- 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.
Number of results to display per page
Search Results
672. 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/A+A/514/A5
- Title:
- PAH luminous galaxies at z~1
- Short Name:
- J/A+A/514/A5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The NEP-deep survey, an extragalactic AKARI survey towards the north ecliptic pole (NEP), provides a comprehensive wavelength coverage from 2 to 24um using all 9 photometric bands of the infrared camera (IRC). It allows us to photometrically identify galaxies whose mid-IR emission is clearly dominated by PAHs. We propose a single-colour selection method to identify such galaxies, using two mid-IR flux ratios at 11-to-7um and 15-to-9um (PAH-to-continuum flux ratio in the rest frame), which are useful for identifying starburst galaxies at z~0.5 and 1, respectively. We perform a fitting of the spectral energy distributions (SEDs) from optical to mid-IR wavelengths, using an evolutionary starburst model with a proper treatment of radiative transfer (SBURT), in order to investigate their nature.
- ID:
- ivo://CDS.VizieR/J/ApJ/899/15
- Title:
- Parameters for the 58 {tau}HI(v) sightlines
- Short Name:
- J/ApJ/899/15
- Date:
- 14 Mar 2022 07:09:23
- Publisher:
- CDS
- Description:
- Resolving the phase structure of neutral hydrogen (HI) is crucial for understanding the life cycle of the interstellar medium (ISM). However, accurate measurements of HI temperature and density are limited by the availability of background continuum sources for measuring HI absorption. Here we test the use of deep learning for extracting HI properties over large areas without optical depth information. We train a 1D convolutional neural network using synthetic observations of 3D numerical simulations of the ISM to predict the fraction (f_CNM_) of cold neutral medium (CNM) and the correction to the optically thin HI column density for optical depth (R_H_I__) from 21cm emission alone. We restrict our analysis to high Galactic latitudes (|b|>30{deg}), where the complexity of spectral line profiles is minimized. We verify that the network accurately predicts f_CNM_ and R_H_I__ by comparing the results with direct constraints from 21cm absorption. By applying the network to the GALFA-HI survey, we generate large-area maps of f_CNM_ and R_H_I__. Although the overall contribution to the total HI column of CNM-rich structures is small (~5%), we find that these structures are ubiquitous. Our results are consistent with the picture that small-scale structures observed in 21cm emission aligned with the magnetic field are dominated by CNM. Finally, we demonstrate that the observed correlation between HI column density and dust reddening (E(B-V)) declines with increasing R_H_I__, indicating that future efforts to quantify foreground Galactic E(B-V) using HI, even at high latitudes, should increase fidelity by accounting for HI phase structure.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A117
- Title:
- Perpendicular HF map to the Orion Bar
- Short Name:
- J/A+A/631/A117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The hydrogen fluoride (HF) molecule is seen in absorption in the interstellar medium (ISM) along many lines of sight. Surprisingly, it is observed in emission toward the Orion Bar, which is an interface between the ionized region around the Orion Trapezium stars and the Orion molecular cloud. We aim to understand the origin of HF emission in the Orion Bar by comparing its spatial distribution with other tracers. We examine three mechanisms to explain the HF emission: thermal excitation, radiative dust pumping, and chemical pumping. We used a Herschel/HIFI strip map of the HF J=1-0 line, covering 0.5' by 1.5' that is oriented perpendicular to the Orion Bar. We used the RADEX non-local thermodynamic equilibrium (non-LTE) code to construct the HF column density map. We use the Meudon PDR code to explain the morphology of HF. The bulk of the HF emission at 10km/s emerges from the CO-dark molecular gas that separates the ionization front from the molecular gas that is deeper in the Orion Bar. The excitation of HF is caused mainly by collisions with H2 at a density of 10^5^cm^-3^ together with a small contribution of electrons in the interclump gas of the Orion Bar. Infrared pumping and chemical pumping are not important. We conclude that the HF J=1-0 line traces CO-dark molecular gas. Similarly, bright photodissociation regions associated with massive star formation may be responsible for the HF emission observed toward active galactic nuclei.
- ID:
- ivo://CDS.VizieR/J/ApJ/793/132
- Title:
- Perseus cloud sources Gaussian parameters
- Short Name:
- J/ApJ/793/132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the Arecibo Observatory, we have obtained neutral hydrogen (HI) absorption and emission spectral pairs in the direction of 26 background radio continuum sources in the vicinity of the Perseus molecular cloud. Strong absorption lines were detected in all cases, allowing us to estimate spin temperature (T_s_) and optical depth for 107 individual Gaussian components along these lines of sight. Basic properties of individual H I clouds (spin temperature, optical depth, and the column density of the cold and warm neutral medium (CNM and WNM), respectively) in and around Perseus are very similar to those found for random interstellar lines of sight sampled by the Millennium H I survey. This suggests that the neutral gas found in and around molecular clouds is not atypical. However, lines of sight in the vicinity of Perseus have, on average, a higher total H I column density and the CNM fraction, suggesting an enhanced amount of cold H I relative to an average interstellar field. Our estimated optical depth and spin temperature are in stark contrast with the recent attempt at using Planck data to estimate properties of the optically thick H I. Only ~15% of lines of sight in our study have a column density weighted average spin temperature lower than 50 K, in comparison with >~85% of Planck's sky coverage. The observed CNM fraction is inversely proportional to the optical depth weighted average spin temperature, in excellent agreement with the recent numerical simulations by Kim et al. (2014ApJ...786...64K). While the CNM fraction is, on average, higher around Perseus relative to a random interstellar field, it is generally low, between 10%-50%. This suggests that extended WNM envelopes around molecular clouds and/or significant mixing of CNM and WNM throughout molecular clouds are present and should be considered in the models of molecule and star formation. Our detailed comparison of H I absorption with CO emission spectra shows that only 3 of the 26 directions are clear candidates for probing the CO-dark gas as they have N(H I)>10^21^/cm2 yet no detectable CO emission.
- ID:
- ivo://CDS.VizieR/J/A+A/587/A106
- Title:
- Perseus dust optical depth and column density maps
- Short Name:
- J/A+A/587/A106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present optical depth and temperature maps of the Perseus molecular cloud, obtained combining dust emission data from the Herschel and Planck satellites and 2MASS/NIR dust extinction maps. The maps have a resolution of 36~arcsec in the Herschel regions, and of 5~arcmin elsewhere. The dynamic range of the optical depth map ranges from 1x10^-2^mag up to 20mag in the equivalent K band extinction. We also evaluate the ratio between the SI2.2{mu} extinction coefficient and the SI850{mu} opacity. The value we obtain is close to the one found in the Orion B molecular cloud. We show that the cumulative and the differential area function of the data (which is proportional to the probability distribution function of the cloud column density) follow power laws with index respectively ~=-2, and ~=-3. We use WISE data to improve current YSO catalogs based mostly on Spitzer data and we build an up-to-date selection of Class I/0 objects. Using this selection, we evaluate the local Schmidt law, {Sigma}_YSO{prop.to}{Sigma}_gas_^{beta}^, showing that {beta}=2.4+/-0.6. Finally, we show that the area-extinction relation is important for determining the star formation rate in the cloud, which is in agreement with other recent works.
- ID:
- ivo://CDS.VizieR/J/ApJS/236/51
- Title:
- PGCCs in lambda Orionis complex. II. Cores at 850um
- Short Name:
- J/ApJS/236/51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on the 850{mu}m dust continuum data from SCUBA-2 at James Clerk Maxwell Telescope (JCMT), we compare overall properties of Planck Galactic Cold Clumps (PGCCs) in the {lambda} Orionis cloud to those of PGCCs in the Orion A and B clouds. The Orion A and B clouds are well-known active star-forming regions, while the {lambda} Orionis cloud has a different environment as a consequence of the interaction with a prominent OB association and a giant HII region. PGCCs in the {lambda} Orionis cloud have higher dust temperatures (T_d_=16.13+/-0.15K) and lower values of dust emissivity spectral index ({beta}=1.65+/-0.02) than PGCCs in the Orion A (T_d_=13.79+/-0.21K, {beta}=2.07+/-0.03) and Orion B (T_d_=13.82+/-0.19K, {beta}=1.96+/-0.02) clouds. We find 119 substructures within the 40 detected PGCCs and identify them as cores. Out of a total of 119 cores, 15 cores are discovered in the {lambda} Orionis cloud, while 74 and 30 cores are found in the Orion A and B clouds, respectively. The cores in the {lambda} Orionis cloud show much lower mean values of size R=0.08pc, column density N(H_2_)=(9.5+/-1.2)x10^22^cm^-2^, number density n(H_2_)=(2.9+/-0.4)x10^5^cm^-3^, and mass M_core_=1.0+/-0.3M_{sun}_ compared to the cores in the Orion A [R=0.11pc, N(H_2_)=(2.3+/-0.3)x10^23^cm^-2^, n(H_2_)=(3.8+/-0.5)x10^5^cm^-3^, and M_core_=2.4+/-0.3M_{sun}_] and Orion B [R=0.16pc, N(H_2_)=(3.8+/-0.4)x10^23^cm^-2^, n(H_2_)=(15.6+/-1.8)x10^5^cm^-3^, and M_core_=2.7+/-0.3M_{sun}_] clouds. These core properties in the {lambda} Orionis cloud can be attributed to the photodissociation and external heating by the nearby H II region, which may prevent the PGCCs from forming gravitationally bound structures and eventually disperse them. These results support the idea of negative stellar feedback on core formation.
- ID:
- ivo://CDS.VizieR/J/ApJ/796/36
- Title:
- PH_2_CN/CH_3_PH_2_ rotational transition frequency
- Short Name:
- J/ApJ/796/36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Millimeter/submillimeter spectra of PH_2_CN(~{X} ^1^A') and CH_3_PH_2_(~{X} ^1^A') have been recorded for the first time using direct absorption techniques. This work extends previous measurements of both molecules beyond the 10-50 GHz range. Both species were created in the presence of an AC discharge by the reaction of phosphorus vapor and either cyanogen and hydrogen (PH_2_CN) or methane (CH_3_PH_2_). Twelve rotational transitions of PH_2_CN were recorded over the region 305-422 GHz for asymmetry components K_a_=0 through 8. For CH_3_PH_2_, eight rotational transitions were measured from 210-470 GHz with K_a_=0 through 16; these spectra exhibited greater complexity due to the presence of internal rotation, which splits the K_a_=1, 2, and 3 asymmetry components into A and E states. Combined analyses of the millimeter/submillimeter and previous microwave data were performed for both molecules. For PH_2_CN, the spectra were fit with a Watson S-reduced asymmetric top Hamiltonian, resulting in more accurate rotational and centrifugal distortion constants. In the case of CH_3_PH_2_, an asymmetric top internal-rotation Hamiltonian was employed in the analysis, significantly improving the rotational and torsional parameters over previous microwave estimates. Searches for both molecules were subsequently conducted toward Sgr B2(N), using the 12 m telescope of the Arizona Radio Observatory (ARO). Neither species was identified, with abundance upper limits, relative to H_2_, of f(PH_2_CN/H_2_)<7.0x10^-12^ and f(CH_3_PH_2_/H_2_)<8.4x10^-12^. The nitrogen analogs NH_2_CN and CH_3_NH_2_ are therefore more abundant in Sgr B2(N) by factors of >2 and >200, respectively.
