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SCUBA-2 850 μ m 48 arcsec radius map showing the central region of the 4 undetected targets stacked together. The cross shows the central pixel. North is up, East is to the left.
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We present SCUBA-2 (Submillimetre Common-User Bolometer Array) 850 μm submillimetre (submm) observations of the fields of
10 dusty, luminous galaxies at z ∼ 1.7–4.6, detected at 12 and/or 22 μm by the Wide-field Infrared Survey Explorer (WISE) all-sky survey, but faint or undetected at 3.4 and 4.6 μm; dubbed hot, dust-obscured galaxies (Hot DOGs)....
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Context 1
... SCUBA-2 observes in the atmospheric windows at 450 μ m and 850 μ m. The diffraction-limited beams have full-width half maxima (FWHM) of approxi- mately 7.5 and 14.5 arcsec, respectively. The optical depth at 225 GHz, τ 225 , during the observations was in the range of JCMT Band 2 conditions: 0.05 < τ 225 < 0.08 (Dempsey et al. 2013). The corresponding opacities for each atmospheric window, 450 μ m and 850 μ m, were 0.61 < τ 450 < 1.18 and 0.24 < τ 850 < 0.40. Therefore, we could not use any 450 μ m data because the atmospheric opacity was too great. All observations were taken in the “CV DAISY” mode that produces a 12-arcmin diameter map, with the deepest coverage in a central 3-arcmin diameter region (Holland et al. 2013). The target stays near the centre of the arrays and the telescope performs a pseudo-circular pattern with a radius of 250 arcsec at a speed of 155 arcsec s − 1 . This mode is best for point-like sources and those smaller than 3- arcmin. Each scan was 30 minutes long and four scans were made per target, totalling a exposure time of 120 minutes per target. The typical 850 μ m noise achieved in these DAISY maps was 1.8 mJy/beam, and the noise increases by ∼ 10% out to a radius of 1.5 arcmin (Table 1). We have treated only this uniform central region of the SCUBA2 DAISY maps in this analysis. Pointing checks were taken throughout the night. The calibration sources observed were Uranus, CRL 2688, CRL 618 and Mars. Calibrations were taken at the start and end of every night in the standard manner (Dempsey et al. 2013), and where consistent with the standard values. The maps were reduced with the STARLINK SubMillimeter User Reduction Facility (SMURF) data reduction package with the “Blank Field” configuration suitable for low SNR point sources (Chapin et al. 2013). SMURF performs pre-processing steps to clean the data by modelling each of the contributions to the signal from each bolometer, flat- fields and removes atmospheric emission, and finally regrids to produce a science-quality image. Using the STARLINK PIpeline for Combining and Analyzing Reduced Data (PI- CARD) package the maps were mosaiced with all four observations per target, beam-match filtered with a 15 arcsec FWHM Gaussian and calibrated with the flux conver- sion factor (FCF) of 2.34 Jy pW − 1 arcsec − 2 (appropriate for aperture photometry) or 537 Jy pW − 1 beam − 1 (in order to measure absolute peak fluxes of discrete sources) that is appropriate for 850 μ m data (Dempsey et al. 2013). The 850 μ m flux densities of the 10 Hot DOGs at their WISE positions and the noise level in the maps are presented in Table 1. Six Hot DOGs are detected at greater than 3 σ significance, while the other four targets had positive flux measurements at the WISE position with signif- icances between 1.1 σ and 1.9 σ . The flux density limits for all the targets were measured in an aperture diameter of 15 arcsec, which is the same size as the FWHM of the telescope beam. This was an appropriate aperture size: for the detected sources, the aperture flux densities on this scale are consistent with the peak flux densities. Figure 1 and Figure 2 show the sensitive 3-arcmin diameter SCUBA-2 850 μ m DAISY fields of the 6 detected Hot DOGs and the 4 undetected Hot DOGs, respectively. The typical error of the WISE position compared to the SCUBA-2 position of the detected targets was 1 arcsec. To test whether the positive flux density of the four targets with upper limits is likely to be real, random points were sampled from the maps, and the stacked average flux density was 0.0 ± 0.5 mJy. This is consistent with the positive flux densities from the Hot DOGs with upper limits being due to fainter, undetected targets. W2026+0716 is the only target whose 850 μ m flux increases when measured in a larger aperture (see Figure 3). It has a 850 μ m flux density of 2.1 mJy with a 15-arcsec beam- sized aperture. However, when increasing the diameter to 29 arcsec, the flux density increases to 7.3 mJy. The higher flux is likely because the target has multiple components on scales bigger than the SCUBA-2 beam. Multiple components have been seen in another Hot DOG, W1814+3412, where several objects on scales less than 10 arcsec are appar- ent (Eisenhardt et al. 2012). Alternatively, there could be an unrelated source or sources. The WISE extended source flag is 0 for the W1 through W4 bands, which means that the detected source is not extended at WISE wavelengths (see Figure 3). There are no obvious signs of a cluster of sources nearby in Spitzer images (Wu et al. priv. comm.). However, Herschel 160 μ m imaging shows a possible companion about 10 arcsec away that could contribute enhanced flux in larger apertures in this source (Bridge et al. priv. comm.). Due to this uncertainty, the quoted 850 μ m flux density in Table 1 is the 15-arcsec beam-sized aperture flux density (2.1 mJy). When the images of the four undetected sources are stacked together into one image (Figure 4) and centred on the WISE-determined position of each target, the net flux is 7.8 ± 2.3 mJy in the central 15 arcsec region, a net detection of 3.4 σ . The four undetected targets are consistent with being on average 2.5 times fainter than the six detected targets. To get deeper observations with SCUBA-2 would require several more hours of integration per target, beyond the existing 120 minutes, but would not add much more value to this stacked result. The flux densities presented in Table 1 can be compared with the results of Wu et al. (2012), who observed 14 WISE-selected Hot DOGs with the Caltech Submillimeter Observatory (CSO) SubMillimeter High Angular Reso- lution Camera II (SHARC-II) at 350 to 850 μ m and 18 Hot DOGs with CSO Bolocam at 1.1 mm. Using a 3 σ threshold, Wu et al. (2012) found that nine out of 14 Hot DOGs were detected at 350 μ m and 6 of the 18 targets were detected at 1.1 mm. Three sources from the Hot DOG sample in this paper were in common with Wu et al. (2012); W1603+2745, W1814+3412 and W1835+4355. These CSO results are consistent with our SCUBA-2 observations at 850 μ m. The relative sensitivities of SHARC-II and Bolocam are such that we believe the SCUBA-2 detections and limits provide a sub- stantial increase in our knowledge of the HotDOGs’ submm properties. Furthermore, W1814+3412 which was detected at 350 μ m by Wu et al. (2012), with upper limits reported at 450 μ m and 1100 μ m was also detected by the Institut de Radioastronomie Millimetrique (IRAM) Plateau de Bure interferometer in the 1.3 mm band in 2013 (Blain et al. in prep.). The SEDs of the 10 SCUBA-2 Hot DOGs are shown in Figure 5. The SEDs are normalised at rest-frame 3 μ m and shown at rest-frame wavelengths in order to compare to various galaxy SED templates (Polletta et al. 2007) in order to try and understand the Hot DOGs nature. The Polletta galaxy templates are Arp 220 (starburst-dominated galaxy), Mrk 231 (heavily obscured AGN-starburst composite), QSO 1 and 2 (optically-selected QSOs of Type 1 and 2) and torus (type-2 heavily-obscured QSO: an accreting SMBH with a hot accretion disk surrounded by dust and Compton-thick gas in a toroidal structure (Krolik & Begelman 1988). The Hot DOG SEDs are broadly similar. They have a steep red power-law IR (1-5 μ m) section with a potential mid-IR peak from hot dust emission, a mid-IR to submm section that appears to be flatter, i.e. less peaked, than the Polletta AGN templates, turning over to a Rayleigh-Jeans spectrum long- wards of 200 μ m from the coolest dust emission. The mid-IR to submm section is consistent with being “flat-topped” (in f ν ), as suggested by Wu et al. (2012), and consistent with the 850 μ m data presented in this paper, and consistent to Herschel results from the most luminous Hot DOGs (Tsai et al. in prep.). However, Herschel data of Lyman-alpha blobs (LABs) (Bridge et al. 2013) that have similar WISE colours to the Hot DOGs in this paper show a far-IR peak in the SED. Further discussion of this point and the presentation of Herschel follow-up of WISE Hot DOGs will be presented by Bridge et al. in prep. and Tsai et al. in prep. A better fitting SED model for these Hot DOGs is also shown in Figure 5 and Figure 6. The W1814+3412 template shown is entirely empirical, and assumes a single- temperature dust spectrum representing the minimum dust temperature present (53 ± 5 K), with an emissivity index of β = 1.5 at longer wavelengths, smoothly interpolated to a power-law spectrum instead of a Wien law at shorter wavelengths, with an opacity factor imposed at the short- est mid-IR wavelengths, to match the WISE data, corresponding to a finite total luminosity L 8 − 1000 μ m = 4.6 × 10 13 L ⊙ for W1814+3412. It is constrained by Herschel data from Wu et al. (2012) and IRAM data from Blain et al. (in prep.), and so unsurprisingly provides a better fit than the Polletta et al. (2007) templates that pre-date these observations. The SEDs are not well-fitted by any of the templates; the closest fitting template is the single torus template, although extra dust extinction is required to fit the W1 and W2 data. Between the Polletta torus template and the mean SED of the 850 μ m detected targets, both normalised at 3 μ m, the extra dust extinction required at rest-frame 1 μ m is 1.6 mag. Converting to a V -band extinction implies an extra dust extinction A V 6 . 8 mag. Eisenhardt et al. (2012) found significant obscuration in the SED of W1814+3412 with a dust extinction value of A V = 48 ± 4 in the rest-frame from optical SED fitting. The gas column density N H can be estimated by applying a standard “gas-to-extinction” equation N H ≈ 2 A V × 10 22 mag − 1 cm − 2 from Maiolino et al. (2001), which estimates the extra N H needed is 10 23 cm − 2 . The Polletta torus template was modelled on a heavily obscured type- 2 QSO, with a rest-frame N H of 2 . 14 +0 − 1 . . 54 34 × 10 24 cm − 2 (Polletta et al. 2006). The extra N H can be added to the ...
Citations
... Peaking at z ∼ 2 − 3 (Assef et al. 2015), their bolometric luminosities (L bol ) exceed 10 13 L ⊙ (and in ∼ 10% exceed 10 14 L ⊙ ; Tsai et al. 2015), and include the most luminous galaxy discovered so far, WISE J224607.56−052634.9 at z = 4.601 (Tsai et al. 2015;Díaz-Santos et al. 2016). Given their WISE colors are similar to those of DOGs, but with higher dust temperatures (> 60K; Wu et al. 2012;Bridge et al. 2013;Jones et al. 2014), these galaxies are referred to as Hot Dust-Obscured Galaxies or Hot DOGs . ...
... We note that it is unlikely that our estimates of MBH are significantly affected by differential BLR scattering, which would lead to an underestimate of the line width and hence of MBH. It is also unlikely that there is substantial, unaccounted host contamination to the MIR emission as different studies have concluded it to be dominate by the AGN emission (see, e.g., Jones et al. 2014, Sun et al. 2024, as well as the discussion in Section 3.1), which would lead to an overestimation of the continuum luminosity and consequently of MBH. ...
... By imaging the [C ii] emission in seven extremely luminous Hot DOGs (L bol > 10 14 L ⊙ ) using ALMA, however, Díaz-Santos et al. (2021) proposed instead that this short-lived phase may be triggered by minor merger and might occur recurrently throughout the history of the galaxy. This is particularly plausible if Hot DOGs will become the BCGs of clusters once the overdensities they live in (Jones et al. 2014;Jones 2017;Assef et al. 2015;Luo et al. 2022;Ginolfi et al. 2022;Zewdie et al. 2023) become virialized. Figure 5 shows for each object the fraction of the observed emission blueward of 1µm that is due to the scattered light AGN component. ...
Hot Dust-Obscured Galaxies (Hot DOGs) are a rare population of hyper-luminous infrared galaxies discovered by the WISE mission. Despite the significant obscuration of the AGN by dust in these systems, pronounced broad and blue-shifted emission lines are often observed. Previous work has shown that 8 Hot DOGs, referred to as Blue-excess Hot DOGs (BHDs), present a blue excess consistent with type 1 quasar emission in their UV-optical SEDs, which has been shown to originate from the light of the obscured central engine scattered into the line of sight. We present an analysis of the rest-frame optical emission characteristics for 172 Hot DOGs through UV-MIR SED modeling and spectroscopic details, with a particular focus on the identification of BHDs. We find that while the optical emission observed in Hot DOGs is in most cases dominated by a young stellar population, 26% of Hot DOGs show a significant enough blue excess emission to be classified as BHDs. Based on their broad CIV and MgII lines, we find that the $M_{\rm BH}$ in BHDs range from $10^{8.7}$ to $10^{10} \ M_{\odot}$. When using the same emission lines in regular Hot DOGs, we find the $M_{\rm BH}$ estimates cover the entire range found for BHDs while also extending to somewhat lower values. This agreement may imply that the broad lines in regular Hot DOGs also originate from scattered light from the central engine, just as in BHDs, although a more detailed study would be needed to rule out an outflow-driven nature. Similar to $z\sim 6$ quasars, we find that Hot DOGs sit above the local relation between stellar and black hole mass, suggesting either that AGN feedback has not yet significantly suppressed the stellar mass growth in the host galaxies, or that they will be outliers of the relation when reaching $z$=0.
... Models predict that the growth of these massive starbursting objects is driven by galaxy mergers 8,9 , which can deliver a significant amount of gas toward their centers, boosting their star formation rate (SFR) up to thousands of M yr −1 10 , and feeding the growth of their supermassive black holes (SMBH), thereby powering the AGN activity 8 . However, while cumulative number counts in wide-field surveys suggest that Hot DOGs tend to lie in dense large-scale environments 11,12 , direct observations of the mechanisms responsible for their rapid growth are still sparse or only restricted to scales of a few tens of kpc 13 . On the other hand, recent works [14][15][16] have demonstrated the potential of spectroscopic imaging studies across the environment of luminous quasars and protocluster galaxies, finding companion galaxies out to hundreds of kpc. ...
The phase transition between galaxies and quasars is often identified with the rare population of hyper-luminous, hot dust-obscured galaxies. Galaxy formation models predict these systems to grow via mergers, that can deliver large amounts of gas toward their centers, induce intense bursts of star formation and feed their supermassive black holes. Here we report the detection of 24 galaxies emitting Lyman-alpha emission on projected physical scales of about 400 kpc around the hyper-luminous hot dust-obscured galaxy W0410-0913, at redshift z = 3.631, using Very Large Telescope observations. While this indicates that W0410-0913 evolves in a very dense environment, we do not find clear signs of mergers that could sustain its growth. Data suggest that if mergers occurred, as models expect, these would involve less massive satellites, with only a moderate impact on the internal interstellar medium of W0410-0913, which is sustained by a rotationally-supported fast-rotating molecular disk, as Atacama Large Millimeter Array observations suggest.
... Models predict that the growth of these massive star-bursting objects is driven by galaxy mergers 8,9 , which can deliver a significant amount of gas toward their centers, boosting their star formation rate (SFR) up to thousands of M ⊙ yr −110 , and feeding the growth of their supermassive black holes (SMBH), thereby powering the AGN activity 8 . However, while cumulative number counts in wide-field surveys suggest that Hot DOGs tend to lie in dense large-scale environments 11,12 , direct observations of the mechanisms responsible for their rapid growth are still sparse or only restricted to scales of a few tens of kpc 13 . On the other hand, recent works [14][15][16] have demonstrated the potential of spectroscopic imaging studies across the environment of luminous quasars and protocluster galaxies, finding companion galaxies out to hundreds of kpc. ...
The phase transition between galaxies and quasars is often identified with the rare population of hyper-luminous, hot dust-obscured galaxies. Galaxy formation models predict these systems to grow via mergers, that can deliver large amounts of gas toward their centers, induce intense bursts of star formation and feed their supermassive black holes. Here we report the detection of 24 galaxies emitting Lyman- α emission on projected physical scales of about 400 kpc around the hyper-luminous hot dust-obscured galaxy W0410-0913, at redshift z = 3.631, using Very Large Telescope observations. While this indicates that W0410-0913 evolves in a very dense environment, we do not find clear signs of mergers that could sustain its growth. Data suggest that if mergers occurred, as models expect, these would involve less massive satellites, with only a moderate impact on the internal interstellar medium of W0410-0913, which is sustained by a rotationally-supported fast-rotating molecular disk, as Atacama Large Millimeter Array observations suggest.
... Follow-up multiwavelength studies have revealed that Hot DOGs are extremely luminous, merger-driven, heavily dust-obscured quasars at high redshift (Piconcelli et al. 2015;Tsai et al. 2015;Fan et al. 2016aFan et al. , 2016bFan et al. , 2017Fan et al. , 2018Assef et al. 2016;Ricci et al. 2017;Zappacosta et al. 2018;Fan et al. 2020). Previous statistical studies have found significant overdensities of mid-IR-selected and sub-millimeter-selected galaxies around Hot DOGs, indicating Hot DOGs may reside in dense regions (Jones et al. 2014;Assef et al. 2015;Fan et al. 2017). ...
... Previous studies on environments of Hot DOGs have suggested that they may live in dense regions (Jones et al. 2014;Assef et al. 2015;Fan et al. 2017). For instance, overdensities of submillimeter galaxies (SMGs) in the vicinity of Hot DOGs have been found in two small samples of Hot DOGs using JCMT SCUBA2 850 μm observations (Jones et al. 2014;Fan et al. 2017). ...
... Previous studies on environments of Hot DOGs have suggested that they may live in dense regions (Jones et al. 2014;Assef et al. 2015;Fan et al. 2017). For instance, overdensities of submillimeter galaxies (SMGs) in the vicinity of Hot DOGs have been found in two small samples of Hot DOGs using JCMT SCUBA2 850 μm observations (Jones et al. 2014;Fan et al. 2017). Jones et al. (2014) detected one SMG within 1 5 radius of W1835, which revealed a moderate overdensity of SMGs compared with the blank field survey (Weiß et al. 2009). ...
Wide-field Infrared Survey Explorer all-sky survey has discovered a new population of hot dust-obscured galaxies (Hot DOGs), which have been confirmed to be dusty quasars. Previous statistical studies have found significant overdensities of submillimeter and mid-IR-selected galaxies around Hot DOGs, indicating they may reside in dense regions. Here we present the near-infrared ( J and K s bands) observations over a 7 .′ 5 × 7 .′ 5 field centered on a Hot DOG W1835+4355 at z ∼ 2.3 using the wide-field infrared camera on the Palomar 200 inch telescope. We use the color criterion J − K s > 2.3 for objects with K S < 20 , to select distant red galaxies (DRGs). We find a significant excess of number density of DRGs in the W1835+4355 field compared to three control fields, by a factor of about two. The overdensity of red galaxies around W1835+4355 is consistent with the multiwavelength environment of Hot DOGs, suggesting that Hot DOGs may be a good tracer for dense regions at high redshift. We find that W1835+4355 does not reside in the densest region of the dense environment traced by itself. A possible scenario is that W1835+4355 is undergoing a merging process, which lowers the local number density of galaxies in its surrounding region.
... Follow-up multiwavelength studies have revealed that Hot DOGs are extremely luminous, merger-driven, heavily dust-obscured quasars at high redshift (Piconcelli et al. 2015;Tsai et al. 2015;Assef et al. 2016;Fan et al. 2016aFan et al. ,b, 2017Fan et al. , 2018bFan et al. , 2020Ricci et al. 2017;Zappacosta et al. 2018). Previous statistical studies have found significant overdensities of mid-IR-selected and submm-selected galaxies around Hot DOGs, indicating Hot DOGs may reside in dense regions (Jones et al. 2014;Fan et al. 2017;Assef et al. 2015). ...
... Previous studies on environments of Hot DOGs have suggested that they may live in dense regions (Jones et al. 2014;Assef et al. 2015;Fan et al. 2017). For instance, overdensities of sub-millimeter galaxies (SMGs) in the vicinity of Hot DOGs have been found in two small samples of Hot DOGs using JCMT SCUBA2 850 µm observations (Jones et al. 2014;Fan et al. 2017). ...
... Previous studies on environments of Hot DOGs have suggested that they may live in dense regions (Jones et al. 2014;Assef et al. 2015;Fan et al. 2017). For instance, overdensities of sub-millimeter galaxies (SMGs) in the vicinity of Hot DOGs have been found in two small samples of Hot DOGs using JCMT SCUBA2 850 µm observations (Jones et al. 2014;Fan et al. 2017). Jones et al. (2014) detected one SMG within 1.5 arcmin radius of W1835, which revealed a moderate overdensity of SMGs compared with blank field survey (Weiß et al. 2009). ...
\emph{Wide-field Infrared Survey Explorer} all-sky survey has discovered a new population of hot dust-obscured galaxies (Hot DOGs), which has been confirmed to be dusty quasars. Previous statistical studies have found significant overdensities of sub-millimeter and mid-IR selected galaxies around Hot DOGs, indicating they may reside in dense regions. Here we present the near-infrared ($J$ and $K_s$ bands) observations over a $7.5'\times 7.5'$ field centered on a Hot DOG W1835$+$4355 at $z \sim 2.3$ using the wide-field infrared camera on the Palomar 200-inch telescope. We use the color criterion $J-K_s>2.3$ for objects with $K_s<20$, to select Distant Red Galaxies (DRGs). We find a significant excess of number density of DRGs in W1835$+$4355 field compared to three control fields, by a factor of about 2. The overdensity of red galaxies around W1835$+$4355 are consistent with the multi-wavelength environment of Hot DOGs, suggesting that Hot DOGs may be a good tracer for dense regions at high redshift. We find that W1835$+$4355 do not reside in the densest region of the dense environment traced by itself. A possible scenario is that W1835$+$4355 is undergoing merging process, which lowers the local number density of galaxies in its surrounding region.
... A number of studies have identified a hyper-luminous, highlyobscured AGN as the primary source of the luminosity in these objects (e.g., Eisenhardt et al. 2012;Assef et al. 2015). This obscured AGN component dominates at mid-IR wavelengths (Assef et al. 2015), but is sometimes luminous enough to dominate the emission at far-IR wavelengths as well (Jones et al. 2014;Díaz-Santos et al. 2016;Diaz-Santos et al. 2021). Hard X-ray spectra have been obtained for several Hot DOGs, leading to the conclusion that the obscuration is close to, or above, the Compton-thick threshold Piconcelli et al. 2015;Assef et al. 2016Assef et al. , 2020Vito et al. 2018). ...
... Hot DOGs have very distinctive UV through IR SEDs (e.g., see Tsai et al. 2015;Assef et al. 2015). The highly-obscured, hyper-luminous AGN dominates the IR SEDs of these objects as well as the bolometric luminosity output, while a moderately star-forming galaxy without significant obscuration typically dominates the UV and optical portions of the SED (see, e.g., Eisenhardt et al. 2012;Jones et al. 2014;Assef et al. 2015). Assef et al. (2016) studied the UV through mid-IR SED of a large number of Hot DOGs and identified 8 objects that showed considerably bluer SEDs. ...
... Hence, dust scattering from the former should dominate over free electrons unless the scattering medium is very dustdeficient. We expect dust to be present in significant quantities in the ISM of the host galaxy as, by selection, Hot DOGs have bright dust emission in the mid-IR and are typically well detected in the far-IR (Jones et al. 2014;Wu et al. 2014;Diaz-Santos et al. 2021) 4 . Hence, the Thomson scattering scenario would only be plausible if the scattering medium is within the dust sublimation radius of the accretion disk, which we estimate to be 8.7 pc using equation (1) of Nenkova et al. (2008) and the bolometric luminosity of W0116-0505 measured by Tsai et al. (2015), adjusted for the differences in the cosmological model assumed. ...
We report on VLT/FORS2 imaging polarimetry observations in the $R_{\rm special}$ band of WISE J011601.41-050504.0 (W0116-0505), a heavily obscured hyper-luminous quasar at $z=3.173$ classified as a Hot, Dust-Obscured Galaxy (Hot DOG) based on its mid-IR colors. Recently, Assef et al. (2020) identified W0116-0505 as having excess rest-frame optical/UV emission, and concluded this excess emission is most likely scattered light from the heavily obscured AGN. We find that the broad-band rest-frame UV flux is strongly linearly polarized (10.8$\pm$1.9\%, with a polarization angle of 74$\pm$9~deg), confirming this conclusion. We analyze these observations in the context of a simple model based on scattering either by free electrons or by optically thin dust, assuming a classical dust torus with polar openings. Both can replicate the degree of polarization and the luminosity of the scattered component for a range of geometries and column densities, but we argue that optically thin dust in the ISM is the more likely scenario. We also explore the possibility that the scattering medium corresponds to an outflow recently identified for W0116-0505. This is a feasible option if the outflow component is bi-conical with most of the scattering occurring at the base of the receding outflow. In this scenario the quasar would still be obscured even if viewed face on, but might appear as a reddened type 1 quasar once the outflow has expanded. We discuss a possible connection between blue-excess Hot DOGs, extremely red quasars (ERQs), reddened type 1 quasars, and unreddened quasars that depends on a combination of evolution and viewing geometry.
... Both radio galaxies and hot dust-obscured galaxies are often found to reside in highly o v erdense environments (e.g. Pentericci et al. 2000 ;Miley et al. 2004 ;Venemans et al. 2007 ;Jones et al. 2014Jones et al. , 2015Fan et al. 2017 ). We investigate whether COS-87259 may reside in an o v erdense environment by comparing the surface density of z 6.6-6.9 ...
... For comparison, radio and hot dust-obscured galaxies at z > 2 are typically found to reside in environments with ∼3-5 × the number of neighbouring sources relative to blank fields (e.g. Venemans et al. 2007 ;Jones et al. 2014 ;Fan et al. 2017 ). Such strong o v erdensities are, at z 7, likely to carve out large ionized regions in the mostly neutral IGM. ...
We report the identification of radio (0.144–3 GHz) and mid-, far-infrared, and sub-mm (24–850μm) emission at the position of one of 41 UV-bright ($\mathrm{M_{\mathrm{UV}}}^{ }\lesssim -21.25$) z ≃ 6.6 − 6.9 Lyman-break galaxy candidates in the 1.5 deg2 COSMOS field. This source, COS-87259, exhibits a sharp flux discontinuity (factor >3) between two narrow/intermediate bands at 9450 Å and 9700 Å and is undetected in all nine bands blueward of 9600 Å, as expected from a Lyman-alpha break at z ≃ 6.8. The full multi-wavelength (X-ray through radio) data of COS-87529 can be self-consistently explained by a very massive (M* = 1010.8 M⊙) and extremely red (rest-UV slope β = −0.59) z ≃ 6.8 galaxy with hyperluminous infrared emission (LIR = 1013.6 L⊙) powered by both an intense burst of highly-obscured star formation (SFR≈1800 M⊙ yr−1) and an obscured ($\tau _{_{\mathrm{9.7\mu m}}} = 7.7\pm 2.5$) radio-loud (L1.4 GHz ≈ 1025.4 W Hz−1) AGN. The radio emission is compact (1.04±0.12 arcsec) and exhibits an ultra-steep spectrum between 1.32–3 GHz ($\alpha =-1.57^{+0.22}_{-0.21}$) that flattens at lower frequencies ($\alpha = -0.86^{+0.22}_{-0.16}$ between 0.144–1.32 GHz), consistent with known z > 4 radio galaxies. We also demonstrate that COS-87259 may reside in a significant (11×) galaxy overdensity, as common for systems hosting radio-loud AGN. While we find that low-redshift solutions to the optical+near-infrared data are not preferred, a spectroscopic redshift will ultimately be required to establish the true nature of COS-87259 beyond any doubt. If confirmed to lie at z ≃ 6.8, the properties of COS-87259 would be consistent with a picture wherein AGN and highly-obscured star formation activity are fairly common among very massive (M* > 1010 M⊙) reionization-era galaxies.
... Both radio galaxies and hot dust-obscured galaxies are often found to reside in highly overdense environments (e.g. Pentericci et al. 2000;Miley et al. 2004;Venemans et al. 2007;Jones et al. 2014Jones et al. , 2015Fan et al. 2017). We investigate whether COS-87259 may reside in an overdense environment by comparing the surface density of 6.6−6.9 ...
... For comparison, radio and hot dust-obscured galaxies at > 2 are typically found to reside in environments with ∼ 3 − 5× the number of neighboring sources relative to blank fields (e.g. Venemans et al. 2007;Jones et al. 2014;Fan et al. 2017). Such strong overdensities are, at 7, likely to carve out large ionized regions in the mostly neutral IGM. ...
We report the identification of radio (1.4 and 3 GHz) and mid-infrared, far-infrared, and sub-mm (24-850$\mu$m) emission at the position of one of 41 UV-bright ($\mathrm{M_{UV}^{}}\lesssim-21.25$) $z\simeq6.6-6.9$ Lyman-break galaxy candidates in the 1.5 deg$^2$ COSMOS field. This source, COS-87259, exhibits a sharp flux discontinuity (factor $>$3) between two narrow/intermediate bands at 9450 $\mathring{A}$ and 9700 $\mathring{A}$ and is undetected in all nine bands blueward of 9600 $\mathring{A}$, as expected from a Lyman-alpha break at $z\simeq6.8$. The full multi-wavelength (X-ray through radio) data of COS-87529 can be self-consistently explained by a very massive (M$_{\ast}=10^{10.8}$ M$_{\odot}$) and extremely red (rest-UV slope $\beta=-0.59$) $z\simeq6.8$ galaxy with hyperluminous infrared emission (L$_{\mathrm{IR}}=10^{13.6}$ L$_{\odot}$) powered by both an intense burst of highly-obscured star formation (SFR$\approx$1800 M$_{\odot}$ yr$^{-1}$) and an obscured ($\tau_{\mathrm{9.7\mu m}}=7.7\pm2.5$) radio-loud (L$_{\mathrm{1.4\ GHz}}\sim10^{25.5}$ W Hz$^{-1}$) AGN. The radio emission is compact (1.04$\pm$0.12 arcsec) and exhibits an ultra-steep spectrum between 1.4-3 GHz ($\alpha=-2.06^{+0.27}_{-0.25}$) with evidence of spectral flattening at lower frequencies, consistent with known $z>4$ radio galaxies. We also demonstrate that COS-87259 may reside in a significant (11$\times$) galaxy overdensity at $z\simeq6.6-6.9$, as common for systems hosting radio-loud AGN. Nonetheless, a spectroscopic redshift will ultimately be required to establish the true nature of COS-87259 as we cannot yet completely rule out low-redshift solutions. If confirmed to lie at $z\simeq6.8$, the properties of COS-87259 would be consistent with a picture wherein AGN and highly-obscured star formation activity are fairly common among very massive (M$_{\ast}>10^{10}$ M$_{\odot}$) reionization-era galaxies.
... Statistically, Hot DOGs seem to be located in galaxy over-densities (Jones et al. 2014;Assef et al. 2015) and host powerful ionized outflows (Wu et al. 2018;Jun et al. 2020b,a;Finnerty et al. 2020), in agreement with the merger-driven model of quasars and their expected feedback, and also suggesting that they may be at the centers of proto-clusters. Further evidence comes from ALMA [C ii] 158 observations of the most luminous obscured quasar and Hot DOG known (L bol = 3.5 × 10 14 L ; Tsai et al. 2015), WISE J224607.55-052634.9 (W2246-0526 hereafter; at z = 4.601), which revealed a highly turbulent ISM, with a FWHM [CII] ≥ 500 km s −1 spread across the entire host galaxy, over ∼ 2.5 kpc (Díaz-Santos et al. 2016). ...
... Given that Hot DOG hosts do not seem to be forming stars at a much higher rate than normal MS galaxies at the same redshifts (see Figure 13 and Section 6), significant turbulent heating could be provided by the energy input from the central SMBH (Díaz-Santos et al. 2016) and/or by the dynamical friction consequence of the accretion of neighbor galaxies (see next section). Both cases would be in concordance with the large velocity dispersion of the [C ii] line seen in all EL Hot DOGs, FWHM 500 km s −1 (Section 5), and with the fact that they seem to live in over-dense, merger-driven environments (e.g., Jones et al. 2014;Assef et al. 2015;Jones et al. 2017;Díaz-Santos et al. 2018). ...
... However, at high-z, galaxies may have large enough gas reservoirs stored in clumpy, unstable disks (e.g., Decarli et al. 2016;Falgarone et al. 2017;Hodge et al. 2019) such that minor mergers could potentially be sufficient to trigger a number of short-lived extremely luminous, highly dissipative phases associated with rapid SMBH and galaxy mass growth. In the particular case of EL Hot DOGs, which seem to be living in over-dense environments (Jones et al. 2014;Assef et al. 2015;Fan et al. 2017;González-López et al. in prep.), a frequent in-fall of gas in the form of whole galaxies, large clumps, or tidally disrupted material would also help to explain the observed widespread turbulence of their ISM, in addition to the energy and momentum injected by the central AGN. Indeed, kpc-scale turbulence is a clear signature of the existing gravitationally bounded gas in a host galaxy attempting to relax while still being subjected to external accretion and/or internal AGN feedback (Appleton et al. 2017). ...
Hot, dust-obscured galaxies (Hot DOGs) are a population of hyper-luminous obscured quasars identified by WISE. We present ALMA observations of the [C II ] 158 μm fine-structure line and underlying dust continuum emission in a sample of seven of the most extremely luminous (EL; L bol ≥ 10 ¹⁴ L ⊙ ) Hot DOGs, at redshifts of z ≃ 3.0−4.6. The [C II ] line is robustly detected in four objects, tentatively in one, and likely to have been red-shifted out of the spectral window in the remaining two, based on additional data. On average, [C II ] is red-shifted by ≃780 km s ⁻¹ from rest-frame ultraviolet emission lines. EL Hot DOGs consistently exhibit very high [C II ] surface densities, with Σ [CII] ≃ 1−2 × 10 ⁹ L ⊙ kpc ⁻² , which is as high as the most extreme cases seen in other high-redshift quasars. As a population, EL Hot DOG hosts seem to be roughly centered on the main sequence of star-forming galaxies, but the uncertainties are substantial and individual sources can fall above and below. The average, intrinsic [C II ] and dust continuum sizes (FWHMs) are ≃2.1 kpc and ≃1.6 kpc, respectively, with a very narrow range of line-to-continuum size ratios, 1.61 ± 0.10, suggesting they could be linearly proportional. The [C II ] velocity fields of EL Hot DOGs are diverse: from barely rotating structures, to resolved hosts with ordered, circular motions, to complex, disturbed systems that are likely the result of ongoing mergers. In contrast, all sources display large line-velocity dispersions, FWHM [CII] ≳ 500 km s ⁻¹ , which are, on average, larger than optically and IR-selected quasars at similar or higher redshifts. We argue that one possible hypothesis that explains the lack of a common velocity structure, the systematically large dispersion of the ionized gas, and the presence of nearby companion galaxies, may be that the EL Hot DOG phase could be recurrent, rather than a single event. The dynamical friction from the frequent in-fall of neighbor galaxies and gas clumps, along with the subsequent quasar feedback, would contribute to the high turbulence of the gas within the host in a process that could potentially trigger not only one continuous EL, obscured event –but instead a number of recurrent, shorter-lived episodes as long as external accretion continues.
... Statistically, Hot DOGs seem to be located in galaxy over-densities (Jones et al. 2014;Assef et al. 2015) and host powerful ionized outflows (Wu et al. 2018;Jun et al. 2020b,a;Finnerty et al. 2020), in agreement with the merger-driven model of quasars and their expected feedback, and also suggesting that they may be at the centers of proto-clusters. Further evidence comes from ALMA [C ii] 158 observations of the most luminous obscured quasar and Hot DOG known (L bol = 3.5 × 10 14 L ; Tsai et al. 2015), WISE J224607.55-052634.9 (W2246-0526 hereafter; at z = 4.601), which revealed a highly turbulent ISM, with a FWHM [CII] ≥ 500 km s −1 spread across the entire host galaxy, over ∼ 2.5 kpc (Díaz-Santos et al. 2016). ...
... Given that Hot DOG hosts do not seem to be forming stars at a much higher rate than normal MS galaxies at the same redshifts (see Figure 13 and Section 6), significant turbulent heating could be provided by the energy input from the central SMBH (Díaz-Santos et al. 2016) and/or by the dynamical friction consequence of the accretion of neighbor galaxies (see next section). Both cases would be in concordance with the large velocity dispersion of the [C ii] line seen in all EL Hot DOGs, FWHM 500 km s −1 (Section 5), and with the fact that they seem to live in over-dense, merger-driven environments (e.g., Jones et al. 2014;Assef et al. 2015;Jones et al. 2017;Díaz-Santos et al. 2018). ...
... However, at high-z, galaxies may have large enough gas reservoirs stored in clumpy, unstable disks (e.g., Decarli et al. 2016;Falgarone et al. 2017;Hodge et al. 2019) such that minor mergers could potentially be sufficient to trigger a number of short-lived extremely luminous, highly dissipative phases associated with rapid SMBH and galaxy mass growth. In the particular case of EL Hot DOGs, which seem to be living in over-dense environments (Jones et al. 2014;Assef et al. 2015;Fan et al. 2017; ?), a frequent in-fall of gas in the form of whole galaxies, large clumps, or tidally disrupted material would also help to explain the observed widespread turbulence of their ISM, in addition to the energy and momentum injected by the central AGN. Indeed, kpc-scale turbulence is a clear signature of the existing gravitationally bounded gas in a host galaxy attempting to relax while still being subjected to external accretion and/or internal AGN feedback (Appleton et al. 2017). ...
Hot, dust-obscured galaxies (Hot DOGs) are a population of hyper-luminous obscured quasars identified by WISE. We present ALMA observations of the [CII] fine-structure line and underlying dust continuum emission in a sample of seven of the most extremely luminous (EL; L_bol >= 10^14 L_sun) Hot DOGs, at redshifts z ~ 3.0-4.6. The [CII] line is robustly detected in four objects, tentatively in one, and likely red-shifted out of the spectral window in the remaining two based on additional data. On average, [CII] is red-shifted by ~ 780 km/s from rest-frame ultraviolet emission lines. EL Hot DOGs exhibit consistently very high ionized gas surface densities, with Sigma_[CII] ~ 1-2 x 10^9 L_sun/kpc^2; as high as the most extreme cases seen in other high-redshift quasars. As a population, EL Hot DOG hosts seem to be roughly centered on the main-sequence of star forming galaxies, but the uncertainties are substantial and individual sources can fall above and below. The average, intrinsic [CII] and dust continuum sizes (FWHMs) are ~ 2.1 kpc and ~ 1.6 kpc, respectively, with a very narrow range of line-to-continuum size ratios, 1.61 +/- 0.10, suggesting they could be linearly proportional. The [CII] velocity fields of EL Hot DOGs are diverse: from barely rotating structures, to resolved hosts with ordered, circular motions, to complex, disturbed systems that are likely the result of ongoing mergers. In contrast, all sources display large line-velocity dispersions, FWHM >~ 500 km/s, which on average are larger than optically and IR-selected quasars at similar or higher redshifts. We argue that a possible hypothesis for the lack of a common velocity structure, the systematically large dispersion of the ionized gas, and the presence of nearby companion galaxies may be that, rather than a continuous single event, the EL Hot DOG phase could be recurrent.
