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Enhanced dust heating in the bulges of early-type spiral galaxies
Stellar density and bar strength should affect the temperatures of the cool (T ~ 20–30 K) dust component in the inner regions of galaxies, which implies that the ratio of temperatures in the circumnuclear regions to the disk should depend on Hubble type. We investigate the differences between cool dust temperatures in the central 3 kpc and disk of 13 nearby galaxies by fitting models to measurements between 70 and 500 μm. We attempt to quantify temperature trends in nearby disk galaxies, with archival data from Spitzer/MIPS and new observations with Herschel/SPIRE, which were acquired during the first phases of the Herschel observations for the KINGFISH (Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel) sample. We fit single-temperature modified blackbodies to far-infrared and submillimeter measurements of the central and disk regions of galaxies to determine the temperature of the component(s) emitting at those wavelengths. We present the ratio of central-region-to-disk-temperatures of the cool dust component of 13 nearby galaxies as a function of morphological type. We find a significant temperature gradient in the cool dust component in all galaxies, with a mean center-to-disk temperature ratio of 1.15 ± 0.03. The cool dust temperatures in the central ~3 kpc of nearby galaxies are 23 (±3)% hotter for morphological types earlier than Sc, and only 9 (±3)% hotter for later types. The temperature ratio is also correlated with bar strength, with only strongly barred galaxies having a ratio over 1.2. The strong radiation field in the high stellar density of a galactic bulge tends to heat the cool dust component to higher temperatures, at least in early-type spirals with relatively large bulges, especially when paired with a strong bar
PRIMUS: The Effect of Physical Scale on the Luminosity-Dependence of Galaxy Clustering via Cross-Correlations
We report small-scale clustering measurements from the PRIMUS spectroscopic
redshift survey as a function of color and luminosity. We measure the
real-space cross-correlations between 62,106 primary galaxies with PRIMUS
redshifts and a tracer population of 545,000 photometric galaxies over
redshifts from z=0.2 to z=1. We separately fit a power-law model in redshift
and luminosity to each of three independent color-selected samples of galaxies.
We report clustering amplitudes at fiducial values of z=0.5 and L=1.5 L*. The
clustering of the red galaxies is ~3 times as strong as that of the blue
galaxies and ~1.5 as strong as that of the green galaxies. We also find that
the luminosity dependence of the clustering is strongly dependent on physical
scale, with greater luminosity dependence being found between r=0.0625 Mpc/h
and r=0.25 Mpc/h, compared to the r=0.5 Mpc/h to r=2 Mpc/h range. Moreover,
over a range of two orders of magnitude in luminosity, a single power-law fit
to the luminosity dependence is not sufficient to explain the increase in
clustering at both the bright and faint ends at the smaller scales. We argue
that luminosity-dependent clustering at small scales is a necessary component
of galaxy-halo occupation models for blue, star-forming galaxies as well as for
red, quenched galaxies.Comment: 13 pages, 6 figures, 5 tables; published in ApJ (revised to match
published version
Dark Matter Halo Models of Stellar Mass-Dependent Galaxy Clustering in PRIMUS+DEEP2 at 0.2<z<1.2
We utilize CDM halo occupation models of galaxy clustering to
investigate the evolving stellar mass dependent clustering of galaxies in the
PRIsm MUlti-object Survey (PRIMUS) and DEEP2 Redshift Survey over the past
eight billion years of cosmic time, between . These clustering
measurements provide new constraints on the connections between dark matter
halo properties and galaxy properties in the context of the evolving
large-scale structure of the universe. Using both an analytic model and a set
of mock galaxy catalogs, we find a strong correlation between central galaxy
stellar mass and dark matter halo mass over the range
-, approximately consistent
with previous observations and theoretical predictions. However, the
stellar-to-halo mass relation (SHMR) and the mass scale where star formation
efficiency reaches a maximum appear to evolve more strongly than predicted by
other models, including models based primarily on abundance-matching
constraints. We find that the fraction of satellite galaxies in haloes of a
given mass decreases significantly from to , partly due to
the fact that haloes at fixed mass are rarer at higher redshift and have lower
abundances. We also find that the ratio, a model parameter
that quantifies the critical mass above which haloes host at least one
satellite, decreases from at to at .
Considering the evolution of the subhalo mass function vis-\`{a}-vis satellite
abundances, this trend has implications for relations between satellite
galaxies and halo substructures and for intracluster mass, which we argue has
grown due to stripped and disrupted satellites between and
.Comment: 17 pages, 9 figures and 4 tables; Astrophysical Journal, publishe
PRIMUS + DEEP2: Clustering of X-ray, Radio and IR-AGN at z~0.7
We measure the clustering of X-ray, radio, and mid-IR-selected active
galactic nuclei (AGN) at 0.2 < z < 1.2 using multi-wavelength imaging and
spectroscopic redshifts from the PRIMUS and DEEP2 redshift surveys, covering 7
separate fields spanning ~10 square degrees. Using the cross-correlation of AGN
with dense galaxy samples, we measure the clustering scale length and slope, as
well as the bias, of AGN selected at different wavelengths. Similar to previous
studies, we find that X-ray and radio AGN are more clustered than
mid-IR-selected AGN. We further compare the clustering of each AGN sample with
matched galaxy samples designed to have the same stellar mass, star formation
rate, and redshift distributions as the AGN host galaxies and find no
significant differences between their clustering properties. The observed
differences in the clustering of AGN selected at different wavelengths can
therefore be explained by the clustering differences of their host populations,
which have different distributions in both stellar mass and star formation
rate. Selection biases inherent in AGN selection, therefore, determine the
clustering of observed AGN samples. We further find no significant difference
between the clustering of obscured and unobscured AGN, using IRAC or WISE
colors or X-ray hardness ratio.Comment: Accepted to ApJ. 23 emulateapj pages, 15 figures, 4 table
PRIMUS: Galaxy Clustering as a Function of Luminosity and Color at 0.2<z<1
We present measurements of the luminosity and color-dependence of galaxy
clustering at 0.2<z<1.0 in the PRIsm MUlti-object Survey (PRIMUS). We quantify
the clustering with the redshift-space and projected two-point correlation
functions, xi(rp,pi) and wp(rp), using volume-limited samples constructed from
a parent sample of over 130,000 galaxies with robust redshifts in seven
independent fields covering 9 sq. deg. of sky. We quantify how the
scale-dependent clustering amplitude increases with increasing luminosity and
redder color, with relatively small errors over large volumes. We find that red
galaxies have stronger small-scale (0.1<rp<1 Mpc/h) clustering and steeper
correlation functions compared to blue galaxies, as well as a strong color
dependent clustering within the red sequence alone. We interpret our measured
clustering trends in terms of galaxy bias and obtain values between
b_gal=0.9-2.5, quantifying how galaxies are biased tracers of dark matter
depending on their luminosity and color. We also interpret the color dependence
with mock catalogs, and find that the clustering of blue galaxies is nearly
constant with color, while redder galaxies have stronger clustering in the
one-halo term due to a higher satellite galaxy fraction. In addition, we
measure the evolution of the clustering strength and bias, and we do not detect
statistically significant departures from passive evolution. We argue that the
luminosity- and color-environment (or halo mass) relations of galaxies have not
significantly evolved since z=1. Finally, using jackknife subsampling methods,
we find that sampling fluctuations are important and that the COSMOS field is
generally an outlier, due to having more overdense structures than other
fields; we find that 'cosmic variance' can be a significant source of
uncertainty for high-redshift clustering measurements.Comment: 22 pages, 21 figures, matches version published in Ap
Spherical Collapse and Cluster Counts in Modified Gravity Models
Modifications to the gravitational potential affect the nonlinear
gravitational evolution of large scale structures in the Universe. To
illustrate some generic features of such changes, we study the evolution of
spherically symmetric perturbations when the modification is of Yukawa type;
this is non-trivial, because we should not and do not assume that Birkhoff's
theorem applies. We then show how to estimate the abundance of virialized
objects in such models. Comparison with numerical simulations shows reasonable
agreement: When normalized to have the same fluctuations at early times, weaker
large scale gravity produces fewer massive halos. However, the opposite can be
true for models that are normalized to have the same linear theory power
spectrum today, so the abundance of rich clusters potentially places
interesting constraints on such models. Our analysis also indicates that the
formation histories and abundances of sufficiently low mass objects are
unchanged from standard gravity. This explains why simulations have found that
the nonlinear power-spectrum at large k is unaffected by such modifications to
the gravitational potential. In addition, the most massive objects in
CMB-normalized models with weaker gravity are expected to be similar to the
high-redshift progenitors of the most massive objects in models with stronger
gravity. Thus, the difference between the cluster and field galaxy populations
is expected to be larger in models with stronger large-scale gravity.Comment: 9 pages, 8 figures Accepted by Phys. Rev.
Gravitational redshift of galaxies in clusters as predicted by general relativity
The theoretical framework of cosmology is mainly defined by gravity, of which
general relativity is the current model. Recent tests of general relativity
within the \Lambda Cold Dark Matter (CDM) model have found a concordance
between predictions and the observations of the growth rate and clustering of
the cosmic web. General relativity has not hitherto been tested on cosmological
scales independent of the assumptions of the \Lambda CDM model. Here we report
observation of the gravitational redshift of light coming from galaxies in
clusters at the 99 per cent confidence level, based upon archival data. The
measurement agrees with the predictions of general relativity and its
modification created to explain cosmic acceleration without the need for dark
energy (f(R) theory), but is inconsistent with alternative models designed to
avoid the presence of dark matter.Comment: Published in Nature issued on 29 September 2011. This version
includes the Letter published there as well as the Supplementary Information.
23 pages, 7 figure
Dissecting the origin of the submillimeter emission in nearby galaxies with Herschel and LABOCA
We model the infrared to submillimeter spectral energy distribution of 11
nearby galaxies of the KINGFISH sample using Spitzer and Herschel data and
compare model extrapolations at 870um (using different fitting techniques) with
LABOCA 870um observations. We investigate how the differences between
predictions and observations vary with model assumptions or environment. At
global scales, we find that modified blackbody models using realistic cold
emissivity indices (beta_c=2 or 1.5) are able to reproduce the 870um observed
emission within the uncertainties for most of the sample. Low values
(beta_c<1.3) would be required in NGC0337, NGC1512 and NGC7793. At local
scales, we observe a systematic 870um excess when using beta_=2.0. The
beta_c=1.5 or the Draine and Li (2007) models can reconcile predictions with
observations in part of the disks. Some of the remaining excesses occur towards
the centres and can be partly or fully accounted for by non-dust contributions
such as CO(3-2) or, to a lesser extent, free-free or synchrotron emission. In
three non-barred galaxies, the remaining excesses rather occur in the disk
outskirts. This could be a sign of a flattening of the submm slope (and
decrease of the effective emissivity index) with radius in these objects.Comment: 31 pages (including appendix), 7 figures, accepted for publication in
MNRA
Non-standard grain properties, dark gas reservoir, and extended submillimeter excess, probed by Herschel in the Large Magellanic Cloud
Context. Herschel provides crucial constraints on the IR SEDs of galaxies, allowing unprecedented accuracy on the dust mass estimates. However, these estimates rely on non-linear models and poorly-known optical properties.
Aims. In this paper, we perform detailed modelling of the Spitzer and Herschel observations of the LMC, in order to: (i) systematically study the uncertainties and biases affecting dust mass estimates; and to (ii) explore the peculiar ISM properties of the LMC.
Methods. To achieve these goals, we have modelled the spatially resolved SEDs with two alternate grain compositions, to study the impact of different submillimetre opacities on the dust mass. We have rigorously propagated the observational errors (noise and calibration) through the entire fitting process, in order to derive consistent parameter uncertainties.
Results. First, we show that using the integrated SED leads to underestimating the dust mass by ≃50% compared to the value obtained with sufficient spatial resolution, for the region we studied. This might be the case, in general, for unresolved galaxies. Second, we show that Milky Way type grains produce higher gas-to-dust mass ratios than what seems possible according to the element abundances in the LMC. A spatial analysis shows that this dilemma is the result of an exceptional property: the grains of the LMC have on average a larger intrinsic submm opacity (emissivity index β ≃ 1.7 and opacity κ_(abs)(160 μm) = 1.6 m^2 kg^(-1)) than those of the Galaxy. By studying the spatial distribution of the gas-to-dust mass ratio, we are able to constrain the fraction of unseen gas mass between ≃10, and ≃100% and show that it is not sufficient to explain the gas-to-dust mass ratio obtained with Milky Way type grains. Finally, we confirm the detection of a 500 μm extended emission excess with an average relative amplitude of ≃15%, varying up to 40%. This excess anticorrelates well with the dust mass surface density. Although we do not know the origin of this excess, we show that it is unlikely the result of very cold dust, or CMB fluctuations
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