We characterize infrared spectral energy distributions of 343 (Ultra) Luminous Infrared Galaxies from z = 0.3 − 2.8. We diagnose the presence of an AGN by decomposing individual Spitzer mid-IR spectroscopy into emission from star-formation and an AGN-powered continuum; we classify sources as star-forming galaxies (SFGs), AGN, or composites. Composites comprise 30% of our sample and are prevalent at faint and bright S 24 , making them an important source of IR AGN emission. We combine spectroscopy with multiwavelength photometry, including Herschel imaging, to create three libraries of publicly available templates (2-1000 µm). We fit the far-IR emission using a two temperature modified blackbody to measure cold and warm dust temperatures (T c and T w ). We find that T c does not depend on mid-IR classification, while T w shows a notable increase as the AGN grows more luminous. We measure a quadratic relationship between mid-IR AGN emission and total AGN contribution to L IR . AGN, composites, and SFGs separate in S 8 /S 3.6 and S 250 /S 24 , providing a useful diagnostic for estimating relative amounts of these sources. We estimate that >40% of IR selected samples host an AGN, even at faint selection thresholds (S 24 > 100 µJy). Our decomposition technique and color diagnostics are relevant given upcoming observations with the James Webb Space Telescope.

We explore the effects of active galactic nuclei (AGN) and star formation activity on the infrared (0.3 -1000 µm) spectral energy distributions of luminous infrared galaxies from z = 0.5 to 4.0. We have compiled a large sample of 151 galaxies selected at 24 µm (S 24 100 µJy) in the GOODS-N and ECDFS fields for which we have deep Spitzer IRS spectroscopy, allowing us to decompose the mid-IR spectrum into contributions from star formation and AGN activity. A significant portion (∼ 25%) of our sample is dominated by an AGN (> 50% of mid-IR luminosity) in the mid-IR. Based on the mid-IR classification, we divide our full sample into four sub-samples: z ∼ 1 starforming (SF) sources; z ∼ 2 SF sources; AGN with clear 9.7 µm silicate absorption; and AGN with featureless mid-IR spectra. From our large spectroscopic sample and wealth of multi-wavelength data, including deep Herschel imaging at 100, 160, 250, 350, and 500 µm, we use 95 galaxies with complete spectral coverage to create a composite spectral energy distribution (SED) for each sub-sample. We then fit a two-temperature component modified blackbody to the SEDs. We find that the IR SEDs have similar cold dust temperatures, regardless of the mid-IR power source, but display a marked difference in the warmer dust temperatures. We calculate the average effective temperature of the dust in each sub-sample and find a significant (∼ 20 K) difference between the SF and AGN systems. We compare our composite SEDs to local templates and find that local templates do not accurately reproduce the mid-IR features and dust temperatures of our high redshift systems. High redshift IR luminous galaxies contain significantly more cool dust than their local counterparts. We find that a full suite of photometry spanning the IR peak is necessary to accurately account for the dominant dust temperature components in high redshift IR luminous galaxies.

Dusty star-forming galaxies at high redshift (1 < z < 3) represent the most intense star-forming regions in the universe. Key aspects to these processes are the gas heating and cooling mechanisms, and although it is well known that these galaxies are gas-rich, little is known about the gas excitation conditions. Only a few detailed radiative transfer studies have been carried out owing to a lack of multiple line detections per galaxy. Here we examine these processes in a sample of 24 strongly lensed star-forming galaxies identified by the Planck satellite (LPs) at z ∼ 1.1–3.5. We analyze 162 CO rotational transitions (ranging from J up = 1 to 12) and 37 atomic carbon fine-structure lines ([C i]) in order to characterize the physical conditions of the gas in the sample of LPs. We simultaneously fit the CO and [C i] lines and the dust continuum emission, using two different non-LTE, radiative transfer models. The first model represents a two-component gas density, while the second assumes a turbulence-driven lognormal gas density distribution. These LPs are among the most gas-rich, IR-luminous galaxies ever observed (μ L L IR ( 8 − 1000 μ m ) ∼ 10 13 − 14.6 L ⊙; 〈 μ L M ISM 〉  = (2.7 ± 1.2) × 1012 M ⊙, with μ L ∼ 10–30 the average lens magnification factor). Our results suggest that the turbulent interstellar medium present in the LPs can be well characterized by a high turbulent velocity dispersion ( 〈 ΔV turb 〉  ∼ 100 km s−1) and ratios of gas kinetic temperature to dust temperature 〈 T kin/T d 〉  ∼ 2.5, sustained on scales larger than a few kiloparsecs. We speculate that the average surface density of the molecular gas mass and IR luminosity, Σ M ISM  ∼ 103–4 M ⊙ pc−2 and Σ L IR  ∼ 1011–12 L ⊙ kpc−2, arise from both stellar mechanical feedback and a steady momentum injection from the accretion of intergalactic gas.

Multi-wavelength surveys covering large sky volumes are necessary to obtain an accurate census of rare objects such as high luminosity and/or high redshift active galactic nuclei (AGN). Stripe 82X is a 31.3 deg 2 X-ray survey with Chandra and XMM-Newton observations overlapping the legacy Sloan Digital Sky Survey (SDSS) Stripe 82 field, which has a rich investment of multi-wavelength coverage from the ultraviolet to the radio. The wide-area nature of this survey presents new challenges for photometric redshifts for AGN compared to previous work on narrow-deep fields because it probes different populations of objects that need to be identified and represented in the library of templates. Here we present an updated X-ray plus multi-wavelength matched catalog, including Spitzer counterparts, and estimated photometric redshifts for 5961 (96% of a total of 6181) X-ray sources, which have a normalized median absolute deviation, σ nmad = 0.06 and an outlier fraction, η = 13.7%. The populations found in this survey, and the template libraries used for photometric redshifts, provide important guiding principles for upcoming large-area surveys such as eROSITA and 3XMM (in X-ray) and the Large Synoptic Survey Telescope (LSST; optical).

Most massive galaxies are thought to have formed their dense stellar cores at early cosmic epochs. [1][2][3] However, cores in their formation phase have not yet been observed. Previous studies have found galaxies with high gas velocity dispersions 4 or small apparent sizes 5-7 but so far no objects have been identified with both the stellar structure and the gas dynamics of a forming core. Here we present a candidate core in formation 11 billion years ago, at z = 2.3. GOODS-N-774 has a stellar mass of 1.0 × 10 11 M⊙, a half-light radius of 1.0 kpc, and a star formation rate of 90 +45 −20 M⊙/yr. The star forming gas has a velocity dispersion 317 ± 30 km/s, amongst the highest ever measured. It is similar to the stellar velocity dispersions of the putative descendants of GOODS-N-774, compact quiescent galaxies at z ∼ 2 8-11 and giant elliptical galaxies in the nearby Universe. Galaxies such as GOODS-N-774 appear to be rare; however, from the star formation rate and size of the galaxy we infer that many star forming cores may be heavily obscured, and could be missed in optical and near-infrared surveys.We identified the candidate forming core, GOODS-N-774, using the 3D-HST catalogs in the five CANDELS fields. 12 GOODS-N-774 has a circularized effective radius re = 1.0 kpc from HST F160W WFC3 imaging; 13 a stellar mass of 1.0 × 10 11 M⊙ 12,14 ; rest-frame U V J colors consistent with a star-forming galaxy; and a MIPS 24 µm flux of 104 µJy. Fig. 1 shows the stellar mass density profile derived from the observed H160 surface brightness profile corrected for the HST PSF. 15 The surface density profile is strikingly similar to the average profile of massive quiescent galaxies at z ≈ 2 (red line), and much more concentrated than the average profile of massive star forming galaxies at that redshift (light blue). 13 The near infrared spectrum of GOODS-N-774 is shown in Fig. 2. The continuum is clearly detected, along with emission lines that we identify as Hα and [N II] redshifted to z = 2.300. The gas velocity dispersion is σ = 317 ± 30 km/s, equivalent to a FWHM ≈ 750 km/s. Typically, objects with such large linewidths are mergers or dominated by active galactic nuclei (AGN). 4 If the line emission in GOODS-N-774 is partially or largely due to the presence of an AGN, its velocity dispersion, size, and stellar mass measurements would not be reliable. There is no evidence for the presence of an active nucleus in GOODS-N-774. It is not detected in the deep Chandra 2 Ms X-ray data in GOODS-North with an upper limit of LX < 1.2 × 10 42 ergs s −1 . While an AGN cannot be conclusively ruled out, this upper limit is consistent with the star formation rate of the galaxy. Also, the galaxy has line ratios [O III]/[O II]= 0.7 ± 0.5, [O III]/Hβ = 1.2 ± 0.9, and [NII]/Hα = 0.4 ± 0.1, indicating a low ionization state of the gas. Therefore stellar photoionization, and hence ultimately star formation, is the likely origin of the line emission. Finally, the observed infrared SED, shown in Fig. 3, requires strong PAH emission to simultan...