Early Galaxy Formation Contrary to Conventional Dark Matter

by Tommy on 15/03/2017

Just when I start thinking deeply and critically about Sabine Hossenfelder’s idea of an inverse baryon anti-correlation of a mass variable gravitational dark matter vector axion boson, deeply tied to universal entropy production and thermodynamic energy balance, there is this result.


Strongly baryon-dominated disk galaxies at the peak of galaxy formation ten billion years ago, R. Genzel, N. M. Förster Schreiber, H. Übler, P. Lang, T. Naab, R. Bender, L. J. Tacconi, E. Wisnioski, S. Wuyts, T. Alexander, A. Beifiori, S. Belli, G. Brammer, A. Burkert, C. M. Carollo, J. Chan, R. Davies, M. Fossati, A. Galametz, S. Genel, O. Gerhard, D. Lutz, J. T. Mendel, I. Momcheva, E. J. Nelson, A. Renzini, R. Saglia, A. Sternberg, S. Tacchella, K. Tadaki and D. Wilman, Nature 543, 397–401 (16 March 2017), doi:10.1038/nature21685

In the cold dark matter cosmology, the baryonic components of galaxies — stars and gas — are thought to be mixed with and embedded in non-baryonic and non-relativistic dark matter, which dominates the total mass of the galaxy and its dark-matter halo. In the local (low-redshift) Universe, the mass of dark matter within a galactic disk increases with disk radius, becoming appreciable and then dominant in the outer, baryonic regions of the disks of star-forming galaxies. This results in rotation velocities of the visible matter within the disk that are constant or increasing with disk radius — a hallmark of the dark-matter model. Comparisons between the dynamical mass, inferred from these velocities in rotational equilibrium, and the sum of the stellar and cold-gas mass at the peak epoch of galaxy formation ten billion years ago, inferred from ancillary data, suggest high baryon fractions in the inner, star-forming regions of the disks. Although this implied baryon fraction may be larger than in the local Universe, the systematic uncertainties (owing to the chosen stellar initial-mass function and the calibration of gas masses) render such comparisons inconclusive in terms of the mass of dark matter. Here we report rotation curves (showing rotation velocity as a function of disk radius) for the outer disks of six massive star-forming galaxies, and find that the rotation velocities are not constant, but decrease with radius. We propose that this trend arises because of a combination of two main factors: first, a large fraction of the massive high-redshift galaxy population was strongly baryon-dominated, with dark matter playing a smaller part than in the local Universe; and second, the large velocity dispersion in high-redshift disks introduces a substantial pressure term that leads to a decrease in rotation velocity with increasing radius. The effect of both factors appears to increase with redshift. Qualitatively, the observations suggest that baryons in the early (high-redshift) Universe efficiently condensed at the centres of dark-matter haloes when gas fractions were high and dark matter was less concentrated.

See also: https://arxiv.org/abs/1703.04321

The evolution of the Tully-Fisher relation between z ∼ 2.3 and z ∼ 0.9 with KMOS3D, H. Übler, N.M. Förster Schreiber, R. Genzel, E. Wisnioski, S. Wuyts, P. Lang, T. Naab, D.J. Wilman, M. Fossati, J.T. Mendel, A. Beifiori, S. Belli, R. Bender, G. Brammer, A. Burkert, J. Chan, R. Davies, M. Fabricius, A. Galametz, D. Lutz, I. Momcheva, E.J. Nelson, R.P. Saglia, S. Seitz, L.J. Tacconi, K. Tadaki and P.G. van Dokkum, Submitted to ApJ (13 March 2017)

We investigate the stellar mass and baryonic mass Tully-Fisher relations (TFRs) of massive star-forming disk galaxies at redshift z ∼ 2.3 and z ∼ 0.9 as part of the KMOS3D integral field spectroscopy survey. Our spatially resolved data allow reliable modelling of individual galaxies, including the effect of pressure support on the inferred gravitational potential. At fixed circular velocity, we find higher baryonic masses and similar stellar masses at z ∼ 2.3 as compared to z ∼ 0.9. Together with the decreasing gas-to-stellar mass ratios with decreasing redshift, this implies that the contribution of dark matter to the dynamical mass at the galaxy scale increases towards lower redshift. A comparison to local relations reveals a negative evolution of the stellar and baryonic TFR zero-points from z = 0 to z ∼ 0.9, no evolution of the stellar TFR zero-point from z ∼ 0.9 to z ∼ 2.3, but a positive evolution of the baryonic TFR zero-point from z ∼ 0.9 to z ∼ 2.3. We discuss a toy model of disk galaxy evolution to explain the observed, non-monotonic TFR evolution, taking into account the empirically motivated redshift dependencies of galactic gas fractions, and of the relative amount of baryons to dark matter on the galaxy and halo scales.

See also also: https://arxiv.org/abs/1703.05491

Falling outer rotation curves of star-forming galaxies at 0.6 < z < 2.6 probed with KMOS3D and SINS/ZC-SINF, P. Lang, N.M. Förster Schreiber, R. Genzel, S. Wuyts, E. Wisnioski, A. Beifiori, S. Belli, R. Bender, G. Brammer, A. Burkert, J. Chan, R. Davies, M. Fossati, A. Galametz, S.K. Kulkarni, D. Lutz, J.T. Mendel, I.G. Momcheva, T. Naab, E.J. Nelson, R.P. Saglia, S. Seitz, S. Tacchella, L.J. Tacconi, K. Tadaki, H. Übler, P.G. van Dokkum and D.J. Wilman, Submitted to the Astrophysical Journal (16 March 2017)

We exploit the deep resolved Halpha kinematic data from the KMOS3D and SINS/zC-SINF surveys to examine the largely unexplored outer disk kinematics of star-forming galaxies (SFGs) out to the peak of cosmic star formation. Our sample contains 101 SFGs representative of the more massive (9.3 < log(M*/Msun) < 11.5) main sequence population at 0.6 < z < 2.6. Through a novel stacking approach we are able to constrain a representative rotation curve extending out to ~ 4 effective radii. This average rotation curve exhibits a significant drop in rotation velocity beyond the turnover, with a slope of Delta(V)/Delta(R) = −0.26+0.10−0.09 in units of normalized coordinates V/Vmax and R/Rturn. This result confirms that the fall-off seen previously in some individual galaxies is a common feature of our sample of high-z disks. We show that this outer fall-off strikingly deviates from the flat or mildly rising rotation curves of local spiral galaxies of similar masses. We furthermore compare our data with models including baryons and dark matter demonstrating that the falling stacked rotation curve can be explained by a high mass fraction of baryons relative to the total dark matter halo (md > ~ 0.05) in combination with a sizeable level of pressure support in the outer disk. These findings are in agreement with recent studies demonstrating that star-forming disks at high redshift are strongly baryon dominated within the disk scale, and furthermore suggest that pressure gradients caused by large turbulent gas motions are present even in their outer disks. We demonstrate that these results are largely independent of our model assumptions such as the presence of a central stellar bulge, the effect of adiabatic contraction at fixed md, and variations in the concentration parameter.

My gravitational axions are looking better all the time.


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