314 research outputs found
The Cosmic Far-Infrared Background Buildup Since Redshift 2 at 70 and 160 microns in the COSMOS and GOODS fields
The Cosmic Far-Infrared Background (CIB) at wavelengths around 160 {\mu}m
corresponds to the peak intensity of the whole Extragalactic Background Light,
which is being measured with increasing accuracy. However, the build up of the
CIB emission as a function of redshift, is still not well known. Our goal is to
measure the CIB history at 70 {\mu}m and 160 {\mu}m at different redshifts, and
provide constraints for infrared galaxy evolution models. We use complete deep
Spitzer 24 {\mu}m catalogs down to about 80 {\mu}Jy, with spectroscopic and
photometric redshifts identifications, from the GOODS and COSMOS deep infrared
surveys covering 2 square degrees total. After cleaning the Spitzer/MIPS 70
{\mu}m and 160 {\mu}m maps from detected sources, we stacked the far-IR images
at the positions of the 24 {\mu}m sources in different redshift bins. We
measured the contribution of each stacked source to the total 70 and 160 {\mu}m
light, and compare with model predictions and recent far-IR measurements made
with Herschel/PACS on smaller fields. We have detected components of the 70 and
160 {\mu}m backgrounds in different redshift bins up to z ~ 2. The contribution
to the CIB is maximum at 0.3 <= z <= 0.9 at 160{\mu}m (and z <= 0.5 at 70
{\mu}m). A total of 81% (74%) of the 70 (160) {\mu}m background was emitted at
z < 1. We estimate that the AGN relative contribution to the far-IR CIB is less
than about 10% at z < 1.5. We provide a comprehensive view of the CIB buildup
at 24, 70, 100, 160 {\mu}m. IR galaxy models predicting a major contribution to
the CIB at z < 1 are in agreement with our measurements, while our results
discard other models that predict a peak of the background at higher redshifts.
Our results are available online http://www.ias.u-psud.fr/irgalaxies/ .Comment: Accepted in Astronomy & Astrophysic
Direct Measurement of the Photon Statistics of a Triggered Single Photon Source
We studied intensity fluctuations of a single photon source relying on the
pulsed excitation of the fluorescence of a single molecule at room temperature.
We directly measured the Mandel parameter Q(T) over 4 orders of magnitude of
observation timescale T, by recording every photocount. On timescale of a few
excitation periods, subpoissonian statistics is clearly observed and the
probablility of two-photons events is 10 times smaller than Poissonian pulses.
On longer times, blinking in the fluorescence, due to the molecular triplet
state, produces an excess of noise.Comment: 4 pages, 3 figures, 1 table submitted to Physical Review Letter
Spitzer Mid-Infrared Spectroscopy of 70um-Selected Distant Luminous Infrared Galaxies
We present mid-infrared spectroscopy obtained with the Spitzer Space
Telescope of a sample of 11 optically faint, infrared luminous galaxies
selected from a Spitzer MIPS 70um imaging survey of the NDWFS Bootes field.
These are the first Spitzer IRS spectra presented of distant 70um-selected
sources. All the galaxies lie at redshifts 0.3<z<1.3 and have very large
infrared luminosities of L_IR~ 0.1-17 x 10^12 solar luminosities. Seven of the
galaxies exhibit strong emission features attributed to polycyclic aromatic
hydrocarbons (PAHs). The average IRS spectrum of these sources is
characteristic of classical starburst galaxies, but with much larger infrared
luminosities. The PAH luminosities of L(7.7) ~ 0.4 - 7 x 10^11 solar
luminosities imply star formation rates of ~ 40 - 720 solar masses per year.
Four of the galaxies show deep 9.7um silicate absorption features and no
significant PAH emission features (6.2um equivalent widths < 0.03um). The large
infrared luminosities and low f70/f24 flux density ratios suggests that these
sources have AGN as the dominant origin of their large mid-infrared
luminosities, although deeply embedded but luminous starbursts cannot be ruled
out. If the absorbed sources are AGN-dominated, a significant fraction of all
far-infrared bright, optically faint sources may be dominated by AGN.Comment: 8 Pages, ApJ accepte
Planck \u27s Dusty GEMS: VIII. Dense-gas reservoirs in the most active dusty starbursts at z âŒ3
We present ALMA, NOEMA, and IRAM-30 m/EMIR observations of the high-density tracer molecules HCN, HCO+, and HNC in three of the brightest lensed dusty star-forming galaxies at zâČ 3-3.5, part of the Planck\u27s Dusty Gravitationally Enhanced subMillimetre Sources (GEMS), with the aim of probing the gas reservoirs closely associated with their exceptional levels of star formation. We obtained robust detections of ten emission lines between Jup = 4 and 6, as well as several additional upper flux limits. In PLCK_G244.8+54.9, the brightest source at z = 3.0, the HNC(5-4) line emission at 0.1âł resolution, together with other spatially-integrated line profiles, suggests comparable distributions of dense and more diffuse gas reservoirs, at least over the most strongly magnified regions. This rules out any major effect from differential lensing. This line is blended with CN(4-3) and in this source, we measure a HNC(5-4)/CN(4-3) flux ratio of 1.76 \ub10. 86. Dense-gas line profiles generally match those of mid-J CO lines, except in PLCK_G145.2+50.8, which also has dense-gas line fluxes that are relatively lower, perhaps due to fewer dense cores and more segregated dense and diffuse gas phases in this source. The HCO+/HCN 1 and HNC/HCN ⌠1 line ratios in our sample are similar to those of nearby ultraluminous infrared galaxies (ULIRGs) and consistent with photon-dominated regions without any indication of important mechanical heating or active galactic nuclei feedback. We characterize the dense-gas excitation in PLCK_G244.8+54.9 using radiative transfer models assuming pure collisional excitation and find that mid-J HCN, HCO+, and HNC lines arise from a high-density phase with an H2 density of n ⌠105-106 cm-3, although important degeneracies hinder a determination of the exact conditions. The three GEMS are consistent with extrapolations of dense-gas star-formation laws derived in the nearby Universe, adding further evidence that the extreme star-formation rates observed in the most active galaxies at z ⌠3 are a consequence of their important dense-gas contents. The dense-gas-mass fractions traced by HCN/[CI] and HCO+/[CI] line ratios are elevated, but not exceptional as compared to other lensed dusty star-forming galaxies at z > 2, and they fall near the upper envelope of local ULIRGs. Despite the higher overall gas fractions and local gas-mass surface densities observed at high redshift, the dense-gas budget of rapidly star-forming galaxies seems to have evolved little between z ⌠3 and z ⌠0. Our results favor constant dense-gas depletion times in these populations, which is in agreement with theoretical models of star formation
The AGN Contribution to the Mid-IR Emission of Luminous Infrared Galaxies
We determine the contribution of AGN to the mid-IR emission of luminous
infrared galaxies (LIRGs) at z>0.6 by measuring the mid-IR dust continuum slope
of 20,039 mid-IR sources. The 24 micron sources are selected from a
Spitzer/MIPS survey of the NOAO Deep Wide-Field Survey Bo\"otes field and have
corresponding 8 micron data from the IRAC Shallow Survey. There is a clear
bimodal distribution in the 24 micron to 8 micron flux ratio. The X-ray
detected sources fall within the peak corresponding to a flat spectrum in
nufnu, implying that it is populated by AGN-dominated LIRGs, whereas the peak
corresponding to a higher 24 micron to 8 micron flux ratio is likely due to
LIRGs whose infrared emission is powered by starbursts. The 24 micron emission
is increasingly dominated by AGN at higher 24 micron flux densities (f_24): the
AGN fraction of the z>0.6 sources increases from ~9% at f_24 ~ 0.35 mJy to
74+/-20% at f_24 ~ 3 mJy in good agreement with model predictions. Deep 24
micron, small area surveys, like GOODS, will be strongly dominated by starburst
galaxies. AGN are responsible for ~ 3-7% of the total 24 micron background.Comment: 6 pages, accepted for publication in Ap
Cosmological model dependence of the galaxy luminosity function: far-infrared results in the LemaĂźtre-Tolman-Bondi model
Aims. This is the first paper of a series aiming at investigating galaxy formation and evolution in the giant-void class of the LemaĂźtre-Tolman-Bondi (LTB) models that best fits current cosmological observations. Here we investigate the luminosity function (LF) methodology, and how its estimates would be affected by a change on the cosmological model assumed in its computation. Are the current observational constraints on the allowed cosmology enough to yield robust LF results
Modeling the evolution of infrared galaxies: A Parametric backwards evolution model
We aim at modeling the infrared galaxy evolution in an as simple as possible
way and reproduce statistical properties among which the number counts between
15 microns and 1.1 mm, the luminosity functions, and the redshift
distributions. We then aim at using this model to interpret the recent
observations (Spitzer, Akari, BLAST, LABOCA, AzTEC, SPT and Herschel), and make
predictions for future experiments like CCAT or SPICA.
This model uses an evolution in density and luminosity of the luminosity
function with two breaks at redshift ~0.9 and 2 and contains the two
populations of the Lagache et al. (2004) model: normal and starburst galaxies.
We also take into account the effect of the strong lensing of high-redshift
sub-millimeter galaxies. It has 13 free parameters and 8 additional calibration
parameters. We fit the parameters to the IRAS, Spitzer, Herschel and AzTEC
measurements with a Monte-Carlo Markov chain.
The model ajusted on deep counts at key wavelengths reproduces the counts
from the mid-infrared to the millimeter wavelengths, as well as the
mid-infrared luminosity functions. We discuss the contribution to the cosmic
infrared background (CIB) and to the infrared luminosity density of the
different populations. We also estimate the effect of the lensing on the number
counts, and discuss the recent discovery by the South Pole Telescope (SPT) of a
very bright population lying at high-redshift. We predict confusion level for
future missions using a P(D) formalism, and the Universe opacity to TeV photons
due to the CIB.Comment: 25 pages, 10 tables, 18 figures, accepted for publication in A&
The Evolution of Galaxy Mergers and Morphology at z<1.2 in the Extended Groth Strip
We present the quantitative rest-frame B morphological evolution and galaxy
merger fractions at 0.2 < z < 1.2 as observed by the All-wavelength Extended
Groth Strip International Survey (AEGIS). We use the Gini coefficent and M_20
to identify major mergers and classify galaxy morphology for a volume-limited
sample of 3009 galaxies brighter than 0.4 L_B^*, assuming pure luminosity
evolution of 1.3 M_B per unit redshift. We find that the merger fraction
remains roughly constant at 10 +/- 2% for 0.2 < z < 1.2. The fraction of
E/S0/Sa increases from 21+/- 3% at z ~ 1.1 to 44 +/- 9% at z ~ 0.3, while the
fraction of Sb-Ir decreases from 64 +/- 6% at z ~ 1.1 to 47 +/- 9% at z ~ 0.3.
The majority of z 10^11 L_sun
are disk galaxies, and only ~ 15% are classified as major merger candidates.
Edge-on and dusty disk galaxies (Sb-Ir) are almost a third of the red sequence
at z ~ 1.1, while E/S0/Sa makeup over 90% of the red sequence at z ~ 0.3.
Approximately 2% of our full sample are red mergers. We conclude (1) the galaxy
merger rate does not evolve strongly between 0.2 < z < 1.2; (2) the decrease in
the volume-averaged star-formation rate density since z ~ 1 is a result of
declining star-formation in disk galaxies rather than a disappearing population
of major mergers; (3) the build-up of the red sequence at z < 1 can be
explained by a doubling in the number of spheroidal galaxies since z ~ 1.2.Comment: 24 pages, including 3 tables and 18 color figures; accepted to the
Astrophysical Journal; high resolution version available at
http://www.noao.edu/noao/staff/lotz/lotz_mergers.pd
Towards an understanding of the rapid decline of the cosmic star formation rate
We present a first analysis of deep 24 micron observations with the Spitzer
Space Telescope of a sample of nearly 1500 galaxies in a thin redshift slice,
0.65<z<0.75. We combine the infrared data with redshifts, rest-frame
luminosities, and colors from COMBO-17, and with morphologies from Hubble Space
Telescope images collected by the GEMS and GOODS projects. To characterize the
decline in star-formation rate (SFR) since z~0.7, we estimate the total thermal
infrared (IR) luminosities, SFRs, and stellar masses for the galaxies in this
sample. At z~0.7, nearly 40% of intermediate and high-mass galaxies (with
stellar masses >2x10^10 solar masses) are undergoing a period of intense star
formation above their past-averaged SFR. In contrast, less than 1% of
equally-massive galaxies in the local universe have similarly intense star
formation activity. Morphologically-undisturbed galaxies dominate the total
infrared luminosity density and SFR density: at z~0.7, more than half of the
intensely star-forming galaxies have spiral morphologies, whereas less than
\~30% are strongly interacting. Thus, a decline in major-merger rate is not the
underlying cause of the rapid decline in cosmic SFR since z~0.7. Physical
properties that do not strongly affect galaxy morphology - for example, gas
consumption and weak interactions with small satellite galaxies - appear to be
responsible.Comment: To appear in the Astrophysical Journal 1 June 2005. 14 pages with 8
embedded figure
The 1<z<5 Infrared Luminosity Function of Type I Quasars
We determine the rest-frame 8 micron luminosity function of type I quasars
over the redshift range 1<z<5. Our sample consists of 292 24 micron sources
brighter than 1 mJy selected from 7.17 square degrees of the Spitzer Space
Telescope MIPS survey of the NOAO Deep Wide-Field Survey Bootes field. The AGN
and Galaxy Evolution Survey (AGES) has measured redshifts for 270 of the R<21.7
sources and we estimate that the contamination of the remaining 22 sources by
stars and galaxies is low. We are able to select quasars missed by ultra-violet
excess quasar surveys, including reddened type I quasars and 2.2<z<3.0 quasars
with optical colors similar to main sequence stars. We find reddened type I
quasars comprise 20% of the type I quasar population. Nonetheless, the shape,
normalization, and evolution of the rest-frame 8 micron luminosity function is
comparable to that of quasars selected from optical surveys. The 8 micron
luminosity function of type I quasars is well approximated by a power-law with
index -2.75(+/-0.14). We directly measure the peak of the quasar space density
to be at z=2.6(+/-0.3).Comment: Accepted for publication in the ApJ, 19 pages, 12 figure
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