Spatially resolved spectrophotometric SED modeling of NGC 253’s central molecular zone

I. Star formation in extragalactic giant molecular clouds

¹ Departamento de Astronomia, Instituto de Astronomia, Geofísica e Ciências Atmosféricas da USP, Cidade Universitária, 05508-090 São Paulo, SP, Brazil
² Astronomical Observatory of the Jagiellonian University, Orla 171, 30-244 Kraków, Poland
³ National Center for Nuclear Research, ul. Pasteura 7, 02-093 Warsaw, Poland
⁴ Scuola Internazionale Superiore di Studi Avanzati (SISSA), Via Bonomea 265, IT-34136 Trieste, Italy
⁵ Institute for Fundamental Physics of the Universe (IFPU), Via Beirut 2, IT-34151 Trieste, Italy
⁶ INAF – Osservatorio di Astrofisica e Scienza dello Spazio (OAS), Via Gobetti 93/3, I-40127 Bologna, Italy
⁷ ICSC – Centro Nazionale di Ricerca in High Performance Computing, Big Data e Quantum Computing, Via Magnanelli 2, Bologna, Italy
⁸ Universidade Federal de Santa Catarina, Campus Universitário Reitor João David Ferreira Lima, 88040-900 Florianópolis, SC, Brazil
⁹ European Southern Observatory, Alonso de Córdova, 3107, Vitacura, Santiago 763-0355, Chile
¹⁰ Joint ALMA Observatory, Alonso de Córdova, 3107, Vitacura Santiago 763-0355, Chile
¹¹ Centro de Estudios de Física del Cosmos de Aragón (CEFCA), Plaza San Juan 1, E–44001 Teruel, Spain
¹² Centro de Astrobiología (CAB), CSIC-INTA, Carretera de Ajalvir km 4, Torrejón de Ardoz, 28850 Madrid, Spain
¹³ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475, USA
¹⁴ Max-Planck-Institut für Radioastronomie, Auf-dem-Hügel 69, 53121 Bonn, Germany
¹⁵ Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 830011 Urumqi, China
¹⁶ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹⁷ Institute of Astronomy and Astrophysics, Academia Sinica, 11F of AS/NTU Astronomy-Mathematics Building, No.1, Sec. 4, Roosevelt Rd, Taipei 106319, Taiwan
¹⁸ Department of Astronomy, School of Science, The Graduate University for Advanced Studies (SOKENDAI), 2-21-1 Osawa, Mitaka, Tokyo 181-1855, Japan
¹⁹ Institute of Astrophysics, Facultad de Ciencias Exactas, Universidad Andrés Bello, Sede Concepción, Talcahuano, Chile
²⁰ New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, NM 87801, USA
²¹ International Gemini Observatory/NSF NOIRLab, Casilla 603, La Serena, Chile
²² Instituto de Astrofísica de La Plata, CONICET-UNLP, Paseo del Bosque s/n, La Plata B1900FWA, Argentina
²³ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, SE-43992 Onsala, Sweden
²⁴ Department of Physics, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Yokohama, Kanagawa 223–8522, Japan
²⁵ Institute of Astronomy, Graduate School of Science, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan
²⁶ NOAO, 950 North Cherry Ave., Tucson, AZ 85719, United States
²⁷ GMTO Corporation, N. Halstead Street 465, Suite 250, Pasadena, CA 91107, United States

^⋆ Corresponding author: pedrokhumire@usp.br

Received: 25 January 2025
Accepted: 14 May 2025

Abstract

Context. Studying the interstellar medium in nearby starbursts is essential for gaining insights into the physical mechanisms driving these extreme objects, which are thought to be analogs of young, primeval, star-forming galaxies. This task is now feasible due to deep spectro-photometric data enabled by rapid advancements in ground- and space-based facilities. To fully leverage this wealth of information, extracting insights from the spectral line properties and the spectral energy distribution (SED) is imperative.

Aims. This study aims to produce and analyze the physical properties of the first spatially resolved multiwavelength SED of an extragalactic source that covers six decades in frequency (from near-ultraviolet, NUV, to centimeter, cm, wavelengths) at an angular resolution of 3″, which corresponds to a linear scale of ∼51 pc at the distance of NGC 253. We focus on the central molecular zone (CMZ) of this starburst galaxy, which contains giant molecular clouds (GMCs) responsible for half of the galaxy’s star formation.

Methods. We retrieved archival data from near-UV to centimeter wavelengths, covering six decades of spectral range. We computed the SEDs to fit the observations, using the GalaPy code and confronting the results with the CIGALE code for validation. We also employed the STARLIGHT code to analyze the stellar optical spectra of the GMCs.

Results. Our results reveal significant differences between internal and external GMCs in terms of stellar and dust masses, star formation rates (SFRs), and bolometric luminosities, among others, with internal GMCs doubling maximum values of the external ones in most of the cases. We obtained tight relations between monochromatic stellar tracers and star-forming conditions obtained from panchromatic emission. We find that the best SFR tracers are radio continuum bands at 33 GHz, radio recombination lines (RRLs), and the total infrared (IR) luminosity range (L_IR; 8–1000 μm) as well as the IR emission at 60 μm. The emission line diagnostics based on the BPT and WHAN diagrams suggest that the nuclear region of NGC 253 exhibits shock signatures, placing it in the composite zone typically associated with hybrids of active galactic nucleus (AGN) hosting and star-forming regions, while the AGN fraction from panchromatic emission is negligible (≤7.5%).

Conclusions. Our findings demonstrate the significant heterogeneity within the CMZ of NGC 253, with central GMCs exhibiting high densities, elevated SFRs, and greater dust masses compared to their external counterparts. We confirm the effectiveness of certain centimeter photometric bands as a reliable method to estimate the global SFR, in accordance with previous studies – this time on GMC scales.