Halpha3: an Halpha imaging survey of HI selected galaxies from ALFALFA. III. Nurture shapes up the Hubble sequence in the Great Wall

TL;DR

This study uses Halpha imaging to examine how environment influences galaxy evolution in the Coma Supercluster, revealing a sequence of gas depletion and star formation quenching driven by environmental factors like ram-pressure stripping.

Contribution

It provides a detailed observational sequence linking gas content, star formation, and morphology in galaxies affected by environment, highlighting ram-pressure as a key transformation mechanism.

Findings

Identification of a four-step galaxy sequence based on gas content and star formation.

Evidence that environmental effects cause radial outside-in quenching of star formation.

Estimation that 100 low-mass galaxies are accreted into the Coma cluster per Gyr over 7.5 Gyr.

Abstract

We present the analysis of Halpha3, an Halpha imaging survey of galaxies selected from the HI ALFALFA Survey in the Coma Supercluster. By using the Halpha line as a tracer of the "instantaneous" star formation, complemented with optical colors from SDSS we explore the hypothesis that a morphological sequence of galaxies of progressively earlier type, lower gas-content exists in the neighborhood of the Coma cluster, with specific star formation activity decreasing with increasing local galaxy density and velocity dispersion. In the dwarf regime (8.5<\log(M*)< 9.5) we identify a 4-step sequence of galaxies with progressively redder colors, i.e. of decreasing specific star formation, from (1) HI-rich Late-Type Galaxies belonging to the blue-cloud exhibiting extended plus nuclear star formation, (2) HI-poor LTGs with nuclear star formation only, (3) HI-poor galaxies with no star formation either extended or nuclear, but with nuclear Post-Star-Burst signature,(4) Early-type Galaxies in the red-sequence, with no gas or star formation on all scales. Along this sequence the quenching of the star formation proceeds radially outside-in. The progression toward redder colors found along this "morphological" (gas content) sequence is comparable to the one obtained increasing the local galaxy density, from the cosmic filaments (1,2), to the rich clusters (2,3,4). In the dwarf regime we find evidence for evolution of HI-rich LTGs into ETGs, passing through HI-poor and PSB galaxies, driven by the environment. We identify ram-pressure as the mechanism most likely responsible for this transformation. We conclude that infall of low-mass galaxies has proceeded for the last 7.5 Gyr building up the Coma cluster at a rate of approximately 100 galaxies per Gyr.