We use optical and near-infrared spectroscopy to observe rest-UV emission lines and estimate the black hole mass of WISEA J224607.56−052634.9 (W2246−0526) at z = 4.601, the most luminous hot, ...dust-obscured galaxy yet discovered by WISE. From the broad component of the Mg ii 2799 emission line, we measure a black hole mass of log(MBH/M☉) = 9.6 0.4. The broad C iv 1549 line is asymmetric and significantly blueshifted. The derived MBH from the blueshift-corrected broad C iv line width agrees with the Mg ii result. From direct measurement using a well-sampled SED, the bolometric luminosity is 3.6 × 1014 L☉. The corresponding Eddington ratio for W2246−0526 is λEdd = LAGN/LEdd = 2.8. This high Eddington ratio may reach the level where the luminosity is saturating due to photon trapping in the accretion flow and may be insensitive to the mass accretion rate. In this case, the MBH growth rate in W2246−0526 would exceed the apparent accretion rate derived from the observed luminosity.
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). The six detected targets all have total infrared luminosities greater than 1013 L⊙, with one greater than 1014 L⊙. Their spectral energy distributions (SEDs) are very blue from mid-infrared to submm wavelengths and not well fitted by standard active galactic nuclei (AGN) SED templates, without adding extra dust extinction to fit the WISE 3.4 and 4.6 μm data. The SCUBA-2 850 μm observations confirm that the Hot DOGs have less cold and/or more warm dust emission than standard AGN templates, and limit an underlying extended spiral or ULIRG-type galaxy to contribute less than about 2 or 55 per cent of the typical total Hot DOG IR luminosity, respectively. The two most distant and luminous targets have similar observed submm to mid-infrared ratios to the rest, and thus appear to have even hotter SEDs. The number of serendipitous submm galaxies detected in the 1.5-arcmin-radius SCUBA-2 850 μm maps indicates there is a significant overdensity of serendipitous sources around Hot DOGs. These submm observations confirm that the WISE-selected ultraluminous galaxies have very blue mid-infrared to submm SEDs, suggesting that they contain very powerful AGN, and are apparently located in unusual arcmin-scale overdensities of very luminous dusty galaxies.
Abstract
We report the discovery of the hyperluminous, highly obscured active galactic nuclei (AGN) WISE J190445.04+485308.9 (W1904+4853, hereafter,
L
bol
∼ 1.1 × 10
13
L
⊙
) at
z
= 0.415. Its ...well-sampled spectral energy distribution (SED) is dominated by infrared dust emission, though broad emission lines are detected in the optical spectra. These features suggest that W1904+4853 contains an actively accreting supermassive black hole hidden in its dusty cocoon, resembling the observed properties of hot dust-obscured galaxies (Hot DOGs), a population previously only identified at
z
> 1.0. Using the broad component of the Mg
ii
2798 Å emission line, we estimate a black hole mass of
log
(
M
BH
/
M
⊙
)
=
8.4
±
0.4
. The corresponding Eddington ratio (
η
) of
1.4
−
0.7
+
1.3
implies that the central black hole accretion is at the theoretical limit of isotropic accretion. The rest-frame UV-optical SED also indicates that the host galaxy of W1904+4853 harbors strong star formation activity at the rate of 6–84
M
⊙
yr
−1
with an independent estimate of star formation rate up to ∼45
M
⊙
yr
−1
using the O
ii
emission line. With an estimated stellar mass of 3 × 10
10
M
⊙
, the host galaxy appears to be a starburst system with respect to the main sequence of the star-forming galaxies at the same redshift. Although blueshifted and asymmetric O
iii
emission provides evidence of an outflow, we estimate it to be an order of magnitude smaller than the star formation rate, indicating that the current obscured AGN activity at the center has not yet produced significant feedback on the host galaxy star formation activity. W1904+4853 supports the interpretation that Hot DOGs are a rare transitional phase of AGN accretion in galaxy evolution, a phase that can persist into the present-day Universe.
Abstract
We have used the Submillimeter Array (SMA) at 860 $\mu$m to observe the brightest sources in the Submillimeter Common User Bolometer Array-2 (SCUBA-2) Cosmology Legacy Survey (S2CLS). The ...goal of this survey is to exploit the large field of the S2CLS along with the resolution and sensitivity of the SMA to construct a large sample of these rare sources and to study their statistical properties. We have targeted 70 of the brightest single-dish SCUBA-2 850 $\mu$m sources down to S850 ≈ 8 mJy, achieving an average synthesized beam of 2.4 arcsec and an average rms of σ860 = 1.5 mJy beam−1 in our primary beam-corrected maps. We searched our SMA maps for 4σ peaks, corresponding to S860 ≳ 6 mJy sources, and detected 62, galaxies, including three pairs. We include in our study 35 archival observations, bringing our sample size to 105 bright single-dish submillimetre sources with interferometric follow-up. We compute the cumulative and differential number counts, finding them to overlap with previous single-dish survey number counts within the uncertainties, although our cumulative number count is systematically lower than the parent S2CLS cumulative number count by 14 ± 6 per cent between 11 and 15 mJy. We estimate the probability that a ≳10 mJy single-dish submillimetre source resolves into two or more galaxies with similar flux densities to be less than 15 per cent. Assuming the remaining 85 per cent of the targets are ultraluminous starburst galaxies between z = 2 and 3, we find a likely volume density of ≳400 M⊙ yr−1 sources to be ${\sim }\,3^{+0.7}_{-0.6}\,{\times }\,10^{-7}$ Mpc−3. We show that the descendants of these galaxies could be ≳4 × 1011 M⊙ local quiescent galaxies, and that about 10 per cent of their total stellar mass would have formed during these short bursts of star formation.
Abstract
Interferometric observations have demonstrated that a significant fraction of single-dish submillimetre (submm) sources are blends of multiple submm galaxies (SMGs), but the nature of this ...multiplicity, i.e. whether the galaxies are physically associated or chance projections, has not been determined. We performed spectroscopy of 11 SMGs in six multicomponent submm sources, obtaining spectroscopic redshifts for nine of them. For an additional two component SMGs, we detected continuum emission but no obvious features. We supplement our observed sources with four single-dish submm sources from the literature. This sample allows us to statistically constrain the physical nature of single-dish submm source multiplicity for the first time. In three $(3/7, \rm{ or}\,\,43^{+39 }_{ -33}\,\,\rm{per\,\,cent\,\,\,\,at\,\,95\,\,{per\,\,cent}\,\,confidence})$ of the single-dish sources for which the nature of the blending is unambiguous, the components for which spectroscopic redshifts are available are physically associated, whereas 4/7 $(57^{+33 }_{ -39} \text{ per cent})$ have at least one unassociated component. When components whose spectra exhibit continuum but no features and for which the photometric redshift is significantly different from the spectroscopic redshift of the other component are also considered, 6/9 $(67^{+26 }_{ -37} \text{ per cent})$ of the single-dish sources are comprised of at least one unassociated component SMG. The nature of the multiplicity of one single-dish source is ambiguous. We conclude that physically associated systems and chance projections both contribute to the multicomponent single-dish submm source population. This result contradicts the conventional wisdom that bright submm sources are solely a result of merger-induced starbursts, as blending of unassociated galaxies is also important.
We present CO(1-0), CO(3-2), and CO(7-6) observations using the Green Bank Telescope (GBT) and the Atacama Large Millimeter Array (ALMA) of the z = 2.8 submillimeter galaxy SMM J02399−0136. This was ...the first submillimeter-selected galaxy discovered and remains an archetype of the class, comprising a merger of several massive and active components, including a quasar-luminosity AGN and a highly obscured, gas-rich starburst spread over a ∼25 kpc extent. The GBT CO(1-0) line profile is comprised of two distinct velocity components separated by about 600 km s−1 and suggests the presence of a new component of molecular gas that had not been previously identified. The CO(3-2) observations with ALMA show that this new component, designated W1, is associated with a large extended structure stretching 13 kpc westward from the AGN. W1 is not detected in the ALMA CO(7-6) data, implying that this gas has much lower CO excitation than the central starburst regions, which are bright in CO(7-6). The molecular gas mass of W1 is about 30% of the total molecular gas mass in the system, depending on the CO-to-H2 conversion factor. W1 is arguably a merger remnant; alternatively, it could be a massive molecular outflow associated with the AGN, or perhaps inflowing metal-enriched molecular gas fueling the ongoing activity.
We report the identification of Lyman break galaxy (LBG) candidates around the most luminous hot dust-Obscured galaxy (Hot DOG) known, WISE J224607.56−052634.9 (W2246−0526) at
z
= 4.601, using deep
...r
-,
i
-, and
z
-band imaging from the Gemini Multi-Object Spectrograph South (GMOS-S). We used the surface density of LBGs to probe the megaparsec-scale environment of W2246−0526 to characterize its richness and evolutionary state. We identified LBG candidates in the vicinity of W2246−0526 using the selection criteria developed in the Subaru Deep Field and in the Subaru
XMM-Newton
Deep Field, slightly modified to account for the difference between the filters used, and we find 37 and 55 LBG candidates, respectively. Matching to the
z
-band depths of those studies, this corresponds to
δ
= 5.8
−1.9
+2.4
times the surface density of LBGs expected in the field. Interestingly, the Hot DOG itself, as well as a confirmed neighbor, do not satisfy either LBG selection criteria, suggesting we may be missing a large number of companion galaxies. Our analysis shows that we have mostly likely only found those with a higher than average intergalactic medium (IGM) optical depth or moderately high dust obscuration. The number density of LBG candidates is not concentrated around W2246−0526, suggesting an early evolutionary stage for the proto-cluster, that the Hot DOG may not be the most massive galaxy, or that the Hot DOG may be affecting the IGM transparency in its vicinity. The overdensity around W2246−0526 is comparable to overdensities found around other Hot DOGs and is somewhat higher than what is typically found for radio galaxies and luminous quasars at a similar redshift.
Abstract
We investigate extremely luminous dusty galaxies in the environments around Wide-field Infrared Survey Explorer (WISE)-selected hot dust-obscured galaxies (Hot DOGs) and WISE/radio-selected ...active galactic nuclei (AGNs) at average redshifts of z = 2.7 and 1.7, respectively. Previous observations have detected overdensities of companion submillimetre-selected sources around 10 Hot DOGs and 30 WISE/radio AGNs, with overdensities of ∼2–3 and ∼5–6, respectively. We find that the space densities in both samples to be overdense compared to normal star-forming galaxies and submillimetre galaxies (SMGs) in the Submillimetre Common-User Bolometer Array 2 (SCUBA-2) Cosmology Legacy Survey (S2CLS). Both samples of companion sources have consistent mid-infrared (mid-IR) colours and mid-IR to submm ratios as SMGs. The brighter population around WISE/radio AGNs could be responsible for the higher overdensity reported. We also find that the star formation rate densities are higher than the field, but consistent with clusters of dusty galaxies. WISE-selected AGNs appear to be good signposts for protoclusters at high redshift on arcmin scales. The results reported here provide an upper limit to the strength of angular clustering using the two-point correlation function. Monte Carlo simulations show no angular correlation, which could indicate protoclusters on scales larger than the SCUBA-2 1.5-arcmin scale maps.
Abstract Hot dust-obscured galaxies (Hot DOGs) are a rare population of hyperluminous infrared galaxies discovered by the Wide-field Infrared Survey Explorer mission. Despite the significant ...obscuration of the active galactic nucleus (AGN) by dust in these systems, pronounced broad and blueshifted emission lines are often observed. Previous work has shown that eight Hot DOGs, referred to as blue-excess Hot DOGs (BHDs), present a blue excess consistent with type 1 quasar emission in their UV–optical spectral energy distributions (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–mid-IR 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 C iv and Mg ii lines, we find that the mass of the black hole M BH in a BHD ranges from 10 8.7 to 10 10 M ⊙ . When using the same emission lines in regular Hot DOGs, we find the M 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 ∼ 6 quasars, we find that Hot DOGs sit above the local relation between stellar and black hole masses, 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.
Abstract
The SCUBA-2 Ultra Deep Imaging EAO Survey (STUDIES) is a three-year JCMT Large Program aiming to reach the 450
μ
m confusion limit in the COSMOS-CANDELS region to study a representative ...sample of the high-redshift far-infrared galaxy population that gives rise to the bulk of the far-infrared background. We present the first-year data from STUDIES. We reached a 450
μ
m noise level of 0.91 mJy for point sources at the map center, covered an area of 151 arcmin
2
, and detected 98 and 141 sources at 4.0
σ
and 3.5
σ
, respectively. Our derived counts are best constrained in the 3.5–25 mJy regime using directly detected sources. Below the detection limits, our fluctuation analysis further constrains the slope of the counts down to 1 mJy. The resulting counts at 1–25 mJy are consistent with a power law having a slope of −2.59 (±0.10 for 3.5–25 mJy, and
−
0.7
+
0.4
for 1–3.5 mJy). There is no evidence of a faint-end termination or turnover of the counts in this flux density range. Our counts are also consistent with previous SCUBA-2 blank-field and lensing-cluster surveys. The integrated surface brightness from our counts down to 1 mJy is 90.0 ± 17.2 Jy deg
−2
, which can account for up to
83
−
16
+
15
%
of the
COBE
450
μ
m background. We show that
Herschel
counts at 350 and 500
μ
m are significantly higher than our 450
μ
m counts, likely caused by its large beam and source clustering. High angular resolution instruments like SCUBA-2 at 450
μ
m are therefore highly beneficial for measuring the luminosity and spatial density of high-redshift dusty galaxies.
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