Mid-infrared Properties Research Articles

Spitzer Identifications and Classifications of Submillimeter Galaxies in Giant, High-Redshift, Lyα-Emission-Line Nebulae

Using Spitzer Space Telescope IRAC (3.6-8um) and MIPS (24um) imaging, as well as Hubble Space Telescope optical observations, we identify the IRAC counterparts of the luminous power sources residing within the two largest and brightest Lyman-alpha emitting nebulae (LABs) in the SA22 protocluster at z=3.09 (LAB1 and LAB2). These sources are also both submillimeter galaxies (SMGs). From their rest-frame optical/near-infrared colors, we conclude that the SMG in LAB1 is likely to be starburst dominated and heavily obscured (Av~3). In contrast, LAB2 has excess rest-frame ~2um emission (over that expected from starlight) and hosts a hard X-ray source at the proposed location of the SMG, consistent with the presence of an active galactic nucleus (AGN). We conclude that LAB1 and LAB2 appear to have very different energy sources despite having similar Lyman-alpha spatial extents and luminosities, although it remains unclear whether on-going star-formation or periodic AGN heating is responsible for the extended Lyman-alpha emission. We find that the mid-infrared properties of the SMGs lying in LAB1 and LAB2 are similar to those of the wider SMG population, and so it is possible that extended Lyman-alpha haloes are a common feature of SMGs in general.

The Mid-Infrared Properties of Embedded Super Star Clusters in He2-10 and IIZw40

We observed embedded super-star clusters (SSCs) in blue compact dwarf galaxies (BCDs) IIZw40 and He2-10 with N-band and Q-band imaging and spectroscopy using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on board the 8m Subaru Telescope. Our infrared images of Henize 2–10 resolve the radio knots (knots I-V; Kobulnicky & Johnson 1999) and the N- and Q-band spectra show the strong [NeII] 12.8 μm and the [SIII] 18.71 μm together with relatively weak [SIV] 10.51 μm and [ArIII] 8.99 μm as well as the distinct unidentified infrared (UIR) bands at 8.6, 11.2 and 12.7 μm. We find the typical stellar spectral type of the members in the SSCs is O9 using the CoStar model (Stasinska & Schaerer 1997) and that the ionization environment in the most deeply embedded SSC(POS/#D) is the softest among those SSCs. The UIR bands exhibit a flat distribution over the galaxy and do not show a correlation with the MIR continuum, suggesting that polycyclic aromatic hydrocarbons (PAHs) are not strongly associated with the SSCs. We also find a possible decrease in the UIR 12.7 μm/11.2 μm ratio inside the embedded SSCs, suggesting that smooth-edged large PAHs are dominant (Hony et al. 2001) there. The small UIR to continuum ratio inside the embedded SSCs also suggests that the size distribution of the carbonaceous dust is skewed to the larger ones inside the embedded SSCs. Possible destruction of smaller species by harsh radiation field in the vicinity of massive stars due to the smaller heat capacity and/or the coagulation process that have been undertaken in dense dusty embedded SSCs would explain our results consistently. From the mid-infrared spectroscopy of IIZw40, the UIR bands are detected only in the south-western border of the mid-infrared peaks, suggesting the uneven distribution of PAHs within 4×106yr (Vanzi et al. 1996) after the nuclear starburst triggered in the merging of two small original galaxies.

Infrared Properties of Nearby Interacting Galaxies: from Spirals to ULIRGs

AbstractI present a brief review of some of the mid-infrared properties of interacting galaxies as these were revealed using observations from the Infrared Space Observatory and Spitzer Space Telescope over the last decade. The variation of the infrared spectral energy distribution in interacting galaxies can be used as an extinction free tracer not only of the location of the star formation activity but also of the physical mechanism dominating their energy production.‡.

Mid‐Infrared Properties of X‐Ray Sources in the Extended Groth Strip

Mid-infrared observations of Active Galactic Nuclei (AGN) are important for understanding of the physical conditions around the central accretion engines. Chandra and XMM-Newton X-ray observations of a 300 arcmin^2 region in the Extended Groth Strip are used to select a sample of~150 AGN. The Spitzer instruments IRAC and MIPS detect 68-80% of these sources, which show a wide range of mid-infrared properties. About 40% of the sources have red power-law spectral energy distributions (f_nu ~ nu^alpha, alpha<0) in the 3.6-8 um IRAC bands. In these sources the central engine dominates the emission at both X-ray and IR wavelengths. Another 40% of the sources have blue mid-IR spectral energy distributions (alpha>0) with their infrared emission dominated by the host galaxy; the remaining 20% are not well-fit by a power law. Published IRAC color criteria for AGN select most of the red sources, but only some of the blue sources. As with all other known methods, selecting AGN with mid-IR colors will not produce a sample that is simultaneously complete and reliable. The IRAC SED type does not directly correspond to X-ray spectral type (hard/soft). The mid-IR properties of X-ray-detected Lyman-break, radio, submillimeter, and optically-faint sources vary widely and, for the most part, are not distinct from those of the general X-ray/infrared source population. X-ray sources emit 6-11% of the integrated mid--IR light, making them significant contributors to the cosmic infrared background.

Pressure-dependent infrared properties of the quasi-one-dimensional metal [formula omitted]- [formula omitted

The pressure-dependent mid-infrared properties of the quasi-one-dimensional metal β - Na 0.33 V 2 O 5 were studied at room temperature. The monotonic changes of the spectra below 12 GPa suggest a pressure-induced dimensional crossover and the relevance of electron–phonon coupling, leading to the formation of polaronic quasiparticles. The changes in the spectra above 12 GPa may be due to a redistribution of charge with a possible relation to structural changes. A possible relation between the interchain coupling and superconductivity is pointed out.

The Diverse Infrared Properties of a Complete Sample of Star‐forming Dwarf Galaxies

We present mid-infrared Spitzer Space Telescope observations of a complete sample of star-forming dwarf galaxies selected from the KPNO International Spectroscopic Survey. The galaxies span a wide range in mid-infrared properties. Contrary to expectations, some of the galaxies emit strongly at 8 μm, indicating the presence of hot dust and/or PAHs. The ratio of this mid-infrared dust emission to the stellar emission is compared with the galaxies' luminosity, star formation rate, metallicity, and optical reddening. We find that the ratio of the 8.0 μm dust emission to the stellar emission is more strongly correlated with the star formation rate than it is with the metallicity or the optical reddening in these systems. Nonetheless, there is a correlation between the 8.0 μm luminosity and metallicity. The slope of this luminosity-metallicity correlation is shallower than corresponding ones in the B band and 3.6 μm. The precise nature of the 8.0 μm emission seen in these galaxies (i.e., PAH vs. hot dust or some combination of the two) will require future study, including deep mid-IR spectroscopy.

Methanol Masers: Reliable Tracers of the Early Stages of High‐Mass Star Formation

The GLIMPSE and MSX surveys have been used to examine the mid-infrared properties of a statistically complete sample of 6.7 GHz methanol masers. The GLIMPSE point sources associated with methanol masers are clearly distinguished from the majority, typically having extremely red mid-infrared colors, similar to those expected of low-mass class 0 young stellar objects. The intensity of the GLIMPSE sources associated with methanol masers is typically 4 magnitudes brighter at 8.0 micron than at 3.6 micron. Targeted searches towards GLIMPSE point sources with [3.6]-[4.5] > 1.3 and an 8.0 micron magnitude less than 10 will detect more than 80% of class II methanol masers. Many of the methanol masers are associated with sources within infrared dark clouds (IRDC) which are believed to mark regions where high-mass star formation is in its very early stages. The presence of class II methanol masers in a significant fraction of IRDC suggests that high-mass star formation is common in these regions. Different maser species are thought to trace different evolutionary phases of the high-mass star formation process. Comparison of the properties of the GLIMPSE sources associated with class II methanol masers and other maser species shows interesting trends, consistent with class I methanol masers tracing a generally earlier evolutionary phase and OH masers tracing a later evolutionary phase.

Midinfrared properties of cuprous oxide: High-order lattice vibrations and intraexcitonic transitions of the1sparaexciton

This contribution addresses both the general mid-infrared (MIR) properties of ${\mathrm{Cu}}_{2}\mathrm{O}$ and induced absorption due to intraexcitonic $1s\ensuremath{\rightarrow}2p$ transitions under simultaneous cw laser excitation. After an overview of the current state of knowledge and remaining open questions concerning excitons in ${\mathrm{Cu}}_{2}\mathrm{O}$ we will first discuss several absorption bands in the spectral range between approximately 100 and $150\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ in terms of multiphonon and biphonon features. The second, more extensive part will concern a pump-probe experiment in the limit of low densities of $1s$ excitons where we investigated intraexcitonic transitions appearing in the MIR spectral range as well. We find a signal which can be clearly assigned to a $1s\phantom{\rule{0.3em}{0ex}}\mathit{para}\ensuremath{\rightarrow}2p\phantom{\rule{0.3em}{0ex}}\mathit{para}$ transition and present various data depending on excitation conditions and sample temperature. Applying the results of detailed theoretical considerations we can estimate the density and lifetime of the $1s$ para-exciton and at least speculate about its dispersion.

Measurement and interpretation of the mid-infrared properties of single crystal and polycrystalline gold

The contribution of electron–phonon scattering and grain boundary scattering to the mid-IR ( λ = 3.392 μm) properties of Au has been assessed by examining both bulk, single crystal samples—Au(1 1 1) and Au(1 1 0)—and thin film, polycrystalline Au samples at 300 K and 100 K by means of surface plasmon polariton excitation. The investigation constitutes a stringent test for the in-vacuo Otto-configuration prism coupler used to perform the measurements, illustrating its strengths and limitations. Analysis of the optical response is guided by a physically based interpretation of the Drude model. Relative to the reference case of single crystal Au at 100 K ( ε = −568 + i 17.5), raising the temperature to 300 K causes increased electron–phonon scattering that accounts for a reduction of ∼40 nm in the electron mean free path. Comparison of a polycrystalline sample to the reference case determines a mean free path due to grain boundary scattering of ∼17 nm, corresponding to about half the mean grain size as determined from atomic force microscopy and indicating a high reflectance coefficient for the Au grain boundaries. An analysis combining consideration of grain boundary scattering and the inclusion of a small percentage of voids in the polycrystalline film by means of an effective medium model indicates a value for the grain boundary reflection coefficient in the range 0.55–0.71.

An ISOCAM survey through gravitationally lensing galaxy clusters

We observed the cluster Abell 2218 (z=0.175), with ISOCAM on board the Infrared Space Observatory, using two filters with reference wavelengths of 6.7 and 14.3 microns. We detected 67 extragalactic mid-infrared sources. Using the ``GRASIL'' models of Silva et al. (1998) we have obtained acceptable and well constrained fits to the observed spectral energy distributions (SEDs) of 41 of these sources, for which additional optical/near-infrared magnitudes, and, in some cases, redshifts, were available. We have then determined the total infrared luminosities and star formation rates (SFRs) of these 41 sources, of which 27 are cluster members and 14 are field galaxies at a median redshift z~0.6. The SEDs of most of the ISOCAM cluster members are best fit by models with negligible star formation in the last ~1 Gyr. The 7 faintest cluster members have a slightly higher, but still very mild, star-formation activity. The ISOCAM-selected cluster galaxies appear to be an unbiased subsample of the overall cluster population. If A2218 is undergoing a merger, as suggested by some optical and X-ray analyses, then this merger does not seem to affect the mid-infrared properties of its galaxies. The SEDs of most ISOCAM-selected field sources are best fit by models with significant ongoing (and recent) star formation, resembling those of massive star-forming spirals or (post)starburst galaxies. Their median SFR is 22 solar masses per year. Eight of the 14 field sources are Luminous IR Galaxies. (Abridged)

Deep Mid‐Infrared Observations of Lyman Break Galaxies

As part of the in-orbit checkout activities for the Spitzer Space Telescope, the Infrared Array Camera (IRAC) team carried out a deep observation (average integration time ~8 hr) of a field surrounding the bright QSO HS 1700+6416. This field contains several hundred z ~ 3 Lyman break galaxy (LBG) candidates, and we report here on their mid-infrared properties, including the IRAC detection rate, flux densities, and colors, and the results of fitting population synthesis models to the optical, near-infrared, and IRAC magnitudes. The results of the model fitting show that previous optical/near-infrared studies of LBGs were not missing large, hidden old stellar populations. The LBG candidates' properties are consistent with those of massive star-forming galaxies at z ~ 3. Other IRAC sources in the same field have similar properties, so IRAC selection may prove to be a promising method of finding additional high-redshift galaxies.

Mid-Infrared properties of Early-type galaxies

Mid-Infrared properties of Early-type galaxies

Infrared photodetection with semiconductor self-assembled quantum dots

Semiconductor self-assembled quantum dots are potential candidates to develop a new class of midinfrared quantum photodetectors and focal plane arrays. In this article, we present the specific midinfrared properties of InAs/GaAs quantum dots associated with the intersublevel transitions. The electronic structure, which accounts for the strain field in the islands, is obtained within the framework of a three-dimensional 8 band k.p formalism. The midinfrared intersublevel absorption in n-doped quantum dots is described. We show that the carrier dynamics can be understood in terms of polarons which result from the strong coupling regime for the electron–phonon interaction in the dots. The principle of operation of vertical and lateral quantum dot infrared photodetectors is described and discussed by comparison with quantum well infrared photodetectors. We review the performances of different type of detectors developed to date and finally give some orientation to realize high performance quantum dot infrared photodetectors. To cite this article: P. Boucaud, S. Sauvage, C. R. Physique 4 (2003).

The impact of bars on the mid-infrared dust emission of spiral galaxies: global and circumnuclear properties

We study the mid-infrared properties of a sample of 69 nearby spiral galaxies, selected to avoid Seyfert activity contributing a significant fraction of the central energetics, or strong tidal interaction, and to have normal infrared luminosities. These observations were obtained with ISOCAM, which provides an angular resolution of the order of (half-power diameter of the point spread function) and low-resolution spectro-imaging information. Between 5 and 18 μm, we mainly observe two dust phases, aromatic infrared bands and very small grains, both out of thermal equilibrium. On this sample, we show that the global colors of galaxies are very uniform, the only increase being found in early-type strongly barred galaxies, consistent with previous IRAS studies. The excesses are unambiguously due to galactic central regions where bar-induced starbursts occur. However, the existence of strongly barred early-type galaxies with normal circumnuclear colors indicates that the relationship between a distortion of the gravitational potential and a central starburst is not straightforward. As the physical processes at work in central regions are in principle identical in barred and unbarred galaxies, and since this is where the mid-infrared activity is mainly located, we investigate the mid-infrared circumnuclear properties of all the galaxies in our sample. We show how surface brightnesses and colors are related to both the available molecular gas content and the mean age of stellar populations contributing to dust heating. Therefore, the star formation history in galactic central regions can be constrained by their position in a color-surface brightness mid-infrared diagram.

The Mid-Infrared Properties of Nearby Spiral Galaxies

The galaxies (~ 40) presented here are part of three ISOCAM guaranteed time programs. Observations consist of raster maps performed with a sampling of 3 and 6 arcsecond per pixel, in the 6.75 μm (LW2) and 15 μm (LW3) bands. The 6.75 μm band samples mostly emission from a blend of aromatic bands, while the 15 μm band is more complex since it generally samples aromatic bands and an associated continuum as well, but can also receive a significant, or even dominant, contribution from a sharply rising continuum emitted by small grains in HII regions or high radiation density environments.

Nanocrystalline vanadium dioxide: synthesis and mid-infrared properties

This work describes the first successful synthesis of nanocrystalline thermochromic VO 2 powder using the low temperature irreversible structural transformation of the metastable VO 2(B). At this step, the transformation is associated with a total rearrangement of VO 6 octahedra, and a strong increasing of density. The reversible metal–insulator phase transition (MIPT) of vanadium dioxide ( T t=68°C) is associated with strong changes in electrical, magnetic and optical properties. The contrast of the optical transition in mid-infrared (MIR) region and the optical transparency are remarkably increased for these nanosized particles. Modifications in coloration are also observed.

Infrared spectroscopy on Y 1− xRE xBa 2Cu 3− yZn yO 6 (RE  Pr, Gd, x = 0 and 0.8; y = 0 and ≈ 0.15)

Far- and mid-infrared properties of antiferromagnetic Y 1− x RE x Ba 2Cu 3− y Zn y O 6 (RE  Pr, Gd, x = 0 and y = 0 and ≈ 0.15) were investigated by infrared reflection and transmission measurements ( κ∥ c-axis). All six phonon modes of E u symmetry and several multi-phonon bands were observed. Zn substitution causes phonon side bands and a surprising temperature dependence of multi-phonon bands, possibly due to spin-lattice interactions. All compounds show several features in the mid-infrared range that might be related to bimagnon-plus-phonon absorption.

Mid-infrared properties of a VO2 film near the metal-insulator transition.

A ${\mathrm{VO}}_{2}$ film was grown on a sapphire(0001) substrate using pulsed laser deposition. The film showed a first-order metal-insulator (MI) transition and its dc conductivity started to increase drastically near 68 \ifmmode^\circ\else\textdegree\fi{}C and changed by three orders of magnitude. Mid-infrared transmittance and reflectance spectra of the ${\mathrm{VO}}_{2}$ film were measured between 20 \ifmmode^\circ\else\textdegree\fi{}C and 90 \ifmmode^\circ\else\textdegree\fi{}C. Using the intensity transfer-matrix method, the frequency-dependent dielectric constant ${\mathrm{\ensuremath{\epsilon}}}_{\mathit{f}}$(\ensuremath{\omega}) and the conductivity ${\mathrm{\ensuremath{\sigma}}}_{\mathit{f}}$(\ensuremath{\omega}) of the film were obtained between 1600 and 4000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ from the measured transmittance and reflectance spectra. With the ${\mathrm{\ensuremath{\epsilon}}}_{\mathit{f}}$(\ensuremath{\omega}) and ${\mathrm{\ensuremath{\sigma}}}_{\mathit{f}}$(\ensuremath{\omega}) spectra, mid-infrared properties of the ${\mathrm{VO}}_{2}$ film near the MI transition region were investigated in detail. Above 78 \ifmmode^\circ\else\textdegree\fi{}C, ${\mathrm{\ensuremath{\epsilon}}}_{\mathit{f}}$(\ensuremath{\omega})0 and d${\mathrm{\ensuremath{\epsilon}}}_{\mathit{f}}$/d\ensuremath{\omega}g0, which is a typical metallic behavior. In particular, ${\mathrm{\ensuremath{\epsilon}}}_{\mathit{f}}$(\ensuremath{\omega}) and ${\mathrm{\ensuremath{\sigma}}}_{\mathit{f}}$(\ensuremath{\omega}) at 88 \ifmmode^\circ\else\textdegree\fi{}C were analyzed in terms of extended Drude model in which the frequency-dependent scattering rate and the effective mass could be obtained. The mean free path of charge carriers in the dc limit was estimated to be larger by an order of magnitude than the previously reported value, i.e., 4 \AA{}. Below 74 \ifmmode^\circ\else\textdegree\fi{}C, ${\mathrm{\ensuremath{\epsilon}}}_{\mathit{f}}$(\ensuremath{\omega})g0 and d${\mathrm{\ensuremath{\epsilon}}}_{\mathit{f}}$/d\ensuremath{\omega}\ensuremath{\approxeq}0, which is characteristic of an insulator. Interestingly, ${\mathrm{\ensuremath{\epsilon}}}_{\mathit{f}}$ in the insulating region increased as the temperature approached the MI transition temperature. To explain this anomalous behavior, the MI transition of the ${\mathrm{VO}}_{2}$ film was modeled with coexistence of metallic and insulating domains and their dynamic evolution. Then the behaviors of ${\mathrm{\ensuremath{\epsilon}}}_{\mathit{f}}$(\ensuremath{\omega}) and ${\mathrm{\ensuremath{\sigma}}}_{\mathit{f}}$(\ensuremath{\omega}) were explained using the effective medium approximation, which is a mean-field theory predicting a percolation transition. This work clearly demonstrates that the transport and optical properties near the MI transition region are strongly influenced by the connectivity of the metallic domains. \textcopyright{} 1996 The American Physical Society.