Unbiased large spectroscopic surveys of galaxies selected by SPICA using dust bands

TL;DR

This paper evaluates the potential of SPICA's low-resolution mid-infrared spectroscopic surveys to study galaxy evolution, star formation, and black hole activity across cosmic time by detecting spectral features like PAHs and dust continuum.

Contribution

It provides estimates of galaxy detection numbers at various redshifts for planned SPICA surveys, highlighting their capability to produce large, valuable spectral samples for galaxy evolution studies.

Findings

Estimated detection of galaxies at z > 0.5 in PAH features and dust continuum.

Predicted detection of debris disks around nearby stars.

Demonstrated efficiency of SPICA surveys in collecting large spectral datasets.

Abstract

The mid-infrared (IR) range contains many spectral features associated with large molecules and dust grains such as polycyclic aromatic hydrocarbons (PAHs) and silicates. These are usually very strong compared to fine-structure gas lines, and thus valuable in studying the spectral properties of faint distant galaxies. In this paper, we evaluate the capability of low-resolution mid-IR spectroscopic surveys of galaxies that could be performed by SPICA. The surveys are designed to address the question how star formation and black hole accretion activities evolved over cosmic time through spectral diagnostics of the physical conditions of the interstellar/circumnuclear media in galaxies. On the basis of results obtained with Herschel far-IR photometric surveys of distant galaxies and Spitzer and AKARI near- to mid-IR spectroscopic observations of nearby galaxies, we estimate the numbers of the galaxies at redshift z > 0.5, which are expected to be detected in the PAH features or dust continuum by a wide (10 deg^2) or deep (1 deg^2) blind survey, both for a given observation time of 600 hours. As by-products of the wide blind survey, we also expect to detect debris disks, through the mid-IR excess above the photospheric emission of nearby main-sequence stars, and we estimate their number. We demonstrate that the SPICA mid-IR surveys will efficiently provide us with unprecedentedly large spectral samples, which can be studied further in the far-IR with SPICA.