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The Herschel exploitation of local galaxy Andromeda (HELGA), II: dust and gas in Andromeda

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Abstract
We present an analysis of the dust and gas in Andromeda, using Herschel images sampling the entire far-infrared peak. We fit a modified-blackbody model to similar to 4000 quasi-independent pixels with spatial resolution of similar to 140 pc and find that a variable dust-emissivity index (beta) is required to fit the data. We find no significant long-wavelength excess above this model, suggesting there is no cold dust component. We show that the gas-to-dust ratio varies radially, increasing from similar to 20 in the center to similar to 70 in the star-forming ring at 10 kpc, consistent with the metallicity gradient. In the 10 kpc ring the average beta is similar to 1.9, in good agreement with values determined for the Milky Way (MW). However, in contrast to the MW, we find significant radial variations in beta, which increases from 1.9 at 10 kpc to similar to 2.5 at a radius of 3.1 kpc and then decreases to 1.7 in the center. The dust temperature is fairly constant in the 10 kpc ring (ranging from 17 to 20 K), but increases strongly in the bulge to similar to 30 K. Within 3.1 kpc we find the dust temperature is highly correlated with the 3.6 mu m flux, suggesting the general stellar population in the bulge is the dominant source of dust heating there. At larger radii, there is a weak correlation between the star formation rate and dust temperature. We find no evidence for "dark gas" in M31 in contrast to recent results for the MW. Finally, we obtained an estimate of the CO X-factor by minimizing the dispersion in the gas-to-dust ratio, obtaining a value of (1.9 +/- 0.4) x 10(20) cm(-2) [K km s(-1)](-1).
Keywords
SPIRAL GALAXIES, MOLECULAR GAS, STAR-FORMATION, GAMMA-RAY EMISSION, CO-TO-H-2 CONVERSION FACTOR, MULTIBAND IMAGING PHOTOMETER, Local Group, galaxies: evolution, galaxies: ISM, galaxies: individual (M31), INFRARED-EMISSION, SPECTRAL INDEX, GALACTIC PLANE, VIRGO CLUSTER

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MLA
Smith, MWL, SA Eales, HL Gomez, et al. “The Herschel Exploitation of Local Galaxy Andromeda (HELGA), II: Dust and Gas in Andromeda.” ASTROPHYSICAL JOURNAL 756.1 (2012): n. pag. Print.
APA
Smith, MWL, Eales, S., Gomez, H., Roman-Duval, J., Fritz, J., Braun, R., Baes, M., et al. (2012). The Herschel exploitation of local galaxy Andromeda (HELGA), II: dust and gas in Andromeda. ASTROPHYSICAL JOURNAL, 756(1).
Chicago author-date
Smith, MWL, SA Eales, HL Gomez, J Roman-Duval, Jacopo Fritz, R Braun, Maarten Baes, et al. 2012. “The Herschel Exploitation of Local Galaxy Andromeda (HELGA), II: Dust and Gas in Andromeda.” Astrophysical Journal 756 (1).
Chicago author-date (all authors)
Smith, MWL, SA Eales, HL Gomez, J Roman-Duval, Jacopo Fritz, R Braun, Maarten Baes, GJ Bendo, JADL Blommaert, M Boquien, A Boselli, DL Clements, AR Cooray, L Cortese, Ilse De Looze, GP Ford, WK Gear, Gianfranco Gentile, Karl Gordon, J Kirk, V Lebouteiller, S Madden, E Mentuch, B O’Halloran, MJ Page, B Schulz, L Spinoglio, Joris Verstappen, CD Wilson, and DA Thilker. 2012. “The Herschel Exploitation of Local Galaxy Andromeda (HELGA), II: Dust and Gas in Andromeda.” Astrophysical Journal 756 (1).
Vancouver
1.
Smith M, Eales S, Gomez H, Roman-Duval J, Fritz J, Braun R, et al. The Herschel exploitation of local galaxy Andromeda (HELGA), II: dust and gas in Andromeda. ASTROPHYSICAL JOURNAL. 2012;756(1).
IEEE
[1]
M. Smith et al., “The Herschel exploitation of local galaxy Andromeda (HELGA), II: dust and gas in Andromeda,” ASTROPHYSICAL JOURNAL, vol. 756, no. 1, 2012.
@article{3075427,
  abstract     = {We present an analysis of the dust and gas in Andromeda, using Herschel images sampling the entire far-infrared peak. We fit a modified-blackbody model to similar to 4000 quasi-independent pixels with spatial resolution of similar to 140 pc and find that a variable dust-emissivity index (beta) is required to fit the data. We find no significant long-wavelength excess above this model, suggesting there is no cold dust component. We show that the gas-to-dust ratio varies radially, increasing from similar to 20 in the center to similar to 70 in the star-forming ring at 10 kpc, consistent with the metallicity gradient. In the 10 kpc ring the average beta is similar to 1.9, in good agreement with values determined for the Milky Way (MW). However, in contrast to the MW, we find significant radial variations in beta, which increases from 1.9 at 10 kpc to similar to 2.5 at a radius of 3.1 kpc and then decreases to 1.7 in the center. The dust temperature is fairly constant in the 10 kpc ring (ranging from 17 to 20 K), but increases strongly in the bulge to similar to 30 K. Within 3.1 kpc we find the dust temperature is highly correlated with the 3.6 mu m flux, suggesting the general stellar population in the bulge is the dominant source of dust heating there. At larger radii, there is a weak correlation between the star formation rate and dust temperature. We find no evidence for "dark gas" in M31 in contrast to recent results for the MW. Finally, we obtained an estimate of the CO X-factor by minimizing the dispersion in the gas-to-dust ratio, obtaining a value of (1.9 +/- 0.4) x 10(20) cm(-2) [K km s(-1)](-1).},
  articleno    = {40},
  author       = {Smith, MWL and Eales, SA and Gomez, HL and Roman-Duval, J and Fritz, Jacopo and Braun, R and Baes, Maarten and Bendo, GJ and Blommaert, JADL and Boquien, M and Boselli, A and Clements, DL and Cooray, AR and Cortese, L and De Looze, Ilse and Ford, GP and Gear, WK and Gentile, Gianfranco and Gordon, Karl and Kirk, J and Lebouteiller, V and Madden, S and Mentuch, E and O'Halloran, B and Page, MJ and Schulz, B and Spinoglio, L and Verstappen, Joris and Wilson, CD and Thilker, DA},
  issn         = {0004-637X},
  journal      = {ASTROPHYSICAL JOURNAL},
  keywords     = {SPIRAL GALAXIES,MOLECULAR GAS,STAR-FORMATION,GAMMA-RAY EMISSION,CO-TO-H-2 CONVERSION FACTOR,MULTIBAND IMAGING PHOTOMETER,Local Group,galaxies: evolution,galaxies: ISM,galaxies: individual (M31),INFRARED-EMISSION,SPECTRAL INDEX,GALACTIC PLANE,VIRGO CLUSTER},
  language     = {eng},
  number       = {1},
  pages        = {17},
  title        = {The Herschel exploitation of local galaxy Andromeda (HELGA), II: dust and gas in Andromeda},
  url          = {http://dx.doi.org/10.1088/0004-637X/756/1/40},
  volume       = {756},
  year         = {2012},
}

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