ABSTRACT The most frequently proposed model for the origin of quasars holds that the high accretion rates seen in luminous active galactic nuclei (AGN) are primarily triggered during major mergers ...between gas-rich galaxies. While plausible for decades, this model has only begun to be tested with statistical rigor in the past few years. Here, we report on a Hubble Space Telescope study to test this hypothesis for z = 2 quasars with high supermassive black hole masses ( ), which dominate cosmic black hole growth at this redshift. We compare Wide Field Camera 3 (rest-frame V-band) imaging of 19 point source-subtracted quasar hosts to a matched sample of 84 inactive galaxies, testing whether the quasar hosts have greater evidence for strong gravitational interactions. Using an expert ranking procedure, we find that the quasar hosts are uniformly distributed within the merger sequence of inactive galaxies, with no preference for quasars in high-distortion hosts. Using a merger/non-merger cutoff approach, we recover distortion fractions of for quasar hosts and for inactive galaxies (distribution modes, 68% confidence intervals), with both measurements subjected to the same observational conditions and limitations. The slight enhancement in distorted fraction for quasar hosts over inactive galaxies is not significant, with a probability that the quasar fraction is higher ( ), in line with results for lower mass and lower z AGN. We find no evidence that major mergers are the primary triggering mechanism for the massive quasars that dominate accretion at the peak of cosmic quasar activity.
We report on a Hubble Space Telescope search for rest-frame ultraviolet emission from the host galaxies of five far-infrared-luminous z 6 quasars and the z = 5.85 hot-dust-free quasar SDSS ...J0005-0006. We perform 2D surface brightness modeling for each quasar using a Markov Chain Monte Carlo estimator, to simultaneously fit and subtract the quasar point source in order to constrain the underlying host galaxy emission. We measure upper limits for the quasar host galaxies of mJ > 22.7 mag and mH > 22.4 mag, corresponding to stellar masses of M* < 2 × 1011M . These stellar mass limits are consistent with the local MBH − M* relation. Our flux limits are consistent with those predicted for the UV stellar populations of z 6 host galaxies, but likely in the presence of significant dust ( mag). We also detect a total of up to nine potential z 6 quasar companion galaxies surrounding five of the six quasars, separated from the quasars by 1 4-3 2, or 8.4-19.4 kpc, which may be interacting with the quasar hosts. These nearby companion galaxies have UV absolute magnitudes of −22.1 to −19.9 mag and UV spectral slopes β of −2.0 to −0.2, consistent with luminous star-forming galaxies at z 6. These results suggest that the quasars are in dense environments typical of luminous z 6 galaxies. However, we cannot rule out the possibility that some of these companions are foreground interlopers. Infrared observations with the James Webb Space Telescope will be needed to detect the z 6 quasar host galaxies and better constrain their stellar mass and dust content.
ABSTRACT
The Deep Extragalactic VIsible Legacy Survey (DEVILS) is an ongoing high-completeness, deep spectroscopic survey of ∼60 000 galaxies to Y < 21.2 mag, over ∼6 deg2 in three well-studied deep ...extragalactic fields: D10 (COSMOS), D02 (XMMLSS), and D03 (ECDFS). Numerous DEVILS projects all require consistent, uniformly derived and state-of-the-art photometric data with which to measure galaxy properties. Existing photometric catalogues in these regions either use varied photometric measurement techniques for different facilities/wavelengths leading to inconsistencies, older imaging data and/or rely on source detection and photometry techniques with known problems. Here, we use the ProFound image analysis package and state-of-the-art imaging data sets (including Subaru-HSC, VST-VOICE, VISTA-VIDEO, and UltraVISTA-DR4) to derive matched-source photometry in 22 bands from the FUV to 500 $\mu$m. This photometry is found to be consistent, or better, in colour analysis to previous approaches using fixed-size apertures (which are specifically tuned to derive colours), but produces superior total source photometry, essential for the derivation of stellar masses, star formation rates, star formation histories, etc. Our photometric catalogue is described in detail and, after internal DEVILS team projects, will be publicly released for use by the broader scientific community.
The first
James Webb
Space Telescope (JWST) data on the massive colliding cluster
El Gordo
allow for 23 known families of multiply lensed images to be confirmed and for eight new members of these ...families to be identified. Based on these families, which have been confirmed spectroscopically by MUSE, we derived an initial lens model. This model guided the identification of 37 additional families of multiply lensed galaxies, among which 28 are entirely new systems, and nine were previously known. The initial lens model determined geometric redshifts for the 37 new systems. The geometric redshifts agree reasonably well with spectroscopic or photometric redshifts when those are available. The geometric redshifts enable two additional models that include all 60 families of multiply lensed galaxies spanning a redshift range 2 <
z
< 6. The derived dark-matter distribution confirms the double-peak configuration of mass found by earlier work with the southern and northern clumps having similar masses. We confirm that El Gordo is the most massive known cluster at
z
> 0.8 and has an estimated virial mass close the maximum mass allowed by standard cosmological models. The JWST images also reveal the presence of small-mass perturbers that produce small lensing distortions. The smallest of these is consistent with being a dwarf galaxy at
z
= 0.87 and has an estimated mass of 3.8 × 10
9
M
⊙
, making it the smallest substructure found at
z
> 0.5. The JWST images also show several candidate caustic-crossing events. One of them is detected at high significance at the expected position of the critical curve and is likely a red supergiant star at
z
= 2.1878. This would be the first red supergiant found at cosmological distances. The cluster lensing should magnify background objects at
z
> 6, making more of them visible than in blank fields of a similar size, but there appears to be a deficiency of such objects.
We report on a complete sample of seven luminous early-type galaxies in the Hubble Ultra Deep Field (UDF) with spectroscopic redshifts between 1.39 and 2.47, and to K sub(AB) < 23. Using the BzK ...selection criterion, we have preselected a set of objects over the UDF, which fulfill the photometric conditions for being passively evolving galaxies at z > 1.4. Low-resolution spectra of these objects have been extracted from the Hubble Space Telescope (HST) ACS grism data taken over the UDF by the Grism ACS Program for Extragalactic Science (GRAPES) project. Redshifts for the seven galaxies have been identified based on the UV feature at rest frame 2640 < l < 2850 AA. This feature is mainly due to a combination of Fe II, Mg I, and Mg II absorptions, which are characteristic of stellar populations dominated by stars older than 60.5 Gyr. The redshift identification and the passively evolving nature of these galaxies is further supported by the photometric redshifts and by the overall spectral energy distribution (SED), with the ultradeep HST ACS NICMOS imaging revealing compact morphologies typical of elliptical/early-type galaxies. From the SED we derive stellar masses of 10 super(11) M sub( )and ages of 61 Gyr. Their space density at < z > = 1.7 appears to be roughly a factor of 2-3 smaller than that of their local counterparts, further supporting the notion that such massive and old galaxies are already ubiquitous at early cosmic times. Much smaller effective radii are derived for some of the objects, compared to local massive ellipticals, which may be due to morphological K-corrections, evolution, or the presence of a central pointlike source. Nuclear activity is indeed present in a subset of the galaxies, as revealed by the fact that they are hard X-ray sources, which suggests that active galactic nucleus (AGN) activity may have played a role in discontinuing star formation.
ABSTRACT
We present the NuSTAR extragalactic survey of the James Webb Space Telescope (JWST) North Ecliptic Pole (NEP) Time-Domain Field. The survey covers a ∼0.16 deg2 area with a total exposure of ...681 ks acquired in a total of nine observations from three epochs. The survey sensitivities at 20 per cent of the area are 2.39, 1.14, 2.76, 1.52, and 5.20 × 10−14 erg cm−2 s−1 in the 3–24, 3–8, 8–24, 8–16, and 16–24 keV bands, respectively. The NEP survey is one of the most sensitive extragalactic surveys with NuSTAR so far. A total of 33 sources were detected above 95 per cent reliability in at least one of the five bands. We present the number counts, logN-logS, measured in the hard X-ray 8–24 and 8–16 keV bands, uniquely accessible by NuSTAR down to such faint fluxes. We performed source detection on the XMM–Newton and Chandra observations of the same field to search for soft X-ray counterparts of each NuSTAR detection. The soft band positions were used to identify optical and infrared associations. We present the X-ray properties (hardness ratio and luminosity) and optical-to-X-ray properties of the detected sources. The measured fraction of candidate Compton-thick (N$\rm _H\ge 10^{24}\, cm^{-2}$) active galactic nuclei, derived from the hardness ratio, is between 3 and 27 per cent. As this survey was designed to have variability as its primary focus, we present preliminary results on multiepoch flux variability in the 3–24 keV band.
We study ∼330 massive (M
* > 109.5 M), newborn spheroidal galaxies (SGs) around the epoch of peak star formation (1 < z < 3) to explore the high-redshift origin of SGs and gain insight into when and ...how the old stellar populations that dominate today's Universe formed. The sample is drawn from the Hubble Space Telescope (HST)/WFC3 Early-Release Science programme, which provides deep 10-filter (0.2-1.7 μm) HST imaging over one-third of the GOODS-South field. We find that the star formation episodes that built our SGs likely peaked in the redshift range 2 < z < 5 (with a median of z ∼ 3) and have decay time-scales shorter than ∼1.5 Gyr. Starburst time-scales and ages show no trend with stellar mass in the range 109.5 < M
* < 1010.5 M. However, the time-scales show increased scatter towards lower values (<0.3 Gyr) for M
* > 1010.5 M, and an age trend becomes evident in this mass regime: SGs with M
* > 1011.5 M are ∼2 Gyr older than their counterparts with M
* < 1010.5 M. Nevertheless, a smooth downsizing trend with galaxy mass is not observed, and the large scatter in starburst ages indicates that SGs are not a particularly coeval population. Around half of the blue SGs appear not to drive their star formation via major mergers, and those that have experienced a recent major merger show only modest enhancements (∼40 per cent) in their specific star formation rates. Our empirical study indicates that processes other than major mergers (e.g. violent disc instability driven by cold streams and/or minor mergers) likely play a dominant role in building SGs, and creating a significant fraction of the old stellar populations that dominate today's Universe.
Osimertinib is a potent and selective EGFR tyrosine kinase inhibitor (EGFR-TKI) of both sensitizing and T790M resistance mutations. To treat metastatic brain disease, blood-brain barrier (BBB) ...permeability is considered desirable for increasing clinical efficacy.
We examined the level of brain penetration for 16 irreversible and reversible EGFR-TKIs using multiple
and
BBB preclinical models.
osimertinib was the weakest substrate for human BBB efflux transporters (efflux ratio 3.2).
rat free brain to free plasma ratios (Kpuu) show osimertinib has the most BBB penetrance (0.21), compared with the other TKIs (Kpuu ≤ 0.12). PET imaging in Cynomolgus macaques demonstrated osimertinib was the only TKI among those tested to achieve significant brain penetrance (
%ID 1.5, brain/blood Kp 2.6). Desorption electrospray ionization mass spectroscopy images of brains from mouse PC9 macrometastases models showed osimertinib readily distributes across both healthy brain and tumor tissue. Comparison of osimertinib with the poorly BBB penetrant afatinib in a mouse PC9 model of subclinical brain metastases showed only osimertinib has a significant effect on rate of brain tumor growth.
These preclinical studies indicate that osimertinib can achieve significant exposure in the brain compared with the other EGFR-TKIs tested and supports the ongoing clinical evaluation of osimertinib for the treatment of EGFR-mutant brain metastasis. This work also demonstrates the link between low
transporter efflux ratios and increased brain penetrance
supporting the use of
transporter assays as an early screen in drug discovery.
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