Wednesday 3rd Apr 2013

arXiv:1304.0443 A study of AGN and supernova feedback in simulations of isolated and merging disc galaxies

Authors: Richard D. A. Newton, Scott T. Kay (Jodrell Bank Centre for Astrophysics)

We perform high resolution N-body+SPH simulations of isolated Milky-Way-like galaxies and major mergers between them, to investigate the effect of feedback from both an active galactic nucleus (AGN) and supernovae on the galaxy’s evolution. Several AGN methods from the literature are used independently and in conjunction with supernova feedback to isolate the most important factors of these feedback processes. We find that in isolated galaxies, supernovae dominate the suppression of star formation but the star formation rate is unaffected by the presence of an AGN. In mergers the converse is true when models with strong AGN feedback are considered, shutting off star formation before a starburst can occur. AGN and supernovae simulated together suppress star formation only slightly more than if they acted independently. This low-level interaction between the feedback processes is due to AGN feedback maintaining the temperature of a hot halo of gas formed by supernovae. For each of the feedback processes the heating temperature is the dominant parameter rather than the overall energy budget or timing of heating events. Finally, we find that the black hole mass is highly resolution dependent, with more massive black holes found in lower resolution simulations.

HerMES: The Contribution to the Cosmic Infrared Background from Galaxies Selected by Mass and Redshift Authors: M. P. Viero, L. Moncelsi, R. F. Quadri, V. Arumugam, R. J. Assef, M. Bethermin, J. Bock, C. Bridge, A. Conley, A. Cooray, D. Farrah, S. Heinis, S. Ikarashi, R. J. Ivison, K. Kohno, G. Marsden, S. J. Oliver, I. G. Roseboom, B. Schulz, D. Scott, P. Serra, M. Vaccari, J. D. Vieira, L. Wang, J. Wardlow, R. J. Williams, G. W. Wilson, M. S. Yun, M. Zemcov

We quantify the fraction of the cosmic infrared background (CIB) that originates from galaxies identified in the UV/optical/near-infrared by stacking 81,250 (~35.7 arcmin^2) K-selected sources, split according to their rest-frame U – V vs. V – J colors into 72,216 star-forming and 9,034 quiescent galaxies, on maps from Spitzer/MIPS (24, 70, 160 {\mu}m), Herschel/SPIRE (250, 350, 500 {\mu}m), and AzTEC (1100 {\mu}m). The fraction of the CIB resolved by our catalog is (67 \pm 16)% at 24 {\mu}m, (72 \pm 17)% at 70 {\mu}m, (76 \pm 18)% at 160 {\mu}m, (78 \pm 18)% at 250 {\mu}m, (70 \pm 15)% at 350 {\mu}m, (67 \pm 13)% at 500 {\mu}m, and (52 \pm 9)% at 1100 {\mu}m. Of that total, about 95% originates from star-forming galaxies, while the remaining 5% is from apparently quiescent galaxies. The CIB at {\lambda} < 200 {\mu}m appears to be sourced predominantly from galaxies at z < 1, while at {\lambda} > 200 {\mu}m the bulk originates from 1 < z < 2. Galaxies with stellar masses log(M/ M_sun)=9.5-11 are responsible for the majority of the CIB, with those in the log(M/ M_sun)=9.5-10 contributing mostly at {\lambda} < 250{\mu}m, and those in the log(M/ M_sun)=10.5-11 jointly dominating at {\lambda} > 350{\mu}m. The contribution from galaxies in the log(M/ M_sun)=9.0$-9.5 (highest) and log(M/ M_sun)=11.0-12.0 (lowest) stellar mass bins contribute the least, both of order 5%. The luminosities of the galaxies responsible for the CIB shifts from a combination of "normal" and luminous infrared galaxies (LIRGs) at \lambda < 160 {\mu}m, to being dominated by LIRGs at longer wavelengths. Stacking analyses were performed using SIMSTACK, a novel algorithm designed to account for possible biases in the stacked flux density due to clustering. It is made available to the public at homepage/toolbox.html.


Millimeter dust emission compared with other mass estimates in N11 molecular clouds in the LMC

Authors: Cinthya N. Herrera, Monica Rubio, Alberto D. Bolatto, Francois Boulanger, Frank P. Israel, Fredrik T. Rantakyro

CO and dust emission at millimeter wavelengths are independent tracers of cold interstellar matter, which have seldom been compared on the scale of GMCs in other galaxies. In this study, and for the first time in the Large Magellanic Cloud, we compute the molecular cloud masses from the mm emission of the dust and compare them with the masses derived from their CO luminosity and virial theorem. We present CO (J=1-0,2-1) and 1.2 mm continuum observations of the N11 star forming region in the LMC obtained with the SEST telescope and the SIMBA bolometer, respectively. We use the CO data to identify individual molecular clouds and measure their physical properties. The correlations between the properties of the N11 clouds are in agreement with those found in earlier studies in the LMC that sample a larger set of clouds and a larger range of cloud masses. For the N11 molecular clouds, we compare the masses estimated from the CO luminosity (Xco\Lco), the virial theorem (Mvir) and the millimeter dust luminosity (L_d). The measured ratios Lco/Mvir and L_d/Mvir constrain the Xco and K_d (dust emissivity at 1.2 mm per unit gas mass) parameters as a function of the virial parameter a_vir. The comparison between the different mass estimates yields a Xco-factor of 8.8×10^20 cm-2/(K km s-1) x a_vir and a K_d parameter of 1.5×10^-3 cm2/g x a_vir. We compare our N11 results with a similar analysis for molecular clouds in the Gould’s Belt. We do not find in N11 a large discrepancy between the dust mm and virial masses as reported in earlier studies of molecular clouds in the SMC. The ratio between L_d and Mvir in N11 is half of that measured for Gould’s Belt clouds, which can be accounted for by a factor of two lower gas-to-dust mass ratio, as the difference in gas metallicities. If the two samples have similar a_vir values, this result implies that their dust far-IR properties are also similar.

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