Measuring cosmological distances of active galactic nuclei from spectroastrometry and reverberation mapping: application to 3C 273. (arXiv:1906.08417v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Wang_J/0/1/0/all/0/1">Jian-Min Wang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Songsheng_Y/0/1/0/all/0/1">Yu-Yang Songsheng</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Li_Y/0/1/0/all/0/1">Yan-Rong Li</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Du_P/0/1/0/all/0/1">Pu Du</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhang_Z/0/1/0/all/0/1">Zhi-Xiang Zhang</a>
Using spectroastrometry, the GRAVITY at The Very Large Telescope
Interferometry successfully revealed the structure and kinematics of the
broad-line region (BLR) of 3C 273 with an unprecedented high spatial
resolution. Spectroastrometry measures the BLR angular sizes of active galactic
nuclei (AGNs) whereas reverberation mapping (RM) of AGNs independently provides
their linear sizes. In this paper, we suggest a new scheme making a joint
analysis of observations of spectroastrometry and RM of AGNs to measure their
cosmological distances. We apply this scheme to 3C 273 observed by both the
GRAVITY and RM campaign, and find its angular distance of
$551.5_{-78.7}^{+97.3}$ Mpc (with an averaged accuracy of $15%$). The
advantages of the scheme rest on the feasibility of directly measuring
cosmological distances without the invoking of otherwise calibrations through
known cosmic ladders. Moreover, we can easily repeat measurements of selected
AGNs to efficiently reduce the statistic and possible systematic measurement
uncertainties. With RM campaigns, a GRAVITY-sample with a reasonable size
($sim 25$ AGNs) will provide accurate measurements of distances of the AGNs
and hence a new way of measuring the Hubble constant with high precision
($lesssim 3%$) for cosmology.
Using spectroastrometry, the GRAVITY at The Very Large Telescope
Interferometry successfully revealed the structure and kinematics of the
broad-line region (BLR) of 3C 273 with an unprecedented high spatial
resolution. Spectroastrometry measures the BLR angular sizes of active galactic
nuclei (AGNs) whereas reverberation mapping (RM) of AGNs independently provides
their linear sizes. In this paper, we suggest a new scheme making a joint
analysis of observations of spectroastrometry and RM of AGNs to measure their
cosmological distances. We apply this scheme to 3C 273 observed by both the
GRAVITY and RM campaign, and find its angular distance of
$551.5_{-78.7}^{+97.3}$ Mpc (with an averaged accuracy of $15%$). The
advantages of the scheme rest on the feasibility of directly measuring
cosmological distances without the invoking of otherwise calibrations through
known cosmic ladders. Moreover, we can easily repeat measurements of selected
AGNs to efficiently reduce the statistic and possible systematic measurement
uncertainties. With RM campaigns, a GRAVITY-sample with a reasonable size
($sim 25$ AGNs) will provide accurate measurements of distances of the AGNs
and hence a new way of measuring the Hubble constant with high precision
($lesssim 3%$) for cosmology.
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