共查询到20条相似文献，搜索用时 642 毫秒
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Timothy Garn David A. Green Julia M. Riley Paul Alexander 《Monthly notices of the Royal Astronomical Society》2009,397(2):1101-1112
We probe the relationship between star formation rate (SFR) and radio synchrotron luminosity in galaxies at 0 < z < 2 within the northern Spitzer Wide-area Infrared Extragalactic survey (SWIRE) fields, in order to investigate some of the assumptions that go into calculating the star formation history of the Universe from deep radio observations. We present new 610-MHz Giant Metrewave Radio Telescope (GMRT) observations of the European Large-Area ISO Survey-North 2 (ELAIS-N2) field, and using this data, along with previous GMRT surveys carried out in the ELAIS-N1 (North 1) and Lockman Hole regions, we construct a sample of galaxies which have redshift and SFR information available from the SWIRE survey. We test whether the local relationship between SFR and radio luminosity is applicable to z = 2 galaxies, and look for evolution in this relationship with both redshift and SFR in order to examine whether the physical processes which lead to synchrotron radiation have remained the same since the peak of star formation in the Universe. We find that the local calibration between radio luminosity and star formation can be successfully applied to radio-selected high-redshift, high-SFR galaxies, although we identify a small number of sources where this may not be the case; these sources show evidence for inaccurate estimations of their SFR, but there may also be some contribution from physical effects such as the recent onset of starburst activity, or suppression of the radio luminosity within these galaxies. 相似文献
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Ignacio Trujillo † C. J. Conselice Kevin Bundy M. C. Cooper P. Eisenhardt Richard S. Ellis 《Monthly notices of the Royal Astronomical Society》2007,382(1):109-120
Using the combined capabilities of the large near-infrared Palomar/DEEP-2 survey, and the superb resolution of the Advanced Camera for Surveys HST camera, we explore the size evolution of 831 very massive galaxies ( M ⋆ ≥ 1011 h −2 70 M⊙ ) since z ∼ 2 . We split our sample according to their light concentration using the Sérsic index n . At a given stellar mass, both low ( n < 2.5) and high ( n > 2.5) concentrated objects were much smaller in the past than their local massive counterparts. This evolution is particularly strong for the highly concentrated (spheroid like) objects. At z ∼ 1.5 , massive spheroid-like objects were a factor of 4 (±0.4) smaller (i.e. almost two orders of magnitudes denser) than those we see today. These small sized, high-mass galaxies do not exist in the nearby Universe, suggesting that this population merged with other galaxies over several billion years to form the largest galaxies we see today. 相似文献
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E. L. Taylor R. G. Mann A. N. Efstathiou T. S. R. Babbedge M. Rowan-Robinson G. Lagache A. Lawrence S. Mei M. Vaccari Ph. Héraudeau S. J. Oliver M. Dennefeld I. Perez-Fournon S. Serjeant E. González-Solares J.-L. Puget H. Dole C. Lari 《Monthly notices of the Royal Astronomical Society》2005,361(4):1352-1374
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N. A. Hatch R. A. Overzier J. D. Kurk G. K. Miley H. J. A. Röttgering A. W. Zirm 《Monthly notices of the Royal Astronomical Society》2009,395(1):114-125
We study the stellar mass assembly of the Spiderweb galaxy (MRC 1138−262) , a massive z = 2.2 radio galaxy in a protocluster and the probable progenitor of a brightest cluster galaxy. Nearby protocluster galaxies are identified and their properties are determined by fitting stellar population models to their rest-frame ultraviolet to optical spectral energy distributions. We find that within 150 kpc of the radio galaxy the stellar mass is centrally concentrated in the radio galaxy, yet most of the dust-uncorrected, instantaneous star formation occurs in the surrounding low-mass satellite galaxies. We predict that most of the galaxies within 150 kpc of the radio galaxy will merge with the central radio galaxy by z = 0 , increasing its stellar mass by up to a factor of ≃2. However, it will take several hundred Myr for the first mergers to occur, by which time the large star formation rates are likely to have exhausted the gas reservoirs in the satellite galaxies. The tidal radii of the satellite galaxies are small, suggesting that stars and gas are being stripped and deposited at distances of tens of kpc from the central radio galaxy. These stripped stars may become intracluster stars or form an extended stellar halo around the radio galaxy, such as those observed around cD galaxies in cluster cores. 相似文献
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Michael C. Cooper Jeffrey A. Newman † Alison L. Coil † Darren J. Croton Brian F. Gerke Renbin Yan Marc Davis S. M. Faber Puragra Guhathakurta David C. Koo Benjamin J. Weiner Christopher N. A. Willmer ‡ 《Monthly notices of the Royal Astronomical Society》2007,376(4):1445-1459
Using a sample of 19 464 galaxies drawn from the DEEP2 Galaxy Redshift Survey, we study the relationship between galaxy colour and environment at 0.4 < z < 1.35 . We find that the fraction of galaxies on the red sequence depends strongly on local environment out to z > 1 , being larger in regions of greater galaxy density. At all epochs probed, we also find a small population of red, morphologically early-type galaxies residing in regions of low measured overdensity. The observed correlations between the red fraction and local overdensity are highly significant, with the trend at z > 1 detected at a greater than 5σ level. Over the entire redshift regime studied, we find that the colour–density relation evolves continuously, with red galaxies more strongly favouring overdense regions at low z relative to their red-sequence counterparts at high redshift. At z ≳ 1.3 , the red fraction only weakly correlates with overdensity, implying that any colour dependence to the clustering of ∼ L * galaxies at that epoch must be small. Our findings add weight to existing evidence that the build-up of galaxies on the red sequence has occurred preferentially in overdense environments (i.e. galaxy groups) at z ≲ 1.5 . Furthermore, we identify the epoch ( z ∼ 2) at which typical ∼ L * galaxies began quenching and moved on to the red sequence in significant number. The strength of the observed evolutionary trends at 0 < z < 1.35 suggests that the correlations observed locally, such as the morphology–density and colour–density relations, are the result of environment-driven mechanisms (i.e. 'nurture') and do not appear to have been imprinted (by 'nature') upon the galaxy population during their epoch of formation. 相似文献
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K. K. Knudsen P. P. van der Werf J.-P. Kneib 《Monthly notices of the Royal Astronomical Society》2008,384(4):1611-1626
We have conducted a submillimetre mapping survey of faint, gravitationally lensed sources, where we have targeted 12 galaxy clusters and additionally the New Technology Telescope (NTT) Deep Field. The total area surveyed is 71.5 arcmin2 in the image plane; correcting for gravitational lensing, the total area surveyed is 40 arcmin2 in the source plane for a typical source redshift z ≈ 2.5. In the deepest maps, an image plane depth of 1σ rms ∼0.8 mJy is reached. This survey is the largest survey to date to reach such depths. In total 59 sources were detected, including three multiply imaged sources. The gravitational lensing makes it possible to detect sources with flux density below the blank field confusion limit. The lensing-corrected fluxes range from 0.11 to 19 mJy. After correcting for multiplicity, there are 10 sources with fluxes <2 mJy of which seven have submJy fluxes, doubling the number of such sources known. Number counts are determined below the confusion limit. At 1 mJy, the integrated number count is ∼104 deg−2 , and at 0.5 mJy it is ∼2 × 104 deg−2 . Based on the number counts, at a source plan flux limit of 0.1 mJy, essentially all of the 850-μm background emission has been resolved. The dominant contribution (>50 per cent) to the integrated background arises from sources with fluxes S 850 between 0.4 and 2.5 mJy, while the bright sources S 850 > 6 mJy contribute only 10 per cent. 相似文献
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H. Sugai R. I. Davies M. Ishii M. J. Ward 《Monthly notices of the Royal Astronomical Society》2000,317(2):447-452
We have obtained an H2 v =1–0 S(1) image of a merging galaxy system, NGC 6090, by using a Fabry–Perot imager. The H2 emission originates between the double nuclei of pre-merger galaxies, and exhibits an arc-like or ring-like structure almost connecting the double nuclei. This structure is similar to that suggested for Arp 220 from the velocity field measured by CO radio emission. The separation of the double nuclei in NGC 6090 is 5–6 arcsec, corresponding to a projected distance of 3–4 kpc. This is much larger than that of Arp 220 and suggests that the molecular gas distribution can form an organized shape between the nuclei, such as a ring, in a rather early phase of merging. 相似文献
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H. Sameshima J. Maza Y. Matsuoka S. Oyabu K. Kawara Y. Yoshii N. Asami N. Ienaka Y. Tsuzuki 《Monthly notices of the Royal Astronomical Society》2009,395(2):1087-1091
We present spectra of six luminous quasars at z ∼ 2 , covering rest wavelengths 1600−3200 Å. The fluxes of the UV Fe ii emission lines and Mg ii λ2798 doublet, the line widths of Mg ii and the 3000 Å luminosity were obtained from the spectra. These quantities were compared with those of low-redshift quasars at z = 0.06–0.55 studied by Tsuzuki et al. In a plot of the Fe ii (UV)/Mg ii flux ratio as a function of the central black hole mass, Fe ii (UV)/Mg ii in our z ∼ 2 quasars is systematically greater than in the low-redshift quasars. We confirmed that luminosity is not responsible for this excess. It is unclear whether this excess is caused by rich Fe abundance at z ∼ 2 over low-redshift or by non-abundance effects such as high gas density, strong radiation field and high microturbulent velocity. 相似文献