116 research outputs found
Are we seeing accretion flows in a 250kpc-sized Ly-alpha halo at z=3?
Using MUSE on the ESO-VLT, we obtained a 4 hour exposure of the z=3.12 radio
galaxy MRC0316-257. We detect features down to ~10^-19 erg/s/cm^2/arcsec^2 with
the highest surface brightness regions reaching more than a factor of 100
higher. We find Ly-alpha emission out to ~250 kpc in projection from the active
galactic nucleus (AGN). The emission shows arc-like morphologies arising at
150-250 kpc from the nucleus in projection with the connected filamentary
structures reaching down into the circum-nuclear region. The most distant arc
is offset by 700 km/s relative to circum-nuclear HeII 1640 emission, which we
assume to be at the systemic velocity. As we probe emission closer to the
nucleus, the filamentary emission narrows in projection on the sky, the
relative velocity decreases to ~250 km/s, and line full-width at half maximum
range from 300-700 km/s. From UV line ratios, the emission on scales of 10s of
kpc from the nucleus along a wide angle in the direction of the radio jets is
clearly excited by the radio jets and ionizing radiation of the AGN. Assuming
ionization equilibrium, the more extended emission outside of the axis of the
jet direction would require 100% or more illumination to explain the observed
surface brightness. High speed (>300 km/s) shocks into rare gas would provide
sufficiently high surface brightness. We discuss the possibility that the arcs
of Ly-alpha emission represent accretion shocks and the filamentary emission
represent gas flows into the halo, and compare our results with gas accretion
simulations.Comment: 4 pages, 2 figures, 1 table, A&A letters accepte
Characterizing the radio continuum emission from intense starburst galaxies
© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.The intrinsic thermal (free-free) and non-thermal (synchrotron) emission components that comprise the radio continuum of galaxies represent unique, dust-free measures of star formation rates (SFR). Such high SFR galaxies will dominate the deepest current and future radio surveys. We disentangle the thermal and non-thermal emission components of the radio continuum of six ultraluminous infrared galaxies (LFIR > 1012.5 L?) at redshifts of 0.2 = z = 0.5 and 22 IR selected galaxies. Radio data over a wide frequency range (0.8 < ? <10 GHz) are fitted with a star-forming galaxy model comprising of thermal and non-thermal components. The luminosities of both radio continuum components are strongly correlated to the 60 ”m luminosity across many orders of magnitude (consistent with the far-IR to radio correlation). We demonstrate that the spectral index of the radio continuum spectral energy distribution is a useful proxy for the thermal fraction. We also find that there is an increase in mean and scatter of the thermal fraction with FIR to radio luminosity ratio which could be influenced by different time-scales of the thermal and non-thermal emission mechanisms
The Herschel view of the environment of the radio galaxy 4C+41.17 at z = 3.8
We present Herschel observations at 70, 160, 250, 350 and 500 ÎŒm of the environment of the radio galaxy 4C+41.17 at z = 3.792. About 65 per cent of the extracted sources are securely identified with mid-infrared sources observed with the Spitzer Space Telescope at 3.6, 4.5, 5.8, 8 and 24 ÎŒm. We derive simple photometric redshifts, also including existing 850 and 1200 ÎŒm data, using templates of active galactic nuclei, starburst-dominated systems and evolved stellar populations. We find that most of the Herschel sources are foreground to the radio galaxy and therefore do not belong to a structure associated with 4C+41.17. We do, however, find that the spectral energy distribution (SED) of the closest (âŒ25 arcsec offset) source to the radio galaxy is fully consistent with being at the same redshift as 4C+41.17. We show that finding such a bright source that close to the radio galaxy at the same redshift is a very unlikely event, making the environment of 4C+41.17 a special case. We demonstrate that multiwavelength data, in particular on the RayleighâJeans side of the SED, allow us to confirm or rule out the presence of protocluster candidates that were previously selected by single wavelength data setsPeer reviewe
Starburst and old stellar populations in the z -~ 3.8 radio galaxies 4c 41.17 and TN J2007-1316
Using the new evolutionary code PĂ©gase.3, we undertook an evolutionary spectral synthesis of the opticalâIRâsubmm spectral energy distribution of two distant (z = 3.8) radio galaxies, 4C 41.17 and TN J2007â1316. These two radio galaxies were selected from the HeRGĂ (Herschel Radio Galaxies Evolution) Project in particular for their faint active galactic nucleus contribution and because they show evidence of a large stellar contribution to their bolometric luminosity. PĂ©gase.3 coherently models the reprocessing of the stellar luminosity to dust emission, allowing us to build UV to IRâsubmm spectral energy distribution libraries that can then be used to fit spectral energy distributions in the observer's frame. Our principal conclusion is that a single stellar population is insufficient to fit the spectral energy distribution of either radio galaxy. Our best fits are a sum of two evolving stellar populations â a recent starburst plus an old population â plus the thermal emission from an active galactic nucleus (which provides a good fit to the mid-IR emission). The two stellar components are: (i) a massive -~ 1011â Mâ) starburst -~30 Myr after formation, which is required simultaneously to fit the far-IR Herschel to submm data and the optical data; and (ii) an older massive (-~ 1011â12â Mâ) early-type galaxy population,-~1.0âGyr old, which is required principally to fit the mid-IR Spitzer/IRAC data.A young population alone is insufficient because an evolved giant star population produces a 1-ÎŒm rest-frame peak that is observed in the IRAC photometry. This discovery confirms that many of the stellar populations in high-redshift radio galaxies were formed by massive starbursts in the early Universe. Gas-rich mergers and/or jetâcloud interactions are favoured for triggering the intense star formation necessary to explain the properties of the spectral energy distributions. The discovery of similar characteristics in two distant radio galaxies suggests that multiple stellar populations, one old and one young, may be a generic feature of the luminous infrared radio galaxy population
The Dragonfly Galaxy: II. ALMA unveils a triple merger and gas exchange in a hyper-luminous radio galaxy at z = 2
The Dragonfly Galaxy (MRCâ0152-209), at redshift zâ~â 2, is one of the most vigorously star-forming radio galaxies in the Universe. What triggered its activity? We present ALMA Cycle 2 observations of cold molecular CO(6â5) gas and dust, which reveal that this is likely a gas-rich triple merger. It consists of a close double nucleus (separation ~4 kpc) and a weak CO-emitter at ~10 âkpc distance, all of which have counterparts in HST/NICMOS imagery. The hyper-luminous starburst and powerful radio-AGN were triggered at this precoalescent stage of the merger. The CO(6â5) traces dense molecular gas in the central region, and complements existing CO(1â0) data, which reveal more widespread tidal debris of cold gas. We also find ~1010âMâ of molecular gas with enhanced excitation at the highest velocities. At least 20â50% of this high-excitation, high-velocity gas shows kinematics that suggests it is being displaced and redistributed within the merger, although with line-of-sight velocities of |v|â<â500âkmâs-1, this gas will probably not escape the system. The processes that drive the redistribution of cold gas are likely related to either the gravitational interaction between two kpc-scale discs, or starburst/AGN-driven outflows. We estimate that the rate at which the molecular gas is redistributed is at least [áčentity!#x2009!]~â1200â±â500 Mââyr-1, and could perhaps even approach the star formation rate of ~3000â±â800âMââyr-1. The fact that the gas depletion and gas redistribution timescales are similar implies that dynamical processes can be important in the evolution of massive high-z galaxies
Elements Discrimination in the Study of Super-Heavy Elements using an Ionization Chamber
Dedicated ionization chamber was built and installed to measure the energy
loss of very heavy nuclei at 2.7 MeV/u produced in fusion reactions in inverse
kinematics (beam of 208Pb). After going through the ionization chamber,
products of reactions on 12C, 18O targets are implanted in a Si detector. Their
identification through their alpha decay chain is ambiguous when their
half-life is short. After calibration with Pb and Th nuclei, the ionization
chamber signal allowed us to resolve these ambiguities. In the search for rare
super-heavy nuclei produced in fusion reactions in inverse or symmetric
kinematics, such a chamber will provide direct information on the nuclear
charge of each implanted nucleus.Comment: submitted to NIMA, 10 pages+4 figures, Latex, uses elsart.cls and
grahpic
Search for a long lived component in the reaction U+U near the Coulomb barrier
Expérience GANILInternational audienceWe performed an experiment to search for a signature of a long living component in the collision of U + U between 6.09 and 7.35A MeV. The experiment was performed at GANIL using the spectrometer VAMOS, tuned for observing reactions with kinematics similar to fusion-fission events. Theoretical calculations indicate that if a long living component would exist for this reaction, the most probable fission channel of such a giant system would be via the emissionof quasi-lead nuclei. We detected events of such a category in the focal plane of VAMOS. These events present an excitation function growing as a function of the bombarding energy
CO(1-0) survey of high-z radio galaxies: alignment of molecular halo gas with distant radio sources
We present a CO(1â0) survey for cold molecular gas in a representative sample of 13 highz
radio galaxies (HzRGs) at 1.4 <z< 2.8, using the Australia Telescope Compact Array.
We detect CO(1â0) emission associated with five sources: MRC 0114-211, MRC 0152-209,
MRC 0156-252, MRC 1138-262 and MRC 2048-272. The CO(1â0) luminosities are in the
range L
CO ⌠(5â9) Ă 1010 K km sâ1 pc2. For MRC 0152-209 and MRC 1138-262, part of the
CO(1â0) emission coincides with the radio galaxy, while part is spread on scales of tens of
kpc and likely associated with galaxy mergers. The molecular gas mass derived for these two
systems is MH2 ⌠6 Ă 1010 Mïżœ (MH2/L
CO = 0.8). For the remaining three CO-detected sources,
the CO(1â0) emission is located in the halo (âŒ50-kpc) environment. These three HzRGs are
among the fainter far-IR emitters in our sample, suggesting that similar reservoirs of cold
molecular halo gas may have been missed in earlier studies due to pre-selection of IR-bright
sources. In all three cases, the CO(1â0) is aligned along the radio axis and found beyond the
brightest radio hotspot, in a region devoid of 4.5 ”m emission in Spitzerimaging. The CO(1â0)
profiles are broad, with velocity widths of âŒ1000â3600 km sâ1. We discuss several possible
scenarios to explain these halo reservoirs of CO(1â0). Following these results, we complement
our CO(1â0) study with detections of extended CO from the literature and find at marginal
statistical significance (95 per cent level) that CO in HzRGs is preferentially aligned towards
the radio jet axis. For the eight sources in which we do not detect CO(1â0), we set realistic
upper limits of L
CO ⌠3â4 Ă 1010 K km sâ1 pc2. Our survey reveals a CO(1â0) detection rate
of 38 per cent, allowing us to compare the CO(1â0) content of HzRGs with that of other types
of high-z galaxies
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