566 research outputs found
The SCUBA Bright Quasar Survey II: unveiling the quasar epoch at submillimetre wavelengths
We present results of the first systematic search for submillimetre continuum emission from z=2, radio-quiet, optically-luminous quasars, using the SCUBA/JCMT. We have observed a homogeneous sample of 57 quasars in the redshift range 1.54) redshift. The target sensitivity of the survey (3sigma=10mJy at 850um) was chosen to enable efficient identification of bright submm sources, suitable for detailed follow-up. 9 targets are detected, with fluxes in the range 7-17mJy. Although there is a suggestion of variation of submm detectability between z=2 and z=4, this is consistent with the K-correction of a characteristic far-infrared spectrum. Additionally, the weighted mean fluxes of non-detections at z=2 and z>4 are comparable
Radio Observations of Infrared Luminous High Redshift QSOs
We present Very Large Array (VLA) observations at 1.4 GHz and 5 GHz of a
sample of 12 Quasi-stellar Objects (QSOs) at z = 3.99 to 4.46. The sources were
selected as the brightest sources at 250 GHz from the recent survey of Omont et
al. (2001). We detect seven sources at 1.4 GHz with flux densities, S_{1.4} >
50 microJy. These centimeter (cm) wavelength observations imply that the
millimeter (mm) emission is most likely thermal dust emission. The
radio-through-optical spectral energy distributions for these sources are
within the broad range defined by lower redshift, lower optical luminosity
QSOs. For two sources the radio continuum luminosities and morphologies
indicate steep spectrum, radio loud emission from a jet-driven radio source.
For the remaining 10 sources the 1.4 GHz flux densities, or limits, are
consistent with those expected for active star forming galaxies. If the radio
emission is powered by star formation in these systems, then the implied star
formation rates are of order 1e3 M_solar/year. We discuss the angular sizes and
spatial distributions of the radio emitting regions, and we consider briefly
these results in the context of co-eval black hole and stellar bulge formation
in galaxies.Comment: to appear in the A
The Radio-to-Submm Spectral Index as a Redshift Indicator
We present models of the 1.4 GHz to 350 GHz spectral index, alpha(350/1.4),
for starburst galaxies as a function of redshift. The models include a
semi-analytic formulation, based on the well quantified radio-to-far infrared
correlation for low redshift star forming galaxies, and an empirical
formulation, based on the observed spectrum of the starburst galaxies M82 and
Arp 220. We compare the models to the observed values of alpha(350/1.4) for
starburst galaxies at low and high redshift. We find reasonable agreement
between the models and the observations, and in particular, that an observed
spectral index of alpha(350/1.4) > +0.5 indicates that the target source is
likely to be at high redshift, z > 1. The evolution of alpha(350/1.4) with
redshift is mainly due to the very steep rise in the Raleigh-Jeans portion of
the thermal dust spectrum shifting into the 350 GHz band with increasing
redshift. We also discuss situations where this relationship could be violated.
We then apply our models to examine the putative identifications of submm
sources in the Hubble Deep Field, and conclude that the submm sources reported
by Hughes et al. are likely to be at high redshifts, z > 1.5.Comment: standard LATEX file plus 1 postscript figure. Added references and
revised figure. second figure revision. Final Proof version. to appear in
Astrophysical Journal Letter
A Search for Dense Molecular Gas in High Redshift Infrared-Luminous Galaxies
We present a search for HCN emission from four high redshift far infrared
(IR) luminous galaxies. Current data and models suggest that these high IR
luminous galaxies represent a major starburst phase in the formation of
spheroidal galaxies, although many of the sources also host luminous active
galactic nuclei (AGN), such that a contribution to the dust heating by the AGN
cannot be precluded. HCN emission is a star formation indicator, tracing dense
molecular hydrogen gas within star-forming molecular clouds (n(H) cm). HCN luminosity is linearly correlated with IR luminosity for
low redshift galaxies, unlike CO emission which can also trace gas at much
lower density. We report a marginal detection of HCN (1-0) emission from the
QSO J1409+5628, with a velocity integrated line luminosity of
K km s pc, while we obtain
3 upper limits to the HCN luminosity of the QSO J0751+2716 of
K km s pc, K km s pc for the starburst galaxy
J1401+0252, and K km s pc for the QSO J1148+5251. We compare the HCN data on these sources, plus three
other high- IR luminous galaxies, to observations of lower redshift
star-forming galaxies. The values of the HCN/far-IR luminosity ratios (or
limits) for all the high sources are within the scatter of the relationship
between HCN and far-IR emission for low star-forming galaxies (truncated).Comment: aastex format, 4 figures. to appear in the Astrophysical Journal;
Revised lens magnification estimate for 1401+025
XMM-Newton Observations of High Redshift Quasars
We report on our XMM observations of the high redshift quasars BR 2237--0607
(z=4.558) and BR 0351--1034 (z=4.351), together with 14 other z>4 objects found
in the XMM public archive. Contrary to former reports, we do not find high
redshift radio-loud quasars to be more absorbed than their radio-quiet
counterparts. We find that the optical to X-ray spectral index alpha-ox is
correlated with the luminosity density at 2500 A, but does not show a
correlation with redshift. The mean 2-10 keV power-law slope of the 9 high
redshift radio-quiet quasars in our sample for which a spectral analysis can be
performed is alpha-x1.23+-0.48, similar to alpha-x=1.19 found from the ASCA
observations of low redshift Narrow-Line Seyfert 1 galaxies (NLS1s), and
significantly different from alpha-x=0.78 found for low redshift Broad-Line
Seyfert galaxies. While the optical/UV spectra of low to high redshift quasars
look remarkably similar, we find a first indication of a difference in their
X-ray spectrum. The steep X-ray spectral index suggests high Eddington ratios
L/L_Edd. These observations give credence to the hypothesis of Mathur (2000)
that NLS1s are low luminosity cousins of high redshift quasars, both likely to
be in their early evolutionary stage.Comment: 25 pages, AJ, in press (Jan 2006
Emission-Line Properties of z > 4 Quasars
We present results of a program of high signal-to-noise spectroscopy for 44
QSOs at redshifts > 4 using the MMT and Keck observatories. The quasar spectra
cover 1100 -- 1700 A in the rest frame for sources spanning a luminosity range
of approximately 2 orders of magnitude. Comparisons between these data and
spectra of lower redshift quasars reveal a high degree of similarity, although
differences are present in the profiles and the strengths of some emission
features. An examination of the luminosity dependence of the emission lines
reveals evidence for a weak or absent Baldwin effect among z > 4 QSOs. We
compare measurements for objects in our sample with results from other high
redshift surveys characterized by different selection techniques. Distributions
of equivalent widths for these different ensembles are consistent with a common
parent population, suggesting that our sample is not strongly biased, or in any
case, subject to selection effects that are not significantly different from
other surveys, including the Sloan Digital Sky Survey. Based on this
comparison, we tentatively conclude that the trends identified here are
representative of high z QSOs. In particular, the data bolster indications of
supersolar metallicities in these luminous, high-z sources, which support
scenarios that assume substantial star formation at epochs preceding or
concurrent with the QSO phenomena.Comment: 26 pages (incl. 9 figures), AASTeX v5.0, to appear in The
Astrophysical Journa
Mid-J CO Emission in Nearby Seyfert Galaxies
We study for the first time the complete sub-millimeter spectra (450 GHz to
1550 GHz) of a sample of nearby active galaxies observed with the SPIRE Fourier
Transform Spectrometer (SPIRE/FTS) onboard Herschel. The CO ladder (from Jup =
4 to 12) is the most prominent spectral feature in this range. These CO lines
probe warm molecular gas that can be heated by ultraviolet photons, shocks, or
X-rays originated in the active galactic nucleus or in young star-forming
regions. In these proceedings we investigate the physical origin of the CO
emission using the averaged CO spectral line energy distribution (SLED) of six
Seyfert galaxies. We use a radiative transfer model assuming an isothermal
homogeneous medium to estimate the molecular gas conditions. We also compare
this CO SLED with the predictions of photon and X-ray dominated region (PDR and
XDR) models.Comment: Proceedings of the Torus Workshop 2012 held at the University of
Texas at San Antonio, 5-7 December 2012. C. Packham, R. Mason, and A.
Alonso-Herrero (eds.); 6 pages, 3 figure
Sensitive Radio Observations of High Redshift Dusty QSOs
We present sensitive radio continuum imaging at 1.4 GHz and 4.9 GHz of seven
high redshift QSOs selected for having a 240 GHz continuum detection, which is
thought to be thermal dust emission. We detect radio continuum emission from
four of the sources: BRI 0952-0115, BR 1202-0725, LBQS 1230+1627B, and BRI
1335-0417. The radio source in BR 1202-0725 is resolved into two components,
coincident with the double mm and CO sources. We compare the results at 1.4 GHz
and 240 GHz to empirical and semi-analytic spectral models based on star
forming galaxies at low redshift. The radio-to-submm spectral energy
distribution for BR 1202-0725, LBQS 1230+1627B, and BRI 1335-0417 are
consistent with that expected for a massive starburst galaxy, with implied
massive star formation rates of order 1000 solar masses per year (without
correcting for possible amplification by gravitational lensing). The
radio-to-submm spectral energy distribution for BRI 0952-0115 suggests a
low-luminosity radio jet source driven by the AGN.Comment: 12 pages, Latex emulateapj format, including 1 table and 3 figures.
The Astrophysical Journal, to appear in the January 2000 issu
Detection of a Lyman-alpha Emission-Line Companion to the z=4.69 QSO BR1202-0725
We report the detection of a nearby emission-line companion to the z=4.695
quasar BR1202-0725. Deep narrow-band exposures on this field from the UH 2.2 m
show a Ly alpha flux of 1.5\times\ten{-16} ergs cm^{-2} s^{-1}. High-resolution
HST WFC2 imaging in the F814W filter band shows continuum structure near the
emission position, at 2.6" NW of the quasar, corresponding to a projected
separation of ~7.5 h^{-1} kpc for \qnought=0.5, where h=\hnought/100\kms
Mpc^{-1}. We discuss possible explanations for the combined line and color
properties. The ionization is most likely produced by the quasar, but if due to
underlying star formation would require a star formation rate of ~7 h^2 solar
masses per yr.Comment: 12 pages LaTeX (aastex4.0 macros: aasms4.sty, flushrt.sty) plus 3
figures. To appear in the Astrophysical Journal Letters. Typo in original
submission ("2" should have been "7" in luminosity: 7e42 h^{-2} ergs and in
the star formation rate: 7 h^{-2} \msun per yr). Resubmitted with figure
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