4,580 research outputs found
Linking the X-ray and infrared properties of star-forming galaxies at z < 1.5
We present the most complete study to date of the X-ray emission from star formation in high-redshift (median z = 0.7; z −3 in both hard and soft X-ray bands. From the sources which are star formation dominated, only a small fraction are individually X-ray detected and for the bulk of the sample we calculate average X-ray luminosities through stacking. We find an average soft X-ray to infrared ratio of log ?L SX /L IR ? = −4.3 and an average hard X-ray to infrared ratio of log?L HX /L IR ?=−3.8.WereportthattheX-ray/IRcorrelationisapproximatelylinearthrough the entire range of L IR and z probed and, although broadly consistent with the local (z < 0.1) one, it does display some discrepancies. We suggest that these discrepancies are unlikely to be physical, i.e. due to an intrinsic change in the X-ray properties of star-forming galaxies with cosmic time, as there is no significant evidence for evolution of the L X /L IR ratio with redshift. Instead, they are possibly due to selection effects and remaining AGN contamination.
We also examine whether dust obscuration in the galaxy plays a role in attenuating X-rays from star formation, by investigating changes in the L X /L IR ratio as a function of the average dust temperature. We conclude that X-rays do not suffer any measurable attenuation in the host galaxy
Proposed identification of Hubble Deep Field submillimeter source HDF 850.1
The IRAM interferometer has been used to detect the submm source HDF 850.1
found by Hughes et al. (1998) in the Hubble Deep Field. The flux density
measured at 1.3mm is 2.2 mJy, in agreement with the flux density measured at
the JCMT. The flux densities and upper limits measured at 3.4, 2.8, 1.3, 0.85,
and 0.45 mm show that the emission is from dust. We suggest that the 1.3mm dust
source is associated with the optical arc-like feature, 3-593.0, that has a
photometric redshift of about 1.7. If HDF 850.1 is at this redshift and
unlensed, its spectral energy distribution, combined with that of 3-593.0,
matches closely that of the ultraluminous galaxy VII Zw 31. Another possibility
is that the dust source may be gravitationally lensed by the elliptical galaxy
3-586.0 at a redshift of 1.Comment: 12 pages, 6 figure
The far-infrared/radio correlation and radio spectral index of galaxies in the SFR-M* plane up to z 2
[Abridged] We study the evolution of the radio spectral index and
far-infrared/radio correlation (FRC) across the star-formation rate-stellar
masse (i.e. SFR-M*) plane up to z 2. We start from a M*-selected sample of
galaxies with reliable SFR and redshift estimates. We then grid the SFR-M*
plane in several redshift ranges and measure the infrared luminosity, radio
luminosity, radio spectral index, and ultimately the FRC index (i.e. qFIR) of
each SFR-M*-z bin. The infrared luminosities of our SFR-M*-z bins are estimated
using their stacked far-infrared flux densities inferred from observations
obtained with Herschel. Their radio luminosities and radio spectral indices
(i.e. alpha, where Snu nu^-alpha) are estimated using their stacked 1.4GHz and
610MHz flux densities from the VLA and GMRT, respectively. Our far-infrared and
radio observations include the most widely studied blank extragalactic fields
-GOODS-N/S, ECDFS, and COSMOS- covering a sky area of 2deg^2. Using this
methodology, we constrain the radio spectral index and FRC index of
star-forming galaxies with M*>10^10Msun and 0<z<2.3. We find that
alpha^1.4GHz_610MHz does not evolve significantly with redshift or with the
distance of a galaxy with respect to the main sequence (MS) of the SFR-M* plane
(i.e. Delta_log(SSFR)_MS=log[SSFR(galaxy)/SSFR_MS(M*,z)]). Instead,
star-forming galaxies have a radio spectral index consistent with a canonical
value of 0.8, which suggests that their radio spectra are dominated by
non-thermal optically thin synchrotron emission. We find that qFIR displays a
moderate but statistically significant redshift evolution as
qFIR(z)=(2.35+/-0.08)*(1+z)^(-0.12+/-0.04), consistent with some previous
literature. Finally, we find no significant correlation between qFIR and
Delta_log(SSFR)_MS, though a weak positive trend, as observed in one of our
redshift bins, cannot be firmly ruled out using our dataset.Comment: Accepted for publication in A&A; 18 pages, 10 figure
Panchromatic spectral energy distributions of Herschel sources
(abridged) Far-infrared Herschel photometry from the PEP and HerMES programs
is combined with ancillary datasets in the GOODS-N, GOODS-S, and COSMOS fields.
Based on this rich dataset, we reproduce the restframe UV to FIR ten-colors
distribution of galaxies using a superposition of multi-variate Gaussian modes.
The median SED of each mode is then fitted with a modified version of the
MAGPHYS code that combines stellar light, emission from dust heated by stars
and a possible warm dust contribution heated by an AGN. The defined Gaussian
grouping is also used to identify rare sources. The zoology of outliers
includes Herschel-detected ellipticals, very blue z~1 Ly-break galaxies,
quiescent spirals, and torus-dominated AGN with star formation. Out of these
groups and outliers, a new template library is assembled, consisting of 32 SEDs
describing the intrinsic scatter in the restframe UV-to-submm colors of
infrared galaxies. This library is tested against L(IR) estimates with and
without Herschel data included, and compared to eight other popular methods
often adopted in the literature. When implementing Herschel photometry, these
approaches produce L(IR) values consistent with each other within a median
absolute deviation of 10-20%, the scatter being dominated more by fine tuning
of the codes, rather than by the choice of SED templates. Finally, the library
is used to classify 24 micron detected sources in PEP GOODS fields. AGN appear
to be distributed in the stellar mass (M*) vs. star formation rate (SFR) space
along with all other galaxies, regardless of the amount of infrared luminosity
they are powering, with the tendency to lie on the high SFR side of the "main
sequence". The incidence of warmer star-forming sources grows for objects with
higher specific star formation rates (sSFR), and they tend to populate the
"off-sequence" region of the M*-SFR-z space.Comment: Accepted for publication in A&A. Some figures are presented in low
resolution. The new galaxy templates are available for download at the
address http://www.mpe.mpg.de/ir/Research/PEP/uvfir_temp
Mid-infrared spectroscopy of infrared-luminous galaxies at z~0.5-3
We present results on low-resolution mid-infrared (MIR) spectra of 70
infrared-luminous galaxies obtained with the Infrared Spectrograph (IRS)
onboard Spitzer. We selected sources from the European Large Area Infrared
Survey (ELAIS) with S15 > 0.8 mJy and photometric or spectroscopic z > 1. About
half of the sample are QSOs in the optical, while the remaining sources are
galaxies, comprising both obscured AGN and starbursts. We classify the spectra
using well-known infrared diagnostics, as well as a new one that we propose,
into three types of source: those dominated by an unobscured AGN (QSOs),
obscured AGN, and starburst-dominated sources. Starbursts concentrate at z ~
0.6-1.0 favored by the shift of the 7.7-micron PAH band into the selection 15
micron band, while AGN spread over the 0.5 < z < 3.1 range. Star formation
rates (SFR) are estimated for individual sources from the luminosity of the PAH
features. An estimate of the average PAH luminosity in QSOs and obscured AGN is
obtained from the composite spectrum of all sources with reliable redshifts.
The estimated mean SFR in the QSOs is 50-100 Mo yr^-1, but the implied FIR
luminosity is 3-10 times lower than that obtained from stacking analysis of the
FIR photometry, suggesting destruction of the PAH carriers by energetic photons
from the AGN. The SFR estimated in obscured AGN is 2-3 times higher than in
QSOs of similar MIR luminosity. This discrepancy might not be due to luminosity
effects or selection bias alone, but could instead indicate a connection
between obscuration and star formation. However, the observed correlation
between silicate absorption and the slope of the near- to mid-infrared spectrum
is compatible with the obscuration of the AGN emission in these sources being
produced in a dust torus.Comment: 32 pages, 24 figures, 15 tables, accepted for publication in MNRA
Emission Features and Source Counts of Galaxies in Mid-Infrared
In this work we incorporate the newest ISO results on the mid-infrared
spectral-energy-distributions (MIR SEDs) of galaxies into models for the number
counts and redshift distributions of MIR surveys. A three-component model, with
empirically determined MIR SED templates of (1) a cirrus/PDR component (2) a
starburst component and (3) an AGN component, is developed for infrared
(3--120\micron) SEDs of galaxies. The model includes a complete IRAS 25\micron
selected sample of 1406 local galaxies (; Shupe et al. 1998a).
Results based on these 1406 spectra show that the MIR emission features cause
significant effects on the redshift dependence of the K-corrections for fluxes
in the WIRE 25\micron band and ISOCAM 15\micron band. This in turn will affect
deep counts and redshift distributions in these two bands, as shown by the
predictions of two evolution models (a luminosity evolution model with
and a density evolution model with ).
The dips-and-bumps on curves of MIR number counts, caused by the emission
features, should be useful indicators of evolution mode. The strong emission
features at --8\micron will help the detections of relatively high
redshift () galaxies in MIR surveys. On the other hand, determinations
of the evolutionary rate based on the slope of source counts, and studies on
the large scale structures using the redshift distribution of MIR sources, will
have to treat the effects of the MIR emission features carefully. We have also
estimated a 15\micron local luminosity function from the predicted 15\micron
fluxes of the 1406 galaxies using the bivariate (15\micron vs. 25\micron
luminosities) method. This luminosity function will improve our understanding
of the ISOCAM 15\micron surveys.Comment: 24 pages, 14 EPS figures. Accepted by Ap
The evolution of the dust temperatures of galaxies in the SFR–M∗plane up to z ~ 2
We study the evolution of the dust temperature of galaxies in the SFR−M ∗ plane up to z ∼ 2 using far-infrared and submillimetre observations from the Herschel Space Observatory taken as part of the PACS Evolutionary Probe (PEP) and Herschel Multi-tiered Extragalactic Survey (HerMES) guaranteed time key programmes. Starting from a sample of galaxies with reliable star-formation rates (SFRs), stellar masses (M ∗ ) and redshift estimates, we grid the SFR−M ∗ parameter space in several redshift ranges and estimate the mean dust temperature (T dust ) of each SFR–M ∗ −z bin. Dust temperatures are inferred using the stacked far-infrared flux densities (100–500μm) of our SFR–M ∗ −z bins. At all redshifts, the dust temperature of galaxies smoothly increases with rest-frame infrared luminosities (L IR ), specific SFRs (SSFR; i.e., SFR/M ∗ ), and distances with respect to the main sequence (MS) of the SFR−M ∗ plane (i.e., Δlog(SSFR) MS = log[SSFR(galaxy)/SSFR MS (M ∗ ,z)]). The T dust −SSFR and T dust – Δlog(SSFR) MS correlations are statistically much more significant than the T dust −L IR one. While the slopes of these three correlations are redshift-independent, their normalisations evolve smoothly from z = 0 and z ∼ 2. We convert these results into a recipe to derive T dust from SFR, M ∗ and z, valid out to z ∼ 2 and for the stellar mass and SFR range covered by our stacking analysis. The existence of a strong T dust −Δlog(SSFR) MS correlation provides us with several pieces of information on the dust and gas content of galaxies. Firstly, the slope of the T dust −Δlog(SSFR) MS correlation can be explained by the increase in the star-formation efficiency (SFE; SFR/M gas ) with Δlog(SSFR) MS as found locally by molecular gas studies. Secondly, at fixed Δlog(SSFR) MS , the constant dust temperature observed in galaxies probing wide ranges in SFR and M ∗ can be explained by an increase or decrease in the number of star-forming regions with comparable SFE enclosed in them. And thirdly, at high redshift, the normalisation towards hotter dust temperature of the T dust −Δlog(SSFR) MS correlation can be explained by the decrease in the metallicities of galaxies or by the increase in the SFE of MS galaxies. All these results support the hypothesis that the conditions prevailing in the star-forming regions of MS and far-above-MS galaxies are different. MS galaxies have star-forming regions with low SFEs and thus cold dust, while galaxies situated far above the MS seem to be in a starbursting phase characterised by star-forming regions with high SFEs and thus hot dust
HerMES: spectral energy distributions of submillimeter galaxies at z > 4.
We present a study of the infrared properties for a sample of seven spectroscopically confirmed submillimetre galaxies (SMGs) at z > 4.0. By combining ground-based near-infrared, Spitzer IRAC and MIPS, Herschel SPIRE, and ground-based submillimetre / millimeter photometry, we construct their spectral energy distributions (SEDs) and a composite model to fit the SEDs. The model includes a stellar emission component at λ rest 50μm. Six objects in the sample are detected at 250 and 350μm. The dust temperatures for the sources in this sample are in the range of 40–80 K, and their L FIR ∼ 10 13 Lo qualifies them as hyper-luminous infrared galaxies. The mean FIR-radio index for this sample is around (q) = 2.2 indicating no radio excess in their radio emission. Most sources in the sample have 24μmdetections corresponding to a rest-frame 4.5μm luminosity of Log 10 (L 4.5 /L ? )=11 ∼ 11.5. Their L 4.5 /L FIR ratios are very similar to those of starburst-dominated SMGs at z ∼ 2. The L CO − L FIR relation for this sample is consistent with that determined for local ULIRGs and SMGs at z ∼ 2. We conclude that SMGs at z > 4 are hotter and more luminous in the FIR but otherwise very similar to those at z ∼ 2. None of these sources show any sign of the strong QSO phase being triggered
The extended counterpart of submm source Lockman850.1
The IRAM Plateau de Bure mm interferometer and deep K-band imaging have been
used to identify the brightest submm source detected in the Lockman field of
the UK 8mJy SCUBA survey. The near infrared counterpart is an extended
(20-30kpc), clumpy, and extremely red object. The spectral energy distribution
suggests it to be a dusty star forming object at a redshift of about 3 (2-4).
Its star formation rate and near-infrared properties are consistent with
Lockman850.1 being a massive elliptical in formation.Comment: 4 ps/eps figures. To appear in A&
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