A1 Refereed original research article in a scientific journal
Unveiling UV-bright stellar populations in red and dead galaxies with CUBES
Authors: Ali Sadman Shariar, De Propris Roberto
Publisher: SPRINGER
Publication year: 2023
Journal: Experimental Astronomy
Journal name in source: EXPERIMENTAL ASTRONOMY
Journal acronym: EXP ASTRON
Number of pages: 9
ISSN: 0922-6435
eISSN: 1572-9508
DOI: https://doi.org/10.1007/s10686-022-09849-6
Web address : https://link.springer.com/article/10.1007/s10686-022-09849-6
Abstract
Early-type galaxies (ETGs) exhibit a rise in their UV flux shortward of 3000 angstrom, a phenomenon dubbed the UV upturn. It is believed that this UV flux in such old systems is driven by highly evolved hot horizontal branch (HB) stars, which are not expected to exist given standard cosmological timescales. However, observations of the evolution of the upturn with redshift suggests that the HB stars could potentially become UV-bright through a process of Helium enhancement, similar to what is observed in the multiple stellar populations of local globular clusters (GC). A highly sensitive UV detector such as CUBES can allow for the analysis of the CN and CH lines between 3000 - 4000 angstrom in local ETGs, as He-rich populations are also found to be heavily enhanced in Nitrogen and have a radial gradient in [N/Fe] (i.e. the Nitrogen is centrally concentrated) in GCs. If the same correlations are recovered in ETGs, it would suggest that the He-enhancement in both systems arose through a universal mechanism and thus have similar formation channels. Furthermore, at slightly higher redshifts (0.2 < z < 0.6), CUBES will allow us to probe directly the rest-frame near-UV indices of ETGs, particularly between 2200 - 3200 angstrom, which consist of the majority of spectral lines driven by the hot HB population and hence can be used to study its intrinsic properties (e.g. temperature, strength, etc). Current detectors require in excess of 20 hours of integration time to observe the brightest ETGs to a sufficient depth in this wavelength range, necessitating a highly efficient multiplexed UV sensitive spectrograph such as CUBES to make further progress, with the potential of improving exposure times by at least a factor of 2 and allowing for nearly all galaxies at or above L* in a given cluster to be simultaneously observed with multi-object spectroscopy.
Early-type galaxies (ETGs) exhibit a rise in their UV flux shortward of 3000 angstrom, a phenomenon dubbed the UV upturn. It is believed that this UV flux in such old systems is driven by highly evolved hot horizontal branch (HB) stars, which are not expected to exist given standard cosmological timescales. However, observations of the evolution of the upturn with redshift suggests that the HB stars could potentially become UV-bright through a process of Helium enhancement, similar to what is observed in the multiple stellar populations of local globular clusters (GC). A highly sensitive UV detector such as CUBES can allow for the analysis of the CN and CH lines between 3000 - 4000 angstrom in local ETGs, as He-rich populations are also found to be heavily enhanced in Nitrogen and have a radial gradient in [N/Fe] (i.e. the Nitrogen is centrally concentrated) in GCs. If the same correlations are recovered in ETGs, it would suggest that the He-enhancement in both systems arose through a universal mechanism and thus have similar formation channels. Furthermore, at slightly higher redshifts (0.2 < z < 0.6), CUBES will allow us to probe directly the rest-frame near-UV indices of ETGs, particularly between 2200 - 3200 angstrom, which consist of the majority of spectral lines driven by the hot HB population and hence can be used to study its intrinsic properties (e.g. temperature, strength, etc). Current detectors require in excess of 20 hours of integration time to observe the brightest ETGs to a sufficient depth in this wavelength range, necessitating a highly efficient multiplexed UV sensitive spectrograph such as CUBES to make further progress, with the potential of improving exposure times by at least a factor of 2 and allowing for nearly all galaxies at or above L* in a given cluster to be simultaneously observed with multi-object spectroscopy.
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