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arXiv · 1206.2645

Halpha Equivalent Widths from the 3D-HST survey: evolution with redshift and dependence on stellar mass

Mattia Fumagalli·Shannon G. Patel·Marijn Franx·Gabriel Brammer·Pieter van Dokkum·Elisabete da Cunha·Mariska Kriek·Britt Lundgren·Ivelina Momcheva·Hans-Walter Rix·Kasper B. Schmidt·Rosalind E. Skelton·Katherine E. Whitaker·Ivo Labbe·Erica Nelson
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Abstract

We investigate the evolution of the Halpha equivalent width, EW(Halpha), with redshift and its dependence on stellar mass, taking advantage of the first data from the 3D-HST survey, a large spectroscopic Treasury program with the Hubble Space Telescope WFC3. Combining our Halpha measurements of 854 galaxies at 0.8<z<1.5 with those of ground based surveys at lower and higher redshift, we can consistently determine the evolution of the EW(Halpha) distribution from z=0 to z=2.2. We find that at all masses the characteristic EW(Halpha) is decreasing towards the present epoch, and that at each redshift the EW(Halpha) is lower for high-mass galaxies. We measure a slope of EW(Halpha) ~ (1+z)^(1.8) with little mass dependence. Qualitatively, this measurement is a model-independent confirmation of the evolution of star forming galaxies with redshift. A quantitative conversion of EW(Halpha) to sSFR is very model dependent, because of differential reddening corrections between the continuum SED and the Balmer lines. The observed EW(Halpha) can be reproduced with a simple model in which the SFR for galaxies rises to the epoch of z~2.5 and then decreases with time to z = 0. The model implies that the EW(Halpha) rises to 400 A at z=8. The sSFR evolves faster than EW(Halpha), as the mass-to-light ratio also evolves with redshift. In this context, we find that the sSFR evolves as (1+z)^(3.2), nearly independent of mass, consistent with previous reddening insensitive estimates. We confirm previous results that the observed slope of the sSFR-z relation is steeper than the one predicted by models, but models and observations agree in finding little mass dependence.

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Mattia Fumagalli, Shannon G. Patel, Marijn Franx, Gabriel Brammer, Pieter van Dokkum, Elisabete da Cunha, Mariska Kriek, Britt Lundgren, Ivelina Momcheva, Hans-Walter Rix, Kasper B. Schmidt, Rosalind E. Skelton, Katherine E. Whitaker, Ivo Labbe, Erica Nelson. 2012-09-06. Halpha Equivalent Widths from the 3D-HST survey: evolution with redshift and dependence on stellar mass. https://doi.org/10.1088/2041-8205%2F757%2F2%2Fl22

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