Monday 10/15/2012

Title: Spectroscopic FIR mapping of the disk and galactic wind of M82 with Herschel-PACS
Authors: Contursi, A.; Poglitsch, A.; Graciá-Carpio, J.; Veilleux, S.; Sturm, E.; Fischer, J.; Verma, A.; Hailey-Dunsheath, S.; Lutz, D.; Davies, R.; González-Alfonso, E.;Sternberg, A.; Genzel, R.; Tacconi, L.
Publication: eprint arXiv:1210.3496
Publication Date: 10/2012
Origin: ARXIV
Keywords: Astrophysics – Galaxy Astrophysics, Astrophysics – Cosmology and Extragalactic Astrophysics
Comment: 26 pages, 23 figures, 4 Tables, Accepted for publication in Astronomy & Astrophysics
Bibliographic Code: 2012arXiv1210.3496C


[Abridged] We present maps of the main cooling lines of the neutral atomic gas ([OI] at 63 and 145 micron and [CII] at 158 micron) and in the [OIII] 88 micron line of the starburst galaxy M82, carried out with the PACS spectrometer on board the Herschel satellite. By applying PDR modeling we derive maps of the main ISM physical parameters, including the [CII] optical depth, at unprecedented spatial resolution (~300 pc). We can clearly kinematically separate the disk from the outflow in all lines. The [CII] and [OI] distributions are consistent with PDR emission both in the disk and in the outflow. Surprisingly, in the outflow, the atomic and the ionized gas traced by the [OIII] line both have a deprojected velocity of ~75 km/s, very similar to the average velocity of the outflowing cold molecular gas (~ 100 km/s) and several times smaller than the outflowing material detected in Halpha (~ 600 km/s). This suggests that the cold molecular and neutral atomic gas and the ionized gas traced by the [OIII] 88 micron line are dynamically coupled to each other but decoupled from the Halpha emitting gas. We propose a scenario where cold clouds from the disk are entrained into the outflow by the winds where they likely evaporate, surviving as small, fairly dense cloudlets (n_H\sim 500-1000 cm^-3, G_0\sim 500- 1000, T_gas\sim300 K). We show that the UV photons provided by the starburst are sufficient to excite the PDR shells around the molecular cores. The mass of the neutral atomic gas in the outflow is \gtrsim 5-12x 10^7 M_sun to be compared with that of the molecular gas (3.3 x 10^8 M_sun) and of the Halpha emitting gas (5.8 x 10^6 M_sun). The mass loading factor, (dM/dt)/SFR, of the molecular plus neutral atomic gas in the outflow is ~ 2. Energy and momentum driven outflow models can explain the data equally well, if all the outflowing gas components are taken into account.

Title: The Star Formation in Radio Survey: GBT 33 GHz Observations of Nearby Galaxy Nuclei and Extranuclear Star-Forming Regions
Authors: Murphy, E. J.; Bremseth, J.; Mason, B. S.; Condon, J. J.; Schinnerer, E.; Aniano, G.; Armus, L.; Helou, G.; Turner, J. L.; Jarrett, T. H.
Publication: eprint arXiv:1210.3360
Publication Date: 10/2012
Origin: ARXIV
Keywords: Astrophysics – Cosmology and Extragalactic Astrophysics
Comment: 25 Pages, 10 Figures, Accepted for publication in ApJ. Figure 1 resolution has been slightly degraded to meet arXiv size guidelines
Bibliographic Code: 2012arXiv1210.3360M


We present 33\,GHz photometry of 103 galaxy nuclei and extranuclear star-forming complexes taken with the Green Bank Telescope (GBT) as part of the Star Formation in Radio Survey (SFRS). Among the sources without evidence for an AGN, and also having lower frequency radio data, we find a median thermal fraction at 33GHz of ~76% with a dispersion of ~24%. For all sources resolved on scales <0.5kpc, the thermal fraction is even larger, being >90%. This suggests that the rest-frame 33GHz emission provides a sensitive measure of the ionizing photon rate from young star-forming regions, thus making it a robust star formation rate indicator. Taking the 33GHz star formation rates as a reference, we investigate other empirical calibrations relying on different combinations of warm 24\mu m dust, total infrared (IR; 8-1000\mu m), H\alpha\ line, and far-UV continuum emission. The recipes derived here generally agree with others found in the literature, albeit with a large dispersion that most likely stems from a combination of effects. Comparing the 33GHz to total IR flux ratios as a function of the radio spectral index, measured between 1.7 and 33GHz, we find that the ratio increases as the radio spectral index flattens which does not appear to be a distance effect. Consequently, the ratio of non-thermal to total IR emission appears relatively constant, suggesting only moderate variations in the cosmic-ray electron injection spectrum and ratio of synchrotron to total cooling processes among star-forming complexes. Assuming that this trend solely arises from an increase in the thermal fraction sets a maximum on the scatter of the non-thermal spectral indices among the star-forming regions of \sigma_\alpha^{NT} < 0.13.

Title: Dwarf Galaxies with Ionizing Radiation Feedback. I: Escape of Ionizing Photons
Authors: Kim, Ji-hoon; Krumholz, Mark R.; Wise, John H.; Turk, Matthew J.; Goldbaum, Nathan J.; Abel, Tom
Publication: eprint arXiv:1210.3361
Publication Date: 10/2012
Origin: ARXIV
Keywords: Astrophysics – Galaxy Astrophysics, Astrophysics – Cosmology and Extragalactic Astrophysics
Comment: 13 pages, 10 figures, Submitted for publication in the Astrophysical Journal, Image resolution reduced, High-resolution version of this article is available at
Bibliographic Code: 2012arXiv1210.3361K


We describe a new method for simulating ionizing radiation and supernova feedback in galaxy simulations. In this method, which we call star-forming molecular cloud (SFMC) particles, we use a ray-tracing technique to solve the radiative transfer equation for ultraviolet photons emitted by thousands of distinct particles on the fly. Joined with high numerical resolution of 3.8 pc, the realistic description of stellar feedback helps to self-regulate star formation. This new feedback scheme also enables us to study the escape of ionizing photons from star-forming clumps and from a galaxy, and to examine the evolving environment of star-forming gas clumps. By simulating a galactic halo of 2.3e11 Msun, we find that the galactic escape fraction, f_esc, fluctuates between 0.08% to 5.9% during a ~20 Myr period with a mean value of 1.1%. The flux of escaped photons is not strongly beamed, but manifests a large opening angle of more than 60 degree from the galactic pole. Further, we investigate the escape fraction per SFMC particle, f_esc(i), and how it evolves as the particle ages. We discover that the galactic escape fraction is dominated by a small number of SFMC particles with high f_esc(i). On average, the escape fraction from a SFMC particle rises from 0.27% at its birth to 2.1% at the end of a particle lifetime, 6 Myrs. This is because SFMC particles drift away from the dense gas clumps in which they were born, and because the gas around the star-forming clumps is dispersed by ionizing radiation and supernova feedback. The framework established in this study brings deeper insight into the physics of photon escape fraction from an individual star-forming clump, and from a galaxy.

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