Spectral Line De-confusion in an Intensity Mapping Survey

Spectral line intensity mapping has been proposed as a promising tool to efficiently probe the cosmic reionization and the large-scale structure. Without detecting individual sources, line intensity mapping makes use of all available photons and measures the integrated light in the source confusion limit, to efficiently map the three-dimensional matter distribution on large scales as traced by a given emission line. One particular challenge is the separation of desired signals from astrophysical continuum foregrounds and line interlopers. Here we present a technique to extract large-scale structure information traced by emission lines from different redshifts, embedded in a three-dimensional intensity mapping data cube. The line redshifts are distinguished by the anisotropic shape of the power spectra when projected onto a common coordinate frame. We consider the case where high-redshift [CII] lines are confused with multiple low-redshift CO rotational lines. We present a semi-analytic model for [CII] and CO line estimates based on the cosmic infrared background measurements, and show that with a modest instrumental noise level and survey geometry, the large-scale [CII] and CO power spectrum amplitudes can be successfully extracted from a confusion-limited data set, without external information. We discuss the implications and limits of this technique for possible line intensity mapping experiments.Comment: 13 pages, 14 figures, accepted by Ap

The Origins Space Telescope

The Origins Space Telescope, one of four large Mission Concept Studies sponsored by NASA for review in the 2020 US Astrophysics Decadal Survey, will open unprecedented discovery space in the infrared, unveiling our cosmic origins

Constraining the ISM Properties of the Cloverleaf Quasar Host Galaxy with Herschel Spectroscopy

We present Herschel observations of the far-infrared (FIR) fine-structure (FS) lines [C II]158 μm, [O I]63 μm, [O III]52 μm, and [Si II]35 μm in the z = 2.56 Cloverleaf quasar, and combine them with published data in an analysis of the dense interstellar medium (ISM) in this system. Observed [C II]158 μm, [O I]63 μm, and FIR continuum flux ratios are reproduced with photodissociation region (PDR) models characterized by moderate far-ultraviolet (FUV) radiation fields with G_0 = 0.3–1 × 10^3 and atomic gas densities n_H = 3–5 × 10^3 cm^(−3), depending on contributions to [C II]158 μm from ionized gas. We assess the contribution to the [C II]158 μm flux from an active galactic nucleus (AGN) narrow line region (NLR) using ground-based measurements of the [N II]122 μm transition, finding that the NLR can contribute at most 20%–30% of the observed [C II]158 μm flux. The PDR density and far-UV radiation fields inferred from the atomic lines are not consistent with the CO emission, indicating that the molecular gas excitation is not solely provided via UV heating from local star formation (SF), but requires an additional heating source. X-ray heating from the AGN is explored, and we find that X-ray-dominated region (XDR) models, in combination with PDR models, can match the CO cooling without overproducing the observed FS line emission. While this XDR/PDR solution is favored given the evidence for both X-rays and SF in the Cloverleaf, we also investigate alternatives for the warm molecular gas, finding that either mechanical heating via low-velocity shocks or an enhanced cosmic-ray ionization rate may also contribute. Finally, we include upper limits on two other measurements attempted in the Herschel program: [C II]158 μm in FSC 10214 and [O I]63 μm in APM 08279+5255

SPIFI: a Direct-Detection Imaging Spectrometer for Submillimeter Wavelengths

The South Pole Imaging Fabry-Perot Interferometer (SPIFI) is the first instrument of its kind -a direct-detection imaging spectrometer for astronomy in the submillimeter band. SPIFI ’s focal plane is a square array of 25 silicon bolometers cooled to 60 mK; the spectrometer consists of two cryogenic scanning Fabry-Perot interferometers in series with a 60-mK bandpass filter. The instrument operates in the short submillimeter windows (350 and 450 μm) available from the ground, with spectral resolving power selectable between 500 and 10,000. At present, SPIFI’s sensitivity is within a factor of 1.5-3 of the photon background limit, comparable with the best heterodyne spectrometers. The instrument ’s large bandwidth and mapping capability provide substantial advantages for specific astrophysical projects, including deep extragalactic observations. We present the motivation for and design of SPIFI and its operational characteristics on the telescope

Investigating Overdensities around z > 6 Galaxies through ALMA Observations of [C II]

We present a search for companion [C II] emitters to known luminous sources at 6 < z < 6.5 in deep, archival ALMA observations. The observations are deep enough to detect sources with L_([CII])∼10⁸ at z ∼6. We identify three new robust line detections from a blind search of five deep fields centered on ultraluminous infrared galaxies and QSOs. We calculate the volume density of companions and find a relative overdensity of 6⁺⁴₋₃ and 86⁺⁶⁰₋₃₇ when comparing to current observational constraints and theoretical predictions, respectively. These results suggest that the central sources may be highly biased tracers of mass in the early universe. We find these companion lines to have comparable properties to other known galaxies at the same epoch. All companions lie less than 650 km s⁻¹ and between 25 and 60 kpc (projected) from their central source. To place these discoveries in context, we employ a mock galaxy catalog to estimate the luminosity function for [C II] during reionization and compare to our observations. The simulations support this result by showing a similar level of elevated counts found around such luminous [C II] sources

A Foreground Masking Strategy for [CII] Intensity Mapping Experiments Using Galaxies Selected by Stellar Mass and Redshift

Intensity mapping provides a unique means to probe the epoch of reionization (EoR), when the neutral intergalactic medium was ionized by the energetic photons emitted from the first galaxies. The [CII] 158$\mu$m fine-structure line is typically one of the brightest emission lines of star-forming galaxies and thus a promising tracer of the global EoR star-formation activity. However, [CII] intensity maps at $6 \lesssim z \lesssim 8$ are contaminated by interloping CO rotational line emission ($3 \leq J_{\rm upp} \leq 6$) from lower-redshift galaxies. Here we present a strategy to remove the foreground contamination in upcoming [CII] intensity mapping experiments, guided by a model of CO emission from foreground galaxies. The model is based on empirical measurements of the mean and scatter of the total infrared luminosities of galaxies at $z 10^{8}\,\rm M_{\rm \odot}$ selected in $K$-band from the COSMOS/UltraVISTA survey, which can be converted to CO line strengths. For a mock field of the Tomographic Ionized-carbon Mapping Experiment (TIME), we find that masking out the "voxels" (spectral-spatial elements) containing foreground galaxies identified using an optimized CO flux threshold results in a $z$-dependent criterion $m^{\rm AB}_{\rm K} \lesssim 22$ (or $M_{*} \gtrsim 10^{9} \,\rm M_{\rm \odot}$) at $z < 1$ and makes a [CII]/CO$_{\rm tot}$ power ratio of $\gtrsim 10$ at $k=0.1$ $h$/Mpc achievable, at the cost of a moderate $\lesssim 8\%$ loss of total survey volume.Comment: 14 figures, 4 tables, re-submitted to ApJ after addressing reviewer's comments. Comments welcom

The Origins Space Telescope

The Origins Space Telescope, one of four large Mission Concept Studies sponsored by NASA for review in the 2020 US Astrophysics Decadal Survey, will open unprecedented discovery space in the infrared, unveiling our cosmic origins

A complete view of galaxy evolution: panchromatic luminosity functions and the generation of metals

When and how did galaxies form and their metals accumulate? Over the last decade, this has moved from an archeological question to a live investigation: there is now a broad picture of the evolution of galaxies in dark matter halos: their masses, stars, metals and supermassive blackholes. Galaxies have been found and studied in which these formation processes are taking place most vigorously, all the way back in cosmic time to when the intergalactic medium (IGM) was still largely neutral. However, the details of how and why the interstellar medium (ISM) in distant galaxies cools, is processed, recycled and enriched in metals by stars, and fuels active galactic nuclei (AGNs) remain uncertain. In particular, the cooling of gas to fuel star formation, and the chemistry and physics of the most intensely active regions is hidden from view at optical wavelengths, but can be seen and diagnosed at mid- & far-infrared (IR) wavelengths. Rest-frame IR observations are important first to identify the most luminous, interesting and important galaxies, secondly to quantify accurately their total luminosity, and finally to use spectroscopy to trace the conditions in the molecular and atomic gas out of which stars form. In order to map out these processes over the full range of environments and large-scale structures found in the universe - from the densest clusters of galaxies to the emptiest voids - we require tools for deep, large area surveys, of millions of galaxies out to z~5, and for detailed follow-up spectroscopy. The necessary tools can be realized technically. Here, we outline the requirements for gathering the crucial information to build, validate and challenge models of galaxy evolution.Comment: A whitepaper submitted on 15th February 2009 in response to the call from the Astro2010 panel: astro2010.org; uploaded as an 8-page pdf fil

Modeling a large submillimeter-wave observatory

The 25 meter aperture Cornell Caltech Atacama Telescope (CCAT) will provide an enormous increase in sensitivity in the submillimeter bands compared to existing observatories, provided it can establish and maintain excellent image quality. To accomplish this at a very low cost, it is necessary to conduct accurate engineering trades, including the most effective segment and wavefront sensing and control approach, to determine the best method for continuously maintaining wavefront quality in the operational environment. We describe an integrated structural/optical/controls model that provides accurate performance prediction. We also detail the analysis methods used to quantify critical design trades