Spiral-like patterns of star formation discovered in old galaxies
2016 November 22

Using data from the SDSS¹ and CALIFA² surveys, a team³ of astronomers, led by Jean Michel Gomes and Polychronis Papaderos from the Instituto de Astrofísica e Ciências do Espaço (IA⁴), in Portugal, discovered in the optical faint star-forming spiral-arm-like features in the periphery of nearby early-type galaxies⁵. This work⁶ was presented yesterday, during the 2nd SELGFIS Advanced School on Integral-Field Spectroscopic Data Analysis , ongoing in Madrid until the 25th of November 2016.

Usually, star-forming regions are blue areas, HII-regions that house short-lived massive blue stars, embedded in the disk section of spiral galaxies. In contrast, Elliptical and Lenticular galaxies (historically referred to as early-type galaxies) are composed of old stars with reddish colors, and are thought to be “dead” spheroids, no longer giving birth to new stars.

However, the CALIFA study led by the IA team has now discovered in the optical spiral features in the outskirts of three nearby early-type galaxies, which points to a still ongoing inside-out growth. This adds valuable observational insight into the origin and evolution of spiral structures in old spheroidal galaxies.

Jean Michel Gomes (IA & University of Porto), co-leader of the SELGIFS⁸ work package Reconstruction of the Star Formation History explains the novelty of this discovery: “According to our current view, grand design spiral-like features are associated with disc galaxies. These are, in general, regions of enhanced star formation. We were surprised to have discovered, for the first time in the optical, spiral-like structures in early-type galaxies, which we believed to have stopped forming stars in the last few billion years and should entirely lack spiral features.”

The discovery of faint spiral-like star-forming features in the periphery of early-type galaxies in this pilot study by Gomes and Papaderos has already motivated a further investigation of this issue by researchers at IA.

To Polychronis Papaderos (IA & University of Porto), founding member and Co-Investigator of SELGIFS and scientist in charge of its Portuguese node: “This study provides further observational evidence for a still ongoing growth of some seemingly “old and dead” early-type galaxies in the local Universe, out of a reservoir of cold gas that feeds low-level star-forming activity in their periphery”.

IA researchers Gomes and Papaderos, together with their PhD students Iris Breda and Sandra Reis, are leading a research within the CALIFA collaboration, on the properties of the diffusely distributed warm ionized gas in early-type galaxies. The main goal of this project is to evaluate the role of various possible gas excitation mechanisms in early-type galaxies.


NOTES:

1. The Sloan Digital Sky Survey (SDSS) has created the most detailed three-dimensional maps of the Universe ever made, with deep multi-color images of one third of the sky, and spectra for more than three million astronomical objects.

2. The Calar Alto Legacy Integral Field spectroscopy Area (CALIFA) survey is a project conceived at the Instituto de Astrofísica de Andalucía (IAA-CSIC) and carried out at the Calar Alto Observatory (Almeria, Spain) with the 3.5 meter reflecting telescope. It uses Integral Field Unit (IFU) spectroscopy, a technique that allows for the simultaneous observation of thousands of spectra per galaxy, thus producing a spatially resolved three dimensional view of its stars and ionized gas. CALIFA is the first IFU survey to make its data public.

3. The team is: J. M. Gomes, P. Papaderos, I. Breda, S. N. dos Reis (Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto), J. M. Vílchez, C. Kehrig, R. M. González Delgado, R. García-Benito, I. Márquez, A. del Olmo (Instituto de Astrofísica de Andalucía, CSIC), J. Iglesias-Páramo (Instituto de Astrofísica de Andalucía & Estación Experimental de Zonas Aridas, CSIC), M. D. Lehnert (Institut d’Astrophysique de Paris), S. F. Sánchez (Instituto de Astronomía, Universidad Nacional Autonóma de Mexico), B. Ziegler (University of Vienna), J. Bland-Hawthorn (Sydney Institute for Astronomy, University of Sydney), L. Galbany (Millennium Institute of Astrophysics & Departamento de Astronomía, Universidad de Chile), D. J. Bomans (Astronomical Institute of the Ruhr-University Bochum & RUB Research Department “Plasmas with Complex Interactions”), F. F. Rosales-Ortega (Instituto Nacional de Astrofísica, Óptica y Electrónica), C. J. Walcher (Leibniz-Institut für Astrophysik Potsdam – AIP), M. Mollá (CIEMAT), R. A. Marino (CEI Campus Moncloa, UCM-UPM, Departamento de Astrofísica y CC. de la Atmósfera, Facultad de CC. Físicas, Universidad Complutense de Madrid & Department of Physics, Institute for Astronomy, ETH Zürich), C. Catalán-Torrecilla (Departamento de Astrofísica y CC. de la Atmósfera, Universidad Complutense de Madrid), Á. R. López-Sánchez (Australian Astronomical Observatory & Department of Physics and Astronomy, Macquarie University), and the CALIFA Collaboration

4. The Instituto de Astrofísica e Ciências do Espaço (Institute of Astrophysics and Space Sciences – IA) is the largest Portuguese research unit of space sciences, which integrates researchers from University of Porto and University of Lisbon, and encompasses most of the field’s national scientific output. It was evaluated as Excellent in the last evaluation from the European Science Foundation (ESF). IA’s activity is funded by national and international funds, including Fundação para a Ciência e a Tecnologia (UID/FIS/04434/2013), POPH/FSE and FEDER through COMPETE 2020.

5. Early-type galaxies are Elliptical and Lenticular (S0) galaxies, with round or elliptical outlines. The “early-type” designation comes from the morphological classification of galaxies, originally created by Edwin Hubble and later expanded by Gérard de Vaucouleurs, which distinguishes galaxies between early-type (Elliptical and Lenticular), and late-type (spirals and irregulars), along a “tuning fork” diagram.

6. The article “Spiral-like star-forming patterns in CALIFA early-type galaxies” was published in the journal Astronomy & Astrophysics  (Vol. 585, A92 January 2016, DOI: 10.1051/0004-6361/201525974.

7. HII Regions are emission nebulae, giant clouds of ionized Hydrogen. The recent star formation that recently occurred in these clouds produced giant, short-lived blue stars, which emit massive amounts of ultraviolet radiation and ionizes the gas around them. In astronomy, the use of the Roman numeral refers to the ionization state, with “I” (Roman numeral for 1) representing a neutral element, “II” an ionized element (in this case, H+), “III” a doubly ionized element (for example Fe2+), and so on.

8. SELGIFS(Study of Emission-Line Galaxies with Integral-Field Spectroscopy) is an international collaboration focused on the study of emission-line galaxies with integral-field spectroscopy. It is funded under the Marie Curie Actions - International Research Staff Exchange Scheme (IRSES) FP7-PEOPLE-2013-IRSES-612701, and it involves institutions from Spain, Mexico, Portugal, Germany and Australia. The Portuguese node is led by Instituto de Astrofísica e Ciências do Espaço / University of Porto.