368 research outputs found
Infrared Spectral Energy Distributions of z~0.7 Star-Forming Galaxies
We analyze the infrared (IR) spectral energy distributions (SEDs) for
10micron < lambda(rest) < 100micron for ~600 galaxies at z~0.7 in the extended
Chandra Deep Field South by stacking their Spitzer 24, 70 and 160micron images.
We place interesting constraints on the average IR SED shape in two bins: the
brightest 25% of z~0.7 galaxies detected at 24micron, and the remaining 75% of
individually-detected galaxies. Galaxies without individual detections at
24micron were not well-detected at 70micron and 160micron even through
stacking. We find that the average IR SEDs of z~0.7 star-forming galaxies fall
within the diversity of z~0 templates. While dust obscuration Lir/Luv seems to
be only a function of star formation rate (SFR; ~ Lir+Luv), not of redshift,
the dust temperature of star-forming galaxies (with SFR ~ 10 solar mass per
year) at a given IR luminosity was lower at z~0.7 than today. We suggest an
interpretation of this phenomenology in terms of dust geometry: intensely
star-forming galaxies at z~0 are typically interacting, and host dense
centrally-concentrated bursts of star formation and warm dust temperatures. At
z~0.7, the bulk of intensely star-forming galaxies are relatively undisturbed
spirals and irregulars, and we postulate that they have large amounts of
widespread lower-density star formation, yielding lower dust temperatures for a
given IR luminosity. We recommend what IR SEDs are most suitable for modeling
intermediate redshift galaxies with different SFRs.Comment: 12 pages, 11 figures, 2 tables, accepted for publication in Ap
Extended mid-infrared emission from VV 114: probing the birth of a ULIRG
We present our 5-16 micron spectro-imaging observations of VV114, an infrared
luminous early-stage merger, taken with the ISOCAM camera on-board ISO. We find
that only 40% of the mid-infrared (MIR) flux is associated with a compact
nuclear region, while the rest of the emission originates from a rather diffuse
component extended over several kpc. This is in stark contrast with the very
compact MIR starbursts usually seen in luminous infrared galaxies. A secondary
peak of MIR emission is associated with an extra-nuclear star forming region
which displays the largest Halpha equivalent width in the whole system.
Comparing our data with the distribution of the molecular gas and cold dust, as
well as with radio observations, it becomes evident that the conversion of
molecular gas into stars can be triggered over large areas at the very first
stages of an interaction. The presence of a very strong continuum at 5 microns
in one of the sources indicates that an enshrouded active galactic nucleus may
contribute to 40% of its MIR flux. We finally note that the relative variations
in the UV to radio spectral properties between the merging galaxies provide
evidence that the extinction-corrected star formation rate of similar objects
at high z, such as those detected in optical deep surveys, can not be
accurately derived from their rest-frame UV properties.Comment: 14 pages, 5 figures, accepted for publication in A&
The PEP Survey: Infrared Properties of Radio-Selected AGN
By exploiting the VLA-COSMOS and the Herschel-PEP surveys, we investigate the
Far Infrared (FIR) properties of radio-selected AGN. To this purpose, from
VLA-COSMOS we considered the 1537, F[1.4 GHz]>0.06 mJy sources with a reliable
redshift estimate, and sub-divided them into star-forming galaxies and AGN
solely on the basis of their radio luminosity. The AGN sample is complete with
respect to radio selection at all z<~3.5. 832 radio sources have a counterpart
in the PEP catalogue. 175 are AGN. Their redshift distribution closely
resembles that of the total radio-selected AGN population, and exhibits two
marked peaks at z~0.9 and z~2.5. We find that the probability for a
radio-selected AGN to be detected at FIR wavelengths is both a function of
radio power and redshift, whereby powerful sources are more likely to be FIR
emitters at earlier epochs. This is due to two distinct effects: 1) at all
radio luminosities, FIR activity monotonically increases with look-back time
and 2) radio activity of AGN origin is increasingly less effective at
inhibiting FIR emission. Radio-selected AGN with FIR emission are
preferentially located in galaxies which are smaller than those hosting
FIR-inactive sources. Furthermore, at all z<~2, there seems to be a
preferential (stellar) mass scale M ~[10^{10}-10^{11}] Msun which maximizes the
chances for FIR emission. We find such FIR (and MIR) emission to be due to
processes indistinguishable from those which power star-forming galaxies. It
follows that radio emission in at least 35% of the entire AGN population is the
sum of two contributions: AGN accretion and star-forming processes within the
host galaxy.Comment: 13 pages, 14 figures, to appear in MNRA
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