Dan Scolnic

I'm a dad; I’m a professor doing cosmology at Duke U. and I have some opinions about basketball.

[Dan Scolnic @DScol]

While this doesn't mean carbon-rich AGB stars can't be useful distance indicators, it now seems not safe to assume they are C-rich AGB stars in spirals like in the LMC. Before treating them as a standard candle to calibrate SN Ia, need to establish that we're actually measuring the same physical population across the distance ladder. From these papers, variability, water bands and metallicity measurements should help.

[Dan Scolnic @DScol]

Two new papers this last week about important challenge for the JAGB distance indicator: stars selected by usual “J-region” color cuts are not necessarily the carbon-rich AGB stars we thought they were. And two very different approaches are finding the same thing.

[Dan Scolnic @DScol]

How come? It looks like pulsating O-rich AGB stars in metal rich spirals like M101 or the MW appear to produce substantially more silicate dust than their LMC counterparts, reddening them into the “carbon-star” color region. So the same broadband color cut can select different physical populations in different environments.

[Dan Scolnic @DScol]

Awesome getting to spend day with the infinitely curious @McConaughey as well as so many from @NASARoman team and @DukePhysics. What an incredible day and great video Matthew!

[Matthew McConaughey @McConaughey]

Big congrats to Dan Scolnic and the Roman Space Telescope Team on the successful launch this AM. Looking forward to what you show us about ourselves.

[Dan Scolnic @DScol]

Got to talk on NPR and WaPost about NASA Roman launch this Sunday!! I can't believe this is finally here! https://t.co/486NGuwjNG and https://t.co/qU1TILH5i7

[Dillon Brout @DillonBrout]

1/ With NASA's Roman Space Telescope launch 🚀 in T-20 days and our official team jerseys in hand, this is the perfect timing to congratulate my PhD student, @rujutapurohit, on her first-first author paper 🎉

Paper: https://t.co/VLz1BgVFyH

Roman Hype: https://t.co/vXBTAP44sW

[Dan Scolnic @DScol]

So the dramatic gain in precision comes from assuming the reconstructed peculiar velocities are known with very little uncertainty. Would be good to propagate the full M25 ensemble, not just its mean corrections, including covariance, residual small-scale velocity dispersion, and selection.

[Dan Scolnic @DScol]

The original MCP analysis, using the 2M++ peculiar-velocity model, gave H0 = 71.8 ± 2.7. Switching to M25 lowers the central value to ~69.7 +/- 2.6, not such a dramatic change. But allowing σv to vanish drives H0 lower and crucially the uncertainty down to ±0.9 km/s/Mpc, roughly 3× more precise than the original megamaser determination.

[Dan Scolnic @DScol]

The paper then concludes that this suggests the Hubble tension may arise from an unidentified systematic in the distance ladder rather than new physics. Conclusion is roughly: six spatially correlated masers + a velocity model whose uncertainty has been dramatically compressed → a ~2σ difference with H0DN → evidence that the cross-checked distance ladder has an unidentified systematic?
.

[Dan Scolnic @DScol]

Leaving out those posteriors and external information leaves little leverage on σv, and its driven toward ~0 km/s, which just can't be. The weights of the masers change dramatically, so that even nearby NGC 4258 itself, just outside the Local Group at ~7.6 Mpc away where peculiar velocity is usually considered a large fraction of the Hubble flow, is claimed to measure H0 very precisely.

[Dan Scolnic @DScol]

M25 doesn’t just give one peculiar velocity per galaxy. It uses constrained realizations to provide uncertainty and covariance in the reconstructed velocity field, which should be propagated into maser analysis. Instead, the paper uses only the central values and replaces all the rest of the information with a single independent velocity dispersion, σv, inferred from just these 6 masers.

[Dan Scolnic @DScol]

New H0 paper https://t.co/kMoUbmrSnV which applies sophisticated Manticore (M25) peculiar-velocity reconstruction to the 6 megamaser galaxies from the MCP (P20). Important idea, but leaves out what makes M25 powerful.

[Department of Physics at University of Oxford @OxfordPhysics]

Prof Maria Vincenzi was awarded the New Horizons in Physics Prize last week! Watch our interview where she discusses her research! @brkthroughprize

[Dan Scolnic @DScol]

@astro_anil That is so amazing!!!

[Dan Scolnic @DScol]

@WKCosmo Read thread and papers. The plots show different supernova analyses can move things below 3sigma, so who is assuming no systematics?

[Dan Scolnic @DScol]

@WKCosmo Ok, I may not be following, but just for record, the three supernova analyses use a ton of the same data (particularly at low redshift), so they absolutely should not be combined. That would be super bad.

[Dan Scolnic @DScol]

Understood. "This implicitly assumes that the systematic offsets between the different measurements are zero, which is an absurd assumption" - I agree with this sentence. Its so absurd, I don't even know who would say this, cause it's definitely not the supernova people whose data this assumption is about.