We used integral field spectroscopy from CALIFA DR3 and multiwavelength publicly available data to investigate the star formation histories of galaxies in the Seyfert's Sextet (SS; HCG 79). The ...galaxies H79a, H79b, H79c, and H79f have low star formation rates despite showing strong signs of interaction. By exploring their individual specific star formation histories, we identified three earlier episodes of strong star formation common to these four galaxies. We use the last two episodes as markers of the epochs when the galaxies were crossing. We suggest that after the first turnaround, initially gas-rich galaxies crossed for the first time, consuming most of their gas. Hence, after the second turnaround most mergers from second crossings would be mixed or dry. The exception would be gas-rich galaxies intruding for the first time. Therefore, we suggest that SS galaxies have survived one crossing during a Hubble time. Strong Balmer absorption lines and the presence of counter-rotating disks provide independent bounds to the second and first crossing, respectively. This scenario provides a plausible way out of the short crossing time paradox.
ABSTRACT
The SuperCLuster Assisted Shear Survey (SuperCLASS) is a legacy programme using the e-MERLIN interferometric array. The aim is to observe the sky at L-band (1.4 GHz) to a r.m.s. of $7\, \mu ...{\rm Jy}\,$beam−1 over an area of $\sim 1\, {\rm deg}^2$ centred on the Abell 981 supercluster. The main scientific objectives of the project are: (i) to detect the effects of weak lensing in the radio in preparation for similar measurements with the Square Kilometre Array (SKA); (ii) an extinction free census of star formation and AGN activity out to z ∼ 1. In this paper we give an overview of the project including the science goals and multiwavelength coverage before presenting the first data release. We have analysed around 400 h of e-MERLIN data allowing us to create a Data Release 1 (DR1) mosaic of $\sim 0.26\, {\rm deg}^2$ to the full depth. These observations have been supplemented with complementary radio observations from the Karl G. Jansky Very Large Array (VLA) and optical/near infrared observations taken with the Subaru, Canada-France-Hawaii, and Spitzer Telescopes. The main data product is a catalogue of 887 sources detected by the VLA, of which 395 are detected by e-MERLIN and 197 of these are resolved. We have investigated the size, flux, and spectral index properties of these sources finding them compatible with previous studies. Preliminary photometric redshifts, and an assessment of galaxy shapes measured in the radio data, combined with a radio-optical cross-correlation technique probing cosmic shear in a supercluster environment, are presented in companion papers.
We present deep Hubble Space Telescope, Chandra, Very Large Array, and Australia Telescope Compact Array images of the jets of PKS 0208-512 and PKS 1202-262, which were found in a Chandra survey of a ...flux-limited sample of flat-spectrum radio quasars with jets. We discuss in detail their X-ray morphologies and spectra. We find optical emission from one knot in the jet of PKS 1202-262 and two regions in the jet of PKS 0208-512. The X-ray emission of both jets is most consistent with external Comptonization of cosmic microwave background photons by particles within the jet, while the optical emission is most consistent with the synchrotron process. We model the emission from the jet in this context and discuss implications for jet emission models, including magnetic field and beaming parameters.
We report new detections of the two transient ultraluminous X-ray sources (ULXs) in NGC 5128 from an ongoing series of Chandra observations. Both sources have previously been observed L sub(x)(2-3) x ...~10 super(39) erg s super(-1), at the lower end of the ULX luminosity range. The new observations allow us to study these sources in the luminosity regime frequented by the Galactic black hole X-ray binaries (BH XBs). We present the recent lightcurves of both ULXs. 1RXH J132519.8-430312 (ULX1) was observed at L sub(x) approx = 1 x 10 super(38) erg s super(-1), while CXOU J132518.2-430304 (ULX2) declined to L sub(x) approx = 2 x 10 super(37) erg s super(-1) and then lingered at this luminosity for hundreds of days. We show that a reasonable upper limit for both duty cycles is 0.2, with a lower limit of 0.12 for ULX2. This duty cycle is larger than anticipated for transient ULXs in old stellar populations. By fitting simple spectral models in an observation with ~50 counts we recover properties consistent with Galactic BH XBs, but inconclusive as to the spectral state. We utilize quantile analyses to demonstrate that the spectra are generally soft, and that in one observation the spectrum of ULX2 is inconsistent with a canonical hard state at > 95% confidence. This is contrary to what would be expected of an accreting intermediate mass black hole primary, which we would expect to be in the hard state at these luminosities. We discuss the paucity of transient ULXs discovered in early-type galaxies and excogitate explanations. We suggest that the number of transient ULXs scales with the giant and sub-giant populations, rather than the total number of XBs.
The XXL Survey Smolčić, Vernesa; Delhaize, Jacinta; Huynh, Minh ...
Astronomy and astrophysics (Berlin),
08/2016, Volume:
592
Journal Article
Peer reviewed
Open access
We present 2.1 GHz imaging with the Australia Telescope Compact Array (ATCA) of a 6.5 deg2 region within the XXM-Newton XXL South field using a band of 1.1−3.1 GHz. We achieve an angular resolution ...of 4.7′′ × 4.2′′ in the final radio continuum map with a median rms noise level of 50 μJy/beam. We identify 1389 radio sources in the field with peak S/N ≥ 5 and present the catalogue of observed parameters. We find that 305 sources are resolved, of which 77 consist of multiple radio components. These number counts are in agreement with those found for the COSMOS-VLA 1.4 GHz survey. We derive spectral indices by a comparison with the Sydney University Molongolo Sky Survey (SUMSS) 843 MHz data. We find an average spectral index of − 0.78 and a scatter of 0.28, in line with expectations. This pilot survey was conducted in preparation for a larger ATCA program to observe the full 25 deg2 southern XXL field. When complete, the survey will provide a unique resource of sensitive, wide-field radio continuum imaging with complementary X-ray data in the field. This will facilitate studies of the physical mechanisms of radio-loud and radio-quiet AGNs and galaxy clusters, and the role they play in galaxy evolution. The source catalogue is publicly available online via the XXL Master Catalogue browser and the Centre de Données astronomiques de Strasbourg (CDS).
Limits on the molecular gas content of z ∼ 5 LBGs Davies, L. J. M.; Bremer, M. N.; Stanway, E. R. ...
Monthly notices of the Royal Astronomical Society,
October 2010, Volume:
408, Issue:
1
Journal Article
Peer reviewed
Open access
We present limits on the molecular gas content of Lyman break galaxies (LBGs) at z ∼ 5 from observations targeting redshifted CO(1–0) and CO(2–1) line emission. We observed a single field containing ...eight spectroscopically confirmed z ∼ 5 LBGs, seven of which are contained within a narrow (z = 4.95 ± 0.08) redshift range and the eighth is at z= 5.2. No source was individually detected. Assuming the CO to H2 conversion factor for vigorous starbursts, we place upper limits on the molecular gas content of individual z∼ 5 LBGs of M(H2) ≲ 1010 M⊙. From a stacking analysis combining all of the non-detections, the typical z ∼ 5 LBG has an H2 mass limit comparable to their stellar mass, <3.1 × 109 M⊙ This limit implies that, given the star formation rates of these systems (measured from their UV emission), star formation could be sustained for at most ∼ 100 Myr, similar to the typical ages of their stellar populations. The lack of a substantially larger reservoir of cold gas argues against the LBGs being UV-luminous superstarbursts embedded in much larger UV-dark systems and as a result increases the likelihood that at least those LBGs with multiple components are starbursts triggered by mergers. The sources responsible for re-ionization are expected to be starbursts similar to these systems, but with lower luminosities, masses and consequently with star formation time-scales far shorter than the recombination time-scale. If so, the ionized bubbles expected in the IGM during the re-ionization era will only infrequently have UV-luminous sources at their centres.
We present a multiwavelength study of the nucleus, environment, jets, and hot spots of the nearby FR II radio galaxy 3C 321, using new and archival data from MERLIN, the VLA, Spitzer, HST, and ...Chandra. An initially collimated radio jet extends northwest from the nucleus of its host galaxy and produces a compact knot of radio emission adjacent (in projection) to a companion galaxy, after which it dramatically flares and bends, extending out in a diffuse structure 35 kpc northwest of the nucleus. We argue that the simplest explanation for the unusual morphology of the jet is that it is undergoing an interaction with the companion galaxy. Given that the northwest hot spot that lies image250 kpc from the core shows X-ray emission, which likely indicates in situ high-energy particle acceleration, we argue that the jet-companion interaction is not a steady state situation. Instead, we suggest that the jet has been disrupted on a timescale less than the light-travel time to the end of the lobe, image10 super(6) yr, and that the jet flow to this hot spot will only be disrupted for as long as the jet- companion interaction takes place. The host galaxy of 3C 321 and the companion galaxy are in the process of merging, and each hosts a luminous AGN. As this is an unusual situation, we investigate the hypothesis that the interacting jet has driven material on to the companion galaxy, triggering its AGN. Finally, we present detailed radio and X-ray observations of both hot spots, which show that there are multiple emission sites, with spatial offsets between the radio and X-ray emission.
ABSTRACT The Yuan-Tseh Lee Array for Microwave Background Anisotropy (AMiBA) is a co-planar interferometer array operating at a wavelength of 3 mm to measure the Sunyaev-Zel'dovich effect (SZE) of ...galaxy clusters at arcminute scales. The first phase of operation-with a compact 7-element array with 0.6 m antennas (AMiBA-7)-observed six clusters at angular scales from to . Here, we describe the expansion of AMiBA to a 13-element array with 1.2 m antennas (AMiBA-13), its subsequent commissioning, and cluster SZE observing program. The most noticeable changes compared to AMiBA-7 are (1) array re-configuration with baselines ranging from 1.4 m to 4.8 m, allowing us to sample structures between and , (2) 13 new lightweight carbon-fiber-reinforced plastic (CFRP) 1.2 m reflectors, and (3) additional correlators and six new receivers. Since the reflectors are co-mounted on and distributed over the entire six-meter CFRP platform, a refined hexapod pointing error model and phase error correction scheme have been developed for AMiBA-13. These effects-entirely negligible for the earlier central close-packed AMiBA-7 configuration-can lead to additional geometrical delays during observations. Our correction scheme recovers at least 80 5% of the point-source fluxes. We, therefore, apply an upward correcting factor of 1.25 to our visibilities to correct for phase decoherence, and a 5% systematic uncertainty is added in quadrature with our statistical errors. We demonstrate the absence of further systematics with a noise level consistent with zero in stacked uv-visibilities. From the AMiBA-13 SZE observing program, we present here maps of a subset of 12 clusters with signal-to-noise ratios above five. We demonstrate combining AMiBA-7 with AMiBA-13 observations on Abell 1689, by jointly fitting their data to a generalized Navarro-Frenk-White model. Our cylindrically integrated Compton-y values for five radii are consistent with results from the Berkeley-Illinois-Maryland Array, the Owens Valley Radio Observatory, the Sunyaev-Zel'dovich Array, and the Planck Observatory. We also report the first targeted SZE detection toward the optically selected cluster RCS J1447+0828, and we demonstrate the ability of AMiBA SZE data to serve as a proxy for the total cluster mass. Finally, we show that our AMiBA-SZE derived cluster masses are consistent with recent lensing mass measurements in the literature.
We present 30-GHz Sunyaev-Zel'dovich (SZ) observations of a statistically complete sample of galaxy clusters with the One Centimetre Receiver Array-prototype (OCRA-p). The clusters are the 18 most ...X-ray luminous clusters at z > 0.2 in the ROSAT Brightest Cluster Sample. We correct for contaminant radio sources via supplementary observations with the Green Bank Telescope, also at 30 GHz, and remove a cluster that is contaminated by an unresolved X-ray source. All 17 remaining clusters have central SZ effects with Comptonization parameter y
0 exceeding 1.9 × 10−4, and 13 are detected at significance ≥3σ. We use our data to examine scalings between y
0 and X-ray temperature, X-ray luminosity and the X-ray mass proxy Y
X, and find good agreement with predictions from self-similar models of cluster formation, with an intrinsic scatter in y
0 of about 25 per cent. We also comment on the success of the observations in the face of the contaminant source population, and the implications for upcoming cm-wave surveys.
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