Deep NIR photometry of HI galaxies in the Zone of Avoidance

TL;DR

This study presents deep near-infrared observations of HI-detected galaxies in the Zone of Avoidance, improving photometry accuracy to facilitate cosmic flow measurements and assessing Galactic extinction ratios.

Contribution

It provides deep NIR imaging of ZoA galaxies, enabling more accurate photometry and extinction analysis, which aids in understanding local cosmic flows.

Findings

NIR magnitudes are accurate within 0.1 mag even in high extinction areas.

The true extinction ratio in the Milky Way is approximately 0.87, consistent with previous independent estimates.

Deep NIR data can improve cosmic flow studies in the Zone of Avoidance.

Abstract

Current studies of the peculiar velocity flow field in the Local Universe are limited by either the lack of detection or accurate photometry for galaxies at low Galactic latitudes. The contribution to the dynamics of the Local Group of the largely unknown mass distribution in this 'Zone of Avoidance' remains controversial. We present here the results of a pilot project to obtain deep near infrared (NIR) observations of galaxies detected in the systematic Parkes deep HI survey of the ZoA - 578 galaxies with recession velocities out to 6000 km/s were observed with the 1.4m InfraRed Survey Facility SIRIUS camera providing J, H and K_s imaging ~2 mag deeper than 2MASS. After star-subtraction, the resulting isophotal magnitudes and inclinations of ZoA galaxies are of sufficient accuracy (magnitude errors under 0.1 mag even at high extinction) to ultimately be used to determine cosmic flow fields "in" the ZoA via the NIR Tully-Fisher relation. We further used the observed NIR colours to assess the ratio of the true extinction to the DIRBE/IRAS extinction deep into the dust layers of the Milky Way. The derived ratio was found to be 0.87 across the HIZOA survey region with no significant variation with Galactic latitude or longitude. This value is in excellent agreement with the completely independently derived factor of 0.86 by Schlafly & Finkbeiner based on Sloan data far away from the Milky Way.