A Bridge from Optical to Infrared Galaxies: Explaining Local Properties and Predicting Galaxy Counts and the Cosmic Background Radiation

The CIBER collaboration released their first observational data of the Cosmic IR background (CIB) radiation, which has significant excesses at around the wavelength $\sim$ 1 $\mu$m compared to theoretically-inferred values. The amount of the CIB radiation has a significant influence on the opaqueness of the Universe for TeV gamma-rays emitted from distant sources such as AGNs. With the value of CIB radiation reported by the CIBER experiment, through the reaction of such TeV gamma-rays with the CIB photons, the TeV gamma-rays should be significantly attenuated during propagation, which would lead to energy spectra in disagreement with current observations of TeV gamma ray sources. In this article, we discuss a possible resolution of this tension between the TeV gamma-ray observations and the CIB data in terms of axion [or Axion-Like Particles (ALPs)] that may increase the transparency of the Universe by the anomaly-induced photon-axion mixing. We find a region in the parameter space of the axion mass, $m_a \sim 7 \times 10^{-10} - 5 \times 10^{-8}$eV, and the axion-photon coupling constant, $1.2 \times 10^{-11} {\rm GeV}^{-1} \lesssim g_{a\gamma} \lesssim 8.8 \times 10^{-10} {\rm GeV}^{-1}$ that solves this problem.

Infrared (IR) emission features at 3.3, 6.2, 7.7, 8.6, and 11.3 ?m are generally attributed to IR fluorescence from (mainly) far-ultraviolet (FUV) pumped large polycyclic aromatic hydrocarbon (PAH) molecules. As such, these features trace the FUV stellar flux and are thus a measure of star formation. We examined the IR spectral characteristics of Galactic massive star-forming regions and of normal and starburst galaxies, as well as active galactic nuclei (AGNs) and ultraluminous infrared galaxies (ULIRGs). The goal of this study is to analyze whether PAH features are a good qualitative and/or quantitative tracer of star formation, and hence to evaluate the application of PAH emission as a diagnostic tool in order to identify the dominant processes contributing to the infrared emission from Seyfert galaxies and ULIRGs. We develop a new mid-infrared (MIR)/far-infrared (FIR) diagnostic diagram based on our Galactic sample and compare it to the diagnostic tools of Genzel and coworkers and Laurent and coworkers, with these diagnostic tools also applied to our Galactic sample. This MIR/FIR diagnostic is derived from the FIR normalized 6.2 ?m PAH flux and the FIR normalized 6.2 ?m continuum flux. Within this diagram, the Galactic sources form a sequence spanning a range of 3 orders of magnitude in these ratios, ranging from embedded compact H II regions to exposed photodissociation regions (PDRs) and the (diffuse) interstellar medium (ISM). However, the variation in the 6.2 ?m PAH feature-to-continuum ratio is relative small. Comparison of our extragalactic sample with our Galactic sources revealed an excellent resemblance of normal and starburst galaxies to exposed PDRs. While Seyfert 2 galaxies coincide with the starburst trend, Seyfert 1 galaxies are displaced by at least a factor of 10 in 6.2 ?m continuum flux, in accordance with general orientation-dependent unification schemes for AGNs. ULIRGs show a diverse spectral appearance. Some show a typical AGN hot dust continuum. More, however, either are starburst-like or show signs of strong dust obscuration in the nucleus. One characteristic of the ULIRGs also seems to be the presence of more prominent FIR emission than either starburst galaxies or AGNs. We discuss the observed variation in the Galactic sample in view of the evolutionary state and the PAH/dust abundance and discuss the use of PAHs as quantitative tracers of star formation activity. Based on these investigations, we find that PAHs may be better suited as a tracer of B stars, which dominate the Galactic stellar energy budget, than as a tracer of massive star formation (O stars).

Spectral Energy Distribution (SED) fitting in the far-infrared (FIR) is greatly limited by a dearth of data and an excess of free parameters - from galaxies' dust composition, temperature, mass, orientation, opacity, to heating from AGN. This paper presents a simple FIR SED fitting technique joining a modified, single dust temperature greybody, representing the reprocessed starburst emission in the whole galaxy, to a mid-infrared powerlaw, which approximates hot-dust emission from AGN heating or clumpy, hot starbursting regions. This FIR SED can be used to measure infrared luminosities, dust temperatures and dust masses for both local and high-z galaxies with 3 to 10+ FIR photometric measurements. This fitting method is compared to infrared template SEDs in the literature using photometric data on 65 local luminous and ultraluminous infrared galaxies, (U)LIRGs. Despite relying only on 2-4 free parameters, the coupled greybody/powerlaw SED fitting described here produces better fits to photometric measurements than best-fit literature template SEDs (with residuals a factor of ~2 lower). A mean emissivity index of beta=1.60+-0.38 and mid-infrared powerlaw slope of alpha=2.0+-0.5 is measured; the former agrees with the widely presumed emissivity index of beta=1.5 and the latter is indicative of an optically-thin dust medium with a shallow radial density profile, ~r^-0.5. Adopting characteristic dust temperature as the inverse wavelength where the SED peaks, dust temperatures ~25-45K are measured for local (U)LIRGs, ~5-15K colder than previous estimates using only simple greybodies. This comparative study highlights the impact of SED fitting assumptions on the measurement of physical properties such as infrared luminosity (and thereby infrared-based star formation rate), dust temperature and dust mass, for both local and high-redshift galaxies. [abridged]

view Abstract Citations (68) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of Abundant Molecular Gas in the UV-Excess Quasar Markarian 1014 Sanders, D. B. ; Scoville, N. Z. ; Soifer, B. T. Abstract CO(1-0) emission has been detected from the UV-excess quasar Mrk 1014 (= PG 0157+001 = IRAS 01572+0009) at z = 0.163. Assuming the same empirical relationship between CO brightness and H_2_ surface mass density as has been found for giant molecular clouds in the Milky Way, the mass of H_2_ gas is ~4 x 10^10^) M_sun_-more than 10 times the H_2_ content of our Galaxy. The infrared and molecular gas properties of Mrk 1014 are similar to other "warm," ultraluminous infrared galaxies such as Mrk 231, and IRAS 15206+3342 (z = 0.125) from which CO(1-0) emission is also reported. The trigger for the intense infrared activity in both Mrk 1014 and IRAS 15206+3342 appears to be a recent galaxy merger. It is suggested that objects such as these represent an important link in the evolution of ultraluminous infrared galaxies into UV excess quasars. Publication: The Astrophysical Journal Pub Date: December 1988 DOI: 10.1086/185326 Bibcode: 1988ApJ...335L...1S Keywords: Interacting Galaxies; Interstellar Matter; Markarian Galaxies; Molecular Spectra; Quasars; Ultraviolet Spectra; Active Galactic Nuclei; Astronomical Models; Carbon Monoxide; Starburst Galaxies; Astrophysics; GALAXIES: INDIVIDUAL NAME: MARKARIAN 1014; INFRARED: SOURCES; INTERSTELLAR: MOLECULES; QUASARS full text sources ADS | data products SIMBAD (5) NED (5)

The Cosmic Background Explorer (COBE) was developed by NASA Goddard Space Flight Center to measure the diffuse infrared and microwave radiation from the early universe. It also measured emission from nearby sources such as the stars, dust, molecules, atoms, ions, and electrons in the Milky Way, and dust and comets in the Solar System. It was launched 18 November 1989 on a Delta rocket, carrying one microwave instrument and two cryogenically cooled infrared instruments. The Differential Microwave Radiometers (DMR) measured the fluctuations in the Cosmic Microwave Background Radiation (CMBR) originating in the Big Bang, with a total amplitude of 11 parts per million on a 10° scale. It also measured the synchrotron and free-free emission of the Galaxy. The Far Infrared Absolute Spectrophotometer (FIRAS) mapped the sky at wavelengths from 0.01 to 1 cm, and compared the CMBR to a precise blackbody. The spectrum of the CMBR differs from a blackbody by less than 0.03%. The FIRAS observed interstellar dust, showing that up to three different temperatures of dust are needed to explain the spectra. It also measured the emission of CO, [C I], [C II], and [N II], tracing several distinct phases of the gas. The Diffuse Infrared Background Experiment (DIRBE) spanned the wavelength range from 1.2 to 240 μm and mapped the sky at a wide range of solar elongation angles to distinguish foreground sources from a possible extragalactic Cosmic Infrared Background Radiation (CIBR). It measured foreground emission from stars, interstellar and interplanetary dust, the polarization of starlight from the Galactic Center, and the reddening of the Galactic plane by the dust absorption.

We investigate the expected submillimeter emission and dust properties of the Lyman break galaxies (LBGs) in the Hubble Deep Field. The SCUBA Deep Survey (Hughes et al.) provides an upper limit of the 850 μm flux densities of the LBGs. With this constraint, we argue that a typical ultraviolet-to-far-infrared spectral shape of the high-redshift LBGs is rather close to a template spectrum of low-reddening starburst galaxies in the local universe but different from that of heavily dust-enshrouded ultraluminous far-infrared (FIR) galaxies like Arp 220. We also evaluate the lower limit temperature of dust in LBGs assuming a single- and two-component-modified blackbody spectrum. To estimate the total amount of energy reemitted in the FIR wavelength, we take two different approaches: the method of model fitting to the UV spectra of LBGs and an empirical method that uses the relationship between the UV spectral shape and the UV/FIR flux ratio observed for local starburst galaxies. Both methods give a lower limit temperature of ~40 K for the LBGs, which is higher than the typical dust temperature of local optical- and infrared-selected galaxies. This result is also supported by the comparison of the expected submillimeter flux of the LBGs with the cosmic FIR background radiation. The high dust temperature may indicate the effective massive star formation or the different dust properties in the high-redshift LBGs.

We investigate the properties of mid- to far-infrared emission in the Large Magellanic Cloud (LMC) based on the COBE DIRBE and IRAS Sky Survey Atlas data sets. We focus on the properties of far-infrared (FIR) thermal emission carried by submicron dust and mid-infrared (MIR) excess emission by very small grains in the LMC in comparison to those in the Milky Way. We carefully estimate the dust temperature by decomposing the various structures including young star clusters, supergiant shells, and CO molecular clouds and examine the MIR to FIR spectral energy distribution (SED) associated with each structure in the LMC. The amount of the MIR excess emission in 12 and 25 ?m relative to the total FIR emission (FFIR) in the LMC is generally smaller than that in the Milky Way, which confirms the scarcity of very small grains suggested by past studies on the extinction curve. The characteristics of 25 and 60 ?m excess emission proportional to the square of the incident radiation field strength appear around young star clusters in the LMC. This sequence can be reproduced by the superposition of dust emission under different radiation field strengths ranging from 1 to 105 times of that in the solar vicinity. Finally, the MIR to FIR SEDs in CO molecular clouds in the LMC are discussed. Through these attempts, we succeed in completely explaining the characteristics of mid- to far-infrared SEDs given by the infrared broadband photometric data sets in terms of the superposition of the standard stochastic heating dust model.

According to the Cosmological Principle, the Universe should appear isotropic, without any preferred directions, to a comoving observer. However, a peculiar motion of the observer, or equivalently of the solar system, might introduce a dipole anisotropy in some of the observed properties of the Cosmos. The peculiar motion of the solar system, determined from the dipole anisotropy in the Cosmic Microwave Background Radiation (CMBR), gave a velocity 370 km/s along l = 264°, b = 48°. However, dipoles from number counts, sky brightness or redshift distributions in large samples of distant active galactic Nuclei (AGNs) have yielded values of the peculiar velocity many times larger than that from the CMBR, though in all cases the directions agreed with the CMBR dipole. Here we determine our peculiar motion from a sample of ~0.28 million AGNs, selected from the Mid Infra Red Active Galactic Nuclei (MIRAGN) sample comprising more than a million sources. We find a peculiar velocity more than four times the CMBR value, although the direction seems to be within ~2σ of the CMBR dipole. Since a real solar peculiar velocity should be the same whatever the data or the technique of observations may be, such discordant dipoles could imply that the explanation for the genesis of these dipoles, including that of the CMBR, might lie elsewhere. At the same time, a common direction for all these dipoles, determined from completely independent surveys by different groups, does indicate that these dipoles are not merely due to some systematics, and it might instead suggest a preferred direction in the Universe implying a genuine anisotropy, which would violate the Cosmological Principle, the core of modern cosmology.

This thesis explores the molecular gas (the raw material for star formation), especially the dense molecular gas content of luminous infrared galaxies (LIGs) and ''normal'' galaxies using millimeter line observations. Most LIGs are closely interacting/merging galaxies and ''normal'' spiral galaxies are believed to be the building blocks of LIGs. We here study and compare the distributions and masses of the total molecular gas and the dense molecular gas, traced by CO and HCN emission respectively, in LIGs, starburst galaxies and ''normal'' spiral galaxies. The molecular gas properties are then compared with the stages of galaxy- galaxy interaction and the far-IR luminosity to understand the star formation process and evolution of LIGs. We first study the dense molecular gas extent and distribution in ~ 10 nearby ''normal'' galaxies by mapping HCN emission (complementary with CO) at least along the major axes. We present the first detailed observational evidence that HCN emission in galaxies, \\ie, the dense molecular gas, is not confined to the inner ~ 1 kpc nuclear region, although the highest concentrations of dense molecular gas are in the center. A significant fraction of dense molecular gas is distributed in the inner disks of galaxies outside the nuclear or inner ring starburst regions, and can be detected to radii as large as a few kpc, perhaps to diameters of ~ D25/4. Then we have further surveyed HCN emission in more than ~ 40 relatively distant IR/CO bright ''normal'' galaxies and LIGs. Therefore, a statistically significant sample of HCN data in galaxies is established. We find that LIGs, especially ultraluminous ones, contain tremendous amount of dense molecular gas fueling the starbursts. Although LIGs are rich in molecular gas, some ''normal'' galaxies could have as much molecular gas as LIGs. However, the dense molecular gas content of even gas-rich ''normal'' galaxies is much less than that of LIGs of comparable molecular gas content. We show that HCN emission is better correlated with IR emission than that of CO. The total dense molecular content, the ratio of HCN/CO luminosity and the distribution of the surface brightness ratio IHCN/ICO are important high mass star formation indicators. We also confirm that the star formation efficiency indicated by LIR/LCO depends on the fraction of dense molecular gas (LHCN/LCO) and that the LIR/LHCN ratio is similar in all galaxies, ultraluminous or not, hot or cold in dust temperature, illustrating the starburst nature of ultraluminous IR galaxies. A second goal of this thesis is to study LIGs in the intermediate merging process, to determine the relationship between the various IR/CO properties and galaxy-galaxy interactions. We find a correlation between the CO luminosity and the projected separation of merger nuclei in a sample of more than ~ 50 LIG mergers, which suggests that the molecular content is decreasing as merging advances. Although the correlation is weak for the truly ultraluminous (LIR>1012 ls ) IR mergers, which could simply be due to the incompleteness of the sample since ultraluminous mergers are at great distances, the correlation is better established with less luminous LIG mergers, more close to a volume-limited statistically complete sample. The correlation slope for this nearby almost complete sample is the same as that of the large, heterogeneous sample of 50 mergers. We conducted new CO observation in ~ 20 LIG mergers to provide the CO data for this statistically complete sample of nearby LIG mergers. This correlation seems to have important constraints on both the merger- induced star formation models and the evolution scenario of LIGs. We have also conducted high resolution interferometry CO imaging in two spectacular LIGs, Arp 118 and Arp 119. We detected strong CO emission from rings/tails more than 10 kpc away from the nuclei, and most molecular gas is extranuclear. Detailed study of the distribution and kinematics of the molecular gas can provide the dynamical clues to the origin and evolution of these LIGs. Finally, we study the environment and spatial distribution of LIGs. We found that LIGs have stronger clustering than that of \\IRAS galaxies, yet most of them are not inside the groups of galaxies. Using various previous studies along with our own present investigations, we suggest that some LIGs are remnants of the merged groups of gas-rich galaxies.

We present new data obtained with the Submillimeter Array for a sample of fourteen nearby luminous and ultraluminous infrared galaxies. The galaxies were selected to have luminosity distances D 11.4. The galaxies were observed with spatial resolutions of order 1 kpc in the CO J=3-2, CO J=2-1, 13CO J=2-1, and HCO+ J=4-3 lines as well as the continuum at 880 microns and 1.3 mm. We have combined our CO and continuum data to measure an average gas-to-dust mass ratio of 120 +/- 28 (rms deviation 109) in the central regions of these galaxies, very similar to the value of 150 determined for the Milky Way. This similarity is interesting given the more intense heating from the starburst and possibly accretion activity in the luminous infrared galaxies compared to the Milky Way. We find that the peak H_2 surface density correlates with the far-infrared luminosity, which suggests that galaxies with higher gas surface densities inside the central kiloparsec have a higher star formation rate. The lack of a significant correlation between total H_2 mass and far-infrared luminosity in our sample suggests that the increased star formation rate is due to the increased availability of molecular gas as fuel for star formation in the central regions. In contrast to previous analyses by other authors, we do not find a significant correlation between central gas surface density and the star formation efficiency, as trace by the ratio of far-infrared luminosity to nuclear gas mass. Our data show that it is the star formation rate, not the star formation efficiency, that increases with increasing central gas surface density in these galaxies.

We present follow-up observations of the far-infrared (FIR) sources at 90,\n150 and 180 mu detected as part of the ISOPHOT EBL project, which has recently\nmeasured the absolute surface brightness of the cosmic infrared background\nradiation (CIRB) for the first time independently from COBE data. We have\nobserved the fields at the North Galactic Pole region in the optical and\nnear-IR, and complement these data with SDSS photometry, and spectroscopy where\navailable, and present identifications of the 25 FIR sources which reach down\nto ~150 mJy in all three ISOPHOT bands. Identifications are done by means of\nfull spectral energy density fitting to all sources in the FIR error circle\nareas. Approximately 80 per cent are identified as star-forming or\nstar-bursting galaxies at z<0.3. We also find that more than half of the\ncounterparts have disturbed morphologies, with signs of past or present\ninteractions. However, only 20 per cent of all the sources are uniquely matched\nwith a single galaxy -- 40 per cent are blends of two or more of these nearby\nstar-forming galaxies, while another 20 per cent are likely blends of nearby\nand fainter galaxies. The final 20 per cent are likely to be more luminous IR\ngalaxies at higher redshifts. The blended sources have an effect on the FIR\nsource counts. In particular, taking into account realistic confusion or\nblending of sources, the differential FIR counts move down by a factor of ~1.5\nand steepen in the 100 to 400 mJy range.\n

In this model the Solar System presented to observers on the planet Earth the elegant gift: the Solar Microwave Background (SMB) formed on the Blackbody Sphere at the distance R = 140 AU. The thermalization of the Hydrogen wall at this distance was described using the Stefan-Boltzmann law where the temperature of the blackbody at the distance R = 1 AU is T = 393.6 K. Newton’s cooling law described the cooling of this blackbody surface temperature with the cooling constant κ = 1.139 × 10−4 s−1 calculated from data of the small planet Pluto (average distance R = 39.5 AU and the temperature T = 44 K). The SMB monopole temperature T = 2.7255 K was fitted for the distance R = 140 AU with the temperature of the surrounding TENV = 2.5887 K. The first important difference with the model of the cosmic microwave background (CMB) is the magnitude and direction of Newton’s dipole v = (200 + 141) kms−1 towards the galactic coordinates (l, b) = (84°, −48°) while the magnitude and the direction of the Doppler’s dipole of CMB is v = 368 kms−1 towards (l, b) = (264°, 48°). This new model enables to estimate the rotation velocity of the Sun in the Milky Way Galaxy, the motion of the Milky Way Galaxy through the Universe, and the Harress-Sagnac color excess: v = 200 + 141 + 27 = 368 kms−1. The total motion of the Milky Way Galaxy through the Universe can be estimated with the knowledge of the Cold Spot direction in the SMB and the motion towards the Galactic South Pole. In this model, the Milky Way Galaxy can avoid collision with the Andromeda Galaxy. The observed quadrupole, octopole, and hemisphere structure of the SMB can be explained as the local motion of the Sun and the Solar axis inclination towards the ecliptic–the Axis of evil should be renamed as the Solar axis bringing to us a good opportunity to discover differences between the SMB and the CMB. The first peak in the power spectrum of the SMB at the distance R = 140 AU is observed from the COBE, WMAP, and PLANCK satellites rotating around the Sun at the distance R = (2×1) AU under the angle θ = 0.818°. The power spectrum observed from the planets Mercury and Jupiter will have different positions of the first and higher peaks. The original Solar signature should be visible as the moving shadows of the Sunspots on the Blackbody Sphere. There were proposed several experiments on how to distinguish between the SMB and the CMB.

We present ALMA observations of the [CII] line and far-infrared (FIR) continuum of a normally star-forming galaxy in the reionization epoch, the z=6.96 Ly-alpha emitter (LAE) IOK-1. Probing to sensitivities of sigma_line = 240 micro-Jy/beam (40 km/s channel) and sigma_cont = 21 micro-Jy/beam, we found the galaxy undetected in both [CII] and continuum. Comparison of UV - FIR spectral energy distribution (SED) of IOK-1, including our ALMA limit, with those of several types of local galaxies (including the effects of the cosmic microwave background, CMB, on the FIR continuum) suggests that IOK-1 is similar to local dwarf/irregular galaxies in SED shape rather than highly dusty/obscured galaxies. Moreover, our 3 sigma FIR continuum limit, corrected for CMB effects, implies intrinsic dust mass M_dust < 6.4 x 10^7 M_sun, FIR luminosity L_FIR < 3.7 x 10^{10} L_sun (42.5 - 122.5 micron), total IR luminosity L_IR < 5.7 x 10^{10} L_sun (8 - 1000 micron) and dust-obscured star formation rate (SFR) < 10 M_sun/yr, if we assume that IOK-1 has a dust temperature and emissivity index typical of local dwarf galaxies. This SFR is 2.4 times lower than one estimated from the UV continuum, suggesting that < 29% of the star formation is obscured by dust. Meanwhile, our 3 sigma [CII] flux limit translates into [CII] luminosity, L_[CII] < 3.4 x 10^7 L_sun. Locations of IOK-1 and previously observed LAEs on the L_[CII] vs. SFR and L_[CII]/L_FIR vs. L_FIR diagrams imply that LAEs in the reionization epoch have significantly lower gas and dust enrichment than AGN-powered systems and starbursts at similar/lower redshifts, as well as local star-forming galaxies.

According to the Cosmological Principle, the Universe is isotropic and no preferred direction would be seen by an observer that might be stationary with respect to the expanding cosmic fluid. However, because of observer’s partaking in the solar system peculiar motion, there would appear in some of the observed properties of the Cosmos a dipole anisotropy, which could in turn be exploited to determine the peculiar motion of the solar system. The dipole anisotropy in the Cosmic Microwave Background Radiation (CMBR) has given a peculiar velocity vector 370 km s−1 along l=264∘,b=48∘. However, some other dipoles, for instance, from the number counts, sky brightness or redshift distributions in large samples of distant Active Galactic Nuclei (AGNs), have yielded values of the peculiar velocity many times larger than that from the CMBR, though surprisingly, in all cases the directions agreed with the CMBR dipole. Here we determine our peculiar motion from a sample of 0.28 million AGNs, selected from the Mid Infra Red Active Galactic Nuclei (MIRAGN) sample comprising more than a million sources. From this, we find a peculiar velocity, which is more than four times the CMBR value, although the direction seems to be within ∼2σ of the CMBR dipole. A genuine value of the solar peculiar velocity should be the same irrespective of the data or the technique employed to estimate it. Therefore, such discordant dipole amplitudes might mean that the explanation for these dipoles, including that of the CMBR, might in fact be something else. The observed fact that the direction in all cases is the same, though obtained from completely independent surveys using different instruments and techniques, by different sets of people employing different computing routines, might nonetheless indicate that these dipoles are not merely due to some systematics, otherwise why would they all be pointing along the same direction. It might instead suggest a preferred direction in the Universe, implying a genuine anisotropy, which would violate the Cosmological Principle, the core of the modern cosmology.

We study the impact on the cosmic microwave background (CMB) landscape of peculiar rotational general relativistic effects. These effects, on galactic scales, do not possess a Newtonian analogue, and therefore could a priori impact CMB analysis. We find that the velocity inferred from the CMB dipole, under the kinematic interpretation, coincides with that measured by a stationary observer within the Milky Way and not with the one measured by the zero angular momentum observer. We show that the galaxy peculiar frame-dragging effects do not impact the standard CMB analysis, as these modify the multipole coefficients only at higher orders with respect to the dominant terms. Moreover, we prove that no general relativistic framework at the galactic scale patched within the standard cosmological model can account for the current tension on the CMB quadrupole amplitude.