We present high-resolution observations of the 880 mum (rest-frame FIR) continuum emission in the z= 4.05 submillimeter galaxy GN20 from the IRAM Plateau de Bure Interferometer (PdBI). These data ...resolve the obscured star formation (SF) in this unlensed galaxy on scales of 0".3 x 0".2 (~2.1 x 1.3 kpc). The observations reveal a bright (16 + or - 1 mJy) dusty starburst centered on the cold molecular gas reservoir and showing a bar-like extension along the major axis. The striking anti-correlation with the Hubble Space Telescope/Wide Field Camera 3 imaging suggests that the copious dust surrounding the starburst heavily obscures the rest-frame UV/optical emission. A comparison with 1.2 mm PdBI continuum data reveals no evidence for variations in the dust properties across the source within the uncertainties, consistent with extended SF, and the peak star formation rate surface density (119 + or - 8 M sub(middot in circle) yr super(-1) kpc super(-2)) implies that the SF in GN20 remains sub-Eddington on scales down to 3 kpc super(2). We find that the SF efficiency (SFE) is highest in the central regions of GN20, leading to a resolved SF law with a power-law slope of Sigma sub(SFR)~ (ProQuest: Formulae and/or non-USASCII text omitted), and that GN20 lies above the sequence of normal star-forming disks, implying that the dispersion in the SF law is not due solely to morphology or choice of conversion factor. These data extend previous evidence for a fixed SFE per free-fall time to include the star-forming medium on ~kiloparsec scales in a galaxy 12 Gyr ago.
The VLA-COSMOS Large Project is described and Its scientific objective is discussed. We present a catalog of similar to 3600 radio sources found in the 2 deg super(2) COSMOS field at 1.4 GHz. The ...observations in the VLA A and C configuration resulted in a resolution of 1.5" x 1.4" and a mean rms noise of similar to 10.5 (15) mu Jy beam super(-1) in the central 1 (2) deg super(2). Eighty radio sources are clearly extended consisting of multiple components, and most of them appear to be double-lobed radio galaxies. The astrometry of the catalog has been thoroughly tested, and the uncertainty in the relative and absolute astrometry are 130 and <55 mas, respectively.
The rest-frame ultraviolet properties of galaxies during the first three billion years of cosmic time (redshift z > 4) indicate a rapid evolution in the dust obscuration of such galaxies. This ...evolution implies a change in the average properties of the interstellar medium, but the measurements are systematically uncertain owing to untested assumptions and the inability to detect heavily obscured regions of the galaxies. Previous attempts to measure the interstellar medium directly in normal galaxies at these redshifts have failed for a number of reasons, with two notable exceptions. Here we report measurements of the forbidden C ii emission (that is, C II) from gas, and the far-infrared emission from dust, in nine typical star-forming galaxies about one billion years after the Big Bang (z ≈ 5-6). We find that these galaxies have thermal emission that is less than 1/12 that of similar systems about two billion years later, and enhanced C II emission relative to the far-infrared continuum, confirming a strong evolution in the properties of the interstellar medium in the early Universe. The gas is distributed over scales of one to eight kiloparsecs, and shows diverse dynamics within the sample. These results are consistent with early galaxies having significantly less dust than typical galaxies seen at z < 3 and being comparable in dust content to local low-metallicity systems.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
Using Chandra X-ray and Very Large Array radio data, we investigate the scaling relationship between jet power, P{sub jet}, and synchrotron luminosity, P{sub radio}. We expand the sample presented in ...BIrzan et al. to lower radio power by incorporating measurements for 21 giant elliptical galaxies (gEs) to determine if the BIrzan et al. P{sub jet}-P {sub radio} scaling relations are continuous in form and scatter from gEs up to brightest cluster galaxies. We find a mean scaling relation of P {sub jet} {approx} 5.8 x 10{sup 43}(P{sub radio}/10{sup 40}){sup 0.70} erg s{sup -1} which is continuous over {approx}6-8 decades in P{sub jet} and P{sub radio} with a scatter of {approx} 0.7 dex. Our mean scaling relationship is consistent with the model presented in Willott et al. if the typical fraction of lobe energy in non-radiating particles to that in relativistic electrons is {approx}>100. We identify several gEs whose radio luminosities are unusually large for their jet powers and have radio sources which extend well beyond the densest parts of their X-ray halos. We suggest that these radio sources are unusually luminous because they were unable to entrain appreciable amounts of gas.
We explore the redshift evolution of the specific star formation rate (SSFR) for galaxies of different stellar mass by drawing on a deep 3.6 Delta *mm selected sample of >105 galaxies in the 2 deg2 ...COSMOS field. The average star formation rate (SFR) for subsets of these galaxies is estimated with stacked 1.4 GHz radio continuum emission. We separately consider the total sample and a subset of galaxies that shows evidence for substantive recent star formation in the rest-frame optical spectral energy distributions. At redshifts 0.2 < z < 3 both populations show a strong and mass-independent decrease in their SSFR toward the present epoch. It is best described by a power law (1 + z) n , where n ~ 4.3 for all galaxies and n ~ 3.5 for star-forming (SF) sources. The decrease appears to have started at z>2, at least for high-mass (M * 4 X 1010 M ) systems where our conclusions are most robust. Our data show that there is a tight correlation with power-law dependence, SSFR M * Delta *b, between SSFR and stellar mass at all epochs. The relation tends to flatten below M * 1010 M if quiescent galaxies are included; if they are excluded from the analysis a shallow index Delta *bSFG --0.4 fits the correlation. On average, higher mass objects always have lower SSFRs, also among SF galaxies. At z>1.5 there is tentative evidence for an upper threshold in SSFR that an average galaxy cannot exceed, possibly due to gravitationally limited molecular gas accretion. It is suggested by a flattening of the SSFR-M * relation (also for SF sources), but affects massive (>1010 M ) galaxies only at the highest redshifts. Since z = 1.5 there thus is no direct evidence that galaxies of higher mass experience a more rapid waning of their SSFR than lower mass SF systems. In this sense, the data rule out any strong 'downsizing' in the SSFR. We combine our results with recent measurements of the galaxy (stellar) mass function in order to determine the characteristic mass of an SF galaxy: we find that since z ~ 3 the majority of all new stars were always formed in galaxies of M * = 1010.6?0.4 M . In this sense, too, there is no 'downsizing.' Finally, our analysis constitutes the most extensive SFR density determination with a single technique out to z = 3. Recent Herschel results are consistent with our results, but rely on far smaller samples.
Context. Quantifying the fraction of active galactic nuclei (AGN) in the faint radio population and understanding their relation with star-forming activity are fundamental to studies of galaxy ...evolution. Very long baseline interferometry (VLBI) observations are able to identify AGN above relatively low redshifts (z> 0.1) since they provide milli-arcsecond resolution. Aims. We have created an AGN catalogue from 2865 known radio sources observed in the Cosmic Evolution Survey (COSMOS) field, which has exceptional multi-wavelength coverage. With this catalogue we intend to study the faint radio sky with statistically relevant numbers and to analyse the AGN – host galaxy co-evolution, making use of the large amount of ancillary data available in the field. Methods. Wide-field VLBI observations were made of all known radio sources in the COSMOS field at 1.4 GHz to measure the AGN fraction, in particular in the faint radio population. We describe in detail the observations, data calibration, source detection and flux density measurements, parts of which we have developed for this survey. The combination of number of sources, sensitivity, and area covered with this project are unprecedented. Results. We have detected 468 radio sources, expected to be AGN, with the Very Long Baseline Array (VLBA). This is, to date, the largest sample assembled of VLBI detected sources in the sub-mJy regime. The input sample was taken from previous observations with the Very Large Array (VLA). We present the catalogue with additional optical, infrared and X-ray information. Conclusions. We find a detection fraction of 20 ± 1%, considering only those sources from the input catalogue which were in principle detectable with the VLBA (2361). As a function of the VLA flux density, the detection fraction is higher for higher flux densities, since at high flux densities a source could be detected even if the VLBI core accounts for a small percentage of the total flux density. As a function of redshift, we see no evolution of the detection fraction over the redshift range 0.5 <z< 3. In addition, we find that faint radio sources typically have a greater fraction of their radio luminosity in a compact core – ~70% of the sub-mJy sources detected with the VLBA have more than half of their total radio luminosity in a VLBI-scale component, whereas this is true for only ~30% of the sources that are brighter than 10 mJy. This suggests that fainter radio sources differ intrinsically from brighter ones. Across our entire sample, we find the predominant morphological classification of the host galaxies of the VLBA detected sources to be early type (57%), although this varies with redshift and at z> 1.5 we find that spiral galaxies become the most prevalent (48%). The number of detections is high enough to study the faint radio population with statistically significant numbers. We demonstrate that wide-field VLBI observations, together with new calibration methods such as multi-source self-calibration and mosaicing, result in information which is difficult or impossible to obtain otherwise.
CLUSTER MAGNETIC FIELDS Carilli, C. L; Taylor, G. B
Annual review of astronomy and astrophysics,
01/2002, Letnik:
40, Številka:
1
Journal Article
Recenzirano
Magnetic fields in the intercluster medium have been measured using a
variety of techniques, including studies of synchrotron relic and halo radio
sources within clusters, studies of inverse Compton ...X-ray emission from
clusters, surveys of Faraday rotation measures of polarized radio sources both
within and behind clusters, and studies of cluster cold fronts in X-ray images.
These measurements imply that most cluster atmospheres are substantially
magnetized, with typical field strengths of order 1 μGauss with high areal
filling factors out to Mpc radii. There is likely to be considerable variation
in field strengths and topologies both within and between clusters, especially
when comparing dynamically relaxed clusters to those that have recently
undergone a merger. In some locations, such as the cores of cooling flow
clusters, the magnetic fields reach levels of 10-40 μG and may be
dynamically important. In all clusters the magnetic fields have a significant
effect on energy transport in the intracluster medium. We also review current
theories on the origin of cluster magnetic fields.
Celotno besedilo
Dostopno za:
CMK, DOBA, FMFMET, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Until recently, determining the rotational properties of galaxies in the early universe ( , universe age Gyr) was impractical, with the exception of a few strongly lensed systems. Combining the high ...resolution and sensitivity of ALMA at (sub-)millimeter wavelengths with the typically high strength of the C ii 158 m emission line from galaxies and long-developed dynamical modeling tools raises the possibility of characterizing the gas dynamics in both extreme starburst galaxies and normal star-forming disk galaxies at . Using a procedure centered around GIPSY's rotcur task, we have fit tilted ring models to some of the best available ALMA C ii data of a small set of galaxies: the MS galaxies HZ9 and HZ10, the damped Ly absorber host galaxy ALMA J0817+1351, the submm galaxies AzTEC/C159 and COSMOS J1000+0234, and the quasar host galaxy ULAS J1319+0950. This procedure directly derives rotation curves and dynamical masses as functions of radius for each object. In one case, we present evidence for a dark matter halo of . We present an analysis of the possible velocity dispersions of two sources based on matching simulated observations to the integrated C ii line profiles. Finally, we test the effects of observation resolution and sensitivity on our results. While the conclusions remain limited at the resolution and signal-to-noise ratios of these observations, the results demonstrate the viability of the modeling tools at high redshift, and the exciting potential for detailed dynamical analysis of the earliest galaxies, as ALMA achieves full observational capabilities.
ABSTRACT We present an analysis of a deep (1 = 13 Jy) cosmological 1.2 mm continuum map based on ASPECS, the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field. In the 1 arcmin2 covered by ...ASPECS we detect nine sources at significance at 1.2 mm. Our ALMA-selected sample has a median redshift of , with only one galaxy detected at z > 2 within the survey area. This value is significantly lower than that found in millimeter samples selected at a higher flux density cutoff and similar frequencies. Most galaxies have specific star formation rates (SFRs) similar to that of main-sequence galaxies at the same epoch, and we find median values of stellar mass and SFRs of and yr−1, respectively. Using the dust emission as a tracer for the interstellar medium (ISM) mass, we derive depletion times that are typically longer than 300 Myr, and we find molecular gas fractions ranging from ∼0.1 to 1.0. As noted by previous studies, these values are lower than those using CO-based ISM estimates by a factor of ∼2. The 1 mm number counts (corrected for fidelity and completeness) are in agreement with previous studies that were typically restricted to brighter sources. With our individual detections only, we recover 55% 4% of the extragalactic background light (EBL) at 1.2 mm measured by the Planck satellite, and we recover 80% 7% of this EBL if we include the bright end of the number counts and additional detections from stacking. The stacked contribution is dominated by galaxies at , with stellar masses of (1-3) × 1010 M . For the first time, we are able to characterize the population of galaxies that dominate the EBL at 1.2 mm.
In the context of the VLA-COSMOS Deep project, additional VLA A array observations at 1.4 GHz were obtained for the central degree of the COSMOS field and combined with the existing data from the ...VLA-COSMOS Large project. A newly constructed Deep mosaic with a resolution of 2.''5 was used to search for sources down to 4{sigma} with 1{sigma} {approx} 12 {mu}Jy beam{sup -1} in the central 50' x 50'. This new catalog is combined with the catalog from the Large project (obtained at 1.''5 x 1.''4 resolution) to construct a new Joint catalog. All sources listed in the new Joint catalog have peak flux densities of {>=}5{sigma} at 1.''5 and/or 2.''5 resolution to account for the fact that a significant fraction of sources at these low flux levels are expected to be slightly resolved at 1.''5 resolution. All properties listed in the Joint catalog, such as peak flux density, integrated flux density, and source size, are determined in the 2.''5 resolution Deep image. In addition, the Joint catalog contains 43 newly identified multi-component sources.
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