SED and Galactic kinematic diagnostics for dormant BH/NS binary candidates

TL;DR

This paper addresses the search for dormant black hole and neutron star binaries with luminous companions using Gaia DR3. It combines broadband SED fitting from optical to infrared with GALEX UV diagnostics to detect hidden hot companions, and Galactic kinematics to identify natal-kick–driven systems. By applying stringent SED quality cuts and ultraviolet consistency tests, it isolates 779 robust candidates, 216 of which show high-velocity kinematics, with 176 in common and 19 BH candidates having previously reported masses ≥3 $M_\odot$. The results yield a prioritized target list for follow-up spectroscopic or time-domain observations, highlighting the synergy between UV excess screening and kinematic indicators in uncovering dormant compact-object binaries.

Abstract

The third data release of the Gaia mission (Gaia DR3) has enabled large-scale searches for dormant black hole and neutron star binaries with stellar companions at wide separations. A recent study has proposed thousands of dormant black hole and neutron star binary candidates using summary statistics from Gaia DR3 by simulating and fitting Gaia observables. In this Letter, we perform broadband spectral energy distribution (SED) fitting from the optical to the infrared for 1,328 candidates, incorporating GALEX ultraviolet photometry to assess the presence of hidden hot companions. We quantify ultraviolet excess by comparing observed near-ultraviolet fluxes with single-star SED predictions and further test whether excesses can be explained by non-degenerate stellar companions for sources exhibiting moderate excess. We additionally examine the Galactic kinematics of the sample to identify systems potentially affected by natal kicks during compact-object formation. By combining the ultraviolet and kinematic diagnostics, we identify 176 sources as the highest-priority candidates for follow-up observations, in which 19 are black hole candidates with previously provided masses $\geq$ 3 $M_\odot$.

Figures (3)

• Figure 1: The ratio of observed NUV flux to model-predicted NUV flux as a function of the previously provided companion mass. The horizontal orange dashed line marks $F_\mathrm{NUV,obs}$/$F_\mathrm{NUV,mod}=1.2$, below which sources are considered to show no significant NUV excess and are directly retained. Sources with moderate excess, $1.2<F_\mathrm{NUV,obs}$/$F_\mathrm{NUV,mod}\leq3$, indicated by the area between the cyan dashed line and orange dashed line, are subjected to further analysis allowing for a luminous stellar companion.
• Figure 2: The ratio of total model-predicted NUV flux to observed NUV flux as a function of the previously provided companion mass. The horizontal orange dashed line marks $F_\mathrm{NUV,tot\_mod}$/$F_\mathrm{NUV,obs}=10$, above which the predicted flux from a non-degenerate luminous companion severely exceeds the observed value, making such companions unlikely.
• Figure 3: (a),$V_{\rm pec}$ as a function of the previously provided companion mass. NS-like zone, transition zone, and BH-like zone are respectively indicate by blue squares, orange squares and red squares. (b),$V_{\rm pec}$ as a function of $R_{\rm NUV}$. (c),$V_{\rm pec}$ as a function of $|Z|_{\rm max}$. In all panels, the horizontal black dashed line marks $V_{\rm pec}$ = 100 km s$^{-1}$, above which sources are considered to be probably accelerated by supernova natal kicks. For NS-like zone, transition zone, and BH-like zone, there are 123, 68, and 25 systems that satisfy this criterion, respectively.