Tuesday Astroph 05/23/2012

Note other papers:
 A multi-wavelength investigation of RCW175: an HII region harboring spinning dust emission; IR-derived covering factors for a large sample of quasars from WISE-UKIDSS-SDSS

Comparison of star formation rates from Halpha and infrared luminosities as seen by Herschel

Authors:H. Domínguez, M. Mignoli, F. Pozzi, F. Calura, A. Cimatti, C. Gruppioni, J. Cepa, M. Sánchez-Portal, G. Zamorani, S. Berta, D. Elbaz, E. LeFloc’h, G. L. Granato, D. Lutz, R. Maiolino, F. Mateucci, P. Nair, R. Nordon, L. Pozzetti, L. Silva, J. Silverman, S. Wuyts, C. M. Carollo, T. Contini, J.-P. Kneib, O. LeFevrè, S. J. Lilly, V. Mainieri, A. Renzini, M. Scodeggio, S. Bardelli, M. Bolzonella, A. Bongiorno, K. Caputi, G. Coppa, O. Cucciati, S. de la Torre, L. de Ravel, P. Franzetti, B. Garilli, A. Iovino, P. Kampczyk, C. Knobel, K. Kovac, F. Lamareille, J.-F. Le Borgne, V. le Brun. C. Maier, B. Magnelli, R. Pellò, Y. Peng, E. Pérez-Montero, E. Riccardelli, L. Riguccini, M. Tanaka, L. A. M. Tasca, L. Tresse, D. Vergani, E. Zucca
(Submitted on 21 May 2012)

Abstract: We empirically test the relation between the SFR(LIR) derived from the infrared luminosity, LIR, and the SFR(Ha) derived from the Ha emission line luminosity using simple conversion relations. We use a sample of 474 galaxies at z = 0.06 – 0.46 with both Ha detection (from 20k zCOSMOS survey) and new far-IR Herschel data (100 and 160 {\mu}m). We derive SFR(Ha) from the Ha extinction corrected emission line luminosity. We find a very clear trend between E(B – V) and LIR that allows to estimate extinction values for each galaxy even if the Ha emission line measurement is not reliable. We calculate the LIR by integrating from 8 up to 1000 {\mu}m the SED that is best fitting our data. We compare SFR(Ha) with the SFR(LIR). We find a very good agreement between the two SFR estimates, with a slope of m = 1.01 \pm 0.03 in the SFR(LIR) vs SFR(Ha) diagram, a normalization constant of a = -0.08 \pm 0.03 and a dispersion of sigma = 0.28 dex.We study the effect of some intrinsic properties of the galaxies in the SFR(LIR)-SFR(Ha) relation, such as the redshift, the mass, the SSFR or the metallicity. The metallicity is the parameter that affects most the SFR comparison. The mean ratio of the two SFR estimators log[SFR(LIR)/SFR(Ha)] varies by approx. 0.6 dex from metal-poor to metal-rich galaxies (8.1 < log(O/H) + 12 < 9.2). This effect is consistent with the prediction of a theoretical model for the dust evolution in spiral galaxies. Considering different morphological types, we find a very good agreement between the two SFR indicators for the Sa, Sb and Sc morphologically classified galaxies, both in slope and normalization. For the Sd, irregular sample (Sd/Irr), the formal best-fit slope becomes much steeper (m = 1.62 \pm 0.43), but it is still consistent with 1 at the 1.5 sigma level, because of the reduced statistics of this sub-sample.

Comments: 13 pages, 11 figures, to be published in MNRAS
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1205.4573v1 [astro-ph.CO]

On the nature of dust clouds in the region towards M81 and NGC3077

Authors:Andreas Heithausen
(Submitted on 21 May 2012)

Abstract: There is some controversy on the nature of dust clouds found in direction of the interacting galaxy triplett M81, M82, and NGC3077. Are they associated with the tidal arms seen in HI around those galaxies or are they simply Galactic foreground clouds? Data from the SPIRE instrument onboard HERSCHEL and MIPS onboard of SPITZER are used to derive physical parameters for the dust clouds. These observions are compared to CO clouds previously mapped with the IRAM and the FCRAO radio telescopes.SPIRE and MIPS maps show several dust clouds north of M81 and south of NGC3077. Modelling of the dust emission provides total hydrogen column densities between 1.5 and 5.0 * 10^20 cm^-2. Dust temperatures are between 13 to 17K. No significant difference in the dust emission can be found between individual clouds. It is shown that CO line emission provides the best clues on the origin of those clouds. Most of the clouds seen towards M81 are associated with small-area molecular structures (SAMS), i.e. tiny CO clouds of Galactic origin. The clouds seen towards NGC3077 are partly associated with the tidal arms and are partly in the Galactic foreground associated with SAMS.

Comments: 7 pages, 7 figures, accepted by A&A
Subjects: Galaxy Astrophysics (astro-ph.GA)
Cite as: arXiv:1205.4531v1 [astro-ph.GA]

Submission history

From: Andreas Heithausen [view email]
[v1] Mon, 21 May 2012 09:14:47 GMT (1009kb)

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