Aims. The EROS-2 project was designed to test the hypothesis that massive compact halo objects (the so-called "machos") could be a major component of the dark matter halo of the Milky Way galaxy. To ...this end, EROS- 2 monitored over 6.7 years 33\times10 similar to stars in the Magellanic clouds for microlensing events caused by such objects. Methods. In this work, we use only a subsample of 7\times10 similar to bright stars spread over 84\,\rm deg arrow up of the LMC and 9\,\rm deg arrow up of the SMC. The strategy of using only bright stars helps to discriminate against background events due to variable stars and allows a simple determination of the effects of source confusion (blending). The use of a large solid angle makes the survey relatively insensitive to effects that could make the optical depth strongly direction dependent. Results. Using this sample of bright stars, only one candidate event was found, whereas similar to 39 events would have been expected if the Halo were entirely populated by objects of mass M\sim0.4 similar to M_{\odot}. Combined with the results of EROS-1, this implies that the optical depth toward the Large Magellanic Cloud ( LMC) due to such lenses is \tau<0.36\times10 (95% CL), corresponding to a fraction of the halo mass of less than 8%. This optical depth is considerably less than that measured by the MACHO collaboration in the central region of the LMC. More generally, machos in the mass range 0.6\times10 contains as a subset _\odot<M<15 similar to M_{\odot} are ruled out as the primary occupants of the Milky Way Halo.
Physical conditions of the interstellar medium in galaxies are closely linked to the ambient radiation field and the heating of dust grains. In order to characterize dust properties in galaxies over ...a wide range of physical conditions, we present here the radial surface brightness profiles of the entire sample of 61 galaxies from Key Insights into Nearby Galaxies: Far-Infrared Survey with Herschel (KINGFISH). The main goal of our work is the characterization of the grain emissivities, dust temperatures, and interstellar radiation fields (ISRFs) responsible for heating the dust. We first fit the radial profiles with exponential functions in order to compare stellar and cool-dust disk scalelengths, as measured by 3.6 μm and 250 μm surface brightnesses. Our results show thatthe stellar and dust scalelengths are comparable, with a mean ratio of 1.04, although several galaxies show dust-to-stellar scalelength ratios of 1.5 or more. We then fit the far-infrared spectral energy distribution (SED) in each annular region with single-temperature modified blackbodies using both variable (MBBV) and fixed (MBBF) emissivity indices β, as well as with physically motivated dust models. The KINGFISH profiles are well suited to examining trends of dust temperature Tdust and β because they span a factor of ~200 in the ISRF intensity heating the bulk of the dust mass, Umin. Results from fitting the profile SEDs suggest that, on average, Tdust, dust optical depth τdust, and Umin decrease with radius. The emissivity index β also decreases with radius in some galaxies, but in others is increasing, or rising in the inner regions and falling in the outer ones. Despite the fixed grain emissivity (average β ~ 2.1) of the physically-motivated models, they are well able to accommodate flat spectral slopes with β ≲ 1. An analysis of the wavelength variations of dust emissivities in both the data and the models shows that flatter slopes (β ≲ 1.5) are associated with cooler temperatures, contrary to what would be expected from the usual Tdust – β degeneracy. This trend is related to variations in Umin since β and Umin are very closely linked over the entire range in Umin sampled by the KINGFISH galaxies: low Umin is associated with flat β ≲ 1. Both these results strongly suggest that the low apparent β values (flat slopes) in MBBV fits are caused by temperature mixing along the line of sight, rather than by intrinsic variations in grain properties. Finally, a comparison of dust models and the data show a slight ~10% excess at 500 μm for low metallicity (12 + log (O/H) ≲ 8) and low far-infrared surface brightness (Σ500).
The Herschel Reference Survey Boselli, A.; Eales, S.; Cortese, L. ...
Publications of the Astronomical Society of the Pacific,
03/2010, Volume:
122, Issue:
889
Journal Article
Peer reviewed
Open access
The Herschel Reference Survey is a Herschel guaranteed time key project and will be a benchmark study of dust in the nearby universe. The survey will complement a number of other Herschel key ...projects including large cosmological surveys that trace dust in the distant universe. We will use Herschel to produce images of a statistically-complete sample of 323 galaxies at 250, 350, and 500 μm. The sample is volume-limited, containing sources with distances between 15 and 25 Mpc and flux limits in the
K
K
band to minimize the selection effects associated with dust and with young high-mass stars and to introduce a selection in stellar mass. The sample spans the whole range of morphological types (ellipticals to late-type spirals) and environments (from the field to the center of the Virgo Cluster) and as such will be useful for other purposes than our own. We plan to use the survey to investigate (i) the dust content of galaxies as a function of Hubble type, stellar mass, and environment; (ii) the connection between the dust content and composition and the other phases of the interstellar medium; and (iii) the origin and evolution of dust in galaxies. In this article, we describe the goals of the survey, the details of the sample and some of the auxiliary observing programs that we have started to collect complementary data. We also use the available multifrequency data to carry out an analysis of the statistical properties of the sample.
We present a detailed analysis of the far-infrared (-IR) properties of the bright, lensed, z = 2.3, submillimetre-selected galaxy (SMG), SMM J2135-0102 (hereafter SMM J2135), using new observations ...with Herschel, SCUBA-2 and the Very Large Array (VLA). These data allow us to constrain the galaxy's spectral energy distribution (SED) and show that it has an intrinsic rest-frame 8-1000-μm luminosity, Lbol, of (2.3±0.2) × 1012 L⊙ and a likely star-formation rate (SFR) of ~400 M⊙ yr-1. The galaxy sits on the far-IR/radio correlation for far-IR-selected galaxies. At ⪆70 μm, the SED can be described adequately by dust components with dust temperatures, Td ~ 30 and 60 k. Using SPIRE's Fourier- transform spectrometer (FTS) we report a detection of the C ii 158 μm cooling line. If the C ii, CO and far-IR continuum arise in photo-dissociation regions (PDRs), we derive a characteristic gas density, n ~ 103 cm-3, and a far-ultraviolet (-UV) radiation field, G0, 103× stronger than the Milky Way. LCII/Lbol is significantly higher than in local ultra-luminous IR galaxies (ULIRGs) but similar to the values found in local star-forming galaxies and starburst nuclei. This is consistent with SMM J2135 being powered by starburst clumps distributed across ~2 kpc, evidence that SMGs are not simply scaled-up ULIRGs. Our results show that SPIRE's FTS has the ability to measure the redshifts of distant, obscured galaxies via the blind detection of atomic cooling lines, but it will not be competitive with ground-based CO-line searches. It will, however, allow detailed study of the integrated properties of high-redshift galaxies, as well as the chemistry of their interstellar medium (ISM), once more suitably bright candidates have been found. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
IBIS: The Imager on-board INTEGRAL Ubertini, P.; Lebrun, F.; Di Cocco, G. ...
Astronomy and astrophysics (Berlin),
11/2003, Volume:
411, Issue:
1
Journal Article
Peer reviewed
Open access
The IBIS telescope is the high angular resolution gamma-ray imager on-board the INTEGRAL Observatory, successfully launched from Baikonur (Kazakhstan) the 17th of October 2002. This medium size ESA ...project, planned for a 2 year mission with possible extension to 5, is devoted to the observation of the gamma-ray sky in the energy range from 3 keV to 10 MeV (Winkler CITE). The IBIS imaging system is based on two independent solid state detector arrays optimised for low ($15{-}1000$ keV) and high ($0.175{-}10.0$ MeV) energies surrounded by an active VETO System. This high efficiency shield is essential to minimise the background induced by high energy particles in the highly excentric out of van Allen belt orbit. A Tungsten Coded Aperture Mask, 16 mm thick and ~1 squared meter in dimension is the imaging device. The IBIS telescope will serve the scientific community at large providing a unique combination of unprecedented high energy wide field imaging capability coupled with broad band spectroscopy and high resolution timing over the energy range from X to gamma rays. To date the IBIS telescope is working nominally in orbit since more than 9 month.
We use Herschel Space Observatory data to place observational constraints on the peak and Rayleigh-Jeans slope of dust emission observed at 70–500 μm in the nearby spiral galaxy M81. We find that the ...ratios of wave bands between 160 and 500 μm are primarily dependent on radius but that the ratio of 70 to 160 μm emission shows no clear dependence on surface brightness or radius. These results along with analyses of the spectral energy distributions imply that the 160–500 μm emission traces 15–30 K dust heated by evolved stars in the bulge and disc whereas the 70 μm emission includes dust heated by the active galactic nucleus and young stars in star forming regions.
For the first time, we investigate the X-ray/infrared (IR) correlation for star-forming galaxies (SFGs) at z∼ 1, using SPIRE submm data from the recently launched Herschel Space Observatory and deep ...X-ray data from the 2-Ms Chandra Deep Field-North survey. We examine the X-ray/IR correlation in the soft X-ray (SX; 0.5-2 keV) and hard X-ray (HX; 2-10 keV) bands by comparing our z∼ 1 SPIRE-detected SFGs to equivalently IR-luminous (L
IR > 1010 L⊙) samples in the local/low-redshift Universe. Our results suggest that the X-ray/IR properties of the SPIRE SFGs are on average similar to those of their local counterparts, as we find no evidence for evolution in the L
SX/L
IR and L
HX/L
IR ratios with redshift. We note, however, that at all redshifts, both L
SX/L
IR and L
HX/L
IR are strongly dependent on IR luminosity, with luminous and ultraluminous IR galaxies (LIRGs and ULIRGs; L
IR > 1011 L⊙) having up to an order of magnitude lower values than normal IR galaxies (L
IR < 1011 L⊙). We derive a L
SX-L
IR relation and confirm the applicability of an existing L
HX-L
IR relation for both local and distant LIRGs and ULIRGs, consistent with a scenario where X-ray luminosity is correlated with the star formation rate.
The wide-area imaging surveys with the Herschel Space Observatory at sub-millimeter (sub-mm) wavelengths have now resulted in catalogs of the order of one-hundred-thousand dusty, star-burst galaxies. ...These galaxies capture an important phase of galaxy formation and evolution, but, unfortunately, the redshift distribution of these galaxies, N(z), is still mostly uncertain due to limitations associated with counterpart identification at optical wavelengths and spectroscopic follow-up. We make a statistical estimate of N(z) using a clustering analysis of sub-mm galaxies detected at each of 250, 350 and 500 mu m from the Herschel Multi-tiered Extragalactic Survey centered on the Bootes field. We create optical and near-IR galaxy samples based on their photometric or spectroscopic redshift distributions and test the accuracy of those redshift distributions with similar galaxy samples defined with catalogs from the Cosmological Evolution Survey (COSMOS), which has superior spectroscopic coverage. We compare our clustering-based N(z) results to sub-mm galaxy model predictions in the literature, and with an estimate of N(z) using a stacking analysis of COSMOS 24 mu m detections.
The Hα and mid-infrared mean disk surface brightnesses are compared in a sample of nearby spirals observed by ISOCAM. This shows that, in spiral disks, dust emission at 7 and 15 μm provides a ...reasonable star formation tracer. The fact that the 15 to 7 μm flux ratio is nearly constant in various global exciting conditions indicates a common origin, namely the aromatic infrared band carriers, and implies that at these wavelengths, dust emission from the disks of normal galaxies is dominated by photodissociation regions and not by Hii regions themselves. We use this newly-found correlation between the mid-infrared and the Hα line to investigate the nature of the link between the far-infrared (60 and 100 μm) and Hα. Although the separation of the central regions from the disk is impossible to achieve in the far-infrared, we show that a circumnuclear contribution to the dust emission, having no equivalent counterpart in Hα, is most likely responsible for the well-known non-linearity between far-infrared and Hα fluxes in spiral galaxies. We derive a calibration of 7 and 15 μm fluxes in terms of star formation rates from a primary calibration of Hα in the literature, and also outline the applicability limits of the proposed conversion, which should not be blindly extrapolated to objects whose nature is unknown.
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