To assess the quality of the data and demonstrate the feasibility of the science goals, in Iodice et al. 2023 (LEWIS paper I), we have published the preliminary results obtained for one of the sample galaxies: UDG11.

For this target, we 

• derived the stellar kinematics, including the 2D maps of line-of-sight velocity and velocity dispersion,

• constrained age and metallicity, 

• studied the GCs population hosted by the UDG. 

1D integrated stellar kinematics for UDG11

By fitting the stacked spectrum inside 1Re with ppxf algorithm over the full MUSE rest-frame wavelength range (4800 − 9000 Å), we obtained  

• Systemic velocity: Vsys=3507±3 km/s

• Effective velocity dispersion: σe = 20 ± 8 km/s

2D kinematic maps for UDG11

The spatially resolved stellar kinematics, obtained from the Voronoi-binned spectra with signal-to-noise ratio S/N = 10, suggests that UDG11 does not show a significant gradient of Vsys and σLOS along major and minor photometric axes (see lower panels). 

The mean value of the velocity dispersion is σe = 27 ± 8 km/s, which is consistent with the estimate from the fit of the stacked spectrum inside 1Re.

Stellar population for UDG11

GC content in UDG11

Stellar kinematics of UDG1 

Integrated stellar kinematics: We started performing an isophotal analysis on the white image to recover the orientation of the galaxy. Once recovered the mean ellipticity and position angle, we extracted the 1D stacked spectrum within an elliptical aperture with semi-major axis equal to 1Re and we fitted with ppxf algorithm the stacked spectrum to derive the systemic velocity (Vsys) and the effective velocity dispersion (σe). We masked the noisy regions and spectral ranges contaminated by sky residuals and tested the convergence of the fitted parameters over a grid of possible additive and multiplicative Legendre polynomial degrees.

Spatially-resolve stellar kinematics: We applied Voronoi binning on the MUSE cube after masking the regions contaminated by nearby sources to obtain high S/N spectra. We applied the same strategy for the 1D case, using the same spectral mask and set of additive and multiplicative Legendre polynomial degrees. We finally extracted the rotation curve along the major photometric axis and recover its amplitude (∆V).

Distributions of σe and ∆V

The average values for σe range in 20 - 50 km/s, consistent with literature data. In LEWIS, we detected two distinct kinematic classes: UDGs with clear sign of stellar rotation and UDGs with no stellar rotation.

Scaling relations

In LEWIS, some UDGs are consistent with the Faber-Jackson relation, some have σe higher/lower than predicted one. UDGs have a dark matter content higher than dwarfs with similar luminosities

Kinematic support of UDGs in LEWIS

UDG 32 was discovered in projection with the stellar filaments of jellyfish galaxy NGC 3314A (Iodice+2021) and is the faintest and most diffuse UDG in the LEWIS sample (μ0,g ≈ 26 mag arcsec⁻², Re ∼3.8 kpc). 

From the analysis of new MUSE data from LEWIS, new emission lines (Hα, [O II], Hβ, [O III], [N II], [S II])  were discovered, probably connected with the stripped gas filaments of NGC3314A. In the pseudo-narrow band Hα image, UDG32 appears overlapped with the ram-pressure stripped tails. 

Analysis of emission lines knots

We identified 12 regions (knots) from the pseudo-narrow band Hα, and derived their spectra to analyse the nature and the type of ionisation. We built a BPT diagram to classify ionisation sources of each knot, and we found that 11 out of 12 knots are star-forming HII region regime, suggesting that these knots are sites of ongoing star-formation. The only knot in the "Not star-forming" regime is a background galaxy located at redshift of z = 0.77.

Stellar kinematics, stellar populations 

and GCs content of UDG32

We extract a spectrum from a circular aperture of radius 3′′ as close as possible to UDG32 but not overlapped with the Hα filaments. The extracted S/N of the spectrum (S/N ~ 3) does not allow to derive the velocity dispersion.

• Stellar kinematics: From the fitting of the spectrum with the ppxf algorithm, we derived: Vsys= 3081 ± 120 km/s. The value is consistent with the Hydra I south-east subgroup of galaxy and is very close with the systemic velociy of NGC3314A.

• Stellar populations: We derived the mean age and metallicity of UDG32 by performing a SED modeling with Bagpipes algorithm using multi-band photometry of UDG32. We obtained Age = 8+3 Gyr and [M/H] = 0.1+0.2 [dex]. UDG 32 is more metal-rich than other UDGs in the Hydra I cluster (Doll et al., submitted)  and field and cluster UDGs from the literature. 

• GC content: We additionally identified 2 GC candidates in the MUSE FOV of UDG32. We fitted their extracted spectra and we derived their systemic velocity (see left panel). Their velocities are consistent with Hydra I intracluster population and are not bound to UDG32.

On the formation channel of UDG32