Spiral-like patterns of star formation discovered in old galaxies
Using data from the SDSS and CALIFA surveys, a team of astronomers, led by Jean Michel Gomes and Polychronis Papaderos from the Instituto de Astrofisica e Ciencias do Espaco (IA), in Portugal, discovered in the optical faint star-forming spiral-arm-like features in the periphery of nearby early-type galaxies. This work was presented yesterday, during the 2nd SELGFIS Advanced School on Integral-Field Spectroscopic Data Analysis, ongoing in Madrid until the 25th of November 2016.
|True color image of galaxy NGC 1167, overlaid with contours depicting the spiral-like |
star-forming regions [Credit: Gomes et al. (2016)]
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 SELGIFS 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."
|'Intensity' of the Equivalent Width in H alpha in galaxy NGC 1167, overlaid with contours depicting|
the spiral-like star-forming regions [Credit: Gomes et al. (2016)]
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.
Source: Instituto de Astrofisica e Ciencias do Espaco [November 23, 2016]