The WISE mission has unveiled a rare population of high-redshift (z = 1 − 4.6), dusty, hyperluminous galaxies, with infrared luminosities L IR > 10 13 L ⊙ , and sometimes exceeding 10 14 L ⊙ . Previous work has shown that their dust temperatures and overall far-IR spectral energy distributions (SEDs) are significantly hotter than expected to be powered by star-formation. We present here an analysis of the rest-frame optical through mid-IR SEDs for a large sample of these so-called "Hot, Dust-Obscured Galaxies" (Hot DOGs). We find that the SEDs of Hot DOGs are generally well modeled by the combination of a luminous, yet obscured AGN that dominates the rest-frame emission at λ > 1µm and the bolometric luminosity output, and a less luminous host galaxy that is responsible for the bulk of the rest optical/UV emission. Even though the stellar mass of the host galaxies may be as large as 10 11 − 10 12 M ⊙ , the AGN emission, with a range of luminosities comparable to those of the most luminous QSOs known, require that either Hot DOGs have black hole masses significantly in excess of the local relations, or that they radiate significantly above the Eddington limit, at a level at least 10 times more efficiently than z ∼ 2 QSOs. We show that, while rare, the number density of Hot DOGs is comparable to that of equally luminous but unobscured (i.e., Type 1) QSOs. This may be at odds with the trend suggested at lower luminosities for the fraction of obscured AGN to decrease with increasing luminosity. That trend may, instead, reverse at higher luminosities. Alternatively, Hot DOGs may not be the torus-obscured counterparts of the known optically selected, largely unobscured Hyper-Luminous QSOs, and may represent a new component of the galaxy evolution paradigm. Finally, we discuss the environments of Hot DOGs and statistically show that these objects are in regions as dense as those of known high-redshift proto-clusters.
We report the discovery by the Wide-field Infrared Survey Explorer of the z = 2.452 source WISE J181417.29+341224.9, the first hyperluminous source found in the WISE survey. WISE 1814+3412 is also the prototype for an all-sky sample of ∼ 1000 extremely luminous "W1W2-dropouts" (sources faint or undetected by WISE at 3.4 and 4.6 µm and well detected at 12 or 22 µm). The WISE data and a 350 µm detection give a minimum bolometric luminosity of 3.7 × 10 13 L ⊙ , with ∼ 10 14 L ⊙ plausible. Followup images reveal four nearby sources: a QSO and two Lyman Break Galaxies (LBGs) at z = 2.45, and an M dwarf star. The brighter LBG dominates the bolometric emission. Gravitational lensing is unlikely given the source locations and their different spectra and colors. The dominant LBG spectrum indicates a star formation rate ∼ 300M ⊙ yr −1 , accounting for ∼ < 10% of the bolometric luminosity. Strong 22 µm emission relative to 350 µm implies that warm dust contributes significantly to the luminosity, while cooler dust normally associated with starbursts is constrained by an upper limit at 1.1 mm.-2 -Radio emission is ∼ 10× above the far-infrared/radio correlation, indicating an active galactic nucleus is present. An obscured AGN combined with starburst and evolved stellar components can account for the observations. If the black hole mass follows the local M BH -bulge mass relation, the implied Eddington ratio is ∼ > 4. WISE 1814+3412 may be a heavily obscured object where the peak AGN activity occurred prior to the peak era of star formation.Subject headings: galaxies: individual (WISE J181417.29+341224.9 ) WISE survey, and may be missed in surveys with substantially smaller areas by e.g., Spitzer and Herschel. Here we report on WISE J181417.29+341224.9 (hereafter WISE 1814+3412), the first hyper-luminous infrared galaxy (L IR > 10 13 L ⊙ ) discovered by WISE.Magnitudes are converted to flux densities using zeropoint values of 3631 Jy for the AB system g' and r' bands. Other magnitudes are on the Vega system, using zeropoints of 1594 and 666.7 Jy for the 2MASS system J and K s bands; 280.9 and 179.7 Jy for Spitzer IRAC [3.6] and [4.5]; and 306.7, 170.7, 29.04 & 8.284 Jy for WISE W1 through W4 respectively (Wright et al. 2010). Luminosities are calculated assuming Ω M = 0.3, Ω Λ = 0.7, and H 0 = 70 km s −1 Mpc −1 . Selection Criteria and Followup ObservationsEarly searches for the most luminous galaxies with WISE data included the investigation of outlier populations, among them objects which were only well detected in W3 and W4, including WISE 1814+3412. This approach proved highly successful (Figure 1), leading to a variety of followup programs now underway on sources which are much fainter in W1 (3.4 µm) and W2 (4.6 µm) than W3 (12 µm) or W4 (22 µm). The selection criteria for these "W1W2-dropouts" are W1 > 17.4 (< 34 µJy), and either: a) W4 < 7.7 (> 6.9 mJy) and W2 − W4 > 8.2; or b) W3 < 10.6 (> 1.7 mJy) and W2 − W3 > 5.3. W1W2-dropouts must also have at least 7 individual WISE exposures available for measurement in W3 or...
We revisit the proposed extended Schmidt law, which posits that the star formation efficiency in galaxies depends on the stellar mass surface density, by investigating spatially resolved star formation rates (SFRs), gas masses, and stellar masses of star formation regions in a vast range of galactic environments, from the outer disks of dwarf galaxies, to spiral disks and to merging galaxies, as well as individual molecular clouds in M33. We find that these regions are distributed in a tight power law as S SFR ∝ S S ( ) star 0.5 gas 1.09 , which is also valid for the integrated measurements of disk and merging galaxies at high-z. Interestingly, we show that star formation regions in the outer disks of dwarf galaxies with S SFR down to 10, which are outliers of both the KennicuttSchmidt and Silk-Elmegreen laws, also follow the extended Schmidt law. Other outliers in the Kennicutt-Schmidt law, such as extremely metal-poor star formation regions, also show significantly reduced deviation from the extended Schmidt law. These results suggest an important role for existing stars in helping to regulate star formation through the effect of their gravity on the midplane pressure in a wide range of galactic environments.
Hot, Dust-Obscured Galaxies, or "Hot DOGs", are a rare, dusty, hyperluminous galaxy population discovered by the WISE mission. Predominantly at redshifts 2-3, they include the most luminous known galaxies in the universe. Their high luminosities likely come from accretion onto highly obscured super massive black holes (SMBHs). We have conducted a pilot survey to measure the SMBH masses of five z ∼ 2 Hot DOGs via broad Hα emission lines, using Keck/MOSFIRE and Gemini/FLAMINGOS-2. We detect broad Hα emission in all five Hot DOGs. We find substantial corresponding SMBH masses for these Hot DOGs (∼ 10 9 M ), and their derived Eddington ratios are close to unity. These z ∼ 2 Hot DOGs are the most luminous AGNs for their BH masses, suggesting they are accreting at the maximum rates for their BHs. A similar property is found for known z ∼ 6 quasars. Our results are consistent with scenarios in which Hot DOGs represent a transitional, high-accretion phase between obscured and unobscured quasars. Hot DOGs may mark a special evolutionary stage before the red quasar and optical quasar phases, and they may be present at other cosmic epochs.
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