66 research outputs found
Spectral Energy Distribution Mapping of Two Elliptical Galaxies on sub-kpc scales
We use high-resolution Herschel-PACS data of 2 nearby elliptical galaxies,
IC1459 & NGC2768 to characterize their dust and stellar content. IC1459 &
NGC2768 have an unusually large amount of dust for elliptical galaxies (1-3 x
10^5 Msun), this dust is also not distributed along the stellar content. Using
data from GALEX (ultraviolet) to PACS (far-infrared), we analyze the spectral
energy distribution (SED) of these galaxies with CIGALEMC as a function of the
projected position, binning images in 7.2" pixels. From this analysis, we
derive maps of SED parameters, such as the metallicity, the stellar mass, the
fraction of young star and the dust mass. The larger amount of dust in FIR maps
seems related in our model to a larger fraction of young stars which can reach
up to 4% in the dustier area. The young stellar population is fitted as a
recent (~ 0.5 Gyr) short burst of star formation for both galaxies. The
metallicities, which are fairly large at the center of both galaxies, decrease
with the radial distance with fairly steep gradient for elliptical galaxies.Comment: 14 pages, 26 figures, to be published in Ap
Anisotropy Studies of the Unresolved Far-infrared Background
Dusty, starforming galaxies and active galactic nuclei that contribute to the
integrated background intensity at far-infrared wavelengths trace the
large-scale structure. Below the point source detection limit, correlations in
the large-scale structure lead to clustered anisotropies in the unresolved
component of the far-infrared background (FIRB). The angular power spectrum of
the FIRB anisotropies could be measured in large-area surveys with the Spectral
and Photometric Imaging Receiver (SPIRE) on the upcoming Herschel observatory.
To study statistical properties of these anisotropies, the confusion from
foreground Galactic dust emission needs to be reduced even in the ``cleanest''
regions of the sky.The multi-frequency coverage of SPIRE allows the foreground
dust to be partly separated from the extragalactic background composed of dusty
starforming galaxies as well as faint normal galaxies. The separation improves
for fields with sizes greater than a few hundred square degrees and when
combined with Planck data. We show that an area of about 400 degrees
observed for about 1000 hours with Herschel-SPIRE and complemented by Planck
provides maximal information on the anisotropy power spectrum. We discuss the
scientific studies that can be done with measurements of the unresolved FIRB
anisotropies including a determination of the large scale bias and the
small-scale halo occupation distribution of FIRB sources with fluxes below the
point-source detection level.Comment: 10 pages, 8 figures, replaced to match the extended version, accepted
by Ap
Mid-IR Enhanced Galaxies in the Coma & Virgo Cluster: lenticulars with a high star formation rate
We explore the properties of early-type galaxies (ETGs), including
ellipticals (E) and lenticulars (S0), in rich environments such as clusters of
galaxies (Virgo and Coma). The L_24/L_K distribution of ETGs in both Virgo and
Coma clusters shows that some S0s have a much larger L_24/L_K ratio (0.5 to ~2
dex) than the bulk of the ETG population. This could be interpreted as an
enhanced star formation rate in these lenticulars. We compare the optical
colors of galaxies in these two clusters and investigate the nature of these
sources with a large L24/L_K ratio by looking at their spatial distribution
within the cluster, by analyzing their optical spectra and by looking at their
optical colors compared to late-types. We obtain 10 Coma and 3 Virgo early-type
sources with larger L24/L_K ratios than the bulk of their population. We call
these sources Mid-Infrared Enhanced Galaxies (MIEGs). In Coma, they are mostly
located in the South-West part of the cluster where a substructure is falling
onto the main cluster. MIEGs present lower g-r color than the rest of the ETG
sample, because of a blue continuum. We interpret the excess L24/L_K ratio as
evidence for an enhanced star-formation induced as a consequence of their
infall into the main cluster.Comment: Accepted for publication in Ap
Estimating the inverse trace using random forests on graphs
Some data analysis problems require the computation of (regularised) inverse
traces, i.e. quantities of the form \Tr (q \bI + \bL)^{-1}. For large
matrices, direct methods are unfeasible and one must resort to approximations,
for example using a conjugate gradient solver combined with Girard's trace
estimator (also known as Hutchinson's trace estimator). Here we describe an
unbiased estimator of the regularized inverse trace, based on Wilson's
algorithm, an algorithm that was initially designed to draw uniform spanning
trees in graphs. Our method is fast, easy to implement, and scales to very
large matrices. Its main drawback is that it is limited to diagonally dominant
matrices \bL.Comment: Submitted to GRETSI conferenc
Lensing and Supernovae: Quantifying The Bias on the Dark Energy Equation of State
The gravitational magnification and demagnification of Type Ia supernovae
(SNe) modify their positions on the Hubble diagram, shifting the distance
estimates from the underlying luminosity-distance relation. This can introduce
a systematic uncertainty in the dark energy equation of state (EOS) estimated
from SNe, although this systematic is expected to average away for sufficiently
large data sets. Using mock SN samples over the redshift range
we quantify the lensing bias. We find that the bias on the dark energy EOS is
less than half a percent for large datasets ( 2,000 SNe). However, if
highly magnified events (SNe deviating by more than 2.5) are
systematically removed from the analysis, the bias increases to 0.8%.
Given that the EOS parameters measured from such a sample have a 1
uncertainty of 10%, the systematic bias related to lensing in SN data out to can be safely ignored in future cosmological measurements.Comment: 5 pages, 4 figures; one figure and references added; minor
modifications to text; reflects version accepted for publication in Ap
Beyond Two Dark Energy Parameters
Our ignorance of the dark energy is generally described by a two-parameter
equation of state. In these approaches a particular {\it ad hoc} functional
form is assumed, and only two independent parameters are incorporated. We
propose a model-independent, multi-parameter approach to fitting the dark
energy, and show that next-generation surveys will constrain the equation of
state in three or more independent redshift bins to better than 10%. Future
knowledge of the dark energy will surpass two numbers (e.g., [,] or
[,]), and we propose a more flexible approach to the analysis of
present and future data.Comment: 4 pages, 1 figure; Discussion expanded to include next-generation BAO
surveys and possible systematics in SN surveys; reflects version accepted for
publication in Phys. Rev. Let
ALMA observations of molecular clouds in three group centered elliptical galaxies: NGC 5846, NGC 4636, and NGC 5044
We present new ALMA CO(2--1) observations of two well studied group-centered
elliptical galaxies: NGC~4636 and NGC~5846. In addition, we include a revised
analysis of Cycle 0 ALMA observations of the central galaxy in the NGC~5044
group that has been previously published. We find evidence that molecular gas,
in the form of off-center orbiting clouds, is a common presence in bright
group-centered galaxies (BGG). CO line widths are times broader
than Galactic molecular clouds, and using the reference Milky Way , the
total molecular mass ranges from as low as in NGC~4636
to in NGC~5044. With these parameters the virial
parameters of the molecular structures is . Complementary observations
of NGC~5846 and NGC~4636 using the ALMA Compact Array (ACA) do not exhibit any
detection of a CO diffuse component at the sensitivity level achieved by
current exposures. The origin of the detected molecular features is still
uncertain, but these ALMA observations suggest that they are the end product of
the hot gas cooling process and not the result of merger events. Some of the
molecular clouds are associated with dust features as revealed by HST dust
extinction maps suggesting that these clouds formed from dust-enhanced cooling.
The global nonlinear condensation may be triggered via the chaotic turbulent
field or buoyant uplift. The large virial parameter of the molecular structures
and correlation with the warm ()/hot () phase velocity
dispersion provide evidence that they are unbound giant molecular associations
drifting in the turbulent field, consistently with numerical predictions of the
chaotic cold accretion process. Alternatively, the observed large CO line
widths may be generated by molecular gas flowing out from cloud surfaces due to
heating by the local hot gas atmosphere.Comment: Revised version to be published in ApJ, 16 pages, 10 figures, 4
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