639 research outputs found
Modified Dark Matter: Relating Dark Energy, Dark Matter and Baryonic Matter
Modified dark matter (MDM) is a phenomenological model of dark matter,
inspired by gravitational thermodynamics. For an accelerating Universe with
positive cosmological constant (), such phenomenological
considerations lead to the emergence of a critical acceleration parameter
related to . Such a critical acceleration is an effective
phenomenological manifestation of MDM, and it is found in correlations between
dark matter and baryonic matter in galaxy rotation curves. The resulting MDM
mass profiles, which are sensitive to , are consistent with
observational data at both the galactic and cluster scales. In particular, the
same critical acceleration appears both in the galactic and cluster data fits
based on MDM. Furthermore, using some robust qualitative arguments, MDM appears
to work well on cosmological scales, even though quantitative studies are still
lacking. Finally, we comment on certain non-local aspects of the quanta of
modified dark matter, which may lead to novel non-particle phenomenology and
which may explain why, so far, dark matter detection experiments have failed to
detect dark matter particles
Principal Component Analysis and Radiative Transfer modelling of Spitzer IRS Spectra of Ultra Luminous Infrared Galaxies
The mid-infrared spectra of ultraluminous infrared galaxies (ULIRGs) contain
a variety of spectral features that can be used as diagnostics to characterise
the spectra. However, such diagnostics are biased by our prior prejudices on
the origin of the features. Moreover, by using only part of the spectrum they
do not utilise the full information content of the spectra. Blind statistical
techniques such as principal component analysis (PCA) consider the whole
spectrum, find correlated features and separate them out into distinct
components.
We further investigate the principal components (PCs) of ULIRGs derived in
Wang et al.(2011). We quantitatively show that five PCs is optimal for
describing the IRS spectra. These five components (PC1-PC5) and the mean
spectrum provide a template basis set that reproduces spectra of all z<0.35
ULIRGs within the noise. For comparison, the spectra are also modelled with a
combination of radiative transfer models of both starbursts and the dusty torus
surrounding active galactic nuclei. The five PCs typically provide better fits
than the models. We argue that the radiative transfer models require a colder
dust component and have difficulty in modelling strong PAH features.
Aided by the models we also interpret the physical processes that the
principal components represent. The third principal component is shown to
indicate the nature of the dominant power source, while PC1 is related to the
inclination of the AGN torus.
Finally, we use the 5 PCs to define a new classification scheme using 5D
Gaussian mixtures modelling and trained on widely used optical classifications.
The five PCs, average spectra for the four classifications and the code to
classify objects are made available at: http://www.phys.susx.ac.uk/~pdh21/PCA/Comment: 11 pages, 12 figures, accepted for publication in MNRA
Multi-band Optical and Near-infrared Properties of Faint Submillimeter Galaxies with Serendipitous ALMA Detections
We present a catalog of 26 faint submillimeter galaxies (SMGs) in the XMM-LSS
field identified by cross-matching serendipitously detected sources in archival
ALMA Band 6 and 7 data with multi-band near-infrared (NIR) and optical data
from the Spitzer Extragalactic Representative Volume Survey, the VISTA Deep
Extragalactic Survey, the Canada-France-Hawaii Telescope Legacy Large Survey,
and the Hyper Suprime-Cam Subaru Strategic Program. Of the 26 SMGs in our
sample, 15 are identified here for the first time. The majority of the sources
in our sample (16/26) have faint submm fluxes (). In addition to the 26 SMGs with multi-band optical and NIR
detections, there are 60 highly-reliable () ALMA sources with no
counterpart in any other band down to an IRAC [4.5] magnitude of . To further characterize the 26 galaxies with both ALMA and optical/NIR
counterparts, we provide 13-band forced photometry for the entire catalog using
the Tractor and calculate photometric redshifts and rest-frame colors. The
median redshift of our sample is . We find that our
sample galaxies have bluer colors compared to bright SMGs, and the UVJ color
plot indicates that their colors are consistent with main sequence star-forming
galaxies. Our results provide new insights into the nature of the faint
population of SMGs, and also highlight opportunities for galaxy evolution
studies based on archival ALMA data.Comment: Accepted for publication in ApJ, 32 pages, 11 figures, 4 table
Testing Modified Dark Matter with Galaxy Clusters: Does Dark Matter know about the Cosmological Constant?
We discuss the possibility that the cold dark matter mass profiles contain
information on the cosmological constant, and that such information constrains
the nature of cold dark matter (CDM). We call this approach Modified Dark
Matter (MDM). In particular, we examine the ability of MDM to explain the
observed mass profiles of 13 galaxy clusters. Using general arguments from
gravitational thermodynamics, we provide a theoretical justification for our
MDM mass profile and successfully compare it to the NFW mass profiles both on
cluster and galactic scales. Our results suggest that indeed the CDM mass
profiles contain information about the cosmological constant in a non-trivial
way
The History of Star Forming Galaxies and their Environment as seen by Spitzer: A Review
The advent of the Spitzer Space Telescope has revolutionized our
understanding of the history of star formation and galaxy mass assembly in the
Universe. The tremendous leap in sensitivity from previous mid-to-far IR
missions has allowed Spitzer to perform deeper, and wider, surveys than
previously possible at these wavelengths. In this brief review I highlight some
of the key results to come out of these surveys, and the implications these
have for current models of galaxy formation and evolution.Comment: 9 pages, 3 figures, invited review, to be published in the
proceedings of the conference "AKARI, a light to illuminate the misty
Universe", University of Tokyo, Japan, 16-19 February 200
Testing MONDian Dark Matter with Galactic Rotation Curves
MONDian dark matter (MDM) is a new form of dark matter quantum that naturally
accounts for Milgrom's scaling, usually associated with modified Newtonian
dynamics (MOND), and theoretically behaves like cold dark matter (CDM) at
cluster and cosmic scales. In this paper, we provide the first observational
test of MDM by fitting rotation curves to a sample of 30 local spiral galaxies
(z approximately 0.003). For comparison, we also fit the galactic rotation
curves using MOND, and CDM. We find that all three models fit the data well.
The rotation curves predicted by MDM and MOND are virtually indistinguishable
over the range of observed radii (~1 to 30 kpc). The best-fit MDM and CDM
density profiles are compared. We also compare with MDM the dark matter density
profiles arising from MOND if Milgrom's formula is interpreted as Newtonian
gravity with an extra source term instead of as a modification of inertia. We
find that discrepancies between MDM and MOND will occur near the center of a
typical spiral galaxy. In these regions, instead of continuing to rise sharply,
the MDM mass density turns over and drops as we approach the center of the
galaxy. Our results show that MDM, which restricts the nature of the dark
matter quantum by accounting for Milgrom's scaling, accurately reproduces
observed rotation curves.Comment: Preprint number IPMU13-0147. Accepted for publication in Ap
The stellar, molecular gas and dust content of the host galaxies of two z~2.8 dust obscured quasars
We present optical through radio observations of the host galaxies of two
dust obscured, luminous quasars selected in the mid-infrared, at z=2.62 and
z=2.99, including a search for CO emission. Our limits on the CO luminosities
are consistent with these objects having masses of molecular gas <~10^10 solar
masses, several times less than those of luminous submillimeter-detected
galaxies (SMGs) at comparable redshifts. Their near-infrared spectral energy
distributions, however, imply that these galaxies have high stellar masses
(~10^11-12 solar masses). The relatively small reservoirs of molecular gas and
low dust masses are consistent with them being relatively mature systems at
high-z.Comment: AJ, in pres
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