- 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.
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Search Results
- 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/ApJ/768/74
- Title:
- PHIBSS: CO observations of star-forming galaxies
- Short Name:
- J/ApJ/768/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present PHIBSS, the IRAM Plateau de Bure high-z blue sequence CO(3-2) survey of the molecular gas properties in massive, main-sequence star-forming galaxies (SFGs) near the cosmic star formation peak. PHIBSS provides 52 CO detections in two redshift slices at z~1.2 and 2.2, with log(M_*_(M_{sun}_))>=10.4 and log(SFR(M_{sun}_/yr))>=1.5. Including a correction for the incomplete coverage of the M_*_-SFR plane, and adopting a "Galactic" value for the CO-H_2_ conversion factor, we infer average gas fractions of ~0.33 at z~1.2 and ~0.47 at z~2.2. Gas fractions drop with stellar mass, in agreement with cosmological simulations including strong star formation feedback. Most of the z~1-3 SFGs are rotationally supported turbulent disks. The sizes of CO and UV/optical emission are comparable. The molecular-gas-star-formation relation for the z=1-3 SFGs is near-linear, with a ~0.7Gyr gas depletion timescale; changes in depletion time are only a secondary effect. Since this timescale is much less than the Hubble time in all SFGs between z~0 and 2, fresh gas must be supplied with a fairly high duty cycle over several billion years. At given z and M_*_, gas fractions correlate strongly with the specific star formation rate (sSFR). The variation of sSFR between z~0 and 3 is mainly controlled by the fraction of baryonic mass that resides in cold gas.
- ID:
- ivo://CDS.VizieR/J/AJ/125/465
- Title:
- Phoenix Deep Survey 1.4-GHz microJy Catalog
- Short Name:
- J/AJ/125/465
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The initial Phoenix Deep Survey (PDS) observations with the Australia Telescope Compact Array have been supplemented by additional 1.4 GHz observations over the past few years. Here we present details of the construction of a new mosaic image covering an area of 4.56 deg2, an investigation of the reliability of the source measurements, and the 1.4 GHz source counts for the compiled radio catalog. The mosaic achieves a 1-sigma rms noise of 12 microJy at its most sensitive, and a homogeneous radio-selected catalog of over 2000 sources reaching flux densities as faint as 60 microJy has been compiled. The source parameter measurements are found to be consistent with the expected uncertainties from the image noise levels and the Gaussian source fitting procedure. A radio-selected sample avoids the complications of obscuration associated with optically selected samples, and by utilizing complementary PDS observations, including multicolor optical, near-infrared, and spectroscopic data, this radio catalog will be used in a detailed investigation of the evolution in star formation spanning the redshift range 0 < z < 1. The homogeneity of the catalog ensures a consistent picture of galaxy evolution can be developed over the full cosmologically significant redshift range of interest.
- ID:
- ivo://CDS.VizieR/J/MNRAS/296/839
- Title:
- Phoenix Deep Survey: 1.4-GHz source counts
- Short Name:
- J/MNRAS/296/839
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results from the Phoenix Deep Survey, a multiwavelength survey of a 2 deg diameter region. Observations in the radio continuum at 1.4 GHz carried out with the Australia Telescope Compact Array are described. The catalogue of over 1000 radio sources compiled from these observations is analyzed, and the source counts are presented. We model the observational source counts using a two-population model and published luminosity functions for these populations. Upon invoking luminosity and density evolution, we find that a luminosity evolution model best fits the radio observations, consistent with earlier work. The redshift distribution of the two galaxy populations investigated is also modeled and discussed.
- ID:
- ivo://CDS.VizieR/J/A+A/375/670
- Title:
- Photographic observations of radio stars
- Short Name:
- J/A+A/375/670
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- At the Engelhardt Astronomical Observatory (EAO), we observed photographic positions of 113 Galactic Radio Sources (GRS) in the system PPM catalogue (Rizvanov & Dautov, 1998, Kinematics and physics celestial bodies, 5, 457). Analysis of their accuracy is made by comparison with the Hipparcos catalogue (Perryman et al., 1997, Vat. <I/239>) and astrometric catalogue of radio stars in the radio window from the article of Walter et al. (1990A&AS...86..357W).
- ID:
- ivo://CDS.VizieR/J/ApJ/704/548
- Title:
- Photometric properties of galaxies at z=4-6
- Short Name:
- J/ApJ/704/548
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new information on galaxies in the vicinity of luminous radio galaxies (RGs) and quasars at z~4, 5, and 6. These fields were previously found to contain overdensities of Lyman Break Galaxies (LBGs) or spectroscopic Ly{alpha} emitters (LAEs), which were interpreted as evidence for clusters-in-formation ("protoclusters"). We use Hubble Space Telescope and Spitzer data to infer stellar masses from stellar synthesis models calibrated against the Millennium Run simulations, and contrast our results with large samples of LBGs in more average environments as probed by the Great Observatories Origins Deep Survey (GOODS).
- ID:
- ivo://CDS.VizieR/J/ApJ/723/492
- Title:
- Physical properties of GRS molecular clouds
- Short Name:
- J/ApJ/723/492
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive the physical properties of 580 molecular clouds based on their ^12^CO and ^13^CO line emission detected in the University of Massachusetts-Stony Brook (UMSB) and Galactic Ring surveys (GRS). We provide a range of values of the physical properties of molecular clouds, and find a power-law correlation between their radii and masses, suggesting that the fractal dimension of the interstellar medium is around 2.36. This relation, M=(228+/-18)R^2.36+/-0.04^, allows us to derive masses for an additional 170 Galactic Ring Survey (GRS) molecular clouds not covered by the UMSB survey. We derive the Galactic surface mass density of molecular gas and examine its spatial variations throughout the Galaxy. We find that the azimuthally averaged Galactic surface density of molecular gas peaks between Galactocentric radii of 4 and 5kpc. Although the Perseus arm is not detected in molecular gas, the Galactic surface density of molecular gas is enhanced along the positions of the Scutum-Crux and Sagittarius arms.
- ID:
- ivo://CDS.VizieR/J/ApJ/725/1792
- Title:
- Pi Ghz Sky Survey (PiGSS). I.
- Short Name:
- J/ApJ/725/1792
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Pi GHz Sky Survey (PiGSS) is a key project of the Allen Telescope Array. PiGSS is a 3.1GHz survey of radio continuum emission in the extragalactic sky with an emphasis on synoptic observations that measure the static and time-variable properties of the sky. During the 2.5 year campaign, PiGSS will twice observe ~250000 radio sources in the 10000deg^2^ region of the sky with b>30{deg} to an rms sensitivity of ~1mJy. Additionally, sub-regions of the sky will be observed multiple times to characterize variability on timescales of days to years. We present here observations of a 10deg^2^ region in the Bootes constellation overlapping the NOAO Deep Wide Field Survey field. The PiGSS image was constructed from 75 daily observations distributed over a 4 month period and has an rms flux density between 200 and 250uJy. This represents a deeper image by a factor of 4-8 than we will achieve over the entire 10000deg^2^. We provide flux densities, source sizes, and spectral indices for the 425 sources detected in the image. We identify ~100 new flat-spectrum radio sources; we project that when completed PiGSS will identify 104 flat-spectrum sources. We identify one source that is a possible transient radio source. This survey provides new limits on faint radio transients and variables with characteristic durations of months.
- ID:
- ivo://CDS.VizieR/J/ApJ/739/76
- Title:
- Pi GHz Sky Survey (PiGSS). II.
- Short Name:
- J/ApJ/739/76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from daily radio continuum observations of the Bootes field as part of the Pi GHz Sky Survey (PiGSS). These results are part of a systematic and unbiased campaign to characterize variable and transient sources in the radio sky. The observations include 78 individual epochs distributed over five months at a radio frequency of 3.1GHz with a median rms image noise in each epoch of 2.8mJy. We produce five monthly images with a median rms of 0.6mJy. No transient radio sources are detected in the daily or monthly images. At 15mJy, we set an upper limit (2{sigma}) to the surface density of one-day radio transients at 0.025deg^-2^. At 5mJy, we set an upper limit (2{sigma}) to the surface density of one-month radio transients at 0.18deg^-2^. We also produce light curves for 425 sources and explore the variability properties of these sources. Approximately 20% of the sources exhibit some variability on daily and monthly timescales. The maximum rms fractional modulations on the one-day and one-month timescales for sources brighter than 10mJy are 2 and 0.5, respectively. The probability of a daily fluctuation for all sources and all epochs by a factor of 10 is less than 10^-4^. We compare the radio to mid-infrared variability for sources in the field and find no correlation. Finally, we apply the statistics of transient and variable populations to constrain models for a variety of source classes.
