formation estimates (Santini et al. 2023; Donnan et al. 2023; Finkelstein et al. 2022; Adams et al. 2023; Harikane et al. 2023; Bouwens et al. 2022) with a set of non-equilibrium hydrodynamical simulations which incorporate the new, rich, and accurate modelling of cosmic structure formation at early times by Maio et al. (2022). This attempt is the first one to try to set constraints on WDM by combining such modelling with state-of-the-art JWST observations at extremely high redshift. Previous works based on high-redshift hydro-simulations have either neglected a fully complete modelling of primordial gas and structures in CDM and WDM or had no or little data support for the primordial regimes probed by JWST.
We contrast galaxy buildup in the standard CDM model against two models with 2 and 3 keV WDM, respectively. We adopted cosmological matter density and expansion parameters that are consistent with both the standard model and WMAP data. The latest Planck measurements (Planck Collaboration XVI 2014; Planck Collaboration VI 2020) suggest slightly different values, while spectral parameters are similar. This is an important point, because early structure formation and halo mass functions are mostly affected by variations in σ8 which is consistently constrained by the aforementioned experiments. Thus, changing the initial parameter set does not lead to appreciable differences in our results and the overall trends are preserved (see also discussions in e.g., Maio et al. 2010, 2011a).
As is typically done, we assumed that the statistical distribution of the primordial matter perturbation field is Gaussian. Deviations from Gaussianity could be present and could enhance or dampen the occurrence of objects with a given mass; nevertheless, the expected level of these primordial non-Gaussianities is so small that possible implications on molecular evolution, popIII and popII-I star formation, metal enrichment, gas temperature, and possibly detectable signals would be negligible and dominated by baryon effects (Maio & Iannuzzi 2011; Maio 2011; Maio & Khochfar 2012; Maio et al. 2012).
More critical uncertainties are about feedback processes and their degeneracies with the nature of dark matter. Fortunately, feedback effects usually have local impacts and alter the local chemical and physical properties of cosmic objects. Although their efficiency is poorly constrained, they play a significant role at low z, when structure evolution is in more advanced stages and possible dark-matter signatures have already been washed out (Schneider et al. 2014). Primordial galaxies are young structures and have experienced little feedback effects; therefore, their statistical occurrence is mainly driven by the underlying dark-matter model. For this reason, the early Universe is a precious window to test dark-matter models and, furthermore, calibrating feedback parameters in the low-z regime together with large high-z data samples might make it possible to both break the degeneracies and to provide hints on the late-time evolution of cosmic structures.
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