Monday, February 11, 2019

More Evidence Re No Dark Matter Galaxies And A New High Dark Matter Compact Elliptical Galaxy Anomaly

The authors of the paper claiming that NGC1052-DF2 and NGC1052-DF4 have little or no dark matter phenomena make a strong case that a potential flaw in their analysis is without merit.
It has been suggested that the dark matter-deficient galaxies NGC1052-DF2 and NGC1052-DF4 might not be members of the NGC1052 group but in the foreground at ∼13 Mpc, and satellites of the bright spiral galaxy NGC1042. We previously showed that the CMDs of the galaxies are inconsistent with this hypothesis, and derived distances of 19-20 Mpc from their surface brightness fluctuation signals. Here we note that NGC1042 is almost certainly a member of the NGC1052 group as well, based on its radial velocity, the HI distribution in the NGC1052/NGC1042 system, and the Tully-Fisher relation.
Pieter van Dokkum, Shany Danieli, Aaron Romanowsky, Roberto Abraham, Charlie Conroy, "The distance to NGC1042 in the context of its proposed association with the dark matter-deficient galaxies NGC1052-DF2 and NGC1052-DF4" (February 5, 2019) (To appear in RNAAS).

The following paper is also a notable observation of an outlier galaxy that seems to be contrary to MOND and the Radial Acceleration Relation (and every other modified gravity theory that reproduces the RAR) and is also an extreme outlier with respect to the less ironclad expectations of ΛCDM theory (in the vicinity of five sigma discovery significance). 

Generally speaking, elliptical galaxies have apparent low dark matter to total mass ratios. Because it is such an extraordinary and singular outlier a first instinct is to look for possible methodological flaws. But, if there aren't any, it is an extremely significant development (far more so than the claimed bullet cluster issues for modified gravity theories). The possibility that "a hydrostatic equilibrium analysis of the luminous and relaxed X-ray plasma emission" is misleading in this case, perhaps because the system in not in equilibrium, or because the luminous and X-ray plasma emissions are atypical for reasons related to the mix of stars in the galaxy for some reason come immediately to mind as possible explanations. Another possibility is that the new and archival observations have some inconsistency that hasn't been properly considered.

The Extremely High Dark Matter Halo Concentration of the Relic Compact Elliptical Galaxy Mrk 1216
Compact elliptical galaxies (CEGs) are candidates for local analogs of the high-redshift "red nuggets" thought to represent the progenitors of today's early-type galaxies (ETGs). To address whether the structure of the dark matter (DM) halo in a CEG also reflects the extremely quiescent and isolated evolution of its stars, we use a new 122 ks Chandra observation together with a shallow 13 ks archival observation of the CEG Mrk 1216 to perform a hydrostatic equilibrium analysis of the luminous and relaxed X-ray plasma emission extending out to a radius 0.85r2500. We examine several DM model profiles and in every case obtain a halo concentration (c200) that is a large positive outlier in the theoretical ΛCDM c200M200 relation; i.e., ranging from 3.4σ6.3σabove the median ΛCDM relation in terms of the intrinsic scatter. The high value of c200 we measure implies an unusually early formation time that firmly establishes the relic nature of the DM halo in Mrk 1216. The highly concentrated DM halo leads to a higher DM fraction and smaller total mass slope at 1Recompared to nearby normal ETGs. In addition, the highly concentrated total mass profile of Mrk 1216 cannot be described by MOND without adding DM, and it deviates substantially from the Radial Acceleration Relation. Mrk 1216 contains 80% of the cosmic baryon fraction within r200. The radial profile of the ratio of cooling time to free-fall time varies within a narrow range (tc/tff1419) over a large central region (r10 kpc) suggesting "precipitation-regulated AGN feedback" for a multiphase plasma, though presently there is little evidence for cool gas in Mrk 1216. The properties of Mrk 1216 are remarkably similar to those of the nearby fossil group NGC 6482.
Comments:28 pages, 12 figures, submitted to The Astrophysical Journal
This image is from that paper:

Footnote: For future reference I'm noting the paper below, primarily as a reference which the mass ranges of low, intermediate and high mass satellite galaxies.

Quenching low-mass satellite galaxies: evidence for a threshold ICM density

We compile a sample of SDSS galaxy clusters with high-quality Chandra X-ray data to directly study the influence of the dense intra-cluster medium (ICM) on the quenching of satellite galaxies. We study the quenched fractions of satellite galaxies as a function of ICM density for low- (109M1010M), intermediate- (1010M1010.5M), and high-mass (M1010.5M) satellite galaxies with >3000 satellite galaxies across 24 low-redshift (z<0.1) clusters. For low-mass galaxies we find evidence for a broken powerlaw trend between satellite quenched fraction and local ICM density. The quenched fraction increases modestly at ICM densities below a threshold before increasing sharply beyond this threshold toward the cluster center. We show that this increase in quenched fraction at high ICM density is well matched by a simple, analytic model of ram pressure stripping. These results are consistent with a picture where low-mass cluster galaxies experience an initial, slow-quenching mode driven by steady gas depletion, followed by rapid quenching associated with ram pressure of cold-gas stripping near (one quarter of the virial radius, on average) the cluster center.
Comments:17 pages plus appendix, 10 figures, accepted to ApJ


neo said...

how would you summarize what these papers mean for mond and dark matter?

andrew said...

The second paper is the big deal. It either blows everything we know from all of the theories out of the water, or the measurement is mistaken.

neo said...

could the second paper be explained in terms of MOND + black holes as dark matter?

andrew said...

Not easily. The problem is that every other elliptical galaxy ever seen has proportionately much less apparent dark matter and there is really no good reason why this one is special.

In a MOND + black holes as dark matter model, or for that matter, any model you can imagine, superficially similar galaxies shouldn't be radical polar extremes away from each other with nothing in between. Why should this galaxy have an immense number of black holes and not other seemingly similar galaxies?

The authors suggest that it may have something to do with the galaxy being extremely old compared to others of its type. But, honestly, this itself seems like their grasping at straws.

Honestly, in a CDM model, elliptical galaxies (which are bigger than spiral ones) having lots of dark matter makes all sorts of sense and the real mystery is not so much why this galaxy has so much, but why other elliptical galaxies have so little.

neo said...

in galaxy clusters, MOND reduces the amount of dark matter needed by a factor of 5, though i can't comment on elliptical galaxy

using occam's razor whats the simplest explanation for observations?

andrew said...

MOND predicts very little dark matter phenomena in elliptical galaxies because almost all of their stars are in gravitational fields stronger than a0. Conformal gravity does the same thing, more or less, but the way it makes it out of the equations to the phenomenology is subtly different from MOND.

Deur predicted and confirmed in his analysis that the more spherically symmetric an elliptical galaxy is the less apparent dark matter it should have, which indeed turns out to be consistent with observation, and that dark matter effects are much stronger in clusters than in spiral galaxies because self-interacting gravitons in weak fields form an astronomy scale analog to QCD flux tubes between large point masses.

In lambdaCDM the amount of dark matter in an elliptical galaxy is also predicted to be very low through a rather more baroque process of accretion of material into galaxies.

Using Occam's Razor, when every independent theory predicting apparent DM amounts in elliptical galaxies the simplest explanation for the observations would be measurement error.

The author argues that the anomalies arise from this system being very, very old to the point of being primordial. But, this explanation from the author only raised more and more complex to measure questions.

Two of the more plausible ways that this could happen would be:

(1) an overestimate of the distance of the system from Earth since we actually measure movement a stars within a galaxy in arcseconds and need to know the distance to convert that to the km/hr used to estimate the combined visible and invisible mass of the system and it will look too fast (and hence too heavy) if you overestimate the distance, or

(2) the old data and the new data haven't been properly compared to each other (the comparison is how you know how faster movement is taking place) and if it has been calibrated properly the stars in the new observation would be closer in location to those of the old measurement causing an illusion of high km/hr measurements which artificially inflates the inferred mass of the system.

Of course, it could e something els entirely as well.

andrew said...

Stacy McGaugh states at his blog regarding to my inquiry:

"Thanks for pointing this out. I have not yet had time to read it closely. In general, claims of high dark matter content in elliptical galaxies are highly degenerate with the adopted mass-to-light ratio of the stars, and it is difficult to disentangle what mass is dark and what is light. I will have to read the paper before I can comment on this particular case."