[en] We explore the detection, with upcoming spectroscopic surveys, of three-dimensional power spectra of emission line fluctuations produced in different phases of the interstellar medium (ISM) by forbidden transitions of ionized carbon [C ii] (157.7 μ m), ionized nitrogen [N ii] (121.9 and 205.2 μ m), and neutral oxygen [O i] (145.5 μ m) at redshift z  > 4. These lines are important coolants of both the neutral and the ionized medium, and probe multiple phases of the ISM. In the framework of the halo model, we compute predictions of the three-dimensional power spectra for two different surveys, showing that they have the required sensitivity to detect cross-power spectra between the [C ii] line and both the [O i] line and the [N ii] lines with sufficient signal-to-noise ratio. The importance of cross-correlating multiple lines with the intensity mapping technique is twofold. On the one hand, we will have multiple probes of the different phases of the ISM, which is key to understanding the interplay between energetic sources, and the gas and dust at high redshift. This kind of study will be useful for a next-generation space observatory such as the NASA Far-IR Surveyor, which will probe the global star formation and the ISM of galaxies from the peak of star formation to the epoch of reionization. On the other hand, emission lines from external galaxies are an important foreground when measuring spectral distortions of the cosmic microwave background spectrum with future space-based experiments like PIXIE; measuring fluctuations in the intensity mapping regime will help constrain the mean amplitude of these lines, and will allow us to better handle this important foreground.

[en] We present an analysis of far-infrared (FIR) dust emission from diffuse cirrus clouds. This study is based on serendipitous observations at 160 μm at high-galactic latitude with the Multiband Imaging Photometer onboard the Spitzer Space Telescope by the Spitzer Infrared Nearby Galaxies Survey. These observations are complemented with IRIS data at 100 and 60 μm and constitute one of the most sensitive and unbiased samples of FIR observations at a small scale of diffuse interstellar clouds. Outside regions dominated by the cosmic infrared background fluctuations, we observe a substantial scatter in the 160/100 colors from cirrus emission. We compared the 160/100 color variations to 60/100 colors in the same fields and find a trend of decreasing 60/100 with increasing 160/100. This trend cannot be accounted for by current dust models by changing solely the interstellar radiation field. It requires a significant change of dust properties such as grain size distribution or emissivity or a mixing of clouds in different physical conditions along the line of sight. These variations are important as a potential confusing foreground for extragalactic studies.

[en] A systematic investigation of dust emission associated with ionized gas has so far been performed only in our Galaxy and for wavelengths longer than 60 μm. Newly available Spitzer data now offer the opportunity to carry out a similar analysis in the Large Magellanic Cloud (LMC). By cross-correlating Spitzer Surveying the Agents of a Galaxy's Evolution (SAGE) data with the Australia Telescope Compact Array/Parkes H I 21 cm data, the NANTEN ¹²CO (J = 1-0) data, and both the Southern H-Alpha Sky Survey Atlas Hα and the Parkes 6 cm data, we investigate the physical properties of dust associated with the different phases of the gas (atomic, molecular, and ionized). In particular, we study the presence and nature of dust from 3.6 to 160 μm and for various regimes of ionized gas, spanning emission measures from ∼1 pc cm^-6 (diffuse component) to ∼10³pc cm^-6 (H II regions). Using a dust emission model and testing our results with several radiation field spectra, we show that dust in ionized gas is warmer than dust associated with other phases (atomic and molecular). We also find a decrease of the polycyclic aromatic hydrocarbon (PAH) relative abundance with respect to big grains, as well as an increase of the near-infrared (NIR) continuum. These three results (i.e., warmer temperature, decrease of PAH abundance, and increase of the NIR continuum) are found consistently for all regimes of ionized gas. On the contrary, the molecular phase appears to provide favorable conditions for the survival of PAHs. Furthermore, the very small grain relative abundance tends to increase in the ionized phase, especially in bright H II regions. Last but not least, our analysis shows that the emissivity of dust associated with ionized gas is lower in the LMC than in our Galaxy and that this difference is not accounted for by the lower metallicity of the LMC.

[en] We present ultra-deep mid-infrared spectra of 48 infrared-luminous galaxies in the GOODS-south field obtained with the Infrared Spectrograph on the Spitzer Space Telescope. These galaxies are selected among faint infrared sources (0.14-0.5 mJy at 24 μm) in two redshift bins (0.76-1.05 and 1.75-2.4) to sample the major contributors to the cosmic infrared background at the most active epochs. We estimate redshifts for 92% of the sample using polycyclic aromatic (PAH) and Si absorption features obtaining, in particular, eight new redshifts difficult to measure from ground-based observations. Only a few of these galaxies (5% at z ∼ 1 and 12% at z ∼ 2) have their total infrared luminosity dominated by emission from active galactic nuclei (AGNs). The averaged mid-IR spectrum of the z ∼ 1 luminous infrared galaxies (LIRGs) is a very good match to the averaged spectrum of local starbursts. The averaged spectrum of the z ∼ 2 ultra-luminous infrared galaxies (ULIRGs), because of a deeper Si absorption, is better fitted by the averaged spectrum of H II-like local ULIRGs. Combining this sample with other published data, we find that 6.2 μm PAH equivalent widths (EW) reach a plateau of ∼ 1 μm for L _24μm ∼< 10¹¹ L_sun. At higher luminosities, EW_6.2μm anti-correlates with L_24μm. Intriguingly, high-z ULIRGs and sub-millimeter galaxies (SMGs) lie above the local EW_6.2μm-L_24μm relationship suggesting that, at a given luminosity, high-z ULIRGs have AGN contributions to their dust emission lower than those of local counterparts. A quantitative analysis of their morphology shows that most of the luminous IR galaxies have morphologies similar to those of IR-quiet galaxies at the same redshift. All z ∼ 2 ULIRGs of our sample are IR-excess BzK galaxies and most of them have L_FIR/L_1600A ratios higher than those of starburst galaxies at a given UV slope. The 'IR excess' is mostly due to strong 7.7 μm PAH emission and underestimation of UV dust extinction. On the basis of the AGN-powered L _6μm continuum measured directly from the mid-IR spectra, we estimate an average intrinsic X-ray AGN luminosity of L_2-10keV = (0.1± 0.6)x 10⁴³ erg s^-1, a value substantially lower than the prediction by Daddi et al.

[en] We reproduce the mid-infrared to radio galaxy counts with a new empirical model based on our current understanding of the evolution of main-sequence (MS) and starburst (SB) galaxies. We rely on a simple spectral energy distribution (SED) library based on Herschel observations: a single SED for the MS and another one for SB, getting warmer with redshift. Our model is able to reproduce recent measurements of galaxy counts performed with Herschel, including counts per redshift slice. This agreement demonstrates the power of our 2-Star-Formation Modes (2SFM) decomposition in describing the statistical properties of infrared sources and their evolution with cosmic time. We discuss the relative contribution of MS and SB galaxies to the number counts at various wavelengths and flux densities. We also show that MS galaxies are responsible for a bump in the 1.4 GHz radio counts around 50 μJy. Material of the model (predictions, SED library, mock catalogs, etc.) is available online.

[en] We report on-off pointed MAMBO observations at 1.2 mm of 61 Spitzer-selected star-forming galaxies from the Spitzer Wide Area Infrared Extragalactic Legacy survey (SWIRE). The sources are selected on the basis of bright 24 μm fluxes (f _24μm > 0.4 mJy) and of stellar dominated near-infrared spectral energy distributions in order to favor z ∼ 2 starburst galaxies. The average 1.2 mm flux for the whole sample is 1.5 ± 0.2 mJy. Our analysis focuses on 29 sources in the Lockman Hole field where the average 1.2 mm flux (1.9 ± 0.3 mJy) is higher than in other fields (1.1 ± 0.2 mJy). The analysis of the multiwavelength spectral energy distributions indicates that these sources are starburst galaxies with far-infrared luminosities from 10¹² to 10^13.3 L _sun, and stellar masses of ∼0.2-6 x 10¹¹ M _sun. Compared to submillimeter selected galaxies (SMGs), the SWIRE-MAMBO sources are among those with the largest 24 μm/1.2 mm flux ratios. The origin of such large ratios is investigated by comparing the average mid-infrared spectra and the stacked far-infrared spectral energy distributions of the SWIRE-MAMBO sources and of SMGs. The mid-infrared spectra, available for a handful of sources, exhibit strong polycyclic aromatic hydrocarbon (PAH) features, and a warm dust continuum. The warm dust continuum contributes ∼34% of the mid-infrared emission, and is likely associated with an AGN component. This contribution is consistent with what is found in SMGs. The large 24 μm/1.2 mm flux ratios are thus not due to AGN emission, but rather to enhanced PAH emission compared to SMGs. The analysis of the stacked far-infrared fluxes yields warmer dust temperatures than typically observed in SMGs. Our selection favors warm ultraluminous infrared sources at high-z, a class of objects that is rarely found in SMG samples. Indeed SMGs are not common among bright 24 μm sources (e.g., only about 20% of SMGs have f _24μm > 0.4 mJy). Our sample is the largest Spitzer-selected sample detected at millimeter wavelengths currently available.