# Spectra of H2O Maser Galaxies

## Contact

Ingyin Zaw
New York University
iz6@nyu.edu

## Summary

Spectra of H2O maser galaxies obtained with the goal of calibrating Cepheid distances, and therefore improving estimates of H0

## Finding Targets

An object whose ANCILLARY_TARGET2 value includes one or more of the bitmasks in the following table was targeted for spectroscopy as part of this ancillary target program. See SDSS bitmasks to learn how to use these values to identify objects in this ancillary target program.

Program (bit name) Bit number Target Description Number of Fibers Number of Unique Primary Objects
IAMASERS 12 Known or potential maser 54 50

## Description

Absolute calibration of Type Ia supernovae (SNe Ia) depends on rare overlap with nearby Cepheid hosts. A new sample of high-accuracy measurements of geometric distances to SNe Ia host galaxies could significantly reduce errors on absolute calibration of SN luminosity and local estimates of H0.

One current route to the absolute calibration of the luminosities of Type Ia supernovae as standard candles uses the 3%-accurate distance to NGC 4258 afforded by the well-studied H2O maser in its center (Humphreys et al. 2013).

Further improvements, by identifying other maser galaxies with supernovae, could decrease the uncertainty on local measurements of the Hubble Constant (Riess et al. 2011). There is an apparent correlation between maser activity and host galaxy properties (Zhu et al. 2011); this correlation will be tested with spectroscopy of known maser host galaxies, and spectroscopy of SN Ia host galaxies will be used to identify plausible maser candidates.

## Target Selection

Targets, identified by IAMASERS flag, were selected with no previous SDSS spectra and imodel < 20 mag. Objects targeted in the Bright Galaxies ancillary program Dawson et al. (2013) were also removed from the IAMASERS target list.

## REFERENCES

Dawson, K., et al. 2013, AJ, 145, 10D
Humphreys, E. et al. 2013, ApJ, 775, 13H
Riess, A. et al. 2011, ApJ, 730, 119R
Zhu, G., Zaw, I., Blanton, M. R., & Greenhill, L. J. 2011, ApJ, 742, 73