The ANCH0R survey program is conducting a volume-limited survey to search every galaxy within 15 Mpc for 22 GHz water megamaser emission, with the goal of finding “the next NGC 4258.”
NGC 4258 is the nearest, brightest, and “cleanest” disk megamaser system known, and its geometric distance carries disproportionate weight in setting the absolute scale of most extragalactic distance-measuring techniques used in cosmology today. This unique role makes NGC 4258 the most important galaxy in the Universe for cosmology, but it also presents a single point of failure that is no longer acceptable in the era of percent-level cosmological measurements and in the face of the current “Hubble tension” (the >5σ discrepancy between the CMB-based value of the Hubble constant and direct local-Universe measurements).
ANCH0R’s strategy is deliberately simple: a comprehensive survey of galaxies out to 15 Mpc. This approach avoids selection-based blind spots (e.g., associated with AGN activity markers) while ensuring that any detected system is nearby enough to enable an anchor-quality distance measurement. The ANCH0R survey will cover a volume roughly an order of magnitude larger than that bounded by NGC 4258 itself. Finding even one additional NGC 4258-like system will immediately reduce the current reliance on a single galaxy, enable consistency checks between calibrators, and harden the absolute distance scale against subtle systematics that can dominate at the percent level.
Because the ANCH0R survey targets are selected purely by proximity and will all be observed to a comparable sensitivity level, the resulting detection statistics will also provide the first genuinely unbiased accounting of the incidence rate and luminosity function for 22 GHz megamaser emission in the local Universe. This sample will thus enable demographic tests of how megamaser occurrence correlates with basic host galaxy properties, removing selection function ambiguities and providing a reference population that can be used to optimize target-selection strategies for the next generation of megamaser discovery experiments.
Team
- Dom Pesce (PI)
- Jim Braatz
- Paola Castangia
- Frédéric Courbin
- Christian Henkel
- Cheng-Yu Kuo
- Elisabetta Ladu
- Mark Reid
- Andrea Tarchi