ORCID Profile
0000-0002-4030-5461
Current Organisation
University of California Davis
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Publisher: American Astronomical Society
Date: 20-08-2012
Publisher: Oxford University Press (OUP)
Date: 12-09-2019
Abstract: We present the measurement of the Hubble constant, H0, with three strong gravitational lens systems. We describe a blind analysis of both PG 1115+080 and HE 0435−1223 as well as an extension of our previous analysis of RXJ 1131−1231. For each lens, we combine new adaptive optics (AO) imaging from the Keck Telescope, obtained as part of the SHARP (Strong-lensing High Angular Resolution Programme) AO effort, with Hubble Space Telescope (HST) imaging, velocity dispersion measurements, and a description of the line-of-sight mass distribution to build an accurate and precise lens mass model. This mass model is then combined with the COSMOGRAIL-measured time delays in these systems to determine H0. We do both an AO-only and an AO + HST analysis of the systems and find that AO and HST results are consistent. After unblinding, the AO-only analysis gives $H_{0}=82.8^{+9.4}_{-8.3}~\\rm km\\, s^{-1}\\, Mpc^{-1}$ for PG 1115+080, $H_{0}=70.1^{+5.3}_{-4.5}~\\rm km\\, s^{-1}\\, Mpc^{-1}$ for HE 0435−1223, and $H_{0}=77.0^{+4.0}_{-4.6}~\\rm km\\, s^{-1}\\, Mpc^{-1}$ for RXJ 1131−1231. The joint AO-only result for the three lenses is $H_{0}=75.6^{+3.2}_{-3.3}~\\rm km\\, s^{-1}\\, Mpc^{-1}$. The joint result of the AO + HST analysis for the three lenses is $H_{0}=76.8^{+2.6}_{-2.6}~\\rm km\\, s^{-1}\\, Mpc^{-1}$. All of these results assume a flat Λ cold dark matter cosmology with a uniform prior on Ωm in [0.05, 0.5] and H0 in [0, 150] $\\rm km\\, s^{-1}\\, Mpc^{-1}$. This work is a collaboration of the SHARP and H0LiCOW teams, and shows that AO data can be used as the high-resolution imaging component in lens-based measurements of H0. The full time-delay cosmography results from a total of six strongly lensed systems are presented in a companion paper.
Publisher: American Astronomical Society
Date: 09-2008
DOI: 10.1086/590377
Publisher: American Astronomical Society
Date: 28-03-2013
Publisher: Oxford University Press (OUP)
Date: 04-06-2018
Publisher: Oxford University Press (OUP)
Date: 16-05-2020
Abstract: We present a study of the stellar host galaxy, CO (1–0) molecular gas distribution and AGN emission on 50–500 pc-scales of the gravitationally lensed dust-obscured AGN MG J0751+2716 and JVAS B1938+666 at redshifts 3.200 and 2.059, respectively. By correcting for the lensing distortion using a grid-based lens modelling technique, we spatially locate the different emitting regions in the source plane for the first time. Both AGN host galaxies have 300–500 pc-scale size and surface brightness consistent with a bulge seudo-bulge, and 2 kpc-scale AGN radio jets that are embedded in extended molecular gas reservoirs that are 5–20 kpc in size. The CO (1–0) velocity fields show structures possibly associated with discs (elongated velocity gradients) and interacting objects (off-axis velocity components). There is evidence for a decrement in the CO (1–0) surface brightness at the location of the host galaxy, which may indicate radiative feedback from the AGN, or offset star formation. We find CO–H2 conversion factors of around αCO = 1.5 ± 0.5 (K km s−1 pc2)−1, molecular gas masses of & × 1010 M⊙, dynamical masses of ∼1011 M⊙, and gas fractions of around 60 per cent. The intrinsic CO line luminosities are comparable to those of unobscured AGN and dusty star-forming galaxies at similar redshifts, but the infrared luminosities are lower, suggesting that the targets are less efficient at forming stars. Therefore, they may belong to the AGN feedback phase predicted by galaxy formation models, because they are not efficiently forming stars considering their large amount of molecular gas.
Publisher: American Astronomical Society
Date: 28-09-2015
Publisher: American Astronomical Society
Date: 04-04-2014
Publisher: Oxford University Press (OUP)
Date: 22-05-2018
Publisher: American Astronomical Society
Date: 04-04-2013
Publisher: Wiley
Date: 02-2009
Abstract: Compact Symmetric Objects (CSOs) are small (less than 1 kpc) radio sources which have symmetric double lobes or jets. The dominant theory for the small size of these objects is that they are young radio sources which could grow into larger radio galaxies, but the currently small population of known CSOs makes it difficult to definitively determine whether or not this is the case. While a greater number of Gigahertz peaked sources can be identified by sifting through spectral surveys, this yields none of the dynamics of the sources, and also brings Quasars into the s le, which although interesting are peaked around 1 Gigahertz for very different reasons. We have used the 5 GHz VLBA Imaging and Polarization Survey (VIPS) to identify 103 CSO candidates morphologically, and are following up on these sources with multifrequency VLBA observations to confirm CSO identifications and to study their dynamics. The identification of candidates from within the survey will be discussed, as well as preliminary results from the follow‐up observations (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Publisher: Springer Science and Business Media LLC
Date: 03-2013
DOI: 10.1038/NATURE12001
Abstract: In the past decade, our understanding of galaxy evolution has been revolutionized by the discovery that luminous, dusty starburst galaxies were 1,000 times more abundant in the early Universe than at present. It has, however, been difficult to measure the complete redshift distribution of these objects, especially at the highest redshifts (z > 4). Here we report a redshift survey at a wavelength of three millimetres, targeting carbon monoxide line emission from the star-forming molecular gas in the direction of extraordinarily bright millimetre-wave-selected sources. High-resolution imaging demonstrates that these sources are strongly gravitationally lensed by foreground galaxies. We detect spectral lines in 23 out of 26 sources and multiple lines in 12 of those 23 sources, from which we obtain robust, unambiguous redshifts. At least 10 of the sources are found to lie at z > 4, indicating that the fraction of dusty starburst galaxies at high redshifts is greater than previously thought. Models of lens geometries in the s le indicate that the background objects are ultra-luminous infrared galaxies, powered by extreme bursts of star formation.
Publisher: Oxford University Press (OUP)
Date: 27-04-2022
Abstract: Strongly lensed quasars can provide measurements of the Hubble constant (H0) independent of any other methods. One of the key ingredients is exquisite high-resolution imaging data, such as Hubble Space Telescope (HST) imaging and adaptive-optics (AO) imaging from ground-based telescopes, which provide strong constraints on the mass distribution of the lensing galaxy. In this work, we expand on the previous analysis of three time-delay lenses with AO imaging (RX J1131−1231, HE 0435−1223, and PG 1115+080), and perform a joint analysis of J0924+0219 by using AO imaging from the Keck telescope, obtained as part of the Strong lensing at High Angular Resolution Program (SHARP) AO effort, with HST imaging to constrain the mass distribution of the lensing galaxy. Under the assumption of a flat Λ cold dark matter (ΛCDM) model with fixed Ωm = 0.3, we show that by marginalizing over two different kinds of mass models (power-law and composite models) and their transformed mass profiles via a mass-sheet transformation, we obtain $\\Delta t_{\\rm BA}=6.89\\substack{+0.8\\\\-0.7}\\, h^{-1}\\hat{\\sigma }_{v}^{2}$ d, $\\Delta t_{\\rm CA}=10.7\\substack{+1.6\\\\-1.2}\\, h^{-1}\\hat{\\sigma }_{v}^{2}$ d, and $\\Delta t_{\\rm DA}=7.70\\substack{+1.0\\\\-0.9}\\, h^{-1}\\hat{\\sigma }_{v}^{2}$ d, where $h=H_{0}/100\\,\\rm km\\, s^{-1}\\, Mpc^{-1}$ is the dimensionless Hubble constant and $\\hat{\\sigma }_{v}=\\sigma ^{\\rm ob}_{v}/(280\\,\\rm km\\, s^{-1})$ is the scaled dimensionless velocity dispersion. Future measurements of time delays with 10 per cent uncertainty and velocity dispersion with 5 per cent uncertainty would yield a H0 constraint of ∼15 per cent precision.
Publisher: American Astronomical Society
Date: 26-11-2013
Publisher: Oxford University Press (OUP)
Date: 03-09-2018
Publisher: American Astronomical Society
Date: 09-01-2004
DOI: 10.1086/379232
Publisher: Oxford University Press (OUP)
Date: 21-05-2013
DOI: 10.1093/MNRAS/STT741
Location: United States of America
Location: United States of America
Location: United States of America
No related grants have been discovered for Christopher Fassnacht.