Cosmic γ rays and the mass of gas in the Galaxy

Bhat, C. L.; Issa, M. R.; Houston, B. P.; Mayer, C. J.; Wolfendale, A. W.

doi:10.1038/314511a0

Cited by 54 publications

(14 citation statements)

References 23 publications

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“…If, as seems possible, it is CR interacting with gas that gives rise to a pseudo‐CMB contribution, then there should be an excess of Δ T (CMB) in regions where the CR intensity is high. Probably the best evidence for high CR intensities comes from studies of gamma‐rays (typically above 100 MeV) from SNR shocks (Bhat et al 1985; Wolfendale & Zhang 1994). It has been known for some years that the famous Loop I SNR has somewhat higher gamma‐ray emission than expected (Bhat et al 1985; Wolfendale & Zhang 1994).…”

Section: Cr–cmb Correlationsmentioning

confidence: 99%

“…Probably the best evidence for high CR intensities comes from studies of gamma‐rays (typically above 100 MeV) from SNR shocks (Bhat et al 1985; Wolfendale & Zhang 1994). It has been known for some years that the famous Loop I SNR has somewhat higher gamma‐ray emission than expected (Bhat et al 1985; Wolfendale & Zhang 1994). Most came from the well‐developed ridge which is seen in radio, e.g.…”

Section: Cr–cmb Correlationsmentioning

confidence: 99%

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Foreground contributions to the cosmic microwave background

Wibig

Wolfendale

2005

Monthly Notices of the Royal Astronomical Society

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A detailed search has been made for evidence of residual foreground contributions to the cosmic microwave background (CMB) in the map generated by the Wilkinson Microwave Anisotropy Probe (WMAP), a map that has been (nominally) cleaned for the foreground already. We find positive results in that various features relate to Galactic properties. For example, on the largest angular scales we find significant differences between the power in the fluctuations for positive and negative Galactic latitudes and between the four Galactic quadrants. There are also differences between the power spectrum at latitudes within 10° of the plane and at higher latitudes. The mean temperature shows similar variations. An explanation in terms of Galactic effects seems inescapable. In an effort to find the origin of these Galactic‐style effects we have examined evidence from Galactic gamma‐rays, specifically from the EGRET instrument. We are mindful that the CMB maps examined have already been ‘cleaned’ (for CR and other effects) in a rather complex way, but, in our view, the cleaning has left some potentially serious ‘contaminations’. A correlation is found between gamma‐ray intensities and the CMB and other CR indicators. For example, regions of the Galaxy having (line‐of‐sight) steep CR energy spectra have low mean CMB temperatures, and the important Loop I edge region, where the CR intensity is high, has a high mean temperature. Most of the large‐scale Galactic asymmetries (e.g. north–south difference and quadrant variations) have analogues in CR asymmetries and also in some other Galactic properties, such as the column density of gas. Thus, it is possible to hypothesize about direct CR‐induced contributions, although it may be that CRs are simply the indicators of Galactic ‘conditions’ which are influencing the residual CMB fluctuations. Irrespective of the actual cause of the correlations we have endeavoured to extrapolate to the situation where the residual foreground is minimized. The effect on the usually derived cosmological properties is briefly examined. The least that can be said is that the ‘error’ in some of these properties has been underestimated.

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Section: Cr–cmb Correlationsmentioning

confidence: 99%

Section: Cr–cmb Correlationsmentioning

confidence: 99%

Foreground contributions to the cosmic microwave background

Wibig

Wolfendale

2005

Monthly Notices of the Royal Astronomical Society

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“…In molecular clouds in our Galaxy, the observed γ-ray flux arising from the cosmic ray interactions with H 2 can be used to recover H 2 gas mass accurately (Bloemen et al 1984(Bloemen et al , 1986Bhat et al 1985), but this method requires information on the cosmic ray distribution not available in other galaxies. Another method to assess H 2 content is to use dust as a tracer, with a presumed or recovered dust-to-gas (DGR) ratio (e.g., Sandstrom et al 2013;Rémy-Ruyer et al 2014).…”

Section: Introductionmentioning

confidence: 99%

LIGHTING THE DARK MOLECULAR GAS: H₂ AS A DIRECT TRACER

Togi

Smith

2016

ApJ

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Robust knowledge of molecular gas mass is critical for understanding star formation in galaxies. The H 2 molecule does not emit efficiently in the cold interstellar medium, hence the molecular gas content of galaxies is typically inferred using indirect tracers. At low metallicity and in other extreme environments, these tracers can be subject to substantial biases. We present a new method of estimating total molecular gas mass in galaxies directly from pure mid-infrared rotational H 2 emission. By assuming a power-law distribution of H 2 rotational temperatures, we can accurately model H 2 excitation and reliably obtain warm (T100 K) H 2 gas masses by varying only the power law's slope. With sensitivities typical of Spitzer/IRS, we are able to directly probe the H 2 content via rotational emission down to ∼80 K, accounting for ∼15% of the total molecular gas mass in a galaxy. By extrapolating the fitted power-law temperature distributions to a calibrated single lower cutoff temperature, the model also recovers the total molecular content within a factor of ∼2.2 in a diverse sample of galaxies, and a subset of broken powerlaw models performs similarly well. In ULIRGs, the fraction of warm H 2 gas rises with dust temperature, with some dependency on α CO . In a sample of five low-metallicity galaxies ranging down to [ ] + = 12 log O H 7.8, the model yields molecular masses up to ∼100×larger than implied by CO, in good agreement with other methods based on dust mass and star formation depletion timescale. This technique offers real promise for assessing molecular content in the early universe where CO and dust-based methods may fail.

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“…Lebrun (34.155.032), The mass of H2 as inferred from y""rad"iation is much lower than that given by CO data (Li et al, 33.155.017;Bhat et al, 1984). A different view is presented by Korchagin et al (33.155.100) who interpret the y-ray emission in terms of galactic shocks.…”

Section: The Galactic Diskmentioning

confidence: 71%

B. Radio Studies

1985

Trans. Int. Astron. Union

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(33.155.068) investigated a field near NGC 7006 using RGU photometry and determined density functions for both populations. The Basel halo program also includes several papers by Fenkart and collaborators (33.113.027, 34. 113.036, and Astron. Astrophys. (in preparation)). Staller et al. (31.155.003) found a large number of red objects near the South galactic pole and discussed the M-dwarf distribution. Trefzger et al. (1984) used Walraven photometry to show a metallicity gradient for stars in SA 141 at the South galactic pole. The density function of faint stars towards the North galactic pole was derived by Yoshii (32. 155.034). Early-type stars near IC 4665 were investigated by Paparo and Balazs (33. 155.124). Kron, Cudworth, and Rybski (Yerkes) are beginning a programme of photometry, spectroscopy and proper motions for complete samples of faint stars in about twenty fields at intermediate latitudes. Tobin (37.113.034, 1984) has continued the studies by Tobin and Kaufmann (37.114.030) of high and intermediate-latitude B stars; uvbyg photometry shows that some of these are more than 500 pc from the galactic plane.The globular cluster system was studied by Frenk and White (31.155.001), who concluded that the sun's distance to the galactic centre is R 0 = 6,8±0.8 kpc. B. RADIO STUDIESSeveral regional surveys of southern HI made with the Argentine 100-m telescope were published (30.155.031). HI and other data were used by Dolidze (30.155. 044) to study the local distribution of gas and star forming regions. The Perseus arm region was the subject of an analogous study by Gerasimenko (34.155.139). Vallee (34.155.005) used rotation measure data from extragalactic sources in the direction of the Perseus arm to determine the magnetic field structure there and to constrain gravitational collapse theories of magnetic compression. HI in the direction of the Puppis window was surveyed by Stacy and Jackson (32.131.277) and used to study the turbulent characteristics of the interstellar medium. HI related to Gould's Belt was studied by Poppel and Olano (32.155.024, 33.155.030). Salter (34. 131.014) reviewed radio and other observations pertaining tc Loop I, the North Polar Spur, and considered the influence which this structure might have on the local medium.Several regional studies were carried out in the radio continuum. Kononov and Pyatunina (34.155.017) surveyed the galactic plane in the region of Mononceros at X7.6 cm. The extended component of the radio continuum at 408, 820, and 1420 MHz from the Cassiopeia-Perseus region was analyzed by Kallas et al. (34.155.069). Kanbach (34.155.020) reviewed the nonthermal radio emission from the local (< 2 kpc) region of the Galaxy and separated the emissivity into thin-and thick-disk components .Shell-like structures in the interstellar medium received much attention during the triennium. Hu (30.155.006) searched for HI shells at |b| > 10 , using filtering in velocity to enhance the shell features; she found correlations of the HI shells with radio continuum loops. Gosa...

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Cosmic γ rays and the mass of gas in the Galaxy

Cited by 54 publications

References 23 publications

Foreground contributions to the cosmic microwave background

Foreground contributions to the cosmic microwave background

LIGHTING THE DARK MOLECULAR GAS: H₂ AS A DIRECT TRACER

B. Radio Studies

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Cosmic γ rays and the mass of gas in the Galaxy

Cited by 54 publications

References 23 publications

Foreground contributions to the cosmic microwave background

Foreground contributions to the cosmic microwave background

LIGHTING THE DARK MOLECULAR GAS: H2 AS A DIRECT TRACER

B. Radio Studies

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LIGHTING THE DARK MOLECULAR GAS: H₂ AS A DIRECT TRACER