252 research outputs found
Informal production of the city: Momos, migrants, and an urban village in Delhi
This paper attempts to understand the production of the city through informality. In particular, informal practices related to the momo (dumpling) industry, concentrated in the ‘urban village’ of Chirag Dilli, are analysed in their dialectic relationship with formal planning and legislation in Delhi. We use a Lefebvrian framework that views city-making as an interaction of formal representations in the form of master plans, etc., informal and formal spatial practices (including momo production and living patterns) and representational (imagined) spaces related to neighbourhoods and the city.
Drawing on primary qualitative data, we examine how informality informed the formal planning. The uneven application of state legislation, in turn, fostered particular informal practices (such as momo manufacturing) and the emergence of a distinct urban morphology and of new cohabitation practices. The informal momo industry also altered the representational associations made with both the Chirag Dilli neighbourhood and the city of Delhi.
The paper shows how informal practices constantly interact with formal frameworks to co-produce urban space and consequently the city. We argue that informal practices are not necessarily in conflict with formal planning or subverting it, but that they play a central role in their own right for the production of space
Constraining the Cosmological Density of Compact Objects with the Long-Term Variability of Quasars
By comparing the results from numerical microlensing simulations to the
observed long-term variability of quasars, strong upper limits on the
cosmological density of compact objects in the 0.0001-1 solar mass range may in
principle be imposed. Here, this method is generalized from the Einstein-de
Sitter universe to the currently favored Omega_M=0.3, Omega_Lambda=0.7
cosmology and applied to the latest observational samples. We show that the use
of high-redshift quasars from variability-selected samples has the potential to
substantially improve current constraints on compact objects in this mass
range. We also investigate to what extent the upper limits on such hypothetical
dark matter populations are affected by assumptions concerning the size of the
optical continuum-emitting region of quasars and the velocity dispersion of
compact objects. We find that mainly due to uncertainties in the typical value
of the source size, cosmologically significant populations of compact objects
cannot safely be ruled out with this method at the present time.Comment: 10 pages, 7 figures, accepted for publication in A&
On Uniqueness of Boundary Blow-up Solutions of a Class of Nonlinear Elliptic Equations
We study boundary blow-up solutions of semilinear elliptic equations
with , or with , where is a second order
elliptic operator with measurable coefficients. Several uniqueness theorems and
an existence theorem are obtained.Comment: To appear in Comm. Partial Differential Equations; 10 page
Mid-infrared selection of AGN
Since a large fraction of active galactic nuclei (AGN) is missed in common
UV-excess surveys and is even hard to find in radio, near-IR and X-ray surveys,
we have used a new AGN selection technique which is expected to be not affected
by extinction. Within the scientific verification of the ISOCAM Parallel Survey
at 6.7 micron we have discovered objects with exceptional mid-infrared (MIR)
emission. They are essentially not detected on IRAS-ADDSCANs and only very few
of them show up in the NVSS and FIRST radio surveys. Various colour criteria of
the 6.7 micron data with 2MASS and optical wavebands show that the sources
reach more extreme IR colours than the sources in the Hubble Deep Field-South
and the ELAIS survey. The comparison with known object types suggests that we
have found AGN with a pronounced MIR emission, probably due to circum-nuclear
dust. First results from optical spectroscopy of ten candidates corroborate
this interpretation showing four AGN, two reddened LINER and four extremely
reddened emission-line galaxies with MIR/FIR flux ratios higher than for known
pure starburst galaxies. The results will make a significant contribution to
the debate on the entire AGN population.Comment: 4 pages, 2 figures, accepted for publication as Letter in Astronomy &
Astrophysic
Multicolor photometry of ten Seyfert 1 galaxies
We present BVI photometry of ten Seyfert 1 galaxies and narrow band H-alpha
images for six of these objects as well. The results indicate that the
luminosity sample distribution has an amplitude of almost 4 magnitudes with an
average of M_B=-20.7. The observed morphologies are confined to early type
galaxies. A barred structure is found in only 2 objects. Despite that early
morphological types are dominant in this sample, integrated (B-V) colors are
very blue. For instance, the SO galaxies show, on average, a (B-V)=0.78. This
effect seems to be caused by the luminosity contribution of the active nucleus
and/or the disk to the total luminosity of the galaxy. In the B band, the
contribution of the active galactic nucleus to the total luminosity of the
galaxy varies from 3% to almost 60% and the bulge to disk luminosity ratio
(L_bulge/L_disk) ranges from 0.6 to 22. Signs of tidal interactions seems to be
a common characteristic since they are observed in 6 of the objects and one of
them seems to be located in a poor cluster not yet identified in the
literature. H_alpha extended emission is rare, with only 1 galaxy showing clear
evidence of it. Luminosity profile decomposition shows that the model Gauss +
bulge + disk properly reproduces the surface brightness of the galaxies.
However, in order to account for the luminosity profile, most of the disk
galaxies needs the inner truncated exponential form with a central cutoff
radius ranging from 3 to 10 kpc. This is interpreted in terms of reddened
regions that are well identified in the B-V color maps. These regions present
very similar colors among them, with (B-V)~1.2. This fact could be associated
to the presence of dust confined in the inner regions of the galaxies.Comment: 14 pages, 25 figures. Accepted to Astronomy & Astrophysic
A 100ks XMM-Newton view of the Seyfert 1.8 ESO113-G010. I. Discovery of large X-ray variability and study of the FeKalpha line complex
(Abridged) We present here a long (100ks) XMM-Newton follow-up of the Seyfert
1.8 galaxy ESO113-G010 performed in November 2005, in order to study over a
longer time-scale its main X-ray properties. The source was found in a
higher/softer time-averaged flux state, and timing analysis of this source
reveals strong, rapid variability. The Power Spectral Density (PSD) analysis
indicates (at 95% c.l.) a break at 3.7 x 10^-4 Hz. This cut-off frequency is
comparable to those measured in some other rapidly-variable Seyferts, such as
MCG-6-30-15 and NGC4051. From the mass-luminosity-time-scale, we infer that
M_BH ranges from 4 x 10^6 - 10^7 M_odot and the source is accreting at or close
to the Eddington rate (or even higher). The existing data cannot distinguish
between spectral pivoting of the continuum and a two-component origin for the
spectral softening, primarily because the data do not span a broad enough flux
range. In the case of the two-component model, the fractional offsets measured
in the flux-flux plots increase significantly toward higher energies (similar
to what is observed in MCG-6-30-15) as expected if there exists a constant
reflection component. Contrary to May 2001, no significant highly redshifted
emission line is observed (which might be related to the source flux level),
while two narrow emission lines at about 6.5keV and 7keV are observed. The S/N
is not high enough to establish if the lines are variable or constant. As
already suggested by the 2001 observation, no significant constant narrow
6.4keV FeK line (EW~32eV) is observed, hence excluding any dominant emission
from distant cold matter such as a torus in this Seyfert type 1.8 galaxy.Comment: Accepted for publication in A&A, 10 pages, 11 figures, 2 table
Implications from the optical to UV flux ratio of FeII emission in quasars
We investigate FeII emission in Broad Line Region (BLR) of AGNs by analyzing
the FeII(UV), FeII(4570) and MgII emission lines in 884 quasars in the Sloan
Digital Sky Survey (SDSS) Quasar catalog in a redshift range of 0.727 < z <
0.804. FeII(4570)/FeII(UV) is used to infer the column density of FeII-emitting
clouds and explore the excitation mechanism of FeII emission lines. As
suggested before in various works, the classical photoionization models fail to
account for FeII(4570)/FeII(UV) by a factor of 10, which may suggest anisotropy
of UV FeII emission; otherwise, an alternative heating mechanism like shock is
working. The column density distribution derived from FeII(4570)/FeII(UV)
indicates that radiation pressure plays an important role in BLR gas dynamics.
We find a positive correlation between FeII(4570)/FeII(UV) and the Eddington
ratio. We also find that almost all FeII-emitting clouds are to be under
super-Eddington conditions unless ionizing photon fraction is much smaller than
that previously suggested. Finally we propose a physical interpretation of a
striking set of correlations between various emission-line properties, known as
``Eigenvector 1''.Comment: 10 pages, 10 figures, accepted for publication in MNRA
The Large Quasar Reference Frame (LQRF) - an optical representation of the ICRS
The large number and all-sky distribution of quasars from different surveys,
along with their presence in large, deep astrometric catalogs,enables the
building of an optical materialization of the ICRS following its defining
principles. Namely: that it is kinematically non-rotating with respect to the
ensemble of distant extragalactic objects; aligned with the mean equator and
dynamical equinox of J2000; and realized by a list of adopted coordinates of
extragalatic sources. Starting from the updated and presumably complete LQAC
list of QSOs, the initial optical positions of those quasars are found in the
USNO B1.0 and GSC2.3 catalogs, and from the SDSS DR5. The initial positions are
next placed onto UCAC2-based reference frames, following by an alignment with
the ICRF, to which were added the most precise sources from the VLBA calibrator
list and the VLA calibrator list - when reliable optical counterparts exist.
Finally, the LQRF axes are inspected through spherical harmonics, contemplating
to define right ascension, declination and magnitude terms. The LQRF contains
J2000 referred equatorial coordinates for 100,165 quasars, well represented
across the sky, from -83.5 to +88.5 degrees in declination, and with 10 arcmin
being the average distance between adjacent elements. The global alignment with
the ICRF is 1.5 mas, and the individual position accuracies are represented by
a Poisson distribution that peaks at 139 mas in right ascension and 130 mas in
declination. It is complemented by redshift and photometry information from the
LQAC. The LQRF is designed to be an astrometric frame, but it is also the basis
for the GAIA mission initial quasars' list, and can be used as a test bench for
quasars' space distribution and luminosity function studies.Comment: 23 pages, 23 figures, 6 tables Accepted for publication by Astronomy
& Astrophysics, on 25 May 200
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