Measurement of the Half-Light Radius for the Tucana Dwarf Spheroidal Galaxy

TL;DR

This work delivers a refined measurement of the Tucana Dwarf galaxy’s half-light radius by combining deep, wide-field LoVoCCS DECam imaging with archival HST data. Through elliptical fitting of the central region, construction of composite stellar density profiles, and a Sérsic model fit to the combined density distribution, the authors obtain a half-light radius of $R_{e} = 0.89_{-0.02}^{+0.06}$ arcmin, translating to $R_{e} = 225.7_{-5.5}^{+14.4}$ pc at a distance of 870 kpc. The result, about 10% larger than previous estimates, benefits from the extended radial coverage that reveals a flattened background and reduces background-related uncertainties via bootstrapping. This improved structural constraint enhances prospects for linking Tucana’s stellar distribution to its dark matter halo, though spectroscopic follow-up is needed to robustly translate the density profile into a dynamical mass estimate and dark matter constraints.

Abstract

We present a new measurement of the half-light radius of the Tucana Dwarf galaxy, based on the combination of wider, deeper imaging conducted as part of the Local Volume Complete Cluster Survey (LoVoCCS) and HST archival images. We obtain a stellar density profile within the Tucana Dwarf field based on elliptical fitting. After background subtraction, we fit a Sérsic profile to the density profile to obtain the half-light radius. We measure the half-light radius to be $0.89_{-0.02}^{+0.06}$ arcmin, corresponding to a value of $R_{e} = 225.7_{-5.5}^{+14.4}$ pc (95% CL). Given the wider-field observations from LoVoCCS used in this analysis, our measurement of the half-light radius represents a $\sim 10 \%$ increased value from the previous results.

Figures (6)

• Figure 1: ACS/WFC F475W band image of Tucana Dwarf from HST Proposal GO-10505.
• Figure 2: Cropped view of Tucana Dwarf from stacked $i$, $r$, $g$ band images, captured by DECam, processed with the LoVoCCS processing pipeline.
• Figure 3: $r$-$i$ vs. $g$-$r$ color-color diagram used to filter for objects consistent with stellar sources in the Tucana Dwarf galaxy. The solid curves show the upper and lower bound criteria for which we made our selection of sources.
• Figure 4: Spatial distribution of objects excluded in color cut selection, outside of first central annulus for which HST data is used. Grey elliptical curves show boundaries for elliptical bins.
• Figure 5: The preliminary Sérsic profile fitting over stellar density profiles calculated based on (top) combined LoVoCCS and HST data, and (bottom) HST-only data. The shaded regions indicate area under the curve out to the effective (or, half-light) radii obtained from the two different Sérsic fits, which are $r_{eff} = 0.0344\degree$ from the combined data and $r_{eff} = 0.0473\degree$ from HST data alone.