1,934 research outputs found
The Future of Direct Supermassive Black Hole Mass Estimates
(Abridged) The repeated discovery of supermassive black holes (SMBHs) at the
centers of galactic bulges, and the discovery of relations between the SMBH
mass (M) and the properties of these bulges, has been fundamental in directing
our understanding of both galaxy and SMBH formation and evolution. However,
there are still many questions surrounding the SMBH - galaxy relations. For
example, are the scaling relations linear and constant throughout cosmic
history, and do all SMBHs lie on the scaling relations? These questions can
only be answered by further high quality direct M estimates from a wide range
in redshift. In this paper we determine the observational requirements
necessary to directly determine SMBH masses, across cosmological distances,
using current M modeling techniques. We also discuss the SMBH detection
abilities of future facilities. We find that if different M modeling
techniques, using different spectral features, can be shown to be consistent,
then both 30 m ground- and 16 m space-based telescopes will be able to sample M
1e9Msol across ~95% of cosmic history. However, we find that the abilities of
ground-based telescopes critically depend on future advancements in adaptive
optics systems; more limited AO systems will result in limited effective
spatial resolutions, and forces observations towards the near-infrared where
spectral features are weaker and more susceptible to sky features. Ground-based
AO systems will always be constrained by relatively bright sky backgrounds and
atmospheric transmission. The latter forces the use of multiple spectral
features and dramatically impacts the SMBH detection efficiency. The most
efficient way to advance our database of direct SMBH masses is therefore
through the use of a large (16 m) space-based UVOIR telescope.Comment: PASP Accepte
A new extensive catalog of optically variable AGN in the GOODS Fields and a new statistical approach to variability selection
Variability is a property shared by practically all AGN. This makes
variability selection a possible technique for identifying AGN. Given that
variability selection makes no prior assumption about spectral properties, it
is a powerful technique for detecting both low-luminosity AGN in which the host
galaxy emission is dominating and AGN with unusual spectral properties. In this
paper, we will discuss and test different statistical methods for the detection
of variability in sparsely sampled data that allow full control over the false
positive rates. We will apply these methods to the GOODS North and South fields
and present a catalog of variable sources in the z band in both GOODS fields.
Out of 11931 objects checked, we find 155 variable sources at a significance
level of 99.9%, corresponding to about 1.3% of all objects. After rejection of
stars and supernovae, 139 variability selected AGN remain. Their magnitudes
reach down as faint as 25.5 mag in z. Spectroscopic redshifts are available for
22 of the variability selected AGN, ranging from 0.046 to 3.7. The absolute
magnitudes in the rest-frame z-band range from ~ -18 to -24, reaching
substantially fainter than the typical luminosities probed by traditional X-ray
and spectroscopic AGN selection in these fields. Therefore, this is a powerful
technique for future exploration of the evolution of the faint end of the AGN
luminosity function up to high redshifts.Comment: Accepted for publication in The Astrophysical Journal (version 2:
minor changes to text after receiving comments
Prevalence of X-ray variability in the Chandra Deep Field South
We studied the X-ray variability of sources detected in the Chandra Deep
Field South (Giacconi et al. 2002), nearly all of which are low to moderate z
AGN (Tozzi et al. 2001). We find that 45% of the sources with >100 counts
exhibit significant variability on timescales ranging from a day up to a year.
The fraction of sources found to be variable increases with observed flux,
suggesting that >90% of all AGNs possess intrinsic variability. We also find
that the fraction of variable sources appears to decrease with increasing
intrinsic absorption; a lack of variability in hard, absorbed AGNs could be due
to an increased contribution of reflected X-rays to the total flux. We do not
detect significant spectral variability in the majority (~70%) of our sources.
In half of the remaining 30%, the hardness ratio is anti-correlated with flux,
mimicking the high/soft-low/hard states of galactic sources. The X-ray
variability appears anti-correlated with the luminosity of the sources, in
agreement with previous studies. High redshift sources, however, have larger
variability amplitudes than expected from extrapolations of their low-z
counterparts, suggesting a possible evolution in the accretion rate and/or size
of the X-ray emitting region. Finally, we discuss some effects that may produce
the observed decrease in the fraction of variable sources from z=0.5 out to
z=2.Comment: 24 pages, including 15 figures and 1 table. In press on Ap
Radio observations of the CDF-South: a possible link between radio emission and star formation in X-ray selected AGN
We explore the nature of the radio emission of X-ray selected AGN by
combining deep radio (1.4GHz; 60micro-Jy) and X-ray data with multiwavelength
(optical, mid-infrared) observations in the Extended Chandra Deep Field South
(E-CDFS). The fraction of radio detected X-ray sources increases from 9% in the
E-CDFS to 14% in the central region of this field, which has deeper X-ray
coverage from the 1Ms CDFS. We find evidence that the radio emission of up to
60% of the hard X-ray/radio matched AGN is likely associated with
star-formation in the host galaxy. Firstly, the mid-IR (24micron) properties of
these sources are consistent with the infrared/radio correlation of starbursts.
Secondly, most of them are found in galaxies with blue rest-frame optical
colours (U-V), suggesting a young stellar population. On the contrary,
X-ray/radio matched AGN which are not detected in the mid-infrared have red U-V
colours suggesting their radio emission is associated with AGN activity. We
also find no evidence for a population of heavily obscured radio-selected AGN
that are not detected in X-rays. Finally, we do no confirm previous claims for
a correlation between radio emission and X-ray obscuration. Assuming that the
radio continuum measures star-formation, this finding is against models where
the dust and gas clouds associated with circumnuclear starbursts are
spherically blocking our view to the central engine.Comment: Accepted by A&
CIR v Niko: A Question of Economic Reality
This article analyses the facts and judgment in CIR v Niko, involving the transfer of business assets from a sole trader to a company, the shares of which were substantially owned by the same sole trader. This case changed the inherently flawed, but prevailing practice at that stage of regarding a lump-sum payment from a lock-stock-and-barrel sale of a business as a receipt of a capital nature, to a receipt that needed to be allocated to the various assets included in the sale, and therefore potentially the receipt would be partly of a capital and partly of a revenue nature. Although the conclusion relating to lock-stock-and-barrel sales in general was sound, the submission made in this article is that, in the particular circumstances of the case, the economic reality of the transaction was not considered – virtually no economic gain was realised by J. Niko, the seller and sole owner of the business to a company of which he was also the substantial shareholder. Two subsequent court decisions, which similarly ignored the economic reality of the transactions in the context of a group of companies, followed this judgment. In this article, the problematic nature of the decisions that ignored the economic reality of the transactions is demonstrated with reference to accepted canons of a good taxation system. The article also explains the partial legislative relief that has subsequently been granted for transfers of assets from a person to a company and for transfers within a group of companies, but concludes that there is a need for full recognition of a group of companies as an economic entity for tax purposes.Keywords: Integrated Group Tax System, Economic Reality, Economic Unit, Group of Companies, Lock-stock-and-barrel Sale, Principles of Equity and Neutrality, Sale of a Busines
New Image Statistics for Detecting Disturbed Galaxy Morphologies at High Redshift
Testing theories of hierarchical structure formation requires estimating the
distribution of galaxy morphologies and its change with redshift. One aspect of
this investigation involves identifying galaxies with disturbed morphologies
(e.g., merging galaxies). This is often done by summarizing galaxy images
using, e.g., the CAS and Gini-M20 statistics of Conselice (2003) and Lotz et
al. (2004), respectively, and associating particular statistic values with
disturbance. We introduce three statistics that enhance detection of disturbed
morphologies at high-redshift (z ~ 2): the multi-mode (M), intensity (I), and
deviation (D) statistics. We show their effectiveness by training a
machine-learning classifier, random forest, using 1,639 galaxies observed in
the H band by the Hubble Space Telescope WFC3, galaxies that had been
previously classified by eye by the CANDELS collaboration (Grogin et al. 2011,
Koekemoer et al. 2011). We find that the MID statistics (and the A statistic of
Conselice 2003) are the most useful for identifying disturbed morphologies.
We also explore whether human annotators are useful for identifying disturbed
morphologies. We demonstrate that they show limited ability to detect
disturbance at high redshift, and that increasing their number beyond
approximately 10 does not provably yield better classification performance. We
propose a simulation-based model-fitting algorithm that mitigates these issues
by bypassing annotation.Comment: 15 pages, 14 figures, accepted for publication in MNRA
Evolution of the Fraction of Clumpy Galaxies at 0.2<z<1.0 in the COSMOS field
Using the Hubble Space Telescope/Advanced Camera for Surveys data in the
COSMOS field, we systematically searched clumpy galaxies at 0.2<z<1.0 and
investigated the fraction of clumpy galaxies and its evolution as a function of
stellar mass, star formation rate (SFR), and specific SFR (SSFR). The fraction
of clumpy galaxies in star-forming galaxies with Mstar > 10^9.5 Msun decreases
with time from ~0.35 at 0.8<z<1.0 to ~0.05 at 0.2<z<0.4 irrespective of the
stellar mass, although the fraction tends to be slightly lower for massive
galaxies with Mstar > 10^10.5 Msun at each redshift. On the other hand, the
fraction of clumpy galaxies increases with increasing both SFR and SSFR in all
the redshift ranges we investigated. In particular, we found that the SSFR
dependences of the fractions are similar among galaxies with different stellar
masses, and the fraction at a given SSFR does not depend on the stellar mass in
each redshift bin. The evolution of the fraction of clumpy galaxies from z~0.9
to z~0.3 seems to be explained by such SSFR dependence of the fraction and the
evolution of SSFRs of star-forming galaxies. The fraction at a given SSFR also
appears to decrease with time, but this can be due to the effect of the
morphological K-correction. We suggest that these results are understood by the
gravitational fragmentation model for the formation of giant clumps in disk
galaxies, where the gas mass fraction is a crucial parameter.Comment: 14 Pages, 13 Figures, 1 Table, Accepted for publication in Ap
The cosmic growth of the active black hole population at 1<z<2 in zCOSMOS, VVDS and SDSS
We present a census of the active black hole population at 1<z<2, by
constructing the bivariate distribution function of black hole mass and
Eddington ratio, employing a maximum likelihood fitting technique. The study of
the active black hole mass function (BHMF) and the Eddington ratio distribution
function (ERDF) allows us to clearly disentangle the active galactic nuclei
(AGN) downsizing phenomenon, present in the AGN luminosity function, into its
physical processes of black hole mass downsizing and accretion rate evolution.
We are utilizing type-1 AGN samples from three optical surveys (VVDS, zCOSMOS
and SDSS), that cover a wide range of 3 dex in luminosity over our redshift
interval of interest. We investigate the cosmic evolution of the AGN population
as a function of AGN luminosity, black hole mass and accretion rate. Compared
to z = 0, we find a distinct change in the shape of the BHMF and the ERDF,
consistent with downsizing in black hole mass. The active fraction or duty
cycle of type-1 AGN at z~1.5 is almost flat as a function of black hole mass,
while it shows a strong decrease with increasing mass at z=0. We are witnessing
a phase of intense black hole growth, which is largely driven by the onset of
AGN activity in massive black holes towards z=2. We finally compare our results
to numerical simulations and semi-empirical models and while we find reasonable
agreement over certain parameter ranges, we highlight the need to refine these
models in order to match our observations.Comment: 31 pages, 28 figures, accepted for publication in MNRA
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