61 research outputs found
Heavily reddened type 1 quasars at z > 2 I: Evidence for significant obscured black-hole growth at the highest quasar luminosities
We present a new population of z>2 dust-reddened, Type 1 quasars with
0.5<E(B-V)<1.5, selected using near infra-red (NIR) imaging data from the
UKIDSS-LAS, ESO-VHS and WISE surveys. NIR spectra obtained using the Very Large
Telescope (VLT) for 24 new objects bring our total sample of spectroscopically
confirmed hyperluminous (>10^{13}L_0), high-redshift dusty quasars to 38. There
is no evidence for reddened quasars having significantly different H
equivalent widths relative to unobscured quasars. The average black-hole masses
(~10^9-10^10 M_0) and bolometric luminosities (~10^{47} erg/s) are comparable
to the most luminous unobscured quasars at the same redshift, but with a tail
extending to very high luminosities of ~10^{48} erg/s. Sixty-six per cent of
the reddened quasars are detected at at 22um by WISE. The average
6um rest-frame luminosity is log10(L6um/erg/s)=47.1+/-0.4, making the objects
among the mid-infrared brightest AGN currently known. The extinction-corrected
space-density estimate now extends over three magnitudes (-30 < M_i < -27) and
demonstrates that the reddened quasar luminosity function is significantly
flatter than that of the unobscured quasar population at z=2-3. At the
brightest magnitudes, M_i < -29, the space density of our dust-reddened
population exceeds that of unobscured quasars. A model where the probability
that a quasar becomes dust-reddened increases at high luminosity is consistent
with the observations and such a dependence could be explained by an increase
in luminosity and extinction during AGN-fuelling phases. The properties of our
obscured Type 1 quasars are distinct from the heavily obscured, Compton-thick
AGN that have been identified at much fainter luminosities and we conclude that
they likely correspond to a brief evolutionary phase in massive galaxy
formation.Comment: 16 pages, 9 figures (+ 2 appendices), Accepted for publication in
MNRA
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Heavily reddened z ~ 2 Type 1 quasars - II. H α star formation constraints from SINFONI IFU observations
We use near infrared integral field unit (IFU) spectroscopy to search for
H emission associated with star formation in a sample of 28 heavily
reddened (0.5-1.9), hyperluminous
(47-48) broad-line quasars at 1.4-2.7.
Sixteen of the 28 quasars show evidence for star formation with an average
extinction-corrected star formation rate (SFR) of 32070Myr.
A stacked spectrum of the detections shows weak [NII], consistent with star
formation as the origin of the narrow H emission. The star-forming
regions are spatially unresolved in 11 of the 16 detections and constrained to
lie within 6kpc of the quasar emission. In the five resolved detections
we find the star-forming regions are extended on scales of 8kpc around
the quasar emission. The prevalence of high SFRs is consistent with the
identification of the heavily reddened quasar population as representing a
transitional phase from apparent `starburst galaxies' to optically-luminous
quasars. Upper limits are determined for 10 quasars in which star formation is
undetected. In two of the quasars the SFR is constrained to be relatively
modest, 50Myr, but significantly higher levels of star
formation could be present in the other eight quasars. The combination of the
16 strong star formation detections and the eight high SFR limits means that
high levels of star formation may be present in the majority of the sample.
Higher spatial resolution data, of multiple emission lines, will allow us to
better understand the interplay between star formation and Active Galactic
Nucleus (AGN) activity in these transitioning quasars.The authors thank the Science and Technology Facilities Council (STFC) via the Consolidated Grant awarded to the Institute of Astronomy, Cambridge. SA-Z acknowledges the support from Peterhouse, Cambridge, and the Institute of Astronomy, Cambridge. The narrow-band imaging study is based on observations made with ESO Telescopes at the La Sill a Paranal Observatory under programme ID: 290.A-5062. The IFU study is based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme IDs:383.A-0573 (PI:McMahon) and 091.A-0341 (PI:Banerji).This is the author accepted manuscript. The final version is available from Oxford University Press via http://dx.doi.org/10.1093/mnras/stw68
The Discovery of Gas-Rich, Dusty Starbursts in Luminous Reddened Quasars at with ALMA
We present ALMA observations of cold dust and molecular gas in four high-luminosity, heavily reddened (A mag) Type 1 quasars at with virial MM, to test whether dusty, massive quasars represent the evolutionary link between submillimetre bright galaxies (SMGs) and unobscured quasars. All four quasars are detected in both the dust continuum and in the CO(3-2) line. The mean dust mass is 610M assuming a typical high redshift quasar spectral energy distribution (T=41K, =1.95 or T=47K, =1.6). The implied star formation rates are very high - 1000 M yr in all cases. Gas masses estimated from the CO line luminosities cover 1-5()M and the gas depletion timescales are very short - Myr. A range of gas-to-dust ratios is observed in the sample. We resolve the molecular gas in one quasar - ULASJ23150143 () - which shows a strong velocity gradient over 20 kpc. The velocity field is consistent with a rotationally supported gas disk but other scenarios, e.g. mergers, cannot be ruled out at the current resolution of these data. In another quasar - ULASJ1234+0907 () - we detected molecular line emission from two millimetre bright galaxies within 200 kpc of the quasar, suggesting that this quasar resides in a significant over-density. The high detection rate of both cold dust and molecular gas in these sources, suggests that reddened quasars could correspond to an early phase in massive galaxy formation associated with large gas reservoirs and significant star formation.MB acknowledges funding from the UK Science and Technology Facilities Council (STFC) via an Ernest Rutherford Fellowship. GJ is grateful for support from NRAO through the Grote Reber Doctoral Fellowship Program. RGM and PCH acknowledge funding from STFC via the Institute of Astronomy, Cambridge Consolidated Grant. SA-Z acknowledges support from Peterhouse, Cambridge
Energetic Galaxy-Wide Outflows in High-Redshift Ultraluminous Infrared Galaxies Hosting AGN Activity
We present integral field spectroscopy observations, covering the [O III]4959,5007 emission-line doublet of eight high-redshift (z=1.4-3.4) ultra-luminous infrared galaxies (ULIRGs) that host Active Galactic Nuclei (AGN) activity, including known sub-millimetre luminous galaxies (SMGs). The targets have moderate radio luminosities that are typical of high-redshift ULIRGs (L(1.4GHz)=10^(24)-10^(25)W/Hz) and therefore are not radio-loud AGN. We de-couple kinematic components due to the galaxy dynamics and mergers from those due to outflows. We find evidence in the four most luminous systems (L([O III])\u3e~10^(43)erg/s) for the signatures of large-scale energetic outflows: extremely broad [O III] emission (FWHM ~ 700-1400km/s) across ~4-15kpc, with high velocity offsets from the systemic redshifts (up to ~850km/s). The four less luminous systems have lower quality data displaying weaker evidence for spatially extended outflows. We estimate that these outflows are potentially depositing energy into their host galaxies at considerable rates (~10^(43)-10^(45)erg/s); however, due to the lack of constraints on the density of the outflowing material and the structure of the outflow, these estimates should be taken as illustrative only. Based on the measured maximum velocities (v(max)~400-1400km/s) the outflows observed are likely to unbind some fraction of the gas from their host galaxies, but are unlikely to completely remove gas from the galaxy haloes. By using a combination of energetic arguments and a comparison to ULIRGs without clear evidence for AGN activity, we show that the AGN activity could be the dominant power source for driving all of the observed outflows, although star formation may also play a significant role in some of the sources
The discovery of gas-rich, dusty starbursts in luminous reddened quasars at z ∼ 2.5 with ALMA
We present ALMA observations of cold dust and molecular gas in four high-luminosity, heavily reddened (AV ∼ 2.5-6 mag) type 1 quasars at z ∼ 2.5 with virial MBH ∼ 1010 M⊙, to test whether dusty, massive quasars represent the evolutionary link between submillimetre-bright galaxies and unobscured quasars. All four quasars are detected in both the dust continuum and in the 12CO(3-2) line. The mean dust mass is 6 × 108 M⊙ assuming a typical high-redshift quasar spectral energy distribution (T = 41 K, β = 1.95 or T = 47 K, β = 1.6). The implied star formation rates are very high - ≳1000 M⊙ yr-1 in all cases. Gas masses estimated from the CO line luminosities cover ∼1-5× 1010(αCO/0.8)M⊙ and the gas depletion time-scales are very short - ∼5-20 Myr. A range of gas-to-dust ratios is observed in the sample. We resolve the molecular gas in one quasar - ULASJ2315+0143 (z = 2.561) - which shows a strong velocity gradient over ∼20 kpc. The velocity field is consistent with a rotationally supported gas disc but other scenarios, e.g. mergers, cannot be ruled out at the current resolution of these data. In another quasar - ULASJ1234+0907 (z = 2.503) - we detected molecular line emission from two millimetre-bright galaxies within 200 kpc of the quasar, suggesting that this quasar resides in a significant overdensity. The high detection rate of both cold dust and molecular gas in these sources, suggests that reddened quasars could correspond to an early phase in massive galaxy formation associated with large gas reservoirs and significant star formation
The properties of (sub)millimetre-selected galaxies as revealed by CANDELS HST WFC3/IR imaging in GOODS-South
We have exploited the HST CANDELS WFC3/IR imaging to study the properties of
(sub-)mm galaxies in GOODS-South. After using the deep radio and Spitzer
imaging to identify galaxy counterparts for the (sub-)mm sources, we have used
the new CANDELS data in two ways. First, we have derived improved photometric
redshifts and stellar masses, confirming that the (sub-)mm galaxies are massive
(=2.2x10^11 M_solar) galaxies at z=1-3. Second, we have exploited the depth
and resolution of the WFC3/IR imaging to determine the sizes and morphologies
of the galaxies at rest-frame optical wavelengths, fitting two-dimensional
axi-symmetric Sersic models. Crucially, the WFC3/IR H-band imaging enables
modelling of the mass-dominant galaxy, rather than the blue high-surface
brightness features which often dominate optical (rest-frame UV) images of
(sub-)mm galaxies, and can confuse visual morphological classification. As a
result of this analysis we find that >95% of the rest-frame optical light in
almost all of the (sub-)mm galaxies is well-described by either a single
exponential disk, or a multiple-component system in which the dominant
constituent is disk-like. We demonstrate that this conclusion is consistent
with the results of high-quality ground-based K-band imaging, and explain why.
The massive disk galaxies which host luminous (sub-)mm emission are reasonably
extended (r_e=4 kpc), consistent with the sizes of other massive star-forming
disks at z~2. In many cases we find evidence of blue clumps within the sources,
with the mass-dominant disk becoming more significant at longer wavelengths.
Finally, only a minority of the sources show evidence for a major galaxy-galaxy
interaction. Taken together, these results support the view that most (sub-)mm
galaxies at z~2 are simply the most extreme examples of normal star-forming
galaxies at that era.Comment: 30 pages, 9 figure
VLT-SINFONI integral field spectroscopy of low-z luminous and ultraluminous infrared galaxies
We present a 2D study of the internal extinction on (sub)kiloparsec scales of a sample of local (z < 0.1) LIRGs (10) and ULIRGs (7), based on near-infrared Paα, Brδ, and Brγ line ratios, obtained with VLT-SINFONI integral-field spectroscopy (IFS). The 2D extinction (AV) distributions of the objects, map regions of ~ 3 × 3 kpc (LIRGs) and ~ 12 × 12 kpc (ULIRGs), with average angular resolutions (FWHM) of ~0.2 kpc and ~0.9 kpc, respectively. The individual AV galaxy distributions indicate a very clumpy dust structure already on sub-kiloparsec scales, with values (per spaxel) ranging from AV ~ 1 to 20 mag in LIRGs, and from AV ~ 2 to 15 mag in ULIRGs. As a class, the median values of the distributions are AV = 5.3 mag and AV = 6.5 mag for the LIRG and ULIRG subsamples, respectively. In ~70% of the objects, the extinction peaks at the nucleus with values ranging from AV ~ 3 to 17 mag. Within each galaxy, the AV radial profile shows a mild decrement in LIRGs within the inner 2 kpc radius, while the same radial variation is not detected in ULIRGs, likely because of the lower linear scale resolution of the observations at the distance of ULIRGs. We evaluated the effects of the galaxy distance in the measurements of the extinction as a function of the linear scale (in kpc) of the spaxel (i.e. due to the limited angular resolution of the observations). If the distribution of the gas/dust and star-forming regions in local LIRGs (63 Mpc, 40 pc/spaxel on average) is the same for galaxies at greater distances, the observed median AV values based on emission line ratios would be a factor ~0.8 lower at the average distance of our ULIRG sample (328 Mpc, 0.2 kpc/spaxel), and a factor ~0.67 for galaxies located at distances of more than 800 Mpc (0.4 kpc/spaxel). This distance effect would have implications for deriving the intrinsic extinction in high-z star-forming galaxies and for subsequent properties such as star formation rate, star formation surface density, and KS- law, based on Hα line fluxes. If local LIRGs are analogues of the main-sequence star-forming galaxies at cosmological distances, the extinction values (AV) derived from the observed emission lines in these high-z sources would need to be increased by a factor 1.4 on average
Obese patients after gastric bypass surgery have lower brain-hedonic responses to food than after gastric banding
Objectives Roux-en-Y gastric bypass (RYGB) has greater efficacy for weight loss in obese patients than gastric banding (BAND) surgery. We hypothesise that this may result from different effects on food hedonics via physiological changes secondary to distinct gut anatomy manipulations.
Design We used functional MRI, eating behaviour and hormonal phenotyping to compare body mass index (BMI)-matched unoperated controls and patients after RYGB and BAND surgery for obesity.
Results Obese patients after RYGB had lower brain-hedonic responses to food than patients after BAND surgery. RYGB patients had lower activation than BAND patients in brain reward systems, particularly to high-calorie foods, including the orbitofrontal cortex, amygdala, caudate nucleus, nucleus accumbens and hippocampus. This was associated with lower palatability and appeal of high-calorie foods and healthier eating behaviour, including less fat intake, in RYGB compared with BAND patients and/or BMI-matched unoperated controls. These differences were not explicable by differences in hunger or psychological traits between the surgical groups, but anorexigenic plasma gut hormones (GLP-1 and PYY), plasma bile acids and symptoms of dumping syndrome were increased in RYGB patients.
Conclusions The identification of these differences in food hedonic responses as a result of altered gut anatomy/physiology provides a novel explanation for the more favourable long-term weight loss seen after RYGB than after BAND surgery, highlighting the importance of the gut–brain axis in the control of reward-based eating behaviour
Integral Field Spectroscopy of 2.0
We present 2D, integral field spectroscopy covering the rest-frame wavelengths of strong optical emission lines in nine submillimetre luminous galaxies (SMGs) at 2.0 \u3c z \u3c 2.7. The Gemini-North/Near-Infrared Integral Field Spectrograph (NIFS) and Very Large Telescope (VLT) Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) imaging spectroscopy allow the mapping of the gas morphologies and dynamics within the sources, and we measure an average Hα velocity dispersion of 〈σ〉 = 220 ± 80 km s−1 and an average half-light radius of 〈r1/2〉 = 3.7 ± 0.8 kpc. The dynamical measure, 〈Vobs/2σ〉 = 0.9 ± 0.1, for the SMGs is higher than in more quiescent star-forming galaxies at the same redshift, highlighting a difference in the dynamics of the two populations. The far-infrared star formation rates (SFRs) of the SMGs, measured using Herschel-SPIRE†far-infrared photometry, are on average 370 ± 90 M⊙ yr−1, which is ∼2 times higher than the extinction-corrected SFRs of the more quiescent star-forming galaxies. Six of the SMGs in our sample show strong evidence for kinematically distinct multiple components with average velocity offsets of 200 ± 100 km s−1 and average projected spatial offsets of 8 ± 2 kpc, which we attribute to systems in the early stages of major mergers. Indeed, all SMGs are classified as mergers from a kinemetry analysis of the velocity and dispersion field asymmetry. We bring together our sample with the seven other SMGs with integral field unit observations to describe the ionized gas morphologies and kinematics in a sample of 16 SMGs. By comparing the velocity and spatial offsets of the SMG Hα components with subhalo offsets in the Millennium Simulation data base, we infer an average halo mass for SMGs in the range of 13 \u3c log (M[h−1 M⊙]) \u3c 14. Finally, we explore the relationship between the velocity dispersion and star formation intensity within the SMGs, finding that the gas motions are consistent with the Kennicutt–Schmidt law and a range of extinction corrections, although they might also be driven by the tidal torques from merging or even the star formation itself
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