[Paper Review] Galaxy peculiar velocities in the Zone of Avoidance

Khaled Said, R. C. Kraan‐Korteweg+1 more|arXiv (Cornell University)|Oct 11, 2014

Galaxies: Formation, Evolution, Phenomena2 references3 citations

TL;DR

This paper presents a new near-infrared Tully-Fisher relation calibrated on deep HI and NIR photometric data to measure galaxy peculiar velocities in the Zone of Avoidance (ZoA), overcoming dust extinction limitations. Using HI Parkes Deep ZoA and 2MASX Redshift ZoA surveys, it derives accurate distances and peculiar velocities for 120 bright, inclined spirals in the southern ZoA, revealing a clear infall toward the Great Attractor with velocities up to 2500 km/s and validating the early Great Attractor model within observational limits.

ABSTRACT

Dust extinction and stellar confusion of the Milky Way hinder the detection of galaxies at low Galactic latitude, creating the so-called Zone of Avoidance (ZoA). This has hampered our understanding of the local dynamics, cosmic flow fields and the origin of the Cosmic Microwave Background dipole. The ZoA ($|b| \le 5^\circ$) is also excluded from the "whole-sky" Two Micron All-Sky Survey (2MASS) Redshift Survey (2MRS) and 2MASS Tully-Fisher Survey (2MTF). The latter aims to provide distances and peculiar velocities for all bright inclined 2MASS galaxies with $K_s^o$ $\leq 11\hbox{$.\!\!^{ m m}$}25$. Correspondingly, knowledge about the density distribution in the ZoA remains limited to statistical interpolations. To improve on this bias we pursued two different surveys to fill in the southern and northern ZoA. These data will allow a direct measurement of galaxy peculiar velocities. In this paper we will present a newly derived optimized Tully-Fisher (TF) relation that allow accurate measures of galaxy distances and peculiar velocities for dust-obscured galaxies. We discuss further corrections for magnitudes and biases and present some preliminary results on flow fields in the southern ZoA.

Motivation & Objective

• To overcome the limitations of optical and near-infrared surveys in the Zone of Avoidance (ZoA) due to dust extinction and stellar confusion.
• To measure accurate peculiar velocities for galaxies in the ZoA using a newly calibrated near-infrared Tully-Fisher relation.
• To fill the observational gap in the southern ZoA by combining HI redshift data from Parkes and Nançay telescopes with deep NIR photometry from the IRSF telescope.
• To enable a complete all-sky peculiar velocity survey by integrating data from this study with the 2MTF survey.
• To test cosmological models of large-scale structure, particularly the Great Attractor's influence on local cosmic flows.

Proposed method

• Utilize blind HI surveys (HIZoA and 2MASX Redshift ZoA) to detect galaxies in the ZoA, avoiding extinction and confusion issues.
• Perform follow-up J, H, Ks-band photometry with the IRSF 1.4m telescope to obtain accurate magnitudes for the Tully-Fisher relation.
• Calibrate a new near-infrared Tully-Fisher template relation using 888 galaxies, applying isophotal magnitudes and correcting for inclination and extinction.
• Derive peculiar velocities as the difference between Hubble-flow velocity (from TF distance) and observed redshift velocity, with error propagation via quadratic combination of magnitude, width, and intrinsic scatter errors.
• Construct a peculiar velocity flow field map by interpolating velocities across Galactic longitude and recession velocity, using color-coded galaxies and the Great Attractor center as a reference.
• Compare observed peculiar velocities with the Faber & Burstein Great Attractor model using parameters: v_A = 535 km/s, d_A = 4844 km/s, c_A = 1430 km/s, n_A = 1.7.

Experimental results

Research questions

• RQ1 Can a near-infrared Tully-Fisher relation be effectively calibrated to measure peculiar velocities in the Zone of Avoidance despite dust extinction?
• RQ2 To what extent do observed peculiar velocities in the southern ZoA confirm the predicted infall pattern toward the Great Attractor?
• RQ3 How do the peculiar velocity errors and sample completeness vary with increasing redshift in the ZoA?
• RQ4 Can the inclusion of HI-detected galaxies in the ZoA improve the accuracy of all-sky cosmic flow models?
• RQ5 How well does the single Great Attractor model fit the observed peculiar velocity data in the southern ZoA?

Key findings

• Peculiar velocities for 120 bright, inclined spiral galaxies in the southern ZoA were successfully measured, with most values within |v_pec| ≤ 1000 km/s and outliers up to |v_pec| ≤ 2500 km/s.
• The peculiar velocity map shows a clear infall pattern toward the Great Attractor, consistent with the Faber & Burstein model, particularly for galaxies with log W > 2.3 and inclination i < 0.5 in the GA region.
• The sample was extended to v_obs ≤ 9000 km/s to better probe the backside infall toward the Great Attractor and the more distant Shapley Concentration.
• Peculiar velocity errors are typically a few hundred km/s, with errors increasing at larger distances due to sparser sampling and higher redshifts.
• The new Tully-Fisher relation, calibrated on isophotal magnitudes and corrected for extinction and inclination, enables robust distance and velocity measurements in the ZoA.
• Combining this data with the 2MTF survey will enable the first complete all-sky peculiar velocity survey, significantly improving cosmic flow modeling.