C. W. Engelbracht, L. K. Hunt, R. A. Skibba, J. L. Hinz, D. Calzetti, K. D. Gordon, H. Roussel, A. F. Crocker, K. A. Misselt, A. D. Bolatto, R. C. Kennicutt, P. N. Appleton, L. Armus, P. Beirão, B. R. Brandl, K. V. Croxall, D. A. Dale, B. T. Draine, G. Dumas, A. Gil de Paz, B. Groves, C. -N. Hao, B. D. Johnson, J. Koda, O. Krause, A. K. Leroy, S. E. Meidt, E. J. Murphy, N. Rahman, H. -W. Rix, K. M. Sandstrom, M. Sauvage, E. Schinnerer, J. -D. T. Smith, S. Srinivasan, L. Vigroux, F. Walter, B. E. Warren, C. D. Wilson, M. G. Wolfire, S. Zibetti
May 11, 2010·astro-ph.CO·PDF Stellar density and bar strength should affect the temperatures of the cool (T ~ 20-30 K) dust component in the inner regions of galaxies, which implies that the ratio of temperatures in the circumnuclear regions to the disk should depend on Hubble type. We investigate the differences between cool dust temperatures in the central 3 kpc and disk of 13 nearby galaxies by fitting models to measurements between 70 and 500 microns. We attempt to quantify temperature trends in nearby disk galaxies, with archival data from Spitzer/MIPS and new observations with Herschel/SPIRE, which were acquired during the first phases of the Herschel observations for the KINGFISH (key insights in nearby galaxies: a far-infrared survey with Herschel) sample. We fit single-temperature modified blackbodies to far-infrared and submillimeter measurements of the central and disk regions of galaxies to determine the temperature of the component(s) emitting at those wavelengths. We present the ratio of central-region-to-disk-temperatures of the cool dust component of 13 nearby galaxies as a function of morphological type. We find a significant temperature gradient in the cool dust component in all galaxies, with a mean center-to-disk temperature ratio of 1.15 +/- 0.03. The cool dust temperatures in the central ~3 kpc of nearby galaxies are 23(+/-3)% hotter for morphological types earlier than Sc, and only 9(+/-3)% hotter for later types. The temperature ratio is also correlated with bar strength, with only strongly barred galaxies having a ratio over 1.2. The strong radiation field in the high stellar density of a galactic bulge tends to heat the cool dust component to higher temperatures, at least in early-type spirals with relatively large bulges, especially when paired with a strong bar.
C. W. Engelbracht, M. J. Rieke, G. H. Rieke, D. M. Kelly, J. M. Achtermann
May 12, 1998·astro-ph·PDF We have obtained long-slit spectra of NGC 253 in the J, H, K, and N bands, broadband images in the J, H, and Ks bands, narrowband images centered at the wavelengths of BrGamma and H2(1,0)S(1), and imaging spectroscopy centered on [NeII](12.8um). We use these data and data from the literature in a comprehensive re-assessment of the starburst in this galaxy. We derive the supernova rate from the strength of the infrared [FeII] lines. We find that most of the H2 infrared luminosity is excited by fluorescence in low density gas. We derive a strong upper limit of ~37,000K for the stars exciting the emission lines. We use velocity-resolved infrared spectra to determine the mass in the starburst region. Most of this mass appears to be locked up in the old, pre-existing stellar population. Using these constraints and others to build an evolutionary synthesis model, we find that the IMF originally derived to fit the starburst in M 82 (similar to a Salpeter IMF) also accounts for the properties of NGC 253. The models indicate that rapid massive star formation has been ongoing for 20-30 million years in NGC 253---that is, it is in a late phase of its starburst. We model the optical emission line spectrum expected from a late phase starburst and demonstrate that it reproduces the observed HII/weak-[OI] LINER characteristics.
C. W. Engelbracht, P. Kundurthy, K. D. Gordon, G. H. Rieke, R. C. Kennicutt, J. -D. T. Smith, M. W. Regan, D. Makovoz, M. Sosey, B. T. Draine, G. Helou, L. Armus, D. Calzetti, M. Meyer, G. J. Bendo, F. Walter, D. Hollenbach, J. M. Cannon, E. J. Murphy, D. A. Dale, B. A. Buckalew, K. Sheth
Mar 20, 2006·astro-ph·PDF We present new images (groundbased optical and mid-infrared (MIR) from the Spitzer Space Telescope) and spectra (from Spitzer) of the archetypal starburst galaxy M 82. The Spitzer data show that the MIR emission extends at least 6 kpc along the minor axis of the galaxy. We use the optical and infrared data to demonstrate that the extended emission is dominated by emission from dust. The colors of the MIR emission and the spectra indicate that there is a strong component of aromatic feature emission (the MIR features commonly attributed to polycyclic aromatic hydrocarbons). The dust continuum and aromatic feature emission are both strong in the well-known superwind region of this galaxy; clearly the carrier of the aromatic features can survive in close proximity to the wind, far from the plane of the galaxy. We also see significant emission by dust well outside the superwind region, providing the clearest picture to date of the dust distribution in the halo of this galaxy.
C. W. Engelbracht, K. D. Gordon, G. J. Bendo, P. G. Perez-Gonzalez, K. A. Misselt, G. H. Rieke, E. T. Young, D. C. Hines, D. M. Kelly, J. A. Stansberry, C. Papovich, J. E. Morrison, E. Egami, K. Y. L. Su, J. Muzerolle, H. Dole, A. Alonso-Herrero, J. L. Hinz, P. S. Smith, W. B. Latter, A. Noriega-Crespo, D. L. Padgett, J. Rho, D. T. Frayer, S. Wachter
We present images of the galaxy NGC 55 at 24, 70, and 160 micron obtained with the Multiband Imaging Photometer for Spitzer (MIPS) instrument aboard the Spitzer Space Telescope. The new images display the far infrared emission in unprecedented detail and demonstrate that the infrared morphology differs dramatically from that at shorter wavelengths. The most luminous emission region in the galaxy is marginally resolved at 24 micron and has a projected separation of nearly 520 pc from the peak emission in the optical and near infrared. This region is responsible for ~9% of the total emission at 24 micron and is likely a young star formation region. We show that this and other compact sources account for more than 1/3 of the total 24 micron emission. We compute a total infrared luminosity for NGC 55 of 1.2*10^9 L_sun. The star formation rate implied by our measurements is 0.22 M_sun/yr. We demonstrate that the cold dust is more extended than the warm dust in NGC 55--the minor-axis scale heights are 0.32, 0.43, and 0.49 kpc at 24, 70 and 160 micron, respectively. The dust temperature map shows a range of temperatures that are well-correlated with the 24 micron surface brightness, from 20 K in low-surface-brightness regions to 26 K in high-surface-brightness regions.
C. W. Engelbracht, M. Blaylock, K. Y. L. Su, J. Rho, G. H. Rieke, J. Muzerolle, D. L. Padgett, D. C. Hines, K. D. Gordon, D. Fadda, A. Noriega-Crespo, D. M. Kelly, W. B. Latter, J. L. Hinz, K. A. Misselt, J. E. Morrison, J. A. Stansberry, D. L. Shupe, S. Stolovy, Wm. A. Wheaton, E. T. Young, G. Neugebauer, S. Wachter, P. G. Pérez-González, D. T. Frayer, F. R. Marleau
Apr 17, 2007·astro-ph·PDF We present the stellar calibrator sample and the conversion from instrumental to physical units for the 24 micron channel of the Multiband Imaging Photometer for Spitzer (MIPS). The primary calibrators are A stars, and the calibration factor based on those stars is 4.54*10^{-2} MJy sr^{-1} (DN/s)^{-1}, with a nominal uncertainty of 2%. We discuss the data-reduction procedures required to attain this accuracy; without these procdures, the calibration factor obtained using the automated pipeline at the Spitzer Science Center is 1.6% +/- 0.6% lower. We extend this work to predict 24 micron flux densities for a sample of 238 stars which covers a larger range of flux densities and spectral types. We present a total of 348 measurements of 141 stars at 24 micron. This sample covers a factor of ~460 in 24 micron flux density, from 8.6 mJy up to 4.0 Jy. We show that the calibration is linear over that range with respect to target flux and background level. The calibration is based on observations made using 3-second exposures; a preliminary analysis shows that the calibration factor may be 1% and 2% lower for 10- and 30-second exposures, respectively. We also demonstrate that the calibration is very stable: over the course of the mission, repeated measurements of our routine calibrator, HD 159330, show a root-mean-square scatter of only 0.4%. Finally, we show that the point spread function (PSF) is well measured and allows us to calibrate extended sources accurately; Infrared Astronomy Satellite (IRAS) and MIPS measurements of a sample of nearby galaxies are identical within the uncertainties.
C. W. Engelbracht, G. H. Rieke, K. D. Gordon, J. -D. T. Smith, M. W. Werner, J. Moustakas, C. N. A. Willmer, L. Vanzi
Jan 11, 2008·astro-ph·PDF We present infrared observations of 66 starburst galaxies over a wide range of oxygen abundances, to measure how metallicity affects their dust properties. The data include imaging and spectroscopy from the Spitzer Space Telescope, supplemented by groundbased near-infrared imaging. We confirm a strong correlation of aromatic emission with metallicity, with a threshold at a metallicity [12+log(O/H)]~8. The large scatter in both the metallicity and radiation hardness dependence of this behavior implies that it is not due to a single effect, but to some combination. We show that the far-infrared color temperature of the large dust grains increases towards lower metallicity, peaking at a metallicity of 8 before turning over. We compute dust masses and compare them to HI masses from the literature to derive the gas to dust ratio, which increases by nearly 3 orders of magnitude between solar metallicity and a metallicity of 8, below which it flattens out. The abrupt change in aromatic emission at mid-infrared wavelengths thus appears to be reflected in the far-infrared properties, indicating that metallicity changes affect the composition of the full range of dust grain sizes that dominate the infrared emission. In addition, we find that the ratio L(8 micron)/L(TIR), important for calibrating 24 micron measurements of high redshift galaxies, increases slightly as the metallicity decreases from ~solar to ~50% of solar, and then decreases by an order of magnitude with further decreases in metallicity. Although the great majority of galaxies show similar patterns of behavior as described above, there are three exceptions, SBS 0335-052E, Haro 11, and SHOC 391. Their infrared SEDs are dominated energetically by the mid-IR near 24 micron rather than by the 60 - 200 micron region. (Abridged)
C. W. Engelbracht, K. D. Gordon, G. H. Rieke, M. W. Werner, D. A. Dale, W. B. Latter
We examine colors from 3.6 micron to 24 micron as a function of metallicity (O/H) for a sample of 34 galaxies. The galaxies range over 2 orders of magnitude in metallicity. They display an abrupt shift in the 8 micron to 24 micron color between metallicities 1/3 to 1/5 of the solar value. The mean 8 micron to 24 micron flux density ratio below and above 12 + log (O/H) = 8.2 is 0.08 +/- 0.04 and 0.70 +/- 0.53, respectively. We use mid-infrared colors and spectroscopy to demonstrate that the shift is primarily due to a decrease in the 8 micron flux density as opposed to an increase in the 24 micron flux density. This result is most simply interpreted as due to a weakening at low metallicity of the mid-infrared emission bands usually attributed to PAHs (polycyclic aromatic hydrocarbons) relative to the small-grain dust emission. However, existing empirical spectral energy distribution models cannot account for the observed short-wavelength (i.e., below 8 micron) colors of the low-metallicity galaxies merely by reducing the strength of the PAH features; some other emission source (e.g., hot dust) is required.
F. Kemper, Paul M. Woods, V. Antoniou, J. -P. Bernard, R. D. Blum, M. L. Boyer, J. Chan, C. -H. R. Chen, M. Cohen, C. Dijkstra, C. Engelbracht, M. Galametz, F. Galliano, C. Gielen, Karl D. Gordon, V. Gorjian, J. Harris, S. Hony, J. L. Hora, R. Indebetouw, O. Jones, A. Kawamura, E. Lagadec, B. Lawton, J. M. Leisenring, S. C. Madden, M. Marengo, M. Matsuura, I. McDonald, C. McGuire, M. Meixner, A. J. Mulia, B. O'Halloran, J. M. Oliveira, R. Paladini, D. Paradis, W. T. Reach, D. Rubin, K. Sandstrom, B. A. Sargent, M. Sewilo, B. Shiao, G. C. Sloan, A. K. Speck, S. Srinivasan, R. Szczerba, A. G. G. M. Tielens, E. van Aarle, S. D. Van Dyk, J. Th. van Loon, H. Van Winckel, Uma P. Vijh, K. Volk, B. A. Whitney, A. N. Wilkins, A. A. Zijlstra
The SAGE-Spec Spitzer Legacy program is a spectroscopic follow-up to the SAGE-LMC photometric survey of the Large Magellanic Cloud carried out with the Spitzer Space Telescope. We present an overview of SAGE-Spec and some of its first results. The SAGE-Spec program aims to study the life cycle of gas and dust in the Large Magellanic Cloud, and to provide information essential to the classification of the point sources observed in the earlier SAGE-LMC photometric survey. We acquired 224.6 hours of observations using the InfraRed Spectrograph and the SED mode of the Multiband Imaging Photometer for Spitzer. The SAGE-Spec data, along with archival Spitzer spectroscopy of objects in the Large Magellanic Cloud, are reduced and delivered to the community. We discuss the observing strategy, the specific data reduction pipelines applied and the dissemination of data products to the scientific community. Initial science results include the first detection of an extragalactic "21 um" feature towards an evolved star and elucidation of the nature of disks around RV Tauri stars in the Large Magellanic Cloud. Towards some young stars, ice features are observed in absorption. We also serendipitously observed a background quasar, at a redshift of z~0.14, which appears to be host-less.
M. Boquien, G. Bendo, D. Calzetti, D. Dale, C. Engelbracht, R. Kennicutt, J. C. Lee, L. van Zee, J. Moustakas
The total infrared (TIR) luminosity from galaxies can be used to examine both star formation and dust physics. We provide here new relations to estimate the TIR luminosity from various Spitzer bands, in particular from the 8 micron and 24 micron bands. To do so, we use 45" subregions within a subsample of nearby face-on spiral galaxies from the Spitzer Infrared Nearby Galaxies Survey (SINGS) that have known oxygen abundances as well as integrated galaxy data from the SINGS, the Local Volume Legacy Survey (LVL) and Engelbracht et al. (2008) samples. Taking into account the oxygen abundances of the subregions, the star formation rate intensity, and the relative emission of the polycyclic aromatic hydrocarbons at 8 micron, the warm dust at 24 micron and the cold dust at 70 micron and 160 micron we derive new relations to estimate the TIR luminosity from just one or two of the Spitzer bands. We also show that the metallicity and the star formation intensity must be taken into account when estimating the TIR luminosity from two wave bands, especially when data longward of 24 micron are not available.
G. H. Rieke, M. Blaylock, L. Decin, C. Engelbracht, P. Ogle, E. Avrett, J. Carpenter, R. M. Cutri, L. Armus, K. Gordon, R. O. Gray, J. Hinz, K. Su, Christopher N. A. Willmer
Jun 11, 2008·astro-ph·PDF We determine an absolute calibration for the MIPS 24 microns band and recommend adjustments to the published calibrations for 2MASS, IRAC, and IRAS photometry to put them on the same scale. We show that consistent results are obtained by basing the calibration on either an average A0V star spectral energy distribution (SED), or by using the absolutely calibrated SED of the sun in comparison with solar-type stellar photometry (the solar analog method). After the rejection of a small number of stars with anomalous SEDs (or bad measurements), upper limits of ~ 1.5% (rms) are placed on the intrinsic infrared SED variations in both A dwarf and solar-type stars. These types of stars are therefore suitable as general-purpose standard stars in the infrared. We provide absolutely calibrated SEDs for a standard zero magnitude A star and for the sun to allow extending this work to any other infrared photometric system. They allow the recommended calibration to be applied from 1 to 25 microns with an accuracy of ~2 %, and with even higher accuracy at specific wavelengths such as 2.2, 10.6, and 24 microns, near which there are direct measurements. However, we confirm earlier indications that Vega does not behave as a typical A0V star between the visible and the infrared, making it problematic as the defining star for photometric systems. The integration of measurements of the sun with those of solar-type stars also provides an accurate estimate of the solar SED from 1 through 30 microns, which we show agrees with theoretical models.
M. Meixner, F. Galliano, S. Hony, J. Roman-Duval, T. Robitaille, P. Panuzzo, M. Sauvage, K. Gordon, C. Engelbracht, K. Misselt, K. Okumura, T. Beck, J. -P. Bernard, A. Bolatto, C. Bot, M. Boyer, S. Bracker, L. R. Carlson, G. C. Clayton, C. -H. R. Chen, E. Churchwell, Y. Fukui, M. Galametz, J. L. Hora, A. Hughes, R. Indebetouw, F. P. Israel, A. Kawamura, F. Kemper, S. Kim, E. Kwon, B. Lawton, A. Li, K. S. Long, M. Marengo, S. C. Madden, M. Matsuura, J. M. Oliveira, T. Onishi, M. Otsuka, D. Paradis, A. Poglitsch, D. Riebel, W. T. Reach, M. Rubio, B. Sargent, M. Sewiło, J. D. Simon, R. Skibba, L. J. Smith, S. Srinivasan, A. G. G. M. Tielens, J. Th. van Loon, B. Whitney, P. M. Woods
The HERschel Inventory of The Agents of Galaxy Evolution (HERITAGE) of the Magellanic Clouds will use dust emission to investigate the life cycle of matter in both the Large and Small Magellanic Clouds (LMC and SMC). Using the Herschel Space Observatory's PACS and SPIRE photometry cameras, we imaged a 2x8 square degree strip through the LMC, at a position angle of ~22.5 degrees as part of the science demonstration phase of the Herschel mission. We present the data in all 5 Herschel bands: PACS 100 and 160 μm and SPIRE 250, 350 and 500 μm. We present two dust models that both adequately fit the spectral energy distribution for the entire strip and both reveal that the SPIRE 500 μm emission is in excess of the models by 6 to 17%. The SPIRE emission follows the distribution of the dust mass, which is derived from the model. The PAH-to-dust mass (f_PAH) image of the strip reveals a possible enhancement in the LMC bar in agreement with previous work. We compare the gas mass distribution derived from the HI 21 cm and CO J=1-0 line emission maps to the dust mass map from the models and derive gas-to-dust mass ratios (GDRs). The dust model, which uses the standard graphite and silicate optical properties for Galactic dust, has a very low GDR = 65(+15,-18) making it an unrealistic dust model for the LMC. Our second dust model, which uses amorphous carbon instead of graphite, has a flatter emissivity index in the submillimeter and results in a GDR = 287(+25,-42) that is more consistent with a GDR inferred from extinction.
S. Kim, E. Kwon, S. C. Madden, M. Meixner, S. Hony, P. Panuzzo, M. Sauvage, J. Roman-Duval, K. D. Gordon, C. Engelbracht, F. P. Israel, K. Misselt, K. Okumura, A. Li, A. Bolatto, R. Skibba, F. Galliano, M. Matsuura, J. -P. Bernard, C. Bot, M. Galametz, A. Hughes, A. Kawamura, T. Onishi, D. Paradis, A. Poglitsch, W. T. Reach, T. Robitaille, M. Rubio, A. G. G. M. Tielens
May 18, 2010·astro-ph.CO·PDF We present clumps of dust emission from Herschel observations of the Large Magellanic Cloud (LMC) and their physical and statistical properties. We catalog cloud features seen in the dust emission from Herschel observations of the LMC, the Magellanic type irregular galaxy closest to the Milky Way, and compare these features with HI catalogs from the ATCA+Parkes HI survey. Using an automated cloud-finding algorithm, we identify clouds and clumps of dust emission and examine the cumulative mass distribution of the detected dust clouds. The mass of cold dust is determined from physical parameters that we derive by performing spectral energy distribution fits to 250, 350, and 500 micronm emission from SPIRE observations using DUSTY and GRASIL radiative transfer calculation with dust grain size distributions for graphite/silicate in low-metallicity extragalactic environments. The dust cloud mass spectrum follows a power law distribution with an exponent of gamma=-1.8 for clumps larger than 400 solar mass and is similar to the HI mass distribution. This is expected from the theory of ISM structure in the vicinity of star formation.
R. D. Blum, J. R. Mould, K. A. Olsen, J. A. Frogel, M. Werner, M. Meixner, F. Markwick-Kemper, R. Indebetouw, B. Whitney, M. Meade, B. Babler, E. B. Churchwell, K. Gordon, C. Engelbracht, B. -Q. For, K. Misselt, U. Vijh, C. Leitherer, K. Volk, S. Points, W. Reach, J. L. Hora, J. -P. Bernard, F. Boulanger, S. Bracker, M. Cohen, Y. Fukui, J. Gallagher, V. Gorjian, J. Harris, D. Kelly, A. Kawamura, W. B. Latter, S. Madden, A. Mizuno, N. Mizuno, A. Nota, M. S. Oey, T. Onishi, R. Paladini, N. Panagia, P. Perez-Gonzalez, H. Shibai, S. Sato, L. Smith, L. Staveley-Smith, A. G. G. M. Tielens, T. Ueta, S. Van Dyk, D. Zaritsky
Color-magnitude diagrams (CMDs) are presented for the Spitzer SAGE (Surveying the Agents of a Galaxy's Evolution) survey of the Large Magellanic Cloud (LMC). IRAC and MIPS 24 um epoch one data are presented. These data represent the deepest, widest mid-infrared CMDs of their kind ever produced in the LMC. Combined with the 2MASS survey, the diagrams are used to delineate the evolved stellar populations in the Large Magellanic Cloud as well as Galactic foreground and extragalactic background populations. Some 32000 evolved stars brighter than the tip of the red giant branch are identified. Of these, approximately 17500 are classified as oxygen-rich, 7000 carbon-rich, and another 1200 as ``extreme'' asymptotic giant branch (AGB) stars. Brighter members of the latter group have been called ``obscured'' AGB stars in the literature owing to their dusty circumstellar envelopes. A large number (1200) of luminous oxygen--rich AGB stars/M supergiants are also identified. Finally, there is strong evidence from the 24 um MIPS channel that previously unexplored, lower luminosity oxygen-rich AGB stars contribute significantly to the mass loss budget of the LMC (1200 such sources are identified).
M. S. Bothwell, R. C. Kennicutt, B. D. Johnson, Y. Wu, J. C. Lee, D. Dale, C. Engelbracht, D. Calzetti, E. Skillman
We present total infrared (IR) and ultraviolet (UV) luminosity functions derived from large representative samples of galaxies at z ~ 0, selected at IR and UV wavelengths from the IRAS IIFSCz catalogue, and the GALEX AIS respectively. We augment these with deep Spitzer and GALEX imaging of galaxies in the 11 Mpc Local Volume Legacy Survey (LVL), allowing us to extend these luminosity functions to lower luminosities (~10^6 L_sun), and providing good constraints on the slope of the luminosity function at the extreme faint end for the first time. Using conventional star formation prescriptions, we generate from our data the SFR distribution function for the local Universe. We find that it has a Schechter form, that the faint-end slope has a constant value (to the limits of our data) of α = -1.51 \pm 0.08, and the 'characteristic' SFR is 9.2 M_sun/yr. We also show the distribution function of the SFR volume density; we then use this to calculate a value for the total SFR volume density at z ~ 0 of 0.025 \pm 0.0016 M_sun/yr/Mpc^-3, of which ~ 20% is occurring in starbursts. Decomposing the total star formation by infrared luminosity, it can be seen that 9 \pm 1% is due to LIRGs, and 0.7 \pm 0.2% is occuring in ULIRGs. By comparing UV and IR emission for galaxies in our sample, we also calculate the fraction of star formation occurring in dust obscured environments, and examine the distribution of dusty star formation: we find a very shallow slope at the highly extincted end, which may be attributable to line of sight orientation effects as well as conventional internal extinction.
E. J. Murphy, J. J. Condon, E. Schinnerer, R. C. Kennicutt, D. Calzetti, L. Armus, G. Helou, J. L. Turner, G. Aniano, P. Beirão, A. D. Bolatto, B. R. Brandl, K. V. Croxall, D. A. Dale, J. L. Donovan Meyer, B. T. Draine, C. Engelbracht, L. K. Hunt, C. -N. Hao, J. Koda, H. Roussel, R. Skibba, J. -D. T. Smith
May 24, 2011·astro-ph.CO·PDF Abridged: Using free-free emission measured in the Ka-band (26-40GHz) for 10 star-forming regions in the nearby galaxy NGC6946, including its starbursting nucleus, we compare a number of SFR diagnostics that are typically considered to be unaffected by interstellar extinction: i.e., non-thermal radio (i.e., 1.4GHz), total infrared (IR; 8-1000um), and warm dust (i.e., 24um) emission, along with the hybrid (obscured + unobscured) indicators of Hα+24um and UV+IR. The 33GHz free-free emission is assumed to provide the most accurate measure of the current SFR. Among the extranuclear star-forming regions, the 24um, Hα+24um and UV+IR SFR calibrations are in good agreement with the 33GHz free-free SFRs. However, each of the SFR calibrations relying on some form of dust emission overestimate the nuclear SFR by a factor of ~2. This is more likely the result of excess dust heating through an accumulation of non-ionizing stars associated with an extended episode of star formation in the nucleus rather than increased competition for ionizing photons by dust. SFR calibrations using the non-thermal radio continuum yield values which only agree with the free-free SFRs for the nucleus, and underestimate the SFRs from the extranuclear star-forming regions by a factor of ~2. This result likely arises from the CR electrons decaying within the starburst region with negligible escape compared to the young extranuclear star-forming regions. Finally, we find that the SFRs estimated using the total 33GHz emission agree well with the free-free SFRs due to the large thermal fractions present at these frequencies even when local diffuse backgrounds are not removed. Thus, rest-frame 33GHz observations may act as a reliable method to measure the SFRs of galaxies at increasingly high redshift without the need of ancillary radio data to account for the non-thermal emission.
M. Galametz, S. Hony, F. Galliano, S. C. Madden, M. Albrecht, C. Bot, D. Cormier, C. Engelbracht, Y. Fukui, F. P. Israel, A. Kawamura, V. Lebouteiller, A. Li, M. Meixner, K. Misselt, E. Montiel, K. Okumura, P. Panuzzo, J. Roman- Duval, M. Rubio, M. Sauvage, J. P. Seale, M. Sewilo, J. Th. van Loon
Feb 12, 2013·astro-ph.CO·PDF We present a study of the infrared/submm emission of the LMC star forming complex N158-N159-N160. Combining observations from the Spitzer Space Telescope (3.6-70um), the Herschel Space Observatory (100-500um) and LABOCA (870um) allows us to work at the best angular resolution available now for an extragalactic source. We observe a remarkably good correlation between SPIRE and LABOCA emission and resolve the low surface brightnesses emission. We use the Spitzer and Herschel data to perform a resolved Spectral Energy Distribution (SED) modelling of the complex. Using MBB, we derive a global emissivity index beta_c of 1.47. If beta cold is fixed to 1.5, we find an average temperature of 27K. We also apply the Galliano et al. (2011) modelling technique (and amorphous carbon to model carbon dust) to derive maps of the star formation rate, the mean starlight intensity, the fraction of PAHs or the dust mass surface density of the region. We observe that the PAH fraction strongly decreases in the HII regions. This decrease coincides with peaks in the mean radiation field intensity map. The dust surface densities follow the FIR distribution, with a total dust mass of 2.1x10^4 Msolar (2.8 times less than when using graphite grains) in the resolved elements we model. We find a non-negligible amount of dust in the molecular cloud N159 South (showing no massive SF). We also investigate the drivers of the Herschel/PACS and SPIRE submm colours as well as the variations in the gas-to-dust mass ratio (G/D) and the XCO conversion factor in the region N159. We finally model individual regions to analyse variations in the SED shape across the complex and the 870um emission in more details. No measurable submm excess emission at 870um seems to be detected in these regions.
E. Le Floc'h, C. Papovich, H. Dole, E. Bell, G. Lagache, G. Rieke, E. Egami, P. Perez-Gonzalez, A. Alonso-Herrero, M. Rieke, M. Blaylock, C. Engelbracht, K. Gordon, D. Hines, K. Misselt, J. Morrison, J. Mould
Jun 20, 2005·astro-ph·PDF We analyze a sample of ~2600 MIPS/Spitzer 24mic sources brighter than ~80muJy and located in the Chandra Deep Field South to characterize the evolution of the comoving infrared (IR) energy density of the Universe up to z~1. Using published ancillary optical data we first obtain a nearly complete redshift determination for the 24mic objects associated with R<24 counterparts at z<1. We find that the 24mic population at 0.5<z<1 is dominated by ``Luminous Infrared Galaxies'' (i.e., 10^11 L_sol < L_IR < 10^12 L_sol), the counterparts of which appear to be also luminous at optical wavelengths and tend to be more massive than the majority of optically-selected galaxies. We finally derive 15mic and total IR luminosity functions (LFs) up to z~1. In agreement with the previous results from ISO and SCUBA and as expected from the MIPS source number counts, we find very strong evolution of the contribution of the IR-selected population with lookback time. Pure evolution in density is firmly excluded by the data, but we find considerable degeneracy between strict evolution in luminosity and a combination of increases in both density and luminosity (L*_IR prop. to (1+z)^{3.2_{-0.2}^{+0.7}}, Phi*_IR prop. to (1+z)^{0.7_{-0.6}^{+0.2}}). Our results imply that the comoving IR energy density of the Universe evolves as (1+z)^(3.9+/-0.4) up to z~1 and that galaxies luminous in the infrared (i.e., L_IR > 10^11 L_IR) are responsible for 70+/-15% of this energy density at z~1. Taking into account the contribution of the UV luminosity evolving as (1+z)^~2.5, we infer that these IR-luminous sources dominate the star-forming activity beyond z~0.7. The uncertainties affecting these conclusions are largely dominated by the errors in the k-corrections used to convert 24mic fluxes into luminosities.
K. D. Gordon, F. Galliano, S. Hony, J. -P. Bernard, A. Bolatto, C. Bot, C. Engelbracht, A. Hughes, F. P. Israel, F. Kemper, S. Kim, A. Li, S. C. Madden, M. Matsuura, M. Meixner, K. Misselt, K. Okumura, P. Panuzzo, M. Rubio, W. T. Reach, J. Roman-Duval, M. Sauvage, R. Skibba, A. G. G. M. Tielens
May 14, 2010·astro-ph.CO·PDF The properties of the dust grains (e.g., temperature and mass) can be derived from fitting far-IR SEDs (>100 micron). Only with SPIRE on Herschel has it been possible to get high spatial resolution at 200 to 500 micron that is beyond the peak (~160 micron) of dust emission in most galaxies. We investigate the differences in the fitted dust temperatures and masses determined using only <200 micron data and then also including >200 micron data (new SPIRE observations) to determine how important having >200 micron data is for deriving these dust properties. We fit the 100 to 350 micron observations of the Large Magellanic Cloud (LMC) point-by-point with a model that consists of a single temperature and fixed emissivity law. The data used are existing observations at 100 and 160 micron (from IRAS and Spitzer) and new SPIRE observations of 1/4 of the LMC observed for the HERITAGE Key Project as part of the Herschel Science Demonstration phase. The dust temperatures and masses computed using only 100 and 160 micron data can differ by up to 10% and 36%, respectively, from those that also include the SPIRE 250 & 350 micron data. We find that an emissivity law proportional to lambda^-1.5 minimizes the 100-350 micron fractional residuals. We find that the emission at 500 micron is ~10% higher than expected from extrapolating the fits made at shorter wavelengths. We find the fractional 500 micron excess is weakly anti-correlated with MIPS 24 micron flux and the total gas surface density. This argues against a flux calibration error as the origin of the 500 micron excess. Our results do not allow us to distinguish between a systematic variation in the wavelength dependent emissivity law or a population of very cold dust only detectable at lambda > 500 micron for the origin of the 500 micron excess.
S. Hony, F. Galliano, S. C. Madden, P. Panuzzo, M. Meixner, C. Engelbracht, K. Misselt, M. Galametz, M. Sauvage, J. Roman-Duval, K. Gordon, B. Lawton, J. -P. Bernard, A. Bolatto, K. Okumura, C. -H. R. Chen, R. Indebetouw, F. P. Israel, E. Kwon, A. Li, F. Kemper, M. S. Oey, M. Rubio
May 11, 2010·astro-ph.CO·PDF We study the structure of the medium surrounding sites of high-mass star formation to determine the interrelation between the HII regions and the environment from which they were formed. The density distribution of the surroundings is key in determining how the radiation of the newly formed stars interacts with the surrounds in a way that allows it to be used as a star formation tracer. We present new Herschel/SPIRE 250, 350 and 500 mum data of LHA 120-N44 and LHA 120-N63 in the LMC. We construct average spectral energy distributions (SEDs) for annuli centered on the IR bright part of the star formation sites. The annuli cover ~10-~100 pc. We use a phenomenological dust model to fit these SEDs to derive the dust column densities, characterise the incident radiation field and the abundance of polycyclic aromatic hydrocarbon molecules. We see a factor 5 decrease in the radiation field energy density as a function of radial distance around N63. N44 does not show a systematic trend. We construct a simple geometrical model to derive the 3-D density profile of the surroundings of these two regions. Herschel/SPIRE data have proven very efficient in deriving the dust mass distribution. We find that the radiation field in the two sources behaves very differently. N63 is more or less spherically symmetric and the average radiation field drops with distance. N44 shows no systematic decrease of the radiation intensity which is probably due to the inhomogeneity of the surrounding molecular material and to the complex distribution of several star forming clusters in the region.
Geoffrey C. Clayton, B. Sargent, M. L. Boyer, B. A. Whitney, Jacco Th. van Loon, M. Meixner, P. Tisserand, C. Engelbracht, S. Hony, R. Indebetouw, K. A. Misselt, K. Okumura, P. Panuzzo, J. Roman-Duval, M. Sauvage, J. M. Oliveira, M. Sewilo, E. Churchwell
Aug 11, 2010·astro-ph.SR·PDF The LMC star, SSTISAGE1C J050756.44-703453.9, was first noticed during a survey of EROS-2 lightcurves for stars with large irregular brightness variations typical of the R Coronae Borealis (RCB) class. However, the visible spectrum showing emission lines including the Balmer and Paschen series as well as many Fe II lines is emphatically not that of an RCB star. This star has all of the characteristics of a typical UX Ori star. It has a spectral type of approximately A2 and has excited an H II region in its vicinity. However, if it is an LMC member, then it is very luminous for a Herbig Ae/Be star. It shows irregular drops in brightness of up to 2 mag, and displays the reddening and "blueing" typical of this class of stars. Its spectrum, showing a combination of emission and absorption lines, is typical of a UX Ori star that is in a decline caused by obscuration from the circumstellar dust. SSTISAGE1C J050756.44-703453.9 has a strong IR excess and significant emission is present out to 500 micron. Monte Carlo radiative transfer modeling of the SED requires that SSTISAGE1C J050756.44-703453.9 has both a dusty disk as well as a large extended diffuse envelope to fit both the mid- and far-IR dust emission. This star is a new member of the UX Ori subclass of the Herbig Ae/Be stars and only the second such star to be discovered in the LMC.