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...

We present an analysis of Two Micron All Sky Survey (2MASS) calibration photometry of the old open cluster M67 (NGC 2682). The proper motion-cleaned color-magnitude diagram (CMD) resulting from these data extends ∼3 magnitudes deeper than one based on data from the point source catalog. The CMD extends from above the helium-burning red clump to a faint limit that is more than 7 magnitudes below the main sequence turnoff in the K S band. After adopting a reddening of E(B-V) = 0.041 ± 0.004 and a metal abundance of [Fe/H] = -0.009 ± 0.009 based on a survey of published values, we fit the unevolved main sequence of M67 to field main sequence stars with 2MASS photometry and Hipparcos parallaxes. This analysis yields distance moduli of (m-M) K S = 9.72 ± 0.05 and (m-M) 0 = 9.70 ± 0.05, which are consistent with published values. We compare the theoretical isochrones of Girardi et al. and Dotter et al. to the CMD of M67 and comment on the relative merits of each set of models. These comparisons suggest an age between 3.5 and 4.0 Gyr for M67. The depth of the M67 data make them ideal for the calibration of a new age indicator that has recently been devised by Calamida et al.-the difference in (J-K S ) color between the main sequence turnoff (TO) and the point on the lower main sequence where it turns down (TD) and becomes nearly vertical [∆(J-K S ) T O T D ]. Coupled with deep 2MASS photometry for three other open clusters, NGC 2516, M44, and NGC 6791, we calibrate ∆(J-K S ) in terms of age and find ∆(J-K S ) T O T D = (3.017 ± 0.347) -(0.259 ± 0.037)*Log Age (yrs).

In order to better understand how active galactic nuclei (AGN) effect the interstellar media of their host galaxies, we perform a meta-analysis of the CO emission for a sample of z = 0.01−4 galaxies from the literature with existing CO detections and well-constrained AGN contributions to the infrared (67 galaxies). Using either Spitzer/IRS mid-IR spectroscopy or Spitzer+Herschel colors we determine the fraction of the infrared luminosity in each galaxy that can be attributed to heating by the AGN or stars. We calculate new average CO spectral line ratios (primarily from Carilli & Walter 2013) to uniformly scale the higher-J CO detections to the ground state and accurately determine our sample's molecular gas masses. We do not find significant differences in the gas depletion timescales/star formation efficiencies (SFEs) as a function of the mid-infrared AGN strength (f (AGN) MIR or L IR (AGN)), which indicates that the presence of an IR-bright AGN is not a sufficient sign-post of galaxy quenching. We also find that the dust-to-gas ratio is consistent for all sources, regardless of AGN emission, redshift, or L IR , indicating that dust is likely a reliable tracer of gas mass for massive dusty galaxies (albeit with a large degree of scatter). Lastly, if we classify galaxies as either AGN or star formation dominated, we do not find a robust statistically significant difference between their CO excitation.

We have compiled a large sample of 151 high redshift (z = 0.5 − 4) 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-infrared spectrum into contributions from star formation and activity in the galactic nuclei. In addition, we have a wealth of photometric data from Spitzer IRAC/MIPS and Herschel PACS/SPIRE. We explore how effective different infrared color combinations are at separating our mid-IR spectroscopically determined active galactic nuclei from our star forming galaxies. We look in depth at existing IRAC color diagnostics, and we explore new colorcolor diagnostics combining mid-IR, far-IR, and near-IR photometry, since these combinations provide the most detail about the shape of a source's IR spectrum. An added benefit of using a color that combines far-IR and mid-IR photometry is that it is indicative of the power source driving the IR luminosity. For our data set, the optimal color selections are S 250 /S 24 vs. S 8 /S 3.6 and S 100 /S 24 vs. S 8 /S 3.6 ; both diagnostics have ∼10% contamination rate in the regions occupied primarily by star forming galaxies and active galactic nuclei, respectively. Based on the low contamination rate, these two new IR color-color diagnostics are ideal for estimating both the mid-IR power source of a galaxy when spectroscopy is unavailable and the dominant power source contributing to the IR luminosity. In the absence of far-IR data, we present color diagnostics using the WISE mid-IR bands which can efficiently select out high z (z ∼ 2) star forming galaxies.