Tuesday, 4/23/13

Not a ton of stuff today, but two papers worth noting that are at the beginning of what some biggish projects will produce. The first is the CALIFA project which is obtaining optical IFU spectroscopy on 600 near-ish by galaxies. The paper, Cid Fernandez et al., describes how they are taking the spectra and processing them to obtain quantities like stellar mass surface density and star formation surface density. The second project is from the HETDEX pilot survey, which has measured [OII] star formation rates for galaxies between z=0.5 and now. Does anyone know why/if I should be particularly impressed that they have [OII] SFRs as opposed to SFRs measured in another way?
-Alison

Title: Resolving galaxies in time and space: I: Applying STARLIGHT to CALIFA data cubes
Authors: Cid Fernandes, R.; Perez, E.; Garcia Benito, R.; Gonzalez Delgado, R. M.; de Amorim, A. L.; Sanchez, S. F.; Husemann, B.; Falcon Barroso, J.;Sanchez-Blazquez, P.; Walcher, C. J.; Mast, D.
Publication: eprint arXiv:1304.5788
Bibliographic Code: 2013arXiv1304.5788C

Abstract

Fossil record methods based on spectral synthesis techniques have matured over the past decade, and their application to integrated galaxy spectra fostered substantial advances on the understanding of galaxies and their evolution. Yet, because of the lack of spatial resolution, these studies are limited to a global view, providing no information about the internal physics of galaxies. Motivated by the CALIFA survey, which is gathering Integral Field Spectroscopy over the full optical extent of 600 galaxies, we have developed an end-to-end pipeline which: (i) partitions the observed data cube into Voronoi zones in order to, when necessary and taking due account of correlated errors, increase the S/N, (ii) extracts spectra, including propagated errors and bad-pixel flags, (iii) feeds the spectra into the STARLIGHT spectral synthesis code, (iv) packs the results for all galaxy zones into a single file, (v) performs a series of post-processing operations, including zone-to-pixel image reconstruction and unpacking the spectral and stellar population properties into multi-dimensional time, metallicity, and spatial coordinates. This paper provides an illustrated description of this whole pipeline and its products. Using data for the nearby spiral NGC 2916 as a show case, we go through each of the steps involved, presenting ways of visualizing and analyzing this manifold. These include 2D maps of properties such as the v-field, stellar extinction, mean ages and metallicities, mass surface densities, star formation rates on different time scales and normalized in different ways, 1D averages in the temporal and spatial dimensions, projections of the stellar light and mass growth (x,y,t) cubes onto radius-age diagrams, etc. The results illustrate the richness of the combination of IFS data with spectral synthesis, providing a glimpse of what is to come from CALIFA and future surveys. (Abridged)

Title: The HETDEX Pilot Survey. IV. The Evolution of [O II] Emitting Galaxies from z ~ 0.5 to z ~ 0
Authors: Ciardullo, Robin; Gronwall, Caryl; Adams, Joshua J.; Blanc, Guillermo A.; Gebhardt, Karl; Finkelstein, Steven L.; Jogee, Shardha; Hill, Gary J.;Drory, Niv; Hopp, Ulrich; Schneider, Donald P.; Zeimann, Gregory R.; Dalton, Gavin B.
Bibliographic Code: 2013arXiv1304.5537C

Abstract

We present an analysis of the luminosities and equivalent widths of the 284 z < 0.56 [O II]-emitting galaxies found in the 169 square arcmin pilot survey for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). By combining emission-line fluxes obtained from the Mitchell spectrograph on the McDonald 2.7-m telescope with deep broadband photometry from archival data, we derive each galaxy’s de-reddened [O II] 3727 luminosity and calculate its total star formation rate. We show that over the last ~5 Gyr of cosmic time there has been substantial evolution in the [O II] emission-line luminosity function, with L* decreasing by ~0.6 +/-0.2 dex in the observed function, and by ~0.9 +/-0.2 dex in the de-reddened relation. Accompanying this decline is a significant shift in the distribution of [O II] equivalent widths, with the fraction of high equivalent-width emitters declining dramatically with time. Overall, the data imply that the relative intensity of star formation within galaxies has decreased over the past ~5 Gyr, and that the star formation rate density of the universe has declined by a factor of ~2.5 between z ~ 0.5 and z ~ 0. These observations represent the first [O II]-based star formation rate density measurements in this redshift range, and foreshadow the advancements which will be generated by the main HETDEX survey.

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