- ID:
- ivo://CDS.VizieR/J/ApJ/772/27
- Title:
- Pa{alpha} (1.87um) LF of HII regions in 12 galaxies
- Short Name:
- J/ApJ/772/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The H II region luminosity function (LF) is an important tool for deriving the birthrates and mass distribution of OB associations and is an excellent tracer of the newly formed massive stars and associations. To date, extensive work (predominantly in H{alpha}) has been done from the ground, which is hindered by dust extinction and the severe blending of adjacent (spatially or in projection) H II regions. Reliably measuring the properties of H II regions requires a linear resolution <40pc, but analyses satisfying this requirement have been done only in a handful of galaxies, so far. As the first space-based work using a galaxy sample, we have selected 12 galaxies from our HST/NICMOS Pa{alpha} survey and studied the LF and size distribution of H II regions both in individual galaxies and cumulatively, using a virtually extinction-free tracer of the ionizing photon rate. The high angular resolution and low sensitivity to diffuse emission of NICMOS also offer an advantage over ground-based imaging by enabling a higher degree of de-blending of the H II regions. We do not confirm the broken power-law LFs found in ground-based studies. Instead, we find that the LFs, both individual and co-added, follow a single power law dN(L)/dlnL{propto}L^-1^, are consistent with the mass function of star clusters in nearby galaxies, and are in agreement with the results of the existing analyses with Hubble Space Telescope (HST) data. The individual and co-added size distributions of H II regions are both roughly consistent with dN(D)/dlnD{propto}D^-3^, but the power-law scaling is probably contaminated by blended regions or complexes.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/892/23
- Title:
- Pa-beta, Ha and attenuation in NGC5194 & NGC6946
- Short Name:
- J/ApJ/892/23
- Date:
- 19 Jan 2022 08:58:18
- Publisher:
- CDS
- Description:
- We combine Hubble Space Telescope Paschen {beta} (Pa{beta}) imaging with ground-based, previously published H{alpha} maps to estimate the attenuation affecting H{alpha}, A(H{alpha}), across the nearby, face-on galaxies NGC 5194 and NGC 6946. We estimate A(H{alpha}) in ~2000 independent 2" ~75pc diameter apertures in each galaxy, spanning out to a galactocentric radius of almost 10kpc. In both galaxies, A(H{alpha}) drops with radius, with a bright, high-attenuation inner region, though in detail the profiles differ between the two galaxies. Regions with the highest attenuation-corrected H{alpha} luminosity show the highest attenuation, but the observed H{alpha} luminosity of a region is not a good predictor of attenuation in our data. Consistent with much previous work, the IR-to-H{alpha} color does a good job of predicting A(H{alpha}). We calculate the best-fit empirical coefficients for use combining H{alpha} with 8, 12, 24, 70, or 100{mu}m to correct for attenuation. These agree well with previous work, but we also measure significant scatter around each of these linear relations. The local atomic plus molecular gas column density, N(H), also predicts A(H{alpha}) well. We show that a screen with magnitude ~0.2 times that expected for a Milky Way gas-to-dust value does a reasonable job of explaining A(H{alpha}) as a function of N(H). This could be expected if only ~40% of gas and dust directly overlap regions of H{alpha} emission.
- ID:
- ivo://CDS.VizieR/J/A+A/638/A84
- Title:
- PACS observations of large main-belt asteroids
- Short Name:
- J/A+A/638/A84
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Non-resolved thermal infrared observations enable studies of thermal and physical properties of asteroid surfaces provided the shape and rotational properties of the target are well determined via thermo-physical models. We used calibration-programme Herschel PACS data (70, 100, 160 microns) and state-of-the-art shape models derived from adaptive-optics observations and/or optical light curves to constrain for the first time the thermal inertia of twelve large main-belt asteroids. We also modelled previously well-characterised targets such as (1) Ceres or (4) Vesta as they constitute important benchmarks. Using the scale as a free parameter, most targets required a re-scaling ~5% consistent with what would be expected given the absolute calibration error bars. This constitutes a good cross-validation of the scaled shape models, although some targets required larger re-scaling to reproduce the IR data. We obtained low thermal inertias typical of large main belt asteroids studied before, which continues to give support to the notion that these surfaces are covered by fine-grained insulating regolith. Although the wavelengths at which PACS observed are longwards of the emission peak for main-belt asteroids, they proved to be extremely valuable to constrain size and thermal inertia and not too sensitive to surface roughness. Finally, we also propose a graphical approach to help examine how different values of the exponent used for scaling the thermal inertia as a function of heliocentric distance (i.e. temperature) affect our interpretation of the results.
894. PAH features of AGN
- ID:
- ivo://CDS.VizieR/J/MNRAS/470/3071
- Title:
- PAH features of AGN
- Short Name:
- J/MNRAS/470/3071
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectral features from polycyclic aromatic hydrocarbon (PAH) molecules observed in the mid-infrared (mid-IR) range are typically used to infer the amount of recent and ongoing star formation on kiloparsec scales around active galactic nuclei (AGN) where more traditional methods fail. This method assumes that the observed PAH features are excited predominantly by star formation. With current ground-based telescopes and the upcoming James Webb Space Telescope, much smaller spatial scales can be probed and we aim at testing if this assumption still holds in the range of few tens to few hundreds of parsecs. For that, we spatially map the emitted 11.3um PAH surface flux as a function of distance from 0.4-4 arcsec from the centre in 28 nearby AGN using ground-based high-angular-resolution mid-IR spectroscopy. We detect and extract the 11.3um PAH feature in 13 AGN. The fluxes within each aperture are scaled to a luminosity-normalized distance from the nucleus to be able to compare intrinsic spatial scales of AGN radiation spanning about two orders of magnitude in luminosity. For this, we establish an empirical relation between the absorption-corrected X-ray luminosity and the sublimation radius in these sources. Once normalized, the radial profiles of the emitted PAH surface flux show similar radial slopes, with a power-law index of approximately -1.1, and similar absolute values, consistent within a factor of a few of each other as expected from the uncertainty in the intrinsic scale estimate. We interpret this as evidence that the profiles are caused by a common compact central physical process, either the AGN itself or circumnuclear star formation linked in strength to the AGN power. A photoionization-based model of an AGN exciting dense clouds in its environment can reproduce the observed radial slope and confirms that the AGN radiation field is strong enough to explain the observed PAH surface fluxes within ~10-500pc of the nucleus. Our results advice caution in the use of PAH emission as a star formation tracer within a kpc around AGN.
- ID:
- ivo://CDS.VizieR/J/ApJ/884/136
- Title:
- PAH features of star-forming gal. using Spitzer/IRS
- Short Name:
- J/ApJ/884/136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Polycyclic aromatic hydrocarbon (PAH) emission has long been proposed to be a potential star formation rate indicator, as it arises from the photodissociation region bordering the Stromgren sphere of young, massive stars. We apply a recently developed technique of mid-infrared spectral decomposition to obtain a uniform set of PAH measurements from Spitzer low-resolution spectra of a large sample of star-forming galaxies spanning a wide range in stellar mass (M_*_~10^6^-10^11.4^M_{sun}_) and star formation rate (~0.1-2000M_{sun}_/yr). High-resolution spectra are also analyzed to measure [NeII]12.8{mu}m and [NeIII]15.6{mu}m, which effectively trace the Lyman continuum. We present a new relation between PAH luminosity and star formation rate based on the [NeII] and [NeIII] lines. Calibrations are given for the integrated 5-15{mu}m PAH emission, the individual features at 6.2, 7.7, 8.6, and 11.3{mu}m, as well as several mid- infrared bandpasses sensitive to PAH. We confirm that PAH emission is suppressed in low-mass dwarf galaxies, and we discuss the possible physical origin of this effect.
896. PAH hypothesis
- ID:
- ivo://CDS.VizieR/J/A+A/319/318
- Title:
- PAH hypothesis
- Short Name:
- J/A+A/319/318
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- IR spectra of anthracene and pyrene derivatives, serving as models for isolated, linear and isolated, compact PAHs, respectively, have been calculated using ab-initio quantum mechanical methods. The separate and combined effects of ionization and multiple dehydrogenation have been studied. This study confirms and refines the trends of our preliminary paper on the smallest possible PAH, naphthalene. If small PAHs are responsible for any UIR bands, they should be ionized and partially dehydrogenated, with a few triple bonds at the periphery of the carbon skeleton. In the appendix are given the complete IR spectra of all the isomers of the derivatives of anthracene and pyrene calculated for the purpose of this study. Tables I are for anthracene and Tables II for pyrene. Positions of the the missing hydrogens in the dehydrogenated species are referred as in Figures 1 and 2 of the original publication.
- ID:
- ivo://CDS.VizieR/J/ApJ/705/885
- Title:
- PAH in galaxies at z~0.1
- Short Name:
- J/ApJ/705/885
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the analysis of the polycyclic aromatic hydrocarbon (PAH) spectra of a sample of 92 typical star-forming galaxies at 0.03<z<0.2 observed with the Spitzer intensified Reticon spectrograph (IRS). We compare the relative strengths of PAH emission features with Sloan Digital Sky Survey optical diagnostics to probe the relationship between PAH grain properties and star formation and active galactic nuclei (AGNs) activity. Short-to-long wavelength PAH ratios, and in particular the 7.7um-to-11.3um feature ratio, are strongly correlated with the star formation diagnostics D_n_(4000) and H{alpha} equivalent width, increasing with younger stellar populations. This ratio also shows a significant difference between active and non-active galaxies, with the active galaxies exhibiting weaker 7.7um emission. A hard radiation field as measured by [OIII]/H{beta} and [NeIII]_15.6um_/[NeII]_12.8um_ effects PAH ratios differently depending on whether this field results from starburst activity or an AGN. Our results are consistent with a picture in which larger PAH molecules grow more efficiently in richer media and in which smaller PAH molecules are preferentially destroyed by the AGN.
- ID:
- ivo://CDS.VizieR/J/ApJS/240/19
- Title:
- Parallaxes of late-T and Y dwarfs
- Short Name:
- J/ApJS/240/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present preliminary trigonometric parallaxes of 184 late-T and Y dwarfs using observations from Spitzer (143), the U.S. Naval Observatory (18), the New Technology Telescope (14), and the United Kingdom Infrared Telescope (9). To complete the 20pc census of >=T6 dwarfs, we combine these measurements with previously published trigonometric parallaxes for an additional 44 objects and spectrophotometric distance estimates for another 7. For these 235 objects, we estimate temperatures, sift into five 150K wide T_eff_ bins covering the range 300-1050K, determine the completeness limit for each, and compute space densities. To anchor the high-mass end of the brown dwarf mass spectrum, we compile a list of early- to mid-L dwarfs within 20pc. We run simulations using various functional forms of the mass function passed through two different sets of evolutionary code to compute predicted distributions in T_eff_. The best fit of these predictions to our L, T, and Y observations is a simple power-law model with {alpha}~0.6 (where dN/dM{propto}M^-{alpha}^), meaning that the slope of the field substellar mass function is in rough agreement with that found for brown dwarfs in nearby star-forming regions and young clusters. Furthermore, we find that published versions of the log-normal form do not predict the steady rise seen in the space densities from 1050 to 350K. We also find that the low-mass cutoff to formation, if one exists, is lower than ~5M_Jup_, which corroborates findings in young, nearby moving groups and implies that extremely low-mass objects have been forming over the lifetime of the Milky Way.
- ID:
- ivo://CDS.VizieR/J/MNRAS/471/770
- Title:
- Parameters and IR excesses of Gaia DR1 stars
- Short Name:
- J/MNRAS/471/770
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Effective temperatures and luminosities are calculated for 1,475,921 Tycho-2 and 107,145 Hipparcos stars, based on distances from Gaia Data Release 1. Parameters are derived by comparing multi-wavelength archival photometry to BT-Settl model atmospheres. The 1-sigma uncertainties for the Tycho-2 and Hipparcos stars are +/-137K and +/-125K in temperature and +/-35 per cent and +/-19 per cent in luminosity. The luminosity uncertainty is dominated by that of the Gaia parallax. Evidence for infrared excess between 4.6 and 25 microns is found for 4256 stars, of which 1883 are strong candidates. These include asymptotic giant branch (AGB) stars, Cepheids, Herbig Ae/Be stars, young stellar objects, and other sources. We briefly demonstrate the capabilities of this dataset by exploring local interstellar extinction, the onset of dust production in AGB stars, the age and metallicity gradients of the solar neighbourhood and structure within the Gould Belt. We close by discussing the potential impact of future Gaia data releases.
- ID:
- ivo://CDS.VizieR/J/AJ/159/254
- Title:
- Parameters for 453 metal-poor stars in NGC5139
- Short Name:
- J/AJ/159/254
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The most massive and complex globular clusters in the Galaxy are thought to have originated as the nuclear cores of now tidally disrupted dwarf galaxies, but the connection between globular clusters and dwarf galaxies is tenuous with the M54/Sagittarius system representing the only unambiguous link. The globular cluster Omega Centauri ({omega}Cen) is more massive and chemically diverse than M54, and is thought to have been the nuclear star cluster of either the Sequoia or Gaia-Enceladus galaxy. Local Group dwarf galaxies with masses equivalent to these systems often host significant populations of very metal-poor stars ([Fe/H]<-2.5), and one might expect to find such objects in {omega}Cen. Using high-resolution spectra from Magellan-M2FS, we detected 11 stars in a targeted sample of 395 that have [Fe/H] ranging from -2.30 to -2.52. These are the most metal-poor stars discovered in the cluster, and are five times more metal-poor than {omega}Cen's dominant population. However, these stars are not so metal-poor as to be unambiguously linked to a dwarf galaxy origin. The cluster's metal-poor tail appears to contain two populations near [Fe/H]~-2.1 and -2.4, which are very centrally concentrated but do not exhibit any peculiar kinematic signatures. Several possible origins for these stars are discussed.
