The halo of M 105 and its group environment as traced by planetary nebula populations

II. Using kinematics of single stars to unveil the presence of intragroup light around the Leo I galaxies NGC 3384 and M 105^⋆

¹ European Southern Observatory, Alonso de Cordova 3107 Vitacura, Casilla, 19001 Santiago de Chile, Chile
e-mail: jhartke@eso.org
² European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
³ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany
⁴ School of Physics and Astronomy, University of Nottingham, NG7 2RD Nottingham, UK
⁵ Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
⁶ DARK, Niels Bohr Institute, University of Copenhagen, Lyngbyvej 2, 2100 Copenhagen, Denmark
⁷ Inter University Centre for Astronomy and Astrophysics, Ganeshkhind, Post Bag 4, Pune 411007, India
⁸ Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
⁹ INAF – Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Naples, Italy
¹⁰ Departamento de Astronomia, Instituto de Astronomia, Geofisica e Ciencias Atmosfericas da USP, Cidade Universitaria, 05508900 Sao Paulo, Brazil
¹¹ Research School of Astronomy & Astrophysics Mount Stromlo Observatory, Cotter Road, 2611 Canberra, Australia
¹² School of Physics and Astronomy, Sun Yat-sen University, DaXue Road 2, 519082 Zhuhai, PR China
¹³ CSST Science Center for the Guangdong-Hongkong-Macau Greater Bay Area, DaXue Road 2, 519082 Zhuhai, PR China
¹⁴ Department of Physics & Astronomy, San José State University, One Washington Square, San Jose, CA 95192, USA
¹⁵ University of California Observatories, 1156 High St., Santa Cruz, CA 95064, USA
¹⁶ Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA

Received: 14 January 2022
Accepted: 14 February 2022

Abstract

Context. M 105 (NGC 3379) is an early-type galaxy in the nearby Leo I group, the closest galaxy group to contain all galaxy types and therefore an excellent environment to explore the low-mass end of intra-group light (IGL) assembly.

Aims. We present a new and extended kinematic survey of planetary nebulae (PNe) in M 105 and the surrounding 30′×30′ in the Leo I group with the Planetary Nebula Spectrograph (PN.S) to investigate kinematically distinct populations of PNe in the halo and the surrounding IGL.

Methods. We use PNe as kinematic tracers of the diffuse stellar light in the halo and IGL, and employ photo-kinematic Gaussian mixture models to (i) separate contributions from the companion galaxy NGC 3384, and (ii) associate PNe with structurally defined halo and IGL components around M 105.

Results. We present a catalogue of 314 PNe in the surveyed area and firmly associate 93 of these with the companion galaxy NGC 3384 and 169 with M 105. The PNe in M 105 are further associated with its halo (138) and the surrounding exponential envelope (31). We also construct smooth velocity and velocity dispersion fields and calculate projected rotation, velocity dispersion, and λ_R profiles for the different components. PNe associated with the halo exhibit declining velocity dispersion and rotation profiles as a function of radius, while the velocity dispersion and rotation of the exponential envelope increase notably at large radii. The rotation axes of these different components are strongly misaligned.

Conclusions. Based on the kinematic profiles, we identify three regimes with distinct kinematics that are also linked to distinct stellar population properties: (i) the rotating core at the centre of the galaxy (within 1R_eff) formed in situ and is dominated by metal-rich ([M/H] ≈ 0) stars that also likely formed in situ, (ii) the halo from 1 to 7.5R_eff consisting of a mixture of intermediate-metallicity and metal-rich stars ([M/H] > −1), either formed in situ or was brought in via major mergers, and (iii) the exponential envelope reaching beyond our farthest data point at 16R_eff, predominately composed of metal-poor ([M/H] < −1) stars. The high velocity dispersion and moderate rotation of the latter are consistent with those measured for the dwarf satellite galaxies in the Leo I group, indicating that this exponential envelope traces the transition to the IGL.