1,346 research outputs found
The Panchromatic Starburst Intensity Limit At Low And High Redshift
The integrated bolometric effective surface brightness S_e distributions of
starbursts are investigated for samples observed in 1. the rest frame
ultraviolet (UV), 2. the far-infrared and H-alpha, and 3. 21cm radio continuum
emission. For the UV sample we exploit a tight empirical relationship between
UV reddening and extinction to recover the bolometric flux. Parameterizing the
S_e upper limit by the 90th percentile of the distribution, we find a mean
S_{e,90} = 2.0e11 L_{sun}/kpc^2 for the three samples, with a factor of three
difference between the samples. This is consistent with what is expected from
the calibration uncertainties alone. We find little variation in S_{e,90} with
effective radii for R_e ~ 0.1 - 10 kpc, and little evolution out to redshifts z
~ 3. The lack of a strong dependence of S_{e,90} on wavelength, and its
consistency with the pressure measured in strong galactic winds, argue that it
corresponds to a global star formation intensity limit (\dot\Sigma_{e,90} ~ 45
M_{sun}/kpc^2/yr) rather than being an opacity effect. There are several
important implications of these results: 1. There is a robust physical
mechanism limiting starburst intensity. We note that starbursts have S_e
consistent with the expectations of gravitational instability models applied to
the solid body rotation portion of galaxies. 2. Elliptical galaxies and spiral
bulges can plausibly be built with maximum intensity bursts, while normal
spiral disks can not. 3. The UV extinction of high-z galaxies is significant,
implying that star formation in the early universe is moderately obscured.
After correcting for extinction, the observed metal production rate at z ~ 3
agrees well with independent estimates made for the epoch of elliptical galaxy
formation.Comment: 31 pages Latex (aas2pp4.sty,psfig.sty), 9 figures, accepted for
publication in the Astronomical Journa
The Panchromatic Starburst Intensity Limit at Low and High Redshift
The integrated bolometric effective surface brightness S distributions of starbursts are investigated for samples observed in (1) the rest frame ultraviolet (UV), (2) the far-infrared and Hα, and (3) 21 cm radio continuum emission. For the UV sample we exploit a tight empirical relationship between UV reddening and extinction to recover the bolometric flux. Parameterizing the S upper limit by the 90th percentile of the distribution, we find a mean S = 2.0×10 L⊙kpc for the three samples, with a factor of 3 difference between the samples. This is consistent with what is expected from the calibration uncertainties alone. We find little variation in S with effective radii for R ∼0.1-10 kpc, and little evolution out to redshifts z≈3. The lack of a strong dependence of S on wavelength, and its consistency with the pressure measured in strong galactic winds, argue that it corresponds to a global star formation intensity limit (Σ ∼45. sript M sign⊙ kpc yr ) rather than being an opacity effect. There are several important implications of these results: (1) There is a robust physical mechanism limiting starburst intensity. We note that starbursts have S consistent with the expectations of gravitational instability models applied to the solid body rotation portion of galaxies. (2) Elliptical galaxies and spiral bulges can plausibly be built with maximum intensity bursts, while normal spiral disks cannot. (3) The UV extinction of high-z galaxies is significant, implying that star formation in the early universe is moderately obscured. After correcting for extinction, the observed metal production rate at z∼3 agrees well with independent estimates made for the epoch of elliptical galaxy formation. © 1997 American Astronomical Society. e e e,90 e,90 e e,90 e,90 e 11 -2 -2 -
Optical Morphologies of Millijansky Radio Galaxies Observed by HST and in the VLA FIRST Survey
We report on a statistical study of the 51 radio galaxies at the millijansky
flux level from the Faint Images of the Radio Sky at Twenty centimeters,
including their optical morphologies and structure obtained with the Hubble
Space Telescope. Our optical imaging is significantly deeper (~2 mag) than
previous studies with the superior angular resolution of space-based imaging.
We that find 8/51 (16%) of the radio sources have no optically identifiable
counterpart to AB~24 mag. For the remaining 43 sources, only 25 are
sufficiently resolved in the HST images to reliably assign a visual
classification: 15 (60%) are elliptical galaxies, 2 (8%) are late-type spiral
galaxies, 1 (4%) is an S0, 3 (12%) are point-like objects (quasars), and 4
(16%) are merger systems. We find a similar distribution of optical types with
measurements of the Sersic index. The optical magnitude distribution of these
galaxies peaks at I~20.7+-0.5 AB mag, which is ~3 mag brighter than the depth
of our typical HST field and is thus not due to the WFPC2 detection limit. This
supports the luminosity-dependent density evolutionary model, where the
majority of faint radio galaxies typically have L*-optical luminosities and a
median redshift of z~0.8 with a relatively abrupt redshift cut-off at z>~2. We
discuss our results in the context of the evolution of elliptical galaxies and
active galactic nuclei.Comment: 20 pages, 8 figures, 51 galaxy images, and 5 tables. Uses
emulateapj.cls and natbib.sty. Accepted to ApJS. High resolution images are
available upon reques
The evolution of Radio Loud Quasar host galaxies: AO observations at z = 3
We report on ESO--VLT adaptive optics imaging of one radio-loud quasar at z
3. In spite of the large distance of the object we are able to detect
its surrounding extended nebulosity the properties of which are consistent with
an underlying massive galaxy of M --27 and effective radius R =
7 kpc. As far as we know this is the clearest detection of a radio loud quasar
host at high redshift. The host luminosity is indicative of the existence of
massive spheroids even at this early cosmic epoch. The host luminosity is about
1 magnitude fainter than the expected value based on the average trend of the
host galaxies of RLQ at lower redshift. The result, which however is based on a
single object, suggests that at z 3 there is a deviation from a
luminosity--redshift dependence regulated only by passive evolution.Comment: 6 pages, 3 figures, TeX uses elsart.cls, from workshop "QSO Host
Galaxies: Evolution and Environment" (Univ. Leiden, Aug. 22-26, 2005
The living and the dead; an investigation into the status of erasure within the floor of Bath Abbey
The floor of Bath Abbey offers a singular test of authenticity. Nineteenth century repairs and additions caused horizontal grave markers, which comprise the majority of the Abbey’s floor, to become separated from the burial sites they were intended to memorialize. A century and a half of further occupation has had the effect of removing many inscriptions as surfaces are worn smooth. The result is a patchwork of unintended edits and accidental poetry. This paper explores the notions of authenticity, essence, memorial and erasure as they pertain to the Abbey floor, in particular with regard to the role the body plays in inhabiting/eroding the floor—from both above and below. The author argues that the stones which are most out of place or worn to a state of erasure are no less authentic than their intact equivalents, but that they can be considered to have moved to another state of authenticity rich in resonance and meaning. This paper, in short, is a defense of erasure and that erosion through occupation may be considered a form of social memory; indeed, the marks of walking become the inscription. In other words, the undesigned (erasure, the cutting and repositioning of ledger stones, the missing inscriptions) becomes considered not as a form of dirt but as the positive traces of on-going and meaningful occupation
Marketing, the past and corporate heritage
Argues for a more expansive conceptualisation of the past’s relevance in, and for, marketing. Such a differentiated approach to the past is pregnant with possibilities in terms of advancing scholarship apropos temporal agency in marketing along with consumption practices. Symptomatic of this perspective is the increased mindfulness of the rich palate of past-related concepts. Significantly, the corporate heritage notion - because of its omni-temporal nature - represents a distinct and meaningful vector on the past by coalescing the past, present and future into a new type of temporality. As such, the authors reason this expansive conceptualisation of ‘the past-in-marketing’ is both timely and efficacious. Whilst sensitive of the importance of the historical method in marketing and the history of marketing scholarship and practice per se. This broader marketing approach to and of the past highlights the ideational and material manifestations of the past-in-the-present and an envisaged past-in-the future
A companion to a quasar at redshift 4.7
There is a growing consensus that the emergence of quasars at high redshifts
is related to the onset of galaxy formation, suggesting that the detection of
concentrations of gas accompanying such quasars should provide clues about the
early history of galaxies. Quasar companions have been recently identified at
redshifts up to . Here we report observations of Lyman-
emission (a tracer of ionised hydrogen) from the companion to a quasar at
=4.702, corresponding to a time when the Universe was less than ten per cent
of its present age. We argue that most of the emission arises in a gaseous
nebula that has been photoionised by the quasar, but an additional component of
continuum light -perhaps quasar light scattered from dust in the companion
body, or emission from young stars within the nebula- appears necessary to
explain the observations. These observations may be indicative of the first
stages in the assembly of galaxy-sized structures.Comment: 8 pages, 4 figures, plain LaTeX. Accepted for publication in Natur
The Nature of Compact Galaxies in the Hubble Deep Field (II): Spectroscopic Properties and Implications for the Evolution of the Star Formation Rate Density of the Universe
We present a spectroscopic study of 51 compact field galaxies with redshifts
z < 1.4 and apparent magnitudes I < 23.74 in the flanking fields of the Hubble
Deep Field. These galaxies are compact in the sense that they have small
apparent half-light radii (r_e < 0.5 arcsec) and high surface brightnesses
(SB_e < 22.2 mag arcsec^-2). The spectra, taken at the Keck telescope, show
emission lines in 88% of our sample, and only absorption lines in the remaining
12%. Emission-line profiles are roughly Gaussian with velocity widths that
range from the measurement limit of sigma = 35 km s^-1 to 150 km s^-1.
Rest-frame [OII]3727 equivalent widths range from 5A to 94A , yielding star
formation rates (SFR) of 0.1 to 14 M yr^-1. The analysis of various line
diagnostic diagrams reveals that 60% of compact emission-line galaxies have
velocity widths, excitations, Hbeta luminosities, SFRs, and mass-to-light
ratios characteristic of young star-forming HII galaxies. The remaining 40%
form a more heterogeneous class of evolved starbursts, similar to local
starburst disk galaxies. We find that, although the compact galaxies at z>0.7
have similar SFRs per unit mass to those at z<0.7, they are on average 10 times
more massive. Our sample implies a lower limit for the global comoving SFR
density of 0.004 M yr^-1 Mpc^-3 at z = 0.55, and 0.008 M yr^-1 Mpc^-3 at z =
0.85 (assuming Salpeter IMF, Ho = 50 km s^-1 Mpc^-1, and qo = 0.5). These
values, when compared to estimates for a sample of local compact galaxies
selected in a similar fashion, support a history of the universe in which the
SFR density declines by a factor 10 from z = 1 to today.Comment: LaTeX, 38 pages, 2 tables, 10 postscript figures. Accepted for
publication in the Astrophysical Journa
Deep 1.1 mm-wavelength imaging of the GOODS-South field by AzTEC/ASTE -- II. Redshift distribution and nature of the submillimetre galaxy population
We report the results of the counterpart identification and a detailed
analysis of the physical properties of the 48 sources discovered in our deep
1.1mm wavelength imaging survey of the GOODS-South field using the AzTEC
instrument on the Atacama Submillimeter Telescope Experiment (ASTE). One or
more robust or tentative counterpart candidate is found for 27 and 14 AzTEC
sources, respectively, by employing deep radio continuum, Spitzer MIPS & IRAC,
and LABOCA 870 micron data. Five of the sources (10%) have two robust
counterparts each, supporting the idea that these galaxies are strongly
clustered and/or heavily confused. Photometric redshifts and star formation
rates (SFRs) are derived by analyzing UV-to-optical and IR-to-radio SEDs. The
median redshift of z~2.6 is similar to other earlier estimates, but we show
that 80% of the AzTEC-GOODS sources are at z>2, with a significant high
redshift tail (20% at z>3.3). Rest-frame UV and optical properties of AzTEC
sources are extremely diverse, spanning 10 magnitude in the i- and K-band
photometry with median values of i=25.3 and K=22.6 and a broad range of red
colour (i-K=0-6). These AzTEC sources are some of the most luminous galaxies in
the rest-frame optical bands at z>2, with inferred stellar masses of (1-30) x
10^{10} solar masses and UV-derived star formation rates of SFR(UV) > 10-1000
solar masses per year. The IR-derived SFR, 200-2000 solar masses per year, is
independent of redshift or stellar mass. The resulting specific star formation
rates, SSFR = 1-100 per Gyr, are 10-100 times higher than similar mass galaxies
at z=0, and they extend the previously observed rapid rise in the SSFR with
redshift to z=2-5. These galaxies have a SFR high enough to have built up their
entire stellar mass within their Hubble time. We find only marginal evidence
for an AGN contribution to the near-IR and mid-IR SEDs. (abridged)Comment: 31 pages including 14 figures, accepted for publication in the MNRAS.
A higher quality Figure 1 is also included as Figure1.jp
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