115 research outputs found
A subarcsecond near-infrared view of massive galaxies at z > 1 with Gemini Multiconjugate Adaptive Optics
We present images taken using the Gemini South Adaptive Optics Imager (GSAOI)
with the Gemini Multiconjugate Adaptive Optics System (GeMS) in three 2
arcmin fields in the Spitzer Extragalactic Representative Volume Survey.
These GeMS/GSAOI observations are among the first resolution
data in the near-infrared spanning extragalactic fields exceeding
in size. We use these data to estimate galaxy sizes, obtaining
results similar to those from studies with the Hubble Space Telescope, though
we find a higher fraction of compact star forming galaxies at . To
disentangle the star-forming galaxies from active galactic nuclei (AGN), we use
multiwavelength data from surveys in the optical and infrared, including
far-infrared data from Herschel, as well as new radio continuum data from the
Australia Telescope Compact Array and Very Large Array. We identify
ultraluminous infrared galaxies (ULIRGs) at , which consist of a
combination of pure starburst galaxies and Active Galactic Nuclei
(AGN)/starburst composites. The ULIRGs show signs of recent merger activity,
such as highly disturbed morphologies and include a rare candidate triple AGN.
We find that AGN tend to reside in hosts with smaller scale sizes than purely
star-forming galaxies of similar infrared luminosity. Our observations
demonstrate the potential for MCAO to complement the deeper galaxy surveys to
be made with the James Webb Space Telescope.Comment: 20 pages, AJ, in pres
Combined analysis of Hubble and VLT photometry of the intermediate mass black hole ESO 243-49 HLX-1
In this paper, we present a combined analysis of data obtained with the Hubble Space Telescope (HST), Very Large Telescope (VLT) and Swift X-ray telescope of the intermediate-mass black hole ESO 243-49 HLX-1 that were taken two months apart between 2010 September and November. Previous separate analyses of these data found that they were consistent with an irradiated accretion disc with contribution from either a very young or very old stellar population, and also indicated that the optical flux of the HLX-1 counterpart could be variable. Such variability could only be attributed to a varying accretion disc, so simultaneous analysis of all data sets should break the degeneracies in the model fits. We thus simultaneously fit the broad-band spectral energy distribution (SED) from near-infrared through to X-ray wavelengths of the two epochs of data with a model consisting of an irradiated accretion disc and a stellar population. We show that this combined analysis rules out an old stellar population, finding that the SED is dominated by emission from an accretion disc with moderate reprocessing in the outer disc around an intermediate-mass black hole imbedded in a young (˜20 Myr) stellar cluster with a mass of ˜105 M&sun;. We also place an upper limit on the mass of an additional hidden old stellar population of ˜106 M&sun;. However, optical r'-band observations of HLX-1 obtained with the Gemini-South telescope covering part of the decay from a later X-ray outburst are consistent with constant optical flux, indicating that the observed variability between the HST and VLT observations could be spurious caused by differences in the background subtraction applied to the two optical data sets. In this scenario, the contribution of the stellar population, and thus the stellar mass of the cluster, may be higher. Nonetheless, variability of <50 per cent cannot be ruled out by the Gemini data and thus they are still consistent within the errors with an exponential decay similar to that observed in X-rays.</p
Host galaxies of luminous z ∼ 0.6 quasars: major mergers are not prevalent at the highest AGN luminosities
Galaxy interactions are thought to be one of the main triggers of active galactic nuclei (AGN), especially at high luminosities, where the accreted gas mass during the AGN lifetime is substantial. Evidence for a connection between mergers and AGN, however, remains mixed. Possible triggering mechanisms remain particularly poorly understood for luminous AGN, which are thought to require triggering by major mergers, rather than secular processes. We analyse the host galaxies of a sample of 20 optically and X-ray selected luminous AGN (log(Lbol [erg s−1]) > 45) at z ∼ 0.6 using Hubble Space Telescope Wide Field Camera 3 data in the F160W/H band. 15/20 sources have resolved host galaxies. We create a control sample of mock AGN by matching the AGN host galaxies to a control sample of non-AGN galaxies. Visual signs of disturbances are found in about 25 per cent of sources in both the AGN hosts and control galaxies. Using both visual classification and quantitative morphology measures, we show that the levels of disturbance are not enhanced when compared to a matched control sample. We find no signs that major mergers play a dominant role in triggering AGN at high luminosities, suggesting that minor mergers and secular processes dominate AGN triggering up to the highest AGN luminosities. The upper limit on the enhanced fraction of major mergers is ≤20 per cent. While major mergers might increase the incidence of luminous AGN, they are not the prevalent triggering mechanism in the population of unobscured AGN
SDSS-III Baryon Oscillation Spectroscopic Survey data release 12 : galaxy target selection and large-scale structure catalogues
The Baryon Oscillation Spectroscopic Survey (BOSS), part of the Sloan Digital Sky Survey (SDSS) III project, has provided the largest survey of galaxy redshifts available to date, in terms of both the number of galaxy redshifts measured by a single survey, and the effective cosmological volume covered. Key to analysing the clustering of these data to provide cosmological measurements is understanding the detailed properties of this sample. Potential issues include variations in the target catalogue caused by changes either in the targeting algorithm or properties of the data used, the pattern of spectroscopic observations, the spatial distribution of targets for which redshifts were not obtained, and variations in the target sky density due to observational systematics. We document here the target selection algorithms used to create the galaxy samples that comprise BOSS. We also present the algorithms used to create large-scale structure catalogues for the final Data Release (DR12) samples and the associated random catalogues that quantify the survey mask. The algorithms are an evolution of those used by the BOSS team to construct catalogues from earlier data, and have been designed to accurately quantify the galaxy sample. The code used, designated mksample, is released with this paper.Publisher PDFPeer reviewe
The Lyman Continuum escape fraction of galaxies at z=3.3 in the VUDS-LBC/COSMOS field
The Lyman continuum (LyC) flux escaping from high-z galaxies into the IGM is
a fundamental quantity to understand the physical processes involved in the
reionization epoch. We have investigated a sample of star-forming galaxies at
z~3.3 in order to search for possible detections of LyC photons escaping from
galaxy halos. UV deep imaging in the COSMOS field obtained with the prime focus
camera LBC at the LBT telescope was used together with a catalog of
spectroscopic redshifts obtained by the VIMOS Ultra Deep Survey (VUDS) to build
a sample of 45 galaxies at z~3.3 with L>0.5L*. We obtained deep LBC images of
galaxies with spectroscopic redshifts in the interval 3.27<z<3.40 both in the R
and deep U bands. A sub-sample of 10 galaxies apparently shows escape
fractions>28% but a detailed analysis of their properties reveals that, with
the exception of two marginal detections (S/N~2) in the U band, all the other 8
galaxies are most likely contaminated by the UV flux of low-z interlopers
located close to the high-z targets. The average escape fraction derived from
the stacking of the cleaned sample was constrained to fesc_rel<2%. The implied
HI photo-ionization rate is a factor two lower than that needed to keep the IGM
ionized at z~3, as observed in the Lyman forest of high-z QSO spectra or by the
proximity effect. These results support a scenario where high redshift,
relatively bright (L>0.5L*) star-forming galaxies alone are unable to sustain
the level of ionization observed in the cosmic IGM at z~3. Star-forming
galaxies at higher redshift and at fainter luminosities (L<<L*) can be the
major contributors to the reionization of the Universe only if their physical
properties are subject to rapid changes from z~3 to z~6-10. Alternatively,
ionizing sources could be discovered looking for fainter sources among the AGN
population at high-z.Comment: 21 pages, 9 figures. Accepted for publication in A&
Herschel-ATLAS: Multi-wavelength SEDs and physical properties of 250 micron-selected galaxies at z < 0.5
We present a pan-chromatic analysis of an unprecedented sample of 1402 250
micron-selected galaxies at z < 0.5 (mean z = 0.24) from the Herschel-ATLAS
survey. We complement our Herschel 100-500 micron data with UV-K-band
photometry from the Galaxy And Mass Assembly (GAMA) survey and apply the
MAGPHYS energy-balance technique to produce pan-chromatic SEDs for a
representative sample of 250 micron selected galaxies spanning the most recent
5 Gyr of cosmic history. We derive estimates of physical parameters, including
star formation rates, stellar masses, dust masses and infrared luminosities.
The typical H-ATLAS galaxy at z < 0.5 has a far-infrared luminosity in the
range 10^10 - 10^12 Lsolar (SFR: 1-50 Msolar/yr) thus is broadly representative
of normal star forming galaxies over this redshift range. We show that 250
micron-selected galaxies contain a larger mass of dust at a given infra-red
luminosity or star formation rate than previous samples selected at 60 micron
from IRAS. We derive typical SEDs for H-ATLAS galaxies, and show that the
emergent SED shape is most sensitive to specific star formation rate. The
optical-UV SEDs also become more reddened due to dust at higher redshifts. Our
template SEDs are significantly cooler than existing infra-red templates. They
may therefore be most appropriate for inferring total IR luminosities from
moderate redshift submillimetre selected samples and for inclusion in models of
the lower redshift submillimetre galaxy populations.Comment: 26 pages, 24 figures, Accepted by MNRA
Combined analysis of Hubble and VLT photometry of the intermediate mass black hole ESO 243-49 HLX-1
In this paper, we present a combined analysis of data obtained with the Hubble Space Telescope (HST), Very Large Telescope (VLT) and Swift X-ray telescope of the intermediate-mass black hole ESO 243−49 HLX-1 that were taken two months apart between 2010 September and November. Previous separate analyses of these data found that they were consistent with an irradiated accretion disc with contribution from either a very young or very old stellar population, and also indicated that the optical flux of the HLX-1 counterpart could be variable. Such variability could only be attributed to a varying accretion disc, so simultaneous analysis of all data sets should break the degeneracies in the model fits. We thus simultaneously fit the broad-band spectral energy distribution (SED) from near-infrared through to X-ray wavelengths of the two epochs of data with a model consisting of an irradiated accretion disc and a stellar population. We show that this combined analysis rules out an old stellar population, finding that the SED is dominated by emission from an accretion disc with moderate reprocessing in the outer disc around an intermediate-mass black hole imbedded in a young (∼20 Myr) stellar cluster with a mass of ∼105 M⊙. We also place an upper limit on the mass of an additional hidden old stellar population of ∼106 M⊙. However, optical r′-band observations of HLX-1 obtained with the Gemini-South telescope covering part of the decay from a later X-ray outburst are consistent with constant optical flux, indicating that the observed variability between the HST and VLT observations could be spurious caused by differences in the background subtraction applied to the two optical data sets.In this scenario, the contribution of the stellar population, and thus the stellar mass of the cluster, may be higher. Nonetheless, variability of <50 per cent cannot be ruled out by the Gemini data and thus they are still consistent within the errors with an exponential decay similar to that observed in X-rays
Host galaxies of luminous z ∼ 0.6 quasars: major mergers are not prevalent at the highest AGN luminosities
Galaxy interactions are thought to be one of the main triggers of active galactic nuclei (AGN), especially at high luminosities, where the accreted gas mass during the AGN lifetime is substantial. Evidence for a connection between mergers and AGN, however, remains mixed. Possible triggering mechanisms remain particularly poorly understood for luminous AGN, which are thought to require triggering by major mergers, rather than secular processes. We analyse the host galaxies of a sample of 20 optically and X-ray selected luminous AGN (log(Lbol [erg s-1]) > 45) at z ∼ 0.6 using Hubble Space Telescope Wide Field Camera 3 data in the F160W/H band. 15/20 sources have resolved host galaxies. We create a control sample of mock AGN by matching the AGN host galaxies to a control sample of non-AGN galaxies. Visual signs of disturbances are found in about 25 per cent of sources in both the AGN hosts and control galaxies. Using both visual classification and quantitative morphology measures, we show that the levels of disturbance are not enhanced when compared to a matched control sample. We find no signs that major mergers play a dominant role in triggering AGN at high luminosities, suggesting that minor mergers and secular processes dominate AGN triggering up to the highest AGN luminosities. The upper limit on the enhanced fraction of major mergers is ≤20 per cent. While major mergers might increase the incidence of luminous AGN, they are not the prevalent triggering mechanism in the population of unobscured AGN
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